Fork tube length (stem & top cap)

Jon_1976

I've got a CAAD8 and the stem is at highest setting (built by bike shop) on top of 25mm of spacers (5x 5mm). I was considering lowering the bars so loosened the stem and removed the top cap. I noticed the gap between the top of the stem and the top of the tube is pretty big (5mm). This means the stem top bolt is actually tightening above the tube, is this safe? I've read that with all carbon fork assemblies it is recommended to put a spacer on top, so the stem doesn't crack the top of the tube. The CAAD, being an alloy tube with carbon fork, is it ok to leave it as is?

On a side note,if I do decide to lower it, due to this setup I cant lower the bars with the standard spacers. If I remove 1 spacer, the stem is flush with the tube top. Resulting in the removed spacer having no tube to sit on when replaced. So I'll either need to remove 2 and put a 10mm on top or get the hacksaw out.

drlodge

I'm a bit confused...to lower the bars you simply swap a spacer from underneath the stem to on top of the stem. If this won't work then your current setup is also wrong so take it back to the shop?

g00se

Personally, I would always make sure there is some steerer showing above the stem. If they've used a large bung that sits deep into the steerer right from the top - like the Deda one - they that may help prevent the steerer being crushed. But I'm with you - have some steerer showing just to be safe.

Buy a couple of 2.5mm spacers - loose two of the 5mm spacers below, put on of the 2.5 spacers on to replace them and you should have enough showing out of the top to use either the other 2.5mm spacer or one of the original 5mm spacers. Alternatively, look for a replacement stem with a smaller stack height.

Jon_1976

Thanks goose

tim_wand

The stem bolt should never tighten above the steerer tube.

Your fork appears to have an alloy steerer(?) , What Goose has shown you is a bung for use with carbon steerers to stop star fangled nuts causing scouring and possible damage to the inside of carbon steerers.

Presuming that your fork steerer is alloy, the optimum set up is for it to stop about 2.5-5 mm below the top of the stem (but above its top fastening bolt) and for the stem cap and star bolt to preload onto one another by drawing up this gap.

It sounds with you current set up that the best way to achieve this is to remove a spacer (or swap a 5mm for 2x2.5mm ones) and place the stem lower down with one 2.5 mm spacer above it and one below it and draw up the gap. You could do this by just taking one 5 mm spacer off, replacing the stem and putting the spacer back on top.

Its probably safer to do it with 2,5 mm spacers though to avoid the initial problem of the stem bolt sitting above the steerer tube.

g00se

Tim's right, I am assuming you have a carbon steerer. If it's alloy, then the steerer can be a couple of mm below the top of the stem clamp - so that the top-cap pushes down directly on the stem rather than use a spacer.

mitchgixer6

I'm slightly confused by some of the above comments. Regardless of whether the steerer is carbon or alloy there should always be a gap between the top of the steerer and the top of the stem. If the steerer is higher than the stem (and no spacers are above the stem) then there is no way to secure the stem and pre load the headset bearings. Otherwise the top cap will just press on the steerer and there will be zero pressure on the stem.

g00se

mitchgixer6 wrote:

I'm slightly confused by some of the above comments. Regardless of whether the steerer is carbon or alloy there should always be a gap between the top of the steerer and the top of the stem. If the steerer is higher than the stem (and no spacers are above the stem) then there is no way to secure the stem and pre load the headset bearings. Otherwise the top cap will just press on the steerer and there will be zero pressure on the stem.

But that's how I've read the thread. If the steerer is carbon, safest solution is to have the steerer protrude a little above the top of the stem and use a spacer above the stem to allow the top cap to push onto the stem. Having the steerer above the stem ensures there's no risk of crushing the top of the steerer when tightening the stem.

If it's alloy, you can have the steerer a few mm below the top of the stem and have the top cap push directly onto the stem.