Raising or lowering the car to cure over/under is a false approach (at least for street cars). Your ride height should be set up as per required for the circumstances, ie. street, track, off-road, race rubber, rain, terrain, etc. Your handling should be set up after the height requirements have been determined.

While there are generalizations that one can follow with regards to handling, there are simply too many variables to make them true or optimum all of the time. Each situation has to be examined independently.

For instance, if your car is understeering, you need to address the issue by finding more grip for the front. Or, less desirably, you can reduce rear grip.

This MAY include adjusting the tire pressure, tire width, tire compound, decreasing front roll stiffness (through softer sways), increasing rear sway stiffness, adjusting camber, etc. More often than not, one has to consider all the variables and consequences, and use a combination of such in order to get as close to the intended result as possible with minimal negative side effects.

There is no universal "best way" to reduce understeer. It really depends on the particular car, setup, and sometimes, driver. While the commonly accepted rule-of-thumbs are applicable... it just depends on how involving one wants to go in fine-tuning the handling.

Ideally, you want to maximize your static mechanical grip (for your given tire choices) at all four corners, and tune the dynamic grip in a manner that is suitable for the driving style (neutral; slight under; slight over; tight in - lose out; high-speed under, low-speed under, etc) and adjust the suspension such that this is maintained as much as possible. You can go so far as to focus on maximizing your chasis for transitions, turn entry, constant radius turns, exits, etc.

For instance, if you want sharper (crisper) turn-in, you can try setting up your front camber with about 1/8 total toe-out for the street. However, how will your chasis respond to this... will it result in snap over-steer... will the rear follow obiediently... will the tramlining be too much for your liking, etc. Perhaps by increasing the front end's response, you will need to add additional rear grip.

Another example... if your tire pressure is such that they are at their maximium static grip, and yet, you've still got understeer, perhaps instead of adjusting the tire pressure to decrease the rear tires' mechanical grip, you should actually be looking at increasing the front tires' grip by increasing rear sway stiffness. Again, it really come down to that particular car and/or driver, and often times, what adjustments are even available for that particular setup.

An entire book can be written (and have been) on handling. There really is no simple way to quantify handling into summaries in these posts. We can only give suggestions to cure certain handling undersirables if they are presented. I realize this is a short explanation on a vast subject, but hope it sheds some light.

Stephen
'01 Turbo Ti Upsolute
1stephen1.com

 

Thanks for the input Stephen. The purpose of this thread is to get people to talk about the subject. In addition, to gaining some knowledge about what different changes do to the handling.

 

Another way to correct understeer is to widen front track (offset or spacers) while corrections to oversteer could be addressed by shortening the front track or widening the track at both front and rear.

Hey Joe W, did I hit another of your hot buttons with spacers?

 

Yep. ;P Widening the track helps a car corner better. Aside from
the mechanical weakness imparted by spacers, when you widen
the track you effectively soften the springs and shocks. This is
because you extend the length of the lever arm that your tire
uses to compress your springs. Usually it's not by much though.
Some track can be gained just by building wheels that go
farther out from the hub (assuming you have the fender
clearance). However, this can put more stress on the hub.

 

CJV
Hey, I agree that this is an important discussion but just like Stephan and Joe have said, it gets way complicated immediately and you need a whole lot of information to make a good decision. All the general rules have been covered so the only thing I will add is to say get someone who knows what they are doing, really knows, because there are many, many ways to address the issue.

 

Don't extreme low profile tires sometimes behave in reverse to pressure increases? The rear of my turbo seems to stick better with 34PSI than 42PSI. I think the higher pressures cause more crowning (O.D. growth) in the center of the tread.
The increased contact patch at lower pressures MAY outweigh the decreased sidewall stiffness.
However higher pressures may reduce the excessive wear on the outside tire edge.
I have no track experience in the turbo. My experience in autocross is to keep the width or the rear track as narrow as possible. Those 13" wide steamroller rear tires knock over pylons and effectively make the gates narrower. My Tiger was about a foot narrower than some of the Porsches and Corvettes I used to run against and I believe this was a big advantage (in autocross).

 

The other possibility is that some of us, me for one, are completely naive to the handling and what would correct certain handling "problems" I am reading this thread with much interest. Great topic.

 

I am an expert to the extent that I know my C4S handles better than my pick-em-up truck.
Beyond that I don't know nutt'n, so I'll just stay up here on the porch and listen to all you Big Dogs.

 

Great topic, I wish I could contribute in some way, but some of this is way over my head. You have me thinkin' though about the handling subject. I like the way my car handles with the front setting "on the pss9s" a bit softer than the rear damping. This seems to allow the car to track better entering and exiting a corner. Just my personal perference that gives me the confidence to drive aggressive through a corner.

 

Chad... this sounds like you have the tire pressure thing backwards.

For correcting understeer (with front tire pressure) you want more front grip (surface area), therefore raising the front pressure, as you suggest, will be counter productive as you will be decreasing the contact patch and promote additional understeer. Front pressure should be reduced to correct understeer.

When correcting oversteer (with front tire pressure) you should increase front tire pressure to reduce front grip and essentially balance the side slip in corners.

Mike

 

This is THE topic which I am most interested in since I do DEs and I feel that my car is now as fast as I need it to be. I have tried the last two DEs to measure tire pressure and temp and have having a hard time. Since this is the starting point - any suggestions on tire pressures for Stock tires (starting presssures and goal pressures.) After I get the pressures right, then I can measure temperatures across the tires. (I have 18" SO2As and plan to go to MPSC.)

 

Keep talkin' guys. I have nothing to contribute unless anybody is interested in how to be clueless. But I've intently read what's been posted so far, so keep on goin'....

 

David:

It is surprisingly difficult to get good tire temperature information. A real good basic resource is the following link. This should help a lot.

http://www.turnfast.com/tech_handlin...pressure.lasso

Further, I really don't think P cars are all about handling. I would say they are the best compromise between, performance, handling, reliability, value, and styling. They are not the best at any one, but the best overall.

 

Zippy,

quote:
--------------------------------------------------------------------------------
Originally posted by cjv
... Take the tire pressures. If you want to correct for understeer you would raise the front tire pressures. If you wanted to correct for oversteer you would lower the front tire pressures. Correct?....
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"Chad... this sounds like you have the tire pressure thing backwards."

As Joe said above, none of the above suggestions can be taken by itself. In addition, you have to start at the middle or suggested setting. Slowly moving and testing. You only want to move and test one parimeter at a time. As for the above statement, it is correct. To see written documentation go to www.rogerkrausracing.com , then click on Tech Sheets, then understeer/oversteer.

 

ebaker,

On tight courses like those in autocross, wouldn't you want to set your car to oversteer a little? That is to allow the rear to slide just a bit.