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Old 02-19-05, 01:29 AM   #1
rykoala
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20" road bikes- why not?

I have a question in my mind that I need answered. I am often thinking of ideas. "gee it would be cool if..." etc.

It would seem to me that with road bikes, the lighter the wheelset the better, and as few spokes that get used, there would be a significant strength increase by shortening the wheel. Why are there not road bikes with 20" wheels? I mean, if you were to put some thought into it, the bottom bracket and all would still be the same height, but instead of the chainstay angling up, it would be angled down a bit to make the bottom bracket higher. The head tube would be signifigantly longer, to compensate for the shorter fork. See the attached image. The black outline would be the standard road layout, and the red outline would show how it would be altered to run 20" wheels.

Am I nuts? There has to be a reason this hasn't been done before. I do realize that the chainrings would have to be quite a bit bigger to compensate for the smaller wheel, but I see no other disadvantages. It seems like the light wheels would have better acceleration. The frame would have more flex, maybe? And be a tad bit heavier?

Obviously I don't know why this would or wouldn't work better or worse than what's out there. Can anyone critique my idea?

Thanks
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Old 02-19-05, 01:47 AM   #2
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20" wheels are little...would spin faster, faster wear on the components, etc...just a few reasons I don't like the idea.
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Old 02-19-05, 03:05 AM   #3
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how about 16" wheels...?
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Old 02-19-05, 03:16 AM   #4
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Quote:
Originally Posted by rykoala
It would seem to me that with road bikes, the lighter the wheelset the better, and as few spokes that get used, there would be a significant strength increase by shortening the wheel. Why are there not road bikes with 20" wheels?
You're correct, a 20" wheel would be marginally more efficient than a standard 700c wheel. When you start pedaling your bike from rest, you must supply enough energy to accelerate the total mass of rider and bike horizontally down the road plus you must also supply energy to overcome your wheel's rotational inertia. A smaller diameter wheel has less rotational inertia, and like you say, the wheels would weigh less (less rim material and shorter spokes). However, the energy savings from smaller wheels are but a small fraction of the total energy needed to move down the road. I'm not sure the efficiencies gained by a smaller wheel would be noticeable.

Quote:
Originally Posted by rykoala
Am I nuts?
Most likely. Anyone who reads and posts in BF is probably nuts.
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Old 02-19-05, 04:13 AM   #5
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Yeah, you're nuts. Next question please.
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Old 02-19-05, 05:31 AM   #6
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Moultons hold some speed records and have been used for the RAAM.
http://www.moultoneers.net/
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Old 02-19-05, 10:20 AM   #7
james Haury
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Quote:
Originally Posted by PWRDbyTRD
20" wheels are little...would spin faster, faster wear on the components, etc...just a few reasons I don't like the idea.
Tell that to all the bike friday owners who love them to death.
I really like the ride on my 20 inch BIke Friday Metro.
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Old 02-19-05, 10:22 AM   #8
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Quote:
Originally Posted by The Fixer
how about 16" wheels...?
Everything pared down to mins for you huh? Does RYKoala know about Bike FRiday?
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Old 02-19-05, 11:23 AM   #9
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I think it(smaller wheels) has a possibility. It gives more flexible design towards better aero dynamics, either on your back recumbent style or on your tummy. The draw back of smaller wheels is it picks up more bumps on the road, I think.
Never say never.
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Old 02-19-05, 11:25 AM   #10
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the real problem with smaller wheels are rough roads. riding my bent on this washboard bike path kocks off 2mph and I have to work to keep that up. the smooth road right beside the path let me find that out when I tried them both.
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Old 02-19-05, 11:51 AM   #11
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Folding Bike forum! Bike Friday, Dahon, Brompton...
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Old 02-19-05, 12:00 PM   #12
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Guess I should be looking into folding bikes then? I know about them but haven't learned much about them. Off to the folding bike forum I go, to start learning more! Thanks for the responses.
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Old 02-19-05, 05:28 PM   #13
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Many low racer recumbents already have front and rear 20" wheels, and they are, indeed, fast.

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Old 02-19-05, 05:59 PM   #14
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Hey, why you gotta post one of the geeky looking lowracers....... heck that isn't even a lowracer. Thats a fast touring machine.
Anyhow, whats this crap about wearing stuff out faster......you mean tires.? I get over 2000 miles on my 20" front wheel.
heres one with a 20" wheel in the front that isn't geeky looking.

http://bentupcycles.com/site/itemdet...=39&sort=Price
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Old 02-19-05, 06:26 PM   #15
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Quote:
Originally Posted by Bud Bent
Many low racer recumbents already have front and rear 20" wheels, and they are, indeed, fast.

