Tire Pressure (again}

[DoubleEagle]

There have been systems that calculate the weight of an axle based on air pressure for decades, but they do not indicate the weight at each individual wheel. The only way to achieve that simultaneously is the use of piezoelectric sensors at each wheel, just like Cliff mentioned being used by coach conversion outfits. Most truck scales weigh a pair of wheels on an axle position at a time, and some have rails on the side so that you cannot weigh one side at a time. Regardless of the airbag or torsilastic system in use (or combo), the weight on an individual tire can vary. It seems very prudent to know how much weight is on each tire position for the sake of tire load safety, and evenly applied braking traction. A lightly loaded tag or bogie is going to lock up and slide before the other positions, and an uneven load on the front wheels (and/or uneven tire pressure) might cause pulling to one side in hard braking.

[dtcerrato]

"and an uneven load on the front wheels (and/or uneven tire pressure) might cause pulling to one side in hard braking." I was going to make mention of that yesterday but was already long winded but the "tripod" automatic height control valve set up did away with an uneven load on the front wheels because there isn't one from the lower air spring supports upward. Of coarse like Clifford said stationary weight on the front axle like power units, steering boxes being off centered ie: would differentiate tire load but only from an imbalance of axle mounted equipment and not body load. (all four front air springs constantly maintain equal PSI. 

[luvrbus]

If you read the post people like me are taking Tom as saying the load is going to be same on each side at the wheels he made no mention of the body or I missed it

[Dave5Cs]

If you are on a 6% slanted road I guarantee you the body and the axle will not be parallel. The passengers will be over on the other side of the aisle. It is a series of loading and unloading the airbages to keep the body as close to level as they can. The rear are side to side and the front up and down as a tri pod.

[lvmci]

Hi All, my tag Toyo's are at 10 years, was going to get Toyo's for the front see if a higher quality tire will ride smoother, but 315s and 12Rs are rated for 65mph, so bit the bullet for Hankook with a 75mph L rating, the Double Coins M rated, are now drives and tags and they never really balanced well. I hope with high speed balance on the Hankooks, will ride smooth all the way to 75mph, lvmci...

[richard5933]

I've found quite a few 12R and 315s rated to 75, including Toyo.

[lvmci]

Well Richard, there were 5, 315-80 Toyos, 3 rated at 70 and 75 mph, much more expensive, but rated for off pavement and long distance, according to their flyer at Southern Tire, they suggested the Hankook L rated 75mph, so I went for it...

[richard5933]

The Hankook is a good tire from what I've read. Since there are a lot of commercial coaches running the 315s, I'm sure there are even more out there than I've seen with the 75 mph rating. You are correct though, they aren't cheap. To replace my Firestone FS400 would require a small mortgage. I'm probably going to go with the FS561 in 12R22.5 in the spring - they are only H rated, but that should be more than enough tire, even with the bus weighing in at 30,000 lbs.


Which Hankook did you go with? I see that their 12R22.5 is only H rated (16 ply), so I'm assuming you went with 315s if you have the L rated.
Both of these show a 9" rim on their charts though, so I'd have a problem since I still have the 8.25" rims.

[TomC]

Cliff-your analogy of the board between to blocks is noble. BUT-blocks are solid whereas air suspension has air lines connecting the two sides to each other. So the two sides are constantly balancing each other out. When you stop and weigh, you'll find that no matter how the bus is sitting, both sides are going to be always equal (with one leveling valve). This is why those bus nuts that have taken off their automatic leveling valves and replaced them with 4 manual valves run the risk of tweaking the body-of which GMC engineers were trying to avoid this with the tri-pod suspension system. My recommendation always to those that have manual leveling valves is to only have one valve for the front axle to maintain what GMC engineers designed into the original buses. Good Luck, TomC

[TomC]

Richard-I just went on the Hankook tire site and it is very incomplete. I have AH37 11R-24.5 on my bus. While they ride just a bit harder then the Michelin XZE2's I took off, $1,500 cheaper for 6 says that I can put up with the harder ride-which now I really don't even notice.
I am normally a Michelin user. But from my days of being a Freightliner new truck engineer and salesman, Freightliner's standard tire is Hankook-unless you order differently. I figure if it is good enough for the biggest truck manufacturer in the US, then they should be good. Just stay away from no brand name Chinese tires! Good Luck, TomC

[dtcerrato]

Tom I totally agree with you, we are on the same wave length pertaining to tripod suspension. It is accurate as Cliff stated that side by side front weight can be different if component placement (steering boxes, power cylinders, etc.) on the front axle are off center & "underneath" the lower air spring supports.

[richard5933]

Richard-I just went on the Hankook tire site and it is very incomplete. I have AH37 11R-24.5 on my bus...

I noticed that too, and had to download their spec book to get more details. The book shows the AH37 11R22.5 on 8.25" rims, and shows 12R22.5 on 9" rims. They don't show any other allowable rim widths.

Firestone lists 9" rims for the tires I am looking at (FS561) but in the back of the book where there is more information about rim widths they include 8.25 as well, just not in bold print (bold print must be their recommended width). For the FS400 tires in 315/80R22.5 they list 9" in the back, with a footnote about using on 8.25" with a slightly reduced weight limit.
I would add the Hankook tires to my list of tires to consider if I knew for certain that they are approved for the 8.25" rims in the 12R22.5 size.

[chessie4905]

With those size tires 3/4" rim difference isn't a cause for concern, unless you are running near maximum rated tire weight.

[luvrbus]

With those size tires 3/4" rim difference isn't a cause for concern, unless you are running near maximum rated tire weight.

The 315's balloon out on the bottom on a 8.25 wheel on the 9 inch the side walls are more vertical and do carry more weight you really need to be careful running 2-315's together on 8.25 wide rims with low air pressure for the smooth ride they will rub the sidewalls out   

[sledhead]

this will save you some money

https://us.amazon.com/dp/B07S2MYFQL/ref=psdc_353633011_t2_B00VO345BM

dave