True corner weights of my car!!!

[Reaper1]

OK, so for my Vehicle Dynamics course I'm anylizing the front suspension of my car. In order to do some of the calculations I needed to find out the wieght of my car and where the center of gravity is.

Well, I got lucky and was able to use a set of race scales today to do just that! So, here are the TRUE corner weights of my 1988 Shelby Z!

The first set I'm going to list is the car sitting static with NO driver, full tank of fuel, full sized spare and associated equipment, no stereo:
LF: 882
RF: 941
LR: 604
RR: 513

Total: 2940
Rear: 1119 37.99%
Left: 1486 50.54%
Cross:1545 52.55%

This second set is the same as above, but with me sitting in the car. Note, check out the front wheel weights and the cross wieght precentage! This car does NOT have coil-overs on it!
LF: 955
RF: 955
LR: 664
RR: 538

Total: 3113
Rear: 1201 39.60%
Left: 1619 52.06%
Cross: 1618 52.01%

So, what did we learn just from these numbers? Well, a 1988 Shelby Z is about 3000#'s wet. Keep in mind my seats are lighter than stock and so are my wheels by a good margin. However, I do have some added stuff like a FMIC and the Devil's Own kit. The brakes are the larger 11" units and the whole front suspension is now '91-up stuff, so it's a bit heavier than the origional stuff, but the geometry and whatnot are is SO much better! The way I weighed the car is how I race it, regardless of the type of racing.

Honestly I was very impressed how well balanced the car actually is! A 60/40 split F/R isn't horrible for a FWD car and having 52% cross weight is VERY acceptable for a daily driven ride! I almost don't want to change my battery now! LOL It will throw the balance of the car off!

Anyways, I hope this gives people an insight on how these cars are balanced and their true wieght. I don't *think* my car is a special case by any means. There are plenty of us running around with Koni's and Eibachs. Now, my Eibachs are trimmed, so my suspension is at some funky angles, which is why I'm doing this project. I want to know exactly where the car stands as fars as good and bad points of having it that low. Thus far, with the newer front suspension on it, from what I've altready modeled in Catia, it really isn't as bad as people make it see, but once I start doing the force calculations and such, that will really tell the tale.

Anyways, I hope that helps some... :thumb:

[turboshad]

Good info. I would be interested in seeing your instant centers, roll centers and CG diagrams when you are done. Are you using any suspension software like Adams Car or something? I think they will give it free to FSAE teams if yours doesn't already have it.

[mario03SRT]

Thanks thats good info.

I put in a lawn tractor battery in mine to even things up a bit over the tranny.

[Reaper1]

I'm doing all the calculations by hand. Although nothing was said that we *couldn't* use computers to do it. The thing is computers and I have a mutual hatred fro each other! That's retarded I know, conisdering what I want to do, but it's true! LOL I might have to look in to this! Thanks!

I will be probably posting all of my results from my report on the forums for all to see. I would like to go more in depth than what I'm going to have time for as well as I only have a few weeks to do this in, which honestly isn't a lot of time. So, we'll see. I'll defnatly post up what I do complete, and then I think i'm going to continue on my own because I find it very interesting and I think there are people out there that will find it useful as well! :thumb:

[turboshad]

I'm doing all the calculations by hand. Although nothing was said that we *couldn't* use computers to do it. The thing is computers and I have a mutual hatred fro each other! That's retarded I know, conisdering what I want to do, but it's true! LOL I might have to look in to this! Thanks!

I will be probably posting all of my results from my report on the forums for all to see. I would like to go more in depth than what I'm going to have time for as well as I only have a few weeks to do this in, which honestly isn't a lot of time. So, we'll see. I'll defnatly post up what I do complete, and then I think i'm going to continue on my own because I find it very interesting and I think there are people out there that will find it useful as well! :thumb:

Ya, a few weeks is pretty slim. It took 4 of us a 2 semester design course to do the FSAE suspension design for the following year.

[zin]

OK, so for my Vehicle Dynamics course I'm anylizing the front suspension of my car. In order to do some of the calculations I needed to find out the wieght of my car and where the center of gravity is.

Well, I got lucky and was able to use a set of race scales today to do just that! So, here are the TRUE corner weights of my 1988 Shelby Z!

The first set I'm going to list is the car sitting static with NO driver, full tank of fuel, full sized spare and associated equipment, no stereo:
LF: 882
RF: 941
LR: 604
RR: 513

Total: 2940
Rear: 1119 37.99%
Left: 1486 50.54%
Cross:1545 52.55%

This second set is the same as above, but with me sitting in the car. Note, check out the front wheel weights and the cross wieght precentage! This car does NOT have coil-overs on it!
LF: 955
RF: 955
LR: 664
RR: 538

Total: 3113
Rear: 1201 39.60%
Left: 1619 52.06%
Cross: 1618 52.01%

Anyways, I hope that helps some... :thumb:

If you jack up the car front and back while on the scales you can figure where your Center of Gravity (CG) is located. This can be very helpful, especially if you road race/rally at all.

