Ratios Re-do and Sprocket Attach Suggestions? - HF 2.5 Trike

Discussion in 'Motorized Trikes' started by Walbird, Apr 25, 2012.

  1. Walbird

    Walbird New Member

    As you will see, I'm really a newb at this and fairly clueless....Please bear w/me;

    Trike engine drive sprocket rebuild :( - Got this 2.5 HF running fair but need to re-do sprocket gears. Could someone please explain what my best bet for gear ratio is on this. It now has a 10T #40 output sprocket at the MaxTorque clutch - goes to a 41T drive wheel sprocket. Doesn't have much power. Speed seems fair, after it gets going, but it takes quite a bit of pedaling to get it going in the first place. I think I'm burning up my clutch. And I'm told that's because my ratio is way off. And, if I'm not going to utilize some sort of jackshaft, I'll need a much larger drive wheel sprocket or I'll will burn up clutch. This is all very new and confusing to me.

    I don't understand ratio's well enough or the jackshaft thing very well either. Is it that a jackshaft allows for a smoother transition of power because of having more sprockets progressively larger, as opposed to simply going from a small output sprocket to large drive wheel sprocket?

    Looks like a big rebuild and re-design if I try to engineer a jackshaft into this...am I right? Can't I just install a bigger drive wheel sprocket? Like a 60T? Please, tell me I can! If my calcs are correct, (probably not), if I go from my existing 10T output sprocket to a 60T sprocket and change from existing 24" wheels, to 20", I get 6.0:1 ratio and at 3600 rpm = about 35mph. Is this right? And will this work? I like the 20" wheel idea for stability. The way it is now w/24", makes for unstable, high center of gravity - but that's a whole other topic...

    If so, how should I attach it (new, big sprocket) to the drive wheel. Whoever attached the 40T that's on there now, didn't do it right, I don't think. Everything in that area is screwed up - bent, spokes and the sprocket wobbles too. It's a mess. Hope pics help explain. I need to order parts but not sure where to start. I really don't want to start tearing this thing apart until I'm more confident in what I'll find and what I'll need.

    I've seen, like a sprocket kit for attaching drive-wheel sprocket to rear bicycle rear wheel (see atached jpg). But is there something similar for attaching a large 60T sprocket in this (trike) case?...and staying with the engine mounting as is?

    Sorry for the long read :ack2: hope it makes sense:poop: Thanks for looking! :sweatdrop:
    Please see more pics....attached below. THANKS!

    Attached Files:

    Last edited: Apr 25, 2012

  2. srdavo

    srdavo Active Member

    In my experience with the 79cc greyhound, I need at least 11:1 with 24" a tire.
    This allowed for a decent amount of power for taking off & hill climbing.
    About 24 mph @ 3600 rpm's.

    (these engines will run more than 3600 rpm's......just unknown for how long :jester: )

    have a look at these gear ratio calculators
  3. Walbird

    Walbird New Member

    Thanks...yes, I've heard that ratio or thereabouts is the place to be. Seems so large a ratio. Well I'll have to research the best (and simplest) way to get there. I don't think I have the room...and definitely don't have the fabrication talent to rig much up...in the way of a jackshaft or transmission. If I can find a good way of securing a large sprocket to my drive wheel, I think I may try that road.

    Sounds kinda crazy, but I think if I could find a 9T (or possibly even an 8T) output sprocket, and an 80T drive wheel sprocket, I might be in business. 80T --- OMG! Maybe using a rear wheel that has a disk brake mount built into the hub then use an adapter to mount the sprocket to that would be the most secure way of mounting such a huge sprocket to the drive wheel.

    Thanks :eek:
  4. landuse

    landuse Member

    You now have a ratio of (41/10) = 4.1:1. That is waaaay to high for your situation. You will be burning clutches up in no time. What you need is to get a larger rear sprocket. A 60T will give you a ratio of 6:1, which is better, but not ideal for your trike. You definately need at least 10:1 for some good torque.

    The higher the number, the lower the gearing. The lower the number, the higher the gearing.

