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Rear axle length? (sanity check)

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Rear axle length? (sanity check)

Old 06-26-12, 11:05 AM
  #1  
JonnyRo
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Rear axle length? (sanity check)

I got a new bike a few days ago. This one: https://bike.capriolo.com/2012/sport/monitor-man It's cheap and it's kinda weird because it has some MTB features, but it's mostly designed for city riding - just what I wanted.

While tinkering with it I found that the rear triangle has an inner spacing of ~136mm, as one would expect, but that the hub is only ~131mm (lock nut to lock nut). Never mind the unnecessary stress on the AL frame, the wheel isn't dished enough to be centered so someone at the store set the axle so it doesn't sit all the way in the dropouts just so it can clear the break pads. I tried adding a couple of washers (5mm total) to the non-drive side of the hub and everything is great, except the axle is now too short and I can't ride it like that.

Am I wrong, or is a ~5mm difference between an untightened rear hub and the frame too much for a new AL bike?
Is the cheapest solution to exchange the axle for a 175mm one, and maybe replace the washers with a lock nut/bearing cone/spacer of appropriate length?
Are these standard dimensions: 135mm hub with a 175mm nut axle for this type of bike?
Should I except a solution (it is under warranty...) with no parts changed which would mean ignoring the difference between the hub and frame dimensions and dishing the wheel even further to the drive side so it would be centered while sitting flush in the dropouts?

Any advice on the subject welcome.
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Old 06-26-12, 11:23 AM
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There's plenty of spring range in the stays so having an axle 5mm short won't hurt the frame, but it's not ideal and shouldn't happen on a new bike.

The frame was clearly made for a 135mm axle, so either it's a case where the factory mixed the spec.s using the same frame for two different model bikes, one with 135 and yours with 130. This isn't usual, but is possible on low stuff intended for big box stores.

More likely, the original wheel for your bike was damaged in transit, or taken off and sold, and the shop put another one from stock on the bike. This is common, and a tip-off would be if the rims, hub, or tires weren't a matched set. I don't have a problem with wheel swaps, and we did it fairly often when I was in retail. But if a wheel was swapped, the pair should have been, and the right 135mm wheel used.

If this was bought as a new bike, you shouldn't have to fuss with it, switch axles, or redish it. You're entitled to a correct set of matched wheels, and the shop should take on the obligation of seeing this through, not you.
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Old 06-26-12, 01:39 PM
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If you decide to return the rear end wheel setup to spec:

Axle = M10 x 135mm x 145mm (Very high quality axles will appear to be M10 x 135mm x 146mm)

Freewheel stop to end of drive side locknut = 40.5mm

Outside non-drive locknut to outside drive side locknut = 135mm (If the best you can do is 134mm or 136mm, that's fine. The non-drive side can be fudge a mm).

=8-)

Of course, you'll want someone to reset the derailleur stop screws and adjust the cable tension and shifting. Wouldn't hurt to have the rear dropout alignment checked to ensure they are parallel - helps stave off bent and broken axles to an extent.

=8-)
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Old 06-26-12, 02:15 PM
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If you bought this bike new, return it to where you bought it and let them sort it out. Most big box stores will simply give you a new bike.

If you wish to fix it, the best solution would be to:
1. loosen the locknut on the drive sidem move the locknut, any spacers, and the cone toward the end of the axle, then re-tighten it with 2.5 mm less axle protruding.
2. take the locknut off the non drive side, screw the cone in until it is close to the bearings, add a 5mm spacer or washer, then re-attach the locknut.
3. adjust the bearings using the non-drive side cone and locknut, and lock it down.
4. re-dish the wheel by adjusting the spoke tension.

THis is much more work than you should be expected to do on a new bike. I would return it.
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Old 06-26-12, 05:59 PM
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Originally Posted by FBinNY View Post
There's plenty of spring range in the stays so having an axle 5mm short won't hurt the frame, but it's not ideal and shouldn't happen on a new bike.
I thought as much, but what really worries me is that the axle was tightened in such a way that it didn't sit all the way in the dropouts. That brings all sorts of cringe inducing torsion images to my mind... I did some quick measurements using the string method and it came out 3.7cm string to seat tube on one side and 4.2cm on the other. I'll have to take a more precise measurement, but I wonder what, if any, would be an acceptable margin for a new frame? The string length is ~106cm head tube to dropouts, and the seat tube is ~66cm away from the head tube at the "intersection" with the string. Don't know if those are important for judging the acceptable frame deviation...

