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Bike Size (frame size or top tube?)

  • 27-02-2009 1:01pm
    #1
    Registered Users, Registered Users 2 Posts: 721 ✭✭✭


    I'm looking to buy my first road bike.
    From all the reading I've done I think im looking for a bike that is 54/55cm (I'm 5'9").
    I'm looking at a GT GTR Series Four on CRC.

    The bike is available in 50/54CM (M/L).
    I assumed the 54Cm would be the one I'm looking for but then I looked at the sizing chart.
    The frame size is 54 (L) but the top tube is 57.6cm, the top tube on the 50CM (M) is 55.5cm.

    I'm just wondering if its the frame size or top tube I should be looking at given that its the top of the inside leg that I was told to use to work out the bike size?

    Also, is that bike ok? I read here that Shimano Tiagra drivetrain is the minimum to go for so I'm guessing that the rest of the spec should be of the same level...


Comments

  • Registered Users, Registered Users 2 Posts: 31,231 ✭✭✭✭Lumen


    In principle, frame size is based on seat tube length, although it's more complicated than that depending on geometry.

    So 54cm frame = 540mm seat tube (see the table on the link you posted).


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    so its the frame size i should be looking at and not worry about the top tube measurement?

    Ok, 54cm should be ok so?


  • Closed Accounts Posts: 2,001 ✭✭✭scottreynolds


    Lumen wrote: »
    In principle, frame size is based on seat tube length, although it's more complicated than that depending on geometry.

    So 54cm frame = 540mm seat tube (see the table on the link you posted).

    Oh yes -- its a sloping frame as well so the sizing is different. I'd say M is the correct size.


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    I'd say M is the correct size.

    I just noticed a typo in my original post, I said the 54cm was M, its L. THe 50cm is M.
    Fixed. oopsie :)


  • Registered Users, Registered Users 2 Posts: 15,995 ✭✭✭✭blorg


    TheTubes wrote: »
    so its the frame size i should be looking at and not worry about the top tube measurement?

    Ok, 54cm should be ok so?
    It's a bit more complicated, bikes are measured on the seat tube measurement (or often effective seat tube on compact frames.) However top tube is arguably more important as it largely dictates how stretched out you will be on the bike. But the two are generally proportionate, e.g. bikes in a given size tend to have similar effective top tube lengths.

    Note also that top tube is almost always measured as "effective" top tube, e.g. the length the top tube would be if it was horizontal rather than sloping.


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  • Registered Users, Registered Users 2 Posts: 31,231 ✭✭✭✭Lumen


    Geometry chart:

    73707.png


  • Closed Accounts Posts: 2,001 ✭✭✭scottreynolds


    TheTubes wrote: »
    I just noticed a typo in my original post, I said the 54cm was M, its L. THe 50cm is M.
    Fixed. oopsie :)

    I think I still vote M. Perhaps call them up and see what they say. I'm 5'10 and I think I would fit it -- althouh as I am not buying it I can't really help. In fact ring GT in the US they are more likely to answer the phone than CRC.


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    emailed both, CRC replied
    A 50cm bike would be suitable for a range of 28 to 32inches.
    A 54cm bike would be suitable for a range of 30 to 34 inches.

    Will measure again when I get home just to be sure.
    Will prob order on monday, looking forward to it :)

    No1 said the bike was rubbish or a rip off so I'll take it that its an ok spec/value (for a beginner) ? :pac:

    Thanks for all replies.


  • Closed Accounts Posts: 730 ✭✭✭short circuit


    You might want to rethink the bike .... the chainrings are oddly sized ... neither double .. nor compact ... seems to be designed for someone who always cycles on inclines between -3% and +3% ...


  • Closed Accounts Posts: 2,001 ✭✭✭scottreynolds


    You might want to rethink the bike .... the chainrings are oddly sized ... neither double .. nor compact ... seems to be designed for someone who always cycles on inclines between -3% and +3% ...

    Freewheel - Shimano HG-50 8 spd 12-25
    Crankset - FSA Varo Compact crankset, 50/39


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  • Closed Accounts Posts: 730 ✭✭✭short circuit


    Freewheel - Shimano HG-50 8 spd 12-25
    Crankset - FSA Varo Compact crankset, 50/39

    Exactly ... I would have expected a 53 or 52 with a 39 ... or a 34/36 with a 50. Its neither here nor there ... doesn't go high enough ... or low enough.


