11-15-2017, 09:24 AM
So I got to thinking about tire pressures.....
What temperature do you check your tires at?
What temperature do you check your tires at? I know the books all say to check your tires when they are cool. But what exactly does that mean? My cool (in central Alabama) maybe 70F while our friends in the ozarks may wake up to 5F and think what a nice day. That range of temperatures surely has an affect on the tire pressures.
So I did a little research....
This chart came from Michelin and reflects the general belief that air pressure should be adjusted by 2% for each 10F change of temperature. (Increase temperature for lower temperatures). (I suspect that these pressures at the cold end are far in excess of what the rims can hold)
So to answer my own question, I think that the charts (see below) that relate pressure to load carrying capacity on tires assume 65F. So, if you are close to 65F in the morning, go for it. If the temps are much higher or lower, adjust accordingly.
How much Pressure?
Of course you have to know what your coach weighs to use this chart, but the point is that the tires are spec'd for a range of pressures. This implies some sort of sweet spot. Too much pressure and your ride is rough and its not good for the tires. Too little and the ride is better but you risk a blowout.
I have decided on 115 lbs (front), 110lbs (drives) and 100lbs (tag).
ps. I used to run 85 lbs in tag (this was from the michelin chart, but I bumped it up to 100 and I think the coach rides smoother. Your milage may vary.
How old is your air gauge?
I have three manual air gauges and a TPMS on my coach. Would a reasonable person assume they all would match? Well....THEY DONT. All the manual gauges are good quality but with slightly different designs. I tested all the tires with all four devices. I found a maximum difference of 2lbs between the lowest and the highest. I know 2lbs is not a lot but it could be just the difference between a low tire and a blowout.
Why is this important? What if your gauge is reading much lower than reality. How would we know? I ended up with two manual gauges reading about the same and the other manual gauge and the TPMS reading about the same. (Again they were all pretty close).
I read a recommendation that we use a new gauge to verify our old gauge....continue using the old gauge and only get the new gauge out to verify the old gauge. (keeping the new gauge in a very protected and safe spot...Like not in your toolbox). It would be fun at the next rally to test our tire gauges and see how much they vary.
Finally, I am going to print some cards that will allow me to keep track of the tire pressures over time. I might put the temperature / pressure conversion chart on the back. Let me know if you are interested and I will print some extras.
Cheers,
bill
What temperature do you check your tires at?
What temperature do you check your tires at? I know the books all say to check your tires when they are cool. But what exactly does that mean? My cool (in central Alabama) maybe 70F while our friends in the ozarks may wake up to 5F and think what a nice day. That range of temperatures surely has an affect on the tire pressures.
So I did a little research....
This chart came from Michelin and reflects the general belief that air pressure should be adjusted by 2% for each 10F change of temperature. (Increase temperature for lower temperatures). (I suspect that these pressures at the cold end are far in excess of what the rims can hold)
So to answer my own question, I think that the charts (see below) that relate pressure to load carrying capacity on tires assume 65F. So, if you are close to 65F in the morning, go for it. If the temps are much higher or lower, adjust accordingly.
How much Pressure?
Of course you have to know what your coach weighs to use this chart, but the point is that the tires are spec'd for a range of pressures. This implies some sort of sweet spot. Too much pressure and your ride is rough and its not good for the tires. Too little and the ride is better but you risk a blowout.
I have decided on 115 lbs (front), 110lbs (drives) and 100lbs (tag).
ps. I used to run 85 lbs in tag (this was from the michelin chart, but I bumped it up to 100 and I think the coach rides smoother. Your milage may vary.
How old is your air gauge?
I have three manual air gauges and a TPMS on my coach. Would a reasonable person assume they all would match? Well....THEY DONT. All the manual gauges are good quality but with slightly different designs. I tested all the tires with all four devices. I found a maximum difference of 2lbs between the lowest and the highest. I know 2lbs is not a lot but it could be just the difference between a low tire and a blowout.
Why is this important? What if your gauge is reading much lower than reality. How would we know? I ended up with two manual gauges reading about the same and the other manual gauge and the TPMS reading about the same. (Again they were all pretty close).
I read a recommendation that we use a new gauge to verify our old gauge....continue using the old gauge and only get the new gauge out to verify the old gauge. (keeping the new gauge in a very protected and safe spot...Like not in your toolbox). It would be fun at the next rally to test our tire gauges and see how much they vary.
Finally, I am going to print some cards that will allow me to keep track of the tire pressures over time. I might put the temperature / pressure conversion chart on the back. Let me know if you are interested and I will print some extras.
Cheers,
bill
Bill Johnson
Birmingham, Alabama