944 NA vs. 951 tire sizes

steveu812 · 09-23-2008, 06:07 AM

944 NA 7" front wheel w/215 tires and 7" rear wheel w/215 tires
951 7" front wheel w/205 tires and 8" rear wheel w/225 tires

On a front engine car with nearly 50/50 balance, why did they go smaller on the fronts? I understand with more power the rears would be larger, but making the fronts smaller don't seem right? Were the 215 fronts overkill just to make all 4 the same size on the NA's? What am I missing?

Dave L · 09-23-2008, 06:48 AM

they wanted to make the car understeer so it was "safer". For your best handling go with equal sized tires all around.

aftermath · aftermath's Garage

Ok, Im interested in this one also. I dont want to hijack the thread. But since my car is a mix of power\944\951, I will

I purchased a 944, turbo suspension \brake upgrades and a 320HP LS1 engine. The seller says 30lb heavier in the front over stock after mods. The tires on it now are 255/40R17 on all corners. Since I need spares, etc Im wondernig what might work for me. I have zero experience with a 944

Tervuren · Tervuren's Garage

Quote:

Originally Posted by Dave L

they wanted to make the car understeer so it was "safer". For your best handling go with equal sized tires all around.

A bigger tire does not mean more grip. Also, this thread is missing that 951's come with 16" wheels, instead of 15". If you put a wider tire on, it would defeat the purpose of going lower profile to start with. A wider tire on a wheel will bulge out at the sidewalls, which under heavy cornering strain will cause the tire to deform, losing grip. I run 205's on the front of my 944, and find it to be quite responsive in a corner. I had 255's on the rear, and moved to 245's, and now have a little more understeer in a corner unless I really try to break it lose.

Dave L · 09-25-2008, 03:54 PM

A bigger tire means a larger "foot print" and more grip. If you put a 255 tire on a 6 inch rim you will run into issues as the tire is "pinched" and will deform as you say but you can easily run a 225 tire on a 7 inch rim according to Porsche and many tire mfgs.

On 7x15 inch rims I have run 215's all around and 225's all around. On 16 inch rims (7&8s) I have 225/245. 225/245 were part of the 944S M030 package on 7 and 8 inch rims and while the 245s look great the conering isnt the best as the front will push a bit. The equal sized tires will still understeer a bit but is much better balanced. I run 225's for track tires and the balance is much better than the staggered set up. Apparently 245's all around is the "hot setup"in the SCCA.

205/245 is a combo Porsche never put on a 944 series car as far as I know but I would bet that your driving style has adjusted to this type of set up. I think you would have to try different sized tires back to back to really see the difference.

Dave L · 09-25-2008, 04:00 PM

here is a good start

http://www.cantonia.com/wheel_offset.html

I dont know about moving to a much larger tire on a 17 or 18 inch rim but you can use this tire calculator to at least see the difference in sizes.

http://www.miata.net/garage/tirecalc.html

Aftermath - I would suspect a 255 tire up front would give you quite a bit of tramlining?

mallard ducks · 09-26-2008, 06:21 AM

it's not just the 205/55 and 225/50 on 7s and 8s that's puzzling; the factory tire pressure recommendation of 29 front and 36 rear with this tire/wheel size set-up is biased toward massive understeer

why? makes no sense to me