New M&H Slicks air presure

[rpmguy]

Just got my new M&H slicks :thumb: What should I start out with air pressure. 14? They are the 7.5 23" running on my 90 shadow.

Going to be racing buddies from work next week at the track. One of them is a 1990 GTA, othe is 1955 chevy shoebox with 502. I think I can take both of them. I will try to post videos. Later ;)

[BIG PSI]

14 psi is a good starting point.

The best way to tell is do a burnout with them and measure the footprint of the rubber laid down compare to the footprint on the slick.

If the footprint is smaller on the ground then you have to much air causing a crown on the slicks.

Chuck

[BadAssPerformance]

14 might work... depending on weight of the car and HP might be a tad high, but start there and go down.

Also, measure before and after every run. The tires heat up during the burnout/run so unless they are still warm, the pressure before wont exactly be accurate...

[Reeves]

+1 to JT's post. This year I have been running 23" M+H on a 13" wheel. Lots of sidewall. I get away with pressures around 6.5psi. But that really depends on weight of car as well.

Start at 14, although I think that will be too much.
Definately check pressure right after your 1st two passes.

[David Rose]

I have a set of M&H 24.5X8.5X15 that i run at 8 psi.I started at 12 but called M&H and they recommended 7-8 psi.By lowering to 8 it dropped my 60ft 1.81 down to 1.69.Call M&H and tell them your set-up they will give you the right pressure to be at.

[BadAssPerformance]

Depends on how heavy the car is... M&H told me 8-9psi too but that is too low for my big heavy FWD car

[shadow88]

I start at 18 and work my way down until I hear them flop around in the shut down area. This is usually around 10-12 psi. I never run under that. Full weight pluss a bit 88 P body.

[Turbo3Iroc]

I called up a few years ago and they told me 15! I was like yeah right, end of asking them questions.

23" tires on a heavy car you don't want to go much below 12. In a P body you might be able to get away with a little less. Be careful on turns.

[rpmguy]

Thanks, going to shim sway bar also. Dont have time to do it right with the end links until winter. I have two v8 to try to put the spank on next week.

[BadAssPerformance]

Shouldnt have to play sway-bar games with slicks... I've never had to.

[rpmguy]

Not woth messing with the sway bar with slicks? What about the water box, will I spin both or just pass side. I need to leave real hard on my bubbies. Any other little trick? How much is pulling the power steering belt worth?

[Vigo]

What about the water box, will I spin both or just pass side

Good thinking, that is the only place you will really have to worry about spinning one.. but even then, pretty much only if you have an auto. If you have a 5spd you can break them both loose pretty consistently, from what ive observed.

If you're auto, definitely have someone watching your burnout to make sure both are spinning.

And remember the speed sensor only reads off the passenger axle so if you're making noise and smoke and the speedo doesnt move, that right side isnt spinning. That situation doesnt come up very often, though.

[Reeves]

Shouldnt have to play sway-bar games with slicks... I've never had to.

Back in the day…..Ken and I both had pretty good luck shimming our sway bars. That was with the old popular MT 22”ers though.


Not woth messing with the sway bar with slicks? What about the water box, will I spin both or just pass side. I need to leave real hard on my bubbies. Any other little trick? How much is pulling the power steering belt worth?

If you got time, I’d still do the sway bar shimming.

If it’s a manual trans, do a 2nd gear burnout in the tail end of the water box. Let it eat there for a while if the back wheels will hold you (ebrake on) and once you see some smoke, let off the brake and let it roll out…..still burning the tires. When they grab and the motor bogs, you should be good. Don’t peg leg a burnout….you’ll be crying when your diff pin sh*ts the bed.

Power steering belt will give you a couple more ponies, but make sure you put your big girl panties on. Turning a power rack without the belt and with slicks is a chore. It is definitely doable…..just be ready by eating your wheaties.

Air up your back tires pretty good for less rolling resistance.

Got air shocks on the back?

Got upgraded control arm bushings? If not, be prepared for possible wheel hop. Bad wheel hop = broken axles. Try not to wheel hop it too bad.

[rpmguy]

Car is an auto. I will try my best to light both. If not I will just drive around the water. So start with a 1/2" shim under bushing of the drivers side sway bar.

[Ondonti]

I don't see you having any performance/hp guesses for yourself in the thread.

Beyond the air pressure making sure you are not completely riding on the rims, you will be in charge of balancing tire spin vs bog. I would suggest not messing with tune/boost when figuring out your slick pressures, and your launching technique better be consistent on that auto.

Its better to err on the side of tire spin then to bog. Slicks still accelerate well when spinning. FWD manual trans cars really need 20% wheel spin in 1st to get the best most consistent 60'.
Auto trans cars with a loose converter can worry less about this. I think your converter is a big deal in figuring out your slicks. Stock converter is going to be more likely to bog.

Buy a 0-15psi gauge and check before every pass, check out the slicks surface and see if the tire is hazing evenly across the tire, just in the center, or cupping badly on the outside. If you have enough power, FWD prefers to cup the tire rather then wear out the middle. Cupping the tire gives even more sidewall flex.

I start out around 9 psi on a fun night and then drop towards 8 if the track is sucking. 15" wheels suck for running low pressure unless you have a 26" tire.

I pre-spin my tires in the water box a few revolutions and pull out of the water box for burnouts, but that is because the track people are picky. The pre-spin gets the tires wet so they will not fight me when I burnout on the dry pavement after the box.

If they will let you start the real burnout in the water box, it should be easy to get both going. I don't bother E braking or anything, I just burnout until the slicks rip me forward. You may not even need a burnout. This is something you get to find out. New slicks are the best btw :evil:
So many people here run old slicks that have dried out rubber and even in big sizes they don't hook up, then you see Reeves running 23's on a 10 second 5 speed.

[rpmguy]

Cool, going to track friday night. Will post results:thumb: I did shim the sway bar with a 5/8" alum block. What a difference, both tires light up with street tires. I did get New M&H, should be fun. Huges converter only lets me stall about 3100 before pushing. Feels like the tires should take it all. Getting a fiver of fuel this week. Not sure about boost, already way off the stock gauge LOL.
Later