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Rear tire size can I run 305’s on rear ? It came with 295 I believe 2013 C2S
Yes you can run 305's with no issues. You might want to double check your wheel width as my car had Sport Technos which are a bit wider than most other OEM wheel options. But 10mm should be no issues even with other 991.1 wheels.
I would double check to see what others are running though.
295 and 305 are both factory sizes. your owners manual should list the "approved sizes" from porsche, but generally speaking a 305 will be just fine and, for all intents and purposes, will make absolutely zero difference other than price for 97% of all 911 owners.
YUP! I just made the switch a couple weeks ago... went from 295 pirelli tires to the 305 michelin PS4S and it actually makes a pretty big visual impact in my opinion. Tires fill the wheel arches a bit better and just look hefty.... the 20in rims allow for both sizes.
Yes but 11" wheels will support 305's. I run 305's on an extra set of 19"s that are 11" wide.
Yes, I know many here are successfully running 305's on the 11" wheels, but from some technical perspective - are 295's more appropriate for that wheel size just as 305's are better suited for 11.5??
If size does not matter (no pun intended) why then Porsche factory fitted two different wheel sizes with the respective tire sizes?
Yes, I know many here are successfully running 305's on the 11" wheels, but from some technical perspective - are 295's more appropriate for that wheel size just as 305's are better suited for 11.5??
If size did not matter (no pun intended) then why did Porsche factory fitted two different wheel sizes with the respective tire sizes?
It has to do with stress on the sidewall.
Think of it as preloading a spring.
Stretching a small tire on a wide wheel effectively preloads the sidewall, making the tire effectively stiffer. Results in a sharper turn-in and a harsher ride. This is because any deflection to the traction surface of the car is attempting to pull the side walls even tighter on the wheel.
Conversely, putting a wider tire on a narrow wheel stretches the sidewall in the opposite way, which leads to a more ambiguous turn-in as the tire effectively has a spring damper in the sidewalls. Deflections to the traction surface as well as lateral loads pull the sidewall into a more upright orientation (where it wants to be).
All things otherwise the same, 295/305 on an 11" or 295/305 on an 11.5" will result in no perceivable change in handling for a street driven car. None. Any change you feel is the fact that you put on new tires to begin with, or placebo effect. Or you're going full tilt on public roads, in which case get your *** to the track where that belongs.
For those who actually track their cars? Sorry to say, it still isn't that cut and dry, and folks who have gone through a bunch of tires can confirm this. A bigger number isn't necessarily more width, and more width isn't necessarily more traction! Go measure your tire, shoulder to shoulder, and tell me that it's actually 295mm or 305mm. For an even more fun exercise, go find the same tire with the same width but a different aspect ratio (like a 225/50 and a 225/60, both Falken Azenis or something), and measure the tread width. Chances are you'll get two different measurements. This was a huge deal in spec racing and autocrossing a while back in the Miata scene -- I believe the Star Specs in 195 measured wider than most other competitive tires in 205, or something to that effect. With regards to a wider tire not necessarily being better, that's an even more nuanced discussion that goes into contact patches and how a wider tire doesn't actually mean more contact patch without adjusting other variables (such as sidewall stiffness, tire pressure, vehicle weight/corner balancing, whether or not the vehicle can actually put enough heat into the extra tire, etc.).
FWIW, Michelin's specifications for the PS4S tires in the 305 size say that they are appropriate for rim widths of 10.5" - 11.5", putting the 11" rim squarely in the middle of this specification. The sticker on the door sill of my 2013 C2S cab indicates that the car came with 305 rear tires, and I have 11" rear rims.
Asellus's point about tire width varying is absolutely correct. The width of a Bridgestone Potenza RE980AS in the 305 size (which I have on my car right now) is about the same as the Michelin PS4S in the 295 size.
04-05-2021, 04:11 PM
