Buying one new tire for AWD Astro Van 2002

I needed a new tire after a rear flat last week. I assumed I would be
buying two tires for the rear. The tire dealer said because I have an
AWD I have to replace all 4 tires so they are all the same size,(worn
vs new). He said running new tires only on the rear would make the
front tires turn faster than the rear because they are worn and are
smaller in diameter. He said I could hurt my drive train or
differential or something like that. I assumed he was just trying to
sell me 2 extra tires. HOWEVER, while driving off the lot at a very
slow speed I felt a kind of clunking in the steering wheel and back
wheels. I have been feeling this all week, (only at speeds under
17mph. It feels like it starts in the front then transfers to the rear
and then back to the front again, all in about 3-4 seconds. Was I
wrong in my assumption, and should I puchase tires for the front as
well? The new tires are the same size as the old ones.
Joel

On 10 Oct 2003 21:03:22 -0700, [email protected] (Joel Brown)
wrote:

>I needed a new tire after a rear flat last week. I assumed I would be
>buying two tires for the rear. The tire dealer said because I have an
>AWD I have to replace all 4 tires so they are all the same size,(worn
>vs new). He said running new tires only on the rear would make the
>front tires turn faster than the rear because they are worn and are
>smaller in diameter. He said I could hurt my drive train or
>differential or something like that. I assumed he was just trying to
>sell me 2 extra tires. HOWEVER, while driving off the lot at a very
>slow speed I felt a kind of clunking in the steering wheel and back
>wheels. I have been feeling this all week, (only at speeds under
>17mph. It feels like it starts in the front then transfers to the rear
>and then back to the front again, all in about 3-4 seconds. Was I
>wrong in my assumption, and should I puchase tires for the front as
>well? The new tires are the same size as the old ones.
>Joel


In a perfect world, you should replace all four as it best that all
tires are exactly the same diameter in an AWD vehicle.

But.... First, I'd look in the owners manual and see if this issue is
addressed.

Second, since you own a 99 and up Astro, the AWD system consists of an
electronic clutch in the transfer case. You can bypass the AWD by
pulling the fuse that controls this clutch. (This would mean you are
now a 2wd Astro.) How many miles are on the three remaining tires?
If those tires are getting close to being worn out, then this might be
an option to allow you to run them down closer to being worn out and
then you could buy four at once. (As for your "clunking", try pulling
the fuse and see if it ceases.)

Third, in reality, you probably won't have any problems anyway. My
AWD Safari ran for about 20,000 miles with stock tires on the front
and new Goodyear Wranglers on the back after losing one to a sharp
rock on a roadtrip in Montana years ago. (Stock Tiger Paws suck!!!)
At the time, my van had about 40,000 miles on it and it now is at
148,000 and the drivetrain is fine. Granted, my transfer case uses a
viscous clutch vs the newer electronic unit, but I would guess the
electronic unit is probably less susceptible to heat than the viscous
unit was, and heat generation is really the issue here.

Replacing them all is the best option, but I doubt you will suffer any
severe drivetrain problems if you don't do it immediately.

Hey, have you visited www.astrosafari.com? If not check it out. (Of
course you may feel the need to swap in a V-8 and put on a lift kit
after you do......)

Matt
99 V-10 Super Duty, Super Cab 4x4
96 GMC Safari AWD Hi-Top Conversion