Quill stems and headset sizes
I just picked up a low end electric assist bicycle today and looking into changing the Zoom CH-140 forks to something better. Axles to crown is 435mm but sags pretty bad as soon as I jump on.
I don't actually know if I've got a 1" threaded fork or a 1 1/1" threaded fork. The headset tube insert is approx 180mm long. I did however measure the promax quill stem on the bike now and it is 25.2mm in diameter (close to 1") on a Mitutoyo calibrated digital caliper.
Seeing as 1" is 25.4mm in diameter, can I safely assume that the steerer tube is 1 1/8"?
I have my doubts that the steerer tube is like 0.1mm thick.
Check out this link to make sure that I'm not miss-interpreting your terminology. But I think the answer to your question is "Yes". If the quill is about 1", the headset is 1 1/8".
Servicing Bicycle Headsets
I don't remember any 1 1/8 " quills. There were some 1 1/4 " quill's for tandem's.
Assuming and bicycles are never a safe combination. However, I believe 1-1/8" threaded is a thing. Something that cropped up on low-end bikes after the introduction of threadless headsets.
I think you should drop the fork out and measure the steerer. Better yet, remove the headset and measure the ID of the head tube. In your shoes, I wouldn't consider whether or not I could keep the existing stem and headset. They're cheap compared to forks and frames. The ID of your head tube's bearing seats is what you really need to know. Most likely, it's sized for a 1-1/8" headset with external cups - the most common standard for most of the last fifteen years. But you've already found one weird part.
Anyway, once you've confirmed your headset compatibility, you'll know what forks you can have. Most likely, anything 1-1/8" straight, but you've already found one weird part...
"Don't buy upgrades; ride up grades." -Eddy Merckx
Re: Quill stems and headset sizes
1 1/8 threaded headsets showed up on alot of mountain bikes between 91 & 95.
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