you'll need to look at, the travel of your original fork, the steerer tube diameter and length, the disc brake mounting tabs, and the wheel retention system.
If I remember correctly the 09 HR Sport Disc came with an 80mm travel Suntour XCT-V2 80mm travel fork. 80mm travel forks aren't that easy to find anymore, there are some that are adjustable down that far, but not a huge number. If you want you could go to 100mm of travel without to much problem. It will change the handling characteristics of the bike just a tad, but it will not be anything epic, that you can't get used to easily. And unless we're talking a hyper tuned geometry race bike (which the HR is not) it will likely actually improve things. So 80 to 100mm of travel is what you'll be looking for.
Steerer tube diameter on the HR is 1 1/8" threadless, so that's pretty standard. The length you will need if you go used is determined by the current set up. The easiest way to determine that is to measure it yourself. Simply measure from the bottom of the headset to the top of the stem with a tape measurer, then add 1/4 inch to be safe, and thats the minimum length of steerer tube you'll need to have on a used fork in order to be sure that it will fit your bike properly. On a new fork it's not an issue, they come with uncut full length steerers that are between 11 and 12 inches in length. Just cut to fit. Just keep in mind that a steerer that is to long can be cut to fit. But a steerer that is to short cannot be lengthened. So have more steerer than you actually need is always a better way to go.
There are two types of disc brake caliper mounts, Post Mount and IS (international standard) mounts. IS mounts are tabs that stick out from the back of the fork leg with holes in them that go left to right, and require an adapter to mount the caliper to usually. Post mounts are just that, posts that stick straight out of the back of the fork leg and have threaded holes bore into them that go front to back. Most brakes with 160mm rotors can be bolted directly to the mounts without an adapter. You'll only need to use an adapter on a post mount fork if you use rotors larger than 160mm. If I remember correctly the Suntour XCT-V2 has IS mounts. Most new forks come with post mounts. Not that big of a deal, you'll just need to unbolt that caliper from the adapter and bolt that caliper directly to the mounts. If you are using a larger rotor than 160mm though you'll need to get a different adapter for the brakes to mount up correctly. If you do happen to find a fork with IS tabs then it's simply a direct swap from your current fork to the new one.
As for the wheel retention system. That's easy, your current fork and wheel use the standard 9mm quick release system. Unless you want to replace your front hub, that's what you'll need, a fork with standard QR drop outs. There are two other common systems out there now, 15mm thru axle and 20mm thru axle. Neither of which will work with your current front wheel. Easy!
It actually sounds more complicated that it is. It simply takes more to tell about it, than it does to look for it. :thumbsup: So look for a 80 to 100mm travel fork, with a 1 1/8" steerer tube that is at least as long as your current steerer, look to see what disc brake mounting system the new fork uses so you can have any additional hardware on hand, and make sure the fork uses a 9mm quick release system.
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