Tire Inflation Dilemma

First thing is to get on the scales so you know if you need new wheels with higher rim specs or not. 65lbs may or may not take your weight at the tires. 8,600 lbs for four 2,150s (but that assumes equal weight sharing---does not happen that way--some tires take more than their share and others less--as seen on the scales if you get the chance to check for that)

If the door says RGAWR is 8,000 and you are at 8,600 and your tires are at 65, you are there for tires, but perhaps not for springs. It is all fingers crossed because we do not know how much "margin" we have so we can say how much "over" is still ok.

Then all the forum guys start in as to how much "over" is ok as far as they are concerned, which does not help you at all. :)

My solution for being a "little over" :( is to take it easy driving, but ignorance is not bliss--know your weight, don't guess. Then you can figure out what to do or not to do.

maillemaker wrote:

I would trust the printing on the sidewall of the tire first.

This could be dangerous. As I said in my example, my rims that came with my RV are only rated for 65 PSI max. My tires can be inflated far beyond that and must be to achieve the full E rating. So I run at 60 PSI and am not getting the full rating.

Load rating D tires could have a load rating of 1,220 pounds at 65 PSI, Load rating E tires could have a load rating of 1,520 at 80 PSI.

I'm running Firestone Transforce HT LT215/85R16 tires that are load rated E at maximum PSI (80 PSI). But my rims are only good for 65. So the tires are de-rated when run at a lower PSI. AT 80 PSI, my tire has a load rating of 2,680 pounds.

Sadly it is hard to get the derating information from the manufacturer. So I just have to hope that at 65 PSI my E-rated tires perform at least at D rating.

Steve

Maybe you need new rims.

Thanks Drew! I argued with a Firestone chat person for about 30 minutes as they tried to convince me the load was the same for any PSI!

Steve

Colour me silly, but I want to know why it’s a Canadian chassis.

Notice all the specs, weight, air pressure, are in metric standards first, imperial second?

maillemaker wrote:

I would trust the printing on the sidewall of the tire first.

This could be dangerous. As I said in my example, my rims that came with my RV are only rated for 65 PSI max. My tires can be inflated far beyond that and must be to achieve the full E rating. So I run at 60 PSI and am not getting the full rating.

Load rating D tires could have a load rating of 1,220 pounds at 65 PSI, Load rating E tires could have a load rating of 1,520 at 80 PSI.

I'm running Firestone Transforce HT LT215/85R16 tires that are load rated E at maximum PSI (80 PSI). But my rims are only good for 65. So the tires are de-rated when run at a lower PSI. AT 80 PSI, my tire has a load rating of 2,680 pounds.

Sadly it is hard to get the derating information from the manufacturer. So I just have to hope that at 65 PSI my E-rated tires perform at least at D rating.

Steve

Here's Firestone's charts for LT tires (and some other flavors as well). LT215/85R16 tires inflated to 65 psi are rated for 2335 lbs (single) or 2150 lbs (dual) per tire. It looks as though they rate the loading at a given pressure identically for all load ranges, with the difference being that the higher load ranges can safely be inflated to a higher pressure and so carry a larger load.

The tire inflation charts vary little if any between tire makers for the same size and type of tire. For practical purposes, this chart could be applied to any LT215/85R16 tire.

I would trust the printing on the sidewall of the tire first.

This could be dangerous. As I said in my example, my rims that came with my RV are only rated for 65 PSI max. My tires can be inflated far beyond that and must be to achieve the full E rating. So I run at 60 PSI and am not getting the full rating.

Load rating D tires could have a load rating of 1,220 pounds at 65 PSI, Load rating E tires could have a load rating of 1,520 at 80 PSI.

I'm running Firestone Transforce HT LT215/85R16 tires that are load rated E at maximum PSI (80 PSI). But my rims are only good for 65. So the tires are de-rated when run at a lower PSI. AT 80 PSI, my tire has a load rating of 2,680 pounds.

Sadly it is hard to get the derating information from the manufacturer. So I just have to hope that at 65 PSI my E-rated tires perform at least at D rating.

Steve

I would trust the printing on the sidewall of the tire first.
If they are the right load range for your outfit and you pay attention to the manufacturers recommendations you will be fine.

IMO any owner of a Class C needs to get on the scales and check the back weight wrt the spec GAWR. It will be more critical with a 28 than a 22 footer, but even so, know your weight.

The incomplete truck was designed per the door specs, but the RV added on was designed by somebody else.

In my case, the RV part is overloading the truck part at the back and was built that way. It even has air bags that appear be OEM, but they don't help with the GAWR.

It may be that 65 lbs at the back vs 60 will be enough for the tires to take the actual weight, but who knows about the springs etc? At the very least, if you have been on the scales, you will know the true situation. I had to cancel all thought of towing anything or putting a generator on the back bumper. You can sometimes play with how much water to take along or not and fill up when you get there if you know they will have water there. Whatever. The thing is to know the actual situation.

My 1990 Winnebago Warrior has rims that say "65 PSI max". So my rims are only good for 65 PSI.

I have put E rated tires on them, which can take more PSI for more load, but I can only put 65 PSI in them, which de-rates their maximum load.

I use E rated tires but inflate to the manufacturer's recommended pressures which is 58 up front and 60 in the back. The tires will not achieve their maximum rated load at this pressure but it should be sufficient for what the RV was designed for.

Steve

centerline wrote:
I will disagree with a lot of others that have posted before me.

the sticker on the door is only be relevant to the OEM tires that was on the unit when it was manufactured, AND loaded within the limits of the GVWR... there are other tires that will have the same specs, but you need to know this before using the tag on the door as the gospel...

snipped some...

I asked on here about this a little while ago, and it came out that my OEM Ds--door says all to be at 58lbs-- with their rims limited to 65 lbs most likely for Ds--and actually having Es on them from some tire change whenever before my time, made the Es limited also to 65 lbs most likely for the rims, unless I got new wheels with higher lb rated rims.

My Class C is overloaded at the back, and probably always was since built. Been on the scales. No way to lighten the load at the back. So all I can do is put 65 in those Es and hope that will work out ok, being more than 58. Michelin tire guide on that is fairly close for actual weight, but I don't have Michelins, just ordinary Es.

If I want to do it right, I have to likely get four new wheels that can take more than 65 at the rims and pump up the Es to whatever the proper psi is for the actual weight. (Even that does not make sure my springs and other components are within their OEM GAWR weight specs.)

Not going to happen! Money for that needed elsewhere at higher priority. This MH has been going since 1991 ok so far somehow, so I am crossing my fingers in hopes it will keep going more or less as is.

Main point is the door spec GAWRs apply even if you change to other tires. Class Cs seem to be built overweight before you even load your camping stuff. The "incomplete truck" the RV people added an RV to (instead of say, an ambulance) did what they did, and you can't do a darn thing about it.

BTW that means the OEM brake specs are being overworked going down hill too, so just take it easy and use your gear shift a lot to help with braking.