Hi guys,

friend of mine with a 997TT just replaced his stock wheels with Champion RS171's.

the rear wheels are half an inch wider than the OEM wheels, and he's using the OEM PS2's with the same inflation pressures.

however he's noticed that the car's ride has become noticeably harsher at the rear since the change.

any idea why this would be the case? i'm not sure what the weight on the Champions is compared to the OEM's, but the RS171's wouldn't be any heavier would they?

would the sidewalls being stretched over the wider wheel effectively make them stiffer, leading to the feeling of a harsher ride?

thanks!

 

"would the sidewalls being stretched over the wider wheel effectively make them stiffer, leading to the feeling of a harsher ride?"

You hit the nail on the head. Try the next size up for the rear tires. 325-30-19.

 

Wow, I thought I know everything about Porsche wheels and yet never did realize this.

So the Champion wheel is actually half an inch wider than stock in the rear, 11.5 instead of 11? Stock rear is 11 right?
http://www.wheelenhancement.com/inde...lDetail&id=199

Interesting also to note that to decrease the Turbo's tendency to understeer, Cargraphic increases the width of the FRONT tire in their Tuner GP competition's Turbo (for those familiar with slip angle concept, this works because it decreases the slip angle in the front). I'll look and see how much the increase was.

 

i think a 305 rear should be fine or 315 at the most

 

well known trick i believe. for example, in FWD based or biased cars, tuners will increase width of front tires relative to the rears to dial out understeer. the monster tuned Mitsu Evo's that frequently rule the roost in Japanese time attack competitions at Tsukuba for instance utilize this.

of course easy to go too far with this. a friend of mine owns a gorgeous original 993 GT2, whose OE size front tires were 235. he ordered a set of aftermarket center lock competition wheels, but the wrong sizes were sent, and he ended up with 265's in front, while rears stayed at the OE 285.

a little clumsy on the gas, and he wound up facing the wrong way down the highway! scary moment for sure!

 

yup some nice sticky bigger tires up front should do it.

instead of 235 i'd go 265-285. if it can fit or course.

it'll make the ride harder when things get stretched.

 

Hesperus - where are you in the Philippines? Manila?

 

My RS171s do not rub. I would be careful changing the overall tire size too much, it can mess with the PSM.

 

Interesting story there. I looked up the article on Cargraphic: To decrease understeer, they increase front tire width by .8 inch (2 cm).
In theory increasing rear tire width would increase understeer, but at .5 inch, maybe not a significant or noticeable amount.