was at REI a few months back or maybe it was last year & picked up 4 rolls of Velox cloth rim tape. 2 narrow & 2 wide cuz I didn't know what I would need. over time I eventually used all 4 rolls. recently used the last of the wide stuff but I trimmed it narrower cuz the tape I was replacing wasn't as wide. remembered I was out of backup tape so I went to order some on Amazon & saw so many widths. took a guess at 16mm. I've got a road bike that currently wears 25mm tires, our family has 4 Trek FX hybrids that typically wear 32-35mm tires. I squeeze wider tires on mine but the rim tape doesn't have to be wider. recently got an old used 29er MTB with really wide tires, but the rims are a tiny bit narrower than the FX rims. but I suspect the tape for the FX wheels would be just fine for the 29er. can anyone make an educated suggestion what size tape for average road bikes & hybrids?

these are sizes Amazon offers

10mm
13mm
16mm
19mm
22mm

You can always go a little wide, but not a little narrow. 16 or 19 would be a good guess. Can you pull a tire and just measure the channel with some calipers?

that's an idea. I have a related bike with a pinch flat I've been meaning to address. so it's an easy peek. it's an older hybrid, but it would be a large clue, thanks for the suggestion!

Tire widths have only indirect reference to rim width at the spoke bead and between any tire bead ledges. You want the tape to be wider then the spoke access holes are(if a double wall/box section rim) and also not riding up the tire bear seat ledges any more then needed. We find that the 16mm width to cover (bad pun) the vast majority of rims but your rims are what's at play, not some statistical average one. Andy

Guessing is a time-honored substitute for measurement. This forum prefers guessing and some here rely on it exclusively.

With Velox and other cloth tape I've had better luck going as narrow as possible while completely covering the spoke nipple holes. If there's a recessed channel, I get the tape that just fits in the channel without going too far over the shoulders.

When I tried wider cloth tape it interfered with seating the bead on most tires -- that goes for the 700x40 tires and wider rims on my hybrid, down to 700x23 tires on my road bike's 622x14 rims -- I think I used 11mm or 12mm cloth tape in those. Narrower tape solved that problem. No problems as long as I was careful to cover the spoke nipple holes.

The thicker cloth tape also fixed that problem with tubes extruding through thin rubber rim tape and splitting at the tips of the dimpled areas where the tube and rim strips extruded into the spoke nipple holes.

When I used tape that was a little too wide I found that it slipped when mounting/dismounting tires, and then would uncover the spoke holes, causing a flat. I recently replaced it with narrower tape and no problems yet, but it took a few years for the tape to slip.

this morning, taking out the trash it occurred to me (DOH) to just measure the red plastic tape I removed from my 29er wheels. pretty clearly shows 16mm & the dimple above shows where the edges form in the channel