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This might seem like a dumb question form someone with 40 years experience.For the last 10 years I have been racing eather on pavement or smooth dry slick tracks.Reciently I joined the sport compact division on a tacky but bumpy track.I thought the ruts were 10 feet deep until I walked the track and discovered the ruts were small so the problem is my setup.It doesnt feel like Im bottoming out but the ride is beating me to pieces.To save time Im asking if I should increase spring rate or shock dampening or both.The car is a FWD with 65% front %.The rear seems to break traction under a large lateral load.

 

I experienced this same thing at HOT years ago.I failed to qualify on Friday so Sat I installed a taller suspension with similar shocks.This raised the roll center but the car quit bottoming out and won the last chance race.I cant remember if the springs were stiffer or just cut less.So to smooth out the ride on a bumpy track what is the best starting point?I run street tires with little sidewall so air is no help.Spring rate?Ride height?Shock dampening?My current set up is fast on slick smooth tracks.

 

I drive 6 hours round trip to race and any help could dimish negative testing.Thanks in advance. G.B.

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I would like to help you out but just about everything I know about racing I learned from you!

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...It doesnt feel like Im bottoming out but the ride is beating me to pieces.To save time Im asking if I should increase spring rate or shock dampening or both.The car is a FWD with 65% front %.The rear seems to break traction under a large lateral load...

As you know, GB, there are about a bazillion possible solutions to the rut problem on dirt tracks and I claim no special corner of the truth. But there are some principles to keep in mind.

 

General rule of thumbs:

 

1) Bottoming out the suspension (springs, shocks, a-arms, etc) at any corner, or bottoming of any body/chassis part on the track is a big no-no. Take the springs out and disconnect the sway bar(s) and run the suspension up and down and see what bottoms or binds up first. Then make a note of where that happened by looking at the shock travel at that point. If you car uses more travel out on the track than the limit you observed at the shop, you're binding or bottoming the suspension. Stiffen the springs a notch or two if that's the case and go with a bit stiffer shocks. Or if the car is hitting the track surface somewhere, you need to stiffen up as well.

 

When I say stiffer, I mean two things. 1) increased spring rates over what's currently in the car 2) stiffer overall rated shocks or greater compression numbers if you have variable rate or adjustable/rebuildable shocks.

 

2) If you car is not bottoming or binding, the general rule of thumb is to go as soft on the springs as you can on a bumpy track. Let the springs and shocks and tires and wheels "float" over the bumps, ruts, drop offs, etc. rather than the whole chassis.

 

3) Raising the vertical roll center will decrease the amount of body roll which may help out if stuff is bottoming out. However, doing so will also increase the horizontal (lateral) loads in the turns. That's because a higher percentage of your weight transfer will be felt at the right side tire contact patches as lateral acceleration rather than as downforce created by the moment-arm formed between the vertical center of gravity and the longitudinal roll axis.

 

Not much help, but hope it helps anyway.

 

Nick

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Thanks for the info.The tire deal is we have to run DOT tires and the 13" tires are no longer sold.The Hoosers Dirt Boss works well with 8# of air but are not legal.No room for big 15s,little choice for 14s.So I have to work the suspension or find 205/13s that Tire Rack or Discount dont sell anymore.

 

The other problem is no aftermarket suspension parts.I change spring rates and shock dampening by using stock pieces from similar but heavier cars.I use a micrometer to measure spring diameter and cut springs for ride hights.It sounds like I need heavier springs,a little more ride highth and stiffer shocks.Maybe from a V6 Jetta.Thanks again for the info. G.B.

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Thanks for the info.The tire deal is we have to run DOT tires and the 13" tires are no longer sold.The Hoosers Dirt Boss works well with 8# of air but are not legal.No room for big 15s,little choice for 14s.So I have to work the suspension or find 205/13s that Tire Rack or Discount dont sell anymore.

 

The other problem is no aftermarket suspension parts.I change spring rates and shock dampening by using stock pieces from similar but heavier cars.I use a micrometer to measure spring diameter and cut springs for ride hights.It sounds like I need heavier springs,a little more ride highth and stiffer shocks.Maybe from a V6 Jetta.Thanks again for the info. G.B.

thats how we used to do the ss when i was a kid, kindof miss those days.

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Thanks for the info.The tire deal is we have to run DOT tires and the 13" tires are no longer sold.The Hoosers Dirt Boss works well with 8# of air but are not legal.No room for big 15s,little choice for 14s.So I have to work the suspension or find 205/13s that Tire Rack or Discount dont sell anymore.

 

The other problem is no aftermarket suspension parts.I change spring rates and shock dampening by using stock pieces from similar but heavier cars.I use a micrometer to measure spring diameter and cut springs for ride hights.It sounds like I need heavier springs,a little more ride highth and stiffer shocks.Maybe from a V6 Jetta.Thanks again for the info. G.B.

 

Can you use INEX 205/60R13's with a Dot stamp... That's the tires the legend guys use and I'm sure you got plenty of guys holding on to plenty. Might be something else to try if your used to those tire sizes...

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That sounds like a good choice to try.Where can they be bought?Any used ones around to try? Thanks again.

 

While I was at the track at Houston Motorsports Park there were a few there that were using used tires. You might put up a post in the classifieds and see if any Legend's cars have any pulloffs available. I know the team that I helped out there had a few that they gave to another driver and he may have extras. But he is in Houston...

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Can you tell me who sells this tire and what brand it is?The 205/60-13 is the perfect size I believe for sport compacts.I need to check it out and see if it can be approved since the tire choices have dwindeled on the open market.Thanks again.

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I believe that you can only get them NEW through INEX for the Legend Class. But there are quite a few of them used in Dallas and Houston. New I believe they I was told they were 140-160 but they get shaved to get different roll outs. I there there are a few guys one here like JC Umshied that might be able to tell you where you can get some of the tires. I believe it is a Federal tire or B.F. Goodrich...

Edited by SASPEEDRACER24

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