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Old 10-11-2015, 11:55 AM   #61
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Location: Akron, Ohio
Posts: 950
It is the responsibility of the vehicle manufacturer to select tires appropriate for the application and to ensure that the load capability of the tire is sufficient to meet the stated GAWR.

Now sometimes an RV company may even lower the states GAWR to avoid having to select larger (more expensive) tires. This has been seen when 6,000# axles were de-rated to 5,500# so the two tires only needed to be capable of 2750#. Obviously this does not address the fact that RV companies are aware of that many users often exceed the published GAWR.
Your calculations of load shift and side wind forces are also something a competent engineer working on vehicle design would / should IMO take into consideration.

I agree that it would be good if there were some stated margin such as 15% load capacity. While this would not eliminate tire overloading it would significantly lower the probability and number of overloaded tires but again lobby efforts from the RV industry would IMO work against the adoption of such requirements.

I write a blog on RV tire application and safety.
Also give seminars on tires at RV events across the US. 40 years experience as tire design & quality engineer for major tire mfg. Freelander 23QB on Chevy chassis is my RV
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Old 10-12-2015, 04:08 PM   #62
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Join Date: Nov 2014
Posts: 147
I just discovered that I've been using old information to calculate the overload of my tires on curved roads. I used 10 degrees on a Ball Bank Indicator since this was mentioned in articles that I found and since some Ball Bank Indicators change from black to red at 10degrees as an aid to civil engineers.

It turns out that the recommendations have been changed from a fixed 10 degrees to a speed based table and the allowed angle has increased to permit higher speeds:
20mph 16degrees
25-30mph 14degrees
35mph 12degrees

By using 10degrees, I've been underestimating the overloading of my tires.
Where I thought I could expect 350lbs of increased load on curves, I now calculate:
35mph 421lbs per tire
25-30mph 494lbs per tire
20mph 569lbs per tire

(When I say '35mph', I'm referring to the reduced advisory speed limit on a yellow sign placed before a curve.)

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Old 10-12-2015, 07:01 PM   #63
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Posts: 162
Just got back from a 2500 mile three week trip and had no troubles with my Constancy tires. I want to replace them with something more reliable but so far there's no clear cut upgrade. I have plenty of clearance in the wheel wells but my axles are too close together to increase size and that may have some issues anyway. Our next big trip is in January when we head to Florida. I hope that our cooler weather travels will help these tires survive.
2015 Flagstaff Super V 26VFKSS Emerald
2013 RAM 2500 CC 4X4 6.7 CTD
Sold... 2013 Shadow Cruiser 260BH
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Old 10-12-2015, 07:13 PM   #64
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Shock loads are probably more of a component as they could be as high as 25% or higher just due to swales and bumps in the highways.

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