Magic Ratio for Single Speed. Any Experiences?
- Thread starter Thame Game
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Thame Game
Retro Guru
I've ordered a ZTTO tensioner to try out. The half link method sounds good except I'll be running an Izumi 'jet black' chain which has gold pins. Where would I get a march for that 1/2"?
Ive had ZTTO bits before. Made somewhere in China, but the CNC work looks good. Can't get any other colour than purple, but I'm guessing that will swap out.
https://ebay.us/m/4tLbvp
Ive had ZTTO bits before. Made somewhere in China, but the CNC work looks good. Can't get any other colour than purple, but I'm guessing that will swap out.
https://ebay.us/m/4tLbvp
Gtpulse
Dyna-Tech Fan
Izumi Half Link you could maybe change the screw for a gold one? Probs you won’t need a half link if you’re running a tensioner.
Thame Game
Retro Guru
Excellent recommendation.
Uncle Grumpy
Retro Guru
Eccentric hub (White Industries).
Eccentric BB (which will mean an outboard bearing type crank which I assume from the chainring being "non-optional" that you want to keep the cranks so an eccentric BB might be out of the question).
Half link, or half link type BMX chain.
As noted above, the chain will wear and you will need to take up the slack over time. I'd run a tensioner or a derailleur set to the right chainlink and be done with it. May not look as simple as a dedicated single speed but that's what happens with a conversion of a gearie to a single speed.
Or learn brazing, sweat the dropouts out and braze in some track tips. No such thing as overkill.
Eccentric BB (which will mean an outboard bearing type crank which I assume from the chainring being "non-optional" that you want to keep the cranks so an eccentric BB might be out of the question).
Half link, or half link type BMX chain.
As noted above, the chain will wear and you will need to take up the slack over time. I'd run a tensioner or a derailleur set to the right chainlink and be done with it. May not look as simple as a dedicated single speed but that's what happens with a conversion of a gearie to a single speed.
Or learn brazing, sweat the dropouts out and braze in some track tips. No such thing as overkill.
Thame Game
Retro Guru
Are the jockey wheels compatible with other dérailleurs? Purple is Out for me.
Done it loads of times in the past. The Magic Gear calculator is excellent to get you in the ball park and try combinations.
In my experience a brand new chain can quickly develop some slack - which is sort of frustrating when experimenting. Always found it best to use chains from a bike with a derailleur first for while. I would always keep low wear chains back for future fiddling about. Also tried one half link, but it was crap and was certainly the weakest link to be honest. Didn't get along with the Gusset tensioner either - rusted to hell in one winter. An old super short cage mech like 105 would have been better.
The best modification / trick I did was file the rear axle where it meets the drop-out in a progressive "cam" shape - dead easy and good enough to take up most chain slack. St Sheldon mentions the "kludge" here, but he filed a flat on the axle.
https://www.sheldonbrown.com/no-derailers.html#workarounds
Plenty of spare rear axles about so it is also a reversible hack so to speak. Would not recommend filing the drop-outs.
In my experience a brand new chain can quickly develop some slack - which is sort of frustrating when experimenting. Always found it best to use chains from a bike with a derailleur first for while. I would always keep low wear chains back for future fiddling about. Also tried one half link, but it was crap and was certainly the weakest link to be honest. Didn't get along with the Gusset tensioner either - rusted to hell in one winter. An old super short cage mech like 105 would have been better.
The best modification / trick I did was file the rear axle where it meets the drop-out in a progressive "cam" shape - dead easy and good enough to take up most chain slack. St Sheldon mentions the "kludge" here, but he filed a flat on the axle.
https://www.sheldonbrown.com/no-derailers.html#workarounds
Plenty of spare rear axles about so it is also a reversible hack so to speak. Would not recommend filing the drop-outs.
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I've have had and still have several singlespeed bikes and have used a 'magic-ratio' a few times. I also have bikes with eccentric BBs, horizontal, slotted and adjustable dropouts too.
I've used tensioners but prefer the clean aesthetics of not having to use one. The Rohloff tensioner I have somewhere is rather nice though.
In my experience, the chain doesn't need to be super tight to stay on and by the time it's worn enough to generate too much slack it's more than likely it's time for a new chain anyway.
1/8th track or BMX chains last forever, with 6/7/8 speed not far behind in terms of longevity.
It also helps to use singlespeed specific, or at least non ramped chainrings and sprockets. The taller, unramped teeth naturally do a much better job at chain retention than chainrings designed for shifting.
My most used singlespeed is built around a custom made frame with Paragon machine works dropouts and does a few thousand kilometers each year.
For high mileage SS I'd avoid magic ratios as you are stuck with limited gearing choices.
Anyway, here are a few examples that have worked for me...
1990 Saracen Tufftrax - 34:15 magic ratio
1990 DiamondBack Ascent : 36:18 magic ratio
1991 Saracen Sahara - 34:18 magic ratio
1993 Raleigh K2 Apex - 40:16 with rear mech for tensioner
2005 DMR Trailstar - 34:18 magic ratio
2016 Holdsworth La Quelda - 42:16 horizontal dropouts
2009 Kinesis Decade Convert 2 - 42:16 modular horizontal dropouts
2014 Genesis Day One Disc - 39:18 horizontal dropouts
2022 Danson Custom - 42:17 adjustable dropouts (Paragon Machine Works)
I've used tensioners but prefer the clean aesthetics of not having to use one. The Rohloff tensioner I have somewhere is rather nice though.
In my experience, the chain doesn't need to be super tight to stay on and by the time it's worn enough to generate too much slack it's more than likely it's time for a new chain anyway.
1/8th track or BMX chains last forever, with 6/7/8 speed not far behind in terms of longevity.
It also helps to use singlespeed specific, or at least non ramped chainrings and sprockets. The taller, unramped teeth naturally do a much better job at chain retention than chainrings designed for shifting.
My most used singlespeed is built around a custom made frame with Paragon machine works dropouts and does a few thousand kilometers each year.
For high mileage SS I'd avoid magic ratios as you are stuck with limited gearing choices.
Anyway, here are a few examples that have worked for me...
1990 Saracen Tufftrax - 34:15 magic ratio
1990 DiamondBack Ascent : 36:18 magic ratio
1991 Saracen Sahara - 34:18 magic ratio
1993 Raleigh K2 Apex - 40:16 with rear mech for tensioner
2005 DMR Trailstar - 34:18 magic ratio
2016 Holdsworth La Quelda - 42:16 horizontal dropouts
2009 Kinesis Decade Convert 2 - 42:16 modular horizontal dropouts
2014 Genesis Day One Disc - 39:18 horizontal dropouts
2022 Danson Custom - 42:17 adjustable dropouts (Paragon Machine Works)
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Oh and don't bother with half links.
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