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Discussion Starter · #1 ·
could you please help me to visualize what complications or possible scenarios I may encounter if I were to remove the linkage system of my Stumpjumper and replace it with one that was made to accomidate a 29" wheel. I do not know any custom frame builders personally. Does this sound like an impossible task, or even one that warrents effort? If I could find someone who would be willing to create such a thing, it seems like if I replaced my 100mm fork with an 80mm fork, then my front end would only be up an additional half inch or so with the bigger wheel.
writing this just makes it sound stupid. some things should just stay in your head, you know? Is this one of them?
 

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Complete Bastard
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I thought about doing this with my epic. I think it can be done. You'll have to offset the rear dropout so you don't end up with your BB too high, and put a 80mm fork on it, and I think it'll handle okay. The big problem is finding someone who can make a rear triangle for you. Custom, one-off, heat treated aluminum. I was going to do it in cromo for those reasons but never got around to it. If specialized won't support 29ers, I will have none of them. Oooh. I've got half a bottle of laphroaig in the bag, take comments with a grain of salt.
 

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It could be done. With a Specialized frame you would not even need to replace the whole rear end. You could keep the swing arm. Design a new dropout/seatstay unit and maybe a new top link.

It would be cool project for a tinkerer with fabrication skills. Otherwise it may be cheaper to buy a new 29" fully frame.
 

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(was) Big in Japan
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I think

We should get BETD to do this for us. After all, they are the Specialized linkage upgrade gurus. You'd be guaranteed that it'd look sweet then too.

shiggy said:
It could be done. With a Specialized frame you would not even need to replace the whole rear end. You could keep the swing arm. Design a new dropout/seatstay unit and maybe a new top link.

It would be cool project for a tinkerer with fabrication skills. Otherwise it may be cheaper to buy a new 29" fully frame.
 

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mward said:
I thought about doing this with my epic. I think it can be done. You'll have to offset the rear dropout so you don't end up with your BB too high, and put a 80mm fork on it, and I think it'll handle okay. The big problem is finding someone who can make a rear triangle for you. Custom, one-off, heat treated aluminum. I was going to do it in cromo for those reasons but never got around to it. If specialized won't support 29ers, I will have none of them. Oooh. I've got half a bottle of laphroaig in the bag, take comments with a grain of salt.
Agree. Either the BB of the bike is going to be very high, which ain't always a bad thing if you can deal with the standover. Or, if you raise the rear DO's to lower the BB, then you'll slack out the STA and HTA. Either way the bottom line is the front Tri of the bike isn't designed for 29" geometry so it's going to be old frame + time + money = less than optimal results. If your money supply is infinite, knock yourself out (and buy me a Deckel-Maho DMU80-FD 5-axis machining and turning center while you're at it). If you're money supply is finite, then IMO, you'd be better off spending it one one of the current properly designed 29 offerings.
 

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DWF said:
Or, if you raise the rear DO's to lower the BB, then you'll slack out the STA and HTA.
Couldn't the DO's be raised just enough that the bb stays at the same height as it is now, raised just enough to offset for the higher axle. Then IF the fork doesn't muck with the front end, he'd be golden.

Monte
 

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shiggy said:
It could be done. With a Specialized frame you would not even need to replace the whole rear end. You could keep the swing arm. Design a new dropout/seatstay unit and maybe a new top link.

It would be cool project for a tinkerer with fabrication skills. Otherwise it may be cheaper to buy a new 29" fully frame.
You could raise the axle position in the dropout to lower the bb height and it might have some of the same affect as a Giant NRS.
 

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Discussion Starter · #9 ·
TheSingleGuy said:
We should get BETD to do this for us. After all, they are the Specialized linkage upgrade gurus. You'd be guaranteed that it'd look sweet then too.
Who is that? Sorry, yet onother abbreviation that escapes me...
It seems to me that there might be a temporary market for someone with the time and inclination to do 29er conversions on certain mid range travel bikes, you know, till folks like Specialilzed get their asses in gear.
 

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rryyddeerr said:
Who is that? Sorry, yet onother abbreviation that escapes me...
It seems to me that there might be a temporary market for someone with the time and inclination to do 29er conversions on certain mid range travel bikes, you know, till folks like Specialilzed get their asses in gear.
BETD is the name of a company in England that makes nice after-market rocker arms and such for Specalized (and other brands) bikes
https://www.betd.co.uk/
 

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featherweight clydesdale
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DWF said:
Either way the bottom line is the front Tri of the bike isn't designed for 29" geometry so it's going to be old frame + time + money = less than optimal results.
This guy knows his stuff.

Don't waste your time and money, unless you've got enough cash to try your experiment and then buy a proper frame after it is over (and not lose sleep).
 

