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Old 01-18-08, 10:55 AM   #1
darronb
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Create asymmetrical rear dropouts to eliminate wheel dish?

When reading about the Surly Pugsley on Sheldon Brown's site, I found the asymmetrical frame and fork ends to be a brilliant idea. I don't know if I'm allowed to post images here from the sites of others, so instead here's a link to an image on Sheldon's site for you to check out, and better understand what I'm referring to.

I'm sure there's a good reason for this, but why don't more bikes with normal-width tires use this system, at least on the rear wheel? This would allow the building of rear wheels with no dish, making them stronger. The main objection I can think of is that the drive side crank arm would not clear the chain stay unless the stay was bent in a dog leg shape right behind the rear-most arc of the crank arm. This would weaken the stay, but it could be beefed up to compensate. This Clyde for one would gladly accept the extra weight in exchange for a stronger rear wheel.

Perhaps even existing old steel frames could be asymmetrically bent to create a zero-dish setup. If there are any spacers on the non drive-side of the rear hub, you would want to remove them, then bend the non drive-side dropout in toward the frame's center-line a little, if possible. The drive side would be bent out to align a zero-dish wheel to the frame center-line . This would move the drive-side dropout ahead of it's opposite number, so horizontal dropouts would be required to allow the axle to be installed perpendicular to the frame's center-line. And the dropouts would have to be bent back into being parallel with the center line, as well.

Hmmm, perhaps it's time to experiment on that freebie xmart gas pipe MTB frame I've got out in the shop...

Darron

Last edited by darronb; 01-18-08 at 11:11 AM.
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Old 01-18-08, 11:21 AM   #2
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Originally Posted by darronb View Post
When reading about the Surly Pugsley on Sheldon Brown's site, I found the asymmetrical frame and fork ends to be a brilliant idea. I don't know if I'm allowed to post images here from the sites of others, so instead here's a link to an image on Sheldon's site for you to check out, and better understand what I'm referring to.

I'm sure there's a good reason for this, but why don't more bikes with normal-width tires use this system, at least on the rear wheel? This would allow the building of rear wheels with no dish, making them stronger. The main objection I can think of is that the drive side crank arm would not clear the chain stay unless the stay was bent in a dog leg shape right behind the rear-most arc of the crank arm. This would weaken the stay, but it could be beefed up to compensate. This Clyde for one would gladly accept the extra weight in exchange for a stronger rear wheel.

Perhaps even existing old steel frames could be asymmetrically bent to create a zero-dish setup. If there are any spacers on the non drive-side of the rear hub, you would want to remove them, then bend the non drive-side dropout in toward the frame's center-line a little, if possible. The drive side would be bent out to align a zero-dish wheel to the frame center-line . This would move the drive-side dropout ahead of it's opposite number, so horizontal dropouts would be required to allow the axle to be installed perpendicular to the frame's center-line. And the dropouts would have to be bent back into being parallel with the center line, as well.

Hmmm, perhaps it's time to experiment on that freebie xmart gas pipe MTB frame I've got out in the shop...

Darron
The biggest drawback I can think of to what your proposing is getting an acceptable chainline. To do so would require putting the right crank and chainrings waaaay out there. The Pugsley is a different animal entirely, and riders who use it for it's intended purpose are not going to care about Q factor or whether their right crank is farther out than the left, but I think your average road rider would not accept such a design.
Just my 2 cents.
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Old 01-18-08, 11:26 AM   #3
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The biggest drawback I can think of to what your proposing is getting an acceptable chainline. To do so would require putting the right crank and chainrings waaaay out there.
D'Oh! Forgot all about that issue...

Perhaps a dog-leg bend in the chain, as well ;-)

Darron
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Old 01-18-08, 11:33 AM   #4
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Framebuilder Tony Oliver produced some dished frames back in the 1980s and illustrated them in his book "Touring Bikers"
The drive side stays looked pretty normal but the non-drive side was dished inboard
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Old 01-18-08, 12:09 PM   #5
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I think that dishing a wheel is a simpler and pretty proven solution.
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Old 01-18-08, 12:21 PM   #6
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Such bikes would be great for people that road track counter-clockwise all the time.

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Old 01-18-08, 12:24 PM   #7
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The biggest drawback I can think of to what your proposing is getting an acceptable chainline.
How about getting the axle square with the rest of the frame? If you bend the right chainstay outward it's going to move the right dropout forward relative to the left dropout.
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Old 01-18-08, 12:52 PM   #8
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How about getting the axle square with the rest of the frame? If you bend the right chainstay outward it's going to move the right dropout forward relative to the left dropout.
Yes, well the OP had already addressed that issue, my comment related to bikes designed around his proposal.
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Old 01-18-08, 04:20 PM   #9
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The easiest and best method would be to make rear hubs without dish. That's accomplished by moving the non-drive-side flange in towards the centre of the hub, making it symmetrical. Just under half an inch in for a typical rear wheel.

I'd much rather have a hub and wheel based on that. Not that I've had a problem with my rear wheels now, but I hate asymmetry. Asymmetry equals weakness. Weakness is not good.
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Old 01-18-08, 04:24 PM   #10
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Orbit in Britain had asymmetrical rear wheels for quite a few years.
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Old 01-18-08, 04:50 PM   #11
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Velocity Aerohead OC (Off-center) rims.

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Old 01-18-08, 08:58 PM   #12
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I've been building frames with offset dropouts and no dish for almost 30 years.

Our 19 year old LWB recumbent tandem carries almost 300 lbs on the rear wheel when we're touring. We run 36 2.0-1.8-2.0 spokes and have never had a wheel problem.
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Old 01-18-08, 10:15 PM   #13
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Internally geared hubs = no rear wheel dish AND symmetrical dropouts.
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