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Thread: Specs and Horsepower Numbers for the 250 2 stroke 3 wheelers

  1. #16
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,896
    Yea, I wouldn't think the motive would be fuel econ either, there was the big oil crisis of the 70's, but I wasn't even alive then xD.

  2. #17
    Join Date
    Jun 2010
    Location
    House Springs MO
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    5,474
    A 10hp and 13ft lb difference between the 250 and 500 is huge in a machine that weighs 200ish lbs. Having owned a modern 250 KX, I can tell you that it's all the power I've ever needed and having ridden a few KX 500's, I can tell you it's all the power you'd ever want unless you were an expert rider.

  3. #18
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,896
    Yea 50hp+ on a bike is pretty crazy.

    Just for fun I grabbed the machine weights.

    kx250 is 213lb
    kx500 is 220lb

    Only 7lb difference, that's quite amazing, almost would suggest to me the same frame was used, just the engine was the difference (know nothing about this model besides specs in the book lol).

    Pretty crazy weight to power ratio too.

    kx250 is 4.01lb of weight per hp
    kx500 is 3.46lb/hp

    That is a huge drop, guess I was just looking at the wrong numbers lol. Just for context, the service manual says the 350x has 26.6hp and weighs 320lb so the weight to power ratio is 12.03lb/hp. that must be one crazy bike to ride.

  4. #19
    Join Date
    Mar 2010
    Location
    Slidell, LA
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    4,687
    Quote Originally Posted by bkm View Post
    A 10hp and 13ft lb difference between the 250 and 500 is huge in a machine that weighs 200ish lbs. Having owned a modern 250 KX, I can tell you that it's all the power I've ever needed and having ridden a few KX 500's, I can tell you it's all the power you'd ever want unless you were an expert rider.
    To dogpile onto this thoughtful comment I would also like to add that I once heard a qoute from a pro racer that the 250 tuned to a 265 when properly used is all the power a racer ever needs. Later I decided to race my 250r with a shaved head and can tell you it’s a lot of power to handle effectively. I honestly couldn’t imagine effectively handling a 500.
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  5. #20
    Join Date
    Apr 2011
    Location
    Mexico
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    8,307
    Quote Originally Posted by ps2fixer View Post
    Yea 50hp+ on a bike is pretty crazy.

    Just for fun I grabbed the machine weights.

    kx250 is 213lb
    kx500 is 220lb

    Only 7lb difference, that's quite amazing, almost would suggest to me the same frame was used, just the engine was the difference (know nothing about this model besides specs in the book lol).

    Pretty crazy weight to power ratio too.

    kx250 is 4.01lb of weight per hp
    kx500 is 3.46lb/hp

    That is a huge drop, guess I was just looking at the wrong numbers lol. Just for context, the service manual says the 350x has 26.6hp and weighs 320lb so the weight to power ratio is 12.03lb/hp. that must be one crazy bike to ride.
    Weight is another area where the factories fudged with the numbers. At one point it got to where they were draining the forks, shocks, radiators, transmission, fuel tank and probably filling the tires with helium before giving out what they called “dry weights”.

    Read through all the old dirtbike magazine and time and time again you’ll see where they put the vehicle on a scale and it was considerably higher than the advertised weights.

  6. #21
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,896
    Yep dry weight by definition is weight with no fluids so it would make sense it's all drained, or more likely assembled and never filled with any fluids. Now if they were removing parts to reduce the weight, then I could see it being a problem. I'm sure the tires sold on stock machines are as light as possible for this spec as well as for the benefits of having lighter suspended parts.

    Newer machines have "curb weight" as the true weight with a full tank of gas etc. Still doesn't account for rider weight and such, but we all don't weigh the same. I think dry weight was used because it was a consistant value, didn't matter if the tank was full or not, the raw machine weighed the same, curb weight requires all fluids to be the same as stock level to get the same weight.

    A good example of a manual that has both weights is the 2003 TRX650FA service manual (Rincon).

    Dry weight is 600lb
    Curb weight is 631lb (31 lbs of fluids)

    Oil capacity is the same way, there's a total when rebuilding an engine vs just draining the oil and changing it. Same machine:

    3.0 US qt after draining
    3.1 US qt after draining + filter change
    4.1 US qt after disassembly

    That means, about 1 qt of oil is left behind in that engine when changing the oil. Some engines are only 0.1 qt difference.

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