Yet Another Cycling Forum
General Category => Freewheeling => Velo Fixe => Topic started by: rogerzilla on 18 August, 2018, 08:44:15 pm
-
One question that is often asked on forums by those new to fixed is "what chainring and sprocket should I choose?". On low-budget fixie conversions, you'll probably be re-using a chainring (since they're more expensive than sprockets of the same quality) so this simplifies things a little.
A good starting point for road use, in terms of gear inches, is 70". This equates to 48 x 18 (most track chainsets have 48T as default), 42 x 16, 52 x 20 or 53 x 20 on a 700c wheel. These feel subtly different; the bigger chainrings are smoother and less sensitive to your chainring being not-quite-circular, but there is a small weight penalty, mainly from the additional chain links. They all work well enough.
70" may seem quite high if you normally spin derailleur gears at 100rpm or more, and you won't be able to really spin this gear on the flat unless you are very powerful. However, the important thing with a fixie is to choose a gear such that you're not spinning out on the downhills, and let the flats and the climbs look after themselves. Fixies climb well even when they might seem to be hopelessly overgeared.
For velodrome use 48 x 15 is typical for a 250m velodrome or larger. For the very small 1/7 km track at Calshot, 48 x 16 (or equivalent - 48 x 16 happens to be a dreadful choice, as I'll explain below) is recommended.
Some people ride velodrome-sized gears on the road, and it works fine for them. They'll find downhills easier and climbs a bit harder.
For time trials the sky is the limit. Traditionslly, TTs were ridden on a medium gear, which was 72" on a 27" wheel, or the usual 48 x 18. These days, short TTs are more like weightlifting on bikes and gears of up to 125" (56 x 12) are not unheard of. It's about having a gear high enough that you can get power down at all times, even on downhill sections. You don't want your feet to be merely following the pedals in a race..
When choosing chainrings and sprockets, avoid those that are a direct multiple, such as 48 x 16 (48/16 = 3). The power strokes will always be on the same teeth at the poor little sprocket and it will wear unevenly and quickly. Ideally the chainring teeth/sprocket teeth should be an irrational number (hence choosing chainrings with prime-numbered teeth is often recommended). Even on a 48 x 15 setup, a used sprocket will show an uneven wear pattern repeating every third tooth (both 48 and 15 are divisible by 3). None of this happens on bikes with derailleur gears because the chain jumps and slips during gearchanges and the chainring and sprocket are not in lockstep with each other.
If you do skip-stops (not that I know anyone who does), the above is even more important, as it also evens out the wear on the rear tyre.
Try to avoid sprockets smaller than 15T as they are less efficient due to the tight radius of the chain. Sometimes you have no choice, e.g. on an MTB conversion where a chainring larger than 40T would hit the chainstay.
Finally, choose good sprockets as cheaper ones can be noisy, soft or have poor threads which can strip your hub. EAI are probably best, and are quiet out of the box, but Surly and Shimano Dura-Ace are also good. The Shimano ones do need a fair bit of running in until they're quiet.
-
Good advice.
The wisdom of the ancients for road fixed was 66-72". I find that the start-stop of city commuting can be tough on my knees when using higher gears.
-
I Audax and commute on 48*16. Never really thought about the effect on sprocket wear but I do swap chains, chainrings and sprockets quite often and don’t skimp on component costs.
TT bike has a 14t sprocket on the disk now as well.
Turns out I’m doing it all wrong.
-
When choosing chainrings and sprockets, avoid those that are a direct multiple, such as 48 x 16 (48/16 = 3). The power strokes will always be on the same teeth at the poor little sprocket and it will wear unevenly and quickly. Ideally the chainring teeth/sprocket teeth should be an irrational number (hence choosing chainrings with prime-numbered teeth is often recommended). Even on a 48 x 15 setup, a used sprocket will show an uneven wear pattern repeating every third tooth (both 48 and 15 are divisible by 3). None of this happens on bikes with derailleur gears because the chain jumps and slips during gearchanges and the chainring and sprocket are not in lockstep with each other.
just being pedantic and adding that the above multipliers are irrelevant on ss bikes as well (i.e. no derailleurs) as the rear sprocket changes it's rotation position randomly every time the bike coasts. i am happily running 48x16 which is a great ratio for not too hilly terrain.
edit: as pointed out by lwab the relevant position of the sprocket doesn't change when coasting (i was thinking about the tyre's load/skid patches which do change), but for some reason i have not experienced irregular wear on the teeth at all. maybe there are differences at microscopic level, but do they really matter?..
