tiger1964 

As I mentioned, I think, in another topic, I was getting some new Continental GP5000 tires. I ended up getting 700x28mm cream sidewall, to put on the 1961 Gitane which has huge amounts of clearance; then the 25mm ones already on the Gitane with almost no miles on them got transferred to my 1980 Palo Alto with already had 25’s but worn out and blackwall. Anyway, while doing all this, just for fun, I stuck the Gitane’s rear wheel on the Palo Alto. OK, it fit but the clearance at the chainstays was only about 4mm per side. What’s the normal minimum clearance desired here? My 1st thought was — if it clears, then it clears. My 2nd thought was, if I broke a spoke while riding and the wheel got out of true, it might bind against the chainstay and strand me.

This new stratagem of wider tires is something I’ve been approaching in baby steps; I do not think I have any 23mm tires left. And I am contemplating perhaps doing a 650B conversion on a yet different bike so knowing minimum clearance is germane there too.

ehcoplex

It depends on how true your wheels are (and stay...)! I've shoe-horned 38c tires on my Cannondale T900, with about 2, maybe 3mm clearance/side at the chain stays. Some would be uncomfortable with things that tight..

gugie 

Pretty much dead on. Since spoke quality has improved a lot over my lifetime, I haven't broken a spoke in years, but I always carry a spoke wrench with me. BITD if I broke a spoke I could true it enough to limp to a bike shop. I always carry a couple of spare spokes when I'm touring, along with a way to remove a cassette, since drive side rear spokes are almost always the ones that break.

So, yeah, that can definitely happen, so carry a spoke wrench.

Rooney 

I wanna say 6mm per side is the generally "safe" rule, that's about the max we would do at the shop I was working in. Working on friend's bikes, I've definitely done some shoe-horning of tires into frames, but I've always been very upfront about the drawbacks and usually recommend going to the next size down when looking for new tires. I've become a little more tempered in my shoe-horning if for no other reason than it's easier to get the wheel in and out with more clearance.

79pmooney

I'd say it's about risk management. And consequences. What is your rear wheel? Rim? Number of spokes? How much do you value your chainstay paint? (I'm assuming steel; this being C & V; carbon fiber changes this one a lot.) Do you carry a spoke wrench and know how to use it? DO you have an acceptable back-up plan? (The call of shame - NBD or martial no-no?)

Two broken spoke scenarios I witnessed. Both on bikes with "plenty" of clearance. First, myself in 1979 on my brand new Peter Mooney. Saturday morning. Santa Cruz Cycling Club ride. Town line sprint. A strong but inexperienced rider put his rear wheel where my front belonged. Eventually I had to return my wheel to under my weight or I was going down at 30 mph+ (and the next half dozen behind me). To stay up, I leaned my wheel into his rear and pushed off. Worked, but - his quick release cut out 8 consecutive spokes! I rode the bike to a standstill with a wild once per revolution throb.

My 28c clincher was rubbing solidly against the fork under the crown and had polished the bare steel. Outside that and a few missing spokes, no damage at all. Wheel went thousands more miles. The fellow on my wheel was a complete stranger but upon my bike handling saving his skin, he turned around in gratitude, got his truck and drove me home. (Robert Wright, gifted bike mechanic and author of a very good and equally simple book on how to build bicycle wheels.) Oh, I was riding the wide Weinmann rims with 36 spokes. I doubt a stiffer side-to-side semi performance rim has ever been made. And TG! Saved my butt.

Other scenario - rider in a small group broke a high-tech, non-steel spoke on a CF bike and rim. No spoke wrench and he had so few spokes to work with I"m not sure it would have helped. The tire had already done a little CF damage to the chainstay. They were debating options. Not my ride; they were complete strangers and I had nothing on me that could help so I rode on. I don't know what he chose to do but already., his bike had suffered more than mine for a far less consequential mishap.

With aluminum rims (I've never owned CF), enough spokes (32, 36), a spoke wrench and a modicum of skill with it, you can often juggle the spoke tensions of the remaining spokes to ride home. If your fork and frame are steel and some hard to see paint scrape is OK, you have little to fear of a spoke breaking, even with very close clearances. (But at speed, you may kill the tire with sidewall wear, especially if you are riding a thin walled performance tire. The medium priced Paselas would not take kindly to that sidewall wear at all.

Look at what you've got, decide what is acceptable and what isn't and go from there.

droppedandlost 

as long as the wheels are good

tiger1964 

Thanks, and I normally only carry a tube, tire irons and a simple multi-tool -- but most rides are short. I've taken longer rides with an old friend who totes along everything short of a shop stand and brazing torch so I can borrow his stuff. Time to find a lightweight spoke wrench. Good advice!

So I'm under the "catch limit" and need to throw this one back? Well, honestly, I have no issues with the 25's but am trying to embrace new concepts like fatter tires...

That's a comprehensive answer! This is Ukai rims, unsure of date or width. 36H as are all my bikes. All of my bikes are steel and most, like this one, freshly powder coated and I'd rather not damage the finish but I have matching touch-up paint. The 8broken-spokes event of yours sounds outside of what I might encounter, although anything can happen (If I get hit be a car, the state of true of the rear wheel might not be my #1 concern). Anyway, it sounds like "it depends, and maybe you'll get lucky and never have to worry about it -- or not!"

Wow -- have feeler gauges handy????

Bad Lag

You need some clearance. Frames and wheels deflect, as in when cornering.

ThermionicScott 

My Bianchi 650B conversion has spent long periods of time with close to zero clearance at the chainstays. The Col de la Vie tires I started with measured about 36.5mm wide, giving about 1-2mm of clearance per side. Then, I switched to Pacenti Pari-Motos, which started at a full 38mm and grew to 40mm! After dimpling my chainstays I'm back to about 2mm clearance per side. With my true wheels and spoke wrench in the bag, I'm completely comfortable with that much.

Classtime 

4mms is HUGE.

top506

Having spent a while stuffing 28/32mm tires into older sport bikes ('just put in the biggest tires that'll fit!'), I've found the tight spot to be the rear brake bridge of caliper, not the stays.

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