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gear ratios for a fixie

samg123samg123 Posts: 275
edited January 2012 in Workshop
Converting my old Bianchi into a fixie, wondering what y'all would recommend for gear ratios? Is 30/16 too small? 42/18 too big? My commute involves a bit of sharp incline right at the end...

Posts

  • moonshinemoonshine Posts: 1,012
    i ride a 42:16.. a good working gear that will get you up ( and down) most hills & set a good pace on mixed terrain.
    go for around 70" ... use an online gear calculator to work out the right sprocketsize. choose a 15/16/17/18 to give the desired gear that matches with your chainring.
  • moonshinemoonshine Posts: 1,012
    ps i'll get up a 1:5 on a 42:16.
    have you semi horizontal rear dropouts? how will you achiece & maintain chain tension?
  • marcusjbmarcusjb Posts: 2,412
    Both the ratios you mention are VERY low - 50ish and 62ish inches - you'd certainly get up the hill, but you'd have been spinning like a loonie to get there - and god help you if you ever have to go down a hill!

    As Moonshine says - somewhere around 70 inches should work just fine for most terrain, maybe 67ish if you live somewhere really hilly. I run about 76 inches - but my fixie is mainly used for commuting in flat London.

    Climbing on fixed is totally different than a geared bike - you'll be amazed at what you can get up with a 70 inch gear. There's no point in gearing down massively just for one hill, the rest of the ride will be far more challenging if you are having to spin like crazy to maintain a decent speed (your 42/18 will need your cadence to be around 110 to go along at 20mph). Even the mental nutter fixie audaxers I know realise there's no shame in utilising the 24 inch gear (2 feet) on a really steep hill - the payoff is gearing that is correct for the rest of the ride.
  • crakercraker Posts: 2,060
    I recently converted my old Raleigh. I've got a hilly commute over 10 miles and went for 42-17 (65") which gives decent cadence on the slighter inclines and declines, at about 21mph I run out of meaningful power. My cassette hasn't got a 16 tooth gear, I did try the 15 once for 42-15 (74") and found I was struggling to get a decent cadence.

    If you've still got your cassette on then experiment a bit. 42-18 does sound too high though.
  • samg123samg123 Posts: 275
    Yeah- the dropouts are horizontal.
    I'm somewhat limited as to my choices: I've only got two single speed sprockets- a 16 and an 18 and i'm doing it from the chainrings I have lying around- from about 39 to 43 I think.
    Here's the elevation profile for my commute:
  • redveeredvee Posts: 11,920
    As well as getting up the hill think about getting down, your legs will be spinning and too low a gear will have them spinning too fast. I run 50:18 on a flat route apart from the 1/10 mile where I have to walk up the steepest part of a hill. Most hills I can go hell for leather and blast up it but it is just that little bit too long after 8 hours at work.
    I've added a signature to prove it is still possible.
  • samg123samg123 Posts: 275
    From Bristol I see! My commute is up and down Whiteladies Road if that helps (just to get the most personalised advice possible!)
  • moonshinemoonshine Posts: 1,012
    going downhill fixed is often more challenging than climbing as you are forced to spin at a very high cadence... i think my record is somewherer around 170rpm - sustained for a couple of minutes on a long decent. (37mph on a 42:16) very uncomfortable indeed!
  • RowCycleRowCycle Posts: 367
    I ride a 48:16 singlespeed (freewheel rather than fixed - couldn't get on with fixed when filtering through traffic or going down hill).

    I like it. I use it to commute to work but this is flat except for a couple of short mounds (hills). I have to work hard on the hills, but allows me to keep up with fellow cyclists without spinning my legs like the clappers.

    A simple way to try a gear would be to pick a gear on your normal bike and not change out of it.
  • crakercraker Posts: 2,060
    edited January 2012
    samg123 wrote:
    From Bristol I see! My commute is up and down Whiteladies Road if that helps (just to get the most personalised advice possible!)

    Cant comment from a fixie perspective, the big hill on my commute home is probably steeper than Whiteladies Road (head out of Bristol north on the A38 and take the first left once you've crossed over the M4 -> freewheeling to about 34 mph.)

