powdrhound

Compared to the 315/30/18, I found the 305/35/18 to have better grip and much less rollover. The 305 has a bigger contact patch due to the 1" larger diameter. It also has a higher load rating and a stiffer sidewall which reduces the tendency of the tire to roll over when highly loaded. I have been able to drop my hot pressures by 3psi running the 305 which further increases the contact patch. The larger rear diameter also gives the car a touch more rake. When I switched to these sizes (which are stock 997GT3 sizes) I had the rear of the car lowered a touch and the car realigned. Finally, the taller rear also improved my gearing which was helpful. Lastly, the byproduct of the taller rear is that it seems my speedometer now indicates accurately instead of a little fast as it did with the shorter rears. The 305/35s are a win win all the way around in my book. Pretty much all the 6GT3 guys are switching to these sizes in my area.

rbahr

Thanks.

To be sure I understand: the comparison is between the 305 Nitto and the 315 v710, NOT the Nitto 305 & 315?

Ray

powdrhound

No, the comparisson is between the 305/35/18 Nitto and the shorter 315/30/18 Nitto.

fbirch

PM's responded

promocop

OK, heres mine I'm about to pull the trigger on a 2010 GTS. The PPI picks up that the tires (near to new) are not "Porsche Approved N tires" they are Bridgestone PO2 Poetenzas . So what's the BFD? And are they good tires or should I make the dealer swap them out?

rbahr

There is indeed a difference. Might be subtle - and I am not positive ...

WRT the difference between the 305 & 315 - I just got off the phone with a Nitto tire engineer - the 305 does NOT give you a stiffer side wall - the higher load range is affected by the shorter side wall. My question was specifically dealing with potential squirm under load - the 315 will indeed have less due to the shorter sidewall.

This does not explain the differences you feel - that I cannot explain :-)

Ray

9.5 Degrees

the PO2 are fine. The marketing department at Porsche has perpetuated this myth that only N rated Michelin tires should go on P cars because those tires were used during the development of that particular model. Dealers are bound by contractual reasons for CPO to have N rated tires on the car when selling, but there is NOTHING wrong with other brands as you will see from this forum as well as others.

powdrhound

Ray,
I ran the 315 for over two years. Probably went through 6-8 pair. All I can tell you is that the 305 does not roll over nearly as much as the 315 did and as a result I can run lower pressures with the 305. It "feels" like the sidewall is stiffer on the 305 which carries a higher load rating. For me, the 305 performs much better and provides more grip.

rbahr

WRT to 'N' rated tires.

There is a difference - but it is not well understood. Porsche does not advertise WHY they are better, or HOW they are better - just that they are different and better suited for the Porsche in question. I suspect that it is a bit more than marketing hype, and at the same time, I don't think the car explode if you run the non N tire - But behavior may be different at the limits...


One source is: http://www.tirerack.com/tires/tirete....jsp?techid=26

which does not help answer anything, but...

powdrhound: wrt the tire sizes, the ONLY thing I can think of that makes any sense is that you car sits low enough that when you strap on a set of the 315's and loose another .5" of height, you end up on a portion of the camber curve that makes your car not play nice, the additional height from the 305's may actually make the car a little better. If you were bored and had nothing to do and a lot of money to waste, I would suggest putting the 315's on and raising the rear ~.5" (and setting all of the other parameters as well) and see how that configuration works out...

In any case, it sounds like you know what works on your car, which is really the important bit of information...

Ray

powdrhound

No. When I went to the taller rears, my ride height, alignment, and CB were reset to the correct values to account for the difference. I've tried various rake setting with the 315s prior to the 305s. Not sure why the 305 is better, but it is. The 305 carries a higher load rating than the 315 which may have something to do with it. It was much easier to overpower the 315 than the 305. The 305 definitely has more grip due to the nature of the larger diameter which provides a larger contact patch. It's beyond my pay grade, but I'm sure there is a reason why Porsche runs a taller rear tire on all the Cup cars (996 included) and why they switched to this set up on all the 997tt/gt2/3 cars.

B Fett

Alright so before I buy a brand new set...

Does anyone have a set of Nitto NT-01's in 245/40/18 and 315/30/18 new sitting around they can sell ME?

A used set in either 235/40/18, 245/40/18, 305/30/18 or 315/30/18 would work too, just so I can try these out and see how I like them.

Please PM ME, as if you post here the vultures will swoop in to buy before I even have a chance lol.

Thanks

powdrhound

check ebay. I think there are a few pair of 235/40/18s floating around. Don't know about the 315s. 305s are readily available right now.

mooty

sometimes physics and paper calc dont work. you have to get the tire on YOUR car with YOU driving it.

some ppl are really fast on R6. i can match MY R6 time (after 3 hc) with my nt01 time. maybe just ME who doesn't like how R6 feels? i am 4 seconds slower with mpsc over RA1 or no-01. i just cant drive that tire. i can produce same lap time with 235 vs 245 nt-01 fronts.....

way too many variables...