Hey so with old steel bikes that predate the mtb but are flat bars do I use mtb sizing or road?

Are you referring to the hybrids that first cam out?

My take... I can ride an 18-20" hybrid, MTB but have to have a 21-23" road bike.

Which bike are you looking at?

If it's an old steel bike 80's or earlier, I'd use road sizing.

I don't think the Op's question has a real answer. Or one which others can answer. Handle bar shape and width are like saddles or shoes a personal issue.


Sure one can make some kind of associative argument for this or that based on era "standards" but these don't mean anything to a non era body (and that is a bit of a tongue in cheek...) Andy

As long as you have at least an inch of clearance between the top bar and the family jewels ...

If you mean horizontal top tube mountain bikes, yup, pretty much, sorta like road bike sizing. At least in crotchal clearance.

Last year I snagged an early '90s rigid mountain bike, horizontal top tube, 58cm frame. Univega Via Carisma, pretty much their early concept of a hybrid, minus the serious off-pavement wheels and stuff they put on their Alpina with pretty much the same frame. Technically my size, but if I'd intended to do any serious single track or downhill, well... first of all, I wouldn't because I'm too old and haz no skilz. But a 56, maybe even a 54, would have been better for that, mostly to protect to boys in the event of unplanned forward dismount.

The top tube is probably a bit longer than a typical 58cm road bike frame of that era. Combined with the original flat bar it was darned uncomfortable for me, at least last year when I was still trying to get back into shape. Hurt my neck trying to ride more than a few miles.

I swapped the 2" riser bar from another bike, which put the height and reach right where I needed for my rides on pavement, gravel, etc. It's basically like a current model sporty hybrid -- feels pretty much like a flat bar Trek 8.something FX I test rode last year.

I've considered putting on some lower all purpose drop bars, but I'd probably need to replace the stem as well. We'll see. A couple of riding buddies like the mustache bars they put on their rigid mountain bikes for gravel rides. Gets them a bit lower when needed, with enough flare in the drops to retain plenty of room for manuvering.

I've found that the first most important measurement for me is the height of the crank. Recently sold an extremely nice mountain bike with the same size frame as my road bike, but the mountain bike crank was almost 2 inches higher.

Impossible for me to get proper leg extension and still mount. it would have caused me great pain to stop without swinging one leg over the top tube and "jumping" off the bike.

Well I see that I assumed the OP was asking about fat bars as in "handle bars". Guess I never heard the "flat bars" reference applied to frame tubes. Andy

I'm with you, Andy! And since OP has not clarified, I'm staying with you.

As far as handlebar diameters go, there are two places to measure, namely the clamp and the bar itself.

The bar itself generally has one of two diameters, best considered as inches: 7/8" (22.2 mm) for flat or upright (including steel drop bars), 15/16" (23.8 mm) for aluminum drop bars. The metric (French) equivalents are 22mm and 24 mm. The reason for this is mostly historical.

Exactly!

The length of the seat tube is dependent on the height of the bottom bracket. Which is why a 20" bike can be really tiny or really huge.

Be aware old ATB/Hybrids generally have very long top tubes for the length of seat tube, so you may want to measure that.

Yeah, this is along the lines of what I was going to say. As long as the frame isn't too large to be safe, the next thing I'd want to check is the top tube length for comparison against my desired reach to the bars.