How do you determine reasonable minimum clearance when going wider tires? The narrowest point being typically between chainstays, how much is enough to allow for natural wheel flexing, possible out-of-perfect-true situation and safe debris clearance?

There are various ways to estimate frame clearance but the only way to be absolutely certain is to mount the tire on the bike. For a road bike a few millimeters is enough, but more is always better...

For a bike that gets ridden in mud, you'll want quite a bit more. Otherwise, mud on the tire can actually wear holes in the chainstays. Yes, this has happened!

See also: https://www.renehersecycles.com/how-...ire-can-i-run/

There's no one "right" answer. How much do you trust the true of your wheels? Are these tires new and going to stretch or been sitting inflated for months? Expensive CF frame, a fancy custom paint job or your pride and joy or a city beater. Are you riding off road and going to see stones stuck to the tread. (Does that tread pick up stones?) Wheel flex - are you an animal or a skinny guy like me? How stiff are your wheels?

I rode the Trask River lumber road across the Oregon coast range on my Mooney set up fix gear and a 35c Pasela in back. With the tire slid forward to use my biggest cog for the way up I had maybe 2mm clearance on the sides but I knew that with the tiny cog for the way down and the wheel pushed back, I'd have clearance for stones, etc for the wild 2000' descent. This was also on a 35 year old paint job that was up for renewal anyway.

4mm

At last, an actual number. So, we know that must be the only right answer Andy (who still thinks in shades of grey and not absolutes that seem so appealing)

I use a 3mm hex for the sidewall. If it slides in there, GTO. If not, no good. 2 mm for the bridge. But, I like to live a little dangerous. YMMV

One needs to not only mount the specific tires to visually see, but also remember, a little extra space is needed to prevent tire rub on the stays fork for when accelerating and turning aggressively. I put 35mm GK semi-slick on my Poprad and the clearance was a shade under 3mm on each side of the chain stays. It was fine my first few rides. Then I went for a faster, more aggressive ride and the tires rubbed on those stays. The seat stays and fork had plenty of room, but the tires came off due to the chain stays. I now have the GK's in 32mm, if I did not already know better, I would swear there was enough room for the 35's.

My 650B bike has very little clearance to the chainstays. It was almost zero at one point before dimpling the stays, now it's about 2mm. If I didn't regularly check the wheels and tires for true, or pack a spoke wrench, I'd probably want more clearance.

I'm going to say 3.5mm, use your 3 and 4mm Allen wrenches for "go- no go."

I've had enough weird stuff happen on long rides that I'm more gun-shy than most here.

I'd rather go with 4 +6/-1 mm.

Also depends on the rims.

Carbon rimmed wheels almost never go out of true. Set em and forget em

You only need a couple of mm.

However, if something goes wrong, a little extra clearance can be nice.



I blew off about 3" of the bead about halfway through a 150 mile ride. There was probably a bike shop 10 miles behind me, or 20 miles ahead. Very narrow chainstays. I struggled to boot the tire and not have it rub.

I've also broken spokes from time to time. So, either riding home with a wobbly wheel, adjusting the wheel so it is marginally true with one less spoke, or replacing the spoke in the field, and truing it the best one can on the side of the road.

And, of course people may change tire sizes from time to time. So, 23mm tires are falling by the wayside for 25mm, or even larger.

Inspirational, now I will always use more than 2 around-wraps of electrical tape on my dropbars.

What are the white/cyan strings/wires btw?

I like to have a roll of electrical tape in my bag. Although it was suggested that Gorilla Tape would have worked better.

As mentioned, I was struggling with clearance issues. I also taped around the frame where it was rubbing.

I started booting with a bit of white cotton T-Shirt rag tucked under the bead visible photo left. A few miles down the road I found some nylon flag that was less stretchable (purple/pink, photo left).

I found the string a little further down the road, and added the tape to hold it in place. The string felt a little rubbery, but seemed to hold some tension. There was also tape around the tire and booting fabric. I pulled one of the brake pads when I added the string, just so I wouldn't make a mistake.

The flat occurred just outside of Jefferson, Oregon, and I had to push it pretty hard to get to a bike shop before closing in south Salem, Oregon, with the choice of backtracking to Albany, or continuing north to Salem (and further to Portland).

Oh, and I carry a "real" pump as I revised the boot a few times. No CO2 cartridges.

Here's the bike.


My tire was 23mm due to clearance. A 25mm would have barely fit, but nothing larger. So, no department store tires. Only bike shop tires.

Horizontal dropouts, so the wheel was imperceptibly shifting in the dropout which I fixed by pulling the skewer back on the Drive side before clamping down.

😉 Lately I've been practicing the art of not over explaining.

And that's one thing I will never achieve, not over explaining Andy