-
A SS sprocket doesn't change its position relative to the chainring when coasting, so the concentrated wear problem still exists. A geared bike changes relative positions of chainring and sprocket every time the rider changes gears.
That said, I've not found concentrated wear to be a major problem but YMMV. Perhaps I have flats often enough to mitigate the effects.
-
70" may seem quite high if you normally spin derailleur gears at 100rpm or more, and you won't be able to really spin this gear on the flat unless you are very powerful. However, the important thing with a fixie is to choose a gear such that you're not spinning out on the downhills, and let the flats and the climbs look after themselves. Fixies climb well even when they might seem to be hopelessly overgeared.
Doesn't it depend on how fast you can ride? I would say choose the gear that lets you pedal with your choice of effort on the flat with no wind, and let the up and down hills sort themselves out.
For velodrome use 48 x 15 is typical for a 250m velodrome or larger. For the very small 1/7 km track at Calshot, 48 x 16 (or equivalent - 48 x 16 happens to be a dreadful choice, as I'll explain below) is recommended.
So you ride faster on a smaller track and slower on the bigger track?
When choosing chainrings and sprockets, avoid those that are a direct multiple, such as 48 x 16 (48/16 = 3). The power strokes will always be on the same teeth at the poor little sprocket and it will wear unevenly and quickly. Ideally the chainring teeth/sprocket teeth should be an irrational number (hence choosing chainrings with prime-numbered teeth is often recommended). Even on a 48 x 15 setup, a used sprocket will show an uneven wear pattern repeating every third tooth (both 48 and 15 are divisible by 3). None of this happens on bikes with derailleur gears because the chain jumps and slips during gearchanges and the chainring and sprocket are not in lockstep with each other.
Err...you could just take the wheel out and put it back in etc, I wouldn't let it affect my choice of gear.
Finally, choose good sprockets as cheaper ones can be noisy, soft or have poor threads which can strip your hub. EAI are probably best, and are quiet out of the box, but Surly and Shimano Dura-Ace are also good. The Shimano ones do need a fair bit of running in until they're quiet.
Shimano Dura-Ace sprockets are good quality and are relatively cheap but don't do bigger than 16 t, otherwise there wouldn't be any need for EAI or other brands.
-
My favourite fixed wheel gear is 44 x I8, gives me a gear in the mid sixties, very good for Warwickshire's rolling countryside. If I'm going well I might go up to 46 x 18 and a gear in the high sixties.
-
hubner, 48 x 16 is a lower gear (slower) than 48 x 15. Very tight tracks have noticeably higher G-forces (rolling resistance) and need a lower gear to accelerate out of the bends, particularly with less distance between the last bend and finish line. The biggest tracks are outdoors with slower surfaces and adverse wind slowing riders. Indoor tracks around 225-300m tend to be the fastest and need the highest gears. I understand that world-class trackies are running over 100" nowadays. I never got above 95" on the track, except for motorpacing, but often used 90-94" as I was more comfortable with a couple of extra gear inches than most on the velodrome.
-
The wisdom of the ancients for road fixed was 66-72". I find that the start-stop of city commuting can be tough on my knees when using higher gears.
I was advised 63-66" by my club in the 1970s. This was in the context of riding through the winter, then adding a few inches for the season-starter medium gear 72" race.
There again, I'm not going that fast...
-
I was in sub-tropical Oz, so riding through the winter there was a little different to doing it in Britain. Significantly colder weather tends towards lower gears.
-
My Reid has 46-16 and the calcumalatoriser I looked at, Sheldon's, puts that at around 76". I am a slow rider and can't spin due to Neurological "Stuff" but I find it a bit low for me. I need to drag the rear brake on, even slight, downhills. Would I be better with bigger at the front or smaller at the rear?
(It's a Flip-flop hub so the freewheel side is okay at that ratio)
-
Any chainring/sprocket combination where the highest common factor is 3 or less is ok for evening out sprocket and tyre wear (which occurs through scrubbing on the road even if you don't skid) even for real up-and-down pedal mashers.
Singlespeeds are immune to the tyre scrub problem because sprocket and tyre are not fixed in relation to one another, but 48 x 16 fixed will give you very uneven tyre wear if you ride out of the saddle much. (Added "fixed" to last sentence for clarity)
-
highest common factor
"greatest common divisor"
-
highest common factor
"greatest common divisor"
"O" level maths was a long time ago ;D
-
I'm TTing on a fixie that I originally built for commuting running 42x16. It's currently got a 52x16 on it - the sprocket is pretty worn (and the 42 tooth chainring is pretty knackered), but the 2 unused sprockets I have (16 and 15) are both 1/8, and the chain (and chainrings) I have are currently 3/32. The PCD is 122mm.
