understanding how tire size affects trail

"LF" wrote:
I have some limited experience with this on a mid 1980s Pinarello
Treviso. When I got the bike it had 23cm (nominally -- don't know the
actual width) Pirelli tires, and the bike seemed "squirrely" to me.
Some might call the same trait "responsive." I changed the tires to
28cm (nominally -- really closer to 25cm), and the bike seemed to ride
and handle better.

I believe what you say, but I doubt it had anything to do with trail.

Art Harris

I just put 25s on my racing bike (I've always used 23 or smaller in the
past, but now I'm old and my butt matters more than my pride.) And I
can't tell any difference in handling whatsoever. Ride is noticeably
improved, though. My bike's geometry: 56x56, parallel 73d angles, 43mm
rake.

I'd say go for it!

Arthur Harris wrote:
"LF" wrote:
I have some limited experience with this on a mid 1980s Pinarello
Treviso. When I got the bike it had 23cm (nominally -- don't know
the actual width) Pirelli tires, and the bike seemed "squirrely" to
me. Some might call the same trait "responsive." I changed the
tires to 28cm (nominally -- really closer to 25cm), and the bike
seemed to ride and handle better.

I believe what you say, but I doubt it had anything to do with trail.

Bingo. Better/bigger/softer tires maybe; TALLER tires...nah.

In article
.com,
" wrote:

How will increasing the tire size from 700x21c to 700x24c affect the
trail of a given fork, and, therefore, the handling of the bike? The
bike in question has a head angle of 73.5°, a 45mm fork offset, and
5.6 trail according to the geometry chart. Assume that the fatter tire
increases the radius of the wheel by 3mm.
Riding this bike now with 700x21c tires, the straight-line tracking is
excellent, and the bike's willingness to carve turns is sluggish. Will
switching to the larger-radius tires appreciably quicken or slow the
steering response? Thanks.

Measure the roll out for the two tires, publish them here,
and I will tell you.
For typical road tires 5 mm difference in diameter will
make a difference of 1 mm in trail.

--
Michael Press

"Bill Sornson" wrote:

Arthur Harris wrote:
"LF" wrote:
I have some limited experience with this on a mid 1980s Pinarello
Treviso. When I got the bike it had 23cm (nominally -- don't know
the actual width) Pirelli tires, and the bike seemed "squirrely" to
me. Some might call the same trait "responsive." I changed the
tires to 28cm (nominally -- really closer to 25cm), and the bike
seemed to ride and handle better.

I believe what you say, but I doubt it had anything to do with trail.

Bingo. Better/bigger/softer tires maybe; TALLER tires...nah.

Exactomundo. The contact patch on a fatter tire is shorter (fore/aft)
and wider (side to side). That will make a considerable difference in
"feel". When you think about the fact that when you turn you're
actually "scrubbing" the front tire's contact patch everywhere but at
the middle of the contact patch, this makes sense.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

French 650b bikes have low geometric trail, about 3.0cm, but handle
very well
due to pneumatic trail. The contact patch scrubbing as you say makes
the bike
steer well. The bikes also have low "flop" you can have 10lbs of stuff
in the bar
bag and still sprint hands off, the bike tracks straight.


Scott G.

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In article .com,
wrote:
How will increasing the tire size from 700x21c to 700x24c affect the
trail of a given fork, and, therefore, the handling of the bike? The
bike in question has a head angle of 73.5°, a 45mm fork offset, and
5.6 trail according to the geometry chart. Assume that the fatter tire
increases the radius of the wheel by 3mm.
Riding this bike now with 700x21c tires, the straight-line tracking is
excellent, and the bike's willingness to carve turns is sluggish. Will
switching to the larger-radius tires appreciably quicken or slow the
steering response? Thanks.


_ Trail is not the only thing affecting the handling of a bike.
Head tube angle matters, wheelbase matters, stem length and bar/tire
width matters. In terms of the speed of initiating a turn, I
think all these factors are more important that trail.

_ If you want to improve the responsiveness of the bike,
technique can help. Google for "bicycle counter steering".
It's something you're doing anyway, but if you conciously
emphasize it you can get much more responsive turn initiation.

_ Booker C. Bense

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Michael Press wrote:
" wrote:

How will increasing the tire size from 700x21c to 700x24c affect the
trail of a given fork, and, therefore, the handling of the bike?

Measure the roll out for the two tires, publish them here,
and I will tell you.
For typical road tires 5 mm difference in diameter will
make a difference of 1 mm in trail.

I found that the difference in measured rollout isn't much. As was
pointed out, the larger tire is fatter with a larger air volume and
wider contact patch, but the difference in height is negligible.

Vittoria CX TT 700x21c @100psi 2088mm
Vittoria Pave EVO CG 700x24c @100psi 2101mm

In article
. com,
" wrote:

Michael Press wrote:
" wrote:

How will increasing the tire size from 700x21c to 700x24c affect the
trail of a given fork, and, therefore, the handling of the bike?

Measure the roll out for the two tires, publish them here,
and I will tell you.
For typical road tires 5 mm difference in diameter will
make a difference of 1 mm in trail.

I found that the difference in measured rollout isn't much. As was
pointed out, the larger tire is fatter with a larger air volume and
wider contact patch, but the difference in height is negligible.

Vittoria CX TT 700x21c @100psi 2088mm
Vittoria Pave EVO CG 700x24c @100psi 2101mm

Head angle: 73,5 degree
Fork offset: 45 mm
Vittoria CX TT 700x21c @100psi 2088mm. Trail: 52 mm

Vittoria Pave EVO CG 700x24c @100psi 2101mm. Trail: 52 mm

Visit
http://www.kreuzotter.de/english/elenk.htm
for a good exposition of the geometry.

--
Michael Press

right. CS technique overrides the trail/tire consideration. No CS tech
relieves the design staff of contact patch responsibility big time.
does MTB geometry reduce the effects of tire design parameters
comparative to road bike design?