Frame alteration - rear triangle modification?

[lawson]

Hey guys, i'm aware i may be shut down fairly quickly for the direction i am wanting to take here, but i thought i'd ask anyway.....

Right, what I'm wanting to do is modify this



I want somebody to rebuild/modify the rear triangle in one way or another to accept a 650b wheel.

Can anybody lend some assistance? Mike

 

[Sketchyxup]

Why would you want to?

Not being antagonistic but curious to the reasoning?

 

[dyna-ti]

Why would you want to?

Not being antagonistic but curious to the reasoning?

Loves bike

 

[mechanical_vandal]

Re:

If he did that would he really be willing to cut it up for 25mm?

 

[lawson]

Re:

I have many reasons for this, but above all else, is to see if I can. Just because.

Much like I fitted a fox shock to a Noleen fork, fitted disc brakes to a non disc bike and made a remote lockout for a shock that didn't have one.

A project to me is just that, modifying for modifying sake.

M

 

[cherrybomb]

Re:

If you really want to give it a go, I'm sure there must be a frame builder local to you in Bristol who could make a replacement rear end.

 

[02gf74]

Assuming 27.5 mm tyres is same height ad 26 in, you are looking at an extra 20 mm.

The simplest and cheapest approach would be to extend the drop outs back by this amount with some gussecs to the chain stays for strength. Cant see how the brake calliper fits to the rear triangle but the bracket for it could be part of it.

This extends wheel base and lifts the rear by 20 mm so geometry is changed, probably in a bad way.

Im guessing for the same amount of money paid to a frame builder to design and build a new triangle you could buy a a 29 frame that will piss on the crummy urt you have there even before its geo has been messed around with.

 

[Osella]

Re:

Remember you've also got to ensure that the front can take a 650b wheel/tyre too..
Many forks will physically fit one, but not under compression (the tyre will contact the brace and...stop.)

If you already have 650b forks, you have no problem; but if not then there are further cost implications.
You may find that a 650b wheel will fit in the back anyway, have you been able to borrow and/or try one?
In this way you can decide perhaps how much modification is required and what the costs will be (esp if you do need a new fork).

Then there's the geo implication, yes you will raise the entire bike, inc BB - you can somewhat overcome this with a shorter shock (again, cost) and you need to remember that the rear wheel, if bigger, will be closer to the seatpost under full compression. Front mech/cable routing may also need alteration.
From that perspective I understand why you ask about modifying/replacing the triangle; but don't forget the forks!

I've done myself a little of what you're suggesting. A '97 Giant ATX990 with discs, running 650b wheels with sensible (2.25") tyres; shorter shock, for geo, etc..http://www.retrobike.co.uk/forum/viewto ... mp;start=0 It's effing brilliant to be honest, fantastic bike, climbs great.
I was lucky however, that the bike fitted the larger wheels comfortably; with mud clearance to spare with no heavy modification required. So I'd suggest that's place #1 to start, less modding needed!

Check out 650bpalace.com, and the original 650b conversions thread on MBR (no registration req'd!) where that originated; there's a wealth of information there inc specific wheel/tyre/frame sizes (in some cases measured in mm) to check cross-compatibility with a number of different combinations.