That PCD is an obsolete Stronglight one - there are some NOS rings about but they are all 3/32 and £30 (and they aren't going to be around for ever). Am I better off just getting a track crankset (or a road crank with a sensible pcd) and going all 1/8th?
-
I got it wrong! The Reid is a 46X18. Had a few more rides and, on reflection, I can cope with that ratio for the time being. When I do change, Rogerski says 48X16 ain't good, Would 46X16 be okay?
-
Mine's 44/16 which I'm very happy with. It may be a little high for optimum on the flat but I'm a bit of a grinder on climbs anyway and I like not having my legs flailing around on the descent.
-
Cheers, bludger. Neurological Damage means I have no "Fast Twitch" muscle co-ordination, can't spin at all. 46/16 feels a little low for me but Acceptable.
-
47/16 is very good.
-
A question , is there any theoretical advantage and or actual advantage to riding larger chainring / larger sprocket , as in 51/19 etc...
-
I've always ridden 43x17, except when I haven't; never competed on fixed.
Currently it's on 43x18 for the sole purpose of making friends laugh as they follow me downhill.
-
94" is where it's at :)
-
94" is where it's at :)
'It' might be there, but I'm not.
-
My heavy winter bike is 64"
My light summer bike is 72"
I'd be fairly happy anywhere between the two but it depends on the bike and your individual ability to spin a low gear and/or grind up hills in a bigger gear.
You can't have a perfect single speed gear ratio but that's the whole point, you don't waste time thinking about gears, you just get on and spin/grind the one you have.
-
94" is where it's at :)
That’s my dual carriageway race gear. Takes a little time to wind it up.
-
67.33" according to http://www.bikecalc.com/gear_inches
-
I'm a low 60s (inches) rider for every day use currently 42x17. Have done a 58 minute 25mie TT on 81" in my day.
-
A question , is there any theoretical advantage and or actual advantage to riding larger chainring / larger sprocket , as in 51/19 etc...
Yes, it feels smoother due to lower chain tension and is less sensitive to things being not quite round. Weighs slightly more. Actually, all this is in the OP.
-
43x17
Best gear ever. The combination of two primes makes for even chain and tyre wear and a beautifully smooth ride.
-
I'm warming to 47 x 18. I liked 52 x 20 a lot, but 20T EAI sprockets are no longer imported, it seems. I have 42 x 16 on a bike at the moment and it's a bit harsh for my liking.
-
Currently on 44 x 17 but it's a tad high for Morth Mcr so I have a 46 x 18 to try. Originally started with 48 x 19 which seemed spinny but comfortable. Interestingly I can now hold a slightly bigger gear uphill on my road bike as a result of the 44. Might try 43 x 17 and never thought about odd/even numbers and wear
-
I have a 47T chainring, which is nice because it's a prime number. I typically either use 65" or 69" gearing which are 19T and 18T respectively.
-
I have a 48 tooth ring on my new crankset. I have 15, 16, 17, and 18 tooth cogs - I figures 18 was probably a reasonable all round gear and the smaller ones would be good for TTs next year. Stupidly, I'm supposed to be doing a hillclimb in a couple of weeks, and I reckon 48x18 might be pushing it on that. Maybe 48x19 would be fine. Means I need yet another sprocket! ::-)
I used to ride 40x16 everywhere, which matches up reasonably well to 48x19.
-
43x17
Best gear ever. The combination of two primes makes for even chain and tyre wear and a beautifully smooth ride.
I'm due to replace 42 x 16 on my Pompino soon.
I'm tempted to give this a try.
-
The street fixie nerds in the US swear by a 19T rear cog because you nearly always get 19 skid patches and no coincidence of teeth (at least, not unless you pick 57 x 19, which would be unlikely and expensive). Prime-numbered chainrings are better than prime-numbered cogs, though, because they absolutely guarantee no concentrated wear.
-
I now have a 48 tooth chainring, and sprockets from 14-20 teeth for my TT/hillclimb fixie.
In order to get it to work properly on the turbo trainer, I'm going to have to get a lower gear than 48x20 though. I have seen 22 tooth Sturmey Archer freewheels, I assume they would fit on a regular flip/flop hub? Are there any better ways of going lower while retaining the same chainring? I don't want to have to switch chainrings to change between turbo and race - I can live with switching wheels (and chains) just about!
