t2d2

iTrader: (8)

Ever since I first got behind the wheel of the car, I've always followed the 32 psi rule of thumb on all but the odd exceptions. It never even occurred to me that that thinking may have changed. Every time I've taken a car to the shop, they always mark it as 32 psi out the door... My mechanic looked at my front wheels today as we were wrapping up front end work and asked if I had them under-inflated, due to the slight bulge. I said no, they're spot on 32 psi (he checked, they were) and that's just how they look.

To my surprise, he said most low profile tires should be inflated to 44 psi. My fronts say 50 psi max and the rears say 51. Nothing about recommended pressure, though. So, we shot 'em up to 44 and I drove it home that way. It feels a lot firmer for sure. I imagine traction will be down a bit but efficiency up some.

I looked around a bit to see if what he told me is true nowadays, with low-pro rapidly becoming the norm. I didn't see anything resembling a consensus... Some people say to stick to the factory specs, while others say to disregard those because they weren't done with low-pros in mind. Some say to go all the way up to the tire's max (yikes), while others say to split the difference between the factory spec and the tire's max.

So, what are you running your SC's tires at?

InLyneTrbo

iTrader: (5)

I normally like to keep it between 35-40 psi for daily driving, but when autocrossing, I'll drop it 10-15 psi

CatManD3W

iTrader: (18)

Everyday driving anywhere from 32-38 psi.....

eknine9

iTrader: (8)

Mine are inflated to 36 psi all around. I like it and havent really noticed anything bad about that level of inflation.
245/35/19 for reference

SC400slide

iTrader: (11)

When in doubt, just go 35 psi. Though my rims/tires are aftermarket, I know the stock tires take 32 psi. When I see a recommended psi, I go 3 above.

t2d2

iTrader: (8)

Thanks for the responses. Has anyone tried 40+, or have you guys stayed in the 30s out of habit? If I were to follow the "split the difference" between spec and max approach, it would put me at 41 psi. That's in line with the upper range of the responses so far. 40 psi is sounding like a nice even number to try.

I'm on 225/50-17 (17x8) front and 245/45/17 (17x9) rear, fwiw.

t2d2

iTrader: (8)

Any particular reason for that? I guess another way of asking the question is, if a tire lists the Max psi but nothing else, how would one figure the recommended level? Is there a rule of thumb for X psi less than Max?

SC400slide

iTrader: (11)

Not the actual max psi that is engraved on the tire, but on the door (or in this case, the glovebox) placard stating the tire size/psi etc. Just use good judgement. Since these are just "car" sized tires, (not truck/LT/ect tires) they should stay below 40 psi. The "max psi" on the side of the tire is not what you go off of, but rather the placard. If aftermarket and you're not sure what you should air them up to, just go 35.

t2d2

iTrader: (8)

Er, that's the point I already raised about the factory specs not being for low profile tires, which is what the question is specific to. Adding 3 psi is pretty arbitrary in that case, no?

KahnBB6

iTrader: (5)

Somewhere between 33-35 psi matched all around. Nothing out of the norm for me. I went with whatever the MKIV TT FSM tire pressures were. I'm sure that was 33 or 35 psi.

I wouldn't exceed the tire manufacturer's maximum pressure. 40 psi is plenty and 44-50... I've yet to encounter a sports car that needs that much pressure. Perhaps in a racing campaign environment where tire wear is heavily accelerated.

Low profile tires... perhaps it would be good to look up a modern RWD vehicle of equivalent weight (around 3500-3600lbs) that has 18, 19 or 20 inch wheel options and look at some tire pressures there. Start with the 2015 Mustang GT, Camaro SS, Cadillac ATS-V and one of the lighter Merc AMG coupes for comparison.

t2d2

iTrader: (8)

That sounds prudent. It's probably a matter of finding FSMs posted online or asking owners in various forums, so it could be slow going.

In the mean time, I think I'll drop mine to 40 psi tomorrow and use that as a starting point.

Edit, here's some info:

'15 Mustang GT: http://www.edmunds.com/ford/mustang/...est-specs.html - 32 psi for 255/40ZR19 & 275/40ZR19

I'm guessing everyone's just going to list the industry standard 32 psi, for the same reason I never realized the thinking had changed...

'15 Cadillac ATS (-V?): http://www.firestonecompleteautocare...el=Performance - 32-40 psi (confusing)
'15 Camaro SS: http://www.firestonecompleteautocare...le.submodel=SS - 36 psi

Or not.

TokinSC400

I run 40 psi in mine and I have 225/40/18 front, 245/40/18 rear. On my '97 Olds 88 I had 225/5516 and ran 36 psi. Less rolling resistance and more even tire wear as long as you rotate and monitor pressure I think.

t2d2

iTrader: (8)

How do you rotate tires with a staggered setup? Do you have non-directionals and swap them from side to side?

TokinSC400

Well of coarse you can't on a staggered set up. But if you run the same size all around then rotate.

t2d2

iTrader: (8)

Gotcha. It wasn't clear if you were saying you rotate them on your SC or if you only did so on the Olds.