Spacer above stem?

TokyoTurtle

Speeding Up
Jun 6, 2013
119
18
38
40
#1
Happy Friday all,

Just wondering if you run a spacer, 3mm, 5mm etc above the stem? Many discussion posts around the Interwebs list that such a spacer above the stem is necessary to:

A. ensure the steerer is not cut at or just above the stem clamp bolt, thus better distributing clamping forces

B. Allow for better compression on the headset bearings

Makes sense right, but walk through an LBS and look at the stock bikes, and you basically never see spacers above the stem, no matter the maker or price class. I know that many folks don't like the asthetics of spacers above the stem, but that is a separate issue.

So, spacer above stem needed or not?

Cheers
 

bloaker

Maximum Pace
Nov 14, 2011
1,564
1,246
433
Miura, Japan
#2
The reason I leave a small spacer - if I change stems down the road and the stack height changes, I want to ensure I have enough tube to support it.
I do NOT have a carbon steer tube.
Opinion:
On a carbon steer tube, I can see the 'slotted' stem may put uneven pressure on a steer tube, but not sure I buy it as a point of failure - but opinion only.
 

AlanW

Maximum Pace
Jan 30, 2007
1,214
436
103
Tokyo
#3
A spacer will ensure the upper stem bolt is clamping the steerer rather than the air above the steerer, so it's a good idea. If you can cut the stem to the right length it's not actually needed though.
Some designs (e.g. Cannondale) use a system where the steerer is supported internally by the adustment cap and for these a spacer should not be used, as the stem could clamp in an unsupported area.
I don't have a spacer above the stem on my bike, but I put a 1mm washer on Naomi's bike which is just enough to clear the top of the steerer and almost invisible.
 

TokyoTurtle

Speeding Up
Jun 6, 2013
119
18
38
40
#4
"If you can cut the stem to the right length it's not actually needed though"

Thanks for the post. What is the right length though? The stem I plan on using on my current build has (what appears to be) about 3mm of space between the top bolt and top of the stem. Was thinking of cutting the steerer to leave 1mm above the stem and use a 3mm spacer between stem and top cap. Or, maybe steerer flush with top of stem and 2mm spacer above. A 2-3mm spacer wouldn't bother me in terms of asthetics.

Cheers
 

bloaker

Maximum Pace
Nov 14, 2011
1,564
1,246
433
Miura, Japan
#5
If the steerer is flush with the stem... what holds the spacer straight? the cap alone?
I would want the steerer past the stem to hold the spacer in line (with little thought given).

Or a little short and put the cap directly on the stem.
 

TokyoTurtle

Speeding Up
Jun 6, 2013
119
18
38
40
#6
"If the steerer is flush with the stem... what holds the spacer straight? "

Top of the compression plug, lip that sits on top of the steerer, would hold the spacer in place no?

Cheers
 

devnull

Cruising
Aug 14, 2013
38
12
18
50
#7
The spacer gives you options.

I'm in Aomori-ken and don't ride my road bike year around. Early in the season I flip the spacer so the handlebar is higher, once I'm stronger and I'm pulling rather than resting on the bars I can set them lower. This saves me a lot of unnecessary back and neck pain.
 

bloaker

Maximum Pace
Nov 14, 2011
1,564
1,246
433
Miura, Japan
#8
"If the steerer is flush with the stem... what holds the spacer straight? "

Top of the compression plug, lip that sits on top of the steerer, would hold the spacer in place no?

Cheers
In one theory, yes - and no.
The top of the spacer would be aligned with the cap.
The cap is aligned by a star nut that was pounded/pushed into the steerer.
Is the nut 100% straight? If no - there is little to make the cap straight if that is just resting on a spacer that is just sitting on the stem.
I realize once in place and the stems pinch bolts are tight, it should not make much of a difference - but I am betting it is not as rigid as having some steerer peaking over the stem to keep things aligned.

* note I am open to being wrong, it is just my opinion.
 

GSAstuto

Maximum Pace
Oct 11, 2009
945
242
103
tokyo
www.roadfixie.com
#9
I dunno - I'm always changing my stem height a couple mm each way. Therefore, I prefer to have enough steering tube available for that purpose - say an extra 5mm. For strictly climbing and very long days in the saddle, I'd be at the top, for more on the rivet days I'd slam it. I love the look of a totally slammed bike - but then, that means the bike geometry is perfect out of the mold. And that ain't too often... As for structural - I can say it means nothing. Because the steering tube is held secure by the stem clamping bolts - NOT the top cap! If you are cranking down on the top cap (or compression nut whatever it is), then you are likely over compressing the angular contact bearings. I see this all the time, by the way. If your headset is developing excess play - or play of any amount - check the preload. The top cap should be just tight enough to bring play to zero. If you have to continually adjust this - then get it checked. Probably the bearings are brinnelled and wearing out.