fixed/ss ratio question

stickman

If two bikes have a 46x16 ratio and one is 650a, the other 26 mtb diameter, how can I make the 26 equal gearing to the 650a? Probably more relevantly, if I put a 48 chainring on how would it compare?

Anonymous

http://eehouse.org/fixin/formfmu.php

Not sure, but this calc designed to help with 'magic gears' might help.

if you out the various gears in it shows the gear inches on the left.

stickman

Thanks, interesting idea but it has neither of my tyre sizes!

(And the one bike is 26x1.25 front, 26x1.4 rear, I forgot to consider this when I first thought about it)

yocto

Don't want to state the obvious but have you played around with Sheldon's Gear Calculator?
http://www.sheldonbrown.com/gears/

It looks to offer your wheel sizes. Would try and work it out but i'm lazy!

redvee

This site might be more accurate

http://software.bareknucklebrigade.com/ ... pplet.html

stickman

Thanks. Can't get that last one to work due to that java plug in stuff. On the Sheldon one it seems if I put a 48 chainring on they'd both be 5.6, as near as I could get it anyway.

edhornby

I wouldn't worry about it too much, the difference in effective wheel size isn't that big between 650 and 26in

if it equates to 1 or 2 teeth on the front then that's relatively small beer

mz__jo

Your best bet is to do a roll test (I usually do this over 3 revolutions to make it a bit more accurate) and work out the maths yourself. I will look up the figures on rabbit but as 1.4 is not a regular size it will be a bit of a compromise. Are your 650a tyres genuine 35 section like proper 26x1 3/8? If they are your cross tyres the diameters may be different. Also what is 5.6? Is this a gain ratio, a gearing ratio or a metric develompment (haven't worked out the figures yet, can't imagine you working in meters development)?
Will look at that when the Test match is over.
Cheers Jo

mz__jo

Done before Sri Lanka are finished. Rabbit has the answers:
46/16 on 26x1 3/8 is 74.5" and 48/16 on 26x1.5 gives 74.6" but always with the cautionary note that these are tyres (particularly knobblies) that can have diameters that vary wildly from nominal so measure to check (sorry I haven't noted the developments in inches, the diameters are 24.9" for the mtb and 25.9" for the 26x1 3/8).
Cheers Jo

stickman

Thanks for checking that out, it seems to be about the same this way too. Don't know what the 5.6 was. The 650a are Schwalbe Delta Cruiser, the 1.4 is Michelin XC Road totally slick, the 1.25 is Panaracer Ribmo slight incised tread.