I have spent a fair amount of time restoring/modernizing a Specialized Sirrus from 1987. When I went to put the 28mm tires on it I had thought I would, I discovered there's nowhere near enough space for them under the rear brake bridge. I then replaced them with some 25mm tires, and I thought all was good. There was a very, very small amount of clearance (~1mm) but it cleared the brake bridge.

I haven't ridden much in the last few weeks, but I got it out and noticed that not only is the clearance completely gone, but the little bulge under the brake bridge has been worn down considerably. Despite this, the tire, which was not rubbing a few weeks ago, now rubs on the brake bridge (which is actually worn down a bit, which should provide MORE clearance).

How is this possible? Can tires "grow" over time? What happened to my clearance? It's gone from having 1mm of clearance without rubbing to having rubbed off a significant amount of steel and despite the additional clearance that should have provided, is now rubbing when it didn't.

I guess the simple fix is to replace this replacement tire that has less than 100 miles on it with a 23mm tire and hope for the best. It's like the frame is shrinking or something. I can't explain it.

Yes, slightly. They can loosen up over time, especially during the initial breaking-in period.

Great. And I wisely chose a model of tire that only comes in 1 size: the Continental Grand Prix Classic. So I can't just get a narrower rear tire and pretend they match. Ugh.

I sort of had a similar situation on my '97 trek 370 with a Specialized Tracer Sport rubbing the chainstays. Found out that by lowering the tire's pressure to my safest low (45-55psi, depending on surface/terrain) I'm able to ride without the issue (and, although the resistance has increased, so has the comfort). Maybe try this first and see?

Yes, tires can grow a little over tire or change shape slightly.

I had a Gatorskin on the front of an old 27" Schwinn Traveler. I guess the wheel the slightly out of true and the tire grew a little, and one ride I heard the tire rubbing once per Revolution on the top of the fork. About a minute after stopping my ride the tube exploded. My guess is that light rub caused enough friction to heat the rubber in that spot.

They do stretch, height and width, more so with high pressure. FWIW - Helped my daughter build & repaint an ‘88 Sirrus from a garage sale into her fixie. We could only fit 23’s.

I think I'll run them at 100psi for now instead of the 120psi on the sidewall. If all else fails, 23mm tires will have to be ordered.

Any chance the whole wheel shifted slightly? I take it no adjustment is possible in the rear dropouts?

One other consideration is that tires back in the 80's and 90's often measured small, like a 700x28C might actually measure 24mm, or a 700x25C might have only been 21mm! Nowadays, tires measure truer to their nominal size, so the crusty old tires on the frame (or the "700x25C" Specialized Turbo listed in the catalog) might not be a good indication what'll actually fit now...

Sounds like you never got the memo about the most efficient pressures in the real world. Everybody was running them too hard for ages until someone realised a smooth drum isn't a good simulation of a not smooth road.

Also, why not file your brake bridge a bit?

You could buy/make your own dropout spacers to give a little more room. You would only need a few millimeters spacing. https://www.ebay.com/itm/Rear-Drop-O...item1ea3ad0428 I believe your bike has vertical dropouts which will also work with spacers.

Unlikely- Think of all the tires rolling on scorching hot asphalt on a hot day.

I have not done the math, but since older bikes sometimes get stretched to fit in newer, wider rear hubs, would this affect the clearance by much?

Good thought, but I'm pretty sure the OP's bike has horizontal dropouts. I can't find a 1987 catalog, but the 1988 catalog shows horizontal dropouts: https://www.retrobike.co.uk/gallery2...PQ4BN.jpg.html

How tight is your rear skewer? I had one that I I thought was tight enough, but was using an adapter to pull a trailer and it didn't "bite" leading to the wheel getting unevenly pulled forward in the dropouts (on the drive side) and rubbing the NDS chainstay.

Yep - it has horizontal dropouts. I removed the dropout adjustment screws so I could pull the wheel all the way back in the dropouts, but that didn't give me more than a fraction of a mm more clearance. Moving the wheel forward made the problem quite a bit worse, so pulling it all the way back was my only option there.

The rubbing is not on either chainstay. It's on the brake bridge. They built them very very tight back in the late 80's. The disgusting part is, if the brake bridge was up a few mm higher and the horizontal dropouts a little shorter, I could probably fit 30mm tires in this thing.

To answer your question, though, my skewer is almost too tight. The powder coat paint is super, super slick and if I don't crank it down tight, it will slip. This is not the issue unfortunately.

The joys of a vintage bicycle.

I did have to cold set the rear out from 126mm to 130mm. 4mm more width would only shorten the effective seat stay length by a fraction of a millimeter. Pretty much impossible to detect.

I was out of cycling for a number of years, and the Center for Cycling World Memo Distribution (CCWMD for short) didn't forward my messages to me.

In all seriousness, I confess I did file the brake bridge down a bit. There's a lot of steel there, and it mostly needs the strength in the forward/back direction, so I figured a couple of millimeters of steel filed off the bottom of the round bulge they brazed into the brake bridge isn't likely to do much of anything. I have clearance now. I just need to find some touch up paint!

Nail polish.

That's what I use!

That's not a coincidence, since it's the cleverest option by far

Good, so not 112 to 136 then

And I never realised so many bike guys used nail polish!