Mike

[johnl]

Wow. I'm completely ignorant about chassis set up but I string my cars (all L bodies) and I've got a homemade camber tool which I use and I've got some good results; that said I'm a know nothing in this area, so I have some questions.

First, to minimize torque steer (with posi and equal length axles) - it would seem that toe might have something to do with it, so what is the best toe? Straightline? Cornering? I mean, camber comes into it if you're cornering and as the wheel moves the toe changes too . . . .

Second, just off hand what is the best "rule of thumb - starter set up" for FWD toe/camber combo for road racing? for auto x?

Third, same question but for FWD rear wheel toe/camber for road racing? for auto x? I have camber/toe plates between the axle and the rear spindles.

[GLHNSLHT2]

1st John we need to see pics of these camber/toe plates. 2nd your alignment in the front has a lot to do with what year suspension you're running and what bushings are in there. But I assume you have regular lbody suspension and Energy Suspension bushings. Toe is best at 0 since you have no or very little flex in the suspension bushings. The car will roll better and not be twitchy in manuevers. And I'd set that all the way around. For camber you want to have a balanced cornering attitude. I've found that having a 1/2 degree less in the rear than in the front really balances these cars well. So if you can get -1.5 in the front then run -1.0 in the rear. You can corner really hard at those settings. Much more so than you can find on the street safely. If you're AutoX you might want to go for 2.0 in the front and -1.0 in the rear depending on how tight the track is and how much you want the rear to rotate out. If the balance is good and you just want a bit more cornering force you might increase both settings a bit from the above -1.5 and -1.0. But with my spherical bearing lower control arms I've found that at -1.5 the tires skip because they're no flex to plant the tire flat so they skip along on the inside edge. With poly bushings they might do this at anything over -1.5. It's tough to say, every car and every driver is a bit different. But the -1.5 front and -1.0 rear is a good starting point in my experience.

Course I've written most of this up in the knowledge center. http://www.turbo-mopar.com/forums/vbarticles.php?do=article&articleid=121

[Reaper1]

Ya, a few weeks is pretty slim. It took 4 of us a 2 semester design course to do the FSAE suspension design for the following year.

Yeah, I understand that! I'm actually the head of the electrical team. Right now we're in the middle of wiring the chassis. It's not that bad, but we haven't run the engine since it's been out of the bike and we don't know waht all we can safely remove(I wasn't around to suggest testing this with the bike still in tact). So, now I'm having to waste time extending wires for crap we're goinf to end up taking off anyways! :bash:


If you jack up the car front and back while on the scales you can figure where your Center of Gravity (CG) is located. This can be very helpful, especially if you road race/rally at all.

Mike

I actually attempted that, but ultimatly forgot that you have to sit the car back down on the scales at the desired attitude so that the entire weight of the car is still on the scales. I lifted the rear exactly an inch with a jack under the rear axle(and verified cerntering by measuring both sides), however, I forgot to take in to account that the jack would be supporting some of the weight of the car. So, my total frontal weight ended up only being 1800#'s! OOPS! :confused: So, I don't want to wear out my welcome as I borrowed those scales on VERY short notice and the guy did it out of pure courtousy. I *may* have to fudge the numbers for now and then correct them later when I can borrow them again as we talked about me borrowing them for a club event. We shall see. If I DO get to do it, I'll post up my findings for sure!


Wow. I'm completely ignorant about chassis set up but I string my cars (all L bodies) and I've got a homemade camber tool which I use and I've got some good results; that said I'm a know nothing in this area, so I have some questions.

First, to minimize torque steer (with posi and equal length axles) - it would seem that toe might have something to do with it, so what is the best toe? Straightline? Cornering? I mean, camber comes into it if you're cornering and as the wheel moves the toe changes too . . . .

Second, just off hand what is the best "rule of thumb - starter set up" for FWD toe/camber combo for road racing? for auto x?

Third, same question but for FWD rear wheel toe/camber for road racing? for auto x? I have camber/toe plates between the axle and the rear spindles.

Pretty much +1 on what GLHNSLHT2 said. On K-based cars I know it is best to have a *tad* bit of toe OUT on the front, even for straight line driving and even with poly bushings. The reason is the way things work in the suspension AND tires under acceleration. They will have a tendancy to toe-in, so that slight amount of toe out (1/16"-1/8" total toe out) will help not only cornering, but striaght line acceleration. On the rear, as close to 0 as you can get it!

Each car and each set-up is different when it comes to camber. The toe out is really not fixed either, but as a general rule based on how FWD works and our cars, that's the "norm". For camber, it is going to depend GREATLY on your driving style and your tires. For me, I had to go to a bit more negative to try and account for the sidewall rolling over during very hard cornering. So far based on the dew times I've actually come even close to pushing the car I think I did meet my goal. Next weekend will be the tell-all...I have a track day! YAY!!

