Bear with me…

So I just bought some forks with that new fangled modern 15mm standard however none of my hubs have off the shelf conversion options available.

What I do have is an Aireal Switch in 20mm, this basically sits on a 20mm axle with an equally sized spacer either side. If I was to get one of those reducer axles off eBay and get a set of spacers made up at half the width (since 20mm is 110mm and 15mm is 100mm) then my hub should be correctly aligned with the brake mount yes?

It almost seems too easy.

Other options can be explored but this just seems the easiest and probably the most cost effective.

You’ve assumed two things;

your hub is 90mm wide, bearing face to bearing face

and

the external spacers are each 10mm wide.

If this isn’t the case your sums don’t work. I think…

Not sure where your figures are from?

I’m assuming that the hub plus spacers in 20mm configuration total 110mm, in 15mm configuration I would need to lose 10mm so shave 5mm off each spacer (whatever width they are) and I’m set. I think. I’m assuming there is no odd offset in 15mm format that would cause the rotor mount to be off centre. The spacing isn’t an issue as the hub comes with it’s own QR adaptor that just screws together through the hub sans spacers.

You said-

and get a set of spacers made up at half the width (since 20mm is 110mm and 15mm is 100mm)

which means each spacer would have to be 10mm wide in order to get the required width if you simply half their width and because half of 20mm is 10mm the width across the bearings would have to be 90mm in order to make the total width, including the modified spacers, 100mm. I think it’s just the way your first post is worded that sort of set the rules for the sums.

Your idea should work though, going from your second post, assuming no weird offsets or anything.

The problem you have is weather or not your hub is a dedicated 20mm hub in which case it won’t work as the hub body will be too wide. Also (assuming standard hub width) you will probably need to take the 10mm off the non disc side and re dish the wheel otherwise the disc will be In the wrong position

The problem you have is weather or not your hub is a dedicated 20mm hub in which case it won’t work as the hub body will be too wide. Also (assuming standard hub width) you will probably need to take the 10mm off the non disc side and re dish the wheel otherwise the disc will be In the wrong position

Nope. The caliper mount and disc mounts are in the same (relative) positions on 20 x 110 and 15 x 100 forks/wheels.

OP, send me a PM if you want, we do this stuff as a job and I recently modded a 20mm hub to fit some 15mm forks.

Ok, I’m not near my bikes to check so I’ll take your word for it ( I may be thinking of boost) But if it’s a dedicated 20mm hub then it could still be too wide right?

No, otherwise how would adaptable hubs work? The disc mounting face must be in the same place. 9mm QR, 15×100 and 20×110 all have the disc mount in the same place. The new boost 20mm thinger is different though- the hubs are the same overall width but the flanges are further apart which pushes the disc mounting face out by just enough to stop new wheels working in old forks easily.

A dedicated 20mm hub is 110 just like a 15mm boost hub is.

I think a reducer that ran the whole depth of the hub would still be feasible in such a situation but I’d expect you’d introduce efficiency losses.

To make this work well you’d need 20mm endcaps that could be removed and swapped for 15mm endcaps that were the same length and used the same method of securing. If you’re happy replacing spokes and don’t need swappable sizes, substituting in a 15mm hub is probably a better solution than trying to make reducers work in a hub not designed for them.

I think a reducer that ran the whole depth of the hub would still be feasible in such a situation but I’d expect you’d introduce efficiency losses.

That’s good, explain how that’d work then 😉

You’d put an axle tube in an axle, essentially. It wouldn’t work well. Admittedly I forgot that regular 15mm isn’t 110 so that would kill the whole idea. Maybe with some really strong threadlock and a file 😂. It wasn’t a serious suggestion as I thought I’d made clear…

Tbh, in this situation I’d just put a hub that offered useful fittings in place. Pretty much anything else you could do is going to be limited by how much meat is on the existing end caps and a lot of machining and effort, either leaving you with a 10mm offset wheel which will limit tyre choices in future or be using so many spacers trying to sort Rotor position out it would be unfunny and possibly problematic. Plus, by the time you’ve removed the hub to do the machining, so long as you don’t demand a bling Hope replacement it would probably be cheaper to replace the hub, too…

The wheel wouldn’t be offset at all. 9×100(ie QR) , 15×100 and 20×110 are interchangeable as far as disc position goes, and the caliper mount is in the same place (relatively). All it needs is the 20mm end caps replacing with some 15mm push-in efforts like Superstar use on their 20mm Switch hubs.

