Morning!

Fancy building up a slack hardtail eventually using my current Rockrider 9.1 as a donor.

I’ve searched and found lots of info about using 26 inch wheels on a 650b frame (fine) and using 650b wheels in 26inch forks (bad) but I can’t find anything out about mismatched frame and forks.

Looking at the geometry charts the only difference is the chainstay length, so does that mean that with 26 inc forks the geo would be the same as a normal 456?

I’ll be sticking 120mm Recons on there if that makes any difference.

Cheers

I doubt the chainstay length is the only difference – the BB height/drop would also be different – you could find your cranks/pedals very low to the ground as a result.

This was in another forum post about wheel sizes, I’m no bike expert but will the BB drop be massively different? I’m used to smacking my pedals off the ground on the full sus.

Do you know/can you find the A-C measurement for the fork you propose to use?

If so have you compared it to the available 27.5″ forks already about? can you adjust the A-C of your forks?

Offset might differ a little bit too, and obviously you’ll be 1/2″ closer to the ground than you would be on 650b wheels.

But I reckon it’ll be fine, there is always the 456 EVO if you’re worried, you could always use one of those for a while and chop it in for a minimal loss should you adopt 650b wheels at a later date…

It’d be useful to know what the BB height is but thats not given on the On-One site. BB height on frames vary so if you knew the frame was designed with a relatively high BB, then dropping 10 odd mm might still keep it with in ‘normal’ BB heights, if a frame has a relatively low BB height already then dropping it could make it too low.

Personally, I say go for it as in practice I’d doubt you’ll really notice…its easy to spend too much time staring at figures

The geometry charts doesn’t state what fork length or static/sagged or the BB height. My guess is that it’s for 140mm static which will be A-C ~535mm. Running a 26″ 120mm fork will be A-C ~505mm and the wheel radius is 13mm less so the front will be ~43mm lower, steepening the angles by ~2 deg and dropping the BB by ~20mm.

Based on a RS 140 650b at 629mm A2C and a Recon 120 26″ at 493mm A2C in geometrycalc the Recon equipped frame would be 67.5 HA, 73 SA, 586mm eTT and a lowing of the BB by 13.3mm + wheel radius difference…hmmm, quite a drop

28mm BB drop, static at 542mm axle to base of head tube. Which is a 140mm Revelation with a 15mm lower headset stack height.

Varying forks affects BB height by 1/3rd of the difference in length.

A standard 456 EVO2 with 26in wheels sits at 17mm static BB drop, and with the nominally 11mm larger 650B wheels.

With HUGE tyres, you’re getting closer running 26in wheels. A 650B fork has a 10mm longer axle-crown dimension than a 26in one. So, statically, a 10mm longer fork has the same stance, though this will vary a bit in sag, but frankly not by much.

As the rear wheel is closer to the BB it’s actually this item that affects BB height mostly. So running a massive rear tyre props the bike up at the back, and then a 150mm fork keeps things better at the front.

Hope this helps.

So far as I recall the “Old” 26″ wheeled 456’s can have BB’s anywhere from ~315mm – 350mm (Ground to Centre) dependant on the combination of Fork and Tyres fitted… that doesn’t actually help answer your question other than the frames typically have quite a range of ride heights due to being quite versatile.

A straight forwards answer to what the BB height (or drop) is meant to be for either model with any sort of reference fork/wheels isn’t really there from OO’s own published numbers, is a tricky one a bit of a “how long is a piece of string?” kind of question…

From the above posted table/illustration you’d think it was a simple as subtracting H (“Stack”) form G (” Standover”) but that just comes up with some odd figures that don’t seem likely to let you estimate a BB position.

All you can really say is that whatever it would be with 27.5″ wheels, it’ll be ~1/2″ lower on 26″ wheels…

And of course that could be offset to a certain extent by a longer A-C forks (although this will slacken the bike a bit too) or if you really want, using larger section tyres, both of which are compromises, but not staggering ones…

A 45650b with 26″ wheels and fork is basically just a slightly longer, slightly lower 456 EVO, if that’s what you’re after, crack on…

EDIT:

Hadn’t seen Brant’s post, seems a bit more useful…

Thanks for all the input chaps, basically in an ideal world the 456 evo 2 would have had a 44mm head tube, there’s not so many options for 1 1/8″ steerer tubes any more.

So is the general consensus it will ride ok, but the BB might be a bit low? I can live with that, I just don’t want to buy a frame and then it but a pos to ride. I would just buy the complete bike but the Mrs has put her foot down. Sad times.

I feel your pain. I have to pay for a new bathroom before new bike.