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Thread: 2000 yz250 trike conversion

  1. #1
    plevib's Avatar
    plevib is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    2000 yz250 trike conversion

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    Man, this bike is in rough shape...... let's add another wheel! XD

    Some of you gents may remember my xt550 trike conversion. I was happy with how it turned out, it was a blast on the trails. But the steering was a little heavy and the trike was very heavy overall, which made you tired when trying to ride aggressively. Someone offered me way too much money for it so I sold it.


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    I'm gonna try again with things I've learned from that project. My goal is to make the geometry of this setup as close as possible to a liquid R, but with modern suspension and easier parts availability. I specifically wanted a steel frame yz250, because I can modify the frame easily, and the engine is cheap and hasn't changed for 20 years.

    I'm gonna tear this bike apart in a couple days, here's my basic plan. Bvc triples, I'll build a custom swingarm and front axle setup to use yfz450 components. I haven't decided if I'll shorten the 250 forks or try to find ktm 85 forks. But my main goal is better handling than my last conversion. I want it to ride like a liquid R.


    I'm going to find a buddy with one I can take a bunch of measurements on, and my main hurdle is head tube angle. 86 r's are 21.5 degrees and the bike frame is like 27 or so. My plan is to change the angle to match. I'll buy beg or build triples with 6-7 degrees of rake, shorten the forks to match, and run a trailing setup.

    This is gonna take a while, wish me luck!
    Atc 500x for the win! (Hopefully.... one day)

  2. #2
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    You don't have to change the rake on the frame. Your swing arm will have to be angled downward to get the ground clearance you need anyway. This will pull a few degrees out of the rake. Next, when you have your tripples built move the fork tube holes more forward of the steering stem hole. This will lessen the "trail" part of the steering geometry to take the "heavy " feel out of it. There is a lot more to steering geometry than rake and too many people get stuck on it. Dirt bikes will have about 4-6 inches of trail where as a trike needs 2-3 inches. The trail number is the one that makes the most difference in the way the trike is going to handle. Cutting the frame and changing the rake angle is one way to do it but not the only way.

    Also, if your modeling it after a 250r frame keep in mind that a 250r has a significant amount of extra rake built into the tripples themselves so you might not be as far off as you think.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
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  3. #3
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    Quote Originally Posted by BOB MARLIN View Post
    Your swing arm will have to be angled downward to get the ground clearance you need anyway.
    Spot on. How exactly are these being designed so the frame doesn't slam into the ground before running out of suspension travel?

    A typical dirt bike has 12 inches of travel and 13 inches of ground clearance, and the frame still touches the ground during full squish. That's with the 21"/18" wheels (not tire size), which are hella taller than quad tires.

    So, putting quad tires on that drop the ground clearance by half a foot, but not limiting suspension travel is supposed to do what?


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  4. #4
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    Sounds like great project and I love the YZ250 base.

    If you weigh much more than 170 pounds with all your gear on and plan to ride that thing hard I would try to steer you away from the SX forks. There’s only so much spring you can get inside there. Shortening any other USD fork isn’t difficult, so probably better you use something a little beefier.

    The Yamaha quad swing arm is said to bolt right up to the 450 bike frames, maybe yours will too? Would save you a lot of work.

    Ground clearance was some thing that I was very concerned about with my conversion. As you can see in the photos it all works out in the shop with 3/4" to spare, but I wouldn’t want to jump it without a lot of air pressure in the tires.

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    Both the forks you mentioned have leading axles, Are you planning to spin the legs around and run the caliper in front?
    Last edited by El Camexican; 02-23-2021 at 02:42 PM.
    It sucks to get old

  5. #5
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    My 450 ended up with 12" of travel and 11" of ground clearance. If I come to a time where I have to take the rear shock apart I'll just add a bigger bump stop. But for now it hasn't really been a problem.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  6. #6
    plevib's Avatar
    plevib is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    Awesome guys I really appreciate the input! So with my experience doing a bike conversion and from what I've seen on here ground clearance and steering angles/ trail are the main problems with bike conversion.

