650b front/700c rear?

[Brad L]

Hi, I have an old Wester Ross touring bike that I believe was a 27" originally.  I am trying to max out tire size and with Tektro 559s, 650b will work in front -- looks like with fender I might be able to get a 650b 48mm in there, but in the rear, the 650b rim is just too small and the 559 won't reach.  I think I can get a 700x38 in the rear.  The result will of course be a smaller outside diameter tire in front.  I know this will slightly mess with the bike's geometry, but maybe not that much?  

Any thoughts?

Is anyone aware of spacers, tall fork races, taller headseats etc. I might be able to use to lift the head tube a little?  

I can of course experiment but would rather not spend the coin on a tire I can't use.  

Alt of course is just to keep 700c front/back.  

Thanks for any thoughts!

I am otherwise a very happy Gitane TdF 650b conversion rider and have been so for many years.  

[etorg...@yahoo.com]

Hi Brad. 

The answer to this problem is a brake drop bolt.  (Especially because, we are, after all, the 650b group.) Sheldon has a page on it here.  I recently (last year) made one for my Merlin Extralight CX.  The bike started with cantilever brakes.  I first drilled the rear bridge and used the Tektro 559s for maybe 10 years.  I never really liked the rear braking that much (probably because I was at the extreme of the adjustment) so finally, one day I made my own drop bolt and then added a Velo Orange Gran Cru brake.  It works great.  I actually think it looks pretty good too. Here is mine.

Good luck.

Eli

In Albuquerque

[etorg...@yahoo.com]

I should add that the fenders will make it a little trickier, but there are workarounds, including one cited by Sheldon.  (That one doesn't look so nice though.)

Eli

In Albuqueerque

[etorg...@yahoo.com]

Another option to to keep the 650b rear wheel is using a set of offset brake pads like these from Blue Lug.  They give you 10mm additional reach.  

Eli

In Albuquerque

[etorg...@yahoo.com]

Sorry for all the advice.  I also used these brakes for this very problem.  However, the long arms made for pretty flexy braking in my opinion which is why I eventually went with the brake drop.  

Eli

In Albuquerque

[Brad L]

Eli, all super helpful.  Worked on the bike today with my nephew and he suggested some type of drop plate.  I showed him my Campy drop bolt.  And here you are suggesting the same thing.  

Those drop brake shoes though might be the easy button.  Smart.  I'm gonna try them.  

I wish someone would just make some decent quality dual pivots with even longer arms, I would think there would be some demand.  

[etorg...@yahoo.com]

Great to hear, Brad.  

Tell us what you decide.  

To round things out, I will add that Moots Mounts plus a set of canti or V brakes would allow you to run the wheel of your choice.  Unfortunately, Moots Mounts are as rare as Hen's Teeth.  

Eli 

In Albuquerque

[Brad L]

Just wanted to report back and thank Eli for the drop shoe rec.  They are Just The Thing.  The 559s aren't the last word in stiffness, I still think there's room for someone to sweep the huge market for a quality conversion extra long reach stiff brakes; we can only hope.

[Bernard Duhon]

I have 2 different sets of “drop Shoe Pads”

Be careful because the upper metal part of the shoe can touch your tire ifyou are running a large tire.  In my case 42mm, 38 mm was ok. Someone on the list warned me about it. 

I located an extra thick pad to keep the shoe from rubbing thru the tire.  I also had to put the pad holder on the grinder to remove some metal.

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[Michael Wong]

Just a bit of advice: Drop pad adapters brake badly.

I used drop shoe adapters in the 27-> 650b conversion I did. You lose a *lot of braking power due to a big loss of mechanical advantage. My Motobecane always braked terribly with that set up. Perhaps not dangerously so, but it was very unpleasant to me. It wasn't just a qualitative feeling. I did a roll-down test comparing 5 other bikes and it had by far the worst stopping distance.

The drop bolt adapter was a much better choice for braking power, but they were a little hard to come by at the time..

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[Andy Beichler]

I am currently using BDop drop pad adapters and have no problem braking.  So, your mileage may vary if you use them.  

[Bernard Duhon]

Was there a drop bolt adaptor manufactured & sold?  I thought you had to fabricate them yourself/

 

 

 

 

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Sent: Thursday, August 6, 2026 7:11 PM
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Subject: Re: [650B] Re: 650b front/700c rear?

 

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[satanas]

Drop bolts tthemselves are pretty much extinct, but there are various brake reach increasing things on Aliexpress; you'll have to guess what they're called though...

Later,

Stephen

[Brad]

You may also want to explore BMX  brakes for the rear.  see for example https://www.danscomp.com/odyssey-1999-caliper-brake-lever-set-black-front-or-rear-odb-238-bk/p1823668?v=305193&absrc=Google&abid=731989190380&abcampid=22092768423&abgroupid=178254796207&abkwdid=pla-60140691390&gad_source=1&gad_campaignid=22092768423

Remember the function of the rear brake is to keep the back wheel on the ground.   The front does a lot of the stopping.