A stem/spacer question for the wrenches

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2008-09-24 2:41 PM

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Elite
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Between the Devil and the Deep Blue Sea
Subject: A stem/spacer question for the wrenches

Hello wrenches,

I'm wondering how one determines the limit of spacer height that can be placed under the stem. If I've maxed out the spacer height, do I then get a new stem which is more upright?

Thanks in advance for your help!

Tom

2008-09-24 2:52 PM
in reply to: #1693843

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Cycling Guru
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Fulton, MD
Subject: RE: A stem/spacer question for the wrenches

You are limited to how much the stem clamps on the steer tube (assuming you have a threadless headset of course).

It is never really a good idea to have more than about a 1/4 inch of stem above the top of the steer tube.

Yes, you can get a mid or high rise stem if needed.  Just bear in mind that it will potentially throw off your steering geometry a little.

2008-09-24 3:03 PM
in reply to: #1693876

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Elite
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2000500
Between the Devil and the Deep Blue Sea
Subject: RE: A stem/spacer question for the wrenches
Daremo - 2008-09-24 2:52 PM

You are limited to how much the stem clamps on the steer tube (assuming you have a threadless headset of course).

It is never really a good idea to have more than about a 1/4 inch of stem above the top of the steer tube.

Yes, you can get a mid or high rise stem if needed.  Just bear in mind that it will potentially throw off your steering geometry a little.

Thanks, Rick! That makes perfect sense.

When you talk about steering geometry, do I assume that the higher the rise on the stem the "twitchier" the steering can become because you've effectively reduced the radius?

2008-09-24 6:07 PM
in reply to: #1693910

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Sensei
Sin City
Subject: RE: A stem/spacer question for the wrenches

I would agree with the 1/4 inch in general, but would even be suspect of that.  I'm sure most manufacturers would say the steer tube should be insterted completly in the stem to get maximum contact area and avoid possible damage to the steer tube if you should over tighten the stem.  However, real world would probably allow 1/4 inch.

I, for sure, wouldn't have the top of the steer tube below the top bolt that holds the stem in place IMO.

2008-09-24 7:00 PM
in reply to: #1694375

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Cycling Guru
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Fulton, MD
Subject: RE: A stem/spacer question for the wrenches

It has to be inset a little bit for the threadless headset cap to seat properly, usually that is about a mm or two.

As for the angle?  When you go higher/shorter it pulls you in closer to the centerline of the steer tube (the long part of the fork that gets clamped to).  The closer you are to the centerline, the more exagerated your movements will make the steering.

2008-09-25 9:06 AM
in reply to: #1693843

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Member
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Motor City USA
Subject: RE: A stem/spacer question for the wrenches
it really depends on the type of Fork you have. Fork mfgs. have very specific guide lines for steerer length above the headset and wether the steerer is supposed to be above or below the stem.

i'd say 1/4 inch is too much of the stem not clamped on the steerer and woudl try to keep it closer to 2mm.

If your steerer is metal (opposed to carbon) you have alot more leeway, but I still dfon't like to take chances in that area of the bike.

depending on the fork you can usually find the proper specs for installation on their website.

good luck

2008-09-25 7:50 PM
in reply to: #1694466

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Expert
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Morgantown, WV
Subject: RE: A stem/spacer question for the wrenches
Daremo - 2008-09-24 8:00 PM

It has to be inset a little bit for the threadless headset cap to seat properly, usually that is about a mm or two.

As for the angle?  When you go higher/shorter it pulls you in closer to the centerline of the steer tube (the long part of the fork that gets clamped to).  The closer you are to the centerline, the more exagerated your movements will make the steering.

Especially if you're in aero bars.  I've got a 120mm stem, and it feels so much more twitchy then my old 100mm that was on my roadie.

1/4inch would be fine- or at least worked for me on my old mtn. build, and 1/8inch on my current tri build.

Whatcha buildin'?  Anything cool?

2008-09-25 11:21 PM
in reply to: #1693910

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Champion
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Tacoma, Washington
Subject: RE: A stem/spacer question for the wrenches

"When you talk about steering geometry, do I assume that the higher the rise on the stem the "twitchier" the steering can become because you've effectively reduced the radius?"

In essence, yes. So when you dramatically change the stem angle, you need to drag out the high school trig and adjust the stem length (the hypotenuse -- sp? -- of the triangle) so that you end up with the bars where you want them to end up.

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