Quote:
Originally Posted by jeepsrule
If my coach were loaded to the max with 275 tires I would have tire pressure at 115 psi in the front tires, if I went up to 295 size tires I could lower pressure by 15 psi. How much would 100 psi compared to 115 change the ride??
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In my opinion you could not feel it, I agree the 255 on the front of your coach are probably over loaded you need to weigh your coach. Here is a good post from another forum on air pressure in tires and the guy that posted this is very knowledgeable on the RV and heavy duty trucks. Your rear tires are not quite 5 yrs old, if it was me I would worry about the front tires and dont give them away I have always got at least $100 for 7 yr old tires.
Walt
A lot of folks strive to go to heavier tires so they can run less air
pressure. Low pressure is the most common cause of tire failure and wear, as you
know. If one can feel a difference in ride running 10 lbs less air they
either have a problem with the suspension system or are sitting on a box to
drive. Going to a heavier tire is in most cases a good idea, it should not
be to run less air. Tires run cooler with more air, less rolling resistance,
less wear and if they lose a little air it is not under inflated. Most
folks have stepped up the air pressure in the front by 10lbs with GY tires,
this is a good idea. As others have stated some like to run 75, 80 or 85 lbs
in the tag tires because the chart says it is okay... If they would run
100lbs in the tag tires the tires are a lot happier. Michelin will tell you
flat out nothing below 85, but if you talk to their engineers, they are hard
to find, they are not the road reps, they will tell you more is better.
Think about it, if you go from 100 to 110 it is a 10% difference. After
suspension, etc 10% would be really hard to feel, if it can be felt something
else is wrong and they are asking the tires to be the suspension system. I
really think one who runs less air and says it rides better just want it to
feel that way so they believe it. Low air pressure causes a lot of squirm in
the tire itself, working or flexing between the plys and structure of the
tire, this causes ply separation, heat and other issues. . A round object
rolls better, ever try to roll a egg? As I have said before fleets typically
run 110 in the steers and 100 in all duals, Tractor trailers as a fleet
travel further in a day than all the motorhomes as a fleet do in a year. the
motorhome fleet is a very small mileage group. Fleets are managed by folks
that look to reduce cost per mile and have engineers, routers, etc to keep
costs and downtime down. We do not need to try to reinvent the wheel, they do
a good job if it. We can learn a lot from them they can do more testing in
a day of their fleet than one of us can in a lifetime.
Now think about this a tractor trailer is limited to 32,000 lbs per tandem
divide that by 8 and they run 4,000 lbs per tire. On spread axle trailers
the limit is 20,000 per axle, they run 100 with a 5,000 lb load. On The
steer axle is limited to 12K in most cases that equals 6,000 per tire. Now a
lot of coaches are at or above 20,000 on the drive axle which is the limit
for the roads (ask Ohio), that is 5,000 per tire. If 100 lbs is good for
them at 4,000 per tire on the drives or 5,000 on spreads. They have
seriously different tire loading and do not adjust their air pressure with every
loading or unloading. The average fleet truck weighs about 33,000 lbs
empty. Fleets strive to be able to scale 47,000 lbs, (80,000 gross loaded) as
they get paid by the pound.
Your comment about rolling resistance is true, if you have see the videos
of a tire going down the road with difference air pressure you will see the
difference. As the air pressure goes down the hump in the front of the tire
gets bigger, a lot like the water the bow of a boat pushes ahead of it
when it is running. This hump or wad increases rolling resistance and causes a
tremendous amount if flex in the tire, flex translates in to heat. As we
have all seen when someone tries to set a mileage record, college contests,
engineering contests, etc, they all run the smallest tire possible inflated
as much as possible.