How To Make Big Bad Tires Fit Your Fork

The printed size on a tire's label is rarely accurate, especially with Continental brand road tires, and double-especially if you stretch them over wide rims. As evidence I submit my new "28mm" Continental 4-Seasons tires, whose actual width measure out to be 31mm on my TK-540 hoops. Man, these dudes fill up like a latex zeppelin.

So, when I ride and hit bumps I can sometimes hear the tire rub on the underside of the fork crown and brake caliper. Also little rocks and sand get stuck up in there and cause a grinding feeling I can sense through the frame. No, no, no. None of that is good. Needs amending, pronto.

This is a guide on how to shave down your fork crown and road caliper to fit larger tires than the manufacturer intended. 

Obvi, there's a chance you can screw up your bike if you don't do this right. So, like, pay attention and don't blame me if something goes wrong. OK? 

What Ya Need: 

1. Basic tools to take off your fork, wheel, and brake caliper. Probably a Y-wrench. Maybe a Torx wrench if you use Campy, Zipp, or Specialized components. 
2. Something to clamp the fork in. I used a normal bike work stand. 
3. A set of "half-round bastard-cut files" and a "Swiss file". Yes, those are the correct, technical names. Round bastard-cut files would probably work too. 
4. Touch-up paint. I guess, if you care about that kind of thing. 

First: 

Before you start horking away with the files ("horking" is another colorful technical term for what you do with a file. Some people call it "hogging." Metalworker's language is fun) Make sure you've properly messed with the brake's centering adjustment bolt. 

This little bolt can change the angle of the brake; screwing it all the way in (or out) can effectively widen the brakes and give you a little more room for big tires. Note: not all brands put the centering adjuster in the same spot. After you mess with it you'll need to re-adjust the brake pads and the securing bolt. 

If that don't work, then do this:

Pull off the tire, yank the fork out the frame, and let loose the brake caliper: we're gonna start hogging. When you get everything taken apart, you'll see exactly where the tire rubs, because the components will be missing paint. 

Yowzers! The good news is that the worn-away paint and scuffs provide a visual cue on where to focus the files. 

Note: Aluminum tends to gunk up files, so have a stiff wire brush handy for cleaning. 

The basic idea here is to hog a little off, check your work, then hog a little more. Filing away material weakens the component, and you can only go so far before altering the structural integrity. 

After shaving the brake, work on the fork. 

On this bike, the fork is steel, so the files get a bit more bite. I started with the biggest file, and worked my way down, using the Swiss file to smooth it all at the end. 

Check your work after every few horks. You can see I put tape where I wanted to protect the finish. 

When you're done hogging and horking, put it all back together, fill the tire to capacity, press down and see if it rubs.

OK, it doesn't look like much of an improvement. But I just wanted a couple millimeters to take the grindy feeling away. There's still more material on the fork and caliper, so if I want bigger tires I've got heft to grind off. 

Now you might be thinking, "This is all well and good on a steel fork with an aluminum brake caliper, but I got carbon baby! Whaddo I do?" 

Here's the thing, forks need a lot of columnar strength, which carbon fibers aren't great at providing. Thus, most "carbon" forks use a whole lot of resin, in terms of weight by volume, because resin provides support. Resin can be filed down, no problem. But once you start getting into the fibers and they start fraying... What I'm trying to say is that carbon is deceptive. On most forks the crotch is not a structural or weight-bearing area, and I've seen many (MANY!) old forks and frames with big old holes in the carbon from tires giving the tickle treatment over thousands of miles. Use your judgement; don't go nuts. 

As for aluminum, titanium, magnesium, and the rest of the metals: GO NUTS! Just keep in mind different metals react differently against a file. 

Oh yeah, at some point you should have applied some layers of touchup paint. Don't forget to do that.