Bike sizing help please - stuck between two frames...

KnightOfTheLongTights
KnightOfTheLongTights Posts: 1,415
edited February 2012 in Road buying advice
I know I had a similar post below but this is a bit different so bear with me please ...

I plugged my measurements into the Competitive Cyclist fit calculator and got the following recommended ranges (from their raciest fit at one end to what they call a 'French fit', i.e., more relaxed, at the other):

Seat tube cc: 49.2-52.6
TT: 53.3-54.5

BMC sizes come out as follows:

49cm frame
ST: 51.1
TT: 53.0

51cm
ST: 52.8
TT: 54.0

In other words the 49cm is great for seat tube height but possibly a bit short on the top tube.
Are these discrepancies worth worrying about - i.e., it will be easy to get a good fit on either frame?
In which case, does anyone know whether one would be preferable to the other?

One racing cyclist mate of mine says if in doubt go for the smaller frame. But then I've also heard that the top tube is the most important thing to get right ...
Thanks

Comments

  • napoleond
    napoleond Posts: 5,992
    Looks like the 51 for you from that but more importantly you said you felt better on that size.
    You can (very) fine tune with stem length and bar reach...
    Insta: ATEnduranceCoaching
    ABCC Cycling Coach
  • KnightOfTheLongTights
    KnightOfTheLongTights Posts: 1,415
    NapoleonD wrote:
    Looks like the 51 for you from that but more importantly you said you felt better on that size.
    You can (very) fine tune with stem length and bar reach...

    thanks ND - said I felt good on the 51 but have not tried the 49 so can't compare yet.
  • amaferanga
    amaferanga Posts: 6,789
    Top tube is the most important, but if you want the front low then a smaller frame is usually better.
    More problems but still living....
  • KnightOfTheLongTights
    KnightOfTheLongTights Posts: 1,415
    also, re. test riding ...

    it's hard to tell on a 10-minute spin isn't it - you might feel different after five hours.
    Plus the shop people are always going to adjust the seat post and bars to be comfortable and 'feel right'.
    So you have 'a fit' - doesn't mean it's the 'right fit'.
    If you know what I mean.
  • napoleond
    napoleond Posts: 5,992
    If its comfortable and fits, it's right!
    Insta: ATEnduranceCoaching
    ABCC Cycling Coach
  • graham_g
    graham_g Posts: 652
    Those measurements mean absolutely jack without the seat angle. Only if they are identical can you compare - don't forget that you'll put the saddle in the same position (dictated by your preferred position relevant to cranks) on either a 73 or 74 degree frame, but if they've the same length top the bars will be ~10mm further away on the 74. ...and you thought trigonometry would never be needed in real life :mrgreen:
  • KnightOfTheLongTights
    KnightOfTheLongTights Posts: 1,415
    Graham G wrote:
    Those measurements mean absolutely jack without the seat angle. Only if they are identical can you compare - don't forget that you'll put the saddle in the same position (dictated by your preferred position relevant to cranks) on either a 73 or 74 degree frame, but if they've the same length top the bars will be ~10mm further away on the 74. ...and you thought trigonometry would never be needed in real life :mrgreen:

    OK, is this were we get into 'stack' and 'reach' or whatever it is .....?

    I have now had a go on the 49cm and it felt if anything better than the 51 - which just goes to show you can feel comfortable on something without it being the right-sized frame.
    We could all probably feel reasonably comfortable on three different-sized frames taking them for a ten-minute spin, with the right seat / bar adjustment.
    You need to look into things a bit closer to get the right one, in my opinion.
    Moreover, I've been overstretched on my current bike but had got used to it: so trying the 51, it felt 'normal' even though I was probably a bit overstretched still (the TT is only 0.8cm shorter than my current bike).
  • graham_g
    graham_g Posts: 652
    'stack and reach' - isn't that just cervelo trying to make simple by complicating things?

    One thing to consider when test riding - different handlebars have different reach on them and even different levers will make a difference (I recently went from riding SRAM brake levers back to the older, pre-2008, campag shape and it was as if I'd added 10mm to the stem). All of this can be adjusted out of with a different stem. The tricky bit is sometimes getting the bars high enough for you on a smaller frame or low enough on a larger frame as you will have the limiting factor of headtube and steerer length.
  • on-yer-bike
    on-yer-bike Posts: 2,974
    If you can handle a large seat to bar drop then you might be OK on the smaller size with a longer stem. You dont want to end up flipping the stem to cure your lower back pain. As previous poster said seat angle is important to take into account.
    Pegoretti
    Colnago
    Cervelo
    Campagnolo
  • Spender
    Spender Posts: 87
    I know from the OP its a new bike we are talking about but if it were an existing bike you owned and you are not as flexible as you once were what is wrong with flipping the stem?
  • tx14
    tx14 Posts: 244
    seattube length is completely irrelevant.
  • MartinB2444
    MartinB2444 Posts: 266
    tx14 wrote:
    seattube length is completely irrelevant.

    That's a radical statement that could do with some explanation if it's to be taken seriously.
  • alwaystoohot
    alwaystoohot Posts: 252
    A larger frame will allow a more relaxed riding position so take into account the length of your rides.

    Next question?
    'I started with nothing and still have most of it left.'
  • tx14
    tx14 Posts: 244
    MartinB2444 wrote:
    tx14 wrote:
    seattube length is completely irrelevant.

    That's a radical statement that could do with some explanation if it's to be taken seriously.
    the only thing it affects is standover, which is of no concern on a road bike.

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