Tire size and handling

[4agdtym]

It's nearly time for a new set of rear tires. I am currently running Falken Azenis AT615

225/40 R18 front

265/35 R18 rear

As far as I know (I'm the second owner) the suspension is stock 2001 986. The car has about 61 thousand miles.

I'm noticing some oversteer or at least a tendency toward it. My first tires were the Dunlop sport 9090. I went threw two sets. I was essentially unable to get oversteer without making major mistakes - she really wanted to understeer with those tires. The Falkens are nearly impossible to understeer - they are so much sticker!

I'm wondering what my options are to address the oversteer - to improve the balance. I feel safer (more control) with understeer than with oversteer.

I'm thinking about wider rubber on the rear...How wide can my rims handle before I'd need a wider rim (I believe they are the 9.5" model).

I just had the car aligned. I notice that the steering feels "lighter" - it is easier to turn. The car doesn't have the same intense desire to go straight that it had before the alignment. The alignment tech said that one rear wheel was way out of camber, but didn't say much about how the other wheels were before his adjustments - and I forgot to ask him. He did say he was surprised to see how evenly the tires were wearing, side to side and across the tread (I think that is a good thing?)

I'd appreciate any thoughts about my options.

Thanks,

David

[wbonsell]

It's nearly time for a new set of rear tires. I am currently running Falken Azenis AT615

225/40 R18 front

265/35 R18 rear

As far as I know (I'm the second owner) the suspension is stock 2001 986. The car has about 61 thousand miles.

I'm noticing some oversteer or at least a tendency toward it. My first tires were the Dunlop sport 9090. I went threw two sets. I was essentially unable to get oversteer without making major mistakes - she really wanted to understeer with those tires. The Falkens are nearly impossible to understeer - they are so much sticker!

I'm wondering what my options are to address the oversteer - to improve the balance. I feel safer (more control) with understeer than with oversteer.

I'm thinking about wider rubber on the rear...How wide can my rims handle before I'd need a wider rim (I believe they are the 9.5" model).

I just had the car aligned. I notice that the steering feels "lighter" - it is easier to turn. The car doesn't have the same intense desire to go straight that it had before the alignment. The alignment tech said that one rear wheel was way out of camber, but didn't say much about how the other wheels were before his adjustments - and I forgot to ask him. He did say he was surprised to see how evenly the tires were wearing, side to side and across the tread (I think that is a good thing?)

I'd appreciate any thoughts about my options.

Thanks,

David

Hey David....

I have never subscribed to the theory that one tire is more prone to understeer/oversteer assuming that the tire is a high performance summer tire. What I have found is that tire pressure and alignment can effect the handling balance. I would be interested in the tire pressure you are running both front and rear as well as the alignment of the car. If you have max'd out the front camber and set the rear camber correctly, the car should be nicely balanced with crisp turnin. I autox extensively and will dial in understeer or oversteer with tire pressure as the course and weather conditions dictate. I currently run Potenza RE050A Pole Positions which I find quite acceptable but am considering a set of Falken 615's for better overall grip. Also, by turning off traction control you can also dial in more oversteer. I find a like the traction control off so that I am better able to rotate the back end (yes induce more oversteer). Going back to the alignment issue, make sure the alignment shop knows what they are doing. If they screw up the toe in the back, it can definitely cause a much more tail happy car. For a stock suspension, I suggest 0toe in front with .8deg neg camber. For the back, slight toe in and approx 1.1deg of neg camber. I think this is a great alignment setting for optimum performance from the stock suspension. Hope this helps somewhat....

[4agdtym]

I was surprised to find the change in steering response after changing to a different brand of tire - which I changed about 6k miles before the alignment was done. I didn't notice it right away. I think I noticed the improvment in traction immediately and it took me a while to increase my speed through corners to the point that I began to notice the different balance.

I did find that tire pressure made a difference with the prior tires and just forgot to play with that on the Falkens. I've been running pretty consistently 29/36 front/rear pressures. Is it possile that the Falkens want a different rear tire pressure to stick better? Which way should I adjust the pressure to increase its stickiness?

:eek: (just checked the tire presure - I have 32 in the rear. Somehow I have read 36 when it says 32. I will change pressure this evening and see what happens). Oh Yeah - I don't have traction control.

The alignment was done by a shop recommended by my mechanic (a former zone autox champ). The alignment tech (an older gentleman) did mention that he doesn't see Porsche often. He did seem to know what he was talking about on the car, but when he didnt know where to find the tool kit - where I keep the wheel lock - I was a bit concerned. I don't konw what settings he used. I'll have to ask him. Sorry for being so specific, but what is "slight" toe-in?

Thanks,

David

Edited March 20, 2008 by 4agdtym