As for rear camber, L-bodies are different than k-based cars, but with similar principles. A lot of negative camber is not going to do any good back there because of the way the suspension works and the way you want the car to be balanced for good cornering. I'd say don't go more than -.75*. Any more than that and it's a waste. I've NEVER rolled the sidewalls on my rear tires on my Daytona, even spinning it out numerous times. I only run -.5* back there. The spinning was due to a braking issue, and possibly a loose nut behind the wheel! :p:amen::lol::nod:

HTH....

[johnl]

This is how the S car, #463, was set up for the Vegas Bash in January -

On the rear - the plates under the spindles were/are Gregg Thewes'/Omnipotent's track widening plates which I had milled to 1* negative camber; then I used a belt sander to give them some toe in. No pics, sorry. The rear wheels measure at 1* negative camber and slight toe in - 1/32 or maybe 1/16th" toe in - just visible when looking at a string.

Swapped in Koni coil overs all around with 600 lb springs up front and 500 pound out back.

I was able to get 2* negative camber up front by turning the lower camber adjusting bolts to the max and then going up top and knocking the plates/screw inward to make sure I got as much as possible with a block 2x4 and a hammer. Fronts were also toed in slightly.

All stock bushings. No poly anywhere. Stock sway bar. So the real change was the springs.

The car handled great. Understeered until I wanted it to rotated when I wanted rotation I could provoke it.

Since Vegas, I went to Willow Springs when the GT40s were there and got out for a couple sessions at the end of the day. The suspension was different; retained the coilovers with 600 lb springs up front but had the stock shocks and stock softer springs out back and set it up with slight toe out up front and the same out back.

My perception is that I got more torque steer and the car did not rotate as well with the softer rear.

[GLHNSLHT2]

your perception is correct. Toe out makes the car hunt around under acceleration as it's trying to steer away from straight. The softer rear won't lift the inside wheel as much and allow the rear to rotate.

[Reaper1]

This is correct, however with FWD due to the dynamics of the power being applied and thus the force being driven through a different portion of the contact patch(they are being pulled), the front wheels under acceleration will tend to want to toe in. Not to be confusing, but the exact opposite happens for RWD, the front wheels will tend to try to toe out under accleration becuase they are being pushed. Of course suspension droop and such has to be accounted for under these conditions, but those general relationships almost always hold true.

For those reasons, and the fact that the slight toe out does make the car inherantly less stable, I set my car up this way. It helps with straight line traction as well as turn-in.

I'm not saying it's for everybody, but it does work very well.

[johnl]

. . . . . . with FWD due to the dynamics of the power being applied and thus the force being driven through a different portion of the contact patch(they are being pulled), the front wheels under acceleration will tend to want to toe in. . .

Not arguing, just baffled or blind. I can't picture this dynamic. How does pulling, necessarily, cause toe in? With negative camber, in a straight line, the inside of the tires . . . . ? While cornering, with a flatter contact patch . . . . ? I can see that the contact patches, acting on the slop, or rubberiness, in the suspension pivot joints would affect the direction of the pull . . . but which direction and why?



For those reasons, and the fact that the slight toe out does make the car inherantly less stable, I set my car up this way. It helps with straight line traction as well as turn-in.



You set it up which way? with toe in or toe out?

At Vegas, in the slower turns, I closed distance, hugely, on the Mustangs, by provoking rotation early, getting the steering wheel/tires pointed where I wanted to go, as straight as I could get it them, and then matting the gas pedal. With the posi, I could get the power down early, and effectively, and could pull up on the inside of the stangs, corner after corner, lap after lap. Being able to rotate . . . . to get the front wheels pointed straight ahead - huge

[GLHNSLHT2]

John, really it sounds like you have the car set up well. If does what you want and goes down the road straight.

[Reaper1]

Not arguing, just baffled or blind. I can't picture this dynamic. How does pulling, necessarily, cause toe in? With negative camber, in a straight line, the inside of the tires . . . . ? While cornering, with a flatter contact patch . . . . ? I can see that the contact patches, acting on the slop, or rubberiness, in the suspension pivot joints would affect the direction of the pull . . . but which direction and why?




You set it up which way? with toe in or toe out?

At Vegas, in the slower turns, I closed distance, hugely, on the Mustangs, by provoking rotation early, getting the steering wheel/tires pointed where I wanted to go, as straight as I could get it them, and then matting the gas pedal. With the posi, I could get the power down early, and effectively, and could pull up on the inside of the stangs, corner after corner, lap after lap. Being able to rotate . . . . to get the front wheels pointed straight ahead - huge

The dynamic of the wheels moving toward a more toe in angle during acceleration has to do with the pivot points of the suspension how the forces end up acting on the wheel in a net manner. After everything is said and done they end up wanting to toe in on a FWD car during acceleration.

