iPhone Gearing App

Just for those down the pub gearing conversations when you can’t consult the late great Sheldons gear calculator there is a superb iPhone App that does everything for you. BIKE GEARS

Dave has bought a new Swift frame; It’s a 29 er Singlespeed only and he like me initially hasn’t got a clue how to gear these big wheels. As he’d quite like to buy some bling sprockets and is waiting for wheels, he’d like to get it right first time.

So how do we compare the standard 32-16 gearing for a 26 and 29 inch tyres.

This illustrates that the gear ratio means nothing. The Gear Inches number is the one we want. So the 32-16 on a 29 x 2.25 tyre is 4 inches higher.

So how do different rear sprockets for our 29 wheel equate:  can we make 54″ the 17 tooth is almost equal.

The iPhone App also allows some speed checks so for our decided on 32-17 for Daves Swift we he be able to manage in the flatlands.

So at 90 RPM (supposed best efficient pedalling revs) he will be doing 14.5 mph which is perfect off road as general pace is about 12mph. But just think how many revs he’s doing to keep up on those road sections hey guys.

If when it comes to hillier events like Mayhem, you could do a quick check on the effects of changing sprockets. As shown here for an 18T

This part of the App is most usefull for allowing you to quickly compare the range of a 9 speed sprocket with single front rings (1×9). You then swap back to the speed page and it tells you how fast you can attain for what ever revs you input.

On my current 32-11 max I can do 22.5 mph at 90 rpm which is more than enough for any race. Flat out at 110rpm say, its up to 28mph, more than enough I’d say.


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