Today I visited Bike Friday dealer ehicle in Shinjuku, Tokyo to have a disc brake installed on the new fork that Bike Friday has made for my 4 year old bike. I had bought the Shimano BR-CX77 calliper second-hand from a friend. This conversion will make for much more consistent braking on rainy brevets or on wet shopping rides.
There was one small issue but it was quickly solved by ehicle. My friend had also given me a SM-MA-F160P/S adapter for fitting a post mount calliper like the BR-CX77 to an IS tab front fork with a 160 mm rotor. That’s exactly what I had on the Bike Friday. However, it did not fit together, the calliper sat too far out from the adapter. Comparing with the setup of a disc-equipped Bike Friday Silk in the shop we found that its Avid BB7 calliper was mated to a Shimano SM-MA-F180P/S, which is meant for a 180 mm rotor at the front or 160 mm at the rear (F180P/S = R160P/S). The adapter I got from my friend was for use with a 160 mm rotor at the front or 140 mm at the rear (F160P/S = R140P/S).
The use of a 160 mm rotor with an F180 adapter (i.e. R160) on the Silk fork suggests that the IS tab to axle distance on the BF fork is the same as on a standard rear setup. This means it takes a 180 mm front adapter for a 160 mm rotor or a 160 mm front adapter for a 140 mm rotor. This is very interesting, since Shimano doesn’t make 140 mm front P/S adapters: Using Shimano parts, you can’t normally use a 140 mm rotor at the front with an IS tab fork, but with Bike Friday’s setup you can because the spacing is like at the rear, where Shimano does support 140 mm rotors with IS tabs. The only thing you give up by using rear spacing at the front is the ability to use 203 mm rotors, but the fork doesn’t have enough clearance for those anyway and they’re not needed on a 20″ wheel bike. The smaller wheel means that a smaller rotor can match or beat a bigger rotor on a 700C wheel on stopping power, though heat dissipation for long descents still depends on rotor size.
Anyway, a cheap 180 mm Shimano adapter instead of the 160 mm one that I had brought along solved the issue and I could use the new brake with the 160 mm rotor on the new fork. The B&M dynamo headlight moved from the brake bolt in the fork crown to its own bolt in the same place. ehicle installed a longer brake cable for me to accommodate the different brake location.
I love the new brake, both its stopping power and modulation. It should make a huge difference on rainy rides, where I have always been uncomfortable with rim brakes, in particular on brevets where I don’t know what the weather will be like on the day when I sign up for an event. I’ve done one 300 km brevet where it was raining for 150 km.
I’d like to thank ehicle for their friendly and efficient service and recommend them to anyone interested in or already riding a Bike Friday 🙂