coldwaves

I recently cut the steer tube to lower the handlebar to my desired position. The bike is a 2012 Scott Foil 40, with a carbon steerer tube. Currently, I have a 20 mm spacer above the headset and then stem above the spacer. The headset cap directly sits on top of the stem (See picture for the setup). The steerer tube has a expander plug that comes with the bike (See picture). The plug has a lip and sits flush on top of the steerer tube.

After installing everything, tighten the headset cap to preload the bearing, tighten the stem bolt, the top of the steerer tube/expander plug is around 4mm (probably 3.8mm or something slightly smaller than 4mm) lower than the top of the stem. I also measured the distance from the center of the top stem pinch bolt to the top of the stem. That distance is about 5mm. So the top of the steerer (including the lip of the expander plug) sits slightly above the center line of the top stem pinch bolt. Do you think this is OK? or is the gap too big?

But when I tighten the two stem pinch bolts to the same torque (5 Nm printed on stem but I just tighten to 4 Nm), the gap of the top pinch bolt is smaller than the bottom one (See picture). Could this be because the steerer tube does not extend far enough to the top of the stem? I need a few mm gap to preload headset bearings so the steerer tube can be 1 or 2 mm longer at the most. I am not sure but I doubt a one or two mm longer steer tube is the culprit. Or could this be because the expander plug bulge the steerer tube very slightly? I certainly cannot see any budge visually but can feel it when inserting the stem to the stem. The Scott stem is quite a snug fit to the steerer tube and sliding it down at the area of the expander plug seems to give more resistance. Do you think it is normal to have unequal gap for the two stem pinch bolt?

dr_lha

5mm after you've pre-loaded is a bit much IMHO. The usual guideline is that you leave 2-3mm between the top of your compression plug and the top lip of the stem, before preload is applied. After pre-load is applied, the gap would naturally be smaller. This is probably why your stem bolts are uneven.

Is it a problem? Dunno.

coldwaves

Thanks! The gap is more like 3.5-4mm after preload. 5mm is the gap between the center of the top pinch bolt to the top of the stem.

What happens is this: I want to remove one 10mm spacer. Before cutting the steerer tube, the gap between top of the steerer tube to top of the stem is probably 1-2mm after preloading. But I recall that the expander plug does not sit flush on top of the steerer tube prior to cutting but instead is lifted slightly. So the actual gap if the plug sits flush is probably bigger than that. I assume that the setup was correct before cutting the steerer tube so I ask the bike shop to just cut out 10mm steerer tube. I don't know whether the gap is around 4mm before or the bike shop cut slightly more than what's needed.

I just want to make sure the stem and steerer tube is not going to break and throw me on the road. I guess I can ride it slowly in the neighborhood to test.

gsa103

It looks like the expander plug is designed for having a ~3mm spacer above the stem. That would center the plug on the stem clamp much better.

What you could do is shift the stem down ~3mm and then put the difference above. That would lower your stem, but hopefully only a small amount.

coldwaves

Thanks! That's definitely a choice. I just need to find the right spacer to do that. At the same time, Scott does not require a spacer above the stem. Regarding headset spacer, Scott says maximum of 5mm spacer above the stem, maximum of 40mm spacer below stem and minimum of 5mm spacer below stem.

The uneven gap of the stem pinch bolt looks concerning to me. I don't remember whether it is like this before cutting the steerer tube or not. I want to seek opinions on whether this is common/normal/OK or not.

AnkleWork

Flip the stem and see if the unevenness flips?

coldwaves

Just took a picture of what I am talking about.

SquidPuppet

Steerer is WAY too deep in the stem.

dr_lha

What's your basis for saying that?

That design of compression plug doesn't need a spacer above the stem, because it provides strength at the top of the steerer, unlike the internal only type.

Honestly I think the issue is that the steerer tube is cut to short.

3alarmer 

.
...take a good look at your photo, and think about what your stem is clamping on when you torque it. You can probably get away with sticking a short piece of something in there to prevent the closing of the gap on top, but the stem was designed to have stem inside there at both bolt locations.

Best bet is to lose the spacer and see where you're at.

coldwaves

Thanks for your insights. I have actually done that. I took out the top bolt and look through the gap to see the relative position of top of the steerer tube and the bolt. I have also measured outside. Here are some of the distance:

top of the steerer to top of stem: slightly less than 4.00mm, maybe 3.7 or 3.8mm
center of the bolt to top of stem: 5mm
top of the bolt to top of the stem: 2.5mm
bottom of the bolt to top of the stem: 7.5mm

So the top of the steerer tube, including the lip of the expander, is slightly above the center of the bolt.

I agree that the steerer tube is cut short. Before I cut the steerer tube, I took out the stem and looked at the gap. It looks good, just 1-2 mm below the top of the stem. So I assumes that the steerer tube length is good. I completely takes out the fork and saw that the expander plug is lifted slightly. So the seemingly 1-2 mm gap is actually bigger if the expander sits flush. I did not measure how much it is lifted. Unfortunately, I did not realize this as a problem when I went to the bike shop. I assumes the length is good. Since I only need to remove a spacer, I asked the shop to cut out the length of that spacer from the steerer tube. I am not sure whether the shop cut a little more or not. It is more likely that it is already short before I cut it. But I am not completely sure.

