Man that looks sick...honestly both setups look fantastic when the car is at that ride height. I've had both on my seal gray TT also and it is the necessary front tire to keep heights within spec that I feel are the problem. I think I'm going to go with 305/30s and stick to 235/35s in front after my current 315s wear out and just hope the front diff doesn't protest.

 

I am temporarily running these myself. There are a lot of facts and theories regarding this. Fact is several front diffs have been ruined with this tire combo in at least 33,000 miles. Fact is that this tire combo is .8 inch difference in height range. Fact is that the factory 18" tires are only .4 in difference.

Theory is that you can go .5 and be okay. Theory is that you can have a .5 difference in height with just tire pressures.

I have ordered some 245/35/19's to go with my 305/30/19's but in the meantime I have inflated my 235/35/19's PS2's to 45 psi with the max listed at 51 psi. I have also lowered the rear pressures to 30 psi. Hopefully this will help negotiate the difference. Hope this helps!

 

0.5" larger in the rear is NOT the same as 0.5" larger in the front. If you have a smaller front tire which as a result is then rotating faster than the rear, how will you transfer torque to the front via the viscous coupler???

 

The fact is the difference is always split when you are rolling, so the size difference (short front or taller rear) doesn't matter.

The big difference is the front diff may not spool up as fast or have the same torque transfer with a shorter front tire. A little bit of GT2!?

 

Please take no offense, but based on the above statement you clearly have no idea how the bone simple mechanical 996tt AWD system functions. With the same final front and rear drive ratio on the 996tt, the rear wheels MUST rotate faster than the fronts for any torque transfer to occur from rear to front.

 

Yes that is my understanding also and I guess I'll have to suck it up and run the 40 series fronts to keep the rear axles spinning ever so slightly faster. I was really considering just doing it the wrong way but I do not want to burn up my front diff...I still like the AWD, as limited as it is in our cars

Is there still an almost 100% backorder for all 315/25s across all brands?

 

I really don't care if the front diff works or not... just so it doesn't toast! I would rather have a rwd car but putting down 650 hp with a tip I can't do an open rear end and nobody is making an LSD.

P.s: I think I addressed the above in the second sentence you didn't quote... or possibly read???

 

[QUOTE=mrmaass;3787160]Yes that is my understanding also and I guess I'll have to suck it up and run the 40 series fronts to keep the rear axles spinning ever so slightly faster.

I don't think anything bigger than 225/40's will clear the front radiators which is a good match for the 305/30/19 being only .1 difference. I asked the same question and was willing to do the same thing but went with 245/35's instead. Cheers!

 

I had Michelin Pilot SS 235/40/19's on it previously and they did wear a hole in the inner fender well. Once that happened they didn't rub anymore
I should have used the heatgun and patience method but the tire the work for me.

 

Good to know. What were you running on the rear??? How did you like the tire combo???

 

On a warm day a few years back and after I got my 235/35/19's & 315/25/19's I was in 1st gear doing maybe 25 mph. The turbos were spooled up and I hit the throttle. Before I knew it I was in a awd spin and in the next lane before the traction control could kick in (I guess that's what massive hp will do).

I think again it wouldn't matter that the back tire is slightly taller and here is why. The awd system was designed for the 415 hp drive train. When the back wheels begin to spin the torque is transferred to the front.

With bigger hp/torque if the wheels don't spin the awd is not needed. When they do break loose it is in a big way! That is when the awd will kick in anyway... no matter what the rear tire size is. There may be a slight mill-a-second delay but as long as the rears are spinning it will transfer torque to the front wheels!

Discussion??? (and please read the whole post)

 

Arent you worried the low(ish) rear pressure may contribute to a cracked wheel?

 

I'm not sure I understand your point, that the front diff isnt getting worked? Doesnt it send 5% up front all the time?

Are you advocating the taller 30 or saying that grip still sucks the same?

 

I ran this combo for only one day. I now have 245/35/19's and 305/30/19's. This is a great combo and I highly recommend it! SteveK from New York turned me on to this combo and he is right!

 

In order for the front diff to work, the rear wheels need to spin faster than the front. How you make that happen is up to you. You can use a shorter tire, but if the rears spin the front diff WILL work!