My bike is a 2019 Boardman Mtr 8.6 and I’m wondering if I am able to fit a 140mm travel fork to my bike? Here’s a link to the bike and it’s specs: https://www.cyclerepublic.com/boardman-mtr-8-6-mens-full-suspension-mountain-bike-2019.html
You can swap out a suspension fork for a different one with more of less travel as long as the new fork has approximately the same axle to crown distance - the distance between the center of the axle and where the fork mates with the bottom of the head tube.
IF this distance is too long the frame is tipped back and the steer angle slackened, if the fork is too short the frame tips forward and the steering angle is steepened. Both can have negative effects on handling.
Longer travel suspension forks tend to have longer axle-crown distances as obviously they need more room for the front wheel to move.
Note that many forks are designed to compress with the rider on the bike. The compressed axle-crown distance is whats important.
As far as I know you should be able to install a fork with any amount of travel as long as a few conditions are met:
PS: I've based the dimensions/sizes in the following text on the info/specs found on this website: https://www.cyclerepublic.com/boardman-mtr-8-6-mens-full-suspension-mountain-bike-2019.html
- steerer tube diameter correct diameter (some headtubes are tapered but from the images I've seen it looks like you have a non tapered 1 1/8" diameter steerer tube)
- fork matches wheel size; get a fork which can fit 27.5" or bigger wheels in order to prevent running into clearance issues or simply not being able to install your front wheel (27.5" wheel size is based off of the previously mentioned link)
- steerer tube length is sufficient (if your steerer tube is too short you won't have enough length sticking out to mount your stem/(potential) spacers. You can always shorten a steerer tube, usually when buying a new fork the steerer tube will have to be cut to size (video: , they use road bikes in the video but the method is exactly the same for mountainbikes).
- also make sure to get the correct axle length/diameter when getting a through axle fork, to make sure your current wheel will fit properly on the new axle.
More travel might mean the front end of the bike will be a bit higher up than on a shorter travel fork but the change of 120mm to 140mm won't make much difference in that aspect.
Also in the description of the Boardman Mtr 8.6 (https://www.cyclerepublic.com/boardman-mtr-8-6-mens-full-suspension-mountain-bike-2019.html) it is mentioned that the Boardman mtr 8.8 has a 140mm fork installed. Quote: "If you want a few upgrades, why not trade-up to the MTR 8.8 for 140mm of Rock Shox travel, 1x10 Shimano Deore gearing and Shimano hydraulic brakes." And it looks like the 8.8 uses exactly the same frame as the 8.6 does.
TL;DR Yes you can as long as you adhere to some rules (mentioned above)