Why is inside dual tire wearing/

[Larry B]

  I was under bus connecting hose to drain water tank. Getting ready for winter storage as I need shop space for another project. I noticed the inside edge of inside dual had wear marks. (both sides of bus-same wear pattern)Tires are 12R22.5 Kumho recaps with at the most 5000miles. Is this what is referred to as scrubbing of a tire from turning sharp corner on dry pavement? I assumed this only happened on tandem axles. Checked tire pressures-inside tires105psi outside 110psi. Both sides of bus same. Changed valves stem valves and all tires are holding at 110. could 5psi diff have caused this? 
    This brings up another issue I do not fully understand. My rear axle weight is 19,000 lbs. On tire is stamped--max load dual 3075kg  (6780lbs) @ 120 psi cold. Four of these tires should be able to carry 6780x4=27,000 lbs. Tire shop told me to carry 100 to110 psi and I would be fine. How did they figure this? I am not at full carrying capability of my tires but how did they arrive at 100 to 110psi? Is there a mathamatic way of figuring this out? Pictures did not come out that clear hope you can see what I am talking about.  Thanks
         Larry B

[lostagain]

You are running too much pressure. Tire shops are used to transport trucks and routinely inflate to at least 100 psi. Might be hard to look up inflation tables for recaps. Maybe look them up on the web site of the manufacturer of the tire casings. As a guide line, I run my drive axle tires at 80 psi (MC5C, same weight give or take a little). Not saying that being over inflated is causing the wear, but that could contribute. Another thing is that the inside duals usually wear faster because of the crown of the road. I don't know what else would cause this.

JC

[RJ]

My rear axle weight is 19,000 lbs.   Is there a mathematical way of figuring this out?

Larry -

There is a formula for figuring this out, and it goes like this:

1) Run your coach in "ready-to-roll" trim across a set of commercial scales.  Be sure to get front axle, rear axle and total vehicle weight.

2) Divide each axle's weight by the total number of tires on that axle.  This will give you the average weight each tire is supporting.

3) As a "fudge factor," add 200 - 250 lbs to each average weight for additional "stuff" that you may carry on board later.

4) Go to the tire casing manufacturer's website and look for their inflation guide for your size tire.  It will be a chart similar to the one posted via the link below.  If you cannot find a chart on the website, call a local dealer for that brand and ask him to look it up.  (If you have to do this, DON'T let him tell you 100 - 120 psi, ask for actual numbers, not "that's what we inflate them all to. . .")

5) Adjust your pressures accordingly, based on the manufacturer's chart.  You will see a big difference in the ride and handling once they're adjusted properly.  As an example, when I first got the 4106 I no longer own, it had 120 psi in all six tires, and rode like a buckboard wagon.  Once I ran it across the scales, the coach was so light I was able to run 80 psi up front and 75 psi in the duals. HUGE difference in the ride as soon as I pulled out of the lot.  So do your homework!

FWIW & HTH. . .



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

[wg4t50]

Tire psi is fine, my take on this would be the cheap rubber compound and tread design used on those recaps. I never run recaps, but I have run similar tread design and got a crazy wear pattern on all 4 on the drive axle, always thought was due to my running hard with 600+ hp.

I also run about the same weight and 105 psi, using Michelins, XZE series,275/80/22.5 LRH, and I just changed them due to age, from wear they still looked great and very evan, had 74,000 miles on them, they still looked great for another 75,000 very easy, just timed out.

[bevans6]

I have found that the load/psi tables for different manufacturers are close to identical for a given size and rating of tire, so I use this one from Firestone.

http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEwQFjAA&url=http%3A%2F%2Fwww.firestonetrucktires.com%2Fpdf%2FFirestone_Load_Table.pdf&ei=YxOCUqDCJKmssATCh4HQCg&usg=AFQjCNEMPCPD81KfgvZtNyI7OgSHoOastw&bvm=bv.56146854,d.cWc&cad=rja

At 4,750 lbs on each tire you find that the load is actually under the lowest load category for load range F tires, if only by a small margin.  The correct inflation pressure for 4780 lbs duals is only 70 psi.  It's also interesting to note that in that size tire, load range F goes up to 5675 at 90 psi, load range G goes up to 6005 lbs at 105 lbs and load range H goes up to 6780 at 120 lbs.  So if you happened to have casings that started out as load range F tires you'd be well within the load capacity but you'd be running them way over-inflated at 105 psi.  That said, I have never heard of a load range F tire in that size actually being available, but you never know.  I have seen G's and H's.

