Tire Pressue

[Eraygunz]

Hi
I have a 1997 Roadtrek 190.
What should the front and rear tire pressue be?
55 front...80 rear?
What to be sure its where it should be.
Thank you
Eddie

[SteveJ]

I and some other folks will run 60-65 up front and 80 in back and spare, cold. Keep in mind that the pressure will vary about one degree per 7 degrees F using air. Not sure of the change if using nitrogen.

[booster]

Most of the Dodge folks I have heard about like 65 front 80 rear.

The change of pressure with temperature is actually a % and has some other corrections in it also, so by the time you get to 80 psi, you are closer to 2 psi per 10*F temp change. It also varies with how cold or hot it is when you start as you have a fixed correction on that also.

Best to use a pressure calculator at the temps and pressures you actually run in the van, which are much higher than car pressures where most of the rules of thumb made.

Martin Schmaltz' pressure calculator

It is very interesting to see just how much the pressure can change within even one trip. We live in the cold north, but we can get south in two days of driving. If we go from -10*F to 80*F the 80psi in the rear tires will be nearly 99psi which is way over max tire rated pressure. A 50* morning 80* afternoon day would change the 80psi to just over 85psi, which is also over rated, but not too bad. Splitting the over and under works well for us, so a bit under pressure in the morning and a bit over in the afternoon.

It all makes for some very interesting opinions of where to set you tire pressures based on what temps you will see. If in the above example you set the pressure to be at max when you got to the warm weather, you would be starting at 61psi, which is way low for fully loaded van.

Going from cold to warm is not too bad, as you just need a tire gauge and let out some air when you see a big shift of warmer weather. Going warm to cold is tougher because you have to add air to the tires as you go, so need to have a compressor or find an air fill station, and of course hope the hose or your stems aren't frozen shut.

[BBQ]

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78 percent of air is nitrogen.

[BBQ]

.

The tire pressure recommendations are "cold-measurements".
ie. before you start driving when the tires have not warmed up yet.

[booster]

Originally Posted by BBQ

.

The tire pressure recommendations are "cold-measurements".
ie. before you start driving when the tires have not warmed up yet.

You can have a lot of fun with tire salesman and even the factory reps at shows in regard to the "cold recommendations". Most of them will tell you it is setup that way so the tires will be at proper inflation once they warm up, as checking them hot is very inconsistent and nobody would do it anyway. Totally agree with them on that. They also say to never go over the recommended sidewall max pressure or "underinflate" the tire with no rules for that.

If you bring up and example of a big ambient temp swing during the day, they really don't know what to tell you from what I have gotten from them. A 50*F ambient swing during the day isn't all that unusual for most of us. High desert day and night, changes in altitude during the day, etc will be that way fairly often. That 50* swing will give nearly a 10psi pressure change in a tire if air is not put in or out. If your van has the rear tires recommended at 80 psi because of big loads, like many of ours are, what do you use for pressure on a cold morning when you know you are going to be 50* warmer in the heat of the day? If you set at 80psi, the tires will show 90psi during the day if you let them cool to ambient. This is above rated sidewall pressure, and will still go up when you are driving at that temperature. If you set the tires at 70psi in the morning, you will be at the rated 80psi in the heat of the day, but possibly have the tires underinflated when starting out. Similar issues if going from hot to colder temps. Often the reps would tell you to adjust the pressure during the day to compensate for the temp increase, but they also don't want pressures set while warm from driving, so the only way to do it would be to take the tire pressure reading and then just reduce whatever it reads by the amount the temp would have changed it. Too complicated for many folks to figure out and do, plus they may have to find a place with air available to increase pressures. Probably 5% compliance to that recommendation?

I don't think there is a answer to the question that is correct, as it is basically impossible unless you have auto inflation or do all the calculations and have the capability to adjust pressures during the day. As I mentioned earlier, I usually split the error up and down so we are 1/2 the pressure change on each side of preferred. If we get to where the change would be more than 10 psi over the day or days, because of temp change, I would adjust them along the way. We are lucky because we have oversize tires on the Roadtrek, so normal pressure is in the 75psi range in the rear, so even a 5psi increase from the splitting won't take us over sidewall rating and 70psi will still carry our load easily per the charts.

Of course 10spi of tire pressure change will be noticeable to many drivers in handling issues, so that may be a bigger incentive to adjust during the day if it is a long drive.

[SteveJ]

Originally Posted by booster

You can have a lot of fun with tire salesman and even the factory reps at shows in regard to the "cold recommendations". Most of them will tell you it is setup that way so the tires will be at proper inflation once they warm up, as checking them hot is very inconsistent and nobody would do it anyway. Totally agree with them on that. They also say to never go over the recommended sidewall max pressure or "underinflate" the tire with no rules for that.

