Winter Tire Pressures

[iso100]

I recently purchased a set of snow tires from Discount Tire Direct in 175/65R15 mounted to 15x6 steelies. There is no tire pressure guidance printed on the tires themselves but the invoice I received does state 34psi front and 31psi rear.

That's quite a bit lower than the door jam placard that says 39/36 (if I recall correctly).

Here's my question: Do you think the tire seller knows something specific about my combination of tire, size and vehicle and that I should heed their pressures over something else?

That said, those of you running 15 inch snow tires, what pressures are you running?

 

[shook sez]

I'veGot 15's and i'm running 35/35. just because. i do keep an eye on the tires for unusual wear though

 

[iso100]

I'veGot 15's and i'm running 35/35. just because. i do keep an eye on the tires for unusual wear though

Thanks... that's one more data point than I had before. I'll compile a list I suppose.

I a bit concerned about the 31psi they wanted... seems like it might be a bit low.

 

[shook sez]

Thanks... that's one more data point than I had before. I'll compile a list I suppose.

I a bit concerned about the 31psi they wanted... seems like it might be a bit low.

well then, nice guy that i am, i'll give you another data point. it'll be useless i suspect, but I run 35/35 in he wifes Fiat too

 

[iso100]

well then, nice guy that i am, i'll give you another data point. it'll be useless i suspect, but I run 35/35 in he wifes Fiat too

What about your stock Fiesta ST setup? Do you run the recommended 39/36 or some other combination?

 

[shook sez]

What about your stock Fiesta ST setup? Do you run the recommended 39/36 or some other combination?

yep, althought hat may chang as i pend more time with them

 

[XuperXero]

For those in snow area, you should run lower... 26-28psi is what I usually run my cars when I lived in Canada.

 

[iso100]

For those in snow area, you should run lower... 26-28psi is what I usually run my cars when I lived in Canada.

Aha! That's what I was looking for. That's a good data point and must be why the tire wholesaler recommended lower than stock pressures. I guess I'll drop the pressures a bit once we actually get some snow on the ground. (if?)

 

[FORZDA 2]

Ok, here's a bit of advice on tire pressures from a guy that has been driving for a long time (5+ decades), millions of street miles, drag racing, and autocrossing from 100+F temps in Texas to -20F temps on frozen lakes in South Dakota.

The "lower pressure in snow/cold" temps is (currently) a myth that began in some truth way back before radial tires and new rubber compounds were the norm. Bias ply tires back in the day sucked in snow/cold mainly because the rubber compounds got so damn hard when cold. The "trick" was to lower the pressures which would cause the tires to flex (a LOT on bias ply) and build up more heat in the carcass and rubber that would soften the rubber enough to improve the grip. It was mainly by allowing the tread area to conform more to the ice/snow surface. I can tell you it wasn't a lot more grip, but it was measureable on the timers.

Today with dedicated winter-compound radial tires, there is no reason to decrease the pressures. In fact, doing so will decrease the maximum grip, but will improve the "ride" quality on rough ice/snow roads. I have proven this fact to folks at ice racing events who were following the myth and lowering the pressures in their dedicated ice/snow tires. I got their attention by killing them on course time with then current-generation all-season tires. When asked about it, I would question their tire pressures and tell them about the myth. They would then try my recommendations and pick up quite a bit of time on course. I still never lost a timed event on the ice though... Afterward, they would also talk about how rough the ride was, but damn it was fast!

That said, if you want a smoother ride on rough surfaces with any (street) tire, you can lower the pressure, but will sacrifice grip and tread life. The FiST recommends relatively high pressures for such a lightweight car because it improves the handling/grip at the limit. If you want the best GRIP vs RIDE, then I recommend staying very near (+/- 3 psi) the OEM pressures, even with dedicated ice/snow tires. I run F36/R33 for the best street compromise.

Oh, and never take advice from someone who SELLS tires for a living. They need to sell more tires, not save them.

Your results may vary...

 

[iso100]

Awesome, thank you! I will run 35/33 per your recommendation.