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Gus, The Rookie Wrencher
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Subject: Review #2 - "Getting a Handle on Handling"          Page 2  Previous  
 
Posted byMessage
Double KPosted on 4/2/2002 1:04:44 PM

As far as the springs go, I've always been one to believe that the RF should be roughly 100 lbs heavier than the LF. My car had a 1300 LF, and a 1400 RF. That seemed to scale the best. But in the case of PA88's car, he had a 200 lb difference with the heavier on the right.

My opinion was that if you were going to put a lighter rated spring on the right rather than the left, it should be done in the rear. I.E., a 250 LR and a 225 RR. That's just an example though, and I never tried it. Mine was 225's (leaf) across the rear.

I had kind of a wierd way of looking at stagger. Some guys live by it, some guys don't get to hung up. Remember what I said about tires????

Well, I used to simply grab tires off the stack at the race shop, and just run whatever I had. I blow them up to about 30 or 40 lbs., and sit them out in the sun for a day to stretch them out good. (We ran the Pro Am McCreary's).

After I stretched them real good, and let the air back down and cooled them off, I'd set the pressure to about 18lbs, then measure all of them.

Once I measure them, I put the tallest tire on the RF, then next one down on the LF, the next one down on the RR, and the shortest on the LR.

I knew after playin' around with my car long enough, about how much cross I would need by my stagger. If the stagger was real close across the rear, I'd take a little cross out. If the stagger was higher, say 2", I'd tighten up a little. Only by 1% or so, maybe 2% at times.

The tire deal got so frustrating trying to find the correct combinations, I went back to a deal I did years ago. We used to run street legal DOT steel belt radials. We never ran any stagger anywhere on the car way back in the late 80's, and I always had success setting up the car, so I figured I'd do the same thing since I didn't care for diggin' through the tire pile for hours!!!! LOL So I adjusted the car to whatever stagger I ended up with.

Now, stagger vs. cross weight. First, stagger will affect cross weight. For instance, you have your car set at 48% cross with 2" of stagger. If you're at the track, and decide to change the RR, and reduce the stagger to 1", the cross weight will increase. Just keep that in mind, and as you know, more cross increases the chances you'll develop a push. What stagger does is turns you rear end. Imagine a tootsie pop laying on a table. You simply give it a push while it's laying down, and the end of the sucker with the candy takes off rolling around the end with nothing. That's what the rear of your car does. If you have a ton of stagger, the right rear will want to take off and it'll feel loose. What I've seen happen, it a guy has a lot of stagger and his car is loose, so he cranks some cross weight in it, and it does little to no good. The reason? The rear end still wants to come around cuz the RR has all the weight on that tire, and, that tire covers more distance more quickly.

So be careful on stagger. It has a direct correlation with cross weight, and can really screw you up sometimes.

Also, and yes I know I'm long winded here, but hang on! I always, always, always suggest starting with a very basic set up before you start experimenting. Start with all the same wheel off sets, a basic "non-split" shock set up, basic tire pressures, and common sense stagger.

As someone said before, caster is critical in my opinion. Toe out should be checked every week. Tire temps can tell you not only where you camber should be set, but camber in the rear end to! If you tires are getting real hot at certain points on the rear, stagger can help you adjust the camber of the rear end. Tire temps will also tell you over/under inflation.

Well, I rambled way longer than I tought I would.

Let me know if you need anything else! But I still say a VERY BASIC beginning set up is key.

KK
 
racer31xPosted on 4/2/2002 1:05:55 PM

First, in response to BEEK, the possibility of him not being able to get as much caster due to the design limitations of his suspension is a good point. I'm not familiar with metric cars, that's why this forum is neat in that it lets people with such a wide range of experience have input. To Brian- are you sure that having too MUCH rear stagger would cause a push when throttle is applied? This seems opposite to what I've always thought, but of course I could be wrong(I thought I was wrong once before, but I was mistaken). I do agree that reducing wedge would help cure the push, but it's possible that would reduce forward drive off the corners as well if done to an extreme. So to try to keep forward bite I'd try the stagger first(whichever way, we decide is appropriate) if possible since he said at the track he runs on getting off the corners is key. From re-reading his first post I see he's already done one of the other things I was going to suggest, which is to run a bit less rear percentage. Also, I'm going to assume that his rules prohibit trailing the right rear.
 
proam88Posted on 4/2/2002 1:52:38 PM

Racer31x, Sorry, I meant to say too little stagger across the rear. Adding more stagger would help the mid-corner push and not affect forward bite as much. Sorry about the mix up!!!! One thing KK and I tried was changing wheel offsets to tighten or loosen a car. We would stick the RR out on a tacky track and tuck it in on a dry slick surface. On the scales it didn't effect bite and cross too much, but it did change it. We were trying to change the roll center of the car and let it roll over harder and the RR. This really tightened up the car for dry slick and we started using offset changes every race night.

Brian Scott
 
Double KPosted on 4/2/2002 2:05:28 PM

Most of us running around the Omaha area in the Pro Am's are allowed to move our upper control arm tower within one inch of factory specs. Most people move the LF out about 1" so that the proper camber in a Camaro can be obtained. We moved mind straight you about 3/4". Some also move it forward or backward depending on the caster to. I thought it was forward, but I can't remember for sure. That way you can get the numbers you need on both caster and camber.