@everyone:
Thanks for helpful advice! The bike is not exactly a supermarket item, at least not where I live, and it is designed, assembled and at least in part made in my country. Just going back to the store, guns blazing and demanding a replacement would cost me too much time and probably wouldn't solve anything since it might be an issue with the entire series.
What I'm looking for right now is to arm myself with facts so I can decide if the problem is something that can be relatively easily and painlessly fixed by the store/manufacturer or I should just return it.
I would be satisfied with a new axle/hub/wheel but if the frame is bent I'll have to return it. Which breaks my heart! I know I'll get more understanding from this audience then from "regular" people when I say - it has only been a few days but I already love this bike!
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Old 06-26-12, 06:31 PM
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Hmmm, 5mm off at the seat-tube is actually closer to 8mm at the rear-drop-outs with your measurements. It's off from perfect, but not completely out of range for production bikes I've seen. The frame most likely came from the factory this way. The 5mm shorter axle would squeeze both sides evenly and won't cause any damage. Don't try to cold-set it like a steel-frame as aluminium's yield-strength is very close to its ultimate-strength. Bending it would reduce it's fatigue-life and durability significantly.

When you added the 5mm spacer to the left non-drive side, did you loosen the locknut & cones on the right drive-side and slide the axle to the left as well? So that you have an even amount of axle-stub on both sides?

Get the hub-adjusted then the rim dished properly to centre between the new 135mm O.L.D. Check dishing on the front wheel as well. Then see if you can ride it no-hands in a straight line without having to lean the bike. Also no pulling to one side. If it rides straight, I'd keep it. Otherwise, see about a replacement from the shop.
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Old 06-26-12, 07:19 PM
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^^
It's quite possible, probable even, that the frame left the factory misaligned. But I won't know for sure until I measure a brand new frame that wasn't on the road with a badly set axle. Like I said, it's not the O.L.D. vs. frame spacing difference that bothers me, but the torsion effects of the axle not sitting properly in the dropouts. I think I'll take your advice and make them fix the axle. Then I'll watch out for real symptoms of a bent frame.

I just added the washers for measurement purposes. I didn't see the point in trying to center anything since it was obvious that there wouldn't be enough axle left.
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Old 06-27-12, 03:19 AM
  #8  
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Originally Posted by JonnyRo View Post
... it's not the O.L.D. vs. frame spacing difference that bothers me, but the torsion effects of the axle not sitting properly in the dropouts..
Huh? Torsion effects are only on IGHs and hub brakes. External gears, there's no torsion in the axle.

Last edited by dabac; 06-27-12 at 06:32 AM.
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Old 06-27-12, 03:44 AM
  #9  
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^^
You're right, I used the term loosely. I should have used plain old twisting since there's no torque involved, just the weight of my ass pressing down on everything.
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Old 06-27-12, 04:44 AM
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Originally Posted by JonnyRo View Post
^^
You're right, I used the term loosely. I should have used plain old twisting since there's no torque involved, just the weight of my ass pressing down on everything.
Ah, you're talking about the bending.
The bending force the axle sees has little to nothing to do with how the axle sits in the dropouts, and is pretty much all determined by hub design - the distance between the dropouts and where in the hub the bearings are located. And rider weight of course.
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Old 06-27-12, 05:26 AM
  #11  
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I dunno; maybe he did mean torsion.

Originally Posted by JonnyRo View Post
I thought as much, but what really worries me is that the axle was tightened in such a way that it didn't sit all the way in the dropouts.
How so?
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Old 06-27-12, 06:37 AM
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Originally Posted by JonnyRo View Post
... just the weight of my ass pressing down on everything.
Come to think of it, if dropouts are badly out of parallell, you can introduce some bending into the axle when mounting the wheel.
Still, axle length isn't a big player in that scenario either - unless from the perspective of allowing OLD adjustment to the point of compensating for the the slant in the dropouts.
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Old 06-27-12, 08:27 AM
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Originally Posted by dabac View Post
Ah, you're talking about the bending.
The bending force the axle sees has little to nothing to do with how the axle sits in the dropouts, and is pretty much all determined by hub design - the distance between the dropouts and where in the hub the bearings are located. And rider weight of course.
Not true. If the dropouts are not paralell then clamping down the nuts or quick release will force the dropouts back towards paralell and an equal and opposite force will act to bend the axle. If the dropouts are close to paralell and the spacing only off by 5 mm then this force is probably not too significant... but on a bike with 136 mm (!) spacing, I don't think we should assume (ass u me) the dropouts are perfectly parallell to begin with.
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Old 06-27-12, 08:42 AM
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Originally Posted by JonnyRo View Post
I just added the washers for measurement purposes. I didn't see the point in trying to center anything since it was obvious that there wouldn't be enough axle left.
Loads actually do not rest on the axle-ends beyond the locknuts. You only need 2-3mm of axle-stub exposed per side to centre the wheel in the dropouts. Once the QR is clamped, all the loads go from the locknut faces to the dropouts. The actual load on the axle is at the cones and bearings.