I set MY car up with 1/8" total toe OUT. I do this becuase I want quicker turn-in as well as comensating for the natural toe-in of the suspesion under acceleration. I don't usually drive the car that much, and when I do it's usually to auto-x it. I just happen to be going to a track day event up at Roebling Road next weekend with the PCA region up there. I suppose I'll finaly get to see what the car can REALLY do compared to other cars that are "classed" higher.


John, really it sounds like you have the car set up well. If does what you want and goes down the road straight.

I agree. If you are happy with the way the car reacts, the just tweak on it. What may work for myself of for GLHNSLHT2 may not work so well for you! Unless the settings are causing adverse tire wear or unwanted reactions from the car under cetain circumstances, everything else is subjective to driver taste! :amen:

[GLHNSLHT2]

As for rear camber, L-bodies are different than k-based cars, but with similar principles. A lot of negative camber is not going to do any good back there because of the way the suspension works and the way you want the car to be balanced for good cornering. I'd say don't go more than -.75*. Any more than that and it's a waste. I've NEVER rolled the sidewalls on my rear tires on my Daytona, even spinning it out numerous times. I only run -.5* back there. The spinning was due to a braking issue, and possibly a loose nut behind the wheel! :p:amen::lol::nod:


Lbodies are different. With the Poly bushings 1 1/8" rear bar on my GLH I can enter the corner, Quickly flip the wheel which will lift the rear inside tire off the ground 6-8" and throw the outside rear tire up onto the sidewall/corner. It's a bit freaky but the car rotates AWESOME! I sometimes wish I could do that with my daytona but I know it'll never happen.

[Reaper1]

^^That sounds scary to me!

[GLHNSLHT2]

yea does sound it, but you just control the pitch with the throttle. I scared the crap outta my g/f when we 1st started dating as I entered this big off camber sweeper on-ramp, lifted off the throttle at 65 or so and the back end slid out and I just kept it out with the throttle pulling us around the corner.

[johnl]

The dynamic of the wheels moving toward a more toe in angle during acceleration has to do with the pivot points of the suspension how the forces end up acting on the wheel in a net manner. After everything is said and done they end up wanting to toe in on a FWD car during acceleration.

I set MY car up with 1/8" total toe OUT. I do this becuase I want quicker turn-in as well as comensating for the natural toe-in of the suspesion under acceleration. I don't usually drive the car that much, and when I do it's usually to auto-x it. I just happen to be going to a track day event up at Roebling Road next weekend with the PCA region up there. I suppose I'll finaly get to see what the car can REALLY do compared to other cars that are "classed" higher.

I agree. If you are happy with the way the car reacts, the just tweak on it. What may work for myself of for GLHNSLHT2 may not work so well for you! Unless the settings are causing adverse tire wear or unwanted reactions from the car under cetain circumstances, everything else is subjective to driver taste! :amen:



Reaper1 - I await your full report from Roebling Road!

Tell us about your total set up - Springs F/R? Dampening F/R? Camber F/R? Toe . . . Tires? Tire pressures? Do you check tire temps?

While I have some ideas, I really know nothing, I'm just learning this stuff . . .

[johnl]

Lbodies are different. With the Poly bushings 1 1/8" rear bar on my GLH I can enter the corner, Quickly flip the wheel which will lift the rear inside tire off the ground 6-8" and throw the outside rear tire up onto the sidewall/corner. It's a bit freaky but the car rotates AWESOME! I sometimes wish I could do that with my daytona but I know it'll never happen.

Sounds like you get it to rotate with bar, while I get it to rotate with spring.

Which is best? or at least pros and cons of each?

The bar adds more weight compared to stiffer springs but I'd think that wheel tracking/compliance with the road surface is better with less spring. Also the bar pushes the other side down which is something stiff springs can't do at all . . .

[Reaper1]

Reaper1 - I await your full report from Roebling Road!

Tell us about your total set up - Springs F/R? Dampening F/R? Camber F/R? Toe . . . Tires? Tire pressures? Do you check tire temps?

While I have some ideas, I really know nothing, I'm just learning this stuff . . .

My set-up is this:
-'91-up k-frame
-'91-up cast control arms with poly bushings
-'91-up spindles
-PB 1.25" endlink front swaybar
-Grant Racing strut tower bar/camber plates
-stock '88 Shelby Z rear axle
-CS Racer panhard bar
-home made rear shock tower bar
-11" brake conversion using Carbotech XP8 front pads, Porterfield R4S rear pads, ATE Super Blue brake fluid
-Eibach ProKit springs that have had some of the progessive coils trimmed off, the spring rates that were put out there are 300#/in front, 330#/in rear
-Koni dampers all around
-camber: front= -1.6*, rear= -.5*
-toe: front= 1/8" total toe out, rear= 0 toe
-wheels: 16x7 Enkie RPF +35mm 5x100
-tires: 225/50/16 Kumho MX (I do NOT suggest these for auto-x...they are a GREAT street tire, but thus far have not performed they way I like for higher performance driving)

I do check tire pressures, but I don't have a propper temp gage.



