Driving to altitude - temperature impact

[mikefocke]

around 9AM after driving 3-4 miles at 40 MPH, I totaled a '99 Boxster on very good tread Pirelli summer UHP tires when I tried to brake hard in a straight line and had no traction at around 30MPH.

You can't tell me those tires had warmed up enough to grip the surface of the road (asphalt) effectively.

So be especially cautious if the temperature is rising, the road surface may be cooling those tires, not warming them.

[Lil bastard]

Altitude has nothing to do with it. You can experience the same temperatures at Sea Level. It takes about 10 miles @45 degrees or below to fully warm the tires.

[blue2000s]

Originally Posted by Lil bastard

Altitude has nothing to do with it. You can experience the same temperatures at Sea Level. It takes about 10 miles @45 degrees or below to fully warm the tires.

When you go up in altitude, the ambient pressure decreases, increasing the effective tire pressure.

[Lil bastard]

Originally Posted by blue2000s

When you go up in altitude, the ambient pressure decreases, increasing the effective tire pressure.

Agreed! But, I took the topic here to be centered mainly on temperatures and their effect on the rubber compounds used in Hi-Per or Summer tires.

There is a pressure differential (the pressure difference between inside the tire and out) which changes with altitude. You're talking about guage pressure which measures pressure above/below atmospheric pressure, and this differs with altitude. So it first matters where you filled your tires.

1ATM (standard atmospheric pressure) is 14.7psi - AT SEA LEVEL. It drops to about 12.2 at 5k' (Denver), and 10.1psi @ 10k'.

So the effect is that your tires become 'over-inflated' as you rise in altitude from where you filled them because the outside air pressure is not acting as strongly on the outside of the tire with increases in altitude. If you filled them in denver, the tires become 'over-inflated' by 2.1psi@ 10k'. But, if you filled them in miami and go to 10k', the tires will be 'over-inflated' by a much more pronouced 4.6psi. If you live in an area with significant changes in elevation, it's a good idea to know the altitude (above sea level) where you live and presumably fill your tires. Solving this issue is easy... just bring a tire gauge along and release the 'excess' air as you gain altitude, just remember to refill once you hit the lowlands again.

[Hops]

Thanks for the good and interesting comments. I didn't know if this would be a very interesting thread, but I think this is an important topic for drivers now that I see everyone's feedback.

The summary I am taking out of this is driving below 45 to 50 degrees = caution, below 40 degrees = warning, below 35 degrees = danger. Again, even below 35 the car handles consistently and predictably, but at any of these temperatures, the margin for error goes away. Any aggressive maneuver in steering or braking may not get the desired results.

BTW, this was focused on temp, not pressure, but good info on effects of pressure is certainly not unwelcome.

[blue2000s]

Originally Posted by Hops

Thanks for the good and interesting comments. I didn't know if this would be a very interesting thread, but I think this is an important topic for drivers now that I see everyone's feedback.

The summary I am taking out of this is driving below 45 to 50 degrees = caution, below 40 degrees = warning, below 35 degrees = danger. Again, even below 35 the car handles consistently and predictably, but at any of these temperatures, the margin for error goes away. Any aggressive maneuver in steering or braking may not get the desired results.

BTW, this was focused on temp, not pressure, but good info on effects of pressure is certainly not unwelcome.

Every tire is different and their characteristics under varying temperatures are different as well. You would need to know how your specific tire reacts to road temps.

Although you may have intended to only address temperature, your experience was no doubt effected by both temperature and the pressure change due to altitude so both should be considered.