I am recently told that having even marginally smaller diameter front tires will cause unavoidable understeer. Anyone have any experience with this phenomena?

Thanks,

 

If you're driving a TT you need to ensure the tires are exactly the same diameter or you're going to have some HUGE problems.

 

I probably should have been more clear. I am talking size differences that are well within the amount that the viscous coupling and software can handle without problem. I am talking about around .2 inch in difference in diameter.

 

sounds to me like you got some bad information.

 

The stock tires are not exactly the same size. I am not using the same size tires. I am using 265/35-18's (25.2) and 315/30-18's (25.5). I have also used 275/35-18's (25.2) and 335/30-18's(25.6).

The car handles like a dream.

If you want some understandable straight poop on the subject go to www.rogerkrausracing.com , then click on Techanical sheets, then click on understeer/oversteer correction sheets.

 

A drastically smaller WIDTH of your front tires in relation to the rears would cause an understeer problem.

 

 

Yes, I have experienced understeer with smaller diameter
front tires. For the way I drive, I definitely prefer a slightly taller
front tire. The differences I am talking about are just a few tenths
of an inch. This would be under extreme cornering loads, not typical street driving.
Even within the limits of what the viscous clutch will bear,
any difference in rolling radius will cause the viscous unit to be
applying torque in one way or the other. With shorter fronts,
the fronts will be turning faster than the rears, so the viscous
unit will be effectively applying a little bit of braking at all times.
That will dampen the front's ability to stick. Yes, the reverse is
true too. With taller fronts, there will be more power delivered
to the fronts and they will tend to pull the car around sharp
corners, but the rear will be 'swishy-loose', which would not
be comfortable at higher speeds.
Joe

 

H'mmm...I have to say that I am surprised that a few tenths would make any real difference. I do find that Porsche specs the car with slightly taller fronts than rears. I have emailed Ruf on this as well...it will be interesting to seem what they say...as well as the Ruf tech. that is coming to Seattle to check out my car on this coming Tuesday.