TIRES
[GENERAL INFO] [LOAD/INFLATION] [BRANDS]
[TIRE AGE] [OPTIONS]
GENERAL INFORMATION
It all comes down to this; the tire
patch, where the rubber meets the road, is the critical function for
tire selection, inflation and construction. Chuck Botts has
written several articles to explain these interactions (
http://www.gmcws.org/Tech/TireSafety/index.html).
The simple explanation is find out the weight that is carried on each
wheel, look up the
load /
inflation rating for your tire, and set the pressure to get the
tire patch to match. Brands, tread selection, and sidewall
selection are your choices. Steel side walls are very stiff and
cause significant handling problems with the GMC. Most owners
have gone back to the nylon cord side walls (rag walls) for their
coaches.
STANDARD
CONFIGURATIONS
16.5
INCH - WHEELS
8.75R16.5LT - TIRES
The
original
tires for the GMC had nylon cord side walls (rag
walls) on 16.5 inch hub centered wheels. The little advisory on
the glove compartment door says use "D"
tires and inflate to 65 PSI which is the maximum for Load Rated D (LRD)
tires. "I found where a later GM bulletin
suggested
going to E rated tires. I had missed that and have been
blissfully
riding around on D rated tires inflated to 65 psi without any
problems.
Next time I'll buy E rated. Justin"
(ALCOA
- WHEEL DEAL)
LT225/75R16 - TIRES
The new direction is to use16
inch wheels made by Alcoa and others.
The Alcoa wheels are hub centered and the others are not. The
tire that is almost the same size as the original tire ( you will not
have to
change your speedometer, see options below) is
the 225/75R16. You can get these in the LRD
or the LRE as shown below.
Many GMCers use LRE tires running at 65 lb and : "The reason for this
is
the steel chord or polyester chord is heavier gage and will withstand a
greater shock like running off the road or hitting a pot hole or a road
hazard. Your interpretation is correct, the difference is
maximum air pressure allowed". Ken
LOAD
/ INFLATION TABLE - ALL TIRES
PSI
|
35
|
40
|
45
|
50
|
55
|
60
|
65
|
70
|
75
|
80
|
LOAD
- POUNDS
|
1500
|
1650
|
1790
|
1940
|
2060
|
2190
|
2335D
|
2440
|
2560
|
2680E
|
LOAD
RANGE D TIRES (LRD)
|
LOAD
RANGE E (LRE)
|
Determine the weight on each tire position and set the tire pressure
to carry the load, typically 65 pounds. Some light weight 23 foot
GMCs go down to 50 pounds. LRE tires running at 80 pounds generate a
very hard ride.
TIRE AGE
Do not run on old tires, one blowout will cost more in damage than
a whole set of new tires. The tire manufactures warranty is 5 or
6 years from the date code on
the tire. This is the time to change the tire. They are seldom
worn out at this age. Be sure you buy only new tires not
old inventory.
Here is how to read the date code. TIRES--AGE CODE
OTHER OPTIONS
Some GMCnetters have reported that they are using wider tires for
their Alcoa wheels. The tires may be wider but they are usually
also larger in diameter. This has the effect of increasing the gear
ratio and can negate some of the benefits of going to a lower ratio
final drive (higher numerically).
The 8.75R16.5LT tire has 719 revolutions per mile. The
LT225/75R16 has 703 rev/mile and the LT235/85R16 has 677 revs/mile.
The use of the 16 inch tires on Alcoa wheels will give the following
effect on the final drive ratio:
3.07 with the 16.5" tires will become 3.00 with the 225 tire and 2.89
with the 235 tire.
3.42 with the 16.5" tires will become 3.34 with the 225 and 3.22 with
the 235.
3.55 with the 16.5" tires will become 3.47 with the 225 and 3.34 with
the 235.
3.70 with the 16.5" tires will become 3.62 with the 225 and 3.48 with
the 235.
The speedometer and odometer can also be affected by a tire change.
Going from the 16.5 tires to the 225 would make the
speedometer/odometer off by 2.2% and the 235 tire would be off by over
6%. The easiest way to correct this is with an accessory gear box
attached to the speedometer connection at the transmission. There might
also be appropriate sized gears that could be installed into the
transmission.>>>>>>
So, you can see that your tire and wheel choice may also somewhat
determine your choice of which final drive to use.Emery Stora
The original 16.5" tires were what is now called D rated tires.
The number of ply used to be the standard. All current LT tires
with the same load rating will carry the same tire load at the same
pressures at rated speeds. It is an industry safety standard. Competive
tire pricing has an effect on wear, noise, ride, temperature, speed and
adhesion ratings. I changed my BFGoodrich front tires at 50,000 miles
because the tread was only 1/16 deep. The rears, being, so lightly
loaded, are only half warn. I drive enough miles that I don't bother
with rotating tires to even out the wear before the time limit. D
rated BFGoodrich tires are harder to find in stock because the E rated
tire was only $3 more, reducing the need to stock both D & E rated
tires. They have the same number of cords of slightly different sizes.
GMC's with E rated tires run at the tire manufactures proper tire load
pressures are running at or below D rated maximum pressures. Trucks run
at maximum load sidewall pressures all the time so there is no driver
option to run under inflated. Where overinflated will increase both
tire
wear and ride harshness, it will also reduce wet and dry adhesion with
a resulting longer stopping distance because of the smaller tire patch
on the road. Under inflation has a long list of problems depending on
the extent of under inflation where overheating due to flexing causing
a
blow out is the major one.
