thefsb

the brake shoe holder on my shimano brakes has a mysterious screw. in the exploded view it is labeled number 12 and listed as "Tire Guide": https://bike.shimano.com/media/techdo...9830609104.pdf

but the service instructions don't mention it at all: https://bike.shimano.com/media/techdo...9830604299.PDF

what's it for? how does one use it?

vpiuva

The Tire Guides are those little wings that hang down from (sometimes molded into) the brake pad holder. Maybe some of that model brake come with a separate screw that hold them on. Usually they are held on by the shoe fixing bolt.

2manybikes

It's to guide the tire in between the brake shoes as you put the wheel on.

thefsb

on these brakes the "wing" is indeed a part of the shoe holder. there is a threaded hole through this wing with a screw in it that can be removed. this screw is what shimano's exploded view calls labels a "tire guide". and i've no idea what it's for.

2manybikes

The head of the screw is what hits the tire in this case not the wings. So it guides the tire into the center between the brake shoes. Making it a "tire guide".

The idea is very old. The wings on other brake shoes are only there to guide the tire into the center as you install the wheel. Guiding the tire in to the middle helps as the wheel goes on helps prevent some people from getting the tire stuck and knocking the brakes out of the center position.

Stacey

The dumbing down of bicycles. Sheesh!

2manybikes

They had it in the 1970's. The old red square brake blocks sometimes had wire under the shoe that is the shape of the wing on that shoe.
Most of the time when someone needs to re center caliper brakes it's because they knocked them off center when putting the wheel on, but don't know it. There's really nothing else to do that unless the mounting bolt is loose.

Like the hundreds of people that have a computer not working because they moved the sensor when they put the wheel on. Many think it is a complicated computer problem.
They think I'm a miracle worker when I just move the sensor back where it was in three seconds!

vpiuva

So we have a tire guide mounted in the tire guide. Boy, must have been a bad day for Shimano's Italian/Japanese translator when deciphering calipers.

thefsb

fair enough. but why would one need to adjust it? without such a need i don't see a motive to go to the trouble to drill and thread the hole and insert a screw.

2manybikes

The only thing I can think of is that it narrows the slot the tire goes into, also the head of the screw lets the tire slide by better than the plastic wings, and makes for a faster wheel change? That's just a guess, I can't think of anything else it could do. For some reason they thought it improved the tire guiding function. Otherwise the name would be different.