Frame geometry/sizing question

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  • I'd also be wary of a short stem, i find that long stems give nice stable handling.

    As i've said before you are welcome to try my bob which has a 52 top tube that i run with a 12cm stem. welcome to borrow it for a day or two as long as it is locked properly, should give you a chance to take it for a proper spin/try some different bars etc.

    You know, Ed, when you asked me about that at the jumble and I told you I thought it was fine, that was before I noticed that I can't take a single hand off the bars without a bit of a wobble, and I also tend to drift more while checking behind me. So you're right. And I might like to ride the Bob this weekend but I heard you're selling it, maybe?

    Oh, and I have your drinks the next time we're both at Souths. Thanks for the help, dude.

  • ................ I also tend to drift more while checking behind me. ...................blah,blah

    your frame might need to be tracked/out of alignment. as an experiment, cycle in a straight line and take both hands off the bars. if the cycle drifts then its out.

  • I'm starting to look at building up a new bike over winter and just want to confirm a few things with people who have more experience than me. I'm 6,2 and currently riding a 55cm road frame (seat post raised very high), not perfect I know. With the next build I'd like to get as well fitted as possible, but know that it's just going to take time to find the "perfect" setup.

    I did some basic measurements and using this fit calculator came up with these measurments:


    Inseam: 88
    Trunk: 60
    Forearm: 37
    Arm: 66
    Thigh: 65
    Lower Leg: 58
    Sternal Notch: 155
    Total Body Height: 180

    The Competitive Fit (cm)

    Seat tube range c-c: 57.0 - 57.5
    Seat tube range c-t: 58.8 - 59.3
    Top tube length: 54.2 - 54.6
    Stem Length: 11.2 - 11.8
    BB-Saddle Position: 75.4 - 77.4
    Saddle-Handlebar: 53.8 - 54.4
    Saddle Setback: 6.9 - 7.3

    The Eddy Fit (cm)

    Seat tube range c-c: 58.2 - 58.7
    Seat tube range c-t: 60.0 - 60.5
    Top tube length: 54.2 - 54.6
    Stem Length: 10.1 - 10.7
    BB-Saddle Position: 74.6 - 76.6
    Saddle-Handlebar: 54.6 - 55.2
    Saddle Setback: 8.1 - 8.5

    I'm guessing this is for road frames and I'm looking for a vintage track frame, so are these going to apply or am I going to have to scale them down a bit? I'm planning on hitting the velodrome at some point for fun, but really it's just for commuting/day rides.

    Currently looking for a track frame of 60cm with a 54-55cm TopTube. Is this correct or have I missed something?

    Thanks for any advice!

  • I've never used that calculator before but it looks fairly concise.
    I tend to ride old 60 or 62cm road frames myself (although should probably ride something bigger) the thing I've noticed (it may be different for track frames) is that all 60-62cm road frames only ever have a 57-58cm top tube (back them top tube length was less important so ppl just had longer or shorter stems). So a 54cm top tube may be hard to find.

    Good luck though.

  • lbs -> go

  • Yeah I've talked to that guy who runs the little shop on the canal between London Fields and Angel.
    I guess I should just save up my budget a bit more and get a nice old frame from him as he seems to have some really nice vintage frames in now and again.


  • check out this thread, these frames seem to be close to those specs. Think the Koga (frame 5) is the best match.

  • Thanks Bernhard, it's not really the kind of frame I'm after, but could be good for my friend actually.
    So shrinking down to 58 would be ok? Bear in mind I'm after supposed "perfect" dimensions rather than "make do"...

    I mean if the perfect frame is 60cm with a 54cm top tube and I find a lovely frame at 59 with a 55 top tube I'm gonna get it. Just wondering what the perfect one to look out for would be and what the lee-way would be either side.

  • Well your specs say 58 c-c seat tube or 60 c-t seat tube so it depends on how it's measured.

    Shrinking down to a 58 would prob be ok, I think it's the top tube length that matters the most, any slight discrepancy can be sorted by shorter - longer stems and seat posts, this is just my opinion mind, I'm sure other people would be able to give you far more qualified advice about bike fit. Good luck with finding your perfect frame, have you considered a custom build?

  • Yeah I have considered a custom build. My missus bumped into an old friend of hers the other day and it turns out he's been training as a bike mechanics for the last few years and can build frames...

    I think that I need to get a nice frame that fits me better than my current one, then tinker with it and come to a better understanding of what I need before going and getting a custom built bike. Also I'm sure with a bit of tweaking any frame would be good enough for me, I don't think I really need to go that far.

    It's good to know that I can tweak the stem and seatpost to fit the center tube properly, so thats a bit of giveway. Do you know why it's the most important part? Is it just the possition you end up in stretching down to the bars?

  • I'm guessing it's not wise to get a 62cm Bob Jackson track frame? :(

  • I'm having some frames built up out east and I wanted some more opinions on Frame Geometry. It's has a very similar geometry to the Surly Steamroller (including room for 38c tires), except it's lugged and has a BB Drop of 63mm (they don't have a molding for the perscribed 70mm drop of the steamroller). Do you think that will make an Awkard, OK, or good ride? Is that too little drop for that big of tire clearance?

  • do you mean drop from the axle line? in which case less is higher

    is your worry stability or stand over height?

    sounds like you're taking it offroad - the drop is only so important there as far as it defines top tube height (standover - you'll want low-ish for off road) i'm pretty sure MTBs and cyclocross bikes have higher BB to improve clearance. i'd have thought shoe sole thickness could differ by more than 7mm - making the standover (or stepping off the crank height) height look marginal. also could try shorter cranks if it's an issue. tyres and rear wheel position (road style dropouts), height of forks, will all very slightly affect overall height too.

    one thing is for sure , any difference in your center of gravity is likely to make no difference, bikes aren't like cars - they are in constant unstable equilibrium (hence look at tyre tracks of a ridden bike - they are never straight always wiggly due to the little corrections) - and also why it's so unnerving to find your self on the kerb side (or even between two) of where the road comes up as a ridge like a bloody ploughed field where lorries have spread the tarmac out toward the kerb - you have to swerve dramatically to get out - and so into the road (or even worse down the slot of a tram line - got to be careful around them ) - oh i've gone off topic a bit

    actually , have a look here - i think it's where i picked up most of the ideas i've written above :­2/bottom-bracket-height.html

  • If you want to find out about bicycle design and science try to get copies of books
    Bicycles & Tricycles (An elemental treatise on their design and construction) by Archibald Sharpe
    Bicycling Science by Frank Rowland Whitt and David Gordon Wilson
    Both Published by MIT press
    Happy reading

  • Is there an idiot's guide to bike geometry?

    I understand what the basic components are but not how all the angles make a difference?

    I also don't understand the importance of the fop tube lenght other than for reach. How would I know which lenght suits me - trail and error?



  • Fop tubes are immeasurable.

  • Fap tubes on the other hand...

  • See also "bike fitting" threads.

  • cheers hippy

  • If I replace a fork on a frame, is the axle to crown measurement the critical factor? Will going from a 371mm, 45mm rake fork to a 385mm, 45mm rake fork make a significant difference to the handling of the bike.

    Will I die, or just make the bike a bit shit?

  • check this link:

  • Mmmm. Thanks Dron, I'll do the maths.

  • I went from 505 to 440 on a 29er, and I'm still here.

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Frame geometry/sizing question

Posted by Avatar for ffub @ffub