Fixie advice

facemunk
facemunk Posts: 55
edited March 2009 in Commuting chat
can anyone tell me if a 48T or a 46T crank is a good or a bad thing?

Actually the thing I want to buy is a 48T track crank.

Ages ago someone on here explained gear inches to me, is it something to do with that - in which case will I need an adjusted chain and a new rear hub/sprocket thing.

... I have no idea what it means (bodes well eh - I am at least just wanting to buy the right bits and then have a professional fit them)

www.bikehike.co.uk/mapview.php?id=22736

Comments

  • gtvlusso
    gtvlusso Posts: 5,112
    Depends on your fitness level! 48T to 16T will give you about 82" - I find that fine for Bristol (Hilly) any higher and it would hurt allot........
    Flat area, I would go 52 x 16.....

    Need more info on the frame you want to fit too if you wan to know about fitting and BB compatibility.....

    Basics are 120mm chainstay width - gives you a 42mm chainline...! If it is a track frame all this is as standard, but then you need to know the BB shell width, spindle length for the correct chainline and clearance on the chainstays.

    Can be messy.....live and learn or buy spare chainrings and sprockets to find your ideal!
  • biondino
    biondino Posts: 5,990
    GTVL, do you seriously think that your average commuter is going to think 82 gear inches in a hilly area is a good idea? Not that they know - that's why they're asking you for advice!!

    48 x 18 seems a good flattish urban ratio, facemunk, perhaps 17 if you're hard. If it's hilly, you want a fair bit spinnier, a 19 or 20 tooth sprocket perhaps?
    My Focus / My Bob Jackson
    Blog (incl. bikes)
  • Eat My Dust
    Eat My Dust Posts: 3,965
    I've just opted for a 46:15 setup (roughly 83"). First ride this weekend, I'll let you know how it feels.
    SNAPS
  • Greg T
    Greg T Posts: 3,266
    You need to consider the gearing on the crank end and the cog at the wheel.

    A 48 T ring on the front with a teeeny cog at the back will be tres stiff, likewise if you have a 24 T cog on the back you'll be spinning out.

    "most people" go for about 48 on the front and 16/17 on the back on the flat plains of Lahndahn (they just man up on the Col de Putney Bridge)

    There are lots of gear inch calculators out there to help you do the maths. - use 48/16 as a "pretty stiff" starting point.

    I'd perhaps start off lighter than that and see how you get on (it's cheaper to have a few cog options as they cost <£10 rather than rings >£lots.
    Fixed gear for wet weather / hairy roadie for posing in the sun.

    What would Thora Hurd do?
  • Greg T
    Greg T Posts: 3,266
    gtvlusso wrote:
    Flat area, I would go 52 x 16.....



    Arnold-Schwarzenegger---Conan-the-Barbarian--C10102051.jpeg

    Conan says you're nails
    Fixed gear for wet weather / hairy roadie for posing in the sun.

    What would Thora Hurd do?
  • gtvlusso
    gtvlusso Posts: 5,112
    biondino wrote:
    GTVL, do you seriously think that your average commuter is going to think 82 gear inches in a hilly area is a good idea? Not that they know - that's why they're asking you for advice!!

    48 x 18 seems a good flattish urban ratio, facemunk, perhaps 17 if you're hard. If it's hilly, you want a fair bit spinnier, a 19 or 20 tooth sprocket perhaps?

    Fair point, I guess I probably do a fair bit more than the average commuter, but I prefer to feel the gear working - I have found that I spin out too easily with less that 75" gear and I don't enjoy it. The 52 x 16 will give you a massive ratio and flat speed - bit bollocks off the lights though! 48 x 16 is about right amount of work for me off the lights, flat and hill climbing in my locum. It is personal tatse - I have a track bag with a slection of chain rings and sprockets - will do a change if I am cycling to Bath fixed (52 x 16) - If I go to Gloucester I would run 46/44 x 16 - couple of big hills!
  • vanquished
    vanquished Posts: 66
    I ride 46/17... on a day like today, with an evil, evil headwind, I was out of the saddle, honking, on a dead-flat strip of road. TBH, I'd think that 46/17 (which works out, according to Sheldon Brown's calculator
    http://www.sheldonbrown.com/gears/ at 71" is about as high as you'd want to go, in the first instance (I'm contemplating moving to 46/18 = 67". From what I seem to have read here and there on the interwebs, mid/high 60s tends to be about right for general fixed on the road.


