Broke my fork, how can I know if another one is compatible?

Question

I've got a Specialized Pitch Pro 2009.

I was casually riding my bike and softly depressed the front brakes. Bam! Metaliic noises! The caliper went flying into the air.

Apparently, the little circle on the fork that the screw that holds the ear for the caliper goes through, broke.

This is unfixable (is it?) and I have to replace the whole damn fork now.

The fork is Rockshox Pike 351 (according to the internet, couldn't find any print on the fork) and I measured 140mm.

I might have a good deal on a lightly used Fox Float 32 150mm (2014).

How can I know that it will fit on my bike?

I understood that a crucial part is the steerer length. How can I measure that on my current broken fork? Like, where does it starts and ends? Both are 1 1/8". Is that all the information necessary?. I also heard that "cutting" a fork is a thing for weird frames. Is this true? Will I have to do this on the fork I buy?

Answer 1

Not fixable. (Or more specifically, not for anything like the cost of just replacing it even if it is theoretically fixable, which with broken magnesium/aluminum parts like this is a black hole of a metallurgy/welding/machining/heat-treating/fatigue/etc question.)

There are two layers to this question - physical compatibility with the frame and parts and whether the resulting bike will have the geometry, handling, and suspension qualities you want for your application. The nature of suspension forks is that there will probably be some degree of change in the latter area when changing models. Some riders have always chosen to dabble with choosing different travel numbers, using forks to tweak geometry, going with something heavier and more aggressive, etc. That is a big conversation and not what you're asking about, so I'll leave it alone other than to say that unless you want to change the bike pretty radically, you're looking for an all-mountain/enduro fork made for the same wheel size and with a travel number in the same ballpark (140-150). Uncompressed axle to crown dimensions are also something to look at, especially on forks with lockout, but they don't tell the whole story.

For the physical part, you're looking at steerer length, steerer type, axle type, wheel size, tire clearance, and brake mounting. Steerer length is measured from the crown race seat (where headset meets fork essentially, looking at an assembled bike) to the end of the steerer. You can get an approximate measurement on the bike by taking the stem off and running a tape measure from the crown race seat up and eyeballing. You tend to need to take the fork and ideally the crown race off to get an exact measurement you can stand by (it's all coming off anyway). Steerers on new forks come very long and are cut to fit the frame they're being installed on for all but the biggest bikes. The headset, spacer stack, and stem being used are also factors in determining fork length. A star nut has to be installed afterward. Both of these operations are easy with the right tools and easy to botch without. If you're looking at used forks that have already been cut, you're basically just seeing if they're your current length or longer, unless you're also dropping spacers.

Steerer type is going to be a key point for you here because your fork is straight 1-1/8" and most similar forks from recent years have had a tapered steerer (1-1/8" on top, 1.5" on the bottom). There is not a way of making a tapered fork work in your frame since it takes traditional external cups for 1-1/8. (There are lower conversion cups that let 1-1/8 zero stack frames take tapered forks, but that's not this bike).

You need another 26" fork, which are also fairly uncommon these days.

I can't tell whether your axle is 15mm or 20mm, but you have to get a fork that matches, unless you happen to have the ability to convert the hub. The brake compatibility part shouldn't be a problem, but you'll probably need an Avid post mount adaptor for your rotor size since most forks are now post mount. Also, your lower radiused brake washers appear to be installed in the wrong order and reversed.

Answer 2

1. No, that's not fixable.

2. To measure the steering tube length accurately, you have to remove the fork. You could get an approximate measure without removing it, but you have to remove it anyway, so might as well do it now. Once it's out, it's pretty self-explanatory - just measure the length of the tube from the point where it joins the fork crown. The tube on the replacement fork has to be at least as long as the one you have now. If it's longer, you'll have to cut it, but if it's too short, there's nothing you can do.

3. I assume that the "140 mm" refers to the suspension travel. If the travel (or, more precisely, the axle-to-crown distance) is different on the replacement fork, it'll affect the handling, so try to keep it close. 10 mm in either direction shouldn't make much difference.

4. It looks like you have a thru-axle. Make sure the new fork is compatible with the axle style you have.

5. There are different styles of brake caliper attachment - but you can get adapters for those.

6. You also have to pay attention to the steering tube diameter, but it looks like you covered that already.