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I bought a RockShox suspension fork for a trekking bike I'm building. My plan was to use a wheel with a Shimano XT Shimano DH-3N72 hub dynamo I have from before on it. The hub has a normal bolt on (9mm?) axle. Before installing the fork, I'm reading through the manual, and they specifically mention you should only use a quick release or thru axle on it, "Do not use a bolt on axle with you fork". When I try, the wheel and axle bolts seem to fit perfectly.

I understand that fork instructions are not something to ignore lightly, but I'd like to know why they advice so clearly against this?

You have to tension the bolts with a torque of 6 - 8 Nm, which is more than quick release I imagine. But I couldn't imagine this would have an effect on the fork?

Also, would it be easy to replace to bolt on axle with a quick release or does the hub need to be different for that?

Edit: correct hub type

Edit: add pictures of the hub to clarify the kind of bolts.

left side right side

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    This is a good question. I assume you mean you have a nutted axle generator hub. I hadn't noticed that in the manual before. I think odds are high it's a generic warning that has to do with the tendency for nutted axle hubs, which by numbers are usually pretty junky, to have the axle nuts chew up the dropouts. Plenty of 26" and 24" dirt jump bikes come with suspension forks and nutted axles. Replacing the axle on a Shimano generator hub is one of those things that might be a distant theoretical possibility but would require jumping through many, many hoops.
    – Nathan Knutson
    May 31, 2017 at 9:25
  • There are two different kinds of nuts: ones that are plain and have a serrated side to prevent slipping and those made of two parts where the serrated ring just presses against the drop-out and doesn't dig into the material like a grinder when you tighten the nut. The caution in the manual could advise against the first and cheaper type. (Serrated washers do exist and would be fine as well.) If the nuts are not of the first kind I'd ignore the warning. Just check the tightness regularly because the movement of the fork might also loosen them.
    – Carel
    Jun 1, 2017 at 12:15
  • Thanks @Carel for the comment. I added some pictures of the hub to show the nuts. I guess this is the first kind you describe, right?
    – bwindels
    Jun 3, 2017 at 13:43
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    I think @Carel is right, but it wouldn't hurt to shoot rockshox a quick email and maybe write a canonical answer.
    – Batman
    Jun 3, 2017 at 20:25
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    @Carel, indeed, that's how you tighten them. If I can find an e-mail address I'll double check with SRAM, but I'll start using the wheel already. Thanks for the advice.
    – bwindels
    Jun 4, 2017 at 17:40

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I came to some assumption why you should not use bolt-on axle. It is hard to screw the axle preserving fork sliders in one plane. They can get positioned ascrew, because of screwing the nuts in the opposite directions. It is not a problem in motorcycle suspension because of lack of fork brace. But here? let's say you sit in front of your front wheel and have two wrenches, one on each nut. When you tighten left-hand nut, left slider is pulled back by the nut and when at the same time you tighten the right slider, it is pulled forward. Fork brace prevent sliders from returning to initial, single-plane position. This result in suspension that does not move freely, because more tension is put on "fore-surface" of left stanchion.

This "ascrewing" is easy to observe when you're mounting an old fashioned mudguard with mudguard stays mounted on the axle.

I'm sure, that you are able to use bolt-on axle and screw it properly (by using proper nut and spacer and by greasing spacer - nut interspace). Keep in mind, that user/service manual has to be idiot-proof.

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