Sounds like you get it to rotate with bar, while I get it to rotate with spring.

Which is best? or at least pros and cons of each?

The bar adds more weight compared to stiffer springs but I'd think that wheel tracking/compliance with the road surface is better with less spring. Also the bar pushes the other side down which is something stiff springs can't do at all . . .

The way it is described in Milliken is that you want to run a spring rate that is going to get you the natural frequency you are looking for, then make up the */g for cornering with the correct bar size. As with anything there are TONS of compromises to be made, and there is definatly more than one way to accomlish certain goals.

[johnl]

Wow. That's a lot of work. We await your report!

[Reaper1]

Well, first day of the track weekend is over. I STILL have the rear lock-up issue and it caused me to spin twice.

The first spin was a pure issue of confusion as to what to truly do. I knew I could have caught the car, but at the driver's meeting they said if you start to spin to put both feet in. So, that's what I did and it caused me to spin completley off track.

The second was me trying to learn some better driving technique and it bit me. I was trying to focus on the upcoming apex while sighting my braking zone in my peripheral. It caused me to accidentally keep the wheel slightly turned while I was in the braking zone. The result was a spin. I tried to catch it, but it was too little to late.

The good news is I learned quite a bit and significantly increased my speed and started to use my brakes more and more effectively

This afternoon I was able to source some regular parts store pads for the rear. I hope it makes my problem more managable.

My instructor is VERY good. He drives a spec E30 which is pretty quick in itself. He commented that my car is his favorite FWD he's ever experienced. Although it's a detriment to MY driving, in his opinion it could be helpful to rotate the car once better car control is learned.

Other than that the car is set-up VERY nicely. It's very controllable with the throttle. There's no understeer issue and the tires are wearing nicely. I'm surprised that I'm not having a sidewall roll-over problem at ALL!! While the tires don't have the ultimate grip of RE01's or the Direzza's, they do hold well, are fairly linear in their breakaway and the grip goes away predictably. The alignment works very well and the tires are wearing nicely besides that one HUGE flat spot from draging my rear tire.

It's a LOT of fun getting wave-byes from Porsches! The car is detuned a bit, but not as much as I normally do...I'm running 18#'s and am seeing 110-115 at the start of the braking zone at the end of the front straight. The car is running well and not showing any signs of issues with this state of tune. I don't know if I'm the quickest car in the novice group as my one buddy with his M3 is pretty quick as well, but there are few other car/driver combos out with us that I haven't gotten a wave-bye from.

Everybody seems to be really cool thoughm and this region of the PCA is VERY accepting of other makes of cars running with them.

My one friend with his MarkV Golf GTI unfortunatly had a nasty off on his second lap of th first run in the morning. He ended up sunk in the mud in the tire wall. All the damage is superficial for the most part. It needs a lot of plastic crap, but otherwise it seems fine.

The M3 had a wierd issue as the right rear lower shock bolt decided to take a vacation for no apperant reason.

I've not been without incident either! Evidently my car is so fast parts FLY off it! I lost the top windsheild trim on the front straight! Of course my two spins count as well I suppose, but the car is doing very well.

Anyways, that's all I have to report at the moment. I hope to have some pictures of the event at some point....

[Reaper1]

OK, so I replaced the rear pads with some Pep-Boys specials...STILL have a rear lock issue! WTF!!! This problem is p*ssing me off!! The car has a LOT more potential in it if I could use the brakes to their fullest potential.

So the second track day...besides the stupid rear brakes the car did AWSOME!!

I let my instructor drive the car during one of his sessions with me riding along...what a ride! On the third lap he decided that he was comfortable enough with the car to REALLY dive in tot eh braking zone for turn one on the front straight...doing about 120mph. I'd been doing my braking at about 400'...he let it go to 300' and railed the brakes. Well, the rears decided that was a great time to show their @ss and locked HORRIBLY. We drug them a good 200' then recovered, but the LR tire went off. It sent the car in to a tank slapper fishtail, which we recovered from and kept going! LOL We talked to several people who saw the smoke and tire marks and they all expected to see a car way off in the grass or worse! LOL

During the same session we got passed by a full race prepped Audi S4 driven by Chip Herr, but we were able to stick with him nose to tail for 3 corners! Now I realize my instructor is a darn good driver, but to be able to stick with a race prepped Audi driven by a top-level driver in pretty much a street car(on street tires) made me VERY happy! Chip was impressed with my car. I also want to comment what a cool guy he is! Very down to Earth and approachable.

