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Minimum axle exposure to contact dropout?

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Minimum axle exposure to contact dropout?

Old 08-14-19, 06:59 AM
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tiger1964 
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Minimum axle exposure to contact dropout?

(Lifted from another thread of mine, which has wandering out into the woods; should not ask technical questions in post 27 of any optic, I presume)

So, what's the minimum # of mm of axle to stick out past the locknut to provide adequate load bearing surface to contact the dropout?

This is my first experience with more than 5 rear sprockets. When leaving the 6th cog for 5th, sometimes the chain jams on the seat stay immediately above the dropout. Hmm, I measured and the hub is clearly 126mm, There is enough free space between the dropouts to go a bit widerÖ add a washer under the RH locknut? (a) how much messing about with the axle before I have to relish the wheel? (b) thereís only about 4mm of open axle to rest on the dropout and the bikeís weight (and mine), whatís the minimum? If I steal a washer from the LH side, and add to RH side, and even out the open axle exposure, arenít I affecting dish even more?
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Old 08-14-19, 08:30 AM
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Velo Mule
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Not much. According to Sheldon, he rode a bike that had no axle stick-out. It relied on the pressure of the quick release skewer to hold the axle and hub in place. If I remember correctly, he did this on a single speed in order to get the chain tension correct. So, if you got just 1mm of stick out, that should be enough to engage in the drop out to keep the axle in the right position until you clamped it with the quick release skewer.

Make sure that QR skewer is German torque, "Good-n-tight".
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Old 08-14-19, 09:43 AM
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Most manufacturers offer axles lengths that are 8mm longer than OLD, so 4mm overlap would be the defacto optimum. for forged dropouts. Many bicycles with stamped dropouts were equipped with QR hubs and a typical stamped dropout is ~3mm thick. so that would also be OK. Going below that, a lot depends on the condition of the axle end. For instance if there's a 1mm bevel, that 3mm overlap is only 2mm of actual bearing surface. I certainly wouldn't risk zero overlap and rely totally on the QR compression. One sudden jolt from hitting a pot hole or similar could cause the the wheel to unseat and jam against the pads or stays. Personally, I wouldn't go below 2mm of bearing surface.
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Old 08-14-19, 11:47 AM
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Agree, I wouldn't want less than 2 mm of protrusion with horizontal dropouts especially. For most rear sprockets of 13 or 14 teeth, you need 3-4 mm of clearance between the outer face of the smallest sprocket and the locknut face. Maybe less for 12 teeth and definitely more for 15 teeth, neither common on freewheels now.

Yes if you put an extra washer under the right locknut to get this clearance, you will be better to re-centre the rim, particularly if you move one from the left side to the right side, and this will make the wheel more off-centre with respect to the hub when you're done. Not everyone would re-centre for a small change like this, but I would, and do, just because otherwise it's not as good as I can make it. If you can get by with only a 0.5 mm washer, so much the better. That might be all it takes. There will be a lot of trial and error, and much adjusting of cones on both sides. You will be taking the freewheel off to adjust the right axle stack, then putting it back on (just till it seats) to check clearance. Repeat until OK.

You say the chain only "sometimes" jams when shifting from smallest to next larger. What happens is that as the derailer first pushes inward to derail the chain, it (the chain) momentarily tilts outward on the cog tooth so the upper outer edge of the outer link plate is now sweeping out a space wider than the chain was when it was running on the smallest sprocket. The chain returns to vertical as it moves inward and gets out of the way. With the jam being a sometimes thing, you might be just a hair's-breadth short of adequate clearance -- enough to clear the inner link edges but not enough to clear all the outer link edges all the time. If the chain is by chance catching on the dropout itself, you can try filing a little relief just where that link plate edge goes by. It might take only a few file strokes. I have a bike with high dropouts where that worked. But alas in your situation I wouldn't file the stay itself, being thin. Is this a frame with vertical dropouts?

But the bottom line is, if you have 4 mm of axle showing now, you can probably fix the problem with 1 mm or less of movement, so you should be fine all around. The filing idea is just if you're that close to clear and have a nice thick dropout to file. Saves having to attack the axle stacks and re-centre the rim.

Last edited by conspiratemus1; 08-14-19 at 11:56 AM.
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Old 08-14-19, 11:50 AM
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Originally Posted by Velo Mule View Post
Not much. According to Sheldon, he rode a bike that had no axle stick-out. It relied on the pressure of the quick release skewer to hold the axle and hub in place. If I remember correctly, he did this on a single speed in order to get the chain tension correct. So, if you got just 1mm of stick out, that should be enough to engage in the drop out to keep the axle in the right position until you clamped it with the quick release skewer.

Make sure that QR skewer is German torque, "Good-n-tight".
Yeah, I've done that too! I just didn't have the appropriate length axle but I needed to ride!! Everything was fine. For this, I recommend an internal cam quick release, like Shimano, Maillard, Sansin, Suntour, or old Campy, for achieving proper guten-tight spec.

If you think about it, any bike with horizontal dropouts is effectively relying on the quick release to keep the rear wheel from slipping forward under chain tension. There's no metal in front of the axle to stop it, so what difference does it make if it is there! That's the reason occasionally you'll hear of people having problems with external cam quick releases having their wheel slip forward in horizontal dropouts. Not capable of getting tight enough!
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Old 08-14-19, 01:35 PM
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For a 6-speed freewheel, I donít see why you would need to go wider than 126.
First, are you certain there isnít a spacer under the freewheel? Assuming there is not, I would go ahead and move a small spacer from the NDS to the DS, and re-dish as necessary, which should be little.
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