I need some help assembling the frame I bought into a bike. I am a little bit ouf of depth with my current knowledge (which is based on googling some headset standards articles).

I bought a Scott Speedster Gravel 10 frame and fork. Due to the painting I believe it's the 2019 model in size XL (see gravelbikedatabase or 99spokes).

My current (main) problem has to do with the headset. Since, I didn't see an angled area for direct installation of bearings and I didn't see outer bearing cups on the online pictures of the bike I saw, I assumed I am going to need a Zero Stack headset. I did measure 44mm and 49,5mm for the upper and lower inside diameter of the frame. So, I bought a ZS44/ZS49 headset. But when putting in the fork (which seems to have an integrated crown race), it looks like this. So, something is wrong. I have added some pictures of how it looks and another online picture of how it's probably supposed to look like. I am also confused about the online picture as there seems to be something installed on top of the integrated crown race?

Additional but unrelated questions:

  • If I understood it correctly, there is always a centering sleeve (other name for compression ring?) above the upper bearing to contacting it? A centering sleeve is also not damaging to a carbon fork?

  • The referenced websites state that the bike was shipped with Shimano Ultegra Road groupsets. I do have some parts of a Shimano Sora group lying around and I was just wondering whether this would fit the frame (regarding chainline and other stuff I don't know a lot about)? I guess this should work since it's also a Road groupset with similar measurements?

Thanks a lot for your help.

Edit: I did measure the fork and at the top it has an outer diameter of 28.8mm, at the bottom just above the integrated crown race it's 29.9mm and at the bottom of the integrated crown race it's roughly 44.5mm. So, the fork is not really a 1¹/⁸ to 1¹/⁴ fork. So, this actually is a straight 1¹/⁸" fork? This seems contradictory to the linked entries from 99spokes/gravelbikedatabase. The fork at least is painted like on the pictures so I guess there wasn't a mixup of forks (which could theoretically be possible since I bought this frame second hand).

The headset I currently have is a ZS44/28.6 ZS49/30, which seems to be fit to the 1¹/⁸ fork but the integrated crown race is just so high that this big gap is created. One comment suggest using an ec49/40 lower headset, which I believe might work. However, on the online picture (last pic linked here) of the bike doesn't seem to show an external cup. In summary, I am still confused.

Edit 2:

Measurements of frame and fork:

  • Upper headtube inner diameter: 44mm
  • Lower headtube inner diameter: 49.5mm
  • top of steering column outer diameter: 28.8mm
  • steering column outer diamter just above the integrated crown race: 29.9mm
  • outer diamter at the bottom of the integrated crown race: 44.5mm
  • height of the integrated crown race: approx. 10mm

Headset (I currently have) (says it's a ZS44/28.6 ZS49/30 headset):

  • Upper bearing cup inner diameter: 41.3mm
  • Lower bearing cup inner diameter: 41.2mm
  • Bearing 1 (outer diameter: 41.1mm, inner diameter: 30.1mm)
  • Bearing 2 (outer diameter: 41.0mm, inner diameter: 30.1mm)



frame headtube


fork with bearing

fork installed

online picture

  • I think you need an external cup (ec4*) lower headset for your tapered - style fork steerer. The bearing on it is clearly too small in internal diameter.
    – Noise
    Commented May 6 at 22:06
  • Hmm, okay. I saw some EC49/40 lower cups online which might be the right size. I am just confused because on the online pictures of the bike (last pic I linked) you don't see an external cup, right?
    – tor
    Commented May 7 at 6:47
  • Now, I also saw some ZS49/40 lower heatset cups. But both for ZS49/40 and EC49/40, it usually stated that this was for a 1¹/² inch (tapered) fork, which mine is not. So, I not sure whether in that case 1. the gap would be better (I mean it will be smaller but still probably doesn't perfectly fit so that water and stuff can still penetrate) and 2. it's actually safe and working as the fork diameter would be wrong
    – tor
    Commented May 7 at 15:48
  • but your frame doesn't look like the photo you supplied.
    – Noise
    Commented May 7 at 18:30
  • Your frame, i go further, is clearly different to your example image. and not just in colour.
    – Noise
    Commented May 7 at 18:43

1 Answer 1


On your 99 Spokes link above the fork is listed as having a tapered carbon steer tube that is 1⅛" top and 1¼" at the bottom. That doesn't help your problem since the bearing appears too small for the crown race. Regarding your headset sizing: it does appear to use a ZS style headset (your reference links above use the term, "integrated steel cup" describing the headset. That term is a bit strange, but the mention of a steel cup makes me lean toward a ZS.

Regarding the size, you'll need to determine what the second numbers listed after the initial "ZS44/?? | ZS49/??" The numbers behind the top 44 should be 28.6 (1⅛" in mm's) and 32 (whole number in mm's closest to 1¼"). These represent internal diameter of the bearings. Unfortunately, I don't see a ZS style headset for 1¼. Is it possible the lower headtube is equipped to accept an integrated bearing (IS). See this Park Tool headset reference table for the 1¼" options. I still don't get why your bearing for the ZS49 appears too small unless you've transposed the bearings and that is the upper 1⅛" one you're trying to use. A ZS49/40 would be for the 1½" tapered fork.

The centering sleeve will need to be used. Some are plastic which may be better on the carbon fiber steer tube, but an aluminum alloy should be ok as the pressure should be spread out around the circumference of the steer tube. Note that you cannot use a star-fangled nut in the carbon steer tube. You'll have to get an expanding nut designed for carbon steerer use. It should be located in the headtube where the clamping force of the stem. This creates even and opposing pressure on the steer tube so there's no chance of damage.

The Shimano Sora road group is 9 speed in the rear, comes in either a 2x or 3x front chain wheel. Fit on your bike should be the same as the Ultegra, except the cassette will be overall narrower and depending on your rear wheel hub (the HG Freehub body specifically), you may have to put on a spacer or two before the 9 speed cassette goes on. Your Sora parts should be the latest, Hollowtech2 style (24mm spindle attached to the drive side crank). In addition, this bike is likely only set up for disc brakes. This requires the STI (Shifter/brake lever combo) to be hydraulic brake capable.

  • Thank you for your answer. I did measure the fork to have an outer diameter of 28.8mm at the top, 29.9 mm just above the crown race and roughly 44.5 mm at the bottom of the integrated crown race. So, the fork doesn't really taper to 1 ¹/⁴"? Which is confusing. Now the cups are installed so it can't really see clearly but I am pretty sure that I inspected it before and there was no angled surface for a direct installation of a bearing. Okay, so I guess the metal centering sleeve will be fine. Just a question regarding your last sentence: Mechanical disc brakes should also be good, right?
    – tor
    Commented May 7 at 7:07
  • I forgot to mention: The top and bottom bearings are actually the same size.
    – tor
    Commented May 7 at 7:21
  • Check if you actually received correct bearings.
    – gschenk
    Commented May 7 at 10:06
  • What exactly do you mean by that? I measured outer and inner diameter of both bearings and they are almost the same (1 or 2mm difference) .
    – tor
    Commented May 7 at 15:38
  • Although this answer certainly has been useful, I still don't know how to proceed with the lower headset issue.
    – tor
    Commented May 7 at 15:50

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