650b wheels in a race frame

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pq
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650b wheels in a race frame

Postby pq » 14 Jul 2020, 9:31pm

I'm toying with the idea of buying a new road bike. Part of that is finding a use for my old one, which is a 1999 Merlin Extralight - it's a very special frame and I'd rather find a use for it than sell it.

I'd love to use it as a winter bike, which means mudguards, but it has extremely tight clearances. With 25mm tyres, there's less than a mm under the brakes, and there's also limited clearance width ways between the chainstays and the forks too.

So I'm wondering how viable it is to use 650B rims, maybe with 28mm tyres. Is there a brake calliper which will reach the rims, and will the braking be OK (I'm spolit with the Record groupset the bike currently has)? Will it screw up the handling?

Thanks as always
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mattsccm
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Re: 650b wheels in a race frame

Postby mattsccm » 14 Jul 2020, 9:40pm

Gravel bike owners swap but thats to fit big tyres. You may find that you loose too much ground clearance. It is hard to calculate dxactly what will fit in. You may get something like a 35mm slick in but the chainstays may be too narrow.
The wheels are 584mm diameter not 622 as you currently have so 38mm difference so 19mm radius. I guess a long drop brake might exist depending on what you currently have.
The are 650 Facebook pages that deal with conversions.

mattsccm
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Re: 650b wheels in a race frame

Postby mattsccm » 14 Jul 2020, 10:06pm

Sheldon Brown discusses this as well

Brucey
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Re: 650b wheels in a race frame

Postby Brucey » 14 Jul 2020, 11:00pm

sample conversion here

http://georgebike.blogspot.com/2013/01/surly-pacer-650b-conversion.html

Image

typically you will have to contend with

- fitting long drop brakes
- tyre clearance at the front and/or back may be limited
- lower BB height
- lower overall gearing

IMHO once you have done this conversion tyres in the 35-38mm range make most sense, but obviously they may be too wide for some frames

19mm more brake drop and +10mm on tyre width (vs 25x622) means 9mm lower BB height, which is manageable.

FWIW there are rim sizes at 590mm and 597mm (which would need less brake drop) but there is very limited rim and tyre choice in these sizes.

NB one way of sorting the brake issue is to fit SA drum brakes. The work well in most steel frames/forks.

cheers
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Valbrona
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Re: 650b wheels in a race frame

Postby Valbrona » 15 Jul 2020, 12:10am

It is wrong to be sentimental over material things like bike frames; not saying sentimentality is behind your thinking though. Switch to your new bike and be done with it.
I should coco.

pq
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Re: 650b wheels in a race frame

Postby pq » 15 Jul 2020, 9:29am

Thanks Brucey, I didn't know about those other wheel sizes, although if I can't get really good tyres I wouldn't use them. I don't mind about lowered gears (actually that's a benefit), a 9mm bb drop sounds OK, so maybe it'll work. The frame is extremely lightweight Ti with carbon forks. When it was new it was astonishingly expensive. It's not something I'd fit SA drum brakes to, but changing the callipers would be fine. I'm just a bit concerned about what width tyres I'll manage to cram in, but I'd be happy with 28s. A smaller wheel will give a little more clearance at the back, so maybe that would be enough. The forks less so, but I'm thinking I should change the fork anyway after 20 years.

Valbrona, this has nothing to do with sentimentality. It just makes sense to use this bike for winter duties if I can.
One link to your website is enough. G

Brucey
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Re: 650b wheels in a race frame

Postby Brucey » 15 Jul 2020, 10:05am

pq wrote:….I'd love to use it as a winter bike, which means mudguards,...


pq wrote:…. The frame is extremely lightweight Ti with carbon forks. When it was new it was astonishingly expensive. It's not something I'd fit SA drum brakes to...…….. It just makes sense to use this bike for winter duties if I can.


Given it is a winter bike and you are (in essence) only using the frame because you have it already, hub brakes seem like a no-brainer to me. They will work way better than long drop calipers. If the frame took disc brakes you'd be happy, right? Well these brakes work more consistently in the weather than discs and weigh about the same. If you are getting another fork anyway I'd suggest getting a steel fork and you can either use caliper brakes or drum brakes with it.

