Author Topic: Should I be able to rotate my ahead spacers?  (Read 464 times)

Should I be able to rotate my ahead spacers?
« on: February 23, 2021, 07:40:41 pm »
If I grip the headset spacers, a stack of 3, between finger and thumb I can rotate them around.  They are not loose, it does requires a grip to turn them but they do turn.

Is this OK as the headset feels as though it is adjusted correctly?

Thanks

Re: Should I be able to rotate my ahead spacers?
« Reply #1 on: February 23, 2021, 07:44:00 pm »
Sounds ok to me. Do the usual brake on and rock test to check. Note that if you have disc brakes you can get some movement there.
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robgul

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Re: Should I be able to rotate my ahead spacers?
« Reply #2 on: Yesterday at 07:39:00 am »
I would suggest that being able to rotate them would be unusual given the way an a-head system works.  As suggested check with the brake and rock test, with your spare hand clasped around the top bearing/spacer area to feel any (excess) movement.
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Re: Should I be able to rotate my ahead spacers?
« Reply #3 on: Yesterday at 09:49:33 am »
Presumably the top 'cup' is held in place by it's 'wedge'?

I'd readjust the headset to take up any 'slack' after checking the top cap isn't bottomed out.
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Re: Should I be able to rotate my ahead spacers?
« Reply #4 on: Yesterday at 09:57:37 am »
Quite normal. I've just checked 4 bikes and 3 can and 1 cannot. There is no brake judder from any of them.

Re: Should I be able to rotate my ahead spacers?
« Reply #5 on: Yesterday at 10:16:09 am »
Is there a clamped spacer or accessory tensioning the headset sitting below the spacer stack?  This would be the only way that I could imagine that you could easily be able to rotate the spacers between it and the stem.  If not then it would appear that some small amount of adjustment may be necessary in my opinion.

robgul

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Re: Should I be able to rotate my ahead spacers?
« Reply #6 on: Yesterday at 11:42:30 am »
I would suggest that being able to rotate them would be unusual given the way an a-head system works.  As suggested check with the brake and rock test, with your spare hand clasped around the top bearing/spacer area to feel any (excess) movement.

The top cap serves no purpose once the pre-load on the stem/spacers is set - the spacers by definition are clamped by the stem onto the headset top cup - thus to me they shouldn't turn.   I've just checked 3 machines here and the spacers are all fixed (one bike with titanium, one aluminium and one carbon)

BUT in the unlikely event that you are talking about spacers above the stem clamp then they, like the top cap serve no purpose once the stem is clamped.
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Re: Should I be able to rotate my ahead spacers?
« Reply #7 on: Yesterday at 12:19:05 pm »
The top cap stops the stem walking up the steerer with long term use under the pressure from the bearing preload. I don't know if that happens on anything more than a glacial timescale though.

Spinnable spacers indicate bearing preload isn't particularly high. It may be possible there's a window where it's still high enough, but I'd consider it to be unusual at least.

MikeFromLFE

  • Previously known as Millimole
Re: Should I be able to rotate my ahead spacers?
« Reply #8 on: Yesterday at 12:32:39 pm »
Quite normal. I've just checked 4 bikes and 3 can and 1 cannot. There is no brake judder from any of them.
Same here
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Re: Should I be able to rotate my ahead spacers?
« Reply #9 on: Today at 07:40:57 am »
I would suggest that being able to rotate them would be unusual given the way an a-head system works.  As suggested check with the brake and rock test, with your spare hand clasped around the top bearing/spacer area to feel any (excess) movement.

The top cap serves no purpose once the pre-load on the stem/spacers is set - the spacers by definition are clamped by the stem onto the headset top cup - thus to me they shouldn't turn.   I've just checked 3 machines here and the spacers are all fixed (one bike with titanium, one aluminium and one carbon)

BUT in the unlikely event that you are talking about spacers above the stem clamp then they, like the top cap serve no purpose once the stem is clamped.

But lightly clamped. Ideally, there should be minimal preload on the bearings, so as said by others further back as long as there's no play in the fork then all's good. If you can't turn the spacers then it's possible (but by no means sure) that the headset might be too tight.

Another variable to consider is that the forces generated in the bearings under heavy braking will tend to push the raceways apart as the balls try to run 'up' the curve of the raceways.  So even immovable spacers don't necessarily mean it's done up properly - it could be that the bearings have been pushed out of adjustment against the spacers by dynamic loads.  The contact angle of the bearings is critical here; an old-fashioned loose-ball headset is much closer to a pure thrust bearing than a newer 'cartridge' type where the bearings have a much greater radial component.  The former will need a greater clamping force to maintain the correct preload, and will experience greater internal thrust loads due to radial external forces, so is less likely to have turnable spacers. 
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citoyen

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Re: Should I be able to rotate my ahead spacers?
« Reply #10 on: Today at 07:50:13 am »
But lightly clamped. Ideally, there should be minimal preload on the bearings, so as said by others further back as long as there's no play in the fork then all's good. If you can't turn the spacers then it's possible (but by no means sure) that the headset might be too tight.

This is exactly how I see it.

It should be *possible* but not *easy* turn them.

Though not being able to turn them might be more a sign of weak grip than them being done up too tight.
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Re: Should I be able to rotate my ahead spacers?
« Reply #11 on: Today at 08:44:57 am »
The top cap stops the stem walking up the steerer with long term use under the pressure from the bearing preload. I don't know if that happens on anything more than a glacial timescale though.

I see the top cap as a preload-setting tool. Once it has done its job, the preload that it has been used to set is maintained by the stem clamp. You could chuck the top cap away after that without any adverse effect other than appearance.

I can’t turn the spacers on either of mine that have spacers. I probably could, if I was able to grip them more tightly, but not with my fingers.

Re: Should I be able to rotate my ahead spacers?
« Reply #12 on: Today at 08:47:36 am »
Though not being able to turn them might be more a sign of weak grip than them being done up too tight.

And the finishing on the contacting surfaces. Carbon spacers just have unpolished cut ends, there’s quite a lot of friction between those when in compression under the stem.

citoyen

  • Occasionally rides a bike
Re: Should I be able to rotate my ahead spacers?
« Reply #13 on: Today at 09:18:27 am »
And the finishing on the contacting surfaces.

Indeed, I was going to add 'and friction' but forgot!
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