Rotor alignment, SRAM Apex 1 callipers and a 100mm hub with 3.5mm end caps...

[FortheFold 2020]

Hi there,

I'm looking for advice with my current conundrum... I'm currently changing a set of 700c road wheels for a set of 650b gravel. On the front I'm limited with what I can change due to the forks and I have bought a 15mm x 100mm front hub with 6 bolt rotors. The first problem I had was that the hub cone ends have an outer diameter of 21mm (standard MTB) and I can only house an OD of 19mm with the fork lips. Searching high and low I've picked up some end caps that will reduce the 15mm thru axle to 12mm (good start) and reduces the end cones to 19mm so will fit in the fork lips. All moving in the right direction, apart from the end caps are 3.5mm width each side, pushing the 100mm hub to 107mm. While the forks can handle this flex each side, it means the disc rotor isn't aligned. So the question, by adding 7mm (3.5mm each side) with the end caps, how many millimetre spacers do I need to use for the rotor so I can do straight swaps without need to adjust the disc brake calliper. Answers on a postcard! Any advice welcome

Thanks

 

[C R]

When you say flex in the forks, do you mean you are jamming the hub in, forcing out the legs? What material are the forks? It may be safe with steel forks but I wouldn't bet on it, and definitely a no no with aluminium forks. In any case, if the disc mount is out of place it means that the wheel will not be central to the fork, so handling will be "interesting".

I would have thought that getting new forks would be a better route than trying to fit a square peg in a round hole.

 

[figbat]

Or a carbon fork?!

Anyway, another issue is that the caliper mounting tabs will no longer be vertical - there may be a enough play in the caliper mounts to account for this, but it all sounds a bit sub-optimal.

 

[Venod]

I have bought a 15mm x 100mm front hub with 6 bolt rotors

What is the make of the new hub ?

Could the endcaps you have bought be for a rear hub that increases the width from 135mm to 142mm for frames that are 142mm.

 

[FortheFold 2020]

Hi @figbat @Venod @C R thanks for your comments. They are Carbon forks, which once the thru bolt is released it naturally opens to allow for the additional 7mm, it doesn't need to be forced so to speak, fits snug. The end caps are for a rear hub to convert a 135 - 142mm and its a Formula hub 15mm x 100mm 32H.

In an ideal world I'd have the wheel re-built on a 12mm x 100mm 32H hub with OD of 19mm but I'm struggling to find a hub to match, so thinking the alignment of the caliper brake is the easiest solution as you are effectively dividing the additional 3.5mm end cap width on the rotor side by the diagonal height of the calliper, so it being marginal enough to work. Eitherway its given me a pickle...

 

[Ajax Bay]

the forks and I have bought a 15mm x 100mm front hub with 6 bolt rotors.

Echoing @Venod give us a link to the fork and to the hub you've bought.
What hubs on the 'old' 700c wheels?

 

[FortheFold 2020]

Hi @Ajax Bay the forks are on a 2018 Cannondale SuperX. The old hub is Formula DC-512 28H 12mm x 100mm and new hub is Formula RX81 32H 15mm x 100mm. The issue is the OD of the new hub being 21mm and the old hub being 19mm. As soon as I covert the new hub to 12mm the 21mm end cones don't sit flush with the lip on the forks, meaning the centre line for the thru axle doesn't line up wit the forks. Hence using end caps to reduce inner diameter and outer diameter, but extending the hub by 3.5mm each side

 

[Ajax Bay]

I would have thought that getting new forks would be a better route

With credit to @C R :
"I would have thought that" procuring a hub, however difficult, to fit the fork, its disc line and its dropouts max OD "would be a better route" and any outcome with the 'wrong' hub will be plagued with friction, not of a good kind.
I appreciate this doesn't answer the 'exam Q' "on a postcard" but maybe it'll be appreciated in the long(er) run.

 

[C R]

With credit to @C R :
"I would have thought that" procuring a hub, however difficult, to fit the fork, its disc line and its dropouts max OD "would be a better route" and any outcome with the 'wrong' hub will be plagued with friction, not of a good kind.
I appreciate this doesn't answer the 'exam Q' "on a postcard" but maybe it'll be appreciated in the long(er) run.

I fear that the OP might encounter a lot of undesirable friction with the road if they were to continue with their current plans.

 

[Venod]

Not that it helps your problem but I think RX81 is a road hub, you can get inserts to reduce it to 12 mm but that wont solve the OD issue.

https://www.formulahubs.com/product.php?t=37

Are the axle and bearings from the old hub interchangeable with the new ?

An email to Formula stating your problem may get an answer.

 

[FortheFold 2020]

Agreed! Wheel rebuild it is... thanks all