I'm looking to get the Trek Domane 4.3 and debating between a size 54 and a 56. One shop I've been to told me I'm a 56 and another said 54. According to Trek's sizing chart I'm 56. I am 5 9" with an inseam of 30.5". Which is the right size for me? Btw, I prefer not to replace any parts or make modifications to the out of the box setup. It should also be noted that I prefer comfort over performance.

  • top tube length, seatpost, crank size all vary depends on manufacturer. for 5'9", go for 54. Because longer top tube are uncom fortable to stretch the posture.
    – mootmoot
    Jun 3 '16 at 8:01
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    My quick and dirty bicycle fitting for top tube : When mount on the bicycle in comfortable posture (not the aggressive racing posture). My head is behind the handlebar but still able to see the front tyre. If you cannot see it, it is too big for you. If your head over the handlebar, it is too small.
    – mootmoot
    Jun 3 '16 at 8:53
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    Is your body built to average ratios? Or did your mum always say "he's got long legs" ? Mine did, so I need a larger frame for legs and a shorter top tube/stem for arms. The only suggestion is for you to go try them out. Talk to the bike shop that said 56 cm first (because it agrees with the maker) and get on it. If it feels alright, go for a ride on rollers in the shop, or around the carpark. If it still feels right, go for a ride for a couple hours. Fit is so personal that the internet at large can't tell you the right answer.
    – Criggie
    Jun 3 '16 at 10:35
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    Go sit on each, and judge which one feels better. Possibly, given the closness of the two sizes, you'll conclude that the answer is "neither", in which case it doesn't really matter. The smaller frame will be a tad lighter and and stiffer.
    – PeteH
    Jun 3 '16 at 11:44
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    The first rule is that you should be able to comfortably stand, with your feet flat on the ground, while straddling the top bar. With traditional diamond frames there should be 2-4 inches between the bar and the stuff between your legs. With newer style frames with the slant top bar there should be an inch or two more. If this size is right then most manufacturers will have the bike sized for an "average" person of that "standover height". Jun 3 '16 at 11:54

There are a ton of info online!

for example: http://www.ebicycles.com/bicycle-tools/frame-sizer

Performance usually mean right size and also same comes for comfort. I don't know why you think that this things are in opposite ways.

If you feel like 56 is too big and 54 too small go for the smaller. Also what use you will give to it ? Smaller frames are better for more aggressive driving like in a urban enviroment.

I know some cases when in a store seller advised wrongly in order to remove some last year(o more) stok. So be careful with this. It may happen in some small stores where the seller is also the owner.

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    well the page states that it is only orientative. It is more like if you feel comfortable. Also op can use more basic measure: while mounted you leg must be almost at max extension when resting on pedals fardest position.
    – kifli
    Jun 3 '16 at 8:40
  • Stock crank length is a problem when using to those calculator. Most bicycle use 165mm stock crank than using 170mm on bike for 54cm top tube
    – mootmoot
    Jun 3 '16 at 8:45
  • Planning on using it for 2-3 hour rides on the weekend, mostly for recreational, exercise and weight loss purposes. I guess what I meant by prefer comfort is that I'm not planning on riding in the "aggressive"/racing position, if that means anything.
    – Dandan
    Jun 3 '16 at 11:36
  • @Dandan well that bike is a beast perfectly capable to compete and "racing" position it is the position to use (may be not "aero" but resting on drifters and low bars it is the most comfortable and secure way). It is up to you what you do whit your money but 2-3 rides on weekend it some thing that any bike can do as long as wheels are going around. Just be sure that you are actually confortable of bike driving position. It is some thing that size have noting to do. Different types of bike have different driving positions.
    – kifli
    Jun 3 '16 at 11:58

Go through this process. It will ask you to measure several body dimensions and will help you pick the right size frame by how long it is rather than where the toptube meets seattube, which makes a lot more sense when you think about it. It will therefore work the same with a road vs a crossbike (which tends to have lower top tubes) and any compact or other frame designs. You can look up the geometry chart for the model you are interested in to find the Virtual / Effective Top Tube Length and pick the one closest to your optimum.

If you are between two frame sizes I recommend choosing the larger one. It is easy to use a shorter stem than what it comes with and should your goals / flexibility change in the future you may appreciate being able to go to a longer stem (if you ever want to lower your handlebars you may also want them further away).


What I have done in the past, is to measure your current bike (top tube, down tube and stem) then locate the size which matches those measurements.

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    Welcome to Bicycles @Chris. We recommend that new members take the tour to make best use of the site. This is start of a useful answer, but it could do with more explanation. I suggest that you explain (check out if you don't know yet) what virtual sizes are, so your answer would end up explaining where the measurements begin and end. Cheers
    – andy256
    Sep 7 '16 at 1:11

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