    Using a 450 swingarm (which I did with my xt550) means too much rear travel which leads to frame bottoming. So that's why I'll be building a custom swingarm based on atc250r dimensions. This will require shock mount modifications which will allow for a much shorter seat height. Another option I'll consider is basing it on banshee measurements. Either way I won't be using the dirt bike shock setup because, as you guys point out, it allows to much rear travel for the shorter tires. (A problem I had with my xt550)

    And to your point Bob, I know I don't have to change the head tube angle, trail can be corrected with rake in the triples and such, but my mindset with this build is to copy the 250r, including the rake in the triples and the leading setup (yes el camexican I think I'll just run the caliper in the front, I had my xt550 like that at one point)

    So it's possibly bull headed and definitely more work, but my thought is we all LOVE the way the R handles. So I'll rather than experiment and calculate with front end setups, I'm going to try to copy paste
    Last edited by plevib; 02-23-2021 at 05:24 PM.
    Atc 500x for the win! (Hopefully.... one day)

  7. #7
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    Might consider something adjustable as well. Probably a little more difficult if you build out of aluminum.

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    It sucks to get old

  8. #8
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    I've been down the the custom triple rabbit hole a few times now and learned a lot from my mistakes so I'll throw out some suggestions before you spend $800 plus on custom triples. Take it or leave it, I'm just throwing it out there.

    First of all the 3rd gen 250r is the worst thing to pattern your steering geometry after. Its a cluster of stuff that doesn't make sense. It has a shallow angle at the neck. Then another angle built into the triples that lengthens the trail number. Then a trailing axle that makes the trail longer again. The trike handles fine, but all that geometry is un-needed if you do your homework. I believe honda had issues with high speed stability and they scrambled with all this weird geometry to fix it.

    If you want it to handle like a 250r you need to find the "trail" number that exists on it and design your new one to match it. There is a lot of factors that go into that number, but that number is the one you have to hit, regardless of everything else. I would leave the neck alone and build around that. The trail number is the distance between the angled strait line of center line of the neck hole to the ground and a strait vertical line from the front axle to the floor. Think of this distance as the length of a lever that you would use to get more power to move something. The longer that lever the more power the trike can use against you- it wants to keep the wheel strait. The bike frame already has more rake than the 250r so the extra rake built into the triples would not be needed. You need to know tire sizes you are going to run to get the new axle to ground number and you need to mock up how your frame is going to sit on those tires to get the actual angle of the new head position. Then you need the to get the distance of the axle centerline from the fork centerline. That should give you enough numbers to crunch to come up with the new calculated trail number. Then that can be factored into where you put the fork hole in the triples in reference to the stem hole to adjust your trail number as close as you can to your 250r target number.


    A couple more things to think about.
    Leading axle vs. trailing axle will greatly affect your trail number as well as other physical dynamics. Trailing axle also throws in a "caster" or "shopping cart" affect making steering heavy but stable at high speeds. Leading axle is pushing the front wheel where as a trailing one is pulling it. That sounds trivial but when the wheel is turned the traction against the ground is either pushing into the turn (leading axle) or trying to pull it strait again (following).

    Supercross bikes have different triples to chose from depending on the track. They all have different fork tube positions as it relates to the stem centerline. Then again, this is to change the trial number to turn quicker or more speed stability.

    All of this is to adjust or hit a desired trail number. The head angle is just a part of the equation that can be compensated for.
    Last edited by BOB MARLIN; 02-24-2021 at 04:16 PM.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  9. #9
    plevib's Avatar
    plevib is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    Alright, I'll keep that in mind bob. I do appreciate the input, I don't know much on the matter. While doing research for this project I came across this https://www.bikeradar.com/features/t...-and-handling/
    This article also talks about wheel flop. Maybe that's the missing piece as to why Honda made the head tube angle steep and put rake in the triples?

    Quote Originally Posted by BOB MARLIN View Post
    First of all the 3rd gen 250r is the worst thing to pattern your steering geometry after. Its a cluster of stuff that doesn't make sense. It has a shallow angle at the neck. Then another angle built into the triples that lengthens the trail number. Then a trailing axle that makes the trail longer again. The trike handles fine, but all that geometry is un-needed if you do your homework. I believe honda had issues with high speed stability and they scrambled with all this weird geometry to fix it.
    I find this very unlikely, especially when you consider that they did change the angle .5 degrees between 85 and 86. If they made a mistake why not fix it then? I think that the Honda engineers actually knew exactly what they were doing when they made what is considered by most to be the best handling 3 wheeler ever. I just can't see such a blunder making it to production especially on their 3rd generation.

