Conversion to Disc Brakes

neilled

Dear All,

I was wondering how difficult it is to convert a hybrid that has a mount for disc brakes from rim to disc?

My trek 7.5 recently was vandalised in crumlin. I went to joe dalys but alas joe was closing for a half day so I went to the guys up the road in cyclesurgery who done a pretty quick turnaround on it. During the investigation into things be discovered that the rear axle of the wheel was a little bit bent and would eventually need replacing as result. Furthermore he wasn't quite able to get the wheel exactly true no matter what he tried. So I've thought to myself - how about it - replace the rear wheel with one of these a Bontrager Select Disc and then add an Avid BB5 or BB7 disc brake. I wouldn't bother with the front seeing the front wheel has a reasonable amount of life and it would be a shame to discard a perfectly good carbon fork.

Can anyone think of any technical problems that might be incurred during the process? Any ideas of differences between the regular and road versions of the Avid BB series of brakes? And finally, would the lack of the little "runners" that hold the cable in place on the left hand seat stay have any effect on brake performance? There was in the past a version of my bike with discs but it lacked a carbon fork - heres the link http://www.bikeradar.com/gear/category/bikes/road/product/75-fx-disc-07-20497

Lumen

Might have been worth considering if it was the front, but sticking a disc brake on the back is pointless.

penexpers

Are you sure the 7.5fx has a mount for disc brakes? It would be strange to have the mount for the brakes but then not have the braze-ons for the cable. From looking at some pictures, the rear may have a disc brake mount but the front definitely doesn't.

Anyway, if it does have a mount for a disc brake on the rear then there shouldn't be any problems. Not having the braze-ons along the seat stay might mean using a zip tie or something similar. There might also be something you can get to convert the brake boss into a cable stop. I think the difference between the road and regular versions on the BB brakes is to do with the amount of cable pull required - road levers wouldn't generate as much cable pull as mountain levers. I have the BB7's myself - great brake and very easy to get setup right.

neilled

Lumen wrote: »

Might have been worth considering if it was the front, but sticking a disc brake on the back is pointless.

It was mainly from a wear and tear point of view and also performance in the wet which I have noticed goes significantly downhill when its wet. Or perhaps i'm just using cheapo pads.

neilled

penexpers wrote: »

Are you sure the 7.5fx has a mount for disc brakes? It would be strange to have the mount for the brakes but then not have the braze-ons for the cable. From looking at some pictures, the rear may have a disc brake mount but the front definitely doesn't.

Anyway, if it does have a mount for a disc brake on the rear then there shouldn't be any problems. Not having the braze-ons along the seat stay might mean using a zip tie or something similar. There might also be something you can get to convert the brake boss into a cable stop. I think the difference between the road and regular versions on the BB brakes is to do with the amount of cable pull required - road levers wouldn't generate as much cable pull as mountain levers. I have the BB7's myself - great brake and very easy to get setup right.

Hi penexpers - they used the same frame on the 7.5 and 7.5 disc if you look at the bike radar review, my bike has the same mounting that the brake attaches to. The front fork doesn't have disc mountain, and the price of a similarly specced fork like a bontrager satellite elite, combined with the price of the wheel and brake, I feel would be uneconomical. At least with the rear wheel its something I will be replacing and could justify!

Lumen

neilled wrote: »

performance in the wet which I have noticed goes significantly downhill when its wet. Or perhaps i'm just using cheapo pads.

You should be able to lock your rear tyre in all conditions with rim brakes. If not there's something wrong with your brakes or pads.

penexpers

neilled wrote: »

It was mainly from a wear and tear point of view and also performance in the wet which I have noticed goes significantly downhill when its wet. Or perhaps i'm just using cheapo pads.

It could be cheapo pads. Don't forget that disc brakes use pads as well that need to be replaced on a regular basis.

rubadub

Also bear in mind your bike is probably going to be more likely to be stolen or vandalised with disc brakes on it.

Much the way a bitter, begrudging chip on the shoulder scumbag is more likely to key a BMW, than a clapped out mini.