frankenmike 

Does anybody know offhand how big(wide) i can go on a 700c tire with regular 105 road calipers?

LarDasse74

It is actually not the brakes that determine the clearance - it is the frame and fork. THe brakes are usually close to flush with the underside of the fork crown or rear brake bridge.

However, depending on how the bike was made, some 105 brake equipped bikes will fit 28mm tires, others will not.

Also, come 28mm tires are wider then other 28mm wide tires. My old road bike currently has a 28mm tire on the rear (can't remember the brand) and they rub when there is dirt ont he tire. I also once raced in a CX race with 28mm wide knobby cx tires and had no clearance issues.

You have to try the tires you have in mind to see if they will fit on your bike.

Retro Grouch 

I've got an old Bridgestone RB2 equipped with 105 brake calipers and 28mm Gatorskin tires.

I had to loosen the cable tension until the lever almost bottoms out against the handlebar before the brake QR would open wide enough for the tire to just barely squeeze past the brake pads.

I've used 28 mm tires on some other bikes in the past. My experience has always been that the brake caliper opening was the limiting factor. I've never experienced chainstay or fork crown interference.

tortugaflats

let the air out once in air tires up

operator

The OP is obviously concerned more about it rubbing AFTER it's inflated than before. Clearing the brake blocks is a trivial issue.

operator

I've seen tight road racing frames that would barely clear 23c's. Regardless of what'll clear the caliper. Most road brakes will clear 25's, 28's depending on WHICH 28's and the specific bike.

OP: Just try some.

Retro Grouch 

So there you are:

One specific data point. Might not be useful in any other case but at least you know which combination it's right for.
One generality. Might be right but might also be useless in your case.

Take your pick.

lunchbox1972

I'm running 28's in my Ultegra 6600 calipers, haven't had any issues.

fietsbob

brake shoe fixing bolt at the lower end of the adjustment slot on your brake, when it meets the rim,

indicates the fork blades are a bit longer, so would have more clearance under the fork-crown too..

TallRider

as people have said, the main determinant variable here is the frame (clearance under the brake attachment point), NOT the model of calipers themselves. This is why brake calipers have adjustment slots where the brake pads connect: because some frames will put the brakes further away from the wheel's axle than others.

So, people telling their experience of which-brakes-work-with-which-tires doesn't really help much here, since the main determinant is the frame. I think the typical (a.k.a. short-reach) brake calipers have reach adjustable from 39-50mm, and long-reach (a.k.a. "standard"-reach) calipers are adjustable from 47-57mm reach.

Many racing-frame makers put brake bridge as close as possible to wheels, assuming racing bikes will only be ridden with 23mm or smaller tires. Some manufacturers design their road frames to work with longer-reach brakes, allowing more room for fatter tires and/or fenders, while Surly designs their road frame with 50mm reach so it will work with normal or "standard"-reach caliper brakes depending on what the buyer has sitting around or wants to build the frame up with (although a "standard" reach brake is recommended).

for more info, see Sheldon Brown's glossary, definition #3 for "reach"

also, Surly's blog has a nice writeup on caliper brake reach.

frankenmike 

Thanks all for your insights. I checked out some mounted 28s the other day, they should work fine. The true determinant in retrospect is the fork/frame's clearance, which is narrower than the actual caliper. As far as reach: that has nothing to do with tire size- only distance from rim to caliper bolt, right?