    Alternatively, work out what gear you tend to ride in at the moment, and try and match that (using Sheldon's afore-linked site). With a fixed, I'd personally suggest to err on the side of caution and gear down, rather than up - the caveat is that you might end up spinning out on the downhills, but grinding away mashing too high a gear doesn't too enjoyable an experience make.

    Note: I am not an expert - best advice I can give is 'try it and see'

    Secondary note: gtvlusso: 52x16???? You have knees of titanium, right?
    2008 carrera vanquish - FCN: 8
    2009 giant bowery 72 - FCN: 5
  • gtvlusso
    gtvlusso Posts: 5,112
    vanquished wrote:
    Secondary note: gtvlusso: 52x16???? You have knees of titanium, right?

    I shall defend my knees with my life! A Bianchi Pista comes with 48 x 16 as standard, which is bloody high for a noob bike.....admittedly, it is a pure track bike, but still high gear.

    I do change my gearing on occasion, but always come back to 48 x 16. Can do most things in that gear - again, I probably do a fair bit more exercise (not necessarily on a bike) than most would do, so I may have a power and fitness advantage......to a point, still get knackered though! I built up from 44 x 16 many years ago...

    Wind is the worst, but sometimes, you just have to get home.....
  • il_principe
    il_principe Posts: 9,155
    I run a 50x16 around London. Doesn't give me any bother, but then I'm a grinder not a spinner.
  • roger_merriman
    roger_merriman Posts: 6,165
    indeed being a fairly heavy bloke and knees that grizzel. i'd probably start at 60/70 and see how it goes. not so much the hills as the pulling away from lights, where i have a tendancy to put a gob of torque down which does my knees no favours if the gearing is too high.
  • gtvlusso
    gtvlusso Posts: 5,112
    I think:

    1 tooth at the back is worth 4 or 5 at the front.....?! Anyone know?!
  • jonginge
    jonginge Posts: 5,945
    52x16 for me. I have gears but can't be bothered to reach for the downtube shifter ;)
    48x16 on the pearson, which can get a bit spinny spinny on embankment
    FCN 2-4 "Shut up legs", Jens Voigt
    Planet-x Scott
    Rides
  • Greg T
    Greg T Posts: 3,266
    gtvlusso wrote:
    I do change my gearing on occasion, but always come back to 48 x 16......

    Ah! now it comes out.

    Personally I ride 60 / 12 pretty much all of the time, unless I'm trying to get somewhere - then I'll go 48 / 16 as the flapping soggy ends of my ripped tendons and ligaments get stuck in my spokes and the blood makes my SPD SLs too slippy.
    Fixed gear for wet weather / hairy roadie for posing in the sun.

    What would Thora Hurd do?
  • gtvlusso
    gtvlusso Posts: 5,112
    Greg T wrote:
    gtvlusso wrote:
    I do change my gearing on occasion, but always come back to 48 x 16......

    Ah! now it comes out.

    Personally I ride 60 / 12 pretty much all of the time, unless I'm trying to get somewhere - then I'll go 48 / 16 as the flapping soggy ends of my ripped tendons and ligaments get stuck in my spokes and the blood makes my SPD SLs too slippy.

    The occasion being a sunny day and a nice flat ride to Bath!!! 60/12 is the same gearing as an intercity train with it's 3500Hp ship engine......50/16 is okay, but I struggle on some hills in Bristol....have to Coca Cola up for them.
  • vanquished
    vanquished Posts: 66
    gtvlusso wrote:
    I think:

    1 tooth at the back is worth 4 or 5 at the front.....?! Anyone know?!

    It's all a matter of ratios, specifically, the number of teeth on the chainring vs the sprocket, since for a given bike the wheel/tyre/crank sizes remain constant.

    Also, it depends on the size of the sprocket - changing a 12t to a 13t is a bigger jump than changing a 22t to a 23t (as you'd expect), irrespective of the size of the chainring.
    2008 carrera vanquish - FCN: 8
    2009 giant bowery 72 - FCN: 5
  • blorg
    blorg Posts: 1,169
    You can change either front or back although back is probably a bit cheaper. Rabbit is a very useful tool for figuring out the result, e.g. what speed at what cadence.

    I have 46-17 (73.1") and 42-15 (75.6"). I find these sort of ratios perfect as I can still get up hills while not being killed on the descents. It's a delicate balance if you do hills, too low a gear and you will get up the hill OK but will be killed going back down.

    If you were in a flat area and don't need to go up any hills you could safely go a fair bit higher.

    There is nothing inherently "hard" about having a bigger gear, most guys with big gears just don't do up hills. Part of the benefit of fixed in any case is that you get comfortable with high cadences.

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