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Swapping wheels round between bikes at the weekend, I was surprised to find that the steel fork on my city bike (a Pompino) has 10 mm wide dropouts. I discovered this when the front wheel from it wouldn't go into the fork on another bike, which has the, what I always though was, standard 9 mm droptouts. This wheel has a nutted axle measuring about 9.5 mm, which I suspect is actually 3/8 inch.

I want to use a 9 mm quick release wheel on the city bike, and since its headset needs replacing too, I was thinking of buying a Surly Cross Check steel fork to replace the Pompino fork. I'll be disappointed if the Surly fork has 10 mm dropouts. It won't will it?

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cat1commuter [1421 posts] 4 years ago
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Got the Surly fork, and it has 10 mm dropouts. Seems that steel forks tend to have 10 mm dropouts. I guess that it doesn't matter, since any sideways forces are resisted by the serrations on outside of the wheel axles which bite into the inside of the dropout. I'm just really surprised that there is more than one dropout size. I have a front wheel with a 9 mm threaded axle, so it isn't the case that all threaded axles are larger than 9 mm.

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velotech_cycling [80 posts] 4 years ago
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Most common road and MTB hubs historically have been 9mm, but dropouts are often made slightly bigger to accomodate 3/8" solid spindles (JoyTech, KK, KT and Sovos being examples) or the Shimano oversize MTB hubs, like HB-M755, M571, M563 etc which are all 10mm spindle.

There are also a raft of other slightly odder standards for special purposes - some Shimano & Shimano clone MTB hubs have used 11mm spindles, then of course there are BMX-style hubs that use 14mm axles.

With the "leakage" of some MTB hubs across to the touring market, and the fact that many "Trekking" and commuter bikes use MTB parts, many fork manufacturers have felt compelled to adopt slacker fitting drop-outs.

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cat1commuter [1421 posts] 4 years ago
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Thanks for the info.

I've now managed to find a suitable fork with 9 mm dropouts - a Thorn Club Tour fork. It has every braze-on and fitting you could possibly want, which probably contributes to its relatively high price, but should be perfect for me.