Looks like a huge neck stiffer to me...
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Old 02-19-05, 09:22 PM   #16
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My LBS has a late 80s Hamilton tri-bike with 24" wheels and a big nasty 60T big ring.
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Old 02-19-05, 09:27 PM   #17
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Quote:
Originally Posted by james Haury
Tell that to all the bike friday owners who love them to death.
I really like the ride on my 20 inch BIke Friday Metro.
Note how I said....reasons I don't like the idea. Sure I'd tell em...
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Old 02-19-05, 09:32 PM   #18
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Quote:
Originally Posted by Bud Bent
Many low racer recumbents already have front and rear 20" wheels, and they are, indeed, fast.


I hear guys say recubs are fast but they seem to be the slowest cyclist on the road. i have never seen a fast recub rider. im not saying there are none just must be rare.
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Old 02-20-05, 04:23 AM   #19
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Well, the smaller the diameter the rougher the ride of the wheels and also the bigger the "pothole effect". By "pothole effect", I mean if you hit one with a small diameter wheel, it is more likely to fall in and cause you all sorts of unpleasant results.

I have a friend how makes "ordinaries". She says because of the huge diameter and the flex of the spokes, ordinaries have really nice rides even with solid rubber tires (no flats ever). The other advantage is with a 60" wheel, you don't have to dodge most potholes. The freaking wheel will span them with no problem at all.
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Old 02-20-05, 06:17 AM   #20
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The disadvantages of a small wheel are countered by the full suspension system of the Moulton. The front suspension is a proper linkage,not a piston.
For performance bikes, there are a number of small wheeled designs which takedown rather than fold. These include Moulton,Friday, Airnimal. Folders. These are a different class to the commuter style folders.
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Old 02-20-05, 09:24 AM   #21
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Quote:
Originally Posted by CrimsonEclipse
Less rotational mass would make it a bit less stable. Makes no hands eating or drinking a bit
difficult.

Has anyone tested these? The Bike Friday is foldable and about 19-21 pounds.
So a properly engineered non foldable could be lighter.

I'd give it a try, but not for $2000-$5000.
CE
Ask koffee Brown what she thinks of hers.
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Old 02-20-05, 09:25 AM   #22
stumpjumper
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Quote:
Originally Posted by PWRDbyTRD
20" wheels are little...would spin faster, faster wear on the components, etc...just a few reasons I don't like the idea.
the '85 Georgina Terry I'm building up for my 7yr olds next birthday has a 24" front and the hub shows no more wear than the 700c rear.
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Old 02-20-05, 09:29 AM   #23
james Haury
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Quote:
Originally Posted by Pat
Well, the smaller the diameter the rougher the ride of the wheels and also the bigger the "pothole effect". By "pothole effect", I mean if you hit one with a small diameter wheel, it is more likely to fall in and cause you all sorts of unpleasant results.

I have a friend how makes "ordinaries". She says because of the huge diameter and the flex of the spokes, ordinaries have really nice rides even with solid rubber tires (no flats ever). The other advantage is with a 60" wheel, you don't have to dodge most potholes. The freaking wheel will span them with no problem at all.
Ordinaries gave way to safties because taking a header can be quite dangerous.
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Old 02-20-05, 10:03 AM   #24
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" I hear guys say recubs are fast but they seem to be the slowest cyclist on the road. i have never seen a fast recub rider. im not saying there are none just must be rare. "


Yep, it's guys like you that motivate me to pass every single uprignt rider I see. You must just live in the wrong part of the country. Recumbent styles are no different than upright styles. You apparently haven't seen a racing recumbent. If all you have seen is bike-e's and rans rockets, then I can understand why you've never seen a fast recumbent. On my lowracer I regularly do sub 4:30 centuries solo. In australia a guy just won a 600 k brvet race on a lowracer recumbent and beat the entire field by an hour, plus smashing the course record by an hour.
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Old 02-20-05, 10:59 AM   #25
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Bu now you have read that..
There ARE road bikes with 20" tires. The most well know is the Moulton. They have been around at least since the 1960,s . The chainrings are not that much bigger. A 52 or 53 is typical.

The reality is that these bikes are not less stable, they feel great at speed too. They can be made to handle quickly if desired. A good 20' wheel bike handles great.

You are right, they do accelerate fast. Also they allow a rider to get close when riding in a group for better drafting, because of the small wheel. Unfortunately as mentioned they are bumpy and the big pothole effect can be a problem. This effects the perceived value from the point of view of a new customer more than the actual use of the bike. Many of the popular 20" wheels bikes have suspension to deal with this.

This makes a 20" wheel bike a harder bike to sell, so that changes how many there are. I love my inexpensive Dahon folder, I found some high pressure slicks for it and it rides very well, no instability at speed. But, yes it is bumpier.

Go on the net and research Molton, Birdy, Bromton, or just folding bikes in gereral. The Airnamal is a great bike.
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