1" threadless fork top cap diameter

Hi

This may be a stupid question but I'm using a 1" threadless fork with a 1 1/8" stem and a 1/8" shim. If I buy a 1" top cap and star fangled nut will the top cap be wide enough to sit against the top of the stem or is it going to be as wide as the shim, as if i was using a 1"stem ?

thanks

You are going to need a 1 1/8" top cap to sit flush on top of your 1 1/8 stem.

starting from the top you will have:

• 1 1/8" top cap
  
• 5mm 1 1/8" spacer
  
• stem + shim
  
• xmm 1" spacer
  
• top headset cap
  
• headtube
  
• ...
  

this explains it

Great thanks that diagram is helpful..why do I need 1 1/8" spacer above the stem and shim? Is this only if it requires one, i.e can the top cap sit directly against the stem?

Also surely will the star fangled nut needs to be 1" to fit inside the steerer? So this is paired with a 1 1/8 top cap?

Apologies its my first time away from quill stems !

You don't really need a spacer between top-cap and stem, but if you do use a spacer, it should be a 1 1/8" one.

No problems in pairing a 1" star-nut with a 1 1/8" top-cap, the bolt dimensions remain the same.

If the steerer is carbon, then it must project above the stem (so you will need a spacer).

If the steerer is aluminium then you can get away with it only projecting above the top screw of the stem, but it's best practice to do as per a carbon steerer.

An alternative to a top cap and a spacer is one of Tester's custom made top caps, which incorporates a spacer.

Thanks for info, so just to clarify - whether the stem is at the top , or it has a spacer above it (as Scilly recommends and is the case for me to acheive the correct stem height), either must be at least a couple of mm higher than the steerer to prevent the top nut bottoming out on the steerer , correct?

Also, I'd like to make some spacers for below the stem that have the internal diameter of a 1" spacer and the external diameter of a 1 1/8" spacer , to give a cleaner appearance. This shouldn't be an issue as far as I can tell?

Thanks for the link Scilly , that's a nice clean solution.

I'd like to make some spacers for below the stem that have the internal diameter of a 1" spacer and the external diameter of a 1 1/8" spacer , to give a cleaner appearance.

Might give a cleaner appearance at the spacer/stem junction but what about the headset/spacer junction?

I think it should look ok, the headset upper race is quite wide on top. I could always taper it slightly . I'm making some today so will check and post pics.

Thanks for info, so just to clarify - whether the stem is at the top , or it has a spacer above it (as Scilly recommends and is the case for me to acheive the correct stem height), either must be at least a couple of mm higher than the steerer to prevent the top nut bottoming out on the steerer , correct?

Nope, I think: there is some confusion on the part of one, or both, of us.

Best practice is that the steerer extends above the stem (around 2mm), to avoid the stem walking up the steerer (and in the case of a carbon steerer, crushing the top edge of it).

You can either use a conventional top cap and a 5mm spacer (both the same size as the stem), or one of Tester's top caps which incorporates a (from memory) 3mm spacer. A 5mm spacer is only specified with a conventional top cap, because you can't buy a smaller one (unless you buy Tester's custom spacer set).

Have a browse of Tester's top cap sales thread, he explains it better than I can.

Im sure we're talking about the same thing, I'm just wording it badly! :) - the steerer extends 2mm above the stem hence 3mm lower than the 5mm topmost spacer , or alternatively the steerer is slightly below the stem - as shown in the photo here:

http://www.parktool.com/blog/repair-help/fork-steering-column-length-and-sizing#article-section-2

The point is that the top cap does not come into contact with the top of the steerer in either case (the Park guide recommends 3mm) otherwise it could not pull the steerer upwards to preload the bearings...or am I still being a complete idiot...

No, I understand what you're saying now.

Yes, you're quite right: the top cap must "float".

The discrepancy over where the steerer should sit (above the top bolt of the stem or above the steerer) arises because carbon steerers didn't exist when the Ahead system was introduced.

All set up and working, build is in current projects thread (Cannondale 3.0). I 3D printed some spacers as described above ,that have the internal diameter of a 1" spacer and the external diameter of a 1 1/8" spacer. Looks much cleaner to my eye, if anyone would like some I'm happy to print some more off.

Am actually looking for some spacers with the same 1" vs 1 1/8 dimensions you just printed. :)
Going to see a mate after work today as he had some spacers around I might take.

Otherwise going to put an order for the tester spacers.

edit: you have a pic of the spacers you printed?

No worries just let me know. Here's a photo, they're not 100% smooth like a polished spacer but you'd be hard pressed to notice from a distance. Could always take some wet and dry to them if you wanted. Been running them since Friday and they've worked perfectly. About 4-5 grams for a 10mm spacer which is pretty good considering the extra thickness.

1 Attachment

Found a spacer I can use until I get some printed myself.
Got a quote in from a supplier we use at work and it won't break the bank.
Looks like u used FDM printing on yours, I will go with SLS as would come in smoother.

Thanks for the tip, wouldn't have come up with 3D printing it myself.

Yeah its FDM, but I think SLS for me is around £5 vs 5p for FDM per spacer. More expense than its worth .. for my bike anyway ! Plus unless its highly polished you still see the granules. Maybe a resin SLA but again even more expensive.