KK


"I was NASCAR.....when NASCAR wasn't cool!!!

 
STOCK64Posted on 4/2/2002 2:11:29 PM

lol....you guys are hitting everything on the nail...i set the toe each week, and i also take tire temps after each race w/ a probe type pyrometer.(not laser)i set all the tires so all the tires are w/in 10 deg across the surfaces... and try to keep the tires w/in 20-25 deg from tire to tire... the other thing is we have to run a spec tire.. all the same... maybe 1"-2" max stagger if stretched... thats such a pain in the ass too... i just measure them all and put them accordingly on the car.. i scale the car each week and set ride heights also...so if i put a new tire on i have already scaled it w/ it and know what to do to get to what i need for scalling purposes. i also run #3 offsets on LF,LR,RR and a #2 on the RF. if it goes dry i put on a #5 RR, and a #2 LR... also remembering for every inch you move a tire out you have to put in 1 turn at that corner or vise versa if you move one in... to keep ride heights and %'s right...
31x you said to trail the RR? i lead the RR about 3/4".. did i go the wrong way.. i guess i wanted to tighten up the car since i was so loose the year b/f.... maybe i went to extremes on everything to fix my problem.. huh... it just really suck spinning out in front of cars....specially when your leading...LOL true story...
 
Double KPosted on 4/2/2002 3:55:30 PM

S64:

My offsets were all 2" all the way around until feature time. I'd switch to a 3" offset on the RR for the feature. I didn't mess with weight jacks at all (leaf rear with weight jacks only in front). I didn't touch them at the track, so I wouldn't throw off anything in the alignment.

My whole deal there was that yes, the cross changed when I changed to the 3" offset. I believe it only lowered the cross by a portion of a percent, but the feel of that right rear tire digging in harder gave the car a little more of a pushy feeling even though the cross lightened a little.

Your wheel offset deal may be a little bit on the radical side, JMO (just my opinion).

As far as the trailing rear, if I read you right, I can't help you much. Our cars had to be the same wheelbase on both sides. So we simply tried to square up the rear end the best we could.

I always set my ride height in a "Z" pattern, with the car changing 1/2" per corner. Using the frame, and watching shock travel, lets say the RF was at 8". The LF with then be 7 1/2", RR at 7", then the LR at 6 1/2". That way, the RF was approximately 1 1/2" higher than the LR. With leafs it was hard to set it exactly, so I didn't get too hung up on it.

Front to rear tracking width is also important. You almost always want the front to track wider than the rear. From center of tire to center of tire from LF to RF should be about 1 1/2" or so wider than center to center of LR to RR on a fairly flat track. High banks you want to make them closer, like 1/2" to 1". On a really flat track, you might want to go to 2".

Making that front end wider on a flat track makes the rear end kind of want to follow the front. It ads a lot of stability to the front, and helps with the creating a tighter condition on the flat track.

On a high bank, you want to be a little loose so you can kick around the rear end. So evening up the track width helps with that.

Picture it and you'll understand!!! LOL

Sounds like you got it all going pretty well. I'd say you're kickin' butt, except for maybe being a little radical in your changes. I'd try "baby steps" first LOL!

KK


"I was NASCAR.....when NASCAR wasn't cool!!!

 
racer31xPosted on 4/2/2002 7:31:20 PM

Brian- I figured you must have made a typo on the stagger deal. 64- I did say trail the right rear. Usually it's best to keep the rearend square, but where you're limited on the amount of stagger you can get, it would be an option. However, since you said you lead it instead, assuming this was before you made the changes to where you are now, it might be a good thing to try squaring it back up again now that you're getting more weight transfer back to the left rear. Most people say to always run the rearend square, however on a latemodel that runs the shock behind on the left rear, which builds a ton of dynamic wedge, Dale McDowell said he generally trails the RR about 3/4". I also agree with what is being said on wheel offsets. Once you get your chassis close, there's alot of fine-tuning you can do there. Also keep in mind that increasing tire pressure has the same effect as putting in a slightly stiffer spring, so there's even more tuneability.
 
TheBad Posted on 4/4/2002 12:41:20 PM

Anyone want to share there expereience on setting bump steer, specifically on a GM Metric car....
 
SLEEPY GOMEZPosted on 4/16/2002 11:09:00 PM

TheBad asked about bump steer setting experience. It has been a while, no one has taken the bait and I can't resist a baited hook. First the definition, bump steer is the steering movement in a wheel when that wheel is cycled through its upward suspension travel. Next, how important is bump steer? To me this is the last thing to worry about until all other items of the front suspension are set right. How much bump steer is acceptable? 1/4" in 4" of bump, 1/8", .060", .010"? In a winston cup car probably .005", in a short track dirt car....? How is this measured, 10" off center of the wheel, 20", 5"? I don't know of a standard which is used across the board to define the amount of bump steer. .010" on one racer's gauge could be 1/16" on another. Setting bump steer is done by means of relocating pivot points of the steering and suspension systems. Is it ok to heat and/or cold bend steering arms? Cut and weld steering parts?

So my questions are: 1 how important is bump steer. 2 what is an acceptable amount. 3 how do you measure it. 4 how do you adjust it?

This ought to get some thinkers working. Educate me and TheBad on this, SLEEPY


 

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