New to the Rs125 NX4 quick questions

Discussion in '2-Stroke Machines' started by Supermotoguy, Jul 29, 2021.

  1. Supermotoguy

    Supermotoguy Member


    I’ll be riding my 04 Honda Rs 125 this weekend and I’m a bit unsure of what gearing as a starting point I need to run. I know this really depends on the track and skill level. I’m not new to racing but I am new to road racing and this motorcycle. I also understand that I’m going to need to change my gearing at some point during the day. Based on what I’ve seen out of r3’s and the like and 600’s on YouTube, the top speeds are somewhere between 85-115 mph. Considering that I’m unfamiliar with this motorcycle and GP shift, I’ve selected my gearing as 15/40, which will give me a top speed of 105 mph according to gearing commander. It’s also been a considerable amount of time since I’ve ridden a two stroke but have a lot of experience with them. Does this sound like an unreasonable choice as a starting point? Is it going to wheelie everywhere? Im a intermediate-expert level supermoto rider and a B class motocrosser if that helps. I’m lost. Help. I’m trying keep the gearing changes to a minimum by choosing the best possible starting point.

    Thanks for reading
  2. Boman Forklift

    Boman Forklift Well-Known Member

    I'm going off 12 year old memory, but I think we ran 36-39 quite a bit. That was with a 100lb kid, so adding some teeth should be fine, to help you get out of the corners.

    Like many things on a RS125, changing the gearing on that bike is very easy. If you have never ridden it, you really need to slip the clutch for awhile to take off. Also warm it up to 45C before taking off.

    I went to look for the USGPRU forum which had a gear chart by track, but it looks like it is gone. Did find this one for you.
    Last edited: Jul 29, 2021
  3. Supermotoguy

    Supermotoguy Member

    What do you recon about that front sprocket. Was it a 15?
  4. parillaguy

    parillaguy vintage+GP racer

    As a beginner on the RS, gear it for acceleration off the corners not top speed. Your going to have a steep learning curve as keeping your drive thru and out of tighter corners is the key to your learning to ride a RS125. Take a 14T front sprocket with you just in case you need more drive out of the corners.
  5. Supermotoguy

    Supermotoguy Member

    I don’t have one yet. I’m praying that I get it in the mail today. The highest I can gear it at the moment is 15/39.
  6. AssClown

    AssClown Well-Known Member

    Here is a link to a document of alot of 125 info collected from different sources. I referenced this when I was going through my learning curve with my 125. Page 22 has the table I think was from the USGPRU site on track gearing. Might be useful starting point.
    Props to Tyler Jensen who is listed as the author of the document. It helped me a lot.
  7. Supermotoguy

    Supermotoguy Member

    All I can say is woah. Woah.
    Thank you. That’s incredible.
  8. AssClown

    AssClown Well-Known Member

    I got a lot of other documents I could share if you want them. I went in to information overload in my learning stage, got confused did a lot of wrong things. The best help I got was a jetting calc spreadsheet shared with me. I'll shoot you a link to that.
  9. RRP

    RRP Kinda Superbikey

    Would any of your info be useful for 250 2 stroke tuning? If so I’d appreciate any you’d care to share.

  10. AssClown

    AssClown Well-Known Member

    There are some HRC docs for the RS250 in there, and just general two stock tuning stuff. I scoured the net for anything two-stroke when I picked up my 125.

    Here is everything I have. Feel free to pick through and grab what you need. Maybe others would want these too.
    Heisenberg and RRP like this.
  11. parillaguy

    parillaguy vintage+GP racer

    Mark: a 250 with power valves is easier to learn on as they don't "fall off" the power quite as dramatically.
    RRP likes this.

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