How does fork steer tube length effect bike fit?
I recently purchased a Reba fork for a Niner EMD I am building. I have been debating what length to cut the steer tube on the fork. For the last two years I have been riding a Surly KM with a Manitou 80 mm fork cut to approximately 7.25 inches and this height seems perfect. Does it make sense to chop the steer tube down to 7.5 or even 8 inches first to see how these heights feel? The niner frame (headtube), stem height, and headset measure in at 6.8 inches. I will likely have this done at a shop because I don't have the tools to install the star nut or fork crown race. I would appreciate anyone's perspective.
That really depends on the frame and you.
But whatever you think it should be, leave a little extra.
You can take up the extra with spacers on top of the stem.
Having extra will allow you room to make adjustments, change a different stem since they sometimes have different clamp sizes, move it to a new frame or sell it somebody else.
Just stick it in granny and start grinding.
How does fork steer tube length effect bike fit?
Steer tube length depends on the frame and the bar height you need. You need enough steer to achieve that (head tube length + headset stack height + stem stack height = minimum steer tube length). It can be longer. Just put spacers above the stem. I always leave the steerer long, and even longer than I think I need at the start of a new build. You can not add length later.
Originally Posted by bsgerig
The trouble with common sense is it is no longer common
crown race setting: Go to Home Depot with the crown race in your hand and find a PVC fitting that fits it nice. Then get a length of pipe and maybe a coupler and you have a race setting tool for $5. The key is that you are pushing on the race all around the ring. Grease the ring and tap it on with a hammer. Before you tap it on, support the steerer tube under the crown, for example with a stick of lumber off the end of a workbench.
To figure the steerer length. What I like to do is to put the steerer through the headset, ensure that it is all the way up, put my intended stem on, and add 25mm. If you want to plan for a taller headtube, headset, or stem, allow for that now. I put a 20mm spacer under the stem and a 5mm spacer on top. Then I scribe a line around the steerer at the 5mm spacer. Next, I take it off and cut it about 2mm (a little less than 1/8th) BELOW the line. The reason is that the top cap should be clamping down on spacers or stem, not on the steerer itself. What I've done is to put it in a vice with a stem and a parts-bin spacer set so that the junk spacer can be my saw guide. Finish with a file and it's ready to go. The reason I do 25mm is that you can do 5mm increments from 0-25mm with a simple 20/15/10/5mm spacer kit.
Set the star nut with a hammer. I'm sure there's a less redneck way to do it, but it's not a big deal.
If you ask a shop to do it, definitely give them the frame, fork, stem, and spacers as you want them installed and tell them to cut it to make it work. Be specific as to exactly what you want and there will be less chance of a screwup.
I've seen some hackish DIY methods of adding length later. I don't know anyone who would ride those solutions though.
Originally Posted by shiggy
For the OP, here's an article with some pictures related to steerer tube length: Tech Tuesday - Steerer tube length - Pinkbike
One thing that should be emphasized is how the headset cap shouldn't be touching the top of the steerer. The cap needs to rest on the stem or a spacer, with a gap large enough to not cause it to contact the steerer, in consideration of the cap compressing all of the parts down. If your goal is to get a steerer length with minimal spacers, you must mind this and how stems has different stack heights, from ~32mm (ex. Syntace Flatforce), 45mm (ex. Truvativ Stylo), to maybe ~60mm (ex. Titec El Norte). There's no standards on stem stack height, so if you cut a steerer too short, maybe you can use a stem with a shorter stack height.
For crown race installation, bring the crown race to your hardware store as suggested before. Beware that there are pipes with different inner diameters, yet might be labeled the same diameter. There's schedule 40 and schedule 80 (and 120) pipe, with the higher number having a thinner wall or larger inner diameter. Pretty sure google has more info on that, if you're curious, but point is, make sure there's good fit at the end of the pipe, with the pipe's end making good contact on the race's flat part, not too far on the edges and not too close on the inside, else you will be at it for a while grinding/filing the inner diameter of the pipe to make it fit better, so it's not sitting on the beveled edge on the inside of the crown race. Maybe getting a junction piece might fit better, but it might just take it to the other extreme and sit on the outer edge of the race. Better to just try to get the better fitting pipe trying out the different "schedule" ratings.
As for the star nut, just thread the top cap bolt in it so that it at least makes contact with all the threads, poking out the bottom maybe 5mm. Line it up and hammer it in until the bolt's almost flush with the top of the steerer (after you cut the steerer). Doing this ensures that when you put the top cap on, and tighten it up, the star nut is at a depth proportionate to how long the top cap bolt is, and has good enough purchase on the threads.
Doesn't cost much as getting a shop to do it and is satisfying to do it yourself. Probably less than $5 for the pipe and less than an hour worth of labor. Some might call these ghetto methods, but if you at least have some mechanical sense, there's not too much risk of screwing anything up.
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