Checkin' in before lowering my tire air pressure

[Water Dog]

Any comments on this, good, bad or otherwise? Weighed our 26' motor home today packed and ready to go.
Front: 5080 pounds,
Rear: 7820 pounds,
Total: 12,900.

Tires are Hankook LT235/85R16 "E" load rating with max loads at 2778 @ 80psi (Dual), and 3042 @ 80psi (Single).

I couldn't find an inflation table from Hankook, but Michelin has one with the exact same values, and according to the weights, my fronts should be aired to between 65 and 70 pounds, and the rears to about 55 pounds. (both are figuring a couple of hundred pounds of fudge room) Does it seem like a mistake to lower the air pressure that significantly, especially in the rears? We are talking 25 pounds less than the max pressure. I'm anxious to get a little more rubber on the ground in the fronts because I think it will improve handling, but I'm not sure about taking the rears that low.

 

[seilerbird]

I would not use another manufacturers psi recommendations. Find out from the maker of your tires what the pressure should be with that weight.

 

[Gary RV_Wizard]

Using the inflation data from another manufacturer's tire is really risky. Too many possible design differences to assume they  are the same.

Your fronts are not over-inflated anyway, once you allow for possible (likely) side-to-side imbalance and some safety margin, so I'd leave them at 80 psi. Maybe try 75 if you really think they are too rough riding, but no lower than that.

Your rear duals are carrying around 2000-2200 each (again, allowing for imbalance), so maybe you could drop them to 70 psi. I wouldn't go lower than that without a Hankook inflation table.

 

[Water Dog]

Thanks for the input....that was kind of my gut feeling. I've searched and searched and cannot find an inflation table from Hankook but did find ones from about three other manufacturers that all had the same data for the same size and load range tire. I agree that one shouldn't go by another manufacture's info, but I figured it would get me in the ballpark. Gary, I think I'll try your suggestion about 75 in the fronts and 70 in the rears and see how it handles it.

 

[Master-Tech]

I would run the Tires at pressure rate on the tire ,  the 80lbs recommeded is for that certain load range,  lower tha pressure less tire can carry an could or will cause unwanted wear and damage,  most Manufactures are Super Close on the weight rates so be very carefull Please !    Rodney

 

[Water Dog]

I would run the Tires at pressure rate on the tire ,  the 80lbs recommeded is for that certain load range,  lower tha pressure less tire can carry an could or will cause unwanted wear and damage,  most Manufactures are Super Close on the weight rates so be very carefull Please !    Rodney

Sorry, going to have to disagree Rodney. The rates on the tires are maximums. That is why there are tire inflation tables. My motorhome doesn't weigh anywhere close to the maximum weights the tires are designed for so running at max pressure is overinflation for the weight they are carrying. It causes the the tire centers to wear quicker and the steering to be not as stable.

 

[Gary RV_Wizard]

Sadly, trailers are generally loaded right near the tire's max capacity, so there is typically no reason to run under the sidewall max. But motorhomes often have some leeway, at least on one axle or the other. Dennis has his actual weights, so he could safely apply the tire inflation tables (if only Hankook would publish theirs).

 

[Just Lou]

Dennis, I agree.......  The max-psi stamped on the tire is for maximum load carrying capability and is not meant to suggest the optimum psi for any other combination of weight load, ride or wear characteristics.

Running with the max psi rating stamped on the tire might be the safe thing to do if one knows nothing about the specific weight, and weight distribution, of your coach, but that's not the case with yours or mine.

My rear tires have the characteristic wear pattern in the center of the tread because I have previously run them at the max (80psi).  After weighing the coach prior to my recent trip, I lowered the pressure to 72psi, and enjoyed a much better ride.  I also lowered the fronts to 75psi and was pleased with the ride and steering improvement.  I'm still above the Goodyear table suggested values, so I don't feel that I've compromised a thing.

 

[Larry N.]

Changing from max on tire to Michelin table recommendations changed my front end from dangerous bouncing under certain conditions to normal behavior -- a GIANT improvement in ride and safety.

 

[Pierat]

Call the place where you bought the Hankooks?

 

[Water Dog]

Changing from max on tire to Michelin table recommendations changed my front end from dangerous bouncing under certain conditions to normal behavior -- a GIANT improvement in ride and safety.

Larry, I noticed a huge improvement in the handling of my Jeep Wrangler when I lowered the max rate 44 psi tires (that I had inflated to about 42) down to 30psi. The wrangler now navigates the freeway like a normal car instead of being kind of squirrely. (Is that a word?)

 

[Larry N.]

Larry, I noticed a huge improvement in the handling of my Jeep Wrangler when I lowered the max rate 44 psi tires (that I had inflated to about 42) down to 30psi. The wrangler now navigates the freeway like a normal car instead of being kind of squirrely. (Is that a word?)

It's a word I use all the time, Dennis. I was in a Grease Monkey a few years ago for an oil change, and they filled my pickup's tires to the sidewall value. I had almost NO traction in the light snow leaving there (with the locking differential I normally had good traction in those conditions, and it was back to normal after I got the pressure right). Although I'd used them many times before, they had a new manager, and when I went back he argued that what they'd done was right (more than 10 lbs too high) and I've not been back since. I usually run 35 psi in my pickups, 32 in my wife's Marquis.

Sure shows how much difference proper pressure makes.