Think about it for a minute, you can take a wheel from a bike with 15mm forks and stick it in a bike with 9mm QR or 20mm forks just by swapping the end caps. No need to space the disc or anything.

If I have to explain it, you don’t get it 😉

You’re still assuming push fit spacers are an option, which I don’t think has been established although the ‘switch’ in the name does imply it. I’ve never come across ‘Aireal’ hubs so no idea. If they’re rebranded Superstar Switches then yep, it will be this easy.

OP, can you pull the encaps off? If so you’re probably looking at success.

Did you think about it for a minute then? Was I right (assuming there’s enough room for push-fit spacers)? Are the disc and caliper mounts in the same (relative) positions? 😉

I changed an old DMR revolver from 20×110 to 15×100 with some spacers it was no bother…

The hub body and relative position of the disc mount was essentially the same between 20×110, 15×100 and QR (9×100) and the axle spacers just suffled about to accomodate…

But then Boost came along and ballsed it all up by moving the caliper mount out board so the spoke flanges could be widened, so if you’ve bought a Boost 15×110 fork you’ll need to shim the rotor out as well as find an axle adapter/two 5mm spacers…

enjoy…

The hub body and relative position of the disc mount was essentially the same between 20×110, 15×110 and QR (9×100) and the axle spacers just shuffled about to accomodate…

Assuming not boost, obvs… 😆

like I said Boost made a bollox of an otherwise ideal situation….

And then along came 20mm Boost to confuse the easily confused even further… 😆

If you have push fit spacers and a compatible system then disc position remains correct.

I’m less certain it’s definitely going to remain correct if you start playing with endcaps on a dedicated 20mm hub. The actual disc flange may remain in relative position to the hub body but the depth of the spacer is going to determine where that ends up relative to the calliper. As above, I’m not sure we’ve established anywhere here that this is definitely a hub with swappable endcaps. The sort of shenanigans you get into with RDS and FDS on older Fatbikes should be enough of a cautionary tale not to assume all unknown hubs are playing the same game regarding what they do with their disc mounts (although I’m not suggesting that specific problem is likely here as I’ve never come across this specific problem in regular MTBs).

I’m guessing these are probably Novotecs in which case it’s probably a win, but I wouldn’t rule out a bit of trial and error and unless you have endcaps designed for the hub.

FFS man, there is no such thing as a ‘dedicated’ 20mm hub in this context. Just be wrong, will you.

Kayla, the 20mm I was talking about refers to the axle diameter and the half refers to the axial length of the spacer.

This thread needs pics, would be a whole lot easier.

FWIW there are no end caps as such, when in 20mm mode the hub mounts straight on the axle with a spacer at either end.

The hub itself is 13 years old and no relation to the Superstar of the same name that I know of. They were an Australian company and it was imported by Topshelf components. It’s also my DH bike wheel so changing it for a dedicated 15mm hub is a non starter.

Okay so a picture says a thousand words…

Here’s a pic of the hub in it’s “naked” state, just chillin’. Kayla, top marks as it is actually 90mm wide.

Here’s the axle spacers for 20mm mode, 10mm each:

And here’s the QR adaptor, this is a 20mm dia tube that screws together at one end (like a Marzocchi 20mm axle) with 5mm wide flanges at each end:

So my plan basically revolves around popping one of these reducers through then adding a 5mm spacer similar to the 10mm ones I already have at either end. I’m not going to lose sleep over 37g on the axle, I can more than make up for that by not having a dropper 😉 Either that or use the QR adaptor as a model for a similar 15mm unit.

I’ll show my backside in Fenwick’s window if some SS 15mm adapters won’t do the job.

edit- I’ve just checked my spare wheels and the SS adapters do indeed have a 5mm tall flange on them, so these-

https://www.ridewill.it/p/en/novatec-320293-adapter-spacers15mm-for-d541-d881-hub/554979/

should do the job.

Just checking you can see all the pics, only the first two are displaying on my mobile! Only asking as as you mention the flange height rather than width (just checking we’re on the same page).

If so job looks a good ‘un! 😀

Yes, I think we’re on the same page 😆

I was just checking! 😛

Made too many cack handed errors through saying or hearing the wrong thing , I have form.