  • Registered Users, Registered Users 2 Posts: 15,995 ✭✭✭✭blorg


    Exactly ... I would have expected a 53 or 52 with a 39 ... or a 34/36 with a 50. Its neither here nor there ... doesn't go high enough ... or low enough.
    It's almost certainly a typo, the picture clearly shows a 34 inner ring (you could clarify to be sure) and it is FSA Vero while they have Varo. CRC has a few typos like that about their site.

    31754.jpg


  • Registered Users, Registered Users 2 Posts: 31,231 ✭✭✭✭Lumen


    I have the brochure in front of me. For the "GTR Series 4" it says "FSA Vero Compact 50/39".


  • Registered Users, Registered Users 2 Posts: 15,995 ✭✭✭✭blorg


    It's a typo CRC just copied then I reckon. I do not believe that a 50/39 "compact" exists and the picture clearly shows a greater difference in the front chainrings (Hell, with 53/39 the rings look closer together than in that pic.)


  • Registered Users, Registered Users 2 Posts: 618 ✭✭✭jdt101


    Check out this link regarding correct size: http://www.cervelo.com/content.aspx?t=Company&i=WhitePapers#1

    Cervelo only do 6 sizes, last year CSC used only 4 sizes to cover all their team (exclude 48 & 61). All bikes should be sized this way, reach is the most important measurment. My pennys worth.


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    I'm not too sure what the deal with the size stuff going on here is but the gt site says its 50/39 aswell (which i take it would be a problem?)
    It was suggested I ring GT about the size, I emailed them and got a reply already :eek: the guy suggested that the M would be ok.
    Should I reply and ask about the issue with the crankset size? i'd prob link to here instead of trying to explain :o


  • Closed Accounts Posts: 70 ✭✭psycholist


    TheTubes wrote: »
    I'm looking to buy my first road bike.
    From all the reading I've done I think im looking for a bike that is 54/55cm (I'm 5'9").
    I'm looking at a GT GTR Series Four on CRC.

    The bike is available in 50/54CM (M/L).
    I assumed the 54Cm would be the one I'm looking for but then I looked at the sizing chart.
    The frame size is 54 (L) but the top tube is 57.6cm, the top tube on the 50CM (M) is 55.5cm.

    I'm just wondering if its the frame size or top tube I should be looking at given that its the top of the inside leg that I was told to use to work out the bike size?


    Also, is that bike ok? I read here that Shimano Tiagra drivetrain is the minimum to go for so I'm guessing that the rest of the spec should be of the same level...

    it all depends ,

    a good bike shop's the best way to go to get it sorted theyll be able to tell you what quality of parts & sizes you need.
    tiagra's grand btw


  • Registered Users, Registered Users 2 Posts: 31,231 ✭✭✭✭Lumen


    blorg wrote: »
    It's a typo CRC just copied then I reckon. I do not believe that a 50/39 "compact" exists and the picture clearly shows a greater difference in the front chainrings (Hell, with 53/39 the rings look closer together than in that pic.)

    50/39 is two-thirds of an FSA Vero 50/39/30 (Triple).

    Surely they haven't just dropped the granny cog?


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    so, what do ye think? any consensus?
    I was going to order it in the morning if I got the go ahead from you guys.
    Should I just let it or should I email crc/gt to ask about the stuff ye noticed?

    Thanks for the help.


  • Registered Users, Registered Users 2 Posts: 721 ✭✭✭TheTubes


    Just an update on this,
    I emailed GT about the size of the chainset, I got a reply in under 2 minutes :)
    Very impressed with the customer service.

    He didn't have a bike in front of him but he is pretty sure its 34/50.

    I'll be ordering tomorrow :)

    Last question, will these 35mm mudguards fit the bike? I saw them recommended in another thread.


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  • Registered Users, Registered Users 2 Posts: 31,231 ✭✭✭✭Lumen


    TheTubes wrote: »
    Last question, will these 35mm mudguards fit the bike? I saw them recommended in another thread.

    Don't think so. Look at the gap (or lack of) between the seat tube and rear wheel - you won't fit normal mudguards in there, even if you have eyelets for them (which I can't see either).

    Maybe clip-on mudguards like SKS Race Blades.


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