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Thread: sprocket sizing questions

  1. #1
    PRAY BEFORE RIDING roadcrave's Avatar
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    sprocket sizing questions

    My daughters has a 1993 yamaha seca 2, it tachs out at 5000rpm at 60mph, 4000 at 50, need info on calculating sprocket teeth to drop the rpm, it currenty has a 48tooth rear sprocket????? i think i want 2500-3000rpm at 60 mph....
    this will be of great help to me, so that we can go on longer distance trips together, planning a trip around washington state...matthew

  2. #2
    Registered User kioolt's Avatar
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    What's a sprocket?
    2004 R1150RT 151,500 miles , 1991 K100LT 128,000 miles, 1982 R100RT 106,900 miles
    Total 386,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  3. #3
    PRAY BEFORE RIDING roadcrave's Avatar
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    -a tooth or projection shaped so as to engage with a chain

  4. #4
    BMWRich58
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    sprocket sizing questions

    Years ago while racing dirtbikes, droping a "one" tooth on the countershaft sprocket (front or the one on the trans) would be like adding 4 teeth on the rear sprocket,giving more pull from the bottom end,but sacrificing top end speed. Engine will still put out the same power, but the speed/power will vary.
    So, if you "lessen/drop" the teeth on the rear sprocket,I believe you'll achieve a higher "top end" speed,and or lower the RPM's,for the same speed, but you of course will suffer the loss of bottom end power,thus she;ll probably ride the clutch more at startup from a stand still/stoplite.
    When you take from one, the other usually suffers....
    The dealer should have a chart to help "balance" what your after.

  5. #5
    Registered User kioolt's Avatar
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    What's a chain?
    2004 R1150RT 151,500 miles , 1991 K100LT 128,000 miles, 1982 R100RT 106,900 miles
    Total 386,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  6. #6
    Curmudgeon 28796's Avatar
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    Mathew - What's redline on the Seca 2? 8 or 9K? Dropping the rpms from 5K to 2500 would take the bike WAY out of it's power band & require a massive change in gearing. What is the frt sprocket size? If it is 15 teeth then going to a 16 with your 48t rear would drop the rpms from 5K to 4650. A noticible difference on the highway.
    John Borella
    MOA Ambassador
    Danielson, Ct.

  7. #7
    PRAY BEFORE RIDING roadcrave's Avatar
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    Bikpaintr, went with your suggestion,had no idea what i was asking.... i phoned the motorcycle shop and they had a breakdown of recommended sprockets, im attemting to gear the bike up so she can keep up on the hwy's....temporarly till we step her into a r1100s next year.... thank you matthew

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