Front brake lacks 2mm in reach. Can it be ironed out?

Question

I have been having some trouble with my 6 years old Tektro R539 brakes, see Tektro rear brake does not stay closed and Road rim bike brakes don't open when using the release . So I am now looking into changing the brakes. I was handed Shimano R7000 rear & front brakes to check the reach. The rear is fine, the front falls short for 2mm as you can see on the photos here. I would like to use this brakes if doable, I think they will be an upgrade from the previous ones when descending.

I found this older thread discussing the topic. It has had no activity in years though so I prefer asking again. Is it safe to remove some of the metal on the caliper 'dropouts' to increase the reach? I do not know who would take that job - I live in a big city too.

Answer 1

R7000 calipers are excellent but doing this with them is an experiment on both the mechanical advantage and safety fronts. The safety aspect is going to be 100% a yolo on your part. Nobody can unequivocally tell you it's safe, and any problems with strength or fatigue are likely to come down the line, not immediately. You're taking a component made to be as light as possible, cutting away material from the most stressed part of it, and then putting more leverage on that part than intended. If you want a new hobby, there's math you can do to get a read on how good of an idea it is based on your exact weight/loading parameters as well as what inferences you're comfortable making about the metallurgy. That's how you would get to a somewhat reasonable answer, there's no other way.

The other thing I would say here is that, while I don't want to second-guess you, you appear to be way underestimating how much would need to be filed to also account for the upwards travel/wear arch, which affects both sides of the Shimano dual pivots where both pivots are offset such as this. You need the pad's starting adjustment to be hitting the bottom edge of the brake track, not the top; much shy and you're asking for finickiness in maintenance that can cause tire failure if not tended to. That is not 2mm judging by the picture. The pictures in your other posts show the pads adjusted near the bottom of your 47-57 slot. Usually that indicates a fork/frame where there's no compromise on needing mid-reach.

The other problem is that longer reach brakes have actuation arms that are also proportionately longer to keep the leverage relationship as intended. Filing the slot will lower the mechanical advantage because it is creating more pad movement per cable movement. It creates a smaller version of the same kind of problem as a shortpull brake on a longpull lever; less power but with a seemingly crisp and responsive lever feel. It may seem like a minor distinction, but the problem is this effect already begins to creep in when you have a brake that locates the pad at the end of the provided slot. You will increase it further.

Your comment suggests you want to maximize power. The Shimano medium reach calipers do tend to outperform Tektro. If you got one, I would take the trouble to match it with the pre- or post-Super SLR-ness of whatever generation brifters you have, i.e. BR-M650 if you have shift-cable-under-the-tape STIs or BR-R451 for anything else. It's not a must but the effect is real in terms of getting a brake that's powerful but not mushy. The most powerful extant brake for your application is probably the adapter version of the Paul Racer Medium, which are rad but require doing other things to the bike re: cable routing.

Answer 2

The Tektro R539s are medium reach brakes. Reach, in this case, is the distance that the pads can travel in their slots relative to some fixed point (probably the brake's pivot). Most performance road bikes with rim brakes have/had use standard or short reach, which is usually something like 39-49mm. The R539s have a reach, as you can see if you find the line in their specifications, of 47-57mm. Actually, you might not see it because not everyone knows about this parameter, and the Tektro specifications call it "dimension", which is spectacularly uninformative. And Shimano's specs for the R7000 calipers are only a little better. They say "Reach (mm): 51" - really, it's a range that contains 51mm, and based on prior knowledge I would infer that this is the maximum reach of the brake, but I'm honestly not 100% sure.

If your bike was specced with mid reach brakes, I would have recommended getting mid reach calipers, but these are a niche product. None of the big 3 make these anymore, although Shimano had an Ultegra-level (and possibly 105-level) mid reach brake at one point. There are indeed third party manufacturers like Tektro.

If you are sure about your measurement that the pads contact the rim correctly on one brake and you really need 2mm more travel on the other brake, then I would argue that it is OK to use a file to extend that slot by 2mm. Normally, we would not advise filing off metal parts like this. However, the brake arm is pretty thick aluminum in that area. You will void the manufacturer warranty, and I would assume that there's now a small but non-zero probability of some sort of stress riser causing a failure some time down the road. However, it should be safe within practical limits. I know I had this done on a rear Campagnolo Chorus caliper for my bike. That bike was custom and it was designed for short reach brakes, but it did push the limits because I asked for some clearance in case I wanted to run fenders. That caliper probably had at least 5 years of service with that modification before I sold it (with disclosure, mind you).

With the brake caliper in the other answer, there doesn't look like much spare metal at the end of the slot. On my R8000 brakes, I made a quick visual check (albeit without calipers), and it does look like there's enough metal for you to file downwards by 2mm safely. R8000 should be the same physical dimensions as R7000.

A linguistic note: in the bicycle industry, "reach" is commonly used to measure how far one part is from another part. Most cyclists think of frame sizing in terms of a key tube length (e.g. seat or top tube length) or an ordinal size (e.g. small, medium, large), but reach is used in this context to state how long a frame is in its horizontal dimension, measured from the center of the bottom bracket. Handlebars have reach figures as well, stating how far the drops are from a hypothetical centerline. Shift levers don't have reach measurements that are clearly defined and made public, but reach adjustment is a common feature whereby you can move the brake lever closer to the handlebar with an allen key. Reach obviously has the same physical dimensions as length. I guess the differentiating factor is that reach seems to be used in reference to a key reference point that's substantively important in its own right.

However, length and width do need similar reference points defined, e.g. are your handlebars 400mm from center to center, or 400mm from outside to outside? In real terms, there's about a 20mm difference in width just between those two measurement styles.

Answer 3

I have been in a similar situation, when moving from 630 wheels to 622 on an old frame.

I had Tektro R559 long-reach calipers, which worked on the front but the rear was still not long enough. I ended up making a dropper plate which provided a lower location to mount the brake.

Would I do this on a front brake? probably not.

If you file the ends of the sliding slot in the brake arms, then the pad will move down a little. Can you file 2mm out without compromising the brake's structural strength? Perhaps, but I wouldn't take more than a 1/4 mm and I'd also polish it to be smooth, and reduce the chance of a stress riser.

I'd recommend buying a longer front brake caliper that will work better, and store the old one for some future project. After all, your front brake does most of the work when stopping.