Has this been done? ( disc brake content )

[SoCalSteve]

Hi all,

This may be a stupid question and maybe an obvious answer that I’m not seeing, but I will ask it anyway...and flame away!!!

On a rim brake bike, what would be the ramifications of replacing the fork, brake caliper and left shifter to a hydro disc brake set up and leaving the rear brake as a rim brake?

As always, thank you all in advance!

Steve

[tuscanyswe]

Sure lots of bikes are set up this way. As long as the fork is specced the same in length and similar rake there is no changes other than the braking which i assume you will prefer since looking to change it to disc.

Obviously you will need at least 1 new extra front wheel as well but other than that..

[SoCalSteve]

Originally Posted by tuscanyswe

Sure lots of bikes are set up this way. As long as the fork is specced the same in length and similar rake there is no changes other than the braking which i assume you will prefer since looking to change it to disc.

Obviously you will need at least 1 new extra front wheel as well but other than that..

I have a set of Reynolds Aero 46 rim brake wheels. Can I just replace the front hub? But there may be a problem finding a 20 hole centerlock thru axle 100 x 12 hub.

Thoughts?

[tuscanyswe]

Originally Posted by SoCalSteve

I have a set of Reynolds Aero 46 rim brake wheels. Can I just replace the front hub? But there may be a problem finding a 20 hole centerlock thru axle 100 x 12 hub.

Thoughts?

Disc wheels are subjected to brake forces bit differently than rim braked wheels. so 20h front hub even if you can find one is likely to be to weak (at least for my taste). Id rather have a 28h or even 32h for disc wheels but yeah some of the disc braked wheels do have 24h spokes these days.

[GregL]

Originally Posted by SoCalSteve

On a rim brake bike, what would be the ramifications of replacing the fork, brake caliper and left shifter to a hydro disc brake set up and leaving the rear brake as a rim brake?

One concern is the change in braking forces as they are transmitted to the frame. I haven't conducted any modeling of the forces involved, but anecdotally would be concerned that the headtube/toptube/downtube junctions could suffer stresses beyond their original design. It would be helpful to have an experienced frame builder chime in.

Greg

[.RJ]

Originally Posted by tuscanyswe

Disc wheels are subjected to brake forces bit differently than rim braked wheels. so 20h front hub even if you can find one is likely to be to weak (at least for my taste). Id rather have a 28h or even 32h for disc wheels but yeah some of the disc braked wheels do have 24h spokes these days.

cant have radial spoke wheels for disc brakes, either. Must be 2x/3x.

[TimD]

Steve, I did this to a mid-90s Trek 750 (aka 520) CrMo frame, replacing the stock tubular steel fork with a Nashbar carbon disk / canti fork, set up with a mechanical disk brake.

The bike isn't used much but it has worked well so far.

[SoCalSteve]

Anyone know of an 1 1/8th straight fork, 43 rake that is 100 x 12 thru axle?Seems the world has moved on from 1 1/8 disc forks and are now all 1 1/4 or tapered.

Thoughts???

Thank you!

S

[pbarry]

They are mostly 1 1/8th tapered to 1 1/4 or 1 1/2 now. Straight with thru axle is a rare bird, but somebody must have made them. For a Mullet application, A straight steering tube qr fork would be fine.

[.RJ]

Originally Posted by SoCalSteve

Anyone know of an 1 1/8th straight fork, 43 rake that is 100 x 12 thru axle?Seems the world has moved on from 1 1/8 disc forks and are now all 1 1/4 or tapered.

Thoughts???

Thank you!

S

Ritchey sells one, or find a used wound up.

[GregL]

Originally Posted by .RJ

Ritchey sells one, or find a used wound up.

The Ritchey gravel fork has a 380mm axle-crown measurement. This would be 8-13mm longer than a typical road fork. If the OP is planning this experiment for an existing road bike, the Ritchey fork would have an impact on the frameset geometry.

Greg

[.RJ]

Originally Posted by GregL

The Ritchey gravel fork has a 380mm axle-crown measurement. This would be 8-13mm longer than a typical road fork. If the OP is planning this experiment for an existing road bike, the Ritchey fork would have an impact on the frameset geometry.

Greg

True, I didnt think about the A-C height. Thats going to be a tall order finding a road fork with disc, thru axle and a 1-1/8" steerer. Maybe ritchey will sell you one when the new road logic disc starts shipping.

[Mark McM]

Originally Posted by GregL

One concern is the change in braking forces as they are transmitted to the frame. I haven't conducted any modeling of the forces involved, but anecdotally would be concerned that the headtube/toptube/downtube junctions could suffer stresses beyond their original design.

If you did model it, you'd find that the rim and disc brake bikes trasmitted exactly the same forces to the frame. The forces within the fork/wheel/caliper system will be different for the two kinds of brakes, but the forces between the fork and frame (which are external to the wheel/caliper system) are the same.

You don't need a complex analysis to know this, you just need to look at the locations that the forces get transferred into and out of the fork/wheel. Forces are transmitted to the wheel/fork from ground at the bottom of the wheel; forces are transmitted from the wheel/fork to the frame at the headset bearings. For the same force applied by the ground to the bottom of the wheel, the same forces will be transmitted to the frame at the headset bearings. What's going on between them won't change the forces transmitted from ground to frame.

[Mark McM]

Originally Posted by SoCalSteve

On a rim brake bike, what would be the ramifications of replacing the fork, brake caliper and left shifter to a hydro disc brake set up and leaving the rear brake as a rim brake?

What you are suggesting has often been done on MTBs and 'cross bikes, and is sometimes referred to as a 'mullet'. As long as the fork has the same dimensions (length,offset), there shouldn't be a problem. Well, other than trying to get the two brake levers to match each other enough that it doesn't feel weird to ride it.

[Mark McM]

Originally Posted by SoCalSteve

I have a set of Reynolds Aero 46 rim brake wheels. Can I just replace the front hub? But there may be a problem finding a 20 hole centerlock thru axle 100 x 12 hub.

As mentioned, a disc brake wheel needs to have crossed spokes (and most people use more spokes on a disc wheel than a rim wheel). I don't know that wheel specifically, but I'll bet that it is currently laced with radial spokes. Many rims are designed for specific spoke angles, so you may not be able to lace the rim with crossed spokes, even if you could find a disc brake hub with the right number of spokes.

I think you're looking at a new wheel for this project.