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Thread: 250sx racer

  1. #16
    Join Date
    Dec 2009
    Location
    BFE
    --
    1,202
    Hot Rod 250sx... the idea has pasted my mind a couple times. Its fun to build a machine that's kind of a sleeper. Yes there are lots of ways to hop one up motor wise but in the end your left with a heavy machine with limited handling and an empty wallet. One other mod for speed that hasn't been mentioned is changing the primary drive gears. guys take the primary drive gears from 250es/sx and 300 fourtrax and put them in foreman 400/450 for a 14.5% gear reduction. Havent heard of anyone trying it but if you could fit foreman 400/450 primary drive gears in a 250es/sx case then you would gain 14.5% higher gearing for more top speed.
    "I'm Kind Of Like The Turtle Man Of 3Wheelers."

    1986 Honda 350X
    1985 Honda 250R
    1985 Honda 200X

  2. #17
    schlepp29 is offline At The Back Of The Pack Arm chair racerAt the back of the pack
    Join Date
    Jun 2015
    Location
    stonecreek ohio usa
    --
    414
    That would be cool! A little bit more speed for the back roads would really nice.

  3. #18
    Join Date
    Apr 2012
    Location
    MI, USA
    --
    2,717
    Quote Originally Posted by swampthang View Post
    Hot Rod 250sx... the idea has pasted my mind a couple times. Its fun to build a machine that's kind of a sleeper. Yes there are lots of ways to hop one up motor wise but in the end your left with a heavy machine with limited handling and an empty wallet. One other mod for speed that hasn't been mentioned is changing the primary drive gears. guys take the primary drive gears from 250es/sx and 300 fourtrax and put them in foreman 400/450 for a 14.5% gear reduction. Havent heard of anyone trying it but if you could fit foreman 400/450 primary drive gears in a 250es/sx case then you would gain 14.5% higher gearing for more top speed.
    Generally most people want lower gearing for racing. My 250SX topped out at 52mph based on a Rincon's speedometer on a dirt road @ ~700ft elevation.

    A cheaper way to get about the same gearing difference is to throw 25in tires on instead of 22's. The machine looks a bit funny but they fit fine. I'm not sure if the 250sx in stock form has enough guts to use the higher gearing to actually go faster and overcome the wind resistance, seems like it didn't fully rev out when I tried the top speed run.


    Another option for lower gearing is to either swap the transmission gears from a 250es, or swap the whole engine. The 250sx rear end + transmission is setup for 22in tires, and the 250es is for 25in tires, from what I've read the final gear ratio (engine rpm vs tire travel speed) is the same on both.

    Also when I was doing that top speed run, my cousin's 87 TRX250X performed about the same as the 250sx. It wasn't my machine, but it seemed to run well. I can't recall who was faster, but it was close for top seed.

    Quick story, my uncle put 14in rimmed car tires (around 25in or 26in tall probably) on his 650 Rincon to travel around 20 miles to state land, then road on the state land trails with the car tires and did fairly well. Only thing he said was a problem was mud because the tires had horrible tread for mud. Pretty much anyone could do the same thing, you just need to get a set of ATV rims that are 14in and throw car tires on them (used or cheap works fine). The ATV is a lot lighter than a car, so in theory the tires should last a long time. It looks a bit funny because they are so skinny, but it is more ideal for road traveling if that's something you do a lot. It should give a little more top end from less wind resistance (skinnier tires), and less rolling resistance assuming you're top speed isn't rpm based. Just don't try to blow up your machine by trying to go 60mph at red line rpm for 20 miles lol.

  4. #19
    Join Date
    Dec 2009
    Location
    BFE
    --
    1,202
    Depending on what type of racing you are doing most people go to a smaller tire like a 18 or 20. I had a sx that had 18s on it when I bought it and it was painfully slow 1st and 2nd gear was nearly unusable as you was only in them for a second, 3rd-5th it pulled good as you actually had time to let the motor rev and use its power. Top speed was terrible never tested it but id guess 30-35 at high rpm and you wouldn't want to run it at that rpm for long.
    "I'm Kind Of Like The Turtle Man Of 3Wheelers."

    1986 Honda 350X
    1985 Honda 250R
    1985 Honda 200X

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