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Evening. I am about to swap the 120s on my 26er Trance for 140s. I know this has been done a lot, but what I want to know is if I keep the steerer tube the same length, what effect will there be on the handling and feel of the bike, or issues such as BB height, head angle etc?
Also, the steerer on the replacement forks is about 5mm longer than the one it will replace, so if I am lazy and don't cut it, will I notice any difference?
Thanks in advance for your advice,
Dom
The steerer length doesn't affect BB height, head angle etc. It's the Axle to Crown (A-C) height that affects how far the bottom of the headset if off the ground - and sets the other parameters. The 140s will _probably_ be about 20mm longer than the 120s you're replacing (it varies by fork though) so you will expect to raise the front of the bike a bit. Not sure how that will affect handling etc.
Steerer length - if they're close, you can just put another spacer on and put spacers above the stem to get the same handlebar height.
It will slacken your head angle by about 1 degree and raise your front end by 20mm. It will also raise your BB but I'm not entirely sure by how much.
The bike will feel a bit more stable on the downs and at speed but the front end might start to wonder a bit more on climbs or front end might wash out a bit more in turns as your weight is a bit further back.
You can counteract the lighter front end by a change in technique and weighting the front more or by either swapping spacers from being under the stem to on top (if you have any) or if you have a rise on your stem run it upside down so you now have a drop.
I think this is quite a common change, heard about people doing a few times. I'm guessing the extra stability gained is greater than loss in climbing ability? Otherwise people wouldn't bother?
Many thanks for the useful replies. I'll give it a go!
Got 140 on mine and it feels fine would be to steep for me at 120
Sprocker - 120 feels ok around Swinley, but I was out in the Alps last week and I definitely felt the need for more travel and a slacker head angle on the long, steep descents. I just hope the bike will still climb well with 140s as it does so very well at the moment.
140s fitted and look lovely. Off to Swinley tomorrow to try them out. I'll let you know how the bike feels.
Just got back from Swinley. Managed to crash on the way there and do a superman down the tarmac. Lucky for me no one saw... Moral of the story: avoid wet smooth red brick pavement edgings.
Anyway, the bike rode well, but did seem a little upright with the new forks. The front was not as planted (although conditions were wet) and a bit more vague on climbs. Half way around I lowered the stem by putting a spacer on top and this made an immediate and very noticeable positive difference. The bike felt like it did with 120s, but the added travel gave it a more plush feel, while still allowing it to climb well. A good compromise, I reckon, if it's a compromise at all. Just wondering if I can now cut the stem shorter. Not too sure about the aesthetics of spacers on top of stems. Looks iffy, to me.
All the best,
Dom
As jairaj suggest, it will be worth flipping the stem. When I first ran 140mm Magura Thors on my Trance X I found the front washed out unexpectedly from time to time, due to me not weighting the front wheel enough. Getting rid of the carbon headset top cap (mine had a low rise alloy cap underneath)and flipping the stem dropped the front end enough to give great traction. I liked it so much I eventually went to 150mm forks. I think the Trance X was compromised by the 120mm forks, the "no compromise" option is 140-150mm.
Thanks, Jules. I've now shortened the steerer and only run a very slim spacer beneath the stem. I still have the top cap, but removing that could be a useful option in the future. My stem is zero rise, so no point in flipping it. The bike rides really well, but it's good to know I could weight the front end further by removing the headset top cap.