During my last session out I was doing VERY well and getting a LOT of wave-byes. I was about to catch a 993 on turn 9(I knew who was driving it), but as I was coming out of turn 6 I realized I had no power...with the throttle matted boost was "0". :( It popped an intercooler hose that was in a PITA spot to fix and it was starting to rain, so my weekend was over. It would have been SO cool to overtake a 993 like that! Oh well...next time.

I got bumped up to "Blue" group which is a lower intermediate group, so I'm excited about that as well!

My catch can set-up(some of you may have seen at at SDAC...affectionatly known as the "JIF" mod as it uses a peanut butter jar as its main component) worked flawlessly. I did end up filling it up by the end of the weekend, but seeing as the car was at high rpms and moderate boost a LOT I don't see that as an issue. I noticed that I have an oil leak on the back side of the engine somewhere as my newly installed k-frame and such were pretty wet. In total I might have lost 1/2 quart of oil, which on a 200,000 mile engine put through that kind of use I don't think it horrible.

The front brakes worked AWSOME! The ATE fluid worked well, although I *should* have bled the system after the first day, but I forgot my crap to do it :( By the end of the second day the pedal felt like a wet sponge, but the car would still stop! As for the rear brakes...I'm completely fed up with them! HOLY CRAP they are annoying! I've done EVERYTHING I know of with stock parts to solve this issue. I've adjusted the suspension, the tire pressure, the pads, the proportioning valve and kept the spare in for ballast as well as a full tank of fuel. The only next option *I* know of is an aftermarket proportioning valve. After talking with my instructor and Chip Herr about the issue it's been agreed that I need about a 70/30 split front/rear. This is proof positive that the vented rear brakes on these cars is WAY overkill!!!

So, the total damage report:
-top windsheild molding blew off
-lost about 1/2 quart of engine oil
-front brake pads will probably be toast after my long road trip I'm about to make in a few weeks
-the tires feel like they are square from the massive flat spots :(
-blew off IC pipe
-got about 8mpg on track! LOL

Not too horrible really. Anyways, I hope this wasn't too long winded and people enjoy reading about it.

My instructor was very impressed with my car's balance and the fact it is VERY neutral. It only pushed ONE time and that was my fault for entering turn 4 too hot. I learned a LOT about recovering from that situation from that...if you feed some power and REDUCE the steering angle the car will turn MORE! It was a weird sensation, but something I'm glad I did!

Oh, last note on tires...After using these Kumho MX's on track I feel they are better suited for that use than for Auto-X. They wore VERY well with no chunking at all. Sidewall flex was evident, but not horrible and with my alignment I did not get down to the sidewall arrows(if they were still there! LOL). They fade progressively and are very controlable even after they are too hot. Their chassis and audible feedback are very nice and help you get the most out of what they can offer, which is quite good. Once they do get too hot, after about 3/4 of a lap of cooling off you can go back to pushing them again to about 80%. I've got about 4 or 5 auto-x's, this track event(7 or 8 20 minute sessions), a few drag races, and around 10,000 street miles on them and they have around 30% life left(if you don't count the flat spots) only because one is showing a tad more inside wear than the rest which I think is simply due to the track and street putting more demand on that side of the car. I feel this is very good for a 220 wear rated tire.

I still would like to try the Direzza's, but depending on price and such I may end up getting another set of these!

[GLHNSLHT2]

glad to hear the alignment is working out for you.

["Top Fuel" Bender]

Sounds like you get it to rotate with bar, while I get it to rotate with spring.

Which is best? or at least pros and cons of each?

The bar adds more weight compared to stiffer springs but I'd think that wheel tracking/compliance with the road surface is better with less spring. Also the bar pushes the other side down which is something stiff springs can't do at all . . .


I'm not a corning guy at all ,(yet :eyebrows:)
but that's what my latemodel guy has been favoring lately
Heavy bar, light spring
asphalt 1/4mile oval
seems tolike it better then heavy springs on moderate sway bar

[Ondonti]

Chris why dont you just try the non vented?
I am definitely going to try to use the non vented in the AWD conversion. No fancy rears for me. no queiro morir

[Juggy]

or an adjustable proportioning valve???

sounds like you have a blast, with a great learning experience!!! theres auto crossing goin on once a month in MI @ belle isle...im planning on joining with a couple friends n making a few visits out there

[Reaper1]

I don't knwo that I have a solid disc set-up that doesn't use the larger piston calipers. Y-bodies had that option...basically it was a non-vented 11" set-up and that's what I had on my '90 for a while.

I'd have to do some calculations to see what that would do for the braking pressures, wheel torques and such. That *may* be an option, but because I have plans of going to longer, faster tracks that might not be a great idea....we'll see...

I was auto-x'ing at least twice a month there for a bit, but school kinda dictated I knock that off :(

[GLHNSLHT2]

time to throw some drum brakes on the back :)

[johnl]

time to throw some drum brakes on the back :)

ditto that, or drill those discs to reduce their surface area.

