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54 minutes ago, bm02tj said:

My Motor home is a 1816MG Renegade  by Kibbe  on a FL80 Freightliner chassis with lots of room  

Does it have wooden spokes and axles? :P

Herman

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Ahhh!  I remember that now! Sorry. :)  I think you outweigh the OP coach, by a bunch...like mine at 30 tons rolling! :lol:

Herman.  Not exactly wooden, but two axles = 10 tires!  Yes, they cost a bit more than yours and mine combined...:o His Jeep Wrangler is in the rear of coach and is tricked out like mine!  Hope he does not have short legs...:wub:

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3 hours ago, hermanmullins said:

Does it have wooden spokes and axles? :P

Herman

No mine was made the year after the stopped using wooden spokes

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2 hours ago, manholt said:

Ahhh!  I remember that now! Sorry. :)  I think you outweigh the OP coach, by a bunch...like mine at 30 tons rolling! :lol:

Herman.  Not exactly wooden, but two axles = 10 tires!  Yes, they cost a bit more than yours and mine combined...:o His Jeep Wrangler is in the rear of coach and is tricked out like mine!  Hope he does not have short legs...:wub:

I was too close to the tire rating so I when with the 275/70R22.5 with more capacity on the front now I am changing all the tires to same size as I have room and the rims are wide enough 

Bruce 

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On ‎8‎/‎6‎/‎2018 at 5:25 AM, manholt said:

bmctx.  Welcome to the Forum! :)

When was the last time you had your coach weight, with every thing in it, for a normal trip?  How long have you owned this coach & what is the DOT # on all your tires, are they the same numbers?

bm02tj..  What year, make & model coach do you have?

Apologies for just returning to this.  We had to take the motor home out on a quick trip this past week.  I weighted it down (all tanks full - LP, diesel, fresh, grey, black) and some typical cargo.  I could not find a handy four-point scale (one trucker tried to tell me they do not exist).  The CAT shows the front axle at 8940 and the rear axle at 17160.  If I factor another 10% on each axle as has been suggested, here are the figures I get:  Front 8940*1.1/2=4917 and Rear 17160*1.1/4=4719. 

The difference from max for the XRV 255/80R22.5 is 288 pounds on each front and 86 on each rear.  This assumes I am going to put another 2,610 pounds on the coach which I cannot imagine.

Bottom line is 1) I now see why you guys are always asking about the actual weight and 2) I feel much better about the XRV stats.  At my actual weight + 10%, the Michelin site shows 100 PSI single and about 105 dual.

In answer to Manholt's questions:  1) those are the weights, 2) owned for a little over a year, and 3) the tires are all at eleven years if memory servers (forgot to get the actual codes) with minimal but noticeable weather checking especially on the front.

Here is a follow-up question related to the XRV load table.  If I took my actual loaded weights and applied the table, I would get 1) 4470 per tire on the front which is close to 85 PSI on the table and 2) 8580 per dual on the rear which would probably need to be rounded to 95 PSI on the table.  These are well below the Winnebago sticker of 105 each.  What should I go by - actual weight on the Michelin table or the 105 PSI on the plate from Winnebago? 

Either way, it looks like the XRVs still fit my need.  Since I am concerned about ride quality as well as safety reputation, I think XRV is in my future unless someone tells me I need to rethink.

Thanks for the opinions.

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I always suggest the inflation be increased by at least 10% above the minimum needed to support the actual or calculated load. (Calculated load is almost never 50% of the truck scale axle readings)  While some RVs have been found with 1,000# side to side un-balance I am suggesting you calculate one end of each axle to have 53% of the total on the axle. So your front 8940 x .53 = 4,739   and 9095# for the rear heavy end  ( yes I always round up)

Michelin table shows 95 psi for the single load of 4,805#  and 100psi for a 9,050# load but that is lower than your calculated 9095 so we go up 9370# 105 Psi

I then add 10% to the above inflation and get 110 and 115.  Obviously, two different approaches and yes I am probably more conservative (asking for more inflation) but I am coming just from the increased margin on the tire loading side of the topic.

I think you can see what happens if we don't know the actual loads. We do need to be on the conservative side with our estimates. Some suggest using s 55% figure rather than a 53%

My +10% on the inflation found in the tables works well when we know the actual load on the tires.

Hope this helps and isn't confusing.

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tireman9,

Thank you for the additional details!  I get your math, and I definitely want to make sure I am not underinflating.  Of course, overinflating has other concerns such as stopping distance or handling/ride issues perhaps.

I will be looking for a four point scale.  Any ideas on finding one in the Dallas-Fort Worth area.  The truck driver at Love's (where the CAT scale was) sort of snickered at me when I suggested that they do exist and this is the proper method to weigh a motor home (I guess he was thinking unicorns and stupid non-pro).

Would you be concerned that the XRV chart for 255/80R22.5 says max at 110 vs. the 115 that one would calc for the rear by adding the extra 10% (after the 0.53 multiplier)?

It seems that multiplying the rear 17140 by 0.53 (9050) is adding nearly 5.5% to each "theoretical" weight/side (17140/2=8580*1.056=9050) ... assumption seems that one side may be carrying an extra 470 lbs.  I can see how that could be (thus need four point weight) given tank locations no matter how I try to balance the onboard weight.

Since I am a math guy, I threw the XRV chart into a spreadsheet and had it calc the % difference between PSI jumps and corresponding single and dual jumps.  It is strange that the PSI jumps are between 7.1 and 4.8 % where as the corresponding lbs jumps do not coincide and are widely inconsistent (not sure I can paste it but will try).  For instance, between 80 & 85, PSI goes down by 0.4%, Single goes down by 2.4%, Dual goes up by 0.5%.  There must be some complex calculus involved in developing this chart.

Michelin XRV 255/80R22.5 Load & Pressure Chart 8-19-2019
https://www.michelinrvtires.com/tires/selector/#!/info/xrv
PSI PSI %dif SINGLE LBS Single %dif DUAL LBS Dual %dif
70 0.0% 3875 0.0% 7050 0.0%
75 7.1% 4070 5.0% 7410 5.1%
80 6.7% 4300 5.7% 7720 4.2%
85 6.3% 4440 3.3% 8080 4.7%
90 5.9% 4620 4.1% 8410 4.1%
95 5.6% 4805 4.0% 8820 4.9%
100 5.3% 4975 3.5% 9050 2.6%
105 5.0% 5150 3.5% 9370 3.5%
110 4.8% 5205 1.1% 9610 2.6%

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Well tell the snickering trucker to come to Alabama, all DOT cars "they look like and are State Trooper Cars", are equipped with portable scales, one scale is placed under each tire or set of duals, these feed into a laptop inside the car. The laptop shows each tire individually, then combines the weight per axel, and includes a total weight readout. Yes, I have had them weigh me upon request, with which I was provided a printout of the results.

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Weighing video and info HERE

Locations with scales HERE

I have seen some say they called their state police and asked where their compliance officer was and explained they wanted to have their RV checked.

Grain & gravel and some building contractors have small platform scales and will let you get 4 corner weights for a low fee.  You still need to do the math though.

Calculation worksheet HERE

 

 

 

 

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