Combining a single sprocket with triple chainset

[Yellow Fang]

Is it possible to combine a single sprocket on the back of a MTB with vertical dropouts, possibly using one of those conversion kits, with a triple chainset. Could you bodge an ordinary rear derailleur to take out the slack? If not, could you use a single-speed chain tensioner, or wouldn't that be able to cope with the large changes in chain slack?

 

[Landslide]

If not, could you use a single-speed chain tensioner, or wouldn't that be able to cope with the large changes in chain slack?

Probably not.

 

[Will1985]

Can't see why not with a derailleur - chainline would have to be straight on the middle chainring.
Never tried it, but would the derailleur stops be long enough? Can't imagine they would be too hard to swap for longer ones if necessary.

 

[ColinJ]

What would the difference be between singlespeed at the back, and having 8/9/10/11 sprockets (whatever)?

It would only be like having a multi-geared cassette but staying in one gear.

Why would you want to do that? If you are using a rear derailleur to tension the chain, why not use it for changing gear?

Surely the good things about singlespeed are lower cost, reliability, simplicity, weight reduction, and forcing yourself to get stronger. By doing what you are suggesting you'd lose the simplicity of singlespeed without gaining the full advantage of gears.

 

[MartinC]

Bodge a rear mech - yes that will work, just lock down the adjustment so that it's in the right place. You may need longer screws to get it where you want. This is what you do on the roadside when the rear gear cable breaks - so you can ride home with 2 or 3 useful gears.

A single speed chain tensioner almost certainly won't have enough capacity but a Shimano Alfine one probably will - it's a bit like a rear mech.

 

[Yellow Fang]

What would the difference be between singlespeed at the back, and having 8/9/10/11 sprockets (whatever)?

It would only be like having a multi-geared cassette but staying in one gear.

Why would you want to do that? If you are using a rear derailleur to tension the chain, why not use it for changing gear?

Surely the good things about singlespeed are lower cost, reliability, simplicity, weight reduction, and forcing yourself to get stronger. By doing what you are suggesting you'd lose the simplicity of singlespeed without gaining the full advantage of gears.

I'm just wondering what my options are. I have been having lots of trouble with my gears recently, and I don't want to waste too much more money on them. My current theory is some of the sprockets are worn, but it might be the gear hanger's not been bent back quite straight. I have quite a good quality chainset and it would be a shame not to use it.

 

[RedBike]

A cheap new cassette and a single speed conversion kit are probably about the same price. A secondhand rear mech and a chain tensioner are about the same price. So it probably wouldn't cost much more to repair your gears than you were planning on spending convert to '3' speed.

The BIG advantage of single speed is the chain no longer goes through the rear mech and you have a perfect chainline. The efficency gain from removing the rear mech from the bike are massive!

To demonstate this lift the rear wheel off the ground on a geared bike and a single speed bike and spin the wheel.
On a single speed bike you should see the pedals whirl round too. The system is so efficient that it's easier for the cranks to turn than it is for the rear wheel to 'freewheel'
Now spin the rear wheel on a geared bike and the freewheel will kick in and the pedals will stay still. The force needed to pull that chain through the rear mech is more than whats required to activate the freewheel.

Your conversion would still have the rear mech and a poor chainline so your drivechain wouldn't have the efficiency of a single speed.

Have a look at the surly Dingle. This is a sort of two speed system for fixed gear bikes. You could do something very similar but single speed.

 

[Yellow Fang]

Sounds very interesting, but don't you get the same loss of efficiency with a chain tensioner as a derailleur? I'd need one or the other because of the vertical dropouts.