If you bring up and example of a big ambient temp swing during the day, they really don't know what to tell you from what I have gotten from them. A 50*F ambient swing during the day isn't all that unusual for most of us. High desert day and night, changes in altitude during the day, etc will be that way fairly often. That 50* swing will give nearly a 10psi pressure change in a tire if air is not put in or out. If your van has the rear tires recommended at 80 psi because of big loads, like many of ours are, what do you use for pressure on a cold morning when you know you are going to be 50* warmer in the heat of the day? If you set at 80psi, the tires will show 90psi during the day if you let them cool to ambient. This is above rated sidewall pressure, and will still go up when you are driving at that temperature. If you set the tires at 70psi in the morning, you will be at the rated 80psi in the heat of the day, but possibly have the tires underinflated when starting out. Similar issues if going from hot to colder temps. Often the reps would tell you to adjust the pressure during the day to compensate for the temp increase, but they also don't want pressures set while warm from driving, so the only way to do it would be to take the tire pressure reading and then just reduce whatever it reads by the amount the temp would have changed it. Too complicated for many folks to figure out and do, plus they may have to find a place with air available to increase pressures. Probably 5% compliance to that recommendation?

I don't think there is a answer to the question that is correct, as it is basically impossible unless you have auto inflation or do all the calculations and have the capability to adjust pressures during the day. As I mentioned earlier, I usually split the error up and down so we are 1/2 the pressure change on each side of preferred. If we get to where the change would be more than 10 psi over the day or days, because of temp change, I would adjust them along the way. We are lucky because we have oversize tires on the Roadtrek, so normal pressure is in the 75psi range in the rear, so even a 5psi increase from the splitting won't take us over sidewall rating and 70psi will still carry our load easily per the charts.

Of course 10spi of tire pressure change will be noticeable to many drivers in handling issues, so that may be a bigger incentive to adjust during the day if it is a long drive.

Then...there are more issues with changing altitudes, or not. According to Tire Rack there is a 4.6 lb increase in tire pressure at 10,000 ft vs sea level. But the temps are cooler so it's close to a wash.

[booster]

Originally Posted by SteveJ

Then...there are more issues with changing altitudes, or not. According to Tire Rack there is a 4.6 lb increase in tire pressure at 10,000 ft vs sea level. But the temps are cooler so it's close to a wash.

Yep, and the tires on the sunny side as you drive will likely run 10-20* hotter than the shady side.

I do think it is important to stay away from going a lot over the max sidewall pressure, or going a lot under full load pressure in the rear if you are near max load, but beyond that, you are never going to get anywhere near optimum on all the tires for very long or often. All you can do is shoot for the middle of the range you like for driving comfort and handling, as long as it can carry the load without going above rating. I can tell you with certainty that there are fully loaded class b's out there that are at 60 psi to 100psi in the rear because many don't ever make any allowances for temp or altitude and may not ever check them on a trip. The TPMS systems that show tire temp and pressure on a screen are very nice for most folks, as they will get close enough to stay safe, and alert if you don't look at the screen often enough. I think everyone should have that setup in their b. I set pressures with a good gauge, but we always try to remember to check the TPMS readout in the morning before we start driving.

[SteveJ]

Originally Posted by booster

Yep, and the tires on the sunny side as you drive will likely run 10-20* hotter than the shady side.

I do think it is important to stay away from going a lot over the max sidewall pressure, or going a lot under full load pressure in the rear if you are near max load, but beyond that, you are never going to get anywhere near optimum on all the tires for very long or often. All you can do is shoot for the middle of the range you like for driving comfort and handling, as long as it can carry the load without going above rating. I can tell you with certainty that there are fully loaded class b's out there that are at 60 psi to 100psi in the rear because many don't ever make any allowances for temp or altitude and may not ever check them on a trip. The TPMS systems that show tire temp and pressure on a screen are very nice for most folks, as they will get close enough to stay safe, and alert if you don't look at the screen often enough. I think everyone should have that setup in their b. I set pressures with a good gauge, but we always try to remember to check the TPMS readout in the morning before we start driving.

I've noticed a 5-8 lbs increase over normal hot pressure in the rr tire with a strong crosswind from the left and ambient temps at about 105(Texas). With my trailer behind I wound up dropping to third gear as the wind was too strong to consistently hold torque converter lock up in fourth, and easing back a bit on speed. A brutal(typical Texas) day. MPG wasn't too good either.

TPMS is a marvelous thing.

[Ron J. Moore]

Wow, this is great info. Think I might have to start walking, ha! Thanks for the info. Ron

[Eraygunz]

Wow.
Almost seems like there is no good answer?
I live in Florida....so my cold tire pressure will be alot diffrent from folks up north?
Maybe i shoild run mine just a little under the usual pressue? As it will almost always be hotter than average temps?
Maybe 60/78 ? Except that couple days a year when it gets SUPER cold like today...in the 40sLOL!
THANKS for all the good info.
Eddie Ray

[booster]

Originally Posted by Eraygunz

Wow.
Almost seems like there is no good answer?
I live in Florida....so my cold tire pressure will be alot diffrent from folks up north?
Maybe i shoild run mine just a little under the usual pressue? As it will almost always be hotter than average temps?
Maybe 60/78 ? Except that couple days a year when it gets SUPER cold like today...in the 40sLOL!
THANKS for all the good info.
Eddie Ray

The pressure you set would be the same as those of us in the north set. The issue comes when you would bring your van to the great north and into the cold. Your tire set tire pressure would drop due to the temp change and require resetting.

If you don't see more than about 30-50* of temp change int he place you go to, it is likely you wouldn't need to change your pressure setting unless you are looking for better ride or handling. Most find the 65 front and 80 rear to drive the best.