Thanks for the reports. Good stuff there. Try the Falken Azenis, 200 tread wear; I love em. For next track day I'm trying to put together an extra set of wheels so I can have dedicated track wheel set with Hoosiers. A pro driver who drove my car said the Hoosiers would drop my car's times by 5 - 8 seconds/lap on the big track at Willow Springs.:wow1:

[Reaper1]

Drum brakes = ICKY!!! I know they are lighter and have a chance at balacing out the car, but they also have unpredicatble locking characteristics and I absolutly HATE working on them!

[johnl]

Drum brakes = ICKY!!! I know they are lighter and have a chance at balacing out the car, but they also have unpredicatble locking characteristics and I absolutly HATE working on them!

Yeah, I hate going back to stock too.:mad:

All my arrogant scheming about how I can do it better than Ma Mopar . . . . :confused:

I've got discs on the rear of my GLHT too; I'll find out if I have the same problem . . . . soon.

[Reaper1]

Thing is that the car came stock with rear discs!! LOL

[GLHNSLHT2]

that love to lock up :)

[Reaper1]

^^Very true! LOL

[mcsvt]

Great info Chris, sounds like you had a blast :thumb:

[Reaper1]

That I did! :D

I've got some preliminary results from my report that I did for my Vehicle Dynamics class, but I don't know how useful it really is for tuning and/or modifying.

The one thing I DID find interesting that might be useful to others is that with the way my suspension is set up my roll center while the car is sitting static on the gorund for the front is 3.3" BELOW the ground!

I also know the exact X-Y location of the CG for my car as well. The front/back postition is 59.53" from the rear axle and the left/right position is 1.17" to the left of the centerline of the car. That's with me in the car. Putting the driver in the car shifted the CG less than an inch in either direction!

Oh, I also calculated the natural frequency of the car with the "known" published spring rates of the Eibach springs!

The front natural frequency is 1.81Hz or 108.6cpm with the spring rate being 300lb/in. This is much too low for a car that only has 3" of jounce travel! It needs to be about 1.92Hz or 115cpm. This yeilds a spring rate of 405lb/in needed for the front of the car with only 3" of jounce travel. Now, keep in mind I set the instalation ratio to be "1", but in reality that is not the case becuase the strut is on an angle.

The rear calculations were ALL guesses unfortunatly. I didn't actually measure the things needed to get an acurate instalation ratio back there, but I came up with .65. I *think* that's kinda close, and based on the numbers I got I think it is. According to what I came up with for a 330lb/in spring(the "published" number for the Eibachs in the rear), the natural frequency is only 1.45Hz or 87cpm. Now, I did give the rear more suspension travel then the front at 3.5". I don't know if that's right, but it was a guess. Based on that information what is NEEDED back there is a natural frequency of 1.68Hz or 101cpm. This equates to about a 447lb/in spring needed for the rear!

Now, knowing what I do about certain people's set-ups, this seems to be about in the ballpark. Keep in mind that these rates are only ONE interation and I think at least 3 more interations including sway bar calculations need to be taken before I'd actually purchase any springs for an initial set-up.

Another thing to keep in mind is that these rates are for a RACE car! I've ridden in a TM that has spring rates about like that and while it is tolerable on the street, one could hardly call in comfortable. These rates are meant to keep the car from bottoming out on the bump stops and I've not taken any roll gradients in to account either, but based on what I know about my personal car's set-up, this is in the ballpark of what should be expected to be needed to have a nice track-day car suspension on one of our chassis.

With all that being said, the Eibach springs, even shortened the way I have them DO work fiarly well for a street driven TM that sees some auto-x and trakc day events on street tires. My DI from the event told me that everything about my car was set-up very well balanced and for my current configuration to leave it alone! :D There's no words to describe how good that makes me feel! :thumb: He did mention that the steering felt a bit heavy, but that's probably due to the fact that #1, he drives a RWD car, #2 I have fairly wide tires on the car, #3 I know the scrub radius is a bit more that stock due to the camber plates, #4 the offest of the wheels put more tire on the outside of the scrub radius, #5 it has an OBX in it!

He also mentioned that my brakes were "American pick-up truck sensitive". Now, he drove the car the second day after the fluid was already cooked pretty well(ATE Super Blue), so you had to have a bit of pedal travel to get initial bite, but once they did they didn't need much more input! I'm thinking about going to the larger D150 MC to try and help with this. I know it will numb the brakes a bit, but that could be helpful. What do you guys think about that?

[johnl]

I wish I knew somethiing about vehicle dynamics.:hail::clap:

[BlueBaron]

If anyone wants to know weight without scales...

Park your car on a flat surface. Slide a sturdy piece of paper (like card stock) against the front of the tire, and another behind.

