Hi,
Bought a bike 2nd hand from ebay. It's really quite old, so I can't just look up the size of the components. Was wondering how to go about measuring parts like the bars/seatpost etc for circumference (the seatpost stem has no marking on it, I already looked).

Thanks

circumference or diameter?


buy a cheap id/od slide caliper from a hardware store. i got one for about $5. measure diameter. c=pi X diameter. OR, measure circumference with a fabric or flexible tape measure and divide by pi to get diameter.

Most bike shops will have a tapered calibrated gauge that slips into the seat tube and measures the inside diameter which tells you the required seatpost size.

A caliper or micrometer will give you the handlebar and stem quill diameter.

The best tool I ever bought for working on bikes was a Digital Caliper. I found one for $35 at Auto Zone that reads both metric and inches.

It's still easy to mis-measure a seatpost though so you might as well take it to a bike shop and let them check it with their tools.

Edit: I meant it's still easy to mis-measure a seat tube when you don't have the original post to measure instead. The tubes usually aren't as round as a post.

Actually, it's also easy to mis-measure a cheap seatpost too. I've seen a couple that gave a different diameter reading at different points around the circumference.

Those digital calipers have been on sale recently for as low as $15 CAD.

I bought a barely used Brown & Sharpe dial caliper on eBay for next to nothing. I find it more aesthetic to use than a digital one. Of course mine is in inches, so I'm always multiplying by 25.4! I also have a micrometer, but it only measures up to an inch, while the caliper is plenty accurate and will go up to 6. Does inside and outside measurements, and depth (inside to outside).

You might be surprised what you can look up. There are size databases out there.