Anyone's cycle computers have a selection for 650b wheel?
 

Mine only has one size - 650b x 37mm. But I am going to run 33mm tires.
Don't know if it is that much of a big deal to not be dead-on, but was wondering if anyone knows off hand of any computers that have more 650b sizes to select from.

I see also that I can measure the tire and input that. I guess I will try that but was wundrin' if anyone's has 650b inputs.

I always enter the actual roll-out measurement.

+1. This is the best option, even if the computer does have your tire size programmed into it.

Do a roll out or use a GPS.

Doing a roll out isn't hard, it's just an inconvenience to do.

When setting up computers for customers in a shop I'd just use the numbers in the manual or sometimes interpolate between two listed tire sizes. Those methods are accurate enough enough for me.

The manual said do roll out in mm's, or measure tire from floor to top. Those mm's x 3.14 = number to input for wheel size.
This is a Sigma 1609 sts computer.

I couldn't get a roll out good, so tried to measure tire, but couldn't eyeball it good, sometimes off by alot. So:

I measured in mm from the floor to center of hub axle (easy to get it right on) x 2 (for overall wheel dimension) x 3.14 = my number.

+1. this is easy and it will give you an accurate reading. But since I quit being Too Serious, I swap my computer back and forth between a bike with 700x37 tires and one with 700x28s, and it's only off by a few yards per mile.

shouldn't matter much,second number is width of tire.

Yeah but.

Try to visualize a bike tire as being circular in section. Wider tires also tend be a bit taller in section. The width of the rim will have an effect too.

Even taking all of that into account, how much precision do you really need? Sometimes close enough is close enough.