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running tire pressures

All things about tire safety

Moderators: Techno Eric, Techno Tami

by castaway » Sun Aug 13, 2017 7:56 pm

My rv runs 75 psi in the front and 80 psi in the rear.

How high should the pressures go while driving the highway?
castaway
 
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by bgibbs » Sun Aug 13, 2017 8:51 pm

I think a rule of thumb is a pressure increase of no more than 10%.
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by Northsite » Mon Aug 14, 2017 9:11 am

The tire should tell you the max cold pressure. If you are in cold country you can set it to max pressure -5 psi to allow for expansion. If you are in warm country set it for 2 psi below max cold pressure.
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by JR1 » Mon Aug 14, 2017 9:13 am

Short answer:

Up to 25% or 94/100 based on your 75/80 information, before you have an issue. Get yourself a tire pressure monitoring system if your are worried about it - our form hosts sell them for example. Cheap insurance and peace of mind.

Long answer:

Unless your tires are worn out, damaged, set at the wrong pressure for the weight of your RV, or your alignment is bad, don't worry about it. The increase in pressure is due to normal temperature rise from the friction and flexing of the tires as they roll. Make sure you set the tire pressures "cold" of course. The "base pressure" to set the tires at "cold" takes into account these factors when driving. However, if you travel from say Seattle to Phoenix where the temperature is significantly higher you might want to check your tire pressures again "cold", say the next morning. Tire pressure monitor systems usually have the alarm set at 25% over the set pressure and 15% under the set pressure. ("Set" meaning what you tell the system you set them to - 75 & 80 in your case) So you could see 94 and 100 before there was an issue. A handy tool to have is a digital non contact instant read , including IR thermometer - you just aim at an object and press the trigger - great for lots of things - Harbor Freight has them quite inexpensive. If you check your tire temperatures and pressures when parked on a sunny afternoon you will see a difference on the sunny side.

Do not listen to the blowhard amateur "experts" who tell you "I run mine at max pressure for longer life". Yep, tires will outlive you for sure if they are not destroyed in the wreck.... Or "I run mine XX psi low for a softer ride" Even worse!! Or any other such BS.

I assume you are setting your tire pressures correctly in the first place. The tire manufacturers know best!!! NEVER set them to the maximum shown on the sidewall. You need to weigh your RV at all four corners, check you are not exceeding half the axle weight rating, take the higher of each side and set both the tire pressures to the manufacturers weight/pressure chart for that specific tire (there are two values - single and dual). You can find the charts on the manufacturer's web site. Public truck weight stations are usually functional even when they are closed, so that's a free and easy way to weight your coach. You don't have to be anal about it, make allowance for normal variations in load - just use your average running weight unless you are making a long trip with a lot of extra weight for example. BTW: Make sure all the tires on each axle are at balanced pressures as closely as you can - it make a lot of difference to stability, especially sway. Invest in a good quality digital tire gauges, don't trust "stick" types or dials (especially the one on your tire inflater!). Note that any sticker in your RV showing tire pressures is most likely incorrect and for bare chassis legal reasons only - typically meaningless.

2 other things. Forget nitrogen - doesn't do anything significant in spite of the "sounds good" claims. Just another way to screw some money out of you and remember that air is 80% nitrogen anyway. Do not use "balance beads" or even worse sand inside your tires. The tire manufacturers will all tell you don't do it, it can (really) void your warranty and can damage the tires. Have them balanced properly when they are installed.

Get all those things right and you should not have to worry about pressure increasing quite normally during driving.
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by JR1 » Mon Aug 14, 2017 9:34 am

I am really sorry to have to say this - and I'm not "flaming" him - but Northsite's response is frankly irresponsible. There are so many problems with doing that and most of them are safety issues.

NEVER EVER run tires at the maximum sidewall pressure. That's only to show the absolute maximum load carrying capacity of the tires and tires should never be selected for normal use close to their max capacity.

If in doubt, just contact the tire manufacturer's customer support for CORRECT information and questions on your tires. You are trusting your tires with you life - and others' lives - trust the experts who design and make the tires and know all about them.
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by castaway » Mon Aug 14, 2017 2:06 pm

These questions came up because of the tire monitoring system we installed. Thank you for the response. It's a good thing to worry about your tires. We are in the rocky mountains now, and am checking the pressure more. Think I have a better idea what pressure to set now.
castaway
 
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by Techno Eric » Mon Aug 14, 2017 8:19 pm

Hey Castaway,
Eric from TechnoRV here. We get this question a good bit. To reiterate some of what has already been said, and some that has not, by all means, go by the tire manufacturers inflation chart. This means, to do it right, you need to get weighed at all four corners of your RV and then apply it to the manufacturers chart. Under inflated tires will create heat, and heat is the enemy to your tires. Under inflation is worse than over inflation if you are not sure of your weight. The debate over the max rating on the tires continues. If you are not sure of your weight, then schedule to get weighed, and in the mean time run the max PSI rating on the tire, again, you certainly do not want to run under inflated. The tire manufacturers know that the tire PSI will go up as the tires heat up, this is normal. As for how much they will increase, good luck on finding that out. I have called all of the big tire companies and no one will give a straight answer.

The TST TPMS system recommends you set the parameters at 10% below the recommended cold tire pressure and 20-25% above. The temperature warning on the TST system is preset to 158 degrees. In most cases this would indicate you have a problem, possibly brakes locking up or bearings seizing. Escapees Boot Camp and RVsafety.com seminars all teach what I have stated here. We present seminars on this topic as well, and this is pretty standard information, but it can be a bit confusing so feel free to ask more questions if you have them.

Eric
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by castaway » Tue Aug 15, 2017 8:35 am

Thank you for the response. Looks like we need to find a scale.
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