reducing 15mm thru axle fork to 12mm

Discuss light weight issues concerning mountain bikes & parts.

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joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

spud wrote:
Sun Dec 31, 2017 9:05 pm
that's a VERY NICE solution. Custom machining would be pricey though. My original hope was to use a stock timesert or something like it, and simply bond in a bushing to the DR side. Maybe someone will do a run of these parts, but I wouldn't hold my breath. I could just buy a new fork for $200.
Thanks! I'm looking into the cost for a small run. I've done stuff like this before (custom short pull arms for TRP HY/RDs among other things). I like the idea of having the option to use either 15mm or 12mm wheels without any special hub parts. I should know whether or not it is worth my time and effort to move forward in a few days when the factory gets back to me with a price.

by Weenie


spud
Posts: 675
Joined: Sat Feb 07, 2009 5:52 am

by spud

very cool - looking forward to your proposal.

ooo
Posts: 629
Joined: Sat May 21, 2016 12:59 pm

by ooo

It looks like that left 12mm insert is not solid, it is only using 2 diameters for support? may be it should have more contact area?

Shimano 12x100 thru-axle standards (no 15x100):
http://productinfo.shimano.com/#/spec/2 ... xle%20(AX)

Sram 12x100 and 15x100 thru-axle standards:
Attachments
maxle-min.gif
12x100 and 15x100 by SRAM
'

joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

ooo wrote:
Mon Jan 01, 2018 4:24 pm
It looks like that left 12mm insert is not solid, it is only using 2 diameters for support? may be it should have more contact area?
Yeah, it might be best to just go solid there rather than try and weight weenie this part. I can let the end user decide if they really want to tune that area to shave a few grams. I need to make a few refinements are taking some more accurate measurements and then do another weight check.

joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

spud wrote:
Mon Jan 01, 2018 3:05 pm
very cool - looking forward to your proposal.
As noted above I still need to make some refinements but assuming that I can move a decent handful of these kits I can offer them at $45/set (special thru axle plus thread adapter) shipped in the US.

spud
Posts: 675
Joined: Sat Feb 07, 2009 5:52 am

by spud

if you can pull it together at that price, I'm in.

joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

spud wrote:
Wed Jan 03, 2018 2:31 pm
if you can pull it together at that price, I'm in.
The pricing will stand provided that I don't uncover any unknowns that make this adapter set not work as intended.

To that end, can you confirm a few things for me?

1. What is the thickness of your dropout tabs where the thru axle passes through?
2. Is the threaded dropout fully tapped or is it counterbored to 15mm on the inside for some distance?
3. What the outer diameter of the end caps on the 12mm thru axle wheelset that you want to use?

This last one is the most critical and something I had overlooked initially. The 12mm end caps for my Bitex hubs use the same OD as the 15mm end caps but I am wondering if this is always going to be the case. If 12mm end caps for other wheels are not larger than 15mm (ideally 17mm or more) they won't have any bearing surface against a 15mm thru axle fork dropout. And in that case, this adapter set won't work, and I don't believe there are any good workarounds either.

spud
Posts: 675
Joined: Sat Feb 07, 2009 5:52 am

by spud

threaded side dropout is threaded all the way through, at 18.1 mm thick. Other side is 17.8mm thick.

The current end cap OD for 15mm is 21mm. The end cap for the 12mm is 19mm. Clearly a difference there. I do wonder how much of the axle load is carried by the through axle (into the dropout) vs via the end cap into the fork. Part of me says that the shoulder made in carbon is probably not very precise, and the wheel is really located by the axle. This is certainly born out in that the wheel needs to be wiggled a tiny bit on the threaded side to get the axle to engage the threads.

As a separate observation, using a bolt head axle means substantial torque will be transmitted to the insert thread, which probably means it will need to be secured in the dropout. A clamping quick release removes that torque load, though is obviously much more involved to manufacture.

Jengaback
Posts: 92
Joined: Thu Jan 29, 2015 9:17 pm

by Jengaback

Any external steps are there purely for the initial locating of the axle. Once it is in it takes the full weight of the wheel

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joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

My concern isn't the shoulders built into the fork dropouts that solely help locate the wheel during installation. The issue I potentially foresaw was the 12mm thru axle hub end cap diameter being smaller than 15mm (the hole size in the fork end that we are adapting) and thus not providing any surface against which the fork legs could be sandwiched by the thru axle. The custom thru axle that fills the 15mm drop out can't provide that surface as it doesn't otherwise restrain the fork leg. A sleeve around a standard 12mm thru axle would have the same issue. The thread adapter could potentially provide that surface on the opposite side but I would constantly question how secure it was.

Given that at least one set of 12mm end caps are large enough to utilize the same clamping/bearing surface as 15mm end caps I am hopeful that this adapter kit still makes sense. It does sound like installing a 12mm wheel might take a little extra care as those shoulders in the fork ends won't provide any alignment help. No big deal for me as I don't race and rarely remove my wheels.

If I am still not making sense I can create a sketch to help explain what my words are likely failing to.

As far as the thread adapter being subject to torque when used with a flush, tool-driven, thru axle, I am thinking that the little holes and a spanner wrench will allow it to be installed securely enough that it won't back out when installing the axle. Perhaps some Teflon tape or a small drop of thread locker will do the trick if torque alone doesn't.

spud
Posts: 675
Joined: Sat Feb 07, 2009 5:52 am

by spud

I speed read your post and misunderstood, figured it out after posting. This system looks like a good solution to my issue.

joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

spud wrote:
Thu Jan 04, 2018 4:11 pm
I speed read your post and misunderstood, figured it out after posting. This system looks like a good solution to my issue.
Ok cool. Do your dropout thickness measurements include those alignment shoulders or not? I need the dimension without. I still need to inspect my own fork and do some online digging for as many fork geometries as I can find. Hoping there is a common set of dimensions to which 15mm road forks have been designed.

spud
Posts: 675
Joined: Sat Feb 07, 2009 5:52 am

by spud

my measurements did not include the locating shoulder. It would not be a big issue to file the insert to shorten it suitably for the dropout.

joejack951
Posts: 451
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

spud wrote:
Thu Jan 04, 2018 6:59 pm
my measurements did not include the locating shoulder. It would not be a big issue to file the insert to shorten it suitably for the dropout.
Thanks for confirming. And yeah, for some of us it's no big deal but I'd rather play it safe leaving it a few tenths of a millimeter short and avoid any potential issues or complaints (you know, from the millions and millions who will buy this adapter set :)). I need to leave the shoulder on the thru axle short, too, for the same reason.

by Weenie


rma
Posts: 165
Joined: Mon Apr 21, 2014 9:17 pm
Location: Belo Horizonte, Brazil

by rma

Very nice! Interested in the follow up of this adapter! My fork is 15mm and if I could safely use a 12mm wheel, it would be awesome

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