[BeRad66]

I was thinking about making a front freewheel set up for my Dh bike. I would make a chainring that would attach to a freewheel that would be mounted to the cranks Like a trials bike. Then i would lockout the freehub body on my rear hub to make it "fixed". The rest of the drivetrain would be standard chain cassette and derailure.
Its simmilar to a groupo that shimano had in the early 80's called FFS Front freewheel shifting. The advantage was that you could shift while your coasting with out having to pedel. It also moves a large part of the machanical movement to the center of the bike and removes that weight from the rear wheel. Inturn less sprung weight better suspention feel and the ability to shift while cornering, jumping, and countless othe rsituations im sure.

Most of you probly think im crazy but it was an idea that if been toying with. Anyone else have any comments or thoughts on this consept?? Im looking for reasons to either mothball this idea or try to make it work. Im thinking it might have more value for DS 4x than DH

 

[al-irl]

try it out its one of the advantages of a gear box bike. I think it would be a cool experiment

 

[djivotno]

To make it work, you'll need to block your rear freewheel and this will have the chain moving when the rear wheel is moving. It'll shift when coasting, but the drivetrain will die young out of old age

It's a good idea for 4x racing... but thats about the only place i'd find any use of it. On a DH rig you'll get some better seperation of chain input from suspension but still won't have the value. For the guy who spends his own $$$ for the bike, the rear-mounted freehub is the better idea.

In trials you're better off with that setup, 'cuz you don't spin the wheel as much as the crancks and there it's got a point

 

[epic]

Seems like a great idea at first, but...

What happens when a stick or whatever jumps into your chain? Total drivetrain meltdown.

 

[DirtyMike]

I was thinking about making a front freewheel set up for my Dh bike. I would make a chainring that would attach to a freewheel that would be mounted to the cranks Like a trials bike. Then i would lockout the freehub body on my rear hub to make it "fixed". The rest of the drivetrain would be standard chain cassette and derailure.
Its simmilar to a groupo that shimano had in the early 80's called FFS Front freewheel shifting. The advantage was that you could shift while your coasting with out having to pedel. It also moves a large part of the machanical movement to the center of the bike and removes that weight from the rear wheel. Inturn less sprung weight better suspention feel and the ability to shift while cornering, jumping, and countless othe rsituations im sure.

Most of you probly think im crazy but it was an idea that if been toying with. Anyone else have any comments or thoughts on this consept?? Im looking for reasons to either mothball this idea or try to make it work. Im thinking it might have more value for DS 4x than DH

I like the idea overall, I like thinking outside the box for new innovations. But what I dont see is how it will be lighter at the rear wheel, your still going to have a casette, derailer and hub in the back. your only difference it you have locked the freehub on the wheel, so your not losing or moving any weight. In fact I thik it would overall be heavier, not something that turns me off right away, I mean we are talking about DH here afterall. I can see teh advantage, just not sure if it is practical.

I say go for it though, there is truly only one way to find out.

 

[OBB]

I think you need to revist the littermag.com archives. Its been done (garage builder style)

 

[jonKranked]

I think you need to revist the littermag.com archives. Its been done (garage builder style)

That was an OBD (on board drivetrain). all he's talking about doing is moving the freewheel mechanism from the R wheel to the cranks, not the entire drivetrain.

The ODB link for reference:
http://www.littermag.com/2008/features/featuremenu.php?featureID=1039

 

[Sandwich]

great idea, but if you get a kink in the chain or a jam you're screwed. that's one of my biggest concerns about the homebrew gearboxes.

 

[DhDork]

I was thinking the same thing. An old Schwinn came into my shop with this on it last week, and it seemed great for DH. Shift when coasting so you're always in the right gear.
It'd be difficult to set up, and as Sandwich stated, you would have to make sure the chain never jams up.

 

[Sandwich]

of course, one option might be to move the cassette and derailleur forward, then enclose the entire drivetrain. Drop some oil in it, and you might be able to get away with minimal maintenance.

 

[OBB]

of course, one option might be to move the cassette and derailleur forward, then enclose the entire drivetrain. Drop some oil in it, and you might be able to get away with minimal maintenance.

 

[CarlE]

There's a company called IPS (Independant Pedaling Systems) that make a tandem crank that sounds exactly like what you're describing. Here's a break down on how they do it, http://www.hostelshoppe.com/atp_archives/ips_instructions.pdf.

