Steering problem on RST

[Fred A-M]

Glad to hear Thorn sorted you out OK, though I never thought they wouldn't.  Based on what you say, I think the Raven will turn out to be the better choice for you - enjoy!

[JimK]

can manage 20mph on the flat in gear 14 without spinning out ( not for long though) need to get my  fitness lever up.

This puzzles me a bit! That seems like a slow cadence. I might ride 14 mph on the flat.. but that is in gear 9 or 10 - and I have a 38 tooth chainring. I find gear 14 useful above 25 mph, and spin out at maybe 32 mph. At 20 mph I am likely in gear 12.

I think a steady 20 mph on the flat is out of my reach in this lifetime!

Jim

[pt88]

hi Jim,

It probably is quite a slow cadence, I am relatively new to cycling and cycle most of the time by myself
so don't really know what the cadence should be, I just change down when it starts to get hard to pedal
the cateye computer fitted to the bike only shows mph distance covered average milage etc, how do you calculate the cadence I have a 40 tooth chainring so to give me an idea, If on the flat in gear 12 and want to travel at 20 mph what would the cadence be, is there an optimum cadence to aim for ?

any info would be much appreciated

Thnks Alastair

[JimK]

Here's a good start:

http://www.kenkifer.com/bikepages/touring/gears.htm

80 rpm is a good cadence to shoot for, as a ballpark figure. You can multiply numbers a variety of ways to get speeds in different gears for that. To get precise about it... it even depends on your tire pressure!

Jim

[JimK]

http://www.rohloff.de/en/products/speedhub/sprocket_ratios/

is another nice page, plus

http://www.schwalbetires.com/tech_info/tire_dimensions#circumference

Note that circumference is a tricky affair. More weight on the bike and/or lower pressure will squish the tire more and reduce the effective circumference.
 
Rohloff says gear 12 is a 1.135 internal ratio. 40 teeth on the front and 16 on the rear means one turn of the pedals gives 2.8375 turns of the wheel.

Suppose you're running something like a 26x2 Marathon Supreme, i.e. a 5-559 tire: Schwalbe says the circumference is 2.075 meters. So one rotation of the pedals moves the bike 5.888 meters.

80 revolutions per minute would then be 471 meters per minute which is 28.26 km per hr which is 17.5 mph.

Try that yourself to check my math and to get the hang of it!

[JimK]

My bike has a 38 tooth chainring with a 16 tooth sprocket. I find I like a cadence of 90 rpm. I am riding Marathon Supreme 2.0 tires, which I measured to have an effective circumference of 2010 mm with my usual load & pressure. This gives a gear to speed relationship of:

 1:   4.46 mph
 2:   5.06 mph
 3:   5.76 mph
 4:   6.55 mph
 5:   7.42 mph
 6:   8.45 mph
 7:   9.61 mph
 8:  10.92 mph
 9:  12.39 mph
10: 14.10 mph
11: 16.01 mph
12: 18.17 mph
13: 20.68 mph
14: 23.49 mph

Probably I spin even a bit above 90 - my experience is that I tend to downshift if I get below these speeds. Except with 1st gear, of course. But once I am below 4.1 or so mph then I have entered the realm of slogging. It happens!

[pt88]

thanks Jim for the info

think I have been pedaling too slow

Alastair.