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I just wanted to try to get opinions on what I think may be occuring with our STU car during autox runs.  Its a STI, running REO1 tires, usual Street Tourings susp mods.

Seems to me the car turns a bit better on the early runs (2 driver car), then seems to transition to more understeer with the late 2nd or 3rd runs.  My impression (and this is purely guessing) is that the front tires heat up faster than the rears, so the front tires grip better then rears during the first few runs.  So we see pretty good front grip (relative to the rear), the rear end rotates nicely, and though a bit loose, is pretty driveable.  Then as the tires continue to warm up, maybe the rears heat up to a more optimal temp, and the fronts may be going toward too hot (we do try to spray the tires), we get the dreaded front understeer.  Of course we could just be driving too hard into the corners trying to keep up with all the fast drivers, but hey, that nut behind the wheel always needs tightening :)

So, what type of suggestions do you all have?  Things I have considered: stiffen the rear shocks in rebound during later runs, try lowering the front tire pressure a few pounds in front to increase grip as the tires heat up (I'm not very sure of this, always have increased tire pressures moderately with heating tires), soften front rebound during later runs, keep the rear tires cool by spraying them every run, put more air into the rear tires with each run.

I guess I'm torn between setting up the car for handling for cold tires or warm tires, and if for warm tires then I have the warm front/cool rear tires balancing act.

Any help out there?  Should we go to race tires ? :)

 Thanks!

Don

Lot of things could cause this kind of behavior! Although I am not an ST-something expert in any way, this looks like that you rear tires gain a bit more grip for the later runs and they start to grip more and car rotates less. Less rotation from the rear end could make you to push harder and as a result you get an oversteer due to overdriving the car. You are also getting more familiar with the course so you are more confident that you can push harder as well.

Now, guessing aside, you need to measure your tire temps after each of the runs and see how things really change in that perspective. What you could also do is to find a driver who is pretty good (not trying to take anything away from your driving skills, btw) and more importantly consistent and give him to take it for a run or three and see what kind of results you are going to get.

Stiffening of the rear rebound for the later runs will help the transition of the car but steady state will not be affected as much. Still, easiest thing to try first!! You also have DCCD and if it is not at the full open getting more toward to that state could help too. Although I doubt this is the case here!

Or, you could just sell the car and get an EVO and forget about all of the issues!!!  

 

Good luck!

 

Fedja

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95 AWD #34 SM or ESP
"Let boost be with you...
...and bring some timing too!"
http://www.geocities.com/esp_er

I had the exact same experience in our 05 STU STi on RE-01Rs.  The car would be crazy good in the cold or on the first run, but once the tires got heat in them, it would push.  From my understanding, this is a function of the weight of the car and the forward weight bias.  You need to find a way to reduce the grip in the rear.

We found that the best solution was to stiffen the rear spring rates, and then concentrate on keeping the tires cool.  We would have a cooler of ice water, with towels soaking in it.  When we finished runs, we would put a wet towel on each tire, which would help keep them cool.  Also, if you found yourself understeering hard on a turn, back off for the rest of the run, so that the tires can cool for the next run.  Once the car understeers hard once, it sucks, and tends to understeer more and more.

In the end, we got tired of the car, and decided that whatever you do to it, it will still push in hot summer heat.  I have heard of others running stiff rear swaybars, low rear camber or higher rear rates to reduce the issue.  It was my wife's car, so she decided the best way to get rid of the push was to sell the car and get an S2000.  But there apparently is hope, as a lot of other people seem content in STU.

-Brian 

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89/189 STS/STX '89 Civic Si

Thanks for the quick reply guys!

Sell the car? Nah, finally paid off so it's probaby cheaper to go with some Hoosiers and play in SM.  Yeah, power!

I appreciate the feedback.  We've taken some steps to improve the front grip, and things have improved, but yes, the rear seems to hook up pretty well.  Seems like whatever we try to do, it needs to be a method that we can vary with each succeeding run. eg, adjusting shock, cooling tire, adjusting pressure.  Nothing seems static.

Good feedback!  Thanks.

 

In addition to softening the front roll and/or stiffening the rear, which will help even out your tire temps, the next step is to size your tires accordingly. A narrower tire in the rear (or wider in the front if the ruls can handle it) will also aid in keeping your front and rear temperatures balanced so that with each consecutive run, the car will have consistent behavior . The key though, is taking tire temperatures to take the guess work out of setup changes as mentioned in an above post.

bsclywilly:

In addition to softening the front roll and/or stiffening the rear, which will help even out your tire temps, the next step is to size your tires accordingly. A narrower tire in the rear (or wider in the front if the ruls can handle it) will also aid in keeping your front and rear temperatures balanced so that with each consecutive run, the car will have consistent behavior . The key though, is taking tire temperatures to take the guess work out of setup changes as mentioned in an above post.

