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Old 06-16-2014, 09:06 PM   #1
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Tire pressures

The reasoning for doing the four corner weighing of your coach, is to make sure you're running enough psi in each tire for the weight on that corner, right?

If this is correct, why not fill your tires to maximum air pressure for maximum weight rating per tire manufacture specs? Wouldn't this eliminate the need for constant weighing, if you change your load? I don't for see running them this way to take away life, since motor home tires time out anyways?
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Old 06-16-2014, 09:13 PM   #2
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Four corner weight to inflate tires correctly. Max pressure for a tire carrying less of a load will wear the center of the tread out faster than if properly inflated. Same goes for under inflated tires, wearing prematurely, the outside edges of the tire. Personally, I prefer to keep the fillings in my teeth.
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Old 06-16-2014, 09:26 PM   #3
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Go ahead and run your tires at max pressure and see how you like the ride. The best ride and control comes when tires are inflated correctly for the weight they are carrying. This holds true for any vehicle.
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Old 06-16-2014, 09:28 PM   #4
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One of my mechanics (yes, I have several I support) said he runs all his tires to the max pressure the manufacturer recommends.

This is not that crazy. Yes you may get more wear at the crown. As I understand it, a harder tire handles heat better (less flex, less heat build up), and it handles water better (more surface area can lead to aquaplaning).

The downside is hard tires cause more wear on suspension and steering components, make the coach ride hash, and on ice more surface area is better.

For the miles we drive I'd go harder (the tires will rot before they wear out), but not the max (I like my teeth).
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Old 06-16-2014, 09:35 PM   #5
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I know I will be burnt for this but..............when a tracter and trailer rig cross' s the US with 10,000 pounds and then comes back with 48,000 pounds do they adjust tire pressures? No. I'm just giving something to compare.
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Old 06-16-2014, 09:35 PM   #6
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I do, and always have ran max air pressure. Haven't seemed to have to change out any tires due to wear, and haven't noticed any suspension components wearing any faster. Maybe this is because I've always ran max? Not just in the motor home, but anything I drive. I tried once, for a few months ( 12ply on my 3/4 ton ) at around 30psi ( due to the tire shop mechanic saying it would make the ride SO much better ) inflated back to max pressure, never noticed a difference.

I was just curious as to why so many are doing it, when it seemed to be too much of a headache. When we bought our coach, the tires were inflated to 70psi, changed all 6 after a couple of trips, New set at max psi and haven't noticed a difference. Maybe I'm not tuned in with it to notice yet, or maybe the coach is riding rough and I don't know what a smooth ride is :-)
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Old 06-16-2014, 09:37 PM   #7
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A properly inflated tire maintains the correct contact patch with the road surface. This maximizes the handling and load carrying characteristics of the vehicle. Braking, turning, traction, wet, or dry roads. Heat will not be a factor unless the tire is under inflated.
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Old 06-16-2014, 09:40 PM   #8
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Quote:
Originally Posted by 336muffin View Post
I know I will be burnt for this but..............when a tracter and trailer rig cross' s the US with 10,000 pounds and then comes back with 48,000 pounds do they adjust tire pressures? No. I'm just giving something to compare.
I manage an oil rig, when we're done with one hole, we tear the rig apart, move it and then put it all back again. We use transport companies that use a variety of trailers ( up to 5 axle for the heavy loads. 1 mud pump weighs in at 70k lbs ) and I can assure you, even on the long distance moves, none of the companies we ever use lower and raise their pressures according to load or being empty.

I rode with my grandpa growing up who drove for Wal-Mart for over 25 years, and he always taught me to run max psi and you'll always be safe. He still does this today. Might just be a bad habit to break.
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Old 06-16-2014, 10:15 PM   #9
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One sure has to wonder why all tire makers publish a load chart telling people the recommended pressures for a given load. Could it be that through research and testing they have determined what pressure will give the best tire life, ride and handling characteristics? That would also result in the safest pressure. I guess I will go with what the tire maker thinks is best.
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Old 06-16-2014, 10:32 PM   #10
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At last I find common sense in this thread. The. constant discussion of some of these items like tire pressure seems to be a boogeyman. Trucks don't adjust pressures and cars don't adjust pressures. Check them occasionally yes. Bang on them like truckers even better. I suspect tire manufacturers publish that data for all tires and it's probably due to some lawyer. I work with the truck industry - don't assume anything from what manufacturers do - look at what is done in practice by people who have to drive to make money.
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Old 06-16-2014, 11:05 PM   #11
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Tire manufacturers design and build a tire. The tire is designed for a maximum weigth at a maximum pressure. At that pressure with the design weight the tire sidewall will deflect a given amount. With that deflection the tire will give a tire contact patch. This will give a predicted rolling resistance, heat, wear pattern, handling characteristics and tire life.

