Looking for Steerer / Stem height clarity.

[gcartelli]

First off, thanks to this forum for supplying really great advice. I've only just dipped my toes into online bike forums and appreciate all the assistance.

I have a specific question concerning stem/steerer stack where the total stack height has to stay the same given component limitations, with very small margins; and I have a more general question concerning spacing between stem cap and top of steerer / compression plug.

Details

My fork is precut to 183mm with a 1mm compression plug (flush with steerer OD) for a grand total of 184mm.
My fork's manufacturer (ENVE) recommends 1mm of total steerer tube above the stem (combined with a 3-5mm spacer for the headset topcap)
My stem's manufacturer (Thompson) recommends 3mm of steerer tube above the stem (combined with a similar stack for headset topcap)
I'm using a King NoThreadset 1 1/8" Headset for a 34ID headtube.
I currently have the supplied ENVE compression plug (height of ~28mm from what I've seen online)



Questions

Is the 1mm above post to be believed? Do I spec my components for the total steerer tube height and go accordingly. i.e. given the steerer in question(183mm tube + 1mm cap lip flush with tube OD), the total stack up to the top of the stem (headset top and bottom, headtube, small spacer, stem) should be ~182-183mm, compared to the 184mm total steerer length. and not flush, nor below the stem top (in this case this would occur when the total stack was anywhere less than <183mm).

Is there not a school of thought (as I've seen on forums and questionboards) that allows for the steerer to be cut 1-3mm under the stem top, with the headset's topcap directly on stem). i.e. given the steerer in question(183mm tube + 1mm cap lip flush with tube OD), the total stack up to the top of the stem (headset top and bottom, headtube, small spacer, stem) could be ~185-187mm,

Do I follow Fork or Stem manufacturer specifications for steerer tube height.


General Question

Can anyone shed light on how exactly preloading and compression differ when the top of the steerer is separated from the topcap by 1-3mm of stem (recessed into stem) or 1-3mm of spacer. OR is the concern less preloading and compression, and more about the tension caused by the stem bolts?

Thanks!

[cuda]

no science but, my common sense tells me that the compression insert and the top of the steerer tube need to be at least as high as the top bolt of the stem.


Aesthetically, I like the cap on the stem look better, especially if you have things slammed.

[Dave]

Compression plugs aren't all the same. What's most important is supporting the steerer at least to the top of the stem clamp bolt. If the plug doesn't do that, then it's less than ideal.

If manufacturers don't take extra precautions with their instructions, inept installers will over tighten the top stem bolt and may crack the steerer.

I've solved all that by filling the entire stem clamp area with solid epoxy, with an M6 thread insert encapsulated in the epoxy. I can cut the steerer slightly below the top of the stem and not worry about the steerer cracking or plug slipping.

[pdmtong]

Is the 1mm above post to be believed? Do I spec my components for the total steerer tube height and go accordingly. i.e. given the steerer in question(183mm tube + 1mm cap lip flush with tube OD), the total stack up to the top of the stem (headset top and bottom, headtube, small spacer, stem) should be ~182-183mm, compared to the 184mm total steerer length. and not flush, nor below the stem top (in this case this would occur when the total stack was anywhere less than <183mm).
> in your example the top of the stem could clamp flush (if done carefully and at torque spec) at 184mm since the compression plug is reinforcing it from the inside. However, when you go to add the top cap there is no recess for it to sit into. So if the top of the stem is a bit lower at 182mm or 183mm you could add a 2.5 spacer and now the cap sits in the spacer. Both enve and thomson want the steerer tube to be 1mm or 3mm respectively above the stem to reduce the chance of you crushing the end of the steerer.

Is there not a school of thought (as I've seen on forums and questionboards) that allows for the steerer to be cut 1-3mm under the stem top, with the headset's topcap directly on stem). i.e. given the steerer in question(183mm tube + 1mm cap lip flush with tube OD), the total stack up to the top of the stem (headset top and bottom, headtube, small spacer, stem) could be ~185-187mm,
> I once had a thomson X2 clamped with the steerer 1mm lower than the top of the stem. top cap fit on and I was slammed. no issues but not the safest set up. I am not a heavy bar torque rider and 170#s.

Do I follow Fork or Stem manufacturer specifications for steerer tube height.
> yes, preferably.

General Question
Can anyone shed light on how exactly preloading and compression differ when the top of the steerer is separated from the topcap by 1-3mm of stem (recessed into stem) or 1-3mm of spacer. OR is the concern less preloading and compression, and more about the tension caused by the stem bolts?
> I do not think it matters. fwiw I haven't cut the steerer on a bike so there are 3cm spacers above the slammed stem. makes for a doirky look and a nice helmet hanger but also allows aging or accommodation if my L5-S1 comes back. enve plug. so that means for sure the torques to spec stem is clamped on the steerer in an internally unsupported area. hasn't been an issue other than getting harassed for aesthetics.