Chain size

[piddleguy]

Just starting building the first off road buggy in about 10 years for the grand kids. I'll post pics as I move along, but planning on spending a couple of months (Christmas present) to finish. I have an old auto diff that came out of some auto from Japan. I was saving it for a Model T project, but right now this is more important. It is made for an IRS and is small and light weight. A VW half shaft will bolt up easy with a small adapter plate and the input for the diff uses a 4 bolt flange. I'm planning on running between a 10 to 13 hp engine with a TC, mounting a sprocket on the input of the diff. and running that from a jack shaft. What size chain should I use. I'm not sure what the ratings are for the sizes. I'm thinking that a 35 is too small. I'm planning on somewhere around a 5 or 6 to 1 on the sprockets, and the diff will give me about 4 to 1 after that. The TC should help some on the other end of the Jack shaft. I'm planning on 3 wheeler size tires on the rear. There should be enough torque to snap the 35, I'm not sure about 40, and the sprocket size for a 50 would make the 5 or 6 to 1 hard to fit. Not looking for fast, safe with lots of suspension travel is a much better option. Have 2 hydraulic calipers for brakes.

Help...

 

[Bluethunder3320]

first off welcome to the forums.

second, how fast do you want this to go? well im not asking how old your grand children are, but if they are young, a 13 horse and a TC has the power of a large riding lawn mower.

all that power to the ground with a TC can get you well over 50mph in a good sized cart.

the brakes sound very good and safe. hydraulic is by far the best method.

a differential is not too common for go karts, but used in high performance racing. it will make your tires spin out off road but turn better on road.

personally, if i were building a go kart for a young one, id use a 3-5 horse engine.
in some cases 2 horse can be sufficient.

 

[redsox985]

With that ratio, it will go no where. Remember, ratios are multiplied, not added. That could be a 24:1 ratio if you have a 4:1 diff. With the motor at WOT, governed for the kids, at 3600 rpm, that a final wheel rpm of 150 with the TC running at 1:1 not to mention it starts at about 2.5:1. With 150 rpm and say, 20" atv tires, that's 9420 in/min or 8.9 mi/hr at WOT and the motor singing.

 

[piddleguy]

Learning already: Sounds like my sprockets should have a reduction of maybe 2 or 3 to one. If I understand correctly, that should give a more realistic final ratio around 8 or 12 to one. Speed wise, 15 to 20 mph is more than enough to keep them busy, but my land (20 acres) is kind of rough, with lots of rolling hills and bumps. With a final drive ratio of 8 or 12 to one, the size 35 chain may be large enough, but I would probably go with a 40 or 50 (I like to over-engineer). For the experts out there, would a 8 hp or so work.

Thanks already

 

[piddleguy]

Probably should mention, this is a 2 seater.

 

[redsox985]

Most production 2 seaters have 5-8hp. There's a speed calculator on this site but there are more accurate ones elsewhere on the internet. For offroading, an open differential will cause nightmares with one wheel grabbing and not moving while the other spins freely. Just play around with a speed calculator until you get a good number. 40 is stronger than 35 and if your ratios are 3ish:1 they will be a reasonable size. I have a 54 tooth sprocket in 40 chain and it's under 8in o.d.