PDA

View Full Version : 24.5" front tires


busnut
03-25-2006, 02:46 PM
For those of us with overloaded front axles :cry: it appears we now have a solution for the tires at least. Both Bridgestone and Michelin have 305/75R24.5 LRJ which will carry 8270 pounds single and 7160 dual. In Michelins case the Revs per mile are 486 vs. 478 for the 11R24.5 LRH

fulltiming
03-25-2006, 07:27 PM
Do you know if steer axle fender clearance would be an issue since the 305/75 is about an inch wider than the 11R?

The 305/75 certainly give extra capacity over the 11R24.5 H rated tires. As you point out, that would at least take one of the limiting factors out of the equation. I would still be weight limited by the Alcoa wheels which are rated at 7200 pounds each and a max cold pressure of 120 psi. My Bridgestone 11R24.5 H rated R280 has a 120 psi load carrying of 7160 pounds while the Bridgestone 307/75R24.5 at 120 psi will carry 7540 (7830 at 125 psi but that would exceed the wheel pressure rating http://www.trucktires.com/us_eng/technical/loadinfl/table05.asp).

If the fender clearance isn't an issue, I would think that they would give you an extra margin of safety on the steer axle.

The front axle on my coach has a GAWR of 13,200 lbs so something other than the wheels must be considered by Newell as the limiting factor. I find it interesting that the G rated tires (6610 pounds max) would have limited them to the 13,200 pounds. However, a post from Newell Tech support http://www.newellcoach.com:591/bboard/FMPro?-db=bboard.fp3&-format=msg.htm&-lay=form%20view&-sortfield=Date%20Created&-sortorder=descend&-sortfield=Time%20Created&-sortorder=descend&App=1&-max=20&-recid=34612&-find= indicates that they used H rated tires at that time. I wish I knew what was the limiting factor on the steer axle as mine is overloaded when my fuel tanks are more than 1/2 full even though I still have lot's of capacity on the rear of the coach.

karlb
03-27-2006, 11:24 AM
Certainly, we have had years of experience at the factory observing the performance of a variety of tire brands and sizes on Newells. The bottom line: don't put reliance solely on the rated capacity when selecting new tires.

From the mid-70s through 1985, Newell installed 11R22.5 Michelin steel belted radial tires with excellent results. With the upgrade to the 8V92 engine in 1985, we began fitting 11R24.5 radials, load range H, most of which were Goodyears (owing to the influence of our customer Roger Penske and his experience with Goodyears on the race track as well as with Hertz Penske truck rental). Once again, the results were excellent. We later switched to Bridgestones to get more even tread wear, but both brands performed very well.

In the early 1990s, we realized we were seeing some fully loaded front axle weights that were bumping up around the rated capacity of the tires, expecially with fully timers who carried an entire house worth of gear. However, with the exception of some failures that appeared linked to underinflation and very high speed cruising, these tires gave good service and were very reliable. The actual capacity appeared to be significantly higher than the rated capacity assigned by the tire manufacturer. Ditto for the wheels.

In 1997 we introduced our first slide-outs and front axle weight took an upward bump. We took another look at the tire situation and saw that we could increase the rated front axle capacity if we changed to 315 load range L "low profile" tires, initially on the steer axle only. We made the change, upgrading our "rated capacity." But in spite of the increased capacity on paper, we immediately began experiencing a pattern of steer axle tire failure. We experienced problems with both Bridgestone and Goodyear tires in the 315 size. We went through several successive tire models with Goodyear, each promised to solve the problem, but without relief until finally changing new production to Michelin with good results. In fact, we were so concerned about the failures we were seeing with Bridgestone and Goodyear that we did a NHTSA reported recall and replaced all the Bridgestone and Goodyear 315s (regardless of mileage) with new Michelins.

Since changing to the 315 Michelins, front tire failures declined and the few we have seen appear to be related to the following factors, often in combination:

1) Underinflation. The 315 should be inflated to a minimum of 130 psi, and we recommend 140 psi for summer high speed crusing.
2) Speed. The Michelin 315 tire model installed should be rated at 75 mph (some models are rated at 55 mph maximum!), and the speed restriction should be observed.
3) Road hazard damage. We recently saw a tire failure caused by a cut on the tread that allowed moisture to rust the steel belt over a few months until the tread separated at highway speed.
4) Age. Tires deteriorate from a variety of age related causes, including UV rays and undetected road hazard damage. We recommend that steer axle tires be replaced at three years. Cheap insurance.

Based on our experience, coaches running 11R24.5 load range H front tires need not be "upgraded" to 305 tires to simply get more rated capacity. However, for both coaches running 11R24.5 tires and later model coaches running 315 low profile tires, we recommend that the front tires be replaced every three years regardless of miles, be kept properly inflated, and excessive speeds be avoided. The tires should be inspected reguarly for damage. For the 315 tires, we recommend Michelins with a speed rating of 75 mph.