I’m looking at a new frame which only comes in 650b. I’ll be buying the frame and a 650b fork to go with it. I’d rather run my 26″ wheels as I have a load of tyres, some of which aren’t even available in 650b yet.

BB height of my 26″ frame is 335mm

BB height of the new 650b frame is 345mm

Front and rear travel of the frames are basically the same.

Taking into consideration the 12mm difference between the radius/BB height, swapping to 170mm cranks will get my a tiny bit more clearance, so I’m assuming everything will be fine and dandy?

I’m assuming the trail will be slightly different between the forks, but is there anything else I’ve overlooked? (Trails not coming alive has been factored in)

I only hope you have life insurance cover !

Check the BB drop rather than height… height means little when comparing just frames, because it depends what build the bike is. No?

Surely the humiliation that you will endure from the on-trend 650b crowd will make life not worth living and death very attractive in comparison! 😆

The trails will die, so will kittens.

Unless the wheels/tyres say “these are not 650b” in massive letters I doubt ANYONE will ever notice.

I’ve got 26″ wheels in a 650b fork and frame that claims to allow both.

I’ve not died yet. Although I have to confess I haven’t actually ridden it yet either.

You’ll be fine. What’s the old and what will the new be?

Check the BB drop rather than height… height means little when comparing just frames, because it depends what build the bike is. No?

Didn’t think BB drop would make much difference, other than stability.

The trails will die, so will kittens.

And puppies, whole sacks of them.

You’ll be fine. What’s the old and what will the new be?

Old is a Stumpy Evo, new is a Foxy.

Old is a Stumpy Evo, new is a Foxy.

Ride the Evo until you’ve worn out the tyres?

I run 26″ wheel in my 650b fork and am still here and a 26″ on the back as it is a 26 frame

Cat is also still around 🙁

That’s what I ride^

I’ve got a 160 fork up front on a 140mm Lapierre and it was pretty awful at full travel but offset bushes make a difference. The biggest being – it feeling quicker in 130mm travel up front, which is around 4mm higher than the fork that came with it. I tried 650 xc wheels in it before the offset bushes but I nearly fell off it on the first turn during a carpark test so decided against splashing out. Looking forward to having a 650×2.8 on a wider rim up front as soon as a certain tyre comes into stock.

Old is a Stumpy Evo, new is a Foxy.

The Foxy has a lot more anti-squat than the Stumpy so should be less prone to strikes when pedalling.

The Foxy has a lot more anti-squat than the Stumpy so should be less prone to strikes when pedalling

No idea what anti-squat is, but it sounds cool, so it must be good.

No idea what anti-squat is, but it sounds cool, so it must be good.

Exactly. 😀

P.S. It’s the difference between a frame that bobs up and down when you pedal (unless you add lots of damping/platform/lockout on the shock) and one that puts all your efforts into going forwards.

P.S. It’s the difference between a frame that bobs up and down when you pedal (unless you add lots of damping/platform/lockout on the shock) and one that puts all your efforts into going forwards.

Ah marketing guff for pedal bob 😆

Almost as bad as running 1.8″ tyres when the frame was designed for 2.4″ ones – that’d make a similar difference to wheel radius

Check the BB drop rather than height… height means little when comparing just frames, because it depends what build the bike is. No?

Hmmmm, OP’s thoughts make perfect sense to me.

BB drop remains the same as it’s measured relative to the axles, drop the axles 12mm, drop remains the same BB height reduces by 12mm also….

This is all static, of course suspension sags, reported numbers are simply a loose indication of how a bike might ride.

Marginally smaller wheels will be fine, give it a whirl…

Ah marketing guff for pedal bob

No, engineering guff – if it was marketing guff you’d read about it in reviews…

Engineering guff, even better!

I’m thinking of doing this to save my trail wheels on an uplift to Antur, which can be pretty hard on wheels and tyres! My cranks are 170mm and pedals only 12mm thick, so should be fine?!

Quoted BB height is useful for comparing bikes, but depends on wheels, tyres, forks, sag etc, so if working out what your build will be like BB drop is the place to start, as it doesn’t include all those variable that don’t apply in the same way to your build with different choices being made. BB height is ultimately the thing that matters in this case, I agree that it is ultimately what you are trying to work out, but comparing two sets of manufacturers BB height figures is fruitless when comparing frames rather than bikes, whereas their BB drop measurement methods should be a bit more consistent.

You are going to have a low BB but apart from that it will be fine.

You’ll be fine, some frames are made for both sizes so it obviously can be done…didnt some bloke at last years mud-fest Megavalanche put 26 inch wheels in his 650b for better mud clearance and do rather well?!

throw all your numbers in and what you come out with is a BB that will be about 4mm lower than you currently have BUT the new Mondy frame IS designed not to squat under load so much. The result? “Pretty f**king close to what you have now” So close in fact that I doubt you would even notice it at all. Forget the frame clearance on rocks for a minute though and tell me honestly, that you are worried about hitting your BB? Honestly??? I’d be more worried about smashing the teeth off my chainring which sits another 70mm lower than your BB. Have you thought about it that way before with your old bike? If not, dont worry about the whole situation because it’s obviously never been an issue.

Cats and dogs will be fine, birds will still tweet and your Mrs will undoubtedly come home with yet another pair of shoes because you have a new bike… take the cost of the shoes on the chin and be content with ‘getting one over’ on the world. The Geometry of the frame will be unchanged, you’ll just be half inch closer to the ground at the axle points from where the designers intended… and they wont give a sh*t.

You’ll be fine, some frames are made for both sizes so it obviously can be done…didnt some bloke at last years mud-fest Megavalanche put 26 inch wheels in his 650b for better mud clearance and do rather well?!

Yeah – it was Karim Amour, European champion. He and quite a lot of the Frenchies did!