Father daughter rebuilding my childhood cart

[Knight]

While looking for some info, I came across this site it's great. I am sure I will need some advice. My childhood cart I think is a mid 60's rupp but I don't know for sure? It's got a split frame with a small bit of travel and 4 springs behind the seat. Anyway just bought a new harbor freight 212 cc. Predator, after what seams to be good over all reviews. Now I need a tire,clutch,sprocket combo to keep the speed low enough for a 10 yr old girl. It will be an off road yard cart, with some running time on a 5 mile stretch of abandon train tracks. I am worried about rear sprocket ground clearance from 2" to 3" rocks. I do have the original (I think) 5" rims I would like to use. I'm thinking a 10 tooth clutch, big sprocket and taller tire with hopefully giving me some sprocket to ground clearance. Any thoughts greatly appreciated. Pictures to come once I figure out how? Lol

 

[OzFab]

Here's your problem: The bigger the tyres the bigger the sprocket needs to be to retain the correct gearing.

I think you may need to invest in a jackshaft; that way you can gear it as low as you like & have a smaller axle sprocket to provide the necessary ground clearance.

 

[Knight]

Ok that sounds like my answer. My old tires are
4.10/3.50x5 that are about 11" tall and 36" around. My cart has a 58 Tooth split gear and hub now. Where can I find a sprocket chart that has sprocket diameter ? How small of a gear can I get? And or tall of a 5" rimmed tire can I get?

 

[landuse]

Ok that sounds like my answer. My old tires are
4.10/3.50x5 that are about 11" tall and 36" around. My cart has a 58 Tooth split gear and hub now. Where can I find a sprocket chart that has sprocket diameter ? How small of a gear can I get? And or tall of a 5" rimmed tire can I get?

Have a look at these charts. They will give you the info you need

Azusa #35 and #40 sprocket diameters
http://www.azusaeng.com/Sprockets/AzSDno35.pdf
http://www.azusaeng.com/Sprockets/AzSDno40.pdf

I would agree with Fabroman about a jackshaft. To gear low enough for your daughter, the rear sprocket would have been larger than your tyre. A jackshaft is probably the only way to go

Oh....and to the forum

 

[Knight]

I have been checking 11 tooth clutch to jack input at 30 to jack output of 11 to axle sprocket of 54 = a 13.3 mph??? with 11" tall tire sound right ? too slow for 10?? no roll cage but NO hills either. With a jack shaft do have to run the more expensive 40/41 type chain and gears or will the 35 chain hold up? thanks again DIY people! Its has been 25+ years since I worked on this cart but glad I keep it! anybody heard of a rupp lancer gt?? all tags and original motor were gone when I go it so this is my best guess as to make. I am in search of a front wheel, mechanically pretty good here but computer illiterate, LOL. I can email pic but to stupid to post #!##!

 

[DaiSan76]

IMHO you should always err on the side of too slow with kids. You can always swap out a jackshaft sprocket for more speed if they complain. Also, it doesn't take a hill to roll a kart. My kid nearly pulled it off on perfectly flat ground with a 10mph kart.

www.youtube.com/watch?v=ulmyEM6QOvI

 

[Doc Sprocket]

For a first time driver (and a kid, too) 13MPH is decent. You can do what I did- build for slow, and regear as the child gains experience and confidence.

 

[Knight]

are my #' s right should it max at 13 mph? I want lots faster as a kid trying hard in dirt and road corners not close to a flip but want to error on caution side! what gears? thanks for video riding surface will be flat or no ride at all.... roll cage in future1

 

[Doc Sprocket]

Actually, my math says it works out to 8.8MPH@3600RPM, with a redux ratio of 13.39:1. That's with 11" tires. With 16" tires, you get a theoretical top end of 12.8 MPH with that ratio, and better ground clearance. I prefer to err on the side of strength, so I would use #40 chain with that much reduction.

 

[Knight]

I like the old cart look with the 5" rim and cant seam to find any tires taller than 11" ? any thoughts ? there cool looking aluminum centers with what used to be chrome outer halves, now painted black still cool , need right gears still, YES like idea of a later FASTER gear swap...maybe I need bigger tires and rims to start ,for ground clearance...

 

[landuse]

I have been checking 11 tooth clutch to jack input at 30 to jack output of 11 to axle sprocket of 54 = a 13.3 mph??? with 11" tall tire sound right ? too slow for 10?? no roll cage but NO hills either. With a jack shaft do have to run the more expensive 40/41 type chain and gears or will the 35 chain hold up? thanks again DIY people! Its has been 25+ years since I worked on this cart but glad I keep it! anybody heard of a rupp lancer gt?? all tags and original motor were gone when I go it so this is my best guess as to make. I am in search of a front wheel, mechanically pretty good here but computer illiterate, LOL. I can email pic but to stupid to post #!##!

Your maths is spot on!! the only problem is that the answer of 13.3 that you came up with is not the speed, but the reduction that you are going to have (13.3:1). Because it is a larger number, you have a low gear ratio. A smaller number means a higher ratio.

Actually, my math says it works out to 8.8MPH@3600RPM, with a redux ratio of 13.39:1. That's with 11" tires. With 16" tires, you get a theoretical top end of 12.8 MPH with that ratio, and better ground clearance. I prefer to err on the side of strength, so I would use #40 chain with that much reduction.

Toystory is spot on with his info

 

[Orange Krate]

Would looove to see some of theis Rupp

 

[OzFab]

Actually, my math says it works out to 8.8MPH@3600RPM, with a redux ratio of 13.39:1. That's with 11" tires. With 16" tires, you get a theoretical top end of 12.8 MPH with that ratio, and better ground clearance. I prefer to err on the side of strength, so I would use #40 chain with that much reduction.

Your maths is spot on!! the only problem is that the answer of 13.3 that you came up with is not the speed, but the reduction that you are going to have (13.3:1). Because it is a larger number, you have a low gear ratio. A smaller number means a higher ratio.

Toystory is spot on with his info

For future reference, here's a jackshaft calculator (not that you need it) & our speed calculator

 

[Knight]

thank you for all the help but still no sure which gears to order...a 100 tooth axle sprocket and 11 clutch is 9.09 ratio with 11" tires at 3600rpm should go 13 mph (my rough goal here) an 11 tooth clutch to a 27 tooth jack shaft input to a 15 jack shaft output to my 56 rear gear is a 9.16 ratio with 11" tall tires should be close right???? thanks again I dont want wrong one s this wont be cheap

 

[OzFab]

11t clutch
19t JS in
11t JS out
56t axle
gives you 8.79:1 which, according to the speed calc, also gives you 13mph.

Smaller sprockets are usually preferable for space reasons

 

[Knight]

before pictures, hoping for some after pics some day

I looking for one of these rims, a front If anyone know where to find one let me know.my new motor just showed up $ 116 delivered to the my door awesome deal. cant find a 19 tooth jack shaft gear thou, I did find one for a 1" shaft and may try to put in a 1" o.d. 3/4 I.d. bushing

 

[Doc Sprocket]

I wish I did. I have a broken front that needs replacing. Same ones!

 

[OzFab]

Now we wait & see who sells what to whom

 

[Knight]

Well it seams I have 3, needing one front, between us there seams like a set, do you need some extra Xmas $$$...??? Shipping from Ontario, Ca. Shouldn't be too bad...lol

 

[Doc Sprocket]

Shipping TO Ontario (via USPS) would be even cheaper!!!