How Much Clearance is Needed?
 

How much clearance is needed between the rear tire and the chain stays? Tires wobble, frames and wheels flex under load, all sorts of things happen during the dynamics of riding that you never see when the bike is static or running in a straight line.

My current tire measures 29 mm wide and has about 1/8" (3 mm) clearance on each side (will measure in a minute).

I was thinking of an even wider tire in the rear (like a Compass Bon Jon or Barlow Pass) but want to ensure I don't go too wide.


Anyone used these tires? What was your experience?


Will they fit securely on an old MAVIC MA-2?

One eighth is pretty tight, IMHO. I can't imagine going a size in that situation.

Someone on these c/v forums recently wrote about dimpling the chainstays for a 650b conversion. He used a couple of wood blocks and a vise, IIRC.

With just 1/8" clearance between the tire and your chain stays, there's a big possibility that you will get your tires rubbing the stays in moderate climbs, unless maybe you have a frame built with more robust tubing like Columbus SP......
It will also help if you have a chainstay bridge on your bike.....

It's really simple: all you need is more than zero clearance. My 650B conversion had a millimeter (or less, with tire variance) to the chainstays and I never had any evidence of tire rub in the first 600 miles. I only dimpled the stays recently because I was bored and wanted to try it. :)

It's nice to have a little bit of margin for if your rim goes out of true during a ride. How much is up to you and your aversion to risk.

I always keep a minimum of 2mm on each side. Mud accumulation, frame flex, wheel wobble: it's a bicycle, not a granite statue.

So, here are the dimensions and clearance of the existing tire.


Width between stays (already crimped): 1.50" (38 mm)
Tire width: 1.11" (28 mm)
Clearance per side: 0.20" (5 mm)



So, the 38 mm Barlow Pass is out, the 32 mm (1 1/4") Jon Pass sounds like it'll fit (with some risk of rubbing).

It occurred to me, if I use a wider tire, it will also have a higher profile. This means the wheel's radius will increase (distance from the wheel's center to the point where the tire is widest increases). This means the stays will be a little more narrow at that new distance. The crimp was made so as to provide roughly parallel inner edges. It is not perfectly parallel but is not as tapered as the stays would have been had they not been crimped.


So, guys, how much clearance is enough? Should I just leave well enough alone?

+1

Well, I'd add a little more than that, wheels go out of true sometimes. 3mm will work just fine.

I have barely 2mm at the chainstays on my current conversion, and it's a little less than I would like. My bikes with 5mm clearance feel positively roomy. There's not too much to worry about if you have well built wheels... but if you break a spoke far from home you're up **** creek.

Sounds like a case for helicopter tape. ;)

My Holdsworth 650b conversion is really tight with 42mm tires (Hetres) on Weinmann ZAC19 rims, especially so since the tires don't seat well.
Really tight, like it varies between 1 and 3 mm over the course of a wheel revolution. Potentially a real problem, but I've ridden it a couple thousand miles without an issue.

Nonetheless, on long rides (i did a fleche and an arrow this year, a 300k last year, &c) I have carried a 38 mm tire (just in case) and obviously I'd have a little less to worry about if I had a little more clearance.

I just finished my International frame with Stampede Pass (32mm). I can fit the thin side of a popsicle stick between the tire and chainstays.
I'm running Barlows on my CX frame, and it has the same clearance, but these chainstays are dished to make tire room - I've had to scrape the mud before, and carry a popsicle stick for that.

Hmmm, with that knowledge I think the vertical dropouts you sent are probably out of the question...

I'd go with 3mm as a reasonable minimum clearance.

As others have pointed out, there's no hard and fast rule. If it fits it works, but if it's very tight, you have to worry about getting home with a bent wheel, broken spoke, etc.

On second though, perhaps people don't worry about getting home with broken spokes anymore now that there's cell phones. Before cell phones wheels had 36 spokes. While I've gone off tangent a bit, the point I'm getting to is that you can push the clearance thing a bit more if you are running 36 spokes rather than say 20.

On the International, at least, if I had to, I could slide the wheel back in the dropouts to make more tire room.

So, 3 mm sounds like a prudent target value.


The wheels are already way back in the (horizontal) dropouts.


The wheels are "aged" , well built and have 36 spokes.


Thanks for the help, guys. I was hoping to get some advise based on past experience rather than experimenting myself, especially at >$75 per tire.

Yeah, i realize that may be the case. But then again, (a) I never had the axle all the way back into the dropout, and (b) perhaps the chain stays can be indented another mm or two?