_[]_

Measure the distance between the two pieces of paper. Important! Make sure the papers are parallel to each other! Now measure with the paper against either side of the tire.

_O_

Multiply these two numbers together, and you have the squarefoot area of the tire's footprint.

Now check the tire pressure with a precise gauge. (hopefully one that can read fractions)

Finally, multiply the pressure by the footprint. This number is the weight of that corner of the car.

[johnl]

If anyone wants to know weight without scales...

Park your car on a flat surface. Slide a sturdy piece of paper (like card stock) against the front of the tire, and another behind.

_[]_

Measure the distance between the two pieces of paper. Important! Make sure the papers are parallel to each other! Now measure with the paper against either side of the tire.

_O_

Multiply these two numbers together, and you have the squarefoot area of the tire's footprint.

Now check the tire pressure with a precise gauge. (hopefully one that can read fractions)

Finally, multiply the pressure by the footprint. This number is the weight of that corner of the car.


Wow. Who'd a thunk . . . ? :thumb::confused:

I can see how this method will yield relative corner weights if the initial pressures are more or less the same. And I can see that if the pressures from tire to tire are different that the lower pressure tires will show more footprint surface area while the higher pressure ones will show less footprint area - all offsetting and adjusting.

[Reaper1]

If anyone wants to know weight without scales...

Park your car on a flat surface. Slide a sturdy piece of paper (like card stock) against the front of the tire, and another behind.

_[]_

Measure the distance between the two pieces of paper. Important! Make sure the papers are parallel to each other! Now measure with the paper against either side of the tire.

_O_

Multiply these two numbers together, and you have the squarefoot area of the tire's footprint.

Now check the tire pressure with a precise gauge. (hopefully one that can read fractions)

Finally, multiply the pressure by the footprint. This number is the weight of that corner of the car.

This will get you close, but not racing scale close. The thing is each tire has its own characteristics regarding the sidewalls and tread. Hell, even two of the same tire at the same pressure will yeild different results!

I'm not knocking the Grassroots style by any means, but I would not try to set my corner or cross weights with this method...

[BlueBaron]

True.
If you drill a hole in the side of a tire, it'll still hold a wheel up. The sidewall has enough strength to hold some weight on it's own.

Definitely a good basic measuring tool though. Especially if your simply playing with a G-tech or such. :D

[GLHNSLHT2]

but, you could calculate a percentage of difference between two sides or front to rear, if not actual weights to get you close.

[Reaper1]

Yeah, you could. I dunno, I just kinda see this method as having a LOT of room for error. It's better than nothing for sure.

I'm just not a fan, that's all....

[GLHNSLHT2]

not all of us have access to cool engineering and race parts every day.

[Reaper1]

I don't either, but I find people who do!!

[t3rse]

no one has pulled out the plank and scale method yet?

[Reaper1]

^^I thought about it, but decided there was too much room for error...

[Speedeuphoria]

OK, so I replaced the rear pads with some Pep-Boys specials...STILL have a rear lock issue! WTF!!! This problem is p*ssing me off!! The car has a LOT more potential in it if I could use the brakes to their fullest potential.


Hey you dont mention what brake hoses you have? With all the other stuff mentioned I assume braided lines that are newer. But if its older hoses that could be your lockup issue.

[Pat]

no one has pulled out the plank and scale method yet?

I will be soon...

[86Shelby]

no one has pulled out the plank and scale method yet?

How about the late night drive to the grain elevator where they leave the scale display on and visible from outside? :amen: Front/rear side to side, however you can think to weight it. Just get out of there before the Sherriff drives by. Easy sheezy lemon peasy. I found less than a 10 pound difference between 3 elevators in the area; which were 25-30 miles away from each other.

[Reaper1]

Hey you dont mention what brake hoses you have? With all the other stuff mentioned I assume braided lines that are newer. But if its older hoses that could be your lockup issue.

Yes, all of the hoses are braided lines.

As an update I don't think the HUGE lock-up that my instructor induced was the rear brakes at all! I had to replace two of my tires, which WERE on the front when that happened, today because they were flat spotted THROUGH the tread of the tire! I would have had to DRAG the rear tires around the course in order to get the same results. So, seeing that I'm 100% positive the front brakes were locked during that little ride....starting at about 120mph at 300' from turn 1!! LOL


How about the late night drive to the grain elevator where they leave the scale display on and visible from outside? :amen: Front/rear side to side, however you can think to weight it. Just get out of there before the Sherriff drives by. Easy sheezy lemon peasy. I found less than a 10 pound difference between 3 elevators in the area; which were 25-30 miles away from each other.

There's not too many grain elevators in my neck of the woods. I know where there is one in Jacksonville around the corner from my house, BUT it is under lock and key! :(

["Top Fuel" Bender]

I will be soon...

Take a drive up to Quakertown,Pa
I can hook you up :thumb: