Frame Design for Smaller Folks
I have had a good number of questions and requests about accommodating smaller cyclists on my bikes. And I am now starting to explore what it would take to make my frame design in a smaller size.
As of now I have had individuals as short as 5'4" on the frames, but seeing as there is a Under 5 foot 1 inch group, I would appreciate any insight (being 6' 2" myself) into the challenges you find - particularly related to a city/commuter bike, such as what I make.
What size wheels, length cranks, components and accessories that do/don't work.
Thanks for any input.
Levi
owner/builder
Views: 3723
Replies to This Discussion
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Permalink Reply by John C. Wilson on
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A few observations:
The only fully supported tire sizes are 622(700C) and 559(26"). 584(650B) is somewhat supported but mostly at the higher end of the market. I cannot imagine any good reason for preferring 571(650C) to 559 or preferring 590(650A) to 584. I have known a few Terrys allowed to rust in peace for lack of 571 tires and rims.
The prime way to get toe clearance is to slacken the head tube angle and increase fork rake. Current manufacturing practice for small frames slackens the head and leaves fork rake untouched or increases rake by trivial and meaningless margins. The short rider in this house has two bikes with real fork rake. One fork has 70mm rake. That was one I commissioned to correct a severe overlap problem. Three so-called custom builders who advertise for building forks with long rakes for the specific purpose of solving overlap issues turned me down flat. 70mm rake was more than they would contemplate. That bike has a 72 degree head and has no problem with a long fork. I did finally find a builder. The other bike has 76mm rake. That fork was built in 1967 when there was nothing at all unusual about such rake. There is a museum of bicycle design rolling down the street. I visit the museum every day. You should too.
Legacy bikes seem to mostly be built with flat bars. If the flat bar sweeps back and the grips are behind the stem by a good margin you can give the bike a toptube as long as you want. No toe overlap then. Lots of old bikes are built this way.
A great many riders are just plain sitting too high in the saddle. Go outside and watch them teetering down the street. Simply by observation high saddles are more common for new riders, for lycra and crabon riders, for short riders and most emphatically for female riders. Also by observation the retail customer most likely to be deluged with information and misinformation is a new short female rider spending money. When you solicit input from short riders I would suggest you do something as basic as going for a ride with them. Do not get all busy correcting them. Watch the pedalling mechanics. Watch the steering. Listen most to the short rider who looks comfortable on the bike who is enjoying the ride. There will be few enough of them but their input means more than all the complaints from riders who are struggling to pound square pegs into round holes. Riders for whom it is just not working can tell you it's not working and they are right, but you are the one who has to figure out why it works or doesn't work. You can build good bikes but you can't control what happens to them.
The genius designer for small bikes was Frank Schwinn. You live in Chicago and you do bikes, you should get to know which bikes are his. Watch the short riders on the old Schwinns and think why it works so well. Raleigh had some good patterns too. All the best I've seen are mass production models from builders who cared.
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Permalink Reply by Legacy Frameworks on
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Ash, It was nice meeting you on the ride from the Plant. I did consider a mini velo format at the beginning of my research, but was dissuaded by an mini-velo owner - not sure the reasons now, but it might be something to re-consider. They are suppose to be super quick and responsive, but not so great at maintaining speed. The smaller footprint would be great for urban environments though.
With such small wheels, the traditional limiting factors are kind of tossed out the window, so it becomes a kind of reverse thinking when you are designing it.
Which brand did you have again? Maybe next time we cross paths, I could take a closer look.
Ash L. said:I just noticed this thread and sorry if I'm beating a dead horse since it seems like you're moving away from the smaller wheel idea but... I do so love my new mini velo and its 20" wheels has enabled me to ride a true diamond frame for the first time. It's worlds above my 42cm Cross Check in terms of toe overlap. The CC is fitted with 700c wheels as some cruel joke and it took quite a learning curve to not endanger my life every time I turned at slow speeds. I haven't taken the mini on hills yet but in the city it's definitely quicker to accelerate from a stop (duh, physics) without noticeable lag on long straightaways.
You're welcome to check it out for measurements anytime if you'd like.
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Permalink Reply by william on
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a) if you need to fix a tubeless puncture, then the tire is toast regardless -- that means a serious tire slash that would render any ride over. tubeless is the future. I have a friend who's been commuting on tubeless for two years now, not a single flat. And the ride is amazing. you realize that mountain bikers out in the middle of nowhere ride tubeless and they have less options than a commuter in a major metropolis that can just hop on a bus or take a cab? Tubeless the mountain world is taking over and for good reason.
b) if it's not dead, then 650c is on life support, at least since the early 90s. Whatever rims/wheel systems/tire/tubes are available arent that great. Like I said, I would never in a million years spent thousands on a custom frame built around 650c. 26" or 650b is the way to go particularly with a commuter.
c) what kind of 32s do you have?
fat tires do not have to be slow. If you use supple and round/smooth tires that does not have some puncture strip (a Grand Bois Cypres or Hetre, a Challenge L'eroica or Paris-Roubaix, a Vittoria Hyper, a Schwalbe Kojak or Ultremo ZX, a Pacenti Parimoto, etc), they're probably faster than a skinny tire at high pressure on a bumpy city street + way more comfortable. Plus, they will not likely pinch flat, and are a better tool for the job of negotiating pot hole laden city streets. Try a lighter, supple tire next time -- you will be surprised and will change your mind.
Kaz said:2. Tubeless is a terrible idea for commuters because fixing a tubeless flat on the road is basically impossible. I would never in a million years consider tubeless for a city/commuter bike.
3. 650c is not a dead standard and is basically what people are doing for road or track bikes for smaller people. Road bikes don't need 38 tires, I run some Vittoria Rubino Pro 23s and they are seriously just as comfy and flat-resistant as the 32s on my other bike but way less rolling resistance. I guess it comes down to deciding if you want to make a quick, light, city bike or a slow, clunky cruiser.
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Permalink Reply by yai danche on
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New riders tend to set their saddles too low! They're also more likely to launch from a stop by sitting and pushing off with one foot often times with assistance of the curb. More experienced riders do the Sheldon Brown preferred launch. Short riders also tend to set their saddle to the lowest because they're accustomed to that being the only allowable height. I'm guessing you are not on short side.
New riders who are teetering are probably not used to riding with drop handlebars and have difficulties starting from a complete stop. My two cents worth of observations. Anyways, new riders would not be interested in a custom build like Legacy. These are definitely not starter bikes.
John C. Wilson said:A few
A great many riders are just plain sitting too high in the saddle. Go outside and watch them teetering down the street. Simply by observation high saddles are more common for new riders, for lycra and crabon riders, for short riders and most emphatically for female riders.
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Permalink Reply by Ash L. on
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I have a Bruno Road 20. I had to order direct from Japan because the US companies that fabricate these bikes (Soma and Bikes Direct) have a 50cm as their smallest frame size. They're missing a huge opportunity in not realizing that these bikes are perfect for short people. The one you saw Saturday is a 46cm but obviously they could be made even smaller without sacrificing the horizontal top tube. The wheelbase is also much shorter than a 26 or 700, so maneuverability and indoor storage is a cinch.
Here's the google images LINK and they do a pretty good job of translating if your Japanese isn't at its best.
Legacy Frameworks said:Ash, It was nice meeting you on the ride from the Plant. I did consider a mini velo format at the beginning of my research, but was dissuaded by an mini-velo owner - not sure the reasons now, but it might be something to re-consider. They are suppose to be super quick and responsive, but not so great at maintaining speed. The smaller footprint would be great for urban environments though.
With such small wheels, the traditional limiting factors are kind of tossed out the window, so it becomes a kind of reverse thinking when you are designing it.
Which brand did you have again? Maybe next time we cross paths, I could take a closer look.
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Permalink Reply by payton on
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I've standardized on 26" wheels, thanks to the Long Haul Trucker. I could deal with 650s, since I could still use 26" inner tubes with those. Couldn't stand the toe overlap on a 50cm/700c road bike that I had, particularly since I like track-standing, and heel clearance for panniers (less so on the Trucker). I do really love those geometry touches on the Trucker, but it's definitely a truck and I'd prefer a vehicle with nimbler handling.
74cm inseam here, bikes are 76cm/78cm standover height at middle of top tube. I tend to prefer a taller bike, since I have a proportionately long torso (even for a short guy) and long stems feel squirrelly.
Kaz said:650c wheels: Some may disagree here but as someone with a proportionally short inseam who doesn't like mixte/step-through frames, smaller wheels are the only way to get a bike that I can comfortably stand over.
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Ok folks, I have ironed out the final geometry and think I have come to a good sizing without compromising the esthetic feel, handling and component options. I also wanted to keep the top tube short while avoiding toe overlap (shoe size in the image is 9 us 42 euro, and rider is estimated 5'0"). Here is the final result that will go under the torch in the coming days.
Specs:
Stand-over: 27.3"
Effective Top Tube: 21.7"
Effective Seat Tube: 19.2"
Wheels: 26" (559 bsd) 32mm tires will be standard, but prototype will have 35mm due to stock issues
Wheelbase: 40.4" - long for stability, close to a touring bike
Frame Geometry Modifications
Head tube angle: Decreased by 1 degree to 70
Fork Offset (rake): decreased by .12", when combined with the new head tube angle creates the same Trail as my other bikes.
Let me know if you want to know any other specs.
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Decreasing head angle increases trail. Decreasing rake increases trail. Back to school for you. Have to agree with Doug now.
Legacy Frameworks said:Ok folks, I have ironed out the final geometry and think I have come to a good sizing without compromising the esthetic feel, handling and component options. I also wanted to keep the top tube short while avoiding toe overlap (shoe size in the image is 9 us 42 euro, and rider is estimated 5'0"). Here is the final result that will go under the torch in the coming days.
Specs:
Stand-over: 27.3"
Effective Top Tube: 21.7"
Effective Seat Tube: 19.2"
Wheels: 26" (559 bsd) 32mm tires will be standard, but prototype will have 35mm due to stock issues
Wheelbase: 40.4" - long for stability, close to a touring bike
Frame Geometry Modifications
Head tube angle: Decreased by 1 degree to 70
Fork Offset (rake): decreased by .12", when combined with the new head tube angle creates the same Trail as my other bikes.
Let me know if you want to know any other specs.
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Thanks for your input John, but if you first take into account the smaller wheel size - by adjusting the fork length - the trail needs to be increased to get it to match my other bikes.
Rather than just decreasing the head angle OR decrease the rake, I did both.
John C. Wilson said:Decreasing head angle increases trail. Decreasing rake increases trail. Back to school for you. Have to agree with Doug now.
Legacy Frameworks said:Ok folks, I have ironed out the final geometry and think I have come to a good sizing without compromising the esthetic feel, handling and component options. I also wanted to keep the top tube short while avoiding toe overlap (shoe size in the image is 9 us 42 euro, and rider is estimated 5'0"). Here is the final result that will go under the torch in the coming days.
Specs:
Stand-over: 27.3"
Effective Top Tube: 21.7"
Effective Seat Tube: 19.2"
Wheels: 26" (559 bsd) 32mm tires will be standard, but prototype will have 35mm due to stock issues
Wheelbase: 40.4" - long for stability, close to a touring bike
Frame Geometry Modifications
Head tube angle: Decreased by 1 degree to 70
Fork Offset (rake): decreased by .12", when combined with the new head tube angle creates the same Trail as my other bikes.
Let me know if you want to know any other specs.
