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Thread: Information Require about relation of RPM with Speed

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    Default Information Require about relation of RPM with Speed

    Dear All,
    I owned a CG-125 and want to know actual knowledge about the relation of RPM with speed. Experts opinions require rather Hearsay.

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    I dont think RPM has anything to do with speed. RPM means revolutions per minute which basically means to measure rotational speed of a mechanical component.

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    RPM measures the revolutions of the crankshaft per minute. At any particular speed, RPM is heavily dependent on the gear ratio applied.

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    In the context of your question, a motorcycle's speed depends on two things: 1-RPM and 2-Gear. For each gear, the speed of the motorcycle is low at low RPM and high at high RPM. I have a Suzuki GS-150 (which has a tachometer showing RPM) and in 5th gear the speed is 12 kilometers per hour per 1,000 RPM. Which means that at 4,000 RPM the motorcycle speed is 48 km per hour, at 5,000 RPM the speed is 60 km per hour and at redline (10,000 RPM) the speed is 120 km per hour.

    With the lower gears the speed is lower than in 5th gear at the same RPM. For example, in 2nd gear the speed is approximately half of the speed in 5th gear, the gear ratio for 5th gear is 0.913 and the gear ratio for 2nd gear is 1.857.
    Asad

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    Quote Originally Posted by asad01 View Post
    In the context of your question, a motorcycle's speed depends on two things: 1-RPM and 2-Gear. For each gear, the speed of the motorcycle is low at low RPM and high at high RPM. I have a Suzuki GS-150 (which has a tachometer showing RPM) and in 5th gear the speed is 12 kilometers per hour per 1,000 RPM. Which means that at 4,000 RPM the motorcycle speed is 48 km per hour, at 5,000 RPM the speed is 60 km per hour and at redline (10,000 RPM) the speed is 120 km per hour.

    With the lower gears the speed is lower than in 5th gear at the same RPM. For example, in 2nd gear the speed is approximately half of the speed in 5th gear, the gear ratio for 5th gear is 0.913 and the gear ratio for 2nd gear is 1.857.
    Thanks Asad, Thats very technical answer but I am still confused. Actually question raised in my mind after seeing below picture that was upload in a thread on travel forum.
    In below picture of GS-150, you can see that its RPM needle is on 6.5 and speed needle is on 80KM/h while my bike gets 80km/h on 8 RPM. Is that Engine power difference or something else?
    Attached Images Attached Images  

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    Quote Originally Posted by syzeeh5 View Post
    Thanks Asad, Thats very technical answer but I am still confused. Actually question raised in my mind after seeing below picture that was upload in a thread on travel forum.
    In below picture of GS-150, you can see that its RPM needle is on 6.5 and speed needle is on 80KM/h while my bike gets 80km/h on 8 RPM. Is that Engine power difference or something else?
    gs have 5 gear mean gear ratio difference 17" and 18" tire difference is also a reason

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    @syzeeh5

    Its because of tha size of engine, the bigger the engine, the Revolution Per Minute (RPM) is decreased at the same speed.

    For e.g, If an 800cc mehran is going at the speed of 60km/h in the 4th gear and an 1800cc civic is going at the speed of 60km/h in the 4th gear, now here the speed and gears are same, but the RPM of mehran will be higher then the RPM of civic, means the crankshaft of small engine is having more revolutions per minute then the bigger engine while producing the same speed.

    Hope it helped...

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    Quote Originally Posted by syzeeh5 View Post
    Thanks Asad, Thats very technical answer but I am still confused. Actually question raised in my mind after seeing below picture that was upload in a thread on travel forum.
    In below picture of GS-150, you can see that its RPM needle is on 6.5 and speed needle is on 80KM/h while my bike gets 80km/h on 8 RPM. Is that Engine power difference or something else?
    he might have left the accelerator while taking the pic. nothing to worry about. what is the model of your gs? condition of clutch plates?
    people need to grow up sometimes and act MATURE !

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    Quote Originally Posted by saboor73 View Post
    gs have 5 gear mean gear ratio difference 17" and 18" tire difference is also a reason
    all the gs have 18 inch tyres. except 2 3 bikes in whole Pakistan which are not having original rims
    people need to grow up sometimes and act MATURE !

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    And yes type of transmission also makes a big difference, For e.g in CVT transmissions we get lowest RPM in high speed.

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    Quote Originally Posted by jadoon1992_vxlimited View Post
    all the gs have 18 inch tyres. except 2 3 bikes in whole Pakistan which are not having original rims
    I know all gs have 18" rim he is was comparing cg rpm and speed with gs rpm and speed so I was try to tell him that gs will travel more km in less rpm due to 18" tire

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    RPM is independent of engine size or number of gears; its purely dependent on the final drive and individual ratios. Case in point: a 4 speed 1500cc EXi spins at 2.5k at 100 km/h (4th gear). The same model in the 5 speed VTi 1600cc trim goes at 3k rpm at the same speed (5th gear).

    BTW, changing the stock tire size also affects the final drive ratio. A larger diameter will decrease the final drive ratio, thereby decreasing the RPM at a given gear and speed.

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    Quote Originally Posted by jadoon1992_vxlimited View Post
    he might have left the accelerator while taking the pic. nothing to worry about. what is the model of your gs? condition of clutch plates?
    BULL's Eye !!!
    Thats the case !
    He had the RMP around at 8 and left the accelerator and RPM needle comes down quickly as compared to speed. That's why his speed is showing 80km/h while rpm at 6.5


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    Quote Originally Posted by saboor73 View Post
    gs have 5 gear mean gear ratio difference 17" and 18" tire difference is also a reason
    This look reasonable! and yes he has narrated in his thread that he replaced rear Tyre with larger one.Thanks

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    Quote Originally Posted by ustaad_007 View Post
    @syzeeh5

    Its because of tha size of engine, the bigger the engine, the Revolution Per Minute (RPM) is decreased at the same speed.

    For e.g, If an 800cc mehran is going at the speed of 60km/h in the 4th gear and an 1800cc civic is going at the speed of 60km/h in the 4th gear, now here the speed and gears are same, but the RPM of mehran will be higher then the RPM of civic, means the crankshaft of small engine is having more revolutions per minute then the bigger engine while producing the same speed.

    Hope it helped...
    Thats much helped me understand. Well narrated example. Thanks

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    Quote Originally Posted by jadoon1992_vxlimited View Post
    he might have left the accelerator while taking the pic. nothing to worry about. what is the model of your gs? condition of clutch plates?
    he might use his left hand to take picture :-) I have CG 2014 not GS. Is this normal for CG?

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    Quote Originally Posted by ustaad_007 View Post
    And yes type of transmission also makes a big difference, For e.g in CVT transmissions we get lowest RPM in high speed.
    Again confused :-(

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    No dont be confused, actually CVT transmission is other kind of transmission technology, specially designed to get maximum fuel economy. It actually lower the RPM as much as it can. Sometimes on light foot acceleration car goes 0-60 while the RPM is still at 1200 RPM.

    For e.g 2008 Premio has CVT, New Corolla Grande has CVT, but 1.6 and 1.3 corolla dosent have CVT.

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    Actually there are no gears in CVT Transmission.

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    To understand RPM you just consider manual transmission, forget this CVT thing. then you will understand much better.

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