Tire Pressure Recommendation for 17"
 

Does anyone have pressure suggestions for 17" 40/45 profile tire for street use? Sizes are 245/40x17 and 275/40x17 Michelin Pilot Sports.

TIA

I'm running 27 psi front and 24 psi rear on Michelin Pilot Sports (275/40/17 front and 335/35/17 rear).

Chris

I was running 26psi in each

OK, not to start a war, but, are 15, 16, or 17's better on our Cobra's???????????????????

I guess I should have specified, better for the normal crusin around town.

Better for what?
 

No war. Do a search and you will find lots of opinions on the subject. In general, there are better tires available for the larger rims with out some of the compromises of the performance 15" tires available but the 15" tires look more correct.

As for pressure, look around the BFG site or do a search here there is a formula for a good starting pressure that I posted some time ago. Beyond that you are talking tire temperatures, desired ride and handling charactoristics etc.

Rick

Thanks Guys!

When they (not ERA) mounted them jacked them up to 45 psi. :eek:

I'll start at 25 and tweak from there.

Earl: Likewise no war, personal preference. 17" do look a bit funny compared to 15", but the grip is incredible, and a wide choice is available - not so with 15". If I had found rubber I was happy with in 15", would have gone that route.

Thanks Again,
Jim

Jim -
I've been 'out of touch' since about the time you posted the question, but I contacted the tech people at Yokohama and Bridgestone (the 2 sets of tires that I have - the Yokos are very similar to the Michelins you have) about tire pressure a couple of years ago. They both said almost exactly the same thing. According to the 'standard' formula for figuring tire pressure, taking into account my weight (mine is a HEAVY Cobra) and weight distribution (mine is 50/50), the formula indicates tire pressures below 25 psi. But, they said that they would NEVER run a tire below 25 psi, so their recommendation (both companies) was to run at 25 psi.
Regards,
Frank Newman

My Pirelli P-Zero tires are recommended cold 50 psi
 

I am running the rears at 40, front at 36

OK, it's a rough ride (with the Carerra coil overs set hard too).. but they handle wonderfully unless you hit a bad bump.. then the tire skates :CRY:

Low profile tires ride rougher, and the wider they are the more "road things" you hit, but on a good surface they handle WAY better.

Here's a good question for any tire pros out there: If the tire is balanced at say 45 psi, then if you change that to 25 psi, won't it be a tiny bit imbalanced? :confused:

Frank,

Thanks for the info - I'm running them at 25 now. I'll keep a close eye on then since they are so close to minimum pressure.

BiB - I haven't noticed any problem with balance since the pressures were dropped - I was concerned about that as well - but the physics are different between a tire with a static balance that is out vs. an out of balance cause by the tire deflection. Perhaps someone with more knowledge can correct or expand on this - but here is my stab at it...

For a static balance that is out, the center of mass will be off center and rotate with the wheel. This will create resonances with the suspension and tire itself that will cause it to shake as the offcenter force is alternately being applied positively then negatively in any given direction.

An imbalance caused by a rolling tire will also move the center of mass of center from the wheel rotation but since the deviation of the tire diameter causing the imbalance always occurs at the same spot - where the tire meets the road - the center of mass also does not move in space and results in no fluctuation in forces to the suspension elements.

I think this is valid for limited deviations of the tire surface, but for larger ones (i.e. very low pressures) I would expect some sort of resonant wave to form in the perimeter and sidewalls because the resonant frequency would be lowered due to the reduced force from tire pressure - just a wild guess on that one.


Thanks for the info, everyone.

Jim