 

[BeRad66]

I definatly see the issue with the if the chain gets jamed up and drivetrain meltdown. But i think in a slalom 4x situation. After doing more research ifound this out about the old shimano groupo:

"A note: the rear cogset had a limited freewheel action built
into it. If something jammed the chain, this would allow the
rear wheel to continue to turn. It felt like a conventional
freewheel with *really* tight bearings."

Having to do this nullifies my idea of reducing the weight of the rear wheel but it dose saave the drivetrain.

 

[Sandwich]

True, but you wouldn't necessarily need a complete freehub. the thing could have a cheap plastic breakaway pawl or something, where it would only freewheel under backwards force.

In theory, the rear wheel would never have to move backwards compared to the chain. so, if it had to, it would snap the cheapo thing and spin.

 

[gemini2k]

well considering I have a bike that's set up like this (GT IT1) I'll chime in.
DONT DO IT. It's the only real shortcoming of the bike IMO. Yes you can shift while pedaling and yes the chain is less likely (impossible) to fall off if you set it up right, there are a few major drawbacks.
1. It's draggy, a lot more resistance and energy taken up by a constantly moving chain
2. Dangerous. Riding gnarly DH tracks things get kicked up into the chain and tensioner once in a while, which causes the rear end to lock up, NOT FUN at high speeds.
3. If the chain gets jammed or ****ed up, and you dont have a chain tool, you can't even coast your way down the hill :'(. Stick to a normal setup, I've been trying to figure out how I might make mine a regular set up.

 

[TomBo]

Weren't the Honda bikes like this? They seemed to work fine.

 

[gemini2k]

Weren't the Honda bikes like this? They seemed to work fine.

It works just fine 95% of the time, swimmingly actually. But those few times it gets screwed up, or something just goes wrong, its a PAIN IN THE ASS. If you don't have a gearbox setup, completely not worth it.

 

[MrPlow]

Its a good idea and it works.

 

[BeRad66]

Hey Gemini2k can you post Pictures of the setup on that bike particulary the freewheel chain guide area and the rear hub im super intrested in seeing it

 

[Rory]

I did the same thing because I thought it would be interesting. I used tensile ISIS trials cranks which I bolted a DMR chainring to with a fixed trials hub. The hub died and unscrewed digging into the frame in the process. Consequently I didn't use it for long, and it doesn't fit my current bike.

It was 3 seconds faster down my track, about a 1 min 40 sec run. It has promise, and I don’t see why no one is doing it, it was the hub that caused the problems in my setup.

Shifters could also be improved to take further advantage of the benefits it offers, I tried gripshift and triggers but it was still hard to change down gears when braking. The only real issues I had were clearances but if one was to be actually designed rather than just bolting stuff together this wouldn't be an issue.

 

[big cal]

I did the same thing because I thought it would be interesting. I used tensile ISIS trials cranks which I bolted a DMR chainring to with a fixed trials hub. The hub died and unscrewed digging into the frame in the process. Consequently I didn't use it for long, and it doesn't fit my current bike.

It was 3 seconds faster down my track, about a 1 min 40 sec run. It has promise, and I don’t see why no one is doing it, it was the hub that caused the problems in my setup.

Shifters could also be improved to take further advantage of the benefits it offers, I tried gripshift and triggers but it was still hard to change down gears when braking. The only real issues I had were clearances but if one was to be actually designed rather than just bolting stuff together this wouldn't be an issue.

That photo looks awesome. Pretty neat execution by the looks of it, and is that a craftworks FRM125? oldschool!

 

[BeRad66]

What trials hub did you use and what freewheel chain ring cambo did you use.

 

[Rory]

They are FRM125 seat stays but it's a DHR208.

It was a viz freewheel and a DMR saturn chainring that I machined out so it would fit around the freewheel, then bolted on with chainring bolts. The hub was an echo 6 speed fixed hub (my old bike had 135 x 10 drop outs) if I do it again I will just zip tie my cassette and hub, or maybe make my own one piece fixed hub?

 

[MobileChernobyl]

Weren't the Honda bikes like this? They seemed to work fine.

Not really - the first gen 'zero-max' ratcheting cvt model had a freewheeling rear weel, as did the next gen derailure in a box design.

 

[BeRad66]

My current idea is to do what you did Rory use a trials crankset attach a freewheel and machine a chainring to fit over the freewheel. Then take my rear hub and cut a peice of tube or an o ring and put it behind the free hub body thus causing the free hub body to have resistance against turning. therefore it sudo "fixed" but if something gets caught in the chain the freehub body will slip thwarting total drivetrain meltdown.

I first want to try this on my DS hardtail and then go to work on my dh bike.