Originally Posted by
Dave Mayer
However, the best rim brake proponents (me and Chris Froome) want rim-brake tech because it is simply better, regardless of cost:
- It is a lot lighter, particularly due to the frame and fork design that doesn't have to support disc-brake forces
- The wheels are lighter, due to not having to deal with greater braking forces.
- The rim-brake forks are more compliant, due to not having to be bulked up for disc braking forces
- Rim brake wheels are more aero
- Rim brakes don't slice you or your pals in a crash
- Rim brakes are cheaper and a lot easier to work on.
So there you go. Yes, I have a high-end road bike with discs. It is a boat anchor compared to the same rim brake bike but 2 years older. I work on discs almost every time I'm in the shop. I have $15k to spend on a new bike; going rim brake with Di2 Dura-Ace. Got all the parts I need, except the frame.
Originally Posted by
Dave Mayer
I forgot a few more road disc-brake downsides, apart from them being heavy, fussy and unnecessary:
- Extra space on the front hub required for the rotor attachments. This introduces dish on the front wheel and means a weaker build, all things being equal. Plus you need 2 different lengths of spokes for building front wheels - a minor PITA, but still a PITA.
- Extra space on the rear wheel for the rotor attachments. This is not a trivial problem, as spoke bracing angles and rear hub flange spacing dimensions have gotten so extreme now, that rear wheels are simply weak and unstable. So we have to go with wider stay spacing, which means more heel strike. And wider crankset Q-factor, biomechanically inefficient.
- Thru-axles. What an absurd PITA! With a QR, you flip the lever and the wheel drops out, just like Tullio Campagnolo meant it to happen. With discs, which tend to eject front wheels, you need a more robust and idiot-proof solution. So now we interminably twiddle away with our thru-axles, and forget them at the trailhead. Of course, there are 20 different thru-axle 'standards'. BTW: thru-axles are not axles, as they do not bear load. They are simply wheel retention devices for riders who cannot be trusted to use a proper QR. Lawyers win this round!
- A rim brake frame can be lighter than a disc brake frame, agreed. 10oz or less in the end. If you are an elite performer, that could definitely make a difference. If you arent, then you are using it as a weak justification.
- Rim brake wheels are not necessarily lighter than disc brake wheels. Rim brake wheels can be lighter, but that doesnt mean they all are lighter. Very few people riding have wheels that weigh less than 1500g so this argument is quite worthless for most people. Disc brake wheels can weigh under 1300g too, so at that point, is this really an argument to make? What are your rim brake wheels and what do they weigh? Again, rim can be lighter, but its not like everyone on rim brakes is riding on wheels that are lighter than disc brake wheels. Stock rim brake wheels on Ultegra level bikes or lower just a few years ago were commonly 1750g to 2050g as a set.
- Rim brake forks can be more compliant. If they have to pass that testing, they will be bulked up well past what most anyone needs, just like disc brake forks. A handmade steel rim brake fork can be very compliant, I do agree with that. .6% of people ride such a fork.
- Rim brake wheels can be more aero. That doesnt mean they all are more aero. There are a ton of disc brake wheels that are clearly more aero than the wheels on any of my rim brake road bikes. Once again you put forth a claim that could be true, but also could be incorrect.
- Rim brakes dont slice you or friends in a crash. Disc brakes also dont slice you of friends in a crash. Lets call this a tie, mkay?
- Rim brakes are cheaper and easier to work on, that is almost universally correct so I will award you this claim as one to continue using. Congrats, you finally got another one.
- A disc wheel up front is perhaps weaker in theory compared to a rim brake wheel due to spoke imbalance. Add 4 spokes and call it good. Thats what November suggests, and I have read similar from many others. Seriously, this is all thats needed and the benefits are wider rims for more comfortable tires, deeper rims for more aero gains, and rims that dont wear out or delaminate from use.
- A rear disc wheel is 142mm vs 130mm for a rim brake wheel. Once the thruaxle is accounted for, a disc wheel is set up as 135mm. The wheel can therefore be plenty strong, contrary to your claim.
- Wider stays dont mean heel strike is an issue. I have size 14 shoes and dont have heel strike. Drop this claim.
- My gravel bike has 43mm tires, it can fit 50mm tires, and I use a road crank and subcompact rings with 147mm Q factor. Drop your claim of needing a wider Q factor. Yes GRX has a wider Q factor, but that isnt needed. Also, wider stay spacing is more for wider tires than disc brakes. Same with a wider Q crank design- you will notice thats associated to a gravel groupset.
- Discs dont tend to eject front wheels. Good lord, settle down with the over the top claims. My kids have MTBs with QR disc forks and there is no ejecting wheel fear. The dropouts are designed differently to account for this and its a non-issue. Drop this claim.
- How many people forget thru-axles at the trailhead? And why are they forgetting thru-axles at the trailhead?
- Thru-axles are not load bearing, correct. They are a piece of metal which GOES THRU THE AXLE and retains the wheel. Who claims they are load bearing? They are no more load bearing than a QR skewer.
- Thru-axles arent just some lawyer creation- they are a better design for centering the rotor each time. You just complained about QR disc design and now you complain about the design that addresses QR discs?
You did manage to make 2 good points in all that.
And as a reminder, my main road bike, backup road bike, backup to the backup road bike, commuter bike and single speed bike are all rim brake. I love rim brakes.