How to determine tire pressure?

[TimLoon]

I just changed out my seven year old Michelin 245/70-19.5's for Hankook AH11's. I had the tire installer set the pressure to 95 lbs. as the previous of the MH had that witten on the manufacturer's spec sheet. I have no idea if that is correct for the Hankooks. I can't find anyhting on their website and the tire sidewalls only state 110 psi max. My workhorse owners manual refers me to specification plate but can't find that anywhere. MH is a 2004 Allegro 32BA on Workorse chassis. Thanks, Tim

[AFChap]

The "plate" should be somewhere by the driver seat ...mine is hard to see, but is on the wall to the left of the driver seat. BUT, that is only accurate for the original tires, and at who knows what weight. Your coach does NOT shave the original tires. If they are the identical make, model, and size the placard could be a guideline. But the only way to know the correct pressure is to get a four wheel weight of your coach, and to then check the tire mfg'er chart for your specific tire. The placard pressures on my coach are 10psi light for my current tires based on the last weights I did, and 5psi light for the original tires.

[TimLoon]

I am sending email to Hankook for a chart for that tire size. Our first trip of the year in May will take us past a scale so I will stop in and have the weights checked. For now, I will base the pressure on manufacturers listed maximum weight.

[Pirate]

You need to weigh your RV soon. You want to try and get the 4 corners individually. Do you live near a highway scale? Moving company? If those aren't available, locate the nearest CAT scale at a truck stop. Try and do this when you start off on a trip, as you want the high average travel weight. With the weights, you will need the tire charts from the manufacturer to determine the proper air pressure. You can't guess.

[Pusherman]

Call Hankook (you can find their tech support # on the web). Ask them to send you the inflation tables as a function of tire size and actual tire weights. They will oblidge.

I too have had difficulty finding out this information on the web for a customer. Telephone support came through.

[TimLoon]

I have emailed Hankook and will also try to calling next week. I won't get near a scale until my first trip next month. There is a moving company on the way that will weigh campers. Not sure f they will let me do the campers but will ask. This will be boondocking so I will have a full tank of water and a full tank of liquid gold (gas) so I should be near my heaviest weight.

[mllk3rd]

I was able to get mine weighed at the locale dump, they were able to do each axle and it was free unless I needed a certification for DMV.

[TimLoon]

Didn't think about usng the scale at the dump. Only problem is most emplyees there are really nice and there is one really cranky guy. Guess who normally operates the scale?

[Ed-Sommers]

Even the manufactures inflation recommendation is, as it states, a recommendation, and probably one or two engineers opinions based on several different factors.

In coming up with the best guess recommendation, the conflicting factors include, but are not limited to safety, longevity, and ride, at a given load.

For longevity, a tire running completely flat in relation to the road would be proper, for safety, a higher pressure is often safer say for an emergency turn to avoid an accident, where a softer pressure may cause the tire to deflate in the emergency turn, and then there is ride considerations where a softer, lower pressure is best.

Given that the majority of the RVing public will never wear out a set of tires, but be retired due to age, it is my opinion that a higher pressure than the manufactures recommendation is the best pressure, except for those that consider ride the highest priority.

Having different pressures on opposing sides of an axle is, IMHO, an exercise if futility. The differing running weight due to water levels, and cargo would necessitate a constant adjustment of differing pressures.

Ed
USN Ret.

[TimLoon]

Hankook was great about answering my weekend email first thing this morning by supplying a chart of pressures/weight capacities for AH11's in 245/70-19.5.
If I take my max axle weights from the coach manufacturer (until I get a live weight), according to Hankook, my front tire pressure should be 85 lbs. and my rear duals would be 80 lbs. For now, I will drop the 95 lbs. to 90 lbs. all around and see how the ride feels. Thanks for all the input.

[jmckinley]

(1) Tire pressure vs load for a given size and load range is the same for every manufacturer. These values are published by the Tire and Rim Manufacturer's Association and have been agreed upon by all the tire makers.

(2) The pressure shown on the charts provided by your tire maker and the TRMA is NOT the RECOMMENDED pressure for a given load. The pressure shown is the MINIMUM pressure for that load. It seems like everybody on all the forums gets this wrong. And, these numbers are not arrived at by a bunch of engineers sitting around in a room. They were developed by years of field and lab testing and are not just guesses. The best thing to do is check the chart, then pick a pressure at least 5psi above the chart number and maybe even more if you will be driving fast or in hot weather or may change load from time to time.

[wolfer]

This is the best way to find out the correct tire pressure on any vehicle. You can take two similar coaches and load them closely and they will be different. Here is how to do it. Get yourself a piece of sidewalk chalk. Prefered white. draw a line across all 4 treads on each tire be setting on a flat smooth surface like a flat parking lot. drive forward or reverse for 3 or 4 revolutions of the tire and look at the wear pattern on the chalk mark. If it is wearing off in the center you need to let some air out and repeat until you get it to wear evenly across the tread. Same goes for wear to the outsides instead of the center. Your tires will get the best mileage possible and handle better than you ever dreamed. Lesson from an old retired truck driver.

[Arch Hoagland]

Originally Posted by wolfer

This is the best way to find out the correct tire pressure on any vehicle. You can take two similar coaches and load them closely and they will be different. Here is how to do it. Get yourself a piece of sidewalk chalk. Prefered white. draw a line across all 4 treads on each tire be setting on a flat smooth surface like a flat parking lot. drive forward or reverse for 3 or 4 revolutions of the tire and look at the wear pattern on the chalk mark. If it is wearing off in the center you need to let some air out and repeat until you get it to wear evenly across the tread. Same goes for wear to the outsides instead of the center. Your tires will get the best mileage possible and handle better than you ever dreamed. Lesson from an old retired truck driver.

At what temperature do you do the test?

Cold or after the tire has been running for an hour?

[Dunner]

Originally Posted by wolfer

This is the best way to find out the correct tire pressure on any vehicle. You can take two similar coaches and load them closely and they will be different. Here is how to do it. Get yourself a piece of sidewalk chalk. Prefered white. draw a line across all 4 treads on each tire be setting on a flat smooth surface like a flat parking lot. drive forward or reverse for 3 or 4 revolutions of the tire and look at the wear pattern on the chalk mark. If it is wearing off in the center you need to let some air out and repeat until you get it to wear evenly across the tread. Same goes for wear to the outsides instead of the center. Your tires will get the best mileage possible and handle better than you ever dreamed. Lesson from an old retired truck driver.

I've been doing it this way for many, many years. I've seen posts saying to drive for a couple blocks or a quarter mile. Wrong. Not necessary.