    Can you try SS first, get the ratio you like then see how it works fixed? You can't go wrong on 42:16 [edited NOT 48:16] or thereabouts.
  • samg123samg123 Posts: 275
    Ahh I may have been using the terminology a bit too interchangeably... I'll be getting a flip flop hub, so I'll be able to choose between freewheel and fixed. I think I'll probably go with the freewheel, at least to begin with.
    The problem with Whiteladies is it's a perfectly acceptable gradient until the very last section onto the Downs, where it just kicks up a bit too much to be manageable in a high gear. But maybe I should just grit my teeth ;)
  • mz__jomz__jo Posts: 398
    As as already been said, 42/18 is too low for fixed; I am currently using it on a single-speed but on fixed I would go up to 42/17 (and I go uphill a bit and am very overweight, otherwise it would be 42/16). 42/17 allows me to spin out at about 50km/h going downhill (on a good day when a knackered knee permits). In your case I would start with 39 or 40 (if you have it) for a chainring with your 16 sprocket (this would be reasonably close to 42/17 in gearing).
  • I ride a single speed 42/16 commuting from North to Central London so only a couple of hills to be concerned with but it's fine really. I have a flip flop hub but haven't had the bottle to go fixed, and after reading the previous comment about filtering I probably wont for a while yet. The only thing I don't like is having to freewheel a bit when it gets too fast on the downhill bits - but need to get my spinning up to speed, pardon the pun
  • marcusjbmarcusjb Posts: 2,412
    craker wrote:
    Can you try SS first, get the ratio you like then see how it works fixed? You can't go wrong on 48:16 or thereabouts.

    Trouble is that you're not quite comparing apples with apples - fixed and SS are a different beast.

    IMHO if you put me on two identical bikes with, let's say, a 70 inch gear - one fixed, one SS - I bet I could get up a steeper gradient on the fixed. On fixed, the bike is 'helping' you all the way, the cranks will spin over the dead spots for you - so it's far easier to climb on fixed than SS (none of this is meant as SS-bashing (I know a lot of fixers look at SS-riders with disdain!)).

    You'd probably want to run 3-4 inches higher on fixed than SS (i.e. usually a 1 tooth difference on rear sprocket).

    48:16 is around 80 inches - that's quite tall unless you live somewhere very flat. I run 48:17 in London (about 76 inches), but I am not a brilliant spinner and found anything lower than that difficult. A lot of people claim 48:18 is the one true gear (71ish inches) - I might try it out over summer where I hope to tackle some longer stuff on fixed, see if I can learn to spin a few more RPM.
  • mmukmmuk Posts: 398
    interesting post - I'm also building a fixed at the moment, and have ended up going for 48:16 - based on going across to Norwich last weekend on 52:19 - (ie stayed in the same gear all the way) but it is relatively flat round here (west Norfolk), and I can always change the ratio if necessary. Next weekend I will know!
  • mz__jomz__jo Posts: 398
    marcusjb wrote:
    craker wrote:
    Can you try SS first, get the ratio you like then see how it works fixed? You can't go wrong on 48:16 or thereabouts.

    Trouble is that you're not quite comparing apples with apples - fixed and SS are a different beast.

    IMHO if you put me on two identical bikes with, let's say, a 70 inch gear - one fixed, one SS - I bet I could get up a steeper gradient on the fixed. On fixed, the bike is 'helping' you all the way, the cranks will spin over the dead spots for you - so it's far easier to climb on fixed than SS (none of this is meant as SS-bashing (I know a lot of fixers look at SS-riders with disdain!)).

    You'd probably want to run 3-4 inches higher on fixed than SS (i.e. usually a 1 tooth difference on rear sprocket).

    .

    +1.
    The difference between ss and fixed is both in climbing and in descending or spinning. Going up you can use a bigger gear than with a freewheel because there is no dead point and also because the transmission is a tiny bit more efficient. There is a definite technique to climbing steep stuff with a fixed which is not at all like climbing on gears. I keep the bike in line and lean on the pedals without trying to force and up it goes nice and easy. (Others might do it differently).
    At the other end of the scale you can spin much faster with a fixed wheel than with a freewheel because the pedals are in permanent contact with the back wheel. With a freewheel it is difficult to stay in contact over a certain cadence (in my case about 120rpm where with a fixed I can usually get over 150 and on a good day closer to 180). All of which makes a fixed wheel a bit quicker than a freewheel, unless you are regularly in situations where a freewheel
    permits really quick descending (much quicker than you can spin).
    Marcus, to get your spinning up you have to work with a much lower fixed gear on a route with lots of hills and preferably reasonably long descents (and you have to work at it if it doesn't come naturally). But you need hills that you have to work to get up otherwise the muscles don't work hard enough. Usually done in winter and early season!
  • bjlbjl Posts: 353
    Been riding around on 42 x 16 and finding it about right,changed to 165mm cranks though and found they help you to spin more easily than usual 170mm cranks . Another question - are you using same saddle position fore and aft?
  • samg123samg123 Posts: 275
    orangei.jpg
    She's all done. I've gone with 42/18- I know this is very small but 18t was what came with the new wheels. As it's a singlespeed rather than a fixie that shouldn't be a problem downhill and I hope it should be easier uphill. I may get a smaller sprocket at some point if I find it too low.
    Thanks for all the help!
  • marcusjbmarcusjb Posts: 2,412
    Nice looking - but I do have a soft spot for orange bikes!
  • samg123samg123 Posts: 275
    I should hope so- I spent about £50 on primer, paint and lacquer!
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