-
Sturmer Archer sprockets for geared hubs are not compatible with the usual ("regular" matches my understanding) threaded flip/flop or double fixed hubs. FWIW I fitted a 22t (biggest that would fit in the chainguard) sprocket to youngest daughter's Shimano 8-speed hub (caution... that was 6 years ago). It seems odd, but I'm sure that those components were 3/32", rather than the traditional 1/8" chain width for fixed gear & single-speed transmissions (I use 3/32", but that's not normal). It's possible that you're referring to freewheels that would fit on a threaded hub. I think that's unlikely, but ICBW.
I've tried to find threaded cogs with more than 22 teeth in the days when Will was still running HubJub. By now, I can't remember who made the 23t, probabaly E.I.A. or Andel. However Will seemed unable to obtain them (on reflection, he might have been able to, but not on terms which would have kept his business solvent). I'm not up to date with Hubjub's offerings (https://www.hubjub.co.uk/cogs-and-freewheels-7-c.asp) (E.A.I. are no longer supplied in 3/32" width), but 22t seems the limit.
Meanwhile I'm untroubled by the fuss about co-prime rear cog & chanring teeth. I ride 50x20 & have yet to observe any wear patterns corresponding to that simple 2½ ratio, though I do rotate the chainring when I renew the chain. Also at 73 I'm a long way past it.
-
Sturmey Archer make bog standard single speed free wheels - nowt to do with their gear hubs. I believe they fit standard threaded hubs.
-
my new build ss is 58x19 which is very similar gear to 48x16* which i currently ride. the reason for change was the need for higher gears (e.g. 58x16) if i do an occasional tt on it.
*works well everywhere with exception of 15%+ hills and 50kph+ sprints
-
Freewheels tend to have a slightly greater chainline than a fixed sprocket. This doesn't usually matter as they are less fussy - there's a bit of wobble in most freewheel bearings. Optimise chainline for the fixed sprocket, if you swap betweenthe two.
-
I guess I can live with a 22 tooth fixed sprocket on the trainer. I hadn't seen any until I checked out Hubjub. Might get a bigger (53 tooth?) chainring as well so that I have the gearing to get a good 10 mile time if I have the legs! Zigzag - where did you get your 58 tooth chainring from?
Is there any difference between the 1/8 chains? They range from £5 to £63. I guess I would pick one of the mid price Izumi chains as my race chain given no further information.
-
Is there any difference between the 1/8 chains? They range from £5 to £63. I guess I would pick one of the mid price Izumi chains as my race chain given no further information.
I have in the past broken two cheap 1/8th chains. Both were sideplates cracked across the hole for the pin, and not where I had joined them.
-
I usually buy KMC 1/8" chains. I would avoid Taya or unbranded ones.
-
General consensus I think that fixed is hard on chains, so cheap ones are A Bad Idea. I'd look to spend up to £15 and buy a recognised brand - KMC or something, as rogerzilla says. Not to important though what brand.
-
I just buy Sachs/SRAM PC1s or KMC chains and rarely spend more than a fiver.
-
Ideally get a chain with non-peened pins, so they can be taken apart and rejoined without special links or pins. The PC-1 is peened, annoyingly. if you never alter chain length this is tolerable because you can just use a master link, but if you want to add a couple of links for a different gear combination (e.g. I want to use 52 x 17 on the track), this means having two master links, and that looks stupid.
-
I figured I'd just have 2 chains - one for TT gears (53x15 or 53x16) and one for the turbo (48x22). So long as they are obviously different (eg one black, the other silver), and I remember which way around they go, I should be OK just using the master link. I won't buy cheap chains, but it sounds like there's no need to spend lots on a chain either...
-
You should be able to use the same chain length for all those, unless you have unusually short dropouts. Just set it up so 48 x 22 has the axle as close to the front of the slot* as possible.
*I mean the front of the bike, in case you have track ends
-
It's not a track bike, so it has short forward facing dropouts. However, I shall experiment once I have the bigger chainring/sprocket.
-
I ended up ordering a 24 tooth sprocket and a 54 tooth chainring. They were basically the biggest I could get for an affordable price.
The sprocket arrived and I've installed it and used it on the turbo. I had to put an extra link in the chain to make it fit (compared to the 20). The chainring hasn't arrived yet - I'll probably wait until the weather improves before I start switching them around - will discover what chain length I need for 54x16 (or 15 if I'm feeling fast) at that point.