I have a set of 19" wheels coming and after reading several threads I am now confused as to what is good and not for an AWD Turbo.

I know that I can go with the Michelin PS2's but the price is ridiculous. $2K on tires is a bit much. I also know that many people run 305/30/19 in the back to accomodate a less costly method.

I am looking to find out if we can fit a 26.1" and 26.3" tire in the front and back respectively. I see some people say yes and others say no. I know its based on the difference to save the diff but see mixed reviews on the overall diameter.

I am considering Bridgestone Potenza S-04 Pole Position
225/40/19 26.1" Overall Diameter and 798 Rev/mi
305/30/19 26.3" Overall Diameter and 793 Rev/mi

These measurements keep me within the tolerance of the diff but want to make sure they fit without rubbing.

Can anyone provide some insight? Would hate to order these only to find that they rub or go with the Michelins and fork over $2k for tires that I know would fit (235/35/19, 315/25/19)

My car is stock height but eventually I'll probably lower with KW's. I drive on the street mostly but plan to take the car to the track (DE events) occasionally, probably a couple times a year.

Thanks,

 

I run a 245/35/19 and 305/30/19 PSS and am lowered heavily on H&R springs for the moment. I rub over compression bumps in the rear near the inner fender liner and intercooler piping. Yes the 225's are closer to the original OD's but these cars need a bit more bite at the front end if possible so I did the 245's which is still well under the 3% mark and has had no issues.

Front is not an issue - but the rear is. So yea - 315's are the way to go if you want to spend 2k on the tires. I'm going to be installing GT2 fender liner brackets in the rear which should alleviate the issues as others have indicated similar issues with the 305/30 and used that as the fix.

This is worth a read: https://www.6speedonline.com/forums/...ml#post3872935

If I were to do it all over again I would just run a 19x11 rear with a 295 and live happily ever after. The extra 1" isn't worth it for the hassles.

 

run a michelin pss
245/305 set up.
should be around $1400 from tire rack.

 

This is exactly what I was going to recommend. I just switched to this a few weeks ago from a 235/315 setup and I am very happy with them. This setup gives you bit more sidewall than 235/315 so the car rides a lot better now.

Also, Michelin Pilot Super Sport is said to be a better tire than PS2. It is a newer design but much lower cost because it hasn't been officially approved by Porsche yet.

 

--------------------------------------------------------------------------------
I just went on Tire rack and got the following recommendation for OZ Utlraleggeras:

Front: 225/35-19 | Tire Size Rear: 315/25-19

I didn't see this combo in the embedded thread. Anyone running this tire setup? The rear OZ is 11.5" vs 12" - is that the reason for the discrepancy?

Thanks
Chris

PS - This thread is a great resource - thanks!

 

Thanks Guys. Looks like I am going to go with the 245/35/19 and 305/30/19.

I spoke to Tire Rack and both brands of the 315's are on backorder with unknown dates. Toyo has been on backorder since May.

BTW, the Tire Thread up above was helpfl but after several pages of reading I was still confused. Oh well, hopefully, I dont rub too much.

 

I run 315/25/19 rears. PS2s. Tracked and had no issues.

 

Did you go with these sizes? I think technically you need a 245/40 in front so that the rears spin faster than the fronts. With a 245/35 you'll have the fronts spinning faster than the rears.

 

Correct. If the fronts are spinning at all faster than the rears than the AWD system is rendered useless. If the ratios are close, you won't harm anything but the smaller front wheels will just be providing drive line drag back to the gearbox. It isn't until the rear wheels begin to turn faster than the fronts that any torque can possibly be transmitted to the front wheels, hence the requirement for the rears to be just a hair smaller than the fronts. As the speed of the car increases, the amount of speed difference between the tires increases which in turn causes more torque to be transmitted to the front wheel via the viscous coupler, I think about 35% or so at top speed according to Porsche IIRC.

 

Thank you for the clarification.

I made a small typo though (just edited my other post). A 245/35 will spin faster than the rear vs a 245/40 - I originally had this as 235/35

Also looks like you can save 3-5lbs per tire going with something like a Pilot Super Sport vs a S04

 

I'm running 245/35/19 and 305/30/19
Research showed that was better than a 235 in front to keep wheel ratios similar

 

This is true...but the 245/35 is moving the ratio in the wrong direction with the fronts spinning faster than the rears. With a 245/40 the rears will spin faster than the fronts in the same ratio as the OEM 18s.

Here's a chart I put together to try and illustrate

 

Ok but if it's still within tolerances what's wrong, I've had no ill effects

 

conventional wisdom on the "tolerance" issue *seems* to be that as long as you're within that magical 3% differential btw front/rear you'll be ok. the problem with testing the tolerance for the front viscous coupler ability/capacity to handle the fronts spinning faster than the rears, is you won't really ever know you have a problem until the vc unit of the front diff gets fried.

 

No one knows the tolerance, and just because people think we can go up 3% doesn't mean you can do down 3%.

The car I purchased is fitted with 305/30 and 235/35, so that's clearly "wrong" for our cars. I have no clue if it has caused any damage to the front diff. I may never know unless it fries/dies.

All I'm saying with my chart is that with a 235/35 the front will spin faster than the rear. My understanding is for torque to transfer to the front the rears need to be going faster, like the OEM setup.