    But hey, if I ever get this project done I suppose we'll find out! Im still planning on trying to copy the 86R, if I do maybe I'll try to meet up with you guys with your converions and we'll compare pros and cons.

    I'll be tearing the bike down tomorrow and I'll post more pictures and plans
    Last edited by plevib; 02-28-2021 at 11:51 PM.
    Atc 500x for the win! (Hopefully.... one day)

  10. #10
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    Quote Originally Posted by plevib View Post
    I think that the Honda engineers actually knew exactly what they were doing when they made what is considered by most to be the best handling 3 wheeler ever. I just can't see such a blunder making it to production especially on their 3rd generation.
    I agree, the 1985-86 250R handles awesome, and does everything that one could ask of it quite well, but I wouldn't attribute those handling qualities solely to the steering head angle, triple clamp rake, & trailing axle fork setup. Tecates handle awesome as well, and they use a leading axle setup. So which is better, leading axle or trailing axle? In my opinion, it doesn't matter, as long as your triple clamps are designed properly, either setup will work awesome. When I designed the triple clamps, for my inverted fork setup, I only looked at duplicating the factory trail spec. I designed the new triple clamps to have the same trail as the original design. I went from trailing axle forks/rake built into triple clamps, to leading axle forks/no rake in triple clamps, and my 250R handles, as near as I can tell, exactly like it did when factory fresh. When I designed the triple clamps, I knew none of the other variables would be changing (ie, same size front tire, inverted forks same length as oem forks, & headtube angle same as oem). If your new forks are designed to be leading axle, that's how I would use them. For me, not only must the trike handle exceptionally well, but it has to be aesthetically pleasing too, which means brake caliper behind the fork tube.
    Last edited by Red Rider; 03-01-2021 at 05:05 AM.
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  11. #11
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    Actually, I believe the 350x handle far better than the 250r and it doesn't have any of the weird stuff going on in the front.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  12. #12
    plevib's Avatar
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    Well i'll come back to the head tube debate when I'm closer to that part of the build. For now I've gotten a better look at this pig, I think it'll work out perfect. Motor is all there (obviously needs a total overhaul), Frame is in pretty nice shape and that's pretty much all I need haha....

    Gonna warn everyone this project is gonna be slow going. I got laid off from the keystone project so I have lots of time and no money haha.... im gonna try to round up a swingarm first, try and get that fabbed in first
    Atc 500x for the win! (Hopefully.... one day)

  13. #13
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    Before you completely rule out the yz shock I used a 92' yz250 shock and 02' warrior 350 swingarm and linkage on my soft tail conversion and don't come close to bottoming out the frame at all.

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    1. 83 185s: (the money pit) xr200 cam, 200cc cylinder, 10.25:1 piston, 83 250r front end, 450r hubs, full suspension
    2. 85 Big Red 250es: in pieces
    3. 85 200m

    4. 00 Polaris Magnum 325 2x4: stays broke
    5. 02 Yamaha Wolverine 350 4x4: trail bike

  14. #14
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    Are you going with a quad swingarm or custom?.
    YAMAHA 450 HYBRID
    85 350X- RED
    85 350x -BLACK
    86 350x-WHITE (with Goki)
    85 250r
    83 atc 70
    84 atc 70
    84 atc 110
    09 yfz 450
    2006 Arctic Cat Prowler
    RZR XP 900

  15. #15
    plevib's Avatar
    plevib is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    I was originally thinking I would start from scratch, but I think I've decided to use a banshee swingarm. Stock length is 18.5, and a +2 is only 300 bucks which will almost match the 250r length. That would equal about 9.5 inches of travel which is perfect. They are very affordable and parts availability is amazing. It'll be easy to modify one to fit exactly as I want, and most importantly the banshee linkage and shock sits very low in frame. Low shock=low seat height
    Atc 500x for the win! (Hopefully.... one day)

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