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Thread: 250es vs 250sx Differential

  1. #1
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    Mar 2003
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    250es vs 250sx Differential

    I know this has been discussed many times over the years but what is everyone’s final verdict on the rear differential with these machines?

    Is this where the crown and pinion was changed to accomodate the smaller 22inch rear tyres in the 250sx while giving it ‘longer legs’ than the 250es?

    I am always looking for a 6th gear on my 250es and would love to swap in a differential from a 250sx to make it more rideable.

    Has anyone actually broken these units down and done an inspection?

    Cheers,

    Matt.
    1980 ATC 70 Needs Restoration
    1985 ATC 250es Fully Refurbed
    1986 ATC 350x Mint Original

  2. #2
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    1985 is a one year differential and yes it will directly swap from 250sx & 250es . 86/87 are interchangeable .
    The 250es has one more tooth on the ring gear for the larger 25” tires .
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  3. #3
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    Great, thanks. So the 85 SX diff will swap into the 85 ES essentially gaining a bit more top end. Do you know if the crown wheel can just be swapped or it has to be the whole differential?

    Matt
    Last edited by atcmatt; 12-14-2019 at 11:08 PM.
    1980 ATC 70 Needs Restoration
    1985 ATC 250es Fully Refurbed
    1986 ATC 350x Mint Original

  4. #4
    Join Date
    Apr 2012
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    Whole diff, you don't want to mis match the gears.

    Also, the transmission in the engine is geared differently too. Note that the "first gear" is Honda's solution to no transfer case, so the first gear is "super low" for pulling/working.

    250es specs






    250sx specs






    You can plug the numbers on this page to calculate the max speed based on gear ratios + tire size + engine rpm. I suspect the 250es/sx maxes out around 8k rpm. Default numbers are for the 85 250es. I popped in the 250es final gear reduction and it jumped from 48mph to 55mph at 8k rpm. You could also go larger tires if you want even taller gearing (I see the tire size box doesn't update the calc on the page, I'll have to fix that, just move the rpm slider to update it).

    http://atvmanual.com/honda/speed-cal...-and-tire-size

  5. #5
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    Mar 2003
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    Hi mate, thanks very much for the reply.
    That makes perfect sense. I have just put some Duro two ply knobbies on it which I think have a smaller circumference than the tyres on it previously. This has enhanced the feeling of needing that 6th gear.

    I just want that little tiny bit of more top end on the 5th gear. Not concerned at all about any other gears. I think the 250es has plenty of low down grunt for that super low even with a taller diff. It would be great to hear any feedback from anyone has done this swap. I guess my next thing is finding an 85 250sx rear diff.

    Thanks for the replies.

    Matt
    1980 ATC 70 Needs Restoration
    1985 ATC 250es Fully Refurbed
    1986 ATC 350x Mint Original

  6. #6
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    I put a 250es diff in a 250sx and it turned into a wheelie monster vs my stock 250sx, so I suspect it would make the 250es a bit doggier on take off but for normal riding first gear is already too low anyway, but for pulling it could be a little lower with bigger loads IMHO. Just going to 26in instead of 25in tires would increase the gearing a bit, just noticed you're from AU and my calc doesn't support metric measurements yet but some day I'll add it in so the rest of the world can use it besides just people from USA and the couple other countries using this odd system of inches and such lol.

  7. #7
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    No that was a great help mate. Thanks very much again.

    Matt
    1980 ATC 70 Needs Restoration
    1985 ATC 250es Fully Refurbed
    1986 ATC 350x Mint Original

  8. #8
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  9. #9
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    Yeah you did put it in the original post mate. Cheers.
    1980 ATC 70 Needs Restoration
    1985 ATC 250es Fully Refurbed
    1986 ATC 350x Mint Original

  10. #10
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