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Converting 1" steerer tube stem to 1-1/8"

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Converting 1" steerer tube stem to 1-1/8"

Old 08-11-18, 02:05 PM
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Converting 1" steerer tube stem to 1-1/8"

I could run down the the LBS and ask these questions but it's so hot I don't want to leave the house.

I am attempting to convert a bike with a 1" diameter carbon steerer tube so it will work with a 1 1/8" stem.
I realize I need a 1-1/8" O.D. sleeve (1" I.D.) that will slip over the 1" steerer tube. I have one but it is longer than the stem so I assume I will have to get it cut/modified to match the length of the stem?
The steerer tube originally had the star washer expander type mounting. From what I can see, the cap will be too small in diameter to hold the stem on. Do I need a bigger cap or am I overlooking something?
I believe there was a spring restrained with a bolt down in the steerer tube - what is it's function?
Any advice is appreciated. Thanks in advance.
Some pics attached
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Old 08-11-18, 02:42 PM
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1) you CAN’T use a star nut in a CF steerer. The ”petals” will skewer through the CF and cause misery, one way or another. It has to be an expander plug or bonded insert.
2) yes, you need a 1”-to-1 1/8” shim. Cutting it to fit the stem clamp is slick, but probably not required.
3) the purpose of the top clamp is to set headset bearing preload, and to reduce the risk of getting gouged in a forward fall. Odds are good-but not guaranteed- that you’d be able to use the existing 1” top cap to push against the bearing and set preload that way. This would allow you to position the stem at any height along the shim w/o upsetting bearing preload.
4) or you can cut the shim to fit the stem, minus 3 mm. Use 1” spacers below the stem. Check that the stem clears the top of the steerer and shim by abt 3 mm and use a 1 1/8” top cap.
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Old 08-11-18, 02:57 PM
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Converting 1" steerer tube stem to 1-1/8"

how do you make a carefully machined smaller hole bigger, is the issue.. ?

you don't. you buy a new stem.

OTOH, you can use a 1.125" stem on a 1.0 inch steerer,
with a reducing shim.
it is 1/16th of an inch thick..

your question should have had an important comma, in it,
but you were asking the opposite of your intended question..

Expansion plugs go into carbon steerers , star nuts in metal ones..


Last edited by fietsbob; 08-11-18 at 03:06 PM.
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