Money D

Lets say a 700x28c tire has 6mm clearance between seatstays and chainstays, but only 4mm clearance to the seattube. If one chooses a 32c tire, that should add 2mm to each side, still giving 4mm clearance. But, does the overall diameter increase by 4mm, or is it more like half just like each side so increase by 2mm? Would it theoretically touch the seattube?

Thanks.

Elvo

There is no definite answer as it depends on the tire, rim, and air pressure. But here's a general rule of thumb:

https://www.bikecalc.com/wheel_size_math

Based on that, 700x28 is 678mm diameter, 700x32 is 786mm diameter. The increase is 8mm diameter or 4mm radius so it will be very tight

Seattle Forrest

You won't really know for sure until you try it. Some tires measure big for their size, some small, and then the rims you put them on have a big effect too.

Iride01 

Over all diameter increases by 8mm. But different makes and models of tire YMMV. It's just an estimate. You do only get roughly 4mm closer to the seat post, brake caliper or whatever is of the most concern on your bike.

The formula to estimate tire diameter is Wheel diameter = rim bsd + tire width * 2

Carbonfiberboy 

Only way to tell is to borrow or buy a candidate tire. Issue with really tight to the fork is that bits of gravel etc. picked up by the tire will scar the fork's crown. No big deal if alu, but not so good if carbon. Seen that happen.

WhyFi

Your direct question has been answered, so to chip in I'll add this: when most manufacturers specify that a frame will clear a certain tire size, it's typically with ~4mm clearance on all sides - that's generally the minimum that they want for clearing debris and whatnot. With that in mind, you may want to ask yourself why manufacturers want that clearance and whether or not you're comfortable going with a thinner margin for error.

MKahrl

If your clearance is tight, you might find it gets tighter as your tire gets older and thinner as the tire will balloon out as it gets more flexible.

Money D

So, there's no such thing as tires that have a reputation as being wide but not tall?

(the wheelset has an inner width of 15mm)

Iride01 

Most bicycle tires aren't designed with profiling as you see in automobile tires. Essentially they are round cross sections when you draw in the missing arc for clinchers. Just like tubulars. Tires that have more tread, like knobbies for off road use externally look like a different profile, but when you look at the cross section, you'll find the casing is essentially round.

Not sure where to go with this. The rim width will make a very minor difference in tire profile unless you are at the extremes.

wphamilton

Well something like this would be taller, and a tire that's stiffer on the tread than the sidewall could be wider, but generally just assume a circular cross section for road bike tires.