2.5 Build, gear ratio suggestions?

Discussion in 'Push Trailers' started by Rgvkid, May 16, 2009.

  1. Rgvkid

    Rgvkid Member

    Im finally getting back to my trailer build but this time im going with the 2.5HP. Since some of you have already had experience with the 2.5, I wanted to know what you would suggest for gear ratios? Im planning on setting it up with a jack shaft to better dial in the gearing.

    So far i have the 2.5 HP HF $80. Im going to try out this 10" Kenda tire and rim i got from the Mini Moto shop for $20. The guy said the tire should last well over 2000 miles. I'll have to figure out how to mount the sprocket or i might swap it over to the Harbor freight $5 rim which might be easier to mount a hub to. I still need a clutch, Jack shaft, and sprockets.

    I weigh 150lbs and my commute will be flat for about 14 miles and last 2miles up a pretty steep hill with some switch backs. Eventually i want to setup a rear trailer brake to help out on the downhill. I'll post pics through the build.

    Here is the wheel.

    Attached Files:

    Last edited: May 16, 2009

  2. s_beaudry

    s_beaudry Member


    My two pushers I have built had a 6.5hp and a 5.5hp engine. Both used the same gearing wich is a 12 tooth clutch sprocket and a 60 tooth rear wheel sprocket.

    I hit 40+ mph one time with a gps unit showing me the speed. I am not one for top speed though, just tested it out that one time. Torque wise though, this had plenty of power for me with NO pedaling what so ever even startiing off going up a steep hill.

    I weigh in at 224lbs myself just to give you an idea of power. Now granted the 2.5hp you have will not be as powerful, but this should work well for you, even with no jackshaft setup.

    Anyone else have any thoughts on gearing??

    Where are you at ZNsaneryder?? Chime in here...
  3. Rgvkid

    Rgvkid Member

    I went through most of the previous push trailer threads but most are gearing ratios for the 6.5 so i just wanted to get some first hand experiences with the 2.5. I'd like to keep a cruising speed at 30mph but would like to be able to hit 35mph max if i have to get out of a tight spot.

    Thanks Beaudry.
  4. ZnsaneRyder

    ZnsaneRyder Member

    SWEET TIRE! That should last.

    Over 35mph is asking a lot out of that little 2.5. It may go 40, but it's a tradeoff between torque and speed.

    I calculated some ratios to try for examples. 3:1, 3.5:1, 4:1, 5:1

    Your speed with a small 10" tire according to the gear ratio calculator at 4200RPM would be:
    25Mph with 5:1
    31mph for 4:1
    36mph for 3.5:1
    42mph for 3:1

    I'd recommend the 4:1 or 3.5:1 ratio (your choice of course) for a combination of speed and power. These engines max out power stock at around 4200RPM, so that's why I used that number, instead of 3600.

    I calculated sprockets for your jackshaft setup for 36MPH (3.5:1 ratio in this example) to be:
    10T Clutch
    14T Jackshaft Sprocket1
    12T Jackshaft Sprocket2
    30T Wheel Sprocket

    This is assuming #40 chain, because a #35 chain clutch as 12 teeth instead of 10. I chose #40 because it's easiest to get sprockets for at Tractor Supply. If you went to #35 chain, change the Jackshaft Sprocket1 to 17T.
    Last edited: May 16, 2009
  5. Rgvkid

    Rgvkid Member

    I just ordered the Hillard Extreme Clutch W/10 tooth #40 chain per Znsanes suggestions on his clutch experience.

    I found that Northern tool has it for $34.99, and MFG Supply has it for $42.99.
    Northern tool doesn't carry the replacement bushing for that clutch but MFG does for $8.99 plus $6.99 shipping for the bearing alone. Northern tools Shipping would have been $7.99 for the clutch alone. It would have come out to the same price if i had just odered them both from MFG. So with shipping from both it would not have been worth buying the clutch and replacement bushing seperatly even though the clutch was $8.00 cheaper from Northern tool.

    Next, i need the rear sprocket. I might just go straight sprocket for now and make the trailer so i can fit a jack shaft later on. I think I'll go with a 40 tooth sprocket. I'll have to figure out how im going to go about to mount the sprocket or if i will be able to use a hub.
  6. Rgvkid

    Rgvkid Member

    Just noticed your post Znsane, Thank you very much for taking the time to give your insight.
    Last edited: May 16, 2009
  7. ZnsaneRyder

    ZnsaneRyder Member

    Did you already order your clutch, or are you still in process? Don't finalize your order just yet.
  8. Rgvkid

    Rgvkid Member

    Already confirmed the purchase. Should i try and cancel it?
  9. ZnsaneRyder

    ZnsaneRyder Member

    If you already ordered, don't worry about it, more hassle than it's worth.

    I already PM'ed you, but I'll also mention here.

    First off, the Hillard Extreme Duty is an excellent clutch!

    However, the HF Chinamotor has a 5/8" crankshaft that's actually a few thousandths smaller than a true 5/8 inch. This causes the Hilliard to wobble slightly because it has a built-in keyway, and no set screws. I recommend when you get your new clutch, wedge something small made of metal in between the gap of the crankshaft and hub-hole to take up the space. My brother broke his clutch keyway because of that play on the shaft. We discovered if you can wedge a thin piece of metal in there, it will stay put. However, my bro's clutch hub keyway was already broken, so we are changing to a cheap clutch with set screws. Other than that, the Hillard gave NO problems with this engine.

    I wanted to get that out, before you use your new clutch, so you won't break the keyway on yours.

    It's only an issue discovered on the HF 2.5, because of the Chinese not making the shaft size truly 5/8". I never had an issue on the 6.5 with a 3/4" shaft, but it also fits snug. I'm sure your clutch will do just fine on your HF 2.5 as long as you take up the small gap. ALL brand clutches have that gap, but most have Set-Screws. Now it is possible to thread a hole in the Hilliard hub for a set-screw, if you have a threader.
    Last edited: May 17, 2009
  10. 5-7HEAVEN

    5-7HEAVEN Guest

    Sorry I can't figure an inexpensive way to mount a sprocket. The hub looks like a front-mounted or freewheeling hub.

    It might be cheaper to use a wheel which will easily accept a sprocket.
  11. Rgvkid

    Rgvkid Member

    Hey 5-7 how you been? Yah i think im going to try that tire on the harbor freight rim since that rim already ahs the 4 bolt pattern. I was thinking of maybe putting the rim i just bought on my friends lathe and turning down the spokes to flatten it out and maybe a hub will sit better.
  12. ZnsaneRyder

    ZnsaneRyder Member

    Rgvkid, It would be cool if you could lathe, and custom make a hub and sprocket fit that wheel.

    However, even if not, the HF rim has a 4-bolt "indus" pattern, and mfgsupply and others have a hub that is made to mount sprockets to that.

    That's the biggest challenge with a push trailer IMO is getting the sprocket and wheel(s) coupled together. I got lucky with my pocketbike wheel, because it usually costs a bit of $$$ for the whole setup meaning axle/bearings/sprocket/rim/tire. Getting a bunch of compatible parts and trying to save $$$ is the challenging part of these projects.

    Speaking of rim and sprocket, 5-7HEAVEN, did you get your sprocket for your bike rim yet?

    Attached Files: