How to Check a Steerer Tube Before Fitting
A new fork can turn up looking perfect in the box and still be wrong for the bike. Most of the trouble comes from the steerer, the tube that runs up through the frame and holds the stem. It’s worth ten minutes with a ruler and some calipers before anything gets cut or pressed on. Once a steerer has been trimmed, there’s no going back. Most modern road and mountain bikes use a 1 1/8 inch steerer at the top, which works out at 28.6mm. Older bikes often have a 1 inch steerer, and plenty of newer frames take a tapered one. A tapered steerer is 1 1/8 inch where the stem clamps on but widens to 1.5 inch at the bottom. It’s easy to spot by eye, since the base flares out near the crown. That bottom size matters a lot. A tapered fork won’t go into a frame built for a straight 1 1/8 inch steerer. It can work the other way round with the right lower headset cup, but it’s best to check the frame’s…