Quote:
Originally Posted by THERAPY GUY
Thanks everyone I have been reading your posts with great interest. I did fail to state that my tires are new TOYOs 305/70R/225. The side wall does show an inflation to 125psi and the Max load of7390# for the tire at 120 psi. That would tell me the max axle load is 14,780 #s at 120psi cold. ....
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Tires will NEVER tell you the axle GAWR. You have a sticker probably just behind your driver seat that tells you that. Tires can be a limiting factor in use of available GAWR. If the tires are of lower load rating values than optimal, they can actually cause you to not be able to use the full GAWR even under best case loading.
Keep in mind that you have two axle weight issues. There is the manufacturer's rated axle weight expressed as total weight. As an example, my DSDP front GAWR is 14,600. No matter what, I should never exceed that weight on the front axle. No matter how much your tires can carry, you should not exceed GAWR.
The other issue is a combination of tire load rating and coach weight balance. It is nearly impossible to have exactly the same weight on both the left and right sides of an axle. It is possible to max out a tire's weight but not the GAWR. That is why you need 4 corner (6 corner for a tag axle) weights. As an example, my tires max weight carrying capacity at 120 PSI is 7830#. If one tire is at 7500#, I can only put 7100# on the other.
BTW, that weight sticker behind your driver's seat lists tire inflation values based on the companies estimated "worse case". My sticker actually says my GAWR is 14,200 thought the axle itself is rated at 14,600 by Spartan. Why is that? It is because Newmar chose to use 305/70s all the way around the coach instead of 315s up front. Also keep in mind that the same chassis is used for several configurations with different slide and floor plans that shift the weight all over the place. Finally there are the options that are later added from standard floor plans. What that gives Newmar is a legal basis to say that if you load the rig to the max axle and tire ratings then inflate to the tire pressures listed on that sticker, your tires will be inflated sufficiently to support those loads.
I have weighed mine multiple times and after any major upgrade or weight shifting in the basement. I have found my unit is well balanced L to R and thus I can run @ 14,600 at 112 PSI (I use 115) and not exceed weight on either of the front tires. I'm not particularly fond of running tires at or near the max PSI because of ride quality so I am looking into upgrading to 315s if feasible but otherwise, I still know I am running at safe tire pressures for the Spartan weight rating.
One other important factor in my decision to run @ 14,600 with full fuel, propane, water, and even as much as 1/4 black and grey tank levels is this... Assuming I am absolutely maxed out at 14,600, I loose nearly 8# of front axle weight per 7 miles of driving due to fuel burn. Unlike the rear wheels where the weight is reasonably static even after fuel burn, the front axle on a DP will get lighter as you drive.
YMMV!