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-   -   Which direction to rotate a 1" steertube shim gap? (https://www.bikeforums.net/bicycle-mechanics/1131639-direction-rotate-1-steertube-shim-gap.html)

passenger 12-27-17 11:55 PM

Which direction to rotate a 1" steertube shim gap?
 
I'm putting a Controltech Ti-mania 1-1/8" stem onto a Columbus Minimal 1" carbon fork. Using a Thomson 1" steertube shim. My question is where should the gap on the shim end up? I've seen shims with diagonal gaps to even the load and even a stem/shim combo that places the gap on the far side of the stem, away from the clamp bolts.

I want to be careful and put the shim gap in the correct spot for even load... but nervous I'd put too much pressure on the clamp bolts (Ti threads, Ti bolts) if I rotate the gap away from the bolt area.

One more question -- Should I pre-load the stem or shim to the bearing cap? This stem has a very thin clamp area that just barely grabs the 1" Ti spacers. The spacers are only about 0.8mm larger diameter than the outer stem clamp area. If I pre-load the shim, I'd use a 1" top cap. If I pre-load the stem, I'd use a 1-1/8" top cap.

Thanks for you help..
-C

Kontact 12-28-17 12:07 AM

I would put the gap opposite stem bolts. This smooths out the split rather than exaggerating it.

Given the thin spacers, put the shim on the bottom. I assume the shim has a lip and the spacers will go against that lip rather than the stem, like this:

http://www.universalcycles.com/image...arge/22222.jpg

Thin Ti spacers are tricky for this reason. I have a thin shim like that, but I'm using a 1" stem, no shim. If you don't have a lipped spacer don't use the Ti spacers.

1 1/8" top cap.

passenger 12-28-17 12:39 AM

Thanks -- good advice, I will rotate the shim gap toward the front of the stem. But my shim is a Thomson (non-flanged). Wondering if I can get by with that (it's one of the few black shims on the market, if you look at the stem, ControlTech Ti-Mania, you can see why color shows). As the for the Ti spacers -- well double-dagnabbit, I really want those to work (Ti-fetish bike). Maybe I will look for thicker 1" Ti spacers?

passenger 12-28-17 01:36 AM

I found a 1" threaded-headset locknut spacer I will try in between the steertube spacers and stem bottom. Otherwise, searching for thicker titanium spacers....!!

I would have just used a 1" threadless Ti stem... but modern, short reach & meaty top section 31.8 handlebars are a must for me. I have never seen a 1" Ti stem that fits a 31.8 handlebar.... not sure it exists.

-C

Kontact 12-28-17 02:27 AM


Originally Posted by passenger (Post 20075669)
I found a 1" threaded-headset locknut spacer I will try in between the steertube spacers and stem bottom. Otherwise, searching for thicker titanium spacers....!!

I would have just used a 1" threadless Ti stem... but modern, short reach & meaty top section 31.8 handlebars are a must for me. I have never seen a 1" Ti stem that fits a 31.8 handlebar.... not sure it exists.

-C

Why don't you just find a shim with a lip? They aren't expensive. Or, a short 2mm aluminum spacer right under the stem if you can't find one.

The problem with the Ti spacers are that they have have diameter of 29mm and your stem's inner diameter is 28.575mm.

passenger 12-28-17 02:50 AM


Originally Posted by Kontact (Post 20075679)
Why don't you just find a shim with a lip? They aren't expensive. Or, a short 2mm aluminum spacer right under the stem if you can't find one.

The problem with the Ti spacers are that they have have diameter of 29mm and your stem's inner diameter is 28.575mm.


Thanks... Like I noted above, there are no black shims with a flange (lip) anywhere. But I will try to find a 1" inner diameter spacer. The threaded-headset locknut spacer seems like the best bet.

Best,
-C

Kontact 12-28-17 04:05 AM


Originally Posted by passenger (Post 20075687)
Thanks... Like I noted above, there are no black shims with a flange (lip) anywhere. But I will try to find a 1" inner diameter spacer. The threaded-headset locknut spacer seems like the best bet.

Best,
-C

That sounds large and ugly. This is all you need between the bottom of the stem and the Ti spacers:

http://cdn3.bigcommerce.com/s-d9og6f...80.500.JPG?c=2

xenologer 12-28-17 09:05 AM

I'd have the split in the shim, facing the same way as the split in the stem.

Because the stem clamp needs to be able to close down and grab the underlying steertube, and they'll have a harder time doing that if they're trying to grab onto the side of a shim that isn't split to allow compressing.


Your Preload cap needs to transfer load down to the headset upper race.
You will do that either through the shim, or through the stem; depending on which one makes contact with that race.
It's a question of what's going on down below where they touch that will make the determination.

Kontact 12-28-17 12:48 PM


Originally Posted by xenologer (Post 20075997)
I'd have the split in the shim, facing the same way as the split in the stem.

Because the stem clamp needs to be able to close down and grab the underlying steertube, and they'll have a harder time doing that if they're trying to grab onto the side of a shim that isn't split to allow compressing.


Your Preload cap needs to transfer load down to the headset upper race.
You will do that either through the shim, or through the stem; depending on which one makes contact with that race.
It's a question of what's going on down below where they touch that will make the determination.

Neither of these is correct. Clamps oriented 180 out for the split are extremely common both in stems and seatposts. The shim or seat tube can easily slide under the clamp/stem to decrease its circumference.


With the type of non-lipped shim the OP says he has, there is now way for the preload top cap to push on the shim without the stem interfering with it because 1" top caps are pretty much the same diameter as shim and the inside of the 1 1/8" stem. So the stem might end up clamping the top cap instead of the shim. It would work if the shim was taller than the stem, but usually the opposite is true.

rosefarts 12-30-17 02:15 AM

Hey Passenger,

Once you've finished your install and ridden a while, will you post back and update on the handling and riding characteristics of this fork?

I've thought of getting one myself. My Columbus steel fork rides really well and I'm concerned I'd lose some of the ride quality with the carbon one.

I'd especially be interested at how it handles over 40mph or through fast switchbacks.

Thanks.

sweeks 12-30-17 06:36 AM


Originally Posted by passenger (Post 20075615)
...clamp bolts (Ti threads, Ti bolts)

Be sure to use anti-seize on the bolts; titanium is said to have a tendency to "cold weld" to itself under pressure. IIRC, a copper-based anti-seize is recommended.
Steve


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