Upgrading wheel sizes

[Dave]

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.

 

[Pat O'Malley]

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

 

[Tom Sherman]

Pat O'Malley wrote:

> ...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

 

[John Duval]

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 protected]> wrote in message
news:[email protected]...
> 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.