FastZ33

iTrader: (29)

stiffen up the rear

dovla

+1
Including myself!


Kolia, I’ll try, although my knowledge on the subject is very limited, hopefully I understood your question:

I read somewhere that tires loose traction with slip angle above +/- 6 (~10) degrees. If you have no other means of controlling weight transfer during cornering (which affects slip angle) then tweaking tire pressures is great (although limited) aid in under/over steer control.

chishifu

iTrader: (5)

I have read the posts about spring rate, in particular what betamotorsports had to say, but I have to believe there is more the the explanation than just spring rate. Agreed that stiffening one end of the car to a point will increase overall grip at that end, which is what increasing front tire pressure would do to cure understeer, but what about contact patch?

Err... I actually think i'm just going in circles and confusing myself, I'm going to talk to some professors and racers later today and try to come up with more comprehensive explanation. Thanks for pointing me back to the tire spring rate conversation though.. it cleared things up a bit.

Regarding, slip angles, I did not imply more slip angle = more grip in a corner. In fact, you pretty much lose all grip after about 10 degrees or so. I guess my example isn't really applicable huh... i think i'll edit it.

dovla

I dont know, internet and either/or Sullivan's "Going Faster" & Smith's "Drive to Win" books.

gunslinger

Well, from reading posts we're getting lots bits and pieces....

Recently I got time in a legends car. They're basically a a spec series based on short wheel base car, a sealed 1250cc yamaha engine, and they run on hard compound dot tires. I found depending on how I hit the brake zone, how I apexed, and when I got on the accelerator I could make the car push or go loose just about anywhere in the turn. The point being, these cars are overpowered for the hard compound tires to the point that they amplify my poor driving techniques. After some time in the car I was able to take a turn I was pushing in and change my technique to the point of being loose. I was told by a course instructor and the reigning road course national champ that the car was tight. I was never consistent enough to truly figure this out (yet!). This is the same reason many experienced drivers tell beginners NOT to use a true R compound tire. Using a sticky tire will compensate for poor skills. A lot of poster were trying to tell the originator of the thread that a faster driver will compensate to get the max out of each turn and learn to do this first before making changes. There's a reason I bring this up...

Now back to discrepancy with the tire pressures and spring rates. First, we'll assume that the tires are running within a near optimal range. Another words, they are not over or under inflated causing any perceptible problems with the contact patch. Of course, in many cases this could be the problem. Second, and probably most important, we'll assume a driver is driving that can get 10/10ths out of the car. Third, we're using a pyrometer to measure the temps. We may have used the pyrometer to get to the optimal tire pressure zone. Now, if the car has a push through the turn AND the front tires are hotter in proportion to the rear, this tells me that there is too much weight up front and the tire adhesion isn't enough to compensate for the inertia that's trying to push the front end out. Again, the experienced driver isn't overdriving the entry causing the push. As one of those links says, were in a steady state understeer. Therefore, increasing the front tire pressure or reducing the rear will transfer some weight to the back, trying to keep the weigh distribution equal so that all the tires work the same. After the change, the car should be more equally balanced. Try the opposite for getting loose through the turn and then try and apply similar reasoning to the others scenarios (loose or tight into, out of, in the middle, etc) with the assumption you are really pushing the limits. BTW, this is just one "cure" that will help get those fractions of seconds out of the car.

Otherwise, it comes to technique. I was told once that you should divide a turn into three parts; brakezone, turning zone, accelerating zone and they should never overlap (at least until you're experienced!). Braking hard too late into a slow turn is surely going to cause the car to push. An experienced driver will avoid this by not overdriving the corner entry. Thereby, running a faster lap.

Ultimately, I think some of these web pages need to be taken with a grain of salt and one must be able to read between the lines or you'll get in a lot more trouble.

betamotorsports

iTrader: (1)

This thread is looking like a dead horse...

A reminder:

There is no one correct answer to solving any handling problem. Those of you who must have clear, precise, unrefutable, fully tested, theory and application (down to the third decimal) regarding vehicle dynamics are either German by birth or have little understanding of the ambiguous nature of the carbon based control unit and the elastomer based contact patch.

Get over it and go out to the track and test, test, test.

eeZee

LOL... This is probably the best advice of this whole thread.

OK, since I started this thread, I completed 4 autoslalom events and here is what worked for me:
1. Slow down!
2. Best tire pressures for stock RE040 on my stock 06 350Z on a 2+ minute airport course that worked for my style of driving were 38 front, 36 rear. FYI, I started with 34 front, 37 rear. Anyways...
3. Slow down!!
4. Slow down some more...

I had an FTD during a test & tune day because I virtually eliminated front tire squeal by slowing down. Competition day was a different story with r-compound shod Miatas with much more experienced and smooth drivers, but I was happy being 6th in my Z.

So there, that's the best advice I got from this thread. Thank you!

jjwalker

iTrader: (2)

Hey eezee, I just realized you are the guy I sold my stock tires to, right? Hows the Z treating you?

black06z

iTrader: (1)

X 1,000,000,000

eeZee

Indeed it's me. As you can see from this thread, I'm really enjoying it!
Sent you pm.