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FAQ on Tires and Road Speed

 

This has been covered over and over again, but here goes the Cliff's Notes
version of the Reader's Digest version:

GMC highway coach powertrains were engineered using tires that turn 495
revs/mile.  That includes your 4104.

If you purchase tires that turn MORE than 495 revs/mile, you'll lose some
top speed, you'll burn a little more fuel, but you'll be able to climb hills
just slightly faster.

If you purchase tires that turn LESS than 495 revs/mile, you'll gain some
top speed, you'll get a little better fuel mileage, but you'll slow down a
little bit more climbing a mountain.

You choose.

Every major truck tire manufacturer has the rev/mile number buried in the
tire's spec sheets - have your friendly tire guy help you find them, or go
to the manufacturer's website and look them up.

Notice I said tires above, not wheels.  There are some 24.5 tires that are
smaller overall than some 22.5s.  Buy wheels in the size necessary to
accomplish what you want to achieve.  New steel wheels are usually less than
$100 each, new Alcoas run around $300 each, and with their new finishing
process, require very little maintenance to stay bright.

Take a look at your lug nuts. You will either have "stud piloted" or "hub
piloted" wheels, easily determined by the lug nuts.  If the nut has an
attached washer assembly, you have "hub piloted" wheels.  If the lug nuts
have a chamfered wheel-side edge like a car's, you've got "stud piloted".
Purchase the appropriate new rims accordingly.  Alcoa aluminum rims require
longer studs front and rear, be prepared.

Insist on the shop using a torque wrench to tighten the lug nuts down, not
the burp gun.  Stressed stud threads from an over-zealous burp-gun jockey
lead to failure.  450 - 500 ft/lbs. is considered normal on a GMC.

Be aware that "drive" tires are generally a little louder while rolling down
the super slab, the knobbier the louder.  Not usually the case with "steer"
or "all-position" tires.  How smooth and quiet of a ride are you seeking?

Most commonly used tires on coaches in RV service are:

11R22.5
11R24.5
12R22.5
and the new metric sizes
275/85R22.5
305/80R22.5

The 11Rs, both in 22.5 and 24.5, are the most commonly available, especially
at truck stops, which might be a factor at Oh Dark Thirty.  Carrying a spare
is up to you. . . do you have one hidden behind your front bumper??

ALWAYS have EVERY tire/wheel combination balanced with the common lead
weights.  DO NOT compromise on this issue w/ the tire guy.  Spend the $$ to
have them balanced properly.  Spin balance (off coach) can be best, but a
good bubble balance done correctly will be almost identical.

Tires are a compromise that only you can decide what is best for you and the
type of use you're subjecting your coach to.  Remember, too, that in RV use,
they'll usually rot from lack of use before you wear them out, so the most
expensive may not be the "best deal" in the real world.

HTH,

RJ
PD4106-2784
Fresno CA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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                                              This page was last updated 12/16/03                                                  Copyright 2000 All rights reserved.