Repair guides › Frame & Fork
Measure tire and chainring clearance
The backbone. Everything bolts to it, and its geometry decides how the bike fits, steers and how wide a tire it clears. 6061 aluminum tubes TIG-welded into a front triangle (top, down, seat and head tube) and a rear triangle (seat stays and chainstays). Threaded inserts (nutserts) take racks, fenders and bottle cages. Aluminum does not rust, but it can crack, especially near welds, and it does not bend back.
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Tools
- Tape measure + 6" steel ruler: Stanley 16 ft tape measure ($)
- Digital calipers: Clockwise Tools DCLR-0605 IP54 Digital Caliper ($$)
Compare Good, Better and Best for each tool
Steps
- Pump the tire to normal pressure. Clearance is measured on an inflated tire.
- Find the tightest spot on the rear: usually where the chainstays meet the tire near the BB, or the seat-stay bridge. On the front: the fork crown.
- Measure the gap on each side of the tire with the calipers (or slide hex keys in to find the biggest that fits).
- Biggest safe tire = current width + (smallest gap × 2) − 8 to 12 mm. You want 4–6 mm per side for mud and wheel flex.
- For chainring size, measure from the chainring teeth to the chainstay at the closest point. Each extra tooth adds about 2 mm of radius.
- Enter the numbers in My Bike → Verify. The Counter tab updates the limits right away.
Diagram
Looking down from aboveChainstays, behind the bottom bracket
Signs it needs doing
- Creaks that follow you even after the BB, pedals and seatpost are greased
- Hairline crack or paint flaking in a line at a weld
- Rear wheel no longer sits centered (bent dropout)
- Dent in the down tube or top tube