Rover gearing

edited June 2010 in Rover
Hi Jess

I am considering a new Rover primarily because of the seat height - I'm old. I live in Florida and there are no hills in the area. I would like a higher top end speed so I was thinking about replacing the crank gear from a 32t to a 46t - what do you think.

Thanks for your help

Comments

  • Well, I'm not Jess, but I'll try to help. More information from you would help.

    Do you have trouble breathing (COPD)/how is your cardiovascular?

    How fit are you/how strong are your legs (do you do squats, etc)?

    I ask these questions because for a couple of reasons: one, for any given speed and selected gear, a 46 tooth front sprocket will make pedaling almost 144% harder just for mechanical reasons, and two, aerodynamic drag increases with the square of the increase in speed, and power to overcome aerodynamic drag increases with the cube of the increase in speed--it's the reason a car may be as fast or faster in fourth gear than it is in fifth, if the engine doesn't have the horsepower to pull the higher gear. You're talking about a potential 1.44 increase in speed, cubed, on a bike that sits you up higher, and with direct-linkage steering, is squirrelier handling at higher speeds.

    Would this gearing be in addition to an eight-speed or a three speed? Top gear on the eight speed (325% of first gear) is 183% of the top gear on the three speed (177% of first gear)--like having a 59 tooth front sprocket. Even seventh gear on the 32 front sprocket eight speed is like having a 45 tooth front sprocket on the three speed.

    Here are some numbers I crunched to help me decide between the 3 speed and 8 speed. They may not be exactly right, but they should be close. The 3-speed looks like a good choice for someone who typically rides between 4 and 8 mph, while the 8-speed takes that "most of the time" range up to 14 mph or more. In fact, the 8-speed Rover with 20" wheels has about the same gear inch range as my 11-34T rear cassette mountain bike on the middle (32T) chain ring with its 26" wheels.

    TerraTryke Rover - 3-speed vs 8-speed
    at 40, 60, 80, and 100 pedal rpm (cadence)

    3-speed (177% range)
    32/19
    rpm 0.75 / 1.0* / 1.33
    040 03.0 / 04.0 / 05.3 mph
    060 04.5 / 06.0 / 08.0 mph
    080 06.0 / 08.0 / 10.6 mph
    100 07.5 / 10.0 / 13.3 mph

    8-speed (325% range)
    32/25
    rpm 1.0* / 1.30 / 1.48 / 1.69 / 1.92 / 2.20 / 2.50 / 3.25
    040 2.80 / 03.7 / 04.2 / 04.8 / 05.4 / 06.2 / 07.0 / 09.2 mph
    060 4.20 / 05.6 / 06.3 / 07.4 / 08.1 / 09.3 / 10.5 / 13.8 mph
    080 5.60 / 07.4 / 08.4 / 09.6 / 10.8 / 12.4 / 14.0 / 18.2 mph
    100 7.00 / 09.3 / 10.5 / 12.0 / 13.5 / 15.5 / 17.5 / 23.0 mph

    * direct drive is 1st gear on 8-speed and 2nd gear on 3-speed,
    however 19/25 = 0.76, so hill-climbing in 1st and 2nd should
    be roughly equal between the 3 and 8 speed.

    Hope this helps. I'm not saying switching to the same front sprocket as the Path isn't the thing to do in your case, just giving you some things to consider.
    --
    Moe
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