RE: [ST] 190 on rear

["David W. Funk" <dwf@xxxxxxxxx>]

On Tue, 17 Dec 2002 11:44:02 -0800 (PST), Bryce wrote:

>Seeing as The factory engineers know a lot more about
>tires and what size to throw to the ST than I, I'd
>assume they were doing it correctly from the get-go in
>terms of tire selection for the best turn-in and
>adhesion while leaned over.

Tire selection is always a compermise. The factory engineer do know more 
about tires, but they may not be trying for the same compermise that I am. 
For one thing I am less concerend about cost.
Also turn-in and adhesion while leaned over do not always go together. May 
be the factory wants easy turn-in so the test ride feels great. But I could get 
use to (live with) more turn-in effert in exchange for more grip, or better life.

  [snip]

>U're actually getting a worse contact patch at full
>lean angle as u cram a bigger and bigger tire on to
>that rim.   A regular 180 that is meant for the
>rim....has a nice profile to it, it curves around the
>rim nicely as it comes to the edge of the rim...giving
>u a steady contact patch for the most part til the
>edge of the tire.  But if u throw a bigger tire on
>there, the angle in which the crown forms around the
>rim is harsher and more steep because there is more
>tire to fit on the same rim, so as u lean the bike
>over u have less a contact patch and the tire will
>tend to flop over at lean.   

This is not true for the Sprint ST with 6 inch rim. What you said is true for 
putting too big a tire on a given rim. In fact the 180 is a little small for a 6 inch 
rim. 180 tires are usually used with 5 or 5.5 inch rims.

>
>This is just how I have read it and have found from
>forcing a wider BT010 on my old Katat 750 because I
>wanted that particular tire so bad.  Even though it
>should have gotten a 150 on the back of it as opposed
>to 160 width.
>
>Links describing contact patches and wider tires
>better than I can:
>
>http://www.christmasinjuly.org/safety20.html
>http://www.ironhorse-uk.com/fluids.htm

Both these web sites talk about too large a tire on a rim. But again a 190 tire 
is designed for a 6 inch rim.

>
>Bryce

David W. Funk
'00 Triumph Sprint ST
Pleasanton, CA




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