NB if you can only fit 28mm tyres on 584mm rims then the BB height will drop by 16mm vs 25-622 tyres. Shooting for fatter tyres on the 584mm rims makes more sense.

cheers
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pq
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Re: 650b wheels in a race frame

Postby pq » 15 Jul 2020, 11:24am

Thanks again Brucey. I'll look into the brakes in more detail - I just remember the horrible steel things of old, I guess they're different now. It's a difficult decision, the bike is really really nice to ride so it would be good to keep it and ride it, but if it's going to end up as an unsatisfactory bodge I should probably sell it, even at 20 years old it's worth a surprising amount of money.
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Brucey
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Re: 650b wheels in a race frame

Postby Brucey » 15 Jul 2020, 3:45pm

FWIW one of my chums owns a (probably unique) Raleigh SBDU 753 frameset which was built (from new in 1985) to be equipped with SA drum brakes. It is a really very classy machine where it matters, i.e. in the frameset and wheelset. My chum doesn't ride much these days but just last week he did a ~150km ride on the bike and (as usual, he puts in a ride like this most years) all was joy and light. The idea that 'these brakes don't go with lightweight machines' doesn't hold water as well as you might expect. More than one way of skinning a cat and all that...

cheers
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NickJP
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Re: 650b wheels in a race frame

Postby NickJP » 16 Jul 2020, 1:18am

I did exactly that almost 20 years back with a Litespeed when I ceased racing it. With 700c wheels 25mm was the max tyre size I could fit - with 650b wheels I could fit 32mm tyres (limiting factor was the clearance where the tyre passed between the chainstays). Tektro R556 calipers (now R559) have enough reach for 650b rims, and work perfectly well with the Ultegra STI levers:

Image
Last edited by NickJP on 17 Jul 2020, 4:31am, edited 1 time in total.

Sid Aluminium
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Re: 650b wheels in a race frame

Postby Sid Aluminium » 16 Jul 2020, 4:37am

I have two different 700c frames I run with EA3 (650A) wheels. Like it. Wouldn't switch back.

Funny thing about different brands and models of the tyres: they're all marked 26x1 3/8 - ISO37x590, but mounted on the same rims they measure from 27 to 38mm.

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Audax67
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Re: 650b wheels in a race frame

Postby Audax67 » 16 Jul 2020, 10:57am

Or you could leave it as it is, fit SKS Raceblades and avoid the pother. OK, you need to wipe off the seat-tube occasionally, but 35€ vs a pair of wheels is a good argument. Depends how much toe-room you've got up front, though: on my old Lapierre racing frame the front mudguard hit my toe. I was fine without it, but I don't live in the UK.
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belgiangoth
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Re: 650b wheels in a race frame

Postby belgiangoth » 16 Jul 2020, 11:35am

What you want is Alhonga deep drop brakes and then respace the rear of your bike to make it a fixed gear winter commuter. (because I have both the brakes and a fixed gear 650b wheelset going spare).

On a more serious tack, if you can have a borrow of the parts for an investigation it would help. I have a carlton track bike that I considered doing this to - it was on 20mm tubulars and it can fit 38s at the front but only 32s at the back. You may have an excesively helpful bike shop that will allow you to try and fit wheels/tyres to your bike to see if they fit or if you live in Brum send me a PM.
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ANTONISH
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Re: 650b wheels in a race frame

Postby ANTONISH » 16 Jul 2020, 1:42pm

I've thought of this for my tourer ( it wouldn't hurt for me to be a fraction closer to the ground), it's currently fitted with cantilevers but I could fit callipers.
I wonder how the braking is with deep drop brakes compared to shallow drop brakes, it seems to me that the MA is reduced.

Brucey
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Re: 650b wheels in a race frame

Postby Brucey » 16 Jul 2020, 3:18pm

ANTONISH wrote:I wonder how the braking is with deep drop brakes compared to shallow drop brakes, it seems to me that the MA is reduced.


if DP calipers are well designed the MA (mid slot) stays about the same in long arm versions. However there is no getting away from the fact that the arms are longer and more flexy.

However the MA also varies with slot position of course: If you have a choice between very long DP calipers with the brake blocks in the top of the slot and shorter DP calipers that use the bottom of the slot, often the former gives stronger brakes than the latter. This is of course completely different to the usual outcome with SP brakes.

cheers
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