I can definitely replace that 20mm spacer below to something slightly shorter. But I also read online that it is fine as long as the top of the steerer tube is above the centerline of the bolt. Scott bike manual in 2012 does not specify the gap but the 2016 manual says a maximum of 2.5mm. I am not sure how accurate that needs to be.

coldwaves

I agree. The plug has a lip and sit flush on top of the steerer tube. The outer diameter of the plug lip is the same as the steerer tube outer diameter. I think it can function as a reinforcement or support of the steerer tube. I guess that's why Scott does not require a spacer on top of the stem. Specialized has a similar design of the plug and they don't require spacer above either. Cannonade is the same and they insist on no spacer above the stem. On the other hand, Trek requires a spacer on top of the stem. So I think it really depends on the type of plug used in the specific bike.

That also makes me think that clamping right at the edge or slightly below the edge of the steerer tube should be OK. The problem is whether that clamping at the edge provide enough grip and is safe enough. I certainly don't want to stem fly off when I am riding.

bradtx

coldwaves, I think that if you reduce the height of the lower spacer(s) 3-5 mm the upper bolt's gap will be okay. When both stem bolts are loose is the gap even top to bottom to begin with?

Brad

gsa103

Not very, that's why they only quote a maximum value. Realistically, just switching to an 18mm spacer should make everything nice and happy.

As for how it got short, probably a combination of things. You mentioned it was already short, the shop probably just removed 10mm and didn't worry about accounting for the cutting blade width, since it doesn't usually matter.

2lo8

If you're going to have a shop do the cutting, it's better to just bring the bike in and tell them the spacer stack you want, and let them figure out the length and be on the hook if they cut it too short.

If you want to know if it's normal for the gap to be smaller, flip the stem upside down and see if the formerly top, now bottom clamp cap is still smaller.

coldwaves

That's a good idea. Regarding the gap, if I just take out the spacer, slide down the stem and tighten the bolt, the gap becomes more equal. It seems to depend on how far the pinch bolt is from the expander. The expander seems to enlarge the steerer very slightly and you can feel it when sliding down a spacer onto the steerer tube.

coldwaves

Thanks! I agree with you. It is probably a combination of things. Now I just need to find some headset spacers slightly shorter than 20 and make this perfect.

coldwaves

Thanks Brad. Yes, I think lower the spacer a few mm should work perfectly. I went to check with the local Scott dealer. They say what I have now is not ideal but they have never seen gap like this fail in reality. They suggest me putting spacers slighter lower than 20mm (what I have now) and then it will be perfect. I probably need to have a few spacers to get somewhere around 16-18mm. They only have black spacers in shop. I guess I will just look online and see if I can find suitable white spacers.

Yes, when both bolt are loose, the gap is equal. Or if I take out the spacer and slide down the stem, the gap will be more equal after tightening. It depends on how far the bolt is from where the bung plug expands. The expander seems to make the steerer tube very slightly bigger.

fietsbob

Less than whats best for Carbon steerers , can you shorten the spacers under it?

Steel steerers let you get away with some things Carbon won't.

coldwaves

From talking to a few local bike shop, the concern is probably not destroying the steerer tube. The particular kind of plug used here supports the steerer tube from inside so clamping on the top is probably not a big deal for the steerer tube. I believe you are right that it does create stress to the top edge of the tube and it is not ideal. But the key issue is whether the area clamped is enough to secure the stem. In this regards, the material of the steerer tube probably does not make much difference.

I can replace the spacer with a shorter one (likely several spacers to achieve a length slightly shorter than the current one). The current spacer is 20mm. Given the size of the current gap, I think something between 16-18 will be ideal. Atheistically, I would like to have white spacers. The choice is a low fewer compared to black spacers.

fietsbob

Best is 100+% contact of stem and carbon steerers , a 5mm spacer above the stem for the pre load cap adjustment gap..

A Machine shop can turn down just the amount you need from Your white spacer and have the cut square

How about carbon spacers and paint them white Yourself?

coldwaves

This definitely make sense. But I have seen different school of thoughts on spacer above stem. For example, Trek requires spacers above the stem while Cannonade insist on no spacers above. I think it depends on the design of the expander plug.

I haven't thought about machine shop. Maybe that is a good option as I can get exactly what I want. But it might be easier to buy a few spacers to achieve the length I need.

dr_lha

Yes, the issue with the internal type expander plug is that it can crush the top of a carbon steerer tube. With the type that lips over the tube at the same diameter, the plug provides strength. I investigated this at length when building my first bike, including calling the manufacturer for their recommendation. Not to say there's anything wrong with still putting a spacer over the stem, it's just not "required".

Of course the other issue with the "spacer on top" solution is that it lowers your stem much more than you probably want.

coldwaves

Thanks for sharing. I agree. There should be no harm to put a spacer on top of stem. That will make sure that stem clamp totally on the steerer. One concern is that too much spacer on top will make the stem clamp in the area of the steerer tube without the bung expander inside. But a few mm spacer should be no problem.

coldwaves

New and interesting adventure about this situation. I brought the spacer to a local machine shop and ask if they could either grind it down or cut it down. Since the inside of the spacer is straight, he suggested putting the spacer on the lathe to cut out how ever mm I want. The gap as of now is about 4mm. SO I ask the mechanic if he could cut out about 2 to 3mm. The mechanic said he will cut 2.5mm. I asked if they can be that precise. The mechanic said yes. He also said that it is quite a easy job and he can make sure the cut is flat and I won't even notice it.

I will update the forum tomorrow when I get the spacer back. Hope this will work out. Finger crossed.