Upgrading wheel sizes

[email hidden] (Dave) wrote in message news:<[email hidden]>...

Quoted message said:

Has anyone tried upgrading a 26" rear wheel with a
700C wheel?

Although I'm happy enough with my new SWB, I just can't
get past the fact that my crappy Blackbent, for all of
it's faults, has that easier-rolling 700C rear wheel. Now,
I'm looking at the wiggle room in the rear fork of my
functional bike, with it's 26" wheel, which I could afford
to buy, and it looks as if I may be able to adjust the
breaks to fit this slightly larger wheel. I guess this
would necessitate increasing the front wheel size as well,
to maintain the seat/bottom bracket ratio. But if all this
can be fit together, does anyone know of a good reason why
one should never do this?

Thanks.

When I got my first bent,a RANS Velocity Squared, I too was
concerned about the smaller 26" wheel. After everbody told
me that the gearing is what really counts I still had to
see for myself. After all, I had test ridden a BikeE and a
RANS Rocket and both of those small wheeled (smaller than
26"😉 bikes were too slow. So I diconnected the rear brake
on my V2 and popped in a 700 wheel. I could feel no
difference. The only advantage I see in having a 700 wheel
is that you can get narrower, and higher pressure tires.
The significant factors that affect a wheel's rollong
resistance are diameter ( not that much diff between a 26
and a 700) tire pressure, and tread width. Wheel weight,in
my opinion,is similar to the diameter differences--not that
significant--but I suppose you have more options to go
lighter weight when shopping for a 700 wheel. I still am
plagued with the same question; however in my case I keep
wondering if my FRONT wheel were larger (ie highracer) how
much of an improvement that would be! If you do change your
wheel let us know how it turned out.

Pat O'Malley said:

...The significant factors that affect a wheel's rollong
resistance are diameter ( not that much diff between a 26
and a 700) tire pressure, and tread width....

Rolling resistance decreases with tire width for a given
inflation pressure [1], as less deformation of the casing
occurs to form the contact area with the road surface.
Hysteresis in the casing (and tube) material is the primary
source of energy loss (and hence rolling resistance).

[1] A narrower tire will be inflated to a higher pressure
for a given stress in the casing.

--
Tom Sherman – Quad Cities

I have been doing a bit of research in this area recently. Here is what I
would point out:

Great tire choices in 700c, but very few matching in 20".

The change is not 'slight' when it comes to geometry. A 700c
is 2.5" larger in diameter than a 26" wheel, so about the
only cantilever brake that will adjust this far is a Paul
Components BMX brake (or disk). You would also need a
shorter travel/higher leverage lever (like a road brake) to
compensate for the decreased leverage. This all adds about
$120 to your conversion.

The change to your bikes geometry would also be more than
slight. You raise the rear by 1.25", and even a 451 front
wheel would leave your front end
3/8" lower.

The change in rolling resistance is very slight. If
anything, raising the back will add air drag that will more
than make up for any gains.

Sacrificing ride quality with a narrower, higher pressure
tire in the same diameter will make a difference. Weight
savings and good bearings don't hurt either. You may need a
narrower rim to match.

650c and 26" are very similar, but tire choices are vastly
better in 26".

John

"Dave" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Has anyone tried upgrading a 26" rear wheel with a
700C wheel?

Although I'm happy enough with my new SWB, I just can't
get past the fact that my crappy Blackbent, for all of
it's faults, has that easier-rolling 700C rear wheel. Now,
I'm looking at the wiggle room in the rear fork of my
functional bike, with it's 26" wheel, which I could afford
to buy, and it looks as if I may be able to adjust the
breaks to fit this slightly larger wheel. I guess this
would necessitate increasing the front wheel size as well,
to maintain the seat/bottom bracket ratio. But if all this
can be fit together, does anyone know of a good reason why
one should never do this?

Thanks.