    The purpose of a jackshaft is not for smooth gear transition, but for compound gear reduction. It allows you to get lowwer gearing using a series of smaller sprockets than you would have to without the jackshaft. Calculation your gear ratio with a jackshaft is as follows:

    (clutch/JS in) * (axle sprocket/JS out)

    You divide the larger sprocket by the smaller one. An example would be:

    clutch - 10T
    JS in - 36T
    JS out 14T
    Axle 48T

    (36/10)*(48/14) = 12.34:1

    I am not too sure how you would do this on your trike, but hopefully someone will chip in with how to attach it to your setup
  5. Walbird

    Walbird New Member

    Hey landuse.......WOW!...THANKS DUDE!!!..that is exactly the tutoring that I needed. Makes one believe in "...there's no such thing as a dumb question". Thanks sooo much for taking the time! I'm actually starting to figure the whole (ratio) thing out. (Keyword=starting). The more I go over it in my mind, the better I can picture it. And as they say "a picture is worth a thousand words". So, if you would take a look at this jackshaft I found. I think this might fit into my set-up. I may have to re-work or build a new motor mount, but I need one that's (more) adjustable anyway.
    Is this how the equation fits?

    Also, since I found King's Sales & Service (Sprocket Co.), I may go the direct drive route. Direct from a 9 or 10T output (clutch) sprocket to...oh say, a 75T or 80T drive wheel sprocket. Especially if I can find a suitable adapter for the wheel to provide a secure mount for such a large sprocket. I saw a post about using a rear wheel that has a disk brake mount built into the hub then use an adapter to mount the sprocket to that, for this idea.

    I'm really not sure which way I'll go. I'll need to keep researching this, as my mech skills are obviously lacking in a few places.

    Also, can you, or anyone tell me why I always see (as pictured here)...
    a second small sprocket that is sitting flush up against the clutch face? Is that just for spacing or something?

    Thanks again 'landuse'!!...I feel like 'new life' has been breathed into this project.
  6. landuse

    landuse Member

    The jackshaft and calculations that you have pictured there are correct. You have done the maths correctly.

    Going direct drive would require you to have a really large rear sprocket, but if you have space for such a large diameter sprocket, then it takes the hassle out of making a jackshaft setup. It is always better to go the simple way if you are able.

    That "second sprocket" that you see on the clutch is not a second sprocket. It is just where they have "mated" the sprocket with th clutch bell. I know it looks weird, but it does not function as anything. It is just how they attached the 2 together.

    Just make sure what size chain you are going to use. Make sure that all your sprockets are the same pitch as your chain, or the other way round. You wont be able to get a 10T clutch for a #40 chain, as the teeth are too far apart to allow for so few teeth with that pitch. I would suggest using a #35 (3/8 pitch) chain for your bike
  7. Walbird

    Walbird New Member

    Thanks landuse...appreciate your input.
    But I AM using (now) a 10T output sprocket on my clutch, with a #40 chain. But I believe going any smaller than 10T would, as you indicated, present a potential problem. I believe that I've heard that a 9T is just too small and, even if one is able to get their hands on it, it may easily get torn up in use, due to some king of over-stressing. Nevertheless, I've asked OMB if they could supply one. They indicated that they may be able to, but that it would run me a hefty $125 - $150 dollars. Sounds like a crock to me....but maybe. And I intend on finding out what other suppliers might have to say.

    I would welcome any other comments, as I am very interested in finding out if this is do-able - because it seems that it would give me an option that would give me some added torque that I need, without having to go to a jack-shaft...which I really don't have room for.

    My plan is to re-outfit my trike with a (3 pc) sprocket adapter from Sportman Flyer (a very nice looking adapter) and an 80T, #40 chain sprocket. The 9T output clutch sprocket would give me a little extra torque, that I believe I'd appreciate for the 'git-go'.

    As stated, ANY MORE INPUT would be greatly appreciated. I'm a total newb to this and I'm worried about 'stumbling', and throwing parts and money....away. Thanks again landuse
  8. landuse

    landuse Member

    Sorry about the #40 chain sprocket tooth brain fart moment. I was just thinking...because you are putting this rear sprocket on a trike, you should have space for quite a large sprocket on the back, so a 80T or higher might be feasable. I am just a bit worrie about how you are going to attach it to the wheel, as well as the weight of such a large sprocket. It is not going to be light. Unfortunately I have never attached sprockets to bicycles, so I cannot give you any help there

    Hopefully someone else here will give you some more help.