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OK, fair enough. I didn't know we were comparing apples and oranges and if I'd read closer I would've known we were comparing apples and oranges.
You seem to have a good temper. You want input. I am an old fart with no interest in scoring points or winning arguments. I would like to see people riding nice bikes. I think you want to see that too. So I'll give you a few bits of input and you can do what you want with it.
622 bikes do not handle like 559 bikes. No way you can make them handle alike. Small wheel bikes have smaller trail numbers. Bromptons are down around 20mm trail. The axle of a small wheel bike is just closer to the ground and the two diverging lines that define trail don't have the distance to spread. 559 and 622 are close enough that using the trail number for one when designing the other will give good enough results but you are not going through this exercise to come up with good enough.
The industry has settled on using low head angles to create toe clearance on small frames. It's cheaper. For someone as low production as you does that really matter? I rode enough 559 MTBs when MTBs were new that had rigid forks and even curved blade rigid forks to know that the steeper head bikes always handled better and they especially handled better on pavement. The only exception would be on balls-out hyper-technical descents. Then shallow heads were better. You're not designing for that. Shallow head bikes are about all that a short rider can find anymore and they are just inferior. FWIW early production Trek MTBs used 72 degree heads and they were great production bikes. And they had toe clearance even in the tiny sizes. With big knobbies.
Leave the head angle alone and give the fork some rake to get toe clearance. You'll be unique in the business. And your riders will have a better bike.
Be happy with the 35mm tires. Small wheels are stiffer. Small frames are stiffer. Small riders weigh less and deflect parts less. There has to be some give somewhere. Small diameter tires strike the ground at what amounts to a sharper angle. Larger tires spread the impact.
Finally there is no way you or I know what it is like to be short and ride a bike. Are you planning to offer customers a choice of 150, 155, or 160mm cranks? My experience is that in the rare cases where shorty good quality cranks are available short riders won't have them. I've tried 180s myself, which would be proportional to 150s for your target market and I can't stand anything that long. But short riders get by on 165s and 170s and seem to like it and I've never heard any plausible theory why it works. Ditto handlebars. My in-house short test-rider uses 38cm drop handlebars which only exist as vintage. Nothing new available at all. And she may go narrower. Not possible except with antiques. Small riders without a live-in parts curator just have to make do. The best you can do is spend some time riding bike with short riders and observe. Listen as much as you feel like, but you must observe how riders interact with different geometries and builds. You can prototype if you want and you have the time and money; you can always observe how riders sit on their bikes and how they pedal them.
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One point that should be brought to your attention is that not all short stature people are short proportionately. In other words, many are just small sized while others are "dysmorphic"-- a physiologic term for a person who is disproportionate. All the dimensions of a bicycle are dependent on the morphological classification of being "short." some persons of short stature may not be aware of their disproportion.
Examples of what I am writing about are ratio of leg to thigh length, torso to lower extremity length, and proportion of upper to lower extremity length. As a consideration, a short-thighed person will need shorter crank arm lengths to pedal at their best advantage. A person with normal forearms and short arms may have his or her seat to stem length miscalculated, etc etc.
So, even though you are getting good responses to the great question you have posed, you need to be atune to the variety of "short" & "tall" people you are trying to fit to a bicycle.
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A quick update on this. If you are following my Instagram ( http://instagram.com/p/dDZNQJEazQ/ ) you may have seen some posts recently of a bike in progress. Well, it's the prototype of the extra small size.
There were a few small tweaks from the last drawing that made the top tube even shorter without compromising toe overlap. But overall it should be the same feel as my other bikes.
The bike will be built up bare and shown at the Oak Park Art Fair this weekend where I will have a booth. http://goo.gl/2gqem9
It is built up with a 3 speed SRAM coaster hub and a SA drum/dyno in the front. Chain drive for now.
Come and check it out. We will also have to setup a meetup so I can get your ride impressions.
Thanks so much chainlink!
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