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Just do it, don't listen to people who say you should save your cash and time. Some people get really grumpy when you color outside the lines. I say go for it, build it. It might be friggin awesome. It might suck, but at least it'll be tried. If every time someone with an idea suggested it and then didn't try it after the naysayers said it was a bad idea, I shudder to think of the state of technological innovation we'd be living in.
 

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Discussion Starter · #13 ·
mward said:
Just do it, don't listen to people who say you should save your cash and time. Some people get really grumpy when you color outside the lines. I say go for it, build it. It might be friggin awesome. It might suck, but at least it'll be tried. If every time someone with an idea suggested it and then didn't try it after the naysayers said it was a bad idea, I shudder to think of the state of technological innovation we'd be living in.
I emailed BETD last night and had a response waiting this morning...

"Yeah it seems the 29ers are getting popular now, we dont do a kit at the moment but we may consider making if we get the demand. At the moment it wouldn't be worthwhile. If you have any questions dont hesitate to ask. "

Dan

I may decide to hang on to my stumpy a little longer to see if this eventually pans out. But, everyone who would even think of being interested should email this guy.
By the way, MWARD, thanks for your encouragement. its all just very serious play when it comes right down to it right?
word
 

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rryyddeerr said:
By the way, MWARD, thanks for your encouragement. its all just very serious play when it comes right down to it right?
word
No kidding, it's not like we're airlifting orphans out of Somalia here. There is a machinist local to me who said he'd do a modification like this once but I never got around to it. He rides, quit savvy on the bike design and has built a few creations including a pedal-powered replica of an early 1900's milk delivery truck in 1/3 scale.
 

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What the F#%*

Yo dude, you should ride on in the snow and ice first...convert a 26? C'mon....! Geezzze....bet you ain't never even been to New England either....Ugh.
 

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mward said:
Just do it, don't listen to people who say you should save your cash and time. Some people get really grumpy when you color outside the lines. I say go for it, build it. It might be friggin awesome. It might suck, but at least it'll be tried. If every time someone with an idea suggested it and then didn't try it after the naysayers said it was a bad idea, I shudder to think of the state of technological innovation we'd be living in.
We're not talking technological advances here. We're talking about easy to understand changes in geometry on a bike that already has its tubes in a fixed relationship. The headtube's height relative to the BB is already determined. If you increase tire radius and increase fork length, you are going to increase BB height and standover. If you try to regain BB drop by raising the rear wheels axle relative to the BB, you are going to slack out the angles. Either way, it's not going to be a well designed bike and the results aren't going to be that great either. Nobody has said he "can't" do it, us grumpy types are just answering his questions and giving him the feedback he requested.
 

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Recovering couch patato
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At first I didn't see the problem. But let's add up :
Going from a 100mm fork to 80 > -20m
Going from a 26" to 29" fork > + ~30mm (31.5mm at an angle
Going from a 26" to 29" front wheel > full 31.5mm taller
Total : a good 40mm taller BB. More than an inch and a half.
Over taking away half of that by placing the rear wheel way up higher than before will still make the bike feeling like a choppered out DH bike.

Your chances may be much better with a bike designed around a 5" fork, prepared to take 6". Going to a 80mm 29" fork would correct for most of the front end height, though still not all. But you'd be converting a perfectly fine FR bike into a slow handling XC 29"er.
 

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Cloxxki said:
At first I didn't see the problem. But let's add up :
Going from a 100mm fork to 80 > -20m
Going from a 26" to 29" fork > + ~30mm (31.5mm at an angle
Going from a 26" to 29" front wheel > full 31.5mm taller
Total : a good 40mm taller BB. More than an inch and a half.
Over taking away half of that by placing the rear wheel way up higher than before will still make the bike feeling like a choppered out DH bike.

Your chances may be much better with a bike designed around a 5" fork, prepared to take 6". Going to a 80mm 29" fork would correct for most of the front end height, though still not all. But you'd be converting a perfectly fine FR bike into a slow handling XC 29"er.
No negative on the fork length. A short 29 fork is about 470-475. A 100mm 26" fork is about the same (for instance a Fox Float 100 which is a relatively tall 26" 100mm fork is 471). If the bike in question was designed for an 80mm fork, the a ballpark length for them is 440-450.
 

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Discussion Starter · #19 ·
mean old hardened fisherman eric

ERoman said:
Yo dude, you should ride on in the snow and ice first...convert a 26? C'mon....! Geezzze....bet you ain't never even been to New England either....Ugh.
Translation: "NYAA NYAA, STUPID SOUTHERNER"
all these northerners are so MEAN. at least the folks in georgia were nice to my face, even if they didnt mean it...
 

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No, but you also have the 31.5mm taller front axle to put it on, that's why I think a 100mm front travel frame is still undersized for the project. And even if you manage to keep it exactly the same height after sag, still the 29"er will have longer trail thus handle slower, unless someone gets busy and makes that 45+mm offset suspension fork happen.
 
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