jollycycle

Hi.



I would like to have a frame built for mid/long reach rim brakes. Shimano BR-R451 or BR-R650 offer up to 57mm of reach (normal Shimano road bike rim brakes have 51mm of reach these days). What is the normal distance from axle to the brake mounting point? What max. distance is possible for long reach brakes? I have found an old Shimano drawing. What is your experience? How much margain should be left?

Thank You.

Julian

PS: Can't upload the Shimano drawing because I don't have 10 posts on this forum so far

jollycycle

OK, that was the 10th post, here is the drawing

unterhausen

What size tires do you want to use? Do you want to run fenders?

Andrew R Stewart 

As a sometimes builder I have to ask why the builder who will do the work won't be responsible for this dimensional detail? Andy (knowing the likely answer).

8aaron8

From the center of the wheels axle to the brake hole 358mm for short/standard reach brakes, 368 for medium reach brakes. Best practice is to have the brake in hand when building, max out the brake pads and line everything up before brazing. If going by the distance to brake hold figure I would probably shoot for 1mm less distance so 357/367 just to make sure the pads don't end up above the rim brake track.

jollycycle

I will use the Whisky No. 7 RD+ fork which allows up to 35mm of tire width. I would be happy if the frame can accept 35mm as well. At least 32mm would be fine. No fenders.

jollycycle

Thank You. That sounds reasonable and that is what the frame builder suggested. However it is a difference of 10mm. The difference of the max. brake reach between standard/normal (Shimano 51mm) and mid/long reach (Shimano 57mm) brakes is just 6mm. That makes me wonder.

jollycycle

I could just follow the advise of the frame builder. However one of my personal failings is that I like to dig into the theory behind things and to confirm it. In this case I can not follow the advise as the numbers do not make sense to me related to the specific Shimano mid/long reach brake type I would prefer to use. But you knew that already.

unterhausen

I use bikecad to make decisions like this, but I start from the clearance I want. I generally put in 25mm of clearance if I want to use fenders. I also have a fixture made from a fork crown to do mockups as a sanity check because Bikecad isn't great for designing forks. Only then do I decide what brakes to use. I never really felt comfortable doing it the other way around. I modified some small locking pliers and welded them to the sides of the blade sockets of a surplus crown. Then I cut the top off of the sockets and cut the sockets in half. That allows me to vary the length of the blades. I messed up a crown for narrow blades cutting the crown race on a lathe so I might make another one. It really makes me feel more confident about my fork designs.

I missed that you are buying a production fork, so most of this conversation is moot.

Andrew R Stewart 

What I thought was going on was you were going to use an Asian "job shop" builder. I forget the most common company doing this but having to design the frame that another (and so far away and with communication challenges so easy to happen) when many far more local (distance and/or cultural/language) builders exist. Thankfully this is not what's going on. Rant over.

Getting the last few MMs of brake hole to axle dimension actually repeated with the frame can be less easy than we would hope. An early lesson for me was the different pad reach for the front Vs the rear pads. As the rim arcs either up from the hole (as in the front) and down from the hole (rear) the pads see about a 3 or 4mm difference between their location within the caliper arm slots. So the front axle to brake hole needs to be about 2mm more and the rears about 1-2 mm less than the in line dimension.

However you do these measurements, run the math and end up with dimensions make sure your builder knows exactly where you were doing the measurements, especially with the front end. Is your axle to brake hole to the center of the steerer/crown (being inside the steerer's end I doubt it) or to the center of the brake hole on the front of the crown? This difference can be about 2mm too. Some frame design software will take this into account but knowing this is just one more small detail that is easily overlooked by the non builder.

These 2mms here and there are not a big deal when one is aiming for the pads to be located at the slot's mid points. A pad a mm or 2 higher or lower really isn't a big deal. Until one is trying to get the pad as low down as possible and the couple of mm tolerance for axle to brake hole dimension that is very common disappears...and one reaches for that small rat tail file. I strongly suggest you consider sending your builder the brakes as well as the actual (not labeled) tire dimensions if you want the max clearance.

I have done this very dimensioning (and the building) for the wife's and my fendered drop bar bikes. We run the same calipers and 622 rims. Each bike has one brake with near perfect clearance and resulting pad locations and the other caliper with about 2mms of less clearance. The widest tires we can run on the near perfect clearance ends are Avocet 700x32 Fast Grips (the last of a decades old stash) which measure at 32mm mounted on 17mm inside width rims. The less clearance ends (thankfully both the front) a 28mm tire is about the reasonable max with fenders.

If one wanted the max clearance the Shimano dual pivot calipers would be gone as they have shapes on the undersides that hang down further than classic single pivot calipers do. Andy

Just read Eric's reply- Production fork? I guess I missed that bit.

unterhausen

It was a bit hidden.
I have occasionally thought about getting one of the Chinese Ti builders to make a frame I design. I have heard good things about one of them. It wasn't waltly.