 

[taoshum]

IMHO, having the tire pressure adjusted properly is critical to steering, handling and braking.  If you cannot get an inflation guide from the tire company, use a chalk test to make sure you get full contact across the tire and then run some driving experiments to verify that the steering and braking are optimized.  You can certainly feel the difference when the tires are properly inflated or not.  The difference is huge, at least as important as having good shocks and suspension springs.  Our tires are rated at 110 psi for instance but after having the weight measured, the chart said they should be inflated to 90 psi... so I tried it and it was a major improvement but it bothered me to have such a low pressure, so I raised it to 95 psi and didn't notice much, if any, degradation so that's where I left it.  I run the rear tires at 90psi though.  The steering is vastly improved.

If you add or delete 1000 to 2000 lbs or so, you probably need to adjust the tire pressure.  A full set of tanks (gas, water, waste) can add up to 1500 lbs, for example so we try to keep the "water" tanks at the same level all the time we are underway and let the tires accommodate the fuel load variation... mostly in the front anyway.

 

[fklskv]

  There should be a tag on the vehicle somewhere listing proper tire sizes and inflation. My class A has it on the dashboard and you view it looking through the windshield from the outside looking in. Cant imagine vehicles these days not having a inflation tag on it.

 

[Just Lou]

  There should be a tag on the vehicle somewhere listing proper tire sizes and inflation. My class A has it on the dashboard and you view it looking through the windshield from the outside looking in. Cant imagine vehicles these days not having a inflation tag on it.

The problems with that are; The data only applies to the original equipment tires and does not take variations in additional loading into account.

 

[Stacy]

Found elsewhere:

"For LT type tires, it does not matter who manufacturers the tire, the load vs inflation pressure relationship is the same.  That relationship is published by The Tire and Rim Association (TRA) in a yearbook.  Unfortunately, the only income TRA gets is from selling the yearbook and they do not allow it to be published, especially over the internet.  BTW, the yearbook costs $85.00.

But the good news is that sometimes you can find bits and pieces of the tables  - and there is one here:

http://www.goodyear.com/truck/pdf/edb_loads.pdf

The table you are looking for is on page 7.

But I should warn you.  The table is a MAXIMUM and applies only for ideal conditions - which really don't exist.  So the actual loading has to be adjusted downward the more deviation there is from ideal conditions.  This is one of the lessons from the Ford / Firestone situation afew years back."

I called BF Goodrich (Owned by Micehlin now) and they referred me to the chart for that tire size at:

http://www.michelinrvtires.com/michelinrv/tires-retreads/load-inflation-tables.jsp


They said DO NOT run at MAX pressure all the time. Weigh your vehicle (on each corner) as loaded for an outing and use the recommended PSI from the chart.

I hope this puts all the miss-information out there to rest... :

PS: From Michelin RV:

For RV use only, Michelin displays tire loads per axle end in the load and inflation tables, as we recommend weighing each axle end separately and using the heaviest end weight to determine the axle's cold inflation tire pressure. For control of your RV, it is critical the tire pressures be the same across an axle, while NEVER exceeding the maximum air pressure limit stamped on the wheels.

To select the proper load and inflation table, locate your tire size in the following pages, then match your tire's sidewall markings to the table with the same sidewall markings. If your tire's sidewall markings do not match any table listed, please contact your Michelin dealer for the applicable load and inflation table.

Industry load and inflation standards are in a constant state of change, and Michelin continually updates its product information to reflect these changes. Printed material may not reflect the latest load and inflation standards.

In the load and inflation tables, SINGLE means an axle with one tire mounted on each end, while DUAL means an axle with two tires mounted on each end. The loads indicated represent the total weight of an axle end in an RV application. When one axle end weighs more than the other, use the heaviest of the two end weights to determine the unique tire pressure for all tires on the axle. The maximum cold air pressure for each axle may vary, depending on their weights. These tables are applicable for all RV axles, whether or not they are power-driven.

 

[Gary RV_Wizard]

"For LT type tires, it does not matter who manufacturers the tire, the load vs inflation pressure relationship is the same.  That relationship is published by The Tire and Rim Association (TRA) in a yearbook.  Unfortunately, the only income TRA gets is from selling the yearbook and they do not allow it to be published, especially over the internet.  BTW, the yearbook costs $85.00.

I don't know where this "elsewhere" was, but it's wrong. Several manufacturers publish their inflation tables for LT tires, including Goodyear, Michelin and Bridgestone.  As for whether the inflation tables are identical, you would have to compare item by item. They will likley be very close, if not identical, for any given load range because the LT load ranges are a fairly tight spec.

The nice thing about the TRA book is that it has all the data in one place. Very convenient, if somewhat expensive for individual use.

 

[Stacy]

Well, for what it's worth Goodrich referred me to the Michelin table. ??? Could be because they make them both. YMMV.

 

[Gary RV_Wizard]

Goodrich IS a Michelin tire. Made in the same factories, using the same designs.

 

[scottydl]

I know we're used to being able to Google everything we want to know, and find it... but you may need to contact Hankook directly in thise case.  They have a "Contact Us" page here on their website which would be my suggestion.  Perhaps they can e-mail you an electronic copy of the inflation tables.  I would not rely on what the dealer or tire installer says... as we've learned, they do not always have the most accurate ideas on tire inflation.