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I have a Giant propel advanced 2 (2017) road bike, 105 groupset, rim brakes. I would like to buy a set of deep section racing wheels and unsure if disc brakes are an option or not.

Is it possible to convert my bike to a disc brake version? If so, what component(s) would I need to change? How much would it cost? What are the differences between hydraulics and mechanical disc brakes? Or should I just get this crazy idea out of my head?

My bike:

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  • This was certainly done, back ca 1970 when disk brakes first started appearing on bikes. But the skill (& expense) required to do this greatly limited it's frequency. – Daniel R Hicks Mar 22 at 0:19
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Rim and disc brakes have completely different mounts. The front disc would be mounted at the bottom of the left fork leg, and the rear would be mounted where the seat and chain stay intersect.

It’s not just the mounting points: the tubes in disc brake bikes are different. the carbon layup is denser or the metal tubing is much thicker at the disc mount point and other places that are affected by the very considerable torque generated when you brake.

You might be able to replace your fork with the Propel disc fork, and mount just a front disc brake. This would not be economical. Also, it appears that the fork crown may be integrated with the frame, so I am not certain what third party options are available. You’d also need to change to a front hydraulic shifter/brake lever. You could just use mechanical disc, but compared to good rim brakes, the advantages aren’t huge. Search on the site for discussions of mechanical versus hydraulic disc.

You can get deep section carbon rims for rim brakes. These have some downsides - the braking is inherently inferior to aluminum rims, and you have to use special brake pads. Depending on the resin used in the rim, it’s possible to overheat carbon clinchers on long descents if you brake for extended periods. In that case, the problem isn’t trivial: you would damage a very expensive rim and you’d need to replace it. For reasons I can’t quite remember, tubular rims are less vulnerable to this issue, although they still have carbon brake surfaces, and tubulars need a different chain of logistics than clinchers.

Hybrid rims, like the Hed Jet, Bontrager Aeolus Comp, and some Flo Cycling rims, have a non-structural carbon fairing bonded to an aluminum rim. These are relatively heavy, but weight matters surprisingly little in cycling. (We are talking a wheel set weight of 1900-2000g for hybrid rims, versus 1500g or so for a full carbon clincher wheel.) Opinions may differ, but I would consider these if you’re set on carbon wheels.

Rim brakes are outdated in some sense. However, speaking from experience with both rim and hydraulic disc brakes, you’ll do fine on rim brakes! Good quality rim brakes have more than enough stopping power on alloy rims in almost all circumstances. That does need one minor caveat: your bike seems to have Giant-branded direct mount brakes that are positioned in non-standard locations for aerodynamics. I’m not certain how good those calipers are. It’s possible they under-perform substantially relative to normal rim brakes. However, the point stands that it is completely un-economical to convert your front brake to disc, and that there is no way at all to mount a rear disc caliper.

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  • Thank you for the extensive answer! That's all I needed to know. I will go for hybrid rims. I never liked the idea of carbon braking surfaces. Especially because I intend to use it year round. Weight is overrated (: And if I really want to, I can put on cheap box sections for hilly rides. – Bas de Weerd Mar 22 at 0:07
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To do this "properly" you need to replace all these parts:

  • a new frame with disk caliper mounts
  • a new fork with disk caliper mounts
  • all the brake system parts, being calipers and rotors, hose etc.
  • new wheel hubs front and rear with disk rotor mounts
  • longer replacement spokes for your front wheel to rebuild it with a cross lacing pattern

It is possible you can use your existing brifters IF you choose a cable-actuated disk brake caliper. However if you're going the whole way, you will need replacement brifters with hydraulic brake support, that match your existing gear setup.

This leaves only these items that could be moved from your existing bike to the new setup

  • Pedals, cranks, chain, cassette
  • Seatpost and saddle
  • Stem, bars, bartape
  • Bottle cages and ancillaries... basically all the cheaper parts of a bike.

To summarise you end up with one nice complete bike and 80% of another bike, and it works out as quite expensive.

Instead, stay with what you have, or buy the bike you want complete and end up with a spare bike for commuting or similar. Or you can clean and sell your current bike and put the proceeds toward the new bike.

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