thehammerdog

I have an old school steel bike I have 23's on it but want to go bigger is there any way to determine what the max tire size a frame can handle.

HillRider

Without trying a range of tires until you run out of clearance, you can only estimate. Measure the clearance between the fork crown, fork blades and brake arches of your current front tires and between the seattube, brake bridge, brake arches and seat stays of your current rear tire. Based on these measurements project the largest tire that will fit. Remember, the size marked on a tire side wall isn't always accurate so one 700x28 may fit while another make and model 700x28 may not.

Generally, older steel frames had pretty generous clearances both front and rear so I expect a 700x28 or even some 700x32 tires may work but try to measure first.

goatalope

I agree with HillRider. No definite way to know. I've fit 32s on a couple older frames - however they originally had 27" wheels that I replaced with the slightly smaller 700c. I've even fit 35s on the front.

Go to a LBS and tell them to sell you the fattest tires that will fit. If they're not busy (winter is coming), they might be willing to put a couple different tires on to ensure they'll fit.

10 Wheels

Borrow a wheel from a friend that has 700 X 28's tires and see if if will fit your bike.

FBinNY 

As Hillrider says, there's no way to know. What you can do is eyeball the clearances at the fork and chainstays and estimate that the radius will increase by the change in tire width, and the chainstay clearance by half the change in width.

Those are fairly coarse guides, and tires aren't often super close to their nominal size, but on the other hand you shouldn't be operating down to the last millimeter or two since you have to allow for wheel alignment issues. There's nothing dumber than being stranded because your wheel is a few millimeters out of true, after a pothole.