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  #61  
Old 04-17-2003, 04:46 PM
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Originally posted by kuoh
So Subaru intentionally designed the SVX with the pressure differentials but failed to do so with the WRX? Personally, I think the pressure recommendations for the SVX was more for ride comfort than any inherent binding or tranny noise issues. The fix may work for the WRX, but I have doubts as to whether it is the root cause of their problem.

KuoH

ALL ALL WHEEL DRIVE EQUIPPED SUBARUS HAVE A RECOMMENDED 3-5PSI DIFFERENCE IN AIR PRESSURE FRONT TO REAR. THIS HOLDS TRUE FOR EVERY AWD SUBARU EVER MADE.
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  #62  
Old 04-17-2003, 04:48 PM
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Originally posted by mbtoloczko
hehe. I wasn't trying to start another argument about tire pressures. I'm a believer. :-) Just trying to convince you of my opinion that the front tires travel further than the rear tires in corners.
Yes, I believe you.


I also believe that when you STOP turning, the variation in rotation also stops.

It's not the distance rotated that is the problem.... it is the fact that that difference in rotation is CONSTANT when the pressures are wrong, and therefore builds heat and viscosity.

The total distance the front and rear sets of wheels have traveled compared to each other is irrelevant. The average of how often there is a difference in rotation front/rear is very relevant.
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  #63  
Old 04-17-2003, 06:12 PM
oab_au oab_au is offline
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Location: Coffs Harb, Australia.
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Cupping and skating.

To get back to the cupping.

This is usually due to suspension faults, as someone has already said. The cause depends on the type eg. how far between peaks. The cause, shocks, loose suspension, alignment.

I don't have cold weather down here, so I use the one set of tyres all year, I suppose that the winter tyres that you use, would be a much softer compound than a summer tyre and would not stand up to the heat as well.

As for Jasion's "go fast handling tip" of running the tyre at max pressure.

The Tyre Co. put a fair bit of work into designing a tyre. The contact patch, as all bike riders know, is all important. The shape, length, cooling, water dispercial and life are the design criteria. These can only be meet if the load @ pressure specifications are complied with. As the load is increased the pressure has to be increased to produce the same patch profile. The rating on the tyre has the sign @ inserted between the load and the pressure. They go together, each is not an option. The pressure on the car sticker is the recommonded pressure for normal use, for more load or sustained high speed the pressure can be increased a few psi. I run 35 front 33 rear on Bridgstone SO-2.

Increasing the pressure to the max will stiffen the side walls, to give faster steering but with the loss of tyre contact patch and designed profile. This sort of pressure is ok for an auto X but it is definitly not to be used on the hi-way for general use.
IT IS DANGEROUS.

With out the necessary load to match the pressure the tyre contact patch will distort to a shallow dome shape. This is diabolical in the wet as it destroys the water handling qualities of the tyre, to produce a condition of aquaplaning. The steering may be quicker but losing it in wet weather, will also be quicker.

Be aware of the reasions and results of doing this and be safe.

Harvey.
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  #64  
Old 04-17-2003, 08:01 PM
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The absolute best results can be reached by using the following procedure... this was stolen from an excellent post on NASIOC:

Quote:
Posted by Dands42 on 04-17-2003 10:50 AM:

You can go a little more high tech with this tire pressure thing and get it perfect for any tire.

Last track event I had a similar issue. It was my first track day in the car and the first time with this brand of tire, so I had no idea where to start.

I borrowed an infrared temperature gun from work. For those of you who have not heard of this I'll give you a brief run through of the process.

1) Take a guess at the right pressures and take an autocross run or a few laps on the track.

2) Measure the temp across the contact patch starting with the outside then the center then the inside. Write it down and go to the next tire.

3) What you are looking for is a trend. If the center is less than the outer areas, add more air. If the center is higher, let some out.

That's the generic version. You can also adjust your camber this way... if you see that outside of the tire is higher then the center is less then the inside in a linear way, then you don't have enough negative camber but the pressure is pretty good because there is no "bow" in the numbers. I have been told that the ideal camber set up is such that the inside temps are slightly higher lets say 120 125 130 from outside to inside. This came from an SCCA club racer who really knew his stuff, a U.S. Marine engineer looking kind of guy.

Looking at the front to rear differences can tell you what you probably already know: it will tell you how much work either end is doing. If the fronts get much hotter than the rears then the rears are not working as hard and the car is understeering. Steering will also add some heat to the fronts. But like I said, you already knew that but it can tell you if the change you made really made a difference.

I got my pressures dialed in and found I needed a lot more negative camber and of course I found out that my car understeers badly.

Hope this helps.

Dan
I edited the post pretty extensively for grammar and content... no offense to the original poster, his ideas are good.
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