Top tube lengths. Confused? ( Road bikes)

Paul8900

Hi,

Can anyone please help me with some sound advise. I am confused!

I have recently been measured at a shop that used bikefitting.com. It costs £50, but money refunded if you end up buying the bike from this shop! The mearsurements taken no problem. I was then given a drawing of the ideal set up for a new racing bike. Frame top tube 550mm, 56cm frame, 115mm stem length. handlebar width 420mm? etc. Happy with this I then set out to buy a bike of this proportion.

A few weeks later I went to another cycle dealer who offered the measuring service but for free. Out of curiosity, I was measured up again, using the same system as before. It transpired that the measurements were different. Suggesting I need a 570mm top tube, 56cm-57cm frame, 115mm stem length and 440mm handle bar width?

I am now totally confused. What is the correct top tube length? How can this be determined?

Are there any advantages or disadvantages for having a longer top tube? I appreciate that you can alter the length of the stem? And a stems ideal length is between 100mm-120mm.
Why would there be conflict with Handlebar width measurements also?


Can anyone please help me.


The bike is intended for regular distance riding at speed/comfort. Sportive type riding mainly and not racing as such.

sogood

The system is as good as user and data supplied. Then there's the issue of different styles of fit.

__________________
Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac

rparedes

well, i can share my experience regarding fit. The final geometry is a function of the type of riding you're going to do. Assuming that the measurements were taken accurately, the longer top tube means also that there will be less of a saddle to handlebar drop. The smaller top tube means that the bars will be lower in relationship to the saddle; remember the saddle to BB is relatively fixed based on your inseam measurement so the only variables left are top tube length and head tube height (which sets the heigth of the stem) If you're looking for comfort, more upright position, my LBS suggested the slightly larger frame with a shorter stem. The smaller frame will handle "quicker" and you may be able to put a hi-rise stem to get the bars up. Personally, I prefer a larger frame with the longer wheelbase for sport, touring, and fitness riding. For example, I can fit on a 57, 58 all the way up to 59 inch frame with a shorter stem. Depending on the geometry, a 59 cm frame may have the stem almost 3 cm higher but it may only be about 2 cm top tube length longer.
Anyway, these are only guidelines. If you can, test ride both frame sizes and see which one "feels" better. The shop should be able to swap stems until you are comfortable with the fit.
Handlebar dimensions are also guidelines: 42 cm vs 44 cm is not a lot of variation (are you narrow chested or big shoulders?). Some prefer the slightly wider bars. I prefer the wider dimension at the drops and the smaller at the hoods (FSA compact bars) so it's a matter of personal preference
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oldbobcat

Wider handlebars seem to give me better leverage when I'm climbing out of the saddle, but I catch more wind with my arms spread wider. Unless you're particularly broad-shouldered or you're already using 44s, I'd recommend the 42s.

Regarding top tube length, I'd test ride several bikes in this size range and go with what feels and looks right.