Converting to larger tires on front axle

[nrhareiner]

I plan to convert the front axle to the 365 sized tires. I kow that the wheels, hubs etc need to be changed. I am planning on doing this due to the weight issue in my 01 xlII s2 coach. The question is will I loose turning ability? One of the people who have done this in the past states you will loose 7 degrees of wheel arc, is this true?

Kim Sloan
02 Vantare XLII S2
06 dodge megacab

[Jon Wehrenberg]

Kim,

Without access to the Prevost factory drawings I don't know if that can be answered. The real answer will be available direct from Prevost engineering.

Since I am a bit of a cynic, I would suggest that when you pursue this you also try to determine the other limiting items. At one time when a couple of converters were overloading the front axles one of the owners of Prevost, Bill Campbell, gave a pretty impassioned talk at one of the seminars advising owners that it takes more than tires to deal with that kind of problem.

He went on to explain how almost everything in the coach has limits, and in the case of the steer axle it could be bearings, wheels, brakes, etc. Exceeding those limits stresses a lot of the components beyond their design limits, and fixing one of the components such as tires does not address the problem.

Aside from limiting the turning radius it might be worthwhile to see if engineering has any concerns about up and down limitiations such that the tires will damage the "fenders" when turned or if the tires will hit the foam insulation in the wheel wells or a critical component such as a brake chamber.

Good luck.

[merle&louise]

Kim,

How many pounds are you overweight on the front axle?

I ask this because I have heard that the GVWR of the axles have a built in margin of error of about 10%. Prevost Car Co. may be able to confirm this.

Its worth asking before you change the tires, wheels, etc.

[nrhareiner]

The problem is that I am around 18K on the front. The tires have to be at 130lbs to cover the wqeight. That is the max for the tire. However ,the wheels are rated for only 120lbs! I use Smartire. When running in heat, the tires are getting too hot for my comfort, even at 65 MPH.

Kim Sloan
02 Vantare XLII S2

[Coloradobus]

Wheel turning radius I understand is not the issue. For those shells that are retr0fitted with the 365 tires, trying to turn the wheels while you are stationary IS the issue. The new shells have a Slave Cylinder added to the drag-link, I think that's where it's added, to help with static turning. We have a friend who has done it to his 2001 Marathon "H" no slide and is absolutely thrilled with the results. He needs only to run 110 psi now instead of 130. Make sure a good alignment is done, so you track down the road. Our friend had a problem with wandering after the retro, and it turned out the drive axle was off a bit.

[Jon Wehrenberg]

I would be a little careful trying to compare the results of the H3 with the XL. On the other site someone mentioned that there might be air bag interference.

Kim,

If someone at POG III has 365 tires and is willing, I have the tools necessary to change your wheels with his so you can check clearances. The problem is all clearances have to be checked in the full range of travel, up down and turns left and right.

[Coloradobus]

Jon,

Several years ago, when we still have Coach 740, 2002 Marathon XLII, Nathan Parker, then Svc Mgr, Mira Loma told me we could change out the coach's 315's for 365's.
But you're right! There is more to the new coaches than just the big tires. There is the additional Slave Cylinder to the Drag Link, and larger airbags, etc. However, that being said, putting the 365's on just by themsleves does make a difference. It just depends if you want to spend the Lew Bucks. We were quoted $8,800.00 back in 2005, for tires, wheels, sealed greased hubs and assorted parts and labour. At least, at that money, it would be cheaper than buying a new bus. But, we ended buying another coach instead. Our "H" drives and rides better than our XLII one slide. The XLII road stiff, but remember the shell is stiffer because of the slide room. So, the lower psi in the 365's would possibly have made the XLII ride softer and smoother. :) We will never know, now./

[Jon Wehrenberg]

Kim,

Thinking out loud here...Do you have any way to transfer weight. For example, if you can move batteries or something else heavy rearward that transfers the weight to the drive and tag and removes it from the steer axle. This is off the deep end, but another way to do that is to decrease the tag axle air bag size. By having less tag axle weight there is a drive axle weight increase along with a slight decrease in front axle weight. I don't know if your drive axle can handle more weight however.

[JIM CHALOUPKA]

That's gona be: ONE BIG TIRE. 14.33" wide!!!!!!!!!!!!!!!1
:p JIM

[merle&louise]

Kim,

Along the lines of Jon's suggestion of relocating the batteries, would carrying less fresh water and less diesel be viable? Depending on where the water tank and diesel fuel tank are located you could save the weight of 80 gallons of water (680#) + 100 gallons of diesel (740#) = 1420# without spending any money!

Just a thought!:D

[nrhareiner]

The problem with transferring weight is the toal weight of the coach is heavy. This was one of the earlier prevost double slides done by Vantare. To say the least it is heavy. total weight with 40% water and full fuel is over 52K! Therefore by transferring weight I will have other problems.

Kim

[JIM KELLER]

Kim Sloan, How did that much weight get on the front axel ? Was it a dependable scale ? Is the Bus remodeled inside with heavy tile or granite ?

[Jon Wehrenberg]

Apart from what may be a very expensive conversion from the 315 to 365 tires I'm not sure there is much that can be done.

That sounds like doom and gloom, but at the weights Kim states the 315 tires are acceptable. According to the Michelin charts the tire is good for 9090 at 130 PSI and speeds to 75.

It is at the limit, but unless the axle weight is greater than 18180 or the weight is biased towards one side or the other it should be perfectly acceptable to run those tires. If it were me I would not start rolling without checking pressures, and when the date code said 5 years those tires would get pulled off, but apart from that I think Kim is OK.

Knowing the front axle loads I would also be very careful about checking my hub oil levels and brake pad thickness. The bearings and brakes are going to get a workout. As a final precaution I would also be running my hands across the tires often to check for the first signs of misalignment or poor balance. Kim made a comment about the heat of his tires, and if the coach has too much toe in for example those tires are going to get real hot real fast.

[nrhareiner]

Jon thank you for all of the help. The alignment is good (checked and corrected by JoSam in Orlando. As stated before I run with Smartire which does inform we of the temps. My concern is not the ability to take the weight by the tires. Michelim does report that the tires wil take the weight at 130lbs (which is the pressure I run). My concern is that the wheels are only good for 120lbs. I know they say there is 10% fudge factor, but I hate being in that area. However, I think I am going to wait until after POG III.

Kim
02 Vantare XLII S2
06 Dodge Megacab