Help with frame size - very confused

Rayleigh1234
Rayleigh1234 Posts: 6
edited August 2011 in Road beginners
Can anyone please help me with my frame size query?

I just purchased a felt z85 online in a 54cm frame size. I took it to a LBS to get the gears sorted, which was all fine however they told me that the frame size is actually 50cm. They measured the frame size from where the seat post joins the bike to the middle of the crank.

Being a little confused I went onto the Felt website and checked the geometry for the bike and it said the length of the tube from the seat to the crank should be 50cm for a 54cm bike. So my question is why would the frame size be 54cm when these measurements are 50cm? And do I have the right size bike seeing as I'm 5ft 8?

Thanks

Comments

  • sloppyschleckonds
    sloppyschleckonds Posts: 8,019
    Get a new LBS
    I'm sorry you don't believe in miracles
  • Rayleigh1234
    Rayleigh1234 Posts: 6
    I take it by that you mean they are talking cr@p?
  • solboy
    solboy Posts: 368
    The seat tube may measure 50cm but if it has a sloping top tube the frame manufactureres give the frame size assuming the tope tube is horizontal hence giving an "effective" frame size - in your case a 54cm assuming what i have said is correct.

    I have had specialized and van nicholas bikes where this has thrown me so dont worry.
  • merak
    merak Posts: 323
    SloppySchleckonds wrote:
    Get a new LBS
    That's really helpful on a beginner's forum, dude.

    To the OP - before sloping top tubes came along there was not much ambiguity. The frame size was measured from the centre of the crank to the top of the seat lug (or, sometimes, particularly by Italians, to the centre of the top tube, if using steel). In any case the measurement gave a good indication of the vertical size of the frame, the stand-over height etc. I know my optimum frame size measured this way is 51cm. Then sloping top tubes came along and some had extensions to the seat tube and some didn't. Some manufacturers started measuring from the crank to the top of the top tube, some measured from the crank to the top of the seat tube even if it was extended, and some measured from the crank to where a horizontal top tube would have met the seat tube. This last gives an equivalent size to the way it was done with a horizontal top tube, and it's the most useful in my view. The only way to be sure what you are getting is to look at a drawing of the frame geometry and see how the manufacturer measures it. In Felt's case, I can't find a drawing, but it seems like they use the last, ie most traditional way of measuruing frame size. So you're getting what was always a 54cm frame even though the seat tube measures less.
  • jonny_trousers
    jonny_trousers Posts: 3,588
    Rayleigh1234 wrote:
    So my question is why would the frame size be 54cm when these measurements are 50cm? And do I have the right size bike seeing as I'm 5ft 8?

    Thanks

    I may be about to contradict the above post, but I thought most manufacturers these days listed the frame size based on the top tube length. This makes much more sense to me as vertical length can be easily adjusted through the seatpost whereas horizontal length along the top tube can only be adjusted slightly via the stem. I suspect your 54 will be the top tube measurement and sounds about right for your size to me.
  • merak
    merak Posts: 323
    Jonny_Trousers wrote:
    Most manufacturers list the frame size based on the top tube length, but some by the seat tube length (not so many, though, which is why I'm surprised your LBS told you something so misleading). Your 54 will be the top tube measurement and sounds about right for your size.
    Not so. See post above for the correct answer. No-one, AFAIK, measures frame size by top tube length. (BTW it's 52.6cm for the 54cm Felt). On many bikes the lengths are similar, but pros specify frames with relatively longer top tubes and even on the same model the top tube length doesn't match the frame size at the extremes of size.
  • Rayleigh1234
    Rayleigh1234 Posts: 6
    Thanks. That has cleared things up for me I think. The bike does have a sloping top tube so looking at it if the top tube was straight it would be around 54cm as the frame size suggests.

    Not sure I will be going to that LBS for any more advice, it's run by an old couple who look like they haven't ridden a bike for several decades. Luckly there is no shortage of bike stores around my are.

    Thanks again
  • nicktheluddite
    nicktheluddite Posts: 221
    I think it's nominally a 54cm frame
    Felt website has frame geometry http://www.feltbicycles.com/United-King ... s/Z85.aspx lists all the measurements of various frame sizes.

    I think every manufacturer describes frame size based on seat tube length, not top tube length. Moving up the saddle obviously suits any frame to your legs but making the handlebars higher isn't so easy.
    The late great Sheldon Brown has wise opinions http://www.sheldonbrown.com/frame-sizing.html

    Is the bike the right size? Does it feel comfortable? In all honesty we can help, but a friend who knows about road bikes and can actually see you on it is possibly more useful..........
  • Rayleigh1234
    Rayleigh1234 Posts: 6
    Yeah the bike feels good, however since I have started using it I have been getting handlebar palsy in my left hand. Not sure that has anything to do with the bike size though. Think I have been putting too much weight on my arms so I have moved the seat back and twisted the handlebars towards me as my wrists were slightly bent when resting ontop of the break leavers.
  • jonny_trousers
    jonny_trousers Posts: 3,588
    nicktheluddite wrote:
    I think every manufacturer describes frame size based on seat tube length, not top tube length. Moving up the saddle obviously suits any frame to your legs but making the handlebars higher isn't so easy.
    The late great Sheldon Brown has wise opinions http://www.sheldonbrown.com/frame-sizing.html

    Well I never did! You learn a new thing every day! Thanks Nick. Just read the Sheldon Brown article and good to see he agrees that top tube length is more important. I guess the bottom line is to look at the entire geometry of the frame and to try before you buy.
  • rolf_f
    rolf_f Posts: 16,015
    merak wrote:
    .... but pros specify frames with relatively longer top tubes and even on the same model the top tube length doesn't match the frame size at the extremes of size.

    I suspect Pros actually specify frames that fit them! Which may or may not involve a longer top tube......
    Faster than a tent.......
  • Rayleigh1234
    Rayleigh1234 Posts: 6
    Yeah the bike feels good, however since I have started using it I have been getting handlebar palsy in my left hand. Not sure that has anything to do with the bike size though. Think I have been putting too much weight on my arms so I have moved the seat back and twisted the handlebars towards me as my wrists were slightly bent when resting ontop of the break leavers.
  • merak
    merak Posts: 323
    Rolf F wrote:
    merak wrote:
    .... but pros specify frames with relatively longer top tubes and even on the same model the top tube length doesn't match the frame size at the extremes of size.

    I suspect Pros actually specify frames that fit them! Which may or may not involve a longer top tube......
    Indeed, but on average they have longer top tubes, size for size, than us motals, and, on average, greater saddle to stem drop. I assume that's because they are, on average, more flexible and able to stretch out more with a straight back while spending six hours a day in the saddle. Which is not to say that all pros have longer top tubes than all amateurs or leisure riders.

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