Home » Public Forums » GMCnet » [GMCnet] Overloading Tires
| Re: [GMCnet] Overloading Tires [message #326065 is a reply to message #326062] |
Thu, 16 November 2017 09:22   |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma:
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Senior Member |
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G'day,
Below you will find the email I send in every time this subject comes up.
OPERATING A GMC ON LESS THAN FOUR REAR WHEELS/TIRES
REFERENCE: GMC Motorhome Operating Manual X-7821A Page 1 - IMPORTANT INFORMATION ON VEHICLE LOADING.
http://www.bdub.net/manuals/X7821A.zip
GVWR (Gross Vehicle Weight Rating) represents the maximum permissible loaded weight of the vehicle.
26 foot GMC GVWR = 12,500 lbs
GAWR (Gross Axle Weight Rating) the maximum weight that the axle can carry.
26 foot GMC GAWR
GAWR = 4,500 lbs Front Wheels
GAWR = 8,000 lbs Rear Wheels
REFERENCE: Tire Load Range: http://gmcmotorhome.info/tires.html
Tire Load Range: The max load a tire can carry and the pressure required to carry that load.
D load range max load @ 65 PSI = 2,235 pounds
E load range tire max load @ 80 psi = 2,680 pounds
REFERENCE: Alcoa Light Truck, SUV, RV and Motorhome Wheels Fitment Guide
http://www.southwestwheel.com/pictures5/LTFitment-Screen_10-18-01.pdf
P/N: 160231
Style: Classic
Max Wheel Load Pounds: 2780
Capacity ratings as dual or single in highway service - bias-ply or radial
P/N: 160251
Style: LTS 5
Max Wheel Load Pounds: 2440
Capacity ratings as dual or single in highway service - bias-ply or radial
P/N: 161251
Style: Hot Shot
Max Wheel Load Pounds: 2780
Capacity ratings as dual or single in highway service - bias-ply or radial
COMMENTS:
The weight distribution per tire would be dependant on the how much pressure was supplied to the air bag supporting the remaining
tire. For ease of calculations we'll divide the rear GAWR of 8,000 lbs as noted above by four which results in a load per tire of
2,000 lbs. Operating the GMC with one wheel removed the load on the remaining tire would double; going from 2,000 to 4,000 lbs. This
is an overload of 1,765 pounds (~79%) on a D range tire at the maximum pressure of 65 psi and an overload of 1320 pounds (~49%) on
an E load range tire at the maximum pressure of 80 psi. If the tires are not inflated to the pressures noted in the previous
sentence the overload would be even higher.
CONCLUSION:
If you drive your GMC with less than four rear tires supporting the load you WILL be operating the GMC with OVERLOADED TIRE(S) and
OVERLOADED WHEELS!
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Richard Denney
Sent: Thursday, November 16, 2017 8:56 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Overloading Tires
Of course, the loading is determined by the load rating based on inflation.
The nominal load rating is based on full inflation (80 psi for Load Range
E, as we usually use).
Looking at Goodyear's chart, the maximum load for a light truck tire at 80
psi is 2680 pounds (65 mph top speed). Last I weighed my coach, it was 5725
pounds on the rear. Half of that is 2862, which overloads a fully inflated
E-range tire by 7%. So, if I was facing that eventuality, and had the
capability to lift a dead tire, I would first put the dead tire on the
middle axle (to move the pivot point back and increase the load on the
front tire), and then inflate the good tire to 80 psi. Then, I would go
slow for the minimum possible time (Goodyear recommends no faster than 55
for a 9% overload). Since I don't have those capabilities, I won't worry
about it. :)
I usually run 50 psi in the rear. According to the chart, the maximum rear
tire weight of 1500 pounds for my early, lightweight coach needs 40 psi,
and I add 10 psi for higher speeds, per their chart. At that pressure, the
65mph-limited load is 1765. 2862 is a 65% overload, for which Goodyear
recommends a 10 psi increase in pressure and a 14 mph speed limit. But
because the tire is well below it's rated pressure, I can increase it to 80
psi and have only a 7% overload.
If my rear weight was 2000 pounds per tire (8000 pounds total on the rear),
Goodyear wants me to run 55 psi in the rear, plus the 10 psi for high
speeds. 4000 pounds on one tire (with the other lifted) would be a 50%
overload of an E-range tire at 80 psi. Goodyear suggests I can carry that
load if I inflate the tire above its maximum rated inflation by 10 psi and
limit my speed to 14 mph.
Here's the Goodyear chart, which includes advice for overloads:
https://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf
Rick "You brought your second purse? Well, dammit, I have to recalculate
all my inflation pressures!" Denney
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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