Trek Steerer tube cutting

saladfunky

Hi, I have a TREK EMONDA SL and wish to cut the steerer tube down a bit because I have lowered the stack and have an excess of steerer tube above the handle bar height. Has anyone done this on a Trek before. It looks diferent to my other non carbon bikes.
thanks
Chris

Semantik

If it's a carbon steerer you can use a carbon specific blade in your hacksaw- Park Tool do one, though a fine tooth blade will do.
But why do you actually NEED to cut your fork down? Can't imagine that it came with more than about 30mm of spacers anyway.I would leave it alone. Not a good selling point if you get bored of it after a year or two. Not everyone wants their stem slammed right down.
IME only worth doing if it's for time trialling or you're road racing at a high level.

saladfunky

Semantik wrote:

If it's a carbon steerer you can use a carbon specific blade in your hacksaw- Park Tool do one, though a fine tooth blade will do.
But why do you actually NEED to cut your fork down? Can't imagine that it came with more than about 30mm of spacers anyway.I would leave it alone. Not a good selling point if you get bored of it after a year or two. Not everyone wants their stem slammed right down.
IME only worth doing if it's for time trialling or you're road racing at a high level.

Thanks for the reply, all valid points. I doubt I'll sell the bike but I take your point. I have tried all the positions and am happiest with it at 1 spacer off the lowest position, I have even changed the stem to get lower. I think I'd have like to be able to afford the SLR H1 frame, but no way can I!! So I have had it like this with 30 mm of spacers for a year now and although I am not that bothered I think it spoils what is a lovely looking machine. It looks like a simple enough task for some bikes looking on Utube but I am not sure about the Trek. . .It looks different inside the tube to my other bike!
Just interested to know for now and open to all comments, positive and negative.
cheers
Chris

964cup

Key things:

1. Wear a mask and/or work outdoors; carbon dust is nasty.
2. Use a cutting guide to make sure your cut is perfectly square: http://www.wiggle.co.uk/park-tool-threa ... -guide-set
3. Measure carefully. If you want to remove all spacers above the stem, the steerer needs to be cut shorter than the top of the stem to allow the top cap space to avoid it contacting the top of the steerer tube once you tighten it up. About 3-5mm depending on the design of the cap. Note that some manufacturers (both fork and stem) recommend a 5mm spacer between the top cap and the stem - worth checking in case Trek are in this group or your stem manufacturer is.
4. As above, use a fine-bladed hacksaw; then use some emery paper to clean off any rough edges inside and out.
5. Once you have a collection of offcuts, you can make a neat desk organiser

stanthomas

I'm guessing you think the steerer tube 'looks different' because of the bung. Non-carbon forks use a nasty, sharp star washer to pull the top cap down on the stem. Trek carbon forks use an expanding bung that is located inside the top of the steerer tube with a flange to locate it against the top of the tube. You need a 6mm hex wrench to release it.

You should have some, 3mm or so, of steerer poking thru the stem when you have it in the desired position. I.e. do not, under any circumstance, cut it below the top of the stem.
Because of the flange on the bung and lip on the top cap, you'll need a 10mm spacer above the stem.

I concur with the other advice on here about cutting the steerer but would simply note that I cut my Domane fork using a normal, albeit fine, hacksaw blade and guide I made from an offcut of steel tubing. However you do it, go slowly and be gentle.

svetty

Semantik wrote:

If it's a carbon steerer you can use a carbon specific blade in your hacksaw- Park Tool do one, though a fine tooth blade will do.
But why do you actually NEED to cut your fork down? Can't imagine that it came with more than about 30mm of spacers anyway.I would leave it alone. Not a good selling point if you get bored of it after a year or two. Not everyone wants their stem slammed right down.
IME only worth doing if it's for time trialling or you're road racing at a high level.

The problem with this is that the bung will be sitting above the stem which will be clamped onto an unsupported section of the steerer tube.

@ OP: go ahead and cut it down - just go steady and use a fine toothed blade. I cut all the way around so that the blade is always cutting towards the centre of the tube orifice - avoids strands of carbon flaking from the outside as you finish the cut and helps keep the cut perpendicular to the tube axis.

The Rookie

With the upper headset bearing operating against an "unsupported section of the steerer", does it really need the bung inside at the stem?

svetty

The Rookie wrote:

With the upper headset bearing operating against an "unsupported section of the steerer", does it really need the bung inside at the stem?

Both headset bearings are enclosed by the head-tube - the steerer here is a fairly loose interference fit in the inner race but isn't under any significant direct compression. Transverse loads when cycling are transmitted through the entire structure of the steerer tube walls to the inner races and thus to the head-tube.

It is the localised compression from the stem clamp that is the issue, not transverse loading of the steerer (for which it is appropriately designed).

The Rookie

I would say the loading on the steerer from the upper headset wedge under braking or hitting bumps far exceeds the compression from the stem!

Noting that a tube form is at its strongest against a compressive near uniform radial load, so I'd say the bung isn't needed in the way you think it is.

svetty

The Rookie wrote:

I would say the loading on the steerer from the upper headset wedge under braking or hitting bumps far exceeds the compression from the stem!

Noting that a tube form is at its strongest against a compressive near uniform radial load, so I'd say the bung isn't needed in the way you think it is.

You may be correct but your opinion flies in the face of that of the majority of the industry and received wisdom. Presumably there is engineering data that underpins this 'standard' advice.

It may be that the potential for user error in stem clamp tightening might underlie some of the justification for the use of a bung however given the potential consequences of steerer tube failure I'd rather go with the mainstream view and would be wary of advising unknown third parties to do otherwise

saladfunky

Well it was a while ago now thanks for all the comments which helped me decide to go for it. . . .
So I did cut the tube down using a tungsten carbide blade. I tried using a jubilee clip after someone suggested it but in the end I used a spacer that was going to be un-needed after the job as a guide for the blade as the jubilee clip wasn't so good. I just held it in place and cut next to it. The cut doesn't need to be 100% accurate anyway. I was worried if it wasn't totally straight the whole thing would be a fail. There is a mm or so room for error. But the tube cut so easily it was no problem. I had no splintering or any issues. I just cut at a steady pace with gentle force. I did sand it slightly afterwards to make it perfect. I didn't even remove the steerer from the head tube. I used a stand to hold the bike at 90 degrees so the steerer was horizontal to make cutting easy and the dust would fall away from the bike.
The bike looks so much better for it! I thought it looked ugly with the 2.5cm sticking up, now with only 5mm sticking up it looks nice. Somehow it seems important even if that seems a bit vain