Singlespeed to TWOSpeed conversion

4kicks

Is it possible to convert a single speed bike to a "twospeed" by having two chainrings, an FD and a chain tensioner at the back?

Ive got a nice singlespeed road frame, but find running a 44-16 round here a bit tough on the knees on some of the climbs, wheras I like the ratio for most situations. Im wondering if a chain tensioner can take up the slack associated with say a 36/38t inner ring...Guess the chain line would be "suboptimal" but dont see why this shoudl be more so than any normal geared bike..would it need to be a singlespeed with a ratchet hub, or could this also work for a fixie?

Any ideas?

meagain

Hmmm! Can't see any reason in principle why a 2 speed freewheeler as you describe would not be possible. I've tried a couple of chain tensioners in the past but I really can't recall whether either would have had sufficient "spring" for your purpose. A rear mech locked via adjusters into one plane presumably would be fine. As you say, a compromise chain line should not be a problem (tho' might run a bit rough through either a mech or a tensioner?

Fixed a different matter. Conventional (and I guess correct) wisdom is that NO tensioner strong enough to take reverse thrust!

There IS a system whereby with a double fixed sprocket and carefully matched double up front can give two ratios with same chain length and hance axle placement. Manual operation however.

Rivendell did a very nice 2 (possibly 4?) ratio "single speeder" a couple of years ago - can't recall its name. If you can find pics might throw up some ideas?

MrHulot

I don't reckon a tensioner would take up enough slack for you. Also to allow you to change the front clanger the chain would have to be too loose to use as a fixed. What you have described is just a geared bike when you change with the front mech in that the rear mech takes up the chain slack. So if you ran a singlespeed - with freewheel - and fit a rear mech adjusted and fixed to give a good chain line - no cable/gear change - then you could just select with the front mech as usual.

mrushton

You need to go to www.paulcomp.com and then the single speed section and look at the Melvin which is a tensioner that will let you do this. I think. HOWEVER, Paul components are crafted bits of kit so poss. expensive.

meagain

so poss. expensive

$75 stateside - don't think I've ever seen one for less than that in gbp here.

Pirahna

Get an old Sturmey 2 speed fixed hub.

bracestower

Good luck with finding a Sturmey 2 or 3 speed fixed hub - those things rarely come up and go for £££.

I agree that a conventional chain tensioner probably will not work.

Not really sure what the point is though? Sounds like you're after a geared bike but don't want to admit it.

4kicks

Agree once you get to a full RD with stops it would be a "geared but dont want to admit it", but I just want something a bit less faff than I have with my 20 speed...willll look at the Paulcomp, thanks..

TractionControl

Hubstripping.com are selling NOS F&S Duomatic and Automatic 2-speed hubs for 100 Euro each - I haven't a clue what they're like but they look interesting.

If you just want less faff than a 20 speed then there are other hub gears to consider - the general consensus seems to be that Sturmey-Archer make the best 3-speed hub, SRAM the best 5 or 7-speed plus Shimano Alfine/'red band' premium version Nexus for 8 speed hubs, though some of these options might be too expensive for you.

GaryGkn

Have a look at the Quickbeam. I am sure that is the Rivendell bike with the attributes that you are after.

http://www.63xc.com/george/qb.htm

http://home.earthlink.net/~rivromulus/quickbeam.html

meagain

"the Quickbeam"

That's the one! I enquired about buying one a few years ago: P&P price they quoted rather implied they didn't want to ship one!

GaryGkn

Get Mercian to build you a better version they can angle the fork ends but I don't think they do cantis on there frames as a rule and you would want them.

meagain

Not as well off now as when I seriously contemplated the Quickbeam - a custom built Mercian way out of my spending power! And given likely economic climate that is fast approaching it's time to batten down the cash hatches I reckon!

That's why there are four hundred quid bikes in the "shed" - doubt I can lose more than a twenty on each of them!

GaryGkn

See what you mean the credit crunch may hit the bike world especially as most people will think £79 in a Halfords sale is the most they want to pay for a new bike with out the credit crunch.

meagain

Never mind the credit crunch (selfishly, it won't really impact on me), it's inflation (especially on non-discretionary spend) that is going to hurt those on (relatively) fixed incomes. It will almost certainly cost (sic) Labour (for want of a better term) the next election.