All the apps for gear ratio on app store are crap and cost, but discovered that you can make your own templates on a free app “Converter+”
So I made one, works ever so well- if you want the rest of the screen shots to produce the whole template follow this flickr link.
it puts in a default wheel diameter of 27" or 685.80mm to give you your Gear Ratio after you put in your ring and sprocket. If you want to be really accurate then just put in your own exact diameter.
The rpm is put in to give you the speed you will go at in that gear.
The templates are case sensitive for items use, it is also worth downloading the template design docs so you can follow my screen shots.
If you need any more help- do post- or meet me at Chandler of a Tuesday evening?
Awesome. Might try and do this when I have some spare time (eg. at work…).
And for Android… the best one I’ve found is called “cycling calculator”. I think it was $2 or so, but does ratio, gear inches, speed, cadence, etc etc, plus things like time taken for a flying 200 with the above factors. I like that it provides a table instead of just 1 answer, and unlike some others it includes 27" wheels for ‘standard’ track gear inches. What puzzles me is what tyre size the nominal ‘gear inches’ are calculated with, because different sources vary.
685.8 mm is 27" Easy enough to put in somewhere or even the title- but like I said can be changed easily. This template was an idea to replace or compliment the “Track Gear Charts” based around a 27" wheel.
The only truly accurate way to get your actual rollout is to measure it, using a tape- there is a lot of difference in the actual diameter of “23mm” tyres. Many juniors have been relgated or dq’d for assumptions in gear charts!!!
Saw the $6 app, it was after seeing someone at the track last week using this, I decided to find something more useful if you turn up at a track and want to borrow bits
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One other useful calculation is a “relative” 200m time. This is for training on slower tracks and in lower gears- so you want to know how fast you need to go for 200m at the same rpm in a lower gear.
That all makes sense.
What leads to people like me being confused is that the “27 inch” measurement (685.8mm) that standard gear-inch calculations are based on hasn’t been seen on real bicycles in the last 50 years. Hence people try to make more “accurate” gear inches with the actual wheel diameter, but since gear inches are for theoretical comparison only, this is completely pointless. So best to stick with 27"/685.8mm, as you’ve got there/
For general reference:
27" rim (630mm dia) with a 1" tyre = 680.8mm dia
27"rim (630mm) with a 1.25" tyre = 685.5mm dia
700c rim (622mm) with a 23mm tyre = 668.0 mm
700c rim (622mm) with a 32mm tyre = 686.0mm