Lower gearing on 8 speed

edited July 2010 in Rover
Hi,

I live in an area that has a few hills. I notice the 8 speed has a low gear of 24". Is there anyway to lower the low gear, say by putting a different chainwheel on it, and if so what would the gear range be then>

Thanks,

Bob

Comments

  • I don't know for sure if you can swap out the chain ring, but would assume so. The 'gear inch page' : http://www.terratrike.com/gears.php : shows a couple of speed drive setup with a 27 tooth chain rings. Don't know why you couldn't just swap chain rings out (while adjusting the chain length to match).

    To figure out the new gear range, just use the ratio of the (new chain ring to the old chain ring) times the existing range.

    i.e. the gear inch page says the stock gear range is 24-75 gear inches, using a 32 inch chainring.

    If you put a 28 tooth chainring on, the new gear range would become
    • (28/32) = .875
    • .875 times 24 = 21
      and
    • .875 times 75 = 65.625
    a new gear range of 21-66 with a 28 tooth chain ring.

    I see, now, that you say 'lower the low gear' by changing the chain ring. If you change the chain ring only, all the gears in your range will change by the ratio used above. Can't change just the low using chain ring only.

    The speed drive shown in the gear inch page would get you down to a 21 inch low and raise your upper to 158, but is a bit costlier than changing just a chain ring.

    Good Luck,
  • I question the numbers on the web site since the the Sturmey Archer 8-speed gives a 325% gearing increase at the top gear.

    If the lower gear-inch number 24 is right, then the top would be 24 *325% = 78

    Here's a quick chart of your top end gear-inches for varying front chainrings and speed with a cadence of 100--assuming a 18.75" tall wheel.
    ring LGI 	MPH	HGI 	MPH
    32	24.0	7.1	78.0	23.2
    31	23.3	6.9	75.6	22.5
    30	22.5	6.7	73.1	21.8
    29	21.8	6.5	70.7	21.0
    28	21.0	6.2	68.3	20.3
    27	20.3	6.0	65.8	19.6
    26	19.5	5.8	63.4	18.9
    25	18.8	5.6	60.9	18.1
    24	18.0	5.4	58.5	17.4
    

    In a nutshell, you gain an easier lower end at the cost of your top end speed potential. Go for it. Putting a smaller granny gear on my mt. bike years ago, gave me a much, much easier time getting up those hills.
  • I'm interested in lowering the gear range myself. All my riding is on trails and I really don't need to be going 25 mph when riding over tree roots :D :D
    If anyone does make a change, please let us all know the make and model of the replacement. Thanks
    Tombent - My Rover
  • Just an update. I currently have been riding a Rans Tailwind Recumbent for about 13 years, and up till last year, my low gear on that 24 speed bike was 24", roughly the same as on the 8 speed Rover. I found out all the other gears on the 8 speed from Terratrike, and took a ride today in the hilly park with my Tailwind, using the gear combinations available on the Rover. I had no problem even climbing the steepest hill, and as far as the high speed end, I could go above 22mph without spinning out. So that gearing on the 8 speed will be fine for the type of riding that I will do. Here are the gear inches for the 8 speed that they emailed me if you are interested.

    1st = 24.58
    2nd = 31.95
    3rd = 36.38
    4th = 41.54
    5th = 47.19
    6th = 54.08
    7th = 61.45
    8th = 79.89
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