Noob with Noob gear and tire questions

[wooley]

My grandson has had his Carter 2235-1015, 5hp kart for 4 days and it's time to get the cut-off wheel and welder out. I would like to
1. Improve traction in the sand with wider tires and a live axle.
2. ~Halve the top speed and increase the low end.

Partly because I'm clueless, I'm not entirely sure where to start.
The kart has 14.5x7-6 knobby tires on all four corners. I’d like something wider and better in the sand. I haven’t found anything wider for 6-inch rims though. Would it help to move up to 18x9.50-8? That will compound my problem of reducing the speed and increasing the torque though. Is there a wider than 7 inch tire out there for 6-inch rims? Or something you recommend?

The drive train is a centrifugal belt clutch to a 5-¾ inch pulley on the 3/4-inch jackshaft. The other end of the jackshaft is a 12-tooth drive gear to a 60-tooth driven sprocket. The chain is #41. I found the gearing calculator posted by someone (thanks!) but hope that one of you might know what parts are available and compatible to gear this thing down. If I mount a larger driven pulley on the engine side of the jackshaft and a 10-tooth drive sprocket on the other end of the jackshaft what would be the result?

I haven’t found anything about changing from a belt clutch to a sprocket clutch and I’m not sure what that would do to the alignment of everything but it may make it easier to reduce the gearing.

I’ve looked at several threads for converting to a live axle and think there will one and some pillow blocks and bearings in the mail this week.

If anyone has any suggestions I would welcome them.

 

[oldyeller]

I am not sure if you have enough room but I would try going with a bigger sprocket on your jackshaft..I just changed from a 12 tooth to 15 tooth on my son's go kart and it made a huge difference in low end power..

 

[j.concepcion54321]

its a little pricey but a torque converter will give you the best of both worlds, high speeds, and low end power/good torque.

 

[redsox985]

j.conception, he wants HALF the speed and more low end...no torque converter needed. For lower speed, putting a larger sprocket on the back will help with this, but you will not be able to totally halve it without a jack shaft. For some better grip in the rear, maybe try some tires like the ones below. I was going to suggest sand paddle tires, but they're all too big.

http://www.bmikarts.com/item/16x8-7-Trail-Wolf-Tire-260028-6247

 

[jernigan]

You could try doing away with the belt. Installing a old school 12 tooth clutch on the motor and a 19 tooth sprocket on the jackshaft. Leave the jackshaft to drivewheel sprockets alone. That combo usually gives me more than enough low end power. I've never had any luck getting real good grip in sand with a single drive wheel. It would be a little bit of work,but if you could find a solid axle you could mount it on pillarbearings right under the bottom and shift the engine and jackshaft over to drive the axle instead of the one drive wheel. Just some ideas to chew on.

 

[r97]

before we work on gear ratios we will need to know what tire you want to use.

the ones redsox suggested are goood, but because you have 6" rims, you will need 7" rims with them, like this:
http://www.bmikarts.com/shop/index....lf+tire+rim&match_criteria=all&x=0&y=0&shop=1

you can also check out:

bmikarts.com

mfgsupply.com

gokartsupply.com

______________________________________________

once you decide on tires we will need to know:

-the size of the new rear tires
-what DIA the pulley on the clutch is
-if you want to switch the belt to a chain

with that information we can suggest what size pulleys and/or sprockets you will need.

 

[wooley]

jerigan a live-axle is first up. I don't really care if we build a new engine mount but does a live-axle have to have the driven sprocket at/near the center? Can all the drive train stay where it is and connect to a somewhat lower live-axle final sprocket next to the left rear tire?

r97 an excellent idea to start at the outside and work in. Does anyone have any experience in dirt/sand on the advantages of a 18x9.5-8 tire like (http://www.bmikarts.com/item/18-Knobby-Tire-Rim-Assembly-260018-105) over a 16x8-7 like (http://www.bmikarts.com/item/16x8-7-Rear-Tire-Tube-&-Rim-260040-6612)?

Is the extra nominal 1.5 inches of width for traction worth the 2-inch height difference for gearing?

 

[redsox985]

Actually, it's best to keep the sprocket as close to a bearing as possible so you don't overload a less supported part.

For tires, look here, go to the rear tire fields, and enter 18 9.5 8. The second option are some nice sand baffles that fit common lawnmower rims. Upgrading to a live axle will help your traction greatly regardless of tires.

I totally missed your photos earlier! You already have a jack shaft which is great for you desired speed reduction. I would upgrade to a high quality cent. clutch and eliminate the belt drive all together due to slippage in the belt. Once you get some tires, we'll help you with the gearing to get the lower speeds and more low end you want.

 

[Odonnellp24]

When I take my truck to the beach I just let the air out of my tires till I get about 10 psi. Should work on a kart, it's the best kind of fix....a free one.

With your tire size You could probably get away with a 72 tooth sprocket and that will knock some of the wind out of your top end. If youre going live axle make sure you get stepped hubs and make sure your keystock matches the cutouts for the axle and wheel.

I totally winged my first live axle build and wasted a bit of coin because I didnt know what all is involved.

 

[redsox985]

If youre going live axle make sure you get stepped hubs

Why is this?

 

[jernigan]

I'll have to agree with redsox985. If you get the sprocket to close to the center the chain could pull on the axle and warp it.

If you could get the sprocket to the inside of the frame though, it would open up a world of rim and tire options

 

[Odonnellp24]

Why is this?

Stepped hubs wont slide up on your axle past a certain point. There is a lip on the axle that is designed to fit on a stepped hub. You slide it on your axle till it stops and bolt it tight and that wheel wont go anywhere. Its the most secure way to attach a wheel.

 

[redsox985]

That's true that it won't slide, but is it worth the additional cost of a new axle that's probably too narrow as is? Putting a small dimple in the axle with a drill and then blue loctiting the set screw in a locking collar will do just fine.

 

[wooley]

I've been hunting for tires as recommended above. But eventually I needed to mow the grass. When I jumped on my little Snapper rear engine rider I took a look at the rear tires. 15x6-6 but the tread area is flat and nearly twice the width of the the 145x70-6 knobbies on the kart now. That's what I'm going with while the kid is still little. Actual height is 14.5 according to my measuring stick and the Carlisle Tire website.

I also found a post on the old minibike forum site that dumbed down gearing to the point that I think I might even understand it. A small collection of jackshaft sprockets is on the way from www.surpluscenter.com. Now I need some chain and a 10-T geared clutch.

Next up is a live axle conversion but hopefully the kid can ride the cart while I build the axle - up to the point I chop off the axle stubs any way. Thanks very much to everyone who contributed to Dave1701's thread for his axle swap.

 

[wooley]

Tonight I got rid of the belt and installed the 10-tooth clutch to a 24-T driven on the jackshaft / 10-T jackshaft drive to the 60-T sprocket and the chains. By then it was too dark to put the kid on it. Tomorrow we'll see what the result was and then on to learning live axles.

 

[jernigan]

Hope everything goes well for you. I just fixed up a manco dingo for my 11 year old step-daughter and live axles are pretty simple to work with. Looking a smaller frame for my 4 year old son now.