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I'm looking into buying inexpensive rigid fork (~50 EUR) for my old GT Avalanche 3.0 (disc brakes) to make it slightly better commuter bike. My daily ride is 10km one way on asphalt surface. What should I consider when choosing a fork? What parts would I need in addition to the fork itself to do the replacement? Won't I make it much worse? I'm okey with what I have now, but would be nice to go little faster.

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    If you have knobbly tyres, you might want to consider something smoother and perhaps a little narrower. – David Richerby Sep 18 '18 at 16:11
  • @DavidRicherby yes, I have Schwalbe Hurricane and they are not really knobbly, but I consider changing them to something narrower – Fedor Sep 19 '18 at 7:48
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To convert to a rigid fork consider

1) Fork length - to maintain head angle geometry This depends on the travel of your existing suspension fork and the wheel size. ie For older 26inch wheels - an 80mm Suspension fork was a 420mm rigid fork and 100mm suspension fork 440mm etc.,

2) Brake mounts - whether your disc brakes are post-mount, IS Mount or flat mount. Adaptors can be bought to convert between them.

3) Disc rotor size - some rigid forks will have a maximum rotor size clearance.

4) Tyre clearance - though you are using it for commuting - bear in mind if you use an MTB tyre in the fork - determine the maximum tyre clearance.

5) Fork steerer length - if you are buying secondhand (especially). New forks will have an ample length of steerer to cut down. But secondhand forks, you must check and measure to make sure there is enough for your frame.

6) Fork steerer width / profile - unlikely to be anything other than a straight 1.125inch on your bike - but with tapered head-tubes you may have to change the lower crown race.

  • Great answer. Unfortunately 420mm axle-crown forks seem to be hard to find these days. – Argenti Apparatus Sep 18 '18 at 14:12
  • Suspension fork on my bike is 100mm and if I measured correctly axle to crown is 480mm. All 480mm rigid forks I found (for instance this one: bike-components.de/en/Surly/Krampus-Disc-29-Starrgabel-p42518) are marked as 29" while I have 26" wheels. Would they fit or my bike and maintain bike geometry? I don't think my suspension fork travels much. Only if I go steep uphill and put weight on the front wheel (but still 10-20mm max). – Fedor Sep 21 '18 at 7:36
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    100mm with 26inch wheels - you need 440mm rigid axle to crown (ideally). Your 480mm measurement doesn't take into account sag on the fork ie. the amount the suspension fork "sits-in" when sat with a rider. This is normally set to around 20-25%. You might be able to get away with shorter or longer - but depends on how steep you like your head angle. – OraNob Sep 25 '18 at 8:40
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Answering secondary questions

What parts would I need in addition to the fork itself to do the replacement?

You should consider replacing the headset, or at the very least servicing the bearings if they are not too worn.

Won't I make it much worse?

I'm okey [sic] with what I have now, but would be nice to go little faster.

If you are riding on paved surfaces you will not really need suspension and you'll appreciate the reduction in mass. I don't think you'll mess up your bike (but do make sure you get the right length fork as a different length will alter your steering geometry).

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