Re: Tire sizes

["Rudy Consolacion" <rconsolacion@kumhotech.com>]

I'd like to comment on the temporary spare tire. The reason why the 
speed is limited to a max of 50 mph is to keep the average driver out 
of trouble.  The handling capability is much lower than a full size 
tire.  In an evasive maneuver, the handling will become non-linear 
with either excessive understeer if mounted on the front, or 
excessive oversteer if mounted on the rear.  To avoid any legalities, 
I'll just say that I drive as fast as surrounding traffic on a 
t-spare.  I think it is more dangerous to drive 50 when everyone 
else is doing 75.  The inflation recommendation is 60 psi.  I usually 
keep mine at 80 psi.  (They'll explode at a lot higher pressure.)  
This helps the high-speed durability.  

The majority of t-spares are still bias construction which means 
higher treadwear rate. So, don't go and drive for 500 miles on one.

If at all possible, put the t-spare on the axle with the lightest 
load.  This makes it easier on the tire especially if you're driving 
fast.

Putting on a new tire when the others have 4k of wear will not affect 
anything.  A tire will maintain its RPK (revs per kilometer) 
throughout its life.  Believe it or not, RPK is a function of the 
steel belt diameter and not the amount of tread.  I've done studies 
where tires were tested for RPK with full tread-depth and then later 
shaved to worn-out conditions.  The results showed that RPK did not 
change with statistical significance.

Keep the hammer down!
Rudy C.
87 5ktq
97 a42.8q

> This new year found me driving from San Diego to Pensacola to report to my
> next duty station. About 125 miles out of SD  on I-8 I pulled out to pass a
> semi when I saw something in the middle of the road. Unfortunately, I did not
> quite miss it and it took a chunk out of my brand new 17" Compomotive wheel
> and cut the sidewall of my tire. I ended up having to drive ~300 miles on that
> stupid donut of a spare tire to Tucson to get the tire replaced (does anyone
> know how much it sucks to have to do 50mph in a 75 zone?). I called ahead to
> Beaudry Porsche/VW/Audi etc, explained my problem, and they called around
> Tucson to find a replacement tire (Pirelli P7000 215/45-17's apparently are
> more rare than gold out there and they were only able to find a Nitto in the
> correct size). They were very pleasant, helpful, and got me back on the road
> in a reasonable amount of time. My question is this: I now have a Nitto NT501
> on the left front with ~1600 miles on it and 3 Pirellis with ~4k miles on
> them. Will replacing the Nitto with a new Pirelli adversely affect the
> drivetrain given the differing tread depth? I doubt that the Nitto and
> Pirellis have the same rolling radius either but I don't have that info handy.
> TIA.
> 
> Chris
> 97 A4q 2.8
> 96 Jetta GLX
>