Results 1 to 10 of 10

Thread: Spring rates for Drag Racing

  1. #1
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Spring rates for Drag Racing

    So I'm looking to upgrade the rear suspension on the Omni. I'm looking for the right spring rates I would need in order to catch the weight and throw it back forward smoothly.

    If the rear corners of the Omni were to weigh around 400lbs each, would it be appropriate to run around a 300lb/in spring? I would think that if you were to match the rear corner weight with a matching spring rate, that it would be too stiff for launching.

  2. #2
    turbo addict
    Join Date
    Dec 2005
    Location
    Woodville Ala.
    Posts
    1,727

    Re: Spring rates for Drag Racing

    This is a good topic! I have put a lot of thought into this topic but I have no solid answers yet as I have not had a running car for several years now. Shocks/struts also play a huge role and are just as important.

  3. #3
    Super Moderator Turbo Mopar Staff contraption22's Avatar
    Join Date
    Dec 2005
    Location
    Havertown, PA
    Posts
    9,517

    Re: Spring rates for Drag Racing

    Might as well put out there that auto and manual cars will have different needs here. My car is auto and is very happy to have 500lb springs in the rear and very soft springs up front.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  4. #4
    turbo addict
    Join Date
    Dec 2005
    Location
    Woodville Ala.
    Posts
    1,727

    Re: Spring rates for Drag Racing

    Quote Originally Posted by contraption22 View Post
    Might as well put out there that auto and manual cars will have different needs here. My car is auto and is very happy to have 500lb springs in the rear and very soft springs up front.
    Agreed on the auto vs. manual needing different rates. I feel the front springs needs to allow enough front end rise/travel during launch to keep the front tires from possibly being jerked off the pavement (wheelie effect) which will cause loss of traction. But then allow the front end to settle back down as quickly as possible. Adjustable rate struts can help accomplish this. Even the number of coils of the springs front and/or rear while keeping the spring rate the same will effect things (stored energy).

  5. #5
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Re: Spring rates for Drag Racing

    Well, what I mean is that spring rate is defined as how many pounds it will take to compress a spring by one inch. So a 100lb/in rated spring will take 100 pounds to compress the spring one inch.

    When a FWD car launches, the rear tires can see a significant increase of load on the rear suspension. At the same time, the front tires will have a decrease of load on the front suspension and on the front tires. So if the rear corners weighed 400 pounds each at static (not moving) and we had 400lb/in springs on them, then they would compress one inch downward. It would take an additional 400 pounds to compress the springs one more inch.

    Now the reason I want to ask if 300lb/in rated springs would be appropriate is for the initial launch. I understand that shocks also help, which is why I've ordered some adjustable rear shocks to dial in the dampening. With 300lb/in springs mounted under the corners of a theoretical 400 pound corner weight rear, the springs will be just soft enough to compress under the static weight of the vehicle plus the extra load on launch in order to give way for the shocks to lend a helping hand.

    The way I see it is that if you have too heavy of a spring supporting the car, you're not really giving the shocks a chance to work..?

  6. #6
    turbo addict
    Join Date
    Dec 2005
    Location
    Woodville Ala.
    Posts
    1,727

    Re: Spring rates for Drag Racing

    Quote Originally Posted by BoostedDrummer View Post
    Well, what I mean is that spring rate is defined as how many pounds it will take to compress a spring by one inch. So a 100lb/in rated spring will take 100 pounds to compress the spring one inch.

    When a FWD car launches, the rear tires can see a significant increase of load on the rear suspension. At the same time, the front tires will have a decrease of load on the front suspension and on the front tires. So if the rear corners weighed 400 pounds each at static (not moving) and we had 400lb/in springs on them, then they would compress one inch downward. It would take an additional 400 pounds to compress the springs one more inch.

    Now the reason I want to ask if 300lb/in rated springs would be appropriate is for the initial launch. I understand that shocks also help, which is why I've ordered some adjustable rear shocks to dial in the dampening. With 300lb/in springs mounted under the corners of a theoretical 400 pound corner weight rear, the springs will be just soft enough to compress under the static weight of the vehicle plus the extra load on launch in order to give way for the shocks to lend a helping hand.

    The way I see it is that if you have too heavy of a spring supporting the car, you're not really giving the shocks a chance to work..?
    I can agree with your logic but I feel this is something that will have to be setup for each car combo to get the best results. In other words document all spring rates and shock settings, then get the 60' times. Make a change (one at a time) then see how that change effects the 60'.

  7. #7
    turbo addict
    Join Date
    Dec 2005
    Location
    Woodville Ala.
    Posts
    1,727

    Re: Spring rates for Drag Racing

    I think it would be awesome and very helpful if someone would post results of how different spring rates and shock/strut settings effect 60' times.

  8. #8
    boostaholic
    Join Date
    Feb 2012
    Location
    socal
    Posts
    1,241

    Re: Spring rates for Drag Racing

    On shock settings, up front I'd think you would want min ride height, minimum rebound dampening and max compression dampening. Kind of the opposite of what you would do in a stock class autocrosser. Jacking up instead of jacking down. When the weight transfer tries to squat the rear, then throws it back up front.. the compression damping will keep the front from squatting back down to where it was, and instead that force will push the tires in to the track. I think this "throwing back" was discussed by a few peeps in a previous thread.

  9. #9
    turbo addict Turbo Mopar Contributor
    Join Date
    Dec 2005
    Location
    Seattle
    Posts
    7,063

    Re: Spring rates for Drag Racing

    Coilover setups you can get away with buying multiple springs since they are affordable. Try some things out because I would take the guesses with a grain of salt. I would also have the adjustable struts that can handle your spring choices. Double adjustable for the most options to play with.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  10. #10
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Re: Spring rates for Drag Racing

    My theory would be that for the front, you would want enough spring weight to hold the engine and all that a a respectable amount with a little bit of softness to them. For dampening, I'd say they would have to be set toward the upper area of stiffness, maybe the 75% range, mainly due to the "in-between" shifts where the nose would dip down.

Similar Threads

  1. Looking for spring rates
    By Force Fed Mopar in forum Suspension, Brakes, Wheels, Traction
    Replies: 50
    Last Post: 01-10-2018, 04:03 PM
  2. Spring Rates
    By 85daytona in forum Suspension, Brakes, Wheels, Traction
    Replies: 6
    Last Post: 10-01-2009, 01:17 PM
  3. Anyone know the spring rates between 86 CS and 88 Shelby Z.
    By Tonatom in forum Suspension, Brakes, Wheels, Traction
    Replies: 0
    Last Post: 02-15-2008, 10:55 PM
  4. Spring rates for drag race
    By contraption22 in forum Suspension, Brakes, Wheels, Traction
    Replies: 6
    Last Post: 03-12-2007, 05:36 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •