Have you ever pondered doing something, decided to look it up online, and found lots of semi-answers that don’t give you the full picture? Yeah, me too! Annoying, isn’t it?
Bicycle articles are particularly bad, because they almost always assume that you have the bike in front of you, and that you know what you’re doing. I don’t! I’m at work, and my bike knowledge may be above average, but I’m still pretty noobish.
So, when trying to find out how to upgrade the nylon headset of the Raleigh Twenty, I was getting annoyed by not knowing the full story. After doing some measurements last night, and having a proper look at what everything does, maybe I can redress the balance myself! 🙂
Firstly, I’d better describe how it all works. It’s not quite the same as a normal fork and stem, because it has a quick release for the stem. The fork steerer has a long slot cut out of it, which allows it to be compressed by the QR, just like how a seat tube is compressed by a seat clamp. The stem, which is just a basic tube, can therefore be gripped in the same way as a seat post. The steerer is extra long, and the QR fits under the locknuts. It’s quite a nice arrangement, really!
Here be the measurements, from top to bottom. Measuring tubes can be a bit tricky, so give or take a millimeter:
- Handlebar OD (where it’s clamped) = 15/16″ / 23.8mm
- Stem OD = 7/8″ / 22mm
- Stem height = 9 7/8″ / 250mm (no minimum insert line, because it’s supposed to be tethered to the front brake with a rigid wire)
- Upper locknut height = 3/8″ / 9.6mm
- Lower locknut height = 3/32″ / 8mm
- Stem QR height = 5/8″ / 16.1mm
- Lamp clamp height = 1/16″ / 2mm
- Nylon bush protective cap height = 1/32″ / 1mm
- Nylon bush lip height = 3/32″ / 3mm
- Nylon bush ID = 1″ / 25.4mm
- Nylon bush OD = 1 1/8″ / 29.8mm
- Fork steerer height (inc thread) = 9 3/16″ / 235mm
- Fork thread height = 3/4″ / 19mm (Raleigh 26TPI thread)
- Fork steerer OD = 1″ / 25.4mm
- Fork steerer ID = 7/8″ / 22mm
- Head tube ID = 1 1/8″ / 30mm
- Head tube OD = 1 5/16″ / 33.1mm
- Head tube height = 7 3/32″ / 186mm
I was only using a digital calliper, which wasn’t long enough to measure the head tube height, and I haven’t got any measurements regarding the lower race or crown race. My measurements were coming out all over the place on those, so thought it best not to include them. If I ever decide to replace the fork (quite likely!), I’ll get them measured.
My intention is to replace the nylon bushing with the top half of a 1″ threadless headset. There’s no issues with diameters, but there is an issue with heights. The bushing, including cap, is only 4mm tall, and you can also add the 2mm from the pointless lamp holder, but the exposed top of most threadless headsets is taller than that. For example; the threadless headset that I randomly bought is about 10mm tall, which would mean the upper locknut would be only half attached. :s
However, all is not lost! It just so happens that BMX seat clamps have a diameter of 25.4mm – the same diameter as the steerer tube. That means I could potentially ditch the tall original QR and replace it with a much shorter seat QR and possibly a couple of spacers. The only problem is knowing how tall the BMX clamps are, as that measurement is never mentioned, and they come in a range of heights. I might have to brave the BMX section of Evans, and have a look for myself! 😮
UPDATE: Evans have a rubbish BMX section! Also, it turns out that only old 80s seat clamps are suitable for the job. The old standard was 22.2mm seat tubes, whereas they’re now 25.4mm. It makes searching for a clamp rather tricky. The old clamps are all quite chunky, though, and most are actually taller than the existing QR. gah!
I also measured the seat tube, but it rather illustrates how I can get things wrong with the callipers. I measured 28mm ID and 32mm OD, but apparently all Raleigh Twenties have a 28.6mm seatpost. Hmph! The seat post is 315mm high (top to bottom) .
UPDATE 17/10/13: Added a few more measurements.
Softy on a bike 