Proper Tire Inflation

Hi Alan,

From another 2003 owner [with 205/45/16 tires],

I researched this subject thoroughly via the 'net. I come from a motorcycle background - where tire pressures are serious business.

Consensus [from my research]: 28 psi [period]. That's it - no more, no less.

James Combs

2003 Silver LS Santa Paula, CA

Don't you think its a little bit foolish to state unequivocally that a

*different* tire (I assumen you aren't using the exact same tire, or you would have mentioned it) would use the exact *same* tire pressure?

Work up and down from the pressure listed on the door sticker, and take what works best for you. My Miata was inflated to 36 psi (by the tire shop) on new Bridgestones once, and it nearly bounced. I brought them dowm to 29-30, and immediately felt better.

The pressure on the sidewall is NOT a recommendation, but the pressure at which the tire is suitable for carrying its maximum rated load. No tire anyone is using on a Miata is carrying anything like its rated maximum load.

Watch your pressure, however- with low-profile tires, severe underinflation is not only hard on the tires, but could make it easy to damage a rim.

Joe Silver '99

The magazine was correct about fuel mileage, but such gross overinflation results in wearing out the tread center prematurely. That sidewall number is the maximum *safe* pressure, not a recommendation--above that, the tire could self destruct. The door sticker number (26 psi) is about as low as you can go for a soft ride without risking a bent rim; I would consider it the minimum safe pressure. 28-30 psi (cold) is a good ride/handling compromise for most Miata drivers, with most wheel/tire combinations. Performance generally deteriorates rapidly below 28, and also above 32 except in track or autocross situations, where 35 (hot) is a usually good place to start.

Experiment to find your personal preferred balance of ride to responsiveness, and keep an eye on tread wear, adjusting pressure if it's not even.

I don't run low-profile tires but have found the recommended 26 psi mushy. I try to maintain 32 all around. It's firmer, not bouncy and the tires seem to last longer.

YMMV. IMHO of course.

-- Nora (imagine a Canadian flag here) =======================and the Rollerskate (imagine a '99 SILVER award-winning Miata here)

Wouldn't this also result in less traction on dry, clean pavement?

While I haven't autocrossed, my own experimentation with tire pressure indicates 28-30 PSI (cold) is the 'zone'.

Dana

Also not low profile, but I've tried 32, 30 and 28. I haven't seen any difference in tread wear across the tire, slight diff on the interstate (favoring the higher pressures), 28 seems to give markedly better (a bit squishy, but more predictable) cornering.

Gary Fuchs '99

Yup. Like you're driving on ball bearings.

I've tried everything from 21 to 35 and settled on 26...

I have tried everything from 0 to 35 and prefer 28.

Leon

Oho! Leon, you have been skewered.

The car is drivable though it feels a bit funny. However, if you have a Discount Tire tire warranty, the Discount Tire guy looks at you very sadly from having a *second* unrepairable tire from the same set of 4 they sold you.

They are happy to replace the tires when you don't have a warranty, however.

Leon

OK, these are not surprising results, I suppose. Another researcher published some interesting results in 1972, where he explored the performance of ordinary street tires with inflation well in excess of 70psi (_Fear And Loathing In Las Vegas_, Thompson, Hunter S.). Are you familiar with this research? Admittedly, it was not on a Miata.

Heh. Need a government grant to continue the project?

Dana

No, let's have it. :)

(Actually, I do not really do research in cars at all. Despite being at an ME department, I am an aerospace engineer who mainly does things in applied math. Car theory is just a hobby after I got my Miata.)

Oh I do not blame them. They are just doing their job. They even installed Tire-Rack T1Ss for me.

Leon