The
light truck industry with high mileage usage is willing to pay the
extra for the all steel casing so they can recap the tires up to 7
times and the thicker sidewall are not as easily damaged when driving
over deep chuck holes and square curbs - like city parking. The all
steel tire weighs more and cost more but has the same 6 year warranted
as polyester LT tire in the US. In Europe, those same tires carry a 10
year warrantee. Litigation in the US has shortened the warrantee times.
Warrantee time starts at the manufacturing date on the sidewall.
Beside the extra weight, the all steel tire has one major use problem
for GMC motorhomes. It is recommended that if any steel sidewall radial
tire has ever been deflated 20% less than its recommended tire load
pressure, it should be removed and inspected by a tire dealer for
ruptured wire cords at the mid line where under inflation cause the
maximum bending. If any broken wires are found inside, the tire should
be discarded because the exposed wires will rust over time and
progressively weaken the side wall. I had that happen and the tire
ruptured 5,000 miles after a fixed puncture. The blow out happened
while the coach was parked, which is why the failure mode in the
sidewall was obvious. Rusted wires. This is a problem when coaches with
all steel tires sit a long time and tires loose pressure. When the
tires are re-inflated it is not unusual that they have blowouts later.
That even happens to spares that have sat on the ground deflated
sometime during their
life.
When we did the weigh in at GMCWS,(http://www.gmcws.org/Tech/TireSafety/index.html)
the only coaches that exceeded the D rated loading were those
where the two front tire loads were far different. The maximum measured
difference was where one front tire was carrying as much 550 pounds
more than the other. It was amazing how many coaches that drove to the
rally had suspension alignment problems creating large different in
measured front tire loadings! No coach with near
balanced front loads exceeded the original design rated loading. There
were no coaches, even with roof pods and towing, that even came up to
the D load
maximum rating on the rears. Weighing individual front tire loads is an
easy and quick way to find front suspension problems. Chuck Botts
RIDE HEIGHT AND WEIGHT ON THE TIRES
I went to two rallies in Florida. Both were doing weigh ins.
First one showed my passenger side front was loaded about 200 lbs more
than the driver side. I moved well over a hundred pounds from the
passenger side to the drivers side up front. Got to the next rally and
the passenger side was 250 lbs heavy. I was not a happy camper.
To make a long story short. I messed with the ride height and
everything else. Found the drivers side rear height control valve would
not always exhaust. Had Dave Lenzi rebuild them and life is much better
now. Last check the weight on both front tires were only 25 pounds
apart. JWID Arch
Spare tire cover
http://www.angelfire.com/fl5/tirecovers/ss.html
WHAT
SOME PEOPLE ARE USING
BFGOODRICH
My personal tire recommendation:
BFGoodrich (Michelin) makes a newer design LT225/75R16 Commercial
T/A All Season D and E polyester side wall tire with a "Cool Wedged
shoulder insert". That reduced the tread's edge rounding on the rear
tires during sharp turns. My tires now have 12,000 miles on them with
nearly the same sharp edge as when new. My light coach runs 50 psi on
those rears. I chose the M/S with dual compound tread for better all
season traction in the wet and comfortable ride. UTQG rating, tread
wear=440, Traction=A. UTQG Tire ratings are reflected in the tire
pricing. There is only a $3/tire difference between D & E rating
with the E having increased tread and puncture resistance so I chose
E's but run them at less than D rating pressures. Both rated tires
consist of two steel belts and two ply polyester carcass. (New
construction methods to equal the old 12 ply rating)
Others have ordered these tires from COSTCO for $113/tire. Installation
and balancing more.Chuck Botts
GOODYEAR
John at Hill Top Tire; Rio Rancho NM will purchase the Alcoa
(classic) rims, mount the Goodyear G159 tire, balance and ship (in
USA-main land) for $382.50 each. NOTE: thats with the Mcgard
Flanged Dualie Lugs. I believe the other lugs are more $. .
505-892-2664
6 EA G-159-215/85/16---E load range--$140 plus $7 balancing,
each
Discount
Tire Co.
MICHELIN
Costco handles Michelin, and has >225/75 R16 10 ply E rated
tires for $111.99.
When you wear them out, try the new Michelin LTX M+S 225/75 R16
LRE Polyester side wall, Steel tread. You will find they
are easier to ballance
BRIDGESTONE
Just got 6 Bridgestones at NTB for $110 each including mounting and
balance. They seem to another tire of choice and Patrick got the
deal first at NTB in Atlanta. I showed them a copy of his invoice
and they did the same for me after a little bitching about different
areas of the country and that they should be charging more because we
are in a high col area. If you want a copy of my invoice let me
know. It also included the Alcoa wheels and lug nuts. Marcus
GENERAL
My total $$ for 7 Generals at Sam's was $555 including mounting
& balancing (<$80 each). The above includes a $60 rebate.
FIRESTONE
I bought Firestones R4S since the Goodyear G159's are
back ordered two months, and didn't want to pay for the Michelins. The
Firestones are
10 ply, E range, all steel....$650 mounted on the rims, driveway price
(6). Larry
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