Disc brakes and chainstays length
Klaus B
Posts: 63
Hi there.
I've just been chatting here and there about the topic disc yes or no..
And as much as I like new technologies and all year round capabilities of discs, i would like to have a rim brakes bike too.
Now I know that for cutting costs the major brands are producing one frame for each model and then add disc or rim brake as the customer likes.
I read one day that since this decision chainstays have grown in length, compromising a little the nippy feeling of road bikes, and the cause of this is discs.
Does anyone know why?
I've just been chatting here and there about the topic disc yes or no..
And as much as I like new technologies and all year round capabilities of discs, i would like to have a rim brakes bike too.
Now I know that for cutting costs the major brands are producing one frame for each model and then add disc or rim brake as the customer likes.
I read one day that since this decision chainstays have grown in length, compromising a little the nippy feeling of road bikes, and the cause of this is discs.
Does anyone know why?
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Comments
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Nevermind, I thought just now at the bigger tires than in the past.. but is it just for that?0
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Also to keep the chain line straight with the wider rear axle0
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There's a couple of reasons I've seen suggested for this. Essentially it comes down to the fact that for disc brakes, the rear end is wider. Rim brake hubs are 130mm between locknuts, disc hubs are 135mm (QR) or 142mm (TA). This can introduce issues with heel rub and chain line. For the chain line, think about the angle that the chain would take when going from the small chainring to the small cog (though you shouldn't use this anyway). The wider rear end puts the chain at a more extreme angle.
There were two possible solutions to this, and interestingly the two main cycling disciplines essentially chose different ones. MTBs are wider at the cranks. If we ignore everything except BSA threaded BB shells for simplicity, road frames are always 68mm, while MTB frames can be 73mm, and all MTB cranks accommodate that 73mm shell using spacers if necessary. On road, the Q factor (the width from one crank arm to another) is perceived as being more important, so the shell stayed narrow. In order to maintain the narrow Q factor, the chainstay lengths had to change.
It's still possible to have chainstays as short as you want, but you have to accept compromises and likely find a custom builder. I know that Shimano have a recommended minimum chainstay length, which the large manufacturers may not want to go against.0 -
oh yes guys! that's the main reason I think. Compromises of the modern era then
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