The owners manual for my 2013 roadster with 195/55 R 16 RFT tires specifies 38 psi inflation regardless of the speed. The manual for the convertible with same size tires specifies 35 psi up to 100 mph and 38 psi over 100 mph.

Why the difference between the roadster and the convertible? Would it be unsafe to run mine at 35 psi as long as I didn't exceed 100 mph?

 

Yes, 35 PSI all of the time is fine.
First, who drives over 100 MPH on the road (at least for any amount of time).
Second, the recommendation is only because a tire generates heat when it flexes, and also generates heat friction from the road. The higher inflation is to reduce the heat from flex at higher speeds to compensate for the increased road heat.

Most of us normal drivers just need to keep the recommended PSI and not let it drop with the weather or neglect.

Track conditions require something else and you can get that info at your HPDE class.

 

Thanks. I wonder why MINI decided to only list one tire pressure for the roadster and (I understand) the coupe rather than listing a below 100 mph pressure and an above 100 mph pressure. Surely there must be some reason.

BTW My wife and I are both originally from Chattanooga. We've been in the St. Louis area for almost 30 years, though. We are really old timers. I was class of '63 Brainerd HS and she was class of '64 City HS.

 

The sticker inside the door of my Coupe indicates 38 psi for below and above 100 mph. My low tire pressure alert went off the other day. Indicated the left front tire. Measured all the tires. The one in alarm was 31 psi and the others were 32 psi. I have had the coupe since April. I never measured the tire pressure when I got the car. I doubt the tires were at 38 psi when I took delivery. Re-checked the measurement on two other tire pressure gauges and they all agreed at 32 psi. I set all the tires to 38 and reset the alert.

 

Better check your oil as well. In fact I would check everything. I always do when buying a new car or after having my cars serviced. I guarantee it will save a headache down the road.

 

Tires can lose 1 psi per month due to permeation through microscopic pores in the tire rubber. In addition, tire pressure will fluctuate plus or minus 1 psi for every 10 degrees of ambient temperature change. Given the six months you've had your coupe the time factor could have resulted in a 6 psi drop. Maybe that was offset during the summer months by the higher temperatures so your tpms just now detected enough drop in psi to set off the alert.

I also doubt my roadster's tires were inflated at 38 psi when I took delivery. I checked cold tire pressure about two weeks after I got it and they were at 36.5 psi (digital gauge). I inflated to 38 psi as recommended and the ride with my run flats immediately got much rougher than I had noticed since I had the car.

This is the reason I am questioning why the roadster and coupe only spedify 38 psi regardless of speed while other models have a below and an above 100 mph specified pressure. I am considering running somewhere between 35 and 38 psi to soften the ride with my run flats. Thulchatt says running 35 psi is okay but I am wonderering, if that is true, why the secified pressures don't reflect that.

 

Tire size will also affect how much pressure is recommended.

 

You are exactly right, but no matter what tire size, on the roadster and the coupe the specified pressure is still the same for below 100 mph and for above 100 mph. I don't think anybody so far here knows why this differs from all other MINIs. If they do, they haven't explained it.

 

Hard to say why that is, but likely the pressure number is fine for higher speeds and they decided to keep it simple for lower speeds, maybe because it works fine at lower speeds as well, resulting in better gas mileage?

In any case, I will often fine tune my tire pressures and invariably, end up with somewhat higher pressures than the factory recommends. I also never run the max listed on the sidewall of the tire unless I'm running very heavily loaded. Since the Mini has more weight on the front than the rear, I bias my pressures accordingly. Mini's recommendation for my tire size (well, the 205/40-18 at any rate, I'm running 215's) is 36/36. I boost that to 38 front, 36 rear and sometimes if I'm going to be out thrashing the twisties, I'll boost each of those numbers just a bit, leaving a 2 to 3 lb difference between the front and rear. It seems to work well.