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Honda CBR 250R (speed to gear).

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by mick No:8, Dec 1, 2007.

  1. I was wondering if anyone here can help me. I just want to know if my Bike is performing well/right.
    1st gear = 0-20km@6-8,000rpm
    2nd gear = 20-40km@6-8,000rpm
    3th gear = 40-80km @6-8,00rpm
    4th gear = 80-120@ 8-9,000rpm
    5th gear = 120-170@9-14,000rpm
    does this sound right? is my bike reving to high or to low? If anyone out there can help that would be great.


     
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  2. Depends on your gearing.
     
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  3. Yeah, depends on sprocket sizes. It is a 250 after all, and for a bike that redlines at what, 19000? that seems about right

    My dad's old 400 Ninja did 110kmh in 2nd gear when I rode it (that was at red line: 12000 rpm I think) and has 4 more gears! Can't wait till I get off P plates in July to ride it properly (and legally- not LAM approved). It's only a 400cc. I couldn't believe it!
     
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  4. I don't think anyone would be able to help you unless they have or have ridden a CBR250R. I'm not sure if the CBR250RR has the same gear ratios.

    How many rpm at 100 km/h in final gear?
     
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  5. For cbr250rr on 6th gear doing 100km it would be at 9000rpm...

    For the gearing part is there anything I could to to have the gear ration so they're not so close together? Since every 10kph I'll be changing the gears. I like to ride my bike so it cruises with the revs at the bottom end of the power band about 7500rpm for my bike. I know different year would have different power band.

    Sometimes its just annoying that I change gear and the revs only drops like 1500rpm for the next gear...Maybe I'll try changing two up when I'm at the top of the powerband. That should bring the rev down abit...
     
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  6. I certainly wouldn't put any more less on the rear, or more on the front - on a cbr. That would lengthen things out, but it'd mean your accel would be down :( Sure you have to shift every milisecond, its a 250, you are supposed to :D
     
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  7. I ride a 250R as well and I'd say that mine revs around 10,000 in top gear. does your bike sound ok when its in top gear 110-120 kph?
     
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  8. That looks about right. It is a property/characteristic of the engine's performance characteristics.

    To get anywhere on this bike, since it is redlined at around 18,000 rpm, you need to rev it high to get anywhere. You can only get so much power out of a given engine size, at a particular rpm level.

    For example, the VTR250 will produce about 2/3 the power of the CB with half as many cylinders and about 2/3 of the rev range. Its redline is around 11,000 (depending on model). The very early VT250 would produce about 20% more power by revving to around 13,000 rpm

    Get the idea? If you rev your CB less it will simply not perform the way it was designed. Maybe you should have bought a 250 v-twin cruiser...at around 100 kmh you will be doing more like 7,000 rpm

    Cheers

    Trevor G

    PS As mentioned elsewhere you have to change sprocket sizes to change gearing to change the revs at any speed.. Go too far and you will simply have a very sluggish bike.
     
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  9. I thought the CBR 250 had 6 gears no ??
     
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  10. Cbr250rr has 6 gears (and single front disc brake)
    Cbr250r has 5 (and dual front disc brake)
     
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  11. WTF.

    Let take an engineering view point!!

    Engines are designed to produce specific types of power delivery supported by gearing and drive ratio’s to deliver torque depending on your needs.

    A race bike does not require torque as much as top end power. Why, because on a race bike we want to extract as much speed as possible. Speed requires power to overcome drag and friction forces applied.

    In short a race bike engine has smaller bore strokes, but achieves much higher RPM’s.

    A cruiser wants torque over top end speed, thus has long bore strokes (which is what in short delivers more torque) but much lower RPM’s

    However, power and torque are still restricted by its cubes!!! You cannot do anything more to deliver power better than having a bigger capacity.

    In the case of a CBR 250. It is no different to any other bike. You need to look at the how the engine converts its power into the drive train.

    First thing is what is your peak RPM? In a CBR 250 its 15,000.
    What is its primary drive ratio (engine to crank)? Its 2.9 to 1
    What is the final drive ratio (front to rear sprocket)? Its 3 to 1
    What is the gear ratio? In 6th, its almost 1 to 1.

    So in a vacuum with no drag or frictional forces.
    15,000 / 2.9 / 3 / 1 = 1724 wheel revolutions per minute.

    What is the tyre circumference = 140/60 17
    60% 0f 140 mm = 84mm
    Rim diameter = 17 inch which is 425 mm

    Total diameter = 84+84+425 = 593mm

    Circumference is 2 * Pi *R
    This is 2 * 3.14 * (593)/2 = 1862mm

    In one minute wheel does 1.862 x 1724 = 3210 m

    3.2km per min = 192 kpm/h.

    However drag and friction forces apply as a coefficient (which for a race bike are between 0.6 to 0.8)

    In 6th gear
    Depending on conditions top speed (192 x 0.6) = 115 kph to (192 x 0.8) = 155 kph.
     
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  12. Oh course you are quoting everything as std, change the front or rear sprocket and you can throw all that out and start again.

    Basic rule of thumb .... smaller front sprocket / std rear = lower top speed but more 'grunt' of the line . lol

    Larger front and std rear, lower rev's @ legal speed's so in theory :wink: you can achieve a higher speed at your usual rev ranges.
    Then you can play with front and rears, to get more torque at the rear wheel for slower road speed but easier mono's and visa versa.
    The options are endless, just depends on the sprocket sizes available for your bike, and how you like to ride.

    I personally leave the rear as std, but raise or lower the front depending on the ride I'm most likely to do on any particular day.

    I know the VTR is a low reving bike at the best of times, but with an extra tooth on the front @ highway speeds :wink: I can loose 1000rpm
     
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  13. no

    and

    u should hit 80 in first
     
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  14. sounds a bit high for a 250.

    I thought some CBR250s had an 18k RPM redline?
     
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  15. Really? I thought the RR's are the MC22's which are the ones with the dual front disc brakes no? and the R's are the mc17-19's ?
     
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