Moving an old 650c bike to 26" (mtn) wheels

[Pete Grey]

I'm looking at moving my mother-in-law's bike to 26" wheels.
Her old 650c set is just about shot (rim wear) and rather than rebuild them
with 650's I was thinking of just getting a set of 26" wheels.
She'd prefer to have a larger tire than when we bought the bike for her
anyway, so the 26" selection would be nice.

Currently the brakes are just about at their largest-diameter limit, so
there's 10-12mm of adjustment to a smaller diameter rim.
It looks to me from reading a bit that the brake reach difference is only
about 5-6mm (shorter with 26")?

Any hints, gotchas, etc would be greatly appreciated!

Thanks,

-pete

 

[[email protected]]

On Feb 8, 12:49 pm, "Pete Grey" <[email protected]> wrote:
> I'm looking at moving my mother-in-law's bike to 26" wheels.
> Her old 650c set is just about shot (rim wear) and rather than rebuild them
> with 650's I was thinking of just getting a set of 26" wheels.
> She'd prefer to have a larger tire than when we bought the bike for her
> anyway, so the 26" selection would be nice.
>
> Currently the brakes are just about at their largest-diameter limit, so
> there's 10-12mm of adjustment to a smaller diameter rim.
> It looks to me from reading a bit that the brake reach difference is only
> about 5-6mm (shorter with 26")?
>
> Any hints, gotchas, etc would be greatly appreciated!
>
> Thanks,
>
> -pete


571 mm for 650c rims.
559 mm for 26" mtb rims
====
12 mm divide by 2
====
6 mm

That's how much you need to move the brake pads.

diameterwise it should work fine.

: tire width clearance issues remain.
: correct number of spokes (rim vs hub)
: brake caliper clearance around bigger tires.

Low end mtb rims tend to come in much wider widths. Look for a decent
quality rim that won't be much wider than the 650c rim.

And you'll probably need new spokes (different length)

R

 

[James Thomson]

"Pete Grey" <[email protected]> a écrit:

> I'm looking at moving my mother-in-law's bike to 26" wheels.
> Her old 650c set is just about shot (rim wear) and rather than
> rebuild them with 650's I was thinking of just getting a set of
> 26" wheels.

> Currently the brakes are just about at their largest-diameter
> limit, so there's 10-12mm of adjustment to a smaller diameter
> rim. It looks to me from reading a bit that the brake reach
> difference is only about 5-6mm (shorter with 26")?

> Any hints, gotchas, etc would be greatly appreciated!

I made the same conversion a year or two ago on a 650c 47cm Cannondale I put
together for a friend. I was prepared to have to use longer-reach brakes,
but the standard brakes worked perfectly. She uses Specialized Fat Boy
tyres, and there's clearance for something slightly fatter.

The difference in rim radius is indeed (571-559)/2, or 6mm.

New mtb wheels will measure 135mm over the rear hub locknuts. Your
mother-in-law's bike is probably narrower, so be prepared to re-space the
new hub or frame. Alternatively, rebuild the old rear hub with a new 26"
rim.

James Thomson

 

[Pete Grey]

Thanks for both the replies, that's the answer I suspected!

Anyone know of a table or similar that defines the rim widths for common
rims? For example, finding a width on a "Ritchey Girder WCS" rim is turning
out to be extremely dificult;-]

Thanks,

-pete

<[email protected]> wrote in message
news:[email protected]...
> On Feb 8, 12:49 pm, "Pete Grey" <[email protected]> wrote:
>> I'm looking at moving my mother-in-law's bike to 26" wheels.
>> Her old 650c set is just about shot (rim wear) and rather than rebuild
>> them
>> with 650's I was thinking of just getting a set of 26" wheels.
>> She'd prefer to have a larger tire than when we bought the bike for her
>> anyway, so the 26" selection would be nice.
>>
>> Currently the brakes are just about at their largest-diameter limit, so
>> there's 10-12mm of adjustment to a smaller diameter rim.
>> It looks to me from reading a bit that the brake reach difference is only
>> about 5-6mm (shorter with 26")?
>>
>> Any hints, gotchas, etc would be greatly appreciated!
>>
>> Thanks,
>>
>> -pete
>
>
> 571 mm for 650c rims.
> 559 mm for 26" mtb rims
> ====
> 12 mm divide by 2
> ====
> 6 mm
>
> That's how much you need to move the brake pads.
>
> diameterwise it should work fine.
>
> : tire width clearance issues remain.
> : correct number of spokes (rim vs hub)
> : brake caliper clearance around bigger tires.
>
> Low end mtb rims tend to come in much wider widths. Look for a decent
> quality rim that won't be much wider than the 650c rim.
>
> And you'll probably need new spokes (different length)
>
> R
>
>

 

[James Thomson]

"Pete Grey" <[email protected]> a écrit:

> Anyone know of a table or similar that defines the rim widths for
> common rims? For example, finding a width on a "Ritchey Girder
> WCS" rim is turning out to be extremely dificult;-]

Generally the manufacturer's website will have this information.

According to the 2006 catalogue (a big pdf download from the Ritchey Logic
website) the Ritchey Girder WCS rim is 23mm wide, which is fairly typical
for a light XC rim.

http://www.ritcheylogic.com/web/Ritchey~Logic/Ritchey~Site/web/EN/main/product/12101.html

If you're looking at buying them as pre-built wheels, I'd avoid the 2006
model. They're light, but those that I've seen have had draggy freehub
ratchets and undersized bearings.

James Thomson