We run into this with out STS car, our solution to cool the front tires only.  We spray the crap out of them.  It is not uncommon for us to go through a 3 gallon sprayer worth of water over 5 runs (2 driver car).

When we get back from runs the first thing we do is spray the tires, you can find our grid spot by following the stream of water up stream.

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Jason Frank
Bridgestone / datatoys.com / Redshift Motorsports STS Civic Si

TeamUndercoatRacing.com

Ok, it seems that we have some interesting options to keep the front gripping, and slow the rears from gripping so well.  If I assume we've done all we can reasonably do to max the front grip, then I guess the next option is to decrease the increasing rear grip.

Increasing rear shock rebound as runs increase, maybe increase rear tire pressure with each run, mount slightly older (and harder) tires in the rears.

Would increasing compression setting in the rears be of any benefit?  I'm inclined to only increase rebound for fear that increasing compression might decrease stability entering turns.  My focus presently if more corner entry turn-in, and not so much steady state cornering grip (which is fairly ok, but could improve too).

Don

I think I would prefer to adjusting the rear tire pressures to reduce grip, it would leave the handling characteristics the same on the, just reducing the overall grip threshold.

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Jason Frank
Bridgestone / datatoys.com / Redshift Motorsports STS Civic Si

TeamUndercoatRacing.com

If your main goal is to increase the corner entry turn-in then a bit of extra rebound in the rear would accomplish that! Adding more of the tire pressure in the rear would act as few extra pounds on your spring rates. Something else that wasn't mentioned is to raise the rear end of the car a bit (1/4" or even 1/2") which might help as well. This way you might have a bit looser car for the first runs, but it would pay much more on the real run when you are more familiar with everything around you - like course for example!

 

Good luck!

Fedja

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95 AWD #34 SM or ESP
"Let boost be with you...
...and bring some timing too!"
http://www.geocities.com/esp_er

Think about a tire change, it's quite possible that another tire doesn't hate heat as much.  The only think "changing" over the runs is the tire temps and how hard they get worked. 

Sure you could more camber in, stiffen the rear in general, try different shock settings and a whole list of other things too.  All of which are band-aids you are applying to the car to cover a heat issue with front tires.  I'm not saying the tires suck or it's the fault of the Re-01r's, I'm saying it's a driver/car/tire temp issue.  And if the car is decently balanced most times the setup can't be completely messed up (in theory).  Testing in involved, sorry to say, testing things up to and including tires because tires do make the most difference to a car's performance.  If you can't find another tire that deals with the issue better, ok, then you need to reinvent your suspension tuning idea's.

 And fwiw, the fact different tires might help does not excuse overdriving... that'll cook any tire. 

 

MHO

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Sam Strano
Owner--Strano Performance Parts
800-729-1831

I appreciate all the feedback and suggestions.  We will continue to test and play with settings.  Maybe it's the tires.  We have a fairly heavy car, and lots of load are on  the front tires.  I stated early on that the front tires are heating up, and faster than the rears.  This is not unexpected in a FWD or AWD car.  I believe this would happen with enough runs, whether I'm driving at 11/10ths and overcooking the tires, or settle down to 8/10ths speed.

Given that the front tires will heat up faster than the rears, regardless of our use of Bridgestones, Yokos, Falkens, Kumhos, or Dunlops, I still wonder how best to adjust other settings of the car (or driver, in the driver/car/tire model) to accomodate the tire performance changes.  As a driver, I'm probably changing every run, my tires are changing every run,  but my susp settings are unchanging.  So, naturally I'm leaning toward minor changes to susp settings with each run.  Call it a bandaid, but one of the things I remember Mark Daddio writing in a tuning article was that he was constantly evaluating and changing car settings with each run.  Every surface is different, every climate plays a role.

Such are the challenges of the sport!

 

Well, I wouldn't just follow the things Mark does for him selves!! Well, at least I would be careful with that particular one. He is one of few that can do these changes after every run due to the his ability and knowledge of what he is doing at the time! There are so many of us who try to do the same, but in most cases just shot ourselves in the foot while doing so. When changing the car too much you could ended up driving a different car for every single run and that would never allow you to get to know the car you are trying to drive. So, from most of the thing Mark does I would be very cautious with this particular one!!

Good luck!

Fedja
 

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95 AWD #34 SM or ESP
"Let boost be with you...
...and bring some timing too!"
http://www.geocities.com/esp_er

No, I won't be crawling underneath adjusting swaybars or changing alignment settings.  Too lazy and slow for that.  Probably just very simple air pressure changes, maybe a slight adjustment of the shocks.  I've been soundly outdriven by Mark at Nats, so I don't even pretend to be in the same universe, but I still play a few things, and go through some motions.

On a postitive note, this past weekend some of the "minor" changes helped a bit.