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I am looking to buy a bike for my wife on the internet, but the challenge is I do not know what frame will be most suitable for her.

We plan to buy a hardtail for leisure rides on the weekends so we favor upright position.

Her inseam is 82 cm and her height is 172 cm.

I have an option to buy Cube Aim 2017 of 17', 18' or 19. https://www.cube.eu/en/2017/hardtail/aim/cube-aim-race-blacknblue-2017/

By looking at geometry charts provided above (including stack and reach) is it possible to recommend the frame size which will most likely feel right for leisure rides?

Thanks

Geometries

17" Geo Chart 18" Geo Chart 19" Geo Chart

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    Buying a bike on the internet is like buying clothing on the internet only much worse. You can have all the right body measurements but each bike company and even each bike model is sized slightly differently. Ultimately, “fit” is only something you can determine by trying different bikes and bike sizes, and making adjustments to crank length, seat height, seat position, stem length, handlebar angle, etc. There’s a reason that buying bikes on the internet is cheaper than at a bike shop and that’s because you’re much less likely to get a good fit.
    – RoboKaren
    Feb 8, 2018 at 21:01
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    Actually, buying bikes is far easier than buying clothes. For clothes you almost never get accurate size tables and often it's even not told which standard the size numbers are, but for bikes you usually have measurements down to millimeter (see the question for examples). If you know which size fits you, it's trivial to pick a bike with correct measurements.
    – ojs
    Feb 8, 2018 at 22:01
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    Politely - try a few bikes out in person. What looks nice might be uncomfortable. Do consider buying retail from your Local Bike Shop too - they aren't a lot more expensive and you get much better service.
    – Criggie ♦
    Feb 8, 2018 at 23:30
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    @Criggie - Frankly, many LBS are piss poor at fit. Often you get someone who is young and flexible prescribing their preferred riding position to if it was "The" position from which all others should be measured, or you have someone who has taken a 3 day course with no formal background in human kinetics who is constantly over reaching their knowledge. You also can get ones trying to push old stock out the door and are more than happy putting you on a frame that doesn't quite fit in order to do so. In my 20+ years experience I only found one LBS that did an okay job at fit.
    – Rider_X
    Feb 8, 2018 at 23:47
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    @Criggie That is a totally fair criticism, there is a lot to be said about a test ride, that said, I often find it takes weeks or months of riding a particular bike before I really get what its about. It is hard to make that assessment on a 5-10 minute spin. Its sort of like a type of theater, its designed to make you feel better about a purchase, but I have personally rarely found it to provide much real insight other than "it is COMPLETELY WRONG". Especially, if it is a "deal" you can convince yourself of all sorts of things on a short ride.
    – Rider_X
    Feb 9, 2018 at 0:10

3 Answers 3

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Strangely your wife's proportions are very close to mine, except I am a little taller. Speaking from experience, in terms of mainstream bicycle fit curves, this a somewhat long inseam for height, which means

  1. You need a relatively taller stack
  2. You need a relatively shorter reach (a relatively taller inseam means a shorter torso).

This is essentially the worst combination for fitting, which means ordering sight unseen will be difficult to guarantee the best fit. Being marketed with the words "race" makes me concern that the frames may not have enough stack, but looking at the geo chart suggests the stack is decent.

All that said, I think either the 17" or 18" could work, the 19" is too big. Both the 17 and 18" have nearly identical stack heights, but differ in front-center dimensions (and reach) due to differences in seat tube angles (the top tube length is also nearly identical between the two).

The two sizes also use different wheel sizes. The 17" uses 29er wheels (larger), a slacker seat tube angle and therefore as has a shorter front to center measurement and a 1 cm shorter reach, while the 18" uses smaller wheels (27.5) and a longer front to center measurement. Perhaps this is to offset handling characteristics of the different wheel sizes? I would almost phone to confirm the geometries.

Choosing between the two may mean picking a wheel size. The larger wheel size will be a bit more stable, which could be good for leisure riding. It also has a shorter reach which is good for a shorter torso. Therefore if I had to hazard a guess (danger) I would suggest the 17". Depending on how your legs are proportioned (i.e., femur to tibia) you may need to move the saddle forward if you have long tibias/short femurs, as a shallow seat tube angle is better suited to someone with longer femurs.

Given that you haven't tried the bike, also be prepared to have to change the stem. Given the long legs, there is a good chance of long arms which could mean a longer stem. Also given that long inseams effectively shorten the stack height relative to someone with shorter inseams, you may need to use a riser stem and possibly a riser handle bars to get the position high enough. A quick check of arm length would be to measure your wing span (an outward facing wall corner can be good for this) and compare it to your height. Most bikes are proportioned as if the two match. If you have a proportionately longer wingspan you will likely need a longer stem so that you don't feel cramped, if you have a shorter wingspan you may need a shorter stem so you don't feel stretched out. Finally, realize that when you flip a stem up (aka riser) you loose reach, so with more aggressive stem rise you may need to find extend the stem length as well.

Geom Charts

17" Geo Chart 18" Geo Chart 19" Geo Chart

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  • Why would the middle-sized frame has a longer headtube than the large frame, and a shorter wheelbase than the small frame ? I'm picking wheel size.
    – Criggie ♦
    Feb 9, 2018 at 0:18
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    @Criggie The stack height between the 17" and 18" is within 2 mm. You are correct, the headtube differences reflect differences in wheel size. It seems bizarre to me that the "smaller" size has the larger wheels, but then again they seem to be alternating wheel size with each frame size bump in the middle size range... just to confuse the @$%# out of everyone.
    – Rider_X
    Feb 9, 2018 at 0:21
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You can use size guides to get a reasonable estimate if the size frame required only. Do not rely on them.

It’s best to visit a physical bike store and try some different size bikes with a knowledgeable bicycle store employee who can provide recommendations and make adjustments.

A reasonable length test ride is also highly recommended to make sure you are getting the fit, handling, ride and comfort you want.

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Maybe I'm just lucky, or more flexible than I think, but for fairly gentle riding up to a few hours on flat bars, I think you can do quite well based on size alone,if you bear a few things in mind:

  • Saddle height: you can't go lower than the bottom, or higher than the minimum insertion point (longer seat tubes exist but don't help because by then you'll be too high for the bars)
  • Bar height/reach: Stems can be changed; many bars have a slight rise and can be rotated a little in the stem clamp for fine tuning.
  • Assuming you're fairly new to riding, start with a quite upright position but expect to drop it a little.

The thing is that many of these need several hours riding to get a feel for. And by that time everything will ache in a new rider so you still won't be able to tell. A test ride of under an hour isn't likely to tell you much more than just sitting on the bike or doing a lap of the shop.

Going to a big chain store and trying something out can be a good way of measuring. One of the "bike shop" chains in the UK isn't good for much more than that and cheap accessories. I wouldn't treat a good bike shop like that. Hiring or borrowing is also good; you may be able to get exactly the same bike, or just get an idea of what size you need.

A little too small is easier to adjust than too big - but free key is a little.

This doesn't apply to road bikes, or any bike that's going to be ridden in a really demanding way.

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  • I thought we needed something a little more optimistic. I can still remember when a gentle ride of a a few hours on lanes or fire roads, complete with picnic, felt like a long ride. Now I ride a lot more on roads, but still feel the same having taken up some fairly gentle MTB and bought a hardtail online.
    – Chris H
    Feb 9, 2018 at 8:04

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