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I just recently obtained a classic style bike frame that has horizontal fork-ends (people call them dropouts but they're different).

I wanted to use hollow axles and skewers on this bike but I think that the skewers will slip. I've seen those chain tug screws but what I'm concerned is the axle slipping out of the fork-end, not slipping in. (which is prevented by pulling the axle out, tensioning the chain)

chain tug here

Normally in single speed bikes, it's the chain that prevents the axle from slipping out of the frame. It's different in my case, as I will be fitting a derailleur on this. (the chain is long, and the derailleur tension might not be enough to keep the axle in)

Is there some sort of reverse chain tug or an axle block for a bike that prevents the axle from moving both ways?

motorcycle axle block

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Nearly all mountain bikes from early 1990's to early 2010s (which is 2 decades) and even now many low cost bikes, use Hollow axle QR on an open dropout without any concern. Sure the opening faces down, but many MTB's spend plenty of time with wheels in the air.....

When pedaling the wheel is pulled forward with extreme force. When not pedaling, the action on the axle moves to a very small upward pull (depending on the derailleur angle). The QR would have to be extremely loose for the wheel to drop out.

Is it a concern - for a manufacturer of frames intended to run as you desire, the lawyers would be insisting on lawyer lugs to protect against liability when someone does not do up the QR. However, if the QR is done up, its not a concern at all.

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  • In case you missed it, my fork-end ('dropout' is a formal term for vertical fork-ends) is horizontal and opens at the back. What I'm concerned is the axle slipping back and out of the fork-end. It doesn't have lawyer tabs or alignment screws. Sure, pedaling might help, but given that the chain is long, generally loose, and only tensioned by a RD, I'm not taking any chances, especially during downhill areas. I could just buy a new frame for convenience, and I'll do just that if there isn't any solution to this problem. (hence my post)
    – Gregory Leo
    Commented Nov 7, 2018 at 14:55
  • The tension on the chain comes from the pedals, not the derailleur. The spring tension on the derailleur is minimal and only there to hold the chain tight enough it doe snot fall off the sprockets and chain rings.
    – mattnz
    Commented Nov 7, 2018 at 20:16
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In the days when bicycles with shifters didn't have vertical rear dropouts but forward facing horizontal ones such as the one in the picture, quick releases were in use and the wheels normally stayed well in place as long as the QR was properly tightened. In case of a slightly loose QR, standing on the pedal would make the wheel come askew, resulting in the tyre rubbing against the left lower stay. No special retaining devices to prevent the forward movement of the axle were in use.

The picture also demonstrates quite well how the serrated side of the QR 'bites' into the dropout, so you don't need to worry about moving the axle through pedalling force.

(The thin spring-loaded screws at the rear are adjusting screws that help always finding the correct position of the axle after putting a wheel back in.)

enter image description here

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  • but in my situation, the horizontal fork-end (again, dropout is a formal term for vertical fork-ends), opens at the rear direction. Thus, I'm more concerned of the axle slipping out than in. The chain won't do much to pull the axle back in as the spring of the RD (which is the one tensioning the spring) isn't strong enough. My fork-end also happens to be pure stainless steel (the whole MTB frame, actually) that doesn't have aluminum lining stamped to it, so the QRs won't bite through.
    – Gregory Leo
    Commented Nov 7, 2018 at 14:48
  • Stainless steel is 'soft' when compared to teeth on serrated QR nuts. These are hardened steel and will bite in. It's not the tensioning spring of a derailleur that keeps an axle in position. The chain-tug screws on a bicycle are more for alignment. On a motorbike, your 2nd picture, it's a different thing, those devices are also meant to keep the axle in position, a) while tightening the axle nut and b) against the much higher engine power which may amount from 50 to 100 times that of a cyclist.
    – Carel
    Commented Nov 7, 2018 at 16:32

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