It's always been my theory that buses got the 12R-22.5 size for supply reasons - commonality between different buses of different sizes, and so they could be run at lower inflation pressures and give a better ride to the passengers.  With around 18,000 lbs on the rear axle of my 5C I run them at 75 psi, I have Firestone FS560 Plus 12R-22.5 load range H.  FWIW, the 275/80-22.5 size needs 90 psi at the same load level since it's a smaller tire.

Brian

[luvrbus]

 Like Dave I never ran across a recap the tire company didn't want you to run almost max pressure me I follow the manufactures of the RV tire chart for new tires  I just figure they did the home work for me on what was best for their vehicle  JMO

[Tony LEE]

I run pressures according to the tables for the actual load on each axle. Tag axle pressure usually ends up way below the limit of the tables so I might go up a bit on those.. Using the correct pressures means the tyres become a part of the suspension and especially on washboard roads or highways with pavement joints, results in a better ride. Improved handling too in most situations.

BTW the rating for 4 duals isn't 4 x the single tyre rating, it is 4 x the dual rating.

Another slight twist - which Michelin address with their RV tyre tables - is that because RVs are often way out of balance sideways, each side should be weighed separately and the heaviest side used for the calculations. Of course that also isn't logical because it results in different footprints and rolling radii on each side, but I guess it does err on the side of tyre safety and anyway there is a limit as to how much messing around normal drivers are going to be bothered with.

Worst thing you can do it take any notice of the staff at the tyre shop because they are taught there is only one pressure for 22.5" tyres - 100psi allround. Easy to remember.

If you are running mostly on rural two-lane roads with a bit of camber, then I guess the inside of the inside duals are taking slightly more load than the rest of the tyre so might wear a bit faster.

[luvrbus]

I just know MCI always used a G rated tire with higher air pressure they left the factory with G rated tires and the pressure was more than most posted here there has to be a reason I believe 

[Jon]

I believe seated bus tire pressures are based on the gross axle weights because there is no way anyone is going to adjust tire pressures based on the number of souls on board.

Motorhome conversions can be based on actual weights.

[luvrbus]

Jon,I believe they base it GVW regardless I know Prevost the tire inflation is the same on the seated coach as the VIP shells in the manuals, not that you Prevost guys have any tires you could run with 70 lbs of air   

It's well documented in the trucking industry a tire inflated to 100# plus will live longer than one at 85#  as you know that is a 50/50 deal 98% of the time they are loaded or unloaded 

My buddy at Arrow runs his seated ,day or corporate  coaches with 110 in the front 100 on the drivers and 90 on the tags regardless of what brand of bus he never has tire problems either 

[TomC]

To me-those tires look like construction tires. What make and model are those tires and are they rated for 75mph? Good Luck, TomC

[rgrauto]

I owned a Ford f-350 wrecker/tow truck and at that time I ran mostly two lane,rural paved roads and the rear tires,all four, had more wear on the inside of the  rear tires because of the roads were crowned(higher in the center than the shoulder) and later when I ran more interstate that problem went away.  Just a thought.

[Jon]

Jon,I believe they base it GVW regardless I know Prevost the tire inflation is the same on the seated coach as the VIP shells in the manuals, not that you Prevost guys have any tires you could run with 70 lbs of air   

It's well documented in the trucking industry a tire inflated to 100# plus will live longer than one at 85#  as you know that is a 50/50 deal 98% of the time they are loaded or unloaded 

My buddy at Arrow runs his seated ,day or corporate  coaches with 110 in the front 100 on the drivers and 90 on the tags regardless of what brand of bus he never has tire problems either 

Cliffird,

Prevost is no longer advising conversion owners to fill to pressures they list, but are instead providing a calculator on their web site for conversion owners to use that provides the pressures suggested by Michelin based on actual weights.

That makes sense because as you know some converters on the same shell would have axle weights as much as 3000 pounds different than another converter.

[luvrbus]

I can believe that Jon they (Prevost) has battle the front end weight for years trying to keep up with the weight they are probably around 20,000# on the front axles now

[lostagain]

The '95 D3 had to be inflated to 105 on the front, 85 drives, and 75 tags, per the manual and the placard in the wheel well. Not 100 psi or more like the tire shop would've liked!

JC