The engineers then sit down and using tables, charts, experience, testing results and maybe a bit of magic to develop a tire pressure chart. If loaded with the correct pressure for the given weight the sidewall deflection, tire patch, rolling resistance, etc will be the same as at the maximum.

Then we get the tires and we use more magic and annecdotal information to further calculate new tire pressures for given loads.

Tires need some heat to work properly, give the best traction and wear characteristics as well as lubricate themselves to help prevent early deterioration.

Underinflation causes too much heat to build and if left long enough the tire will self destruct.

Overinflation leads to unenven tire wear, undesireable steering characteristics, harsher ride, and reduced traction in wet or icy conditions. In addition it can cause extra damage to road surfaces because of higher point loading.

There are many off road trucks that use a variable cab controlled air pressure system. The systems are very expensive so may not be practical for the normal OTR truck.
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Old 06-17-2014, 12:06 AM   #12
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Quote:
Originally Posted by Gordon Dewald View Post
Tire manufacturers design and build a tire. The tire is designed for a maximum weigth at a maximum pressure. At that pressure with the design weight the tire sidewall will deflect a given amount. With that deflection the tire will give a tire contact patch. This will give a predicted rolling resistance, heat, wear pattern, handling characteristics and tire life.

The engineers then sit down and using tables, charts, experience, testing results and maybe a bit of magic to develop a tire pressure chart. If loaded with the correct pressure for the given weight the sidewall deflection, tire patch, rolling resistance, etc will be the same as at the maximum.

Then we get the tires and we use more magic and annecdotal information to further calculate new tire pressures for given loads.

Tires need some heat to work properly, give the best traction and wear characteristics as well as lubricate themselves to help prevent early deterioration.

Underinflation causes too much heat to build and if left long enough the tire will self destruct.

Overinflation leads to unenven tire wear, undesireable steering characteristics, harsher ride, and reduced traction in wet or icy conditions. In addition it can cause extra damage to road surfaces because of higher point loading.

There are many off road trucks that use a variable cab controlled air pressure system. The systems are very expensive so may not be practical for the normal OTR truck.
The off highway trucks that use central air systems use them for traction purposes only. My son drives a log truck with that system on it and they will drop the air to 50 pounds to climb a steep muddy hill. It gives an unreal amount of traction. They are lucky to get 3 months out of a set of tires.

I personally years ago sat through hrs and hrs of Michelin test track videos on running tires at different inflation pressures and I am firmly in the camp of running tires at the pressures stated on the sidewall.

If my coach needs a 14 ply tire to carry the weight then that is what I would put on it. I would not downgrade it to 10 ply just to think it would ride better.
I would not put a bigger heavier tire on and run it half flat either.
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Old 06-17-2014, 02:03 AM   #13
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Agree

Quote:
Originally Posted by slickest1 View Post
The off highway trucks that use central air systems use them for traction purposes only. My son drives a log truck with that system on it and they will drop the air to 50 pounds to climb a steep muddy hill. It gives an unreal amount of traction. They are lucky to get 3 months out of a set of tires.

I personally years ago sat through hrs and hrs of Michelin test track videos on running tires at different inflation pressures and I am firmly in the camp of running tires at the pressures stated on the sidewall.

If my coach needs a 14 ply tire to carry the weight then that is what I would put on it. I would not downgrade it to 10 ply just to think it would ride better.
I would not put a bigger heavier tire on and run it half flat either.
I agree with Dennis. And again, if we drove RVs long enough to wear out tires then there "might" be a point. Or if someone could detect a hard ride that might be a point. But these things don't seem to occur with motorhomes.
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Old 06-17-2014, 02:23 AM   #14
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so if the weight of your front left corner requires you to run at 60 pounds and the weight on the right front corner requires you to run 90 pounds, how do you think that rigs is going to steer ? Would you weight police out there do it ? Now I suppose the air pressure difference in the back tires wouldn't make as much difference as the front tires would in the steering input.
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