In this case, it's best to expand your hub to 135mm so that there's no compression on the rear-triangle of the frame. This will also keep the dropout-faces parallel. Then there's no bending of the axle.

Last edited by DannoXYZ; 06-27-12 at 08:49 AM.
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Old 06-27-12, 08:56 AM
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Originally Posted by DannoXYZ View Post
Loads actually do not rest on the axle-ends beyond the locknuts. You only need 2-3mm of axle-stub exposed per side to centre the wheel in the dropouts. Once the QR is clamped, all the loads go from the locknut faces to the dropouts. The actual load on the axle is at the cones and bearings.

In this case, it's best to expand your hub to 135mm so that there's no compression on the rear-triangle of the frame. This will also keep the dropout-faces parallel. Then there's no bending of the axle.
I agree that respacing the hub to 135 is the best bet, though it might call for redishing the wheel. As Danno says you don't need much axle in the dropout, but I always try to have enough that 1-2mm of full diameter are exposed. Otherwise you run the risk of mounting on the tapered (chamfered) end of the axle. This isn't a strength issue, since there's bite on the axle faces, but makes for unreliable locating of the wheel, which may vary depending on which way the axle is rotated.
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Old 06-27-12, 09:09 AM
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It's a nut axle, not QR. Hopefully the axle discussion will be moot because I'm negotiating with the factory to send a new QR freehub (this one is freewheel + nut) and cassette. That would mean relacing the wheel instead of replacing the axle. It had to be redished anyway, so it's less hastle for everyone and I would end up with better parts.
After that I'm off to try riding sans hands. And after that, if all goes well, you won't see me again until I get a phone with a decent browser so I can stay in touch while on the road.

Seriously people, thanks for all the help, you got a great community going here!

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Old 06-29-12, 08:39 AM
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Update: I returned the bike! Now I got my eye on another one. Help if you can.
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Old 06-29-12, 10:12 AM
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Originally Posted by JonnyRo View Post
Update: I returned the bike! Now I got my eye on another one. Help if you can.
I'm glad to see you returned the other one rather than deal with the unnecessary complications. The Scott seems like a decent basic bike, but I can't comment on value because I have no idea of prices in Serbia. If this doesn't work out, your best bet might be to find a ride to either Austria or Italy, where you're likely to find a broader selection.

If you do buy this bike, I suggest you save up a few dollars and buy a replacement derailleur hanger. These are breakaway parts, and shouldn't be an issue unless the derailleur is misadjusted and over shifts into the wheel. But they have been known to break prematurely (on all bikes) and there are so many, and they change so often, that you may not be able to find one in a few years (especially in Serbia). It's not a do it immediately kind of thing, but you'll want the assurance of having a spare available within a year or two before they disappear entirely.
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Old 06-29-12, 02:15 PM
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^^
Thank you very much, that's useful to know about the hangers! I got the bike from the official Scott distributor but it will surely be easier to stock some parts now than possibly wait for them to arrive. And that's if there are any left... Any others that easily break but often change in design?

I'm always thinking about going on a shopping spree to Vienna but never actually do it.

@Everyone: Once again, thanks to every participant in this thread, your advice and assurance really meant a lot to me! Now I can relax and enjoy my new found love affair with bikes.

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Old 06-30-12, 10:47 AM
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Originally Posted by FBinNY View Post
I agree that respacing the hub to 135 is the best bet, though it might call for redishing the wheel.
Which is a fine thing, since you'd be removing dish and making the wheel stronger.

Originally Posted by JonnyRo View Post
until I get a phone with a decent browser
If you have an Android phone, you can install another browser, you know... Opera Mini is pretty sweet. Dolphin HD isn't too bad either.

Originally Posted by JonnyRo View Post
Any others that easily break but often change in design?
Nothing else springs to mind.

Last edited by Kimmo; 06-30-12 at 10:52 AM.
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Old 06-30-12, 12:42 PM
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Originally Posted by Kimmo View Post
Which is a fine thing, since you'd be removing dish and making the wheel stronger.
The wheel was actually dished for 135! That's what was annoying me the most. I figured that out by putting some washers on the axle and setting it all the way in the dropouts.
It was all clearly a factory mistake and a time bomb. Glad I got rid of it...
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