More take off?

[kartnewbie27e]

I just switched for 13" tires to 15" tires and the take off dropped a lot.

I've never counted the size of the drive sprocket on my kart, but the engine sprocket is 12 teeth. In theory, if I put a bigger drive sprocket on it, it'll have better acceleration, right?

I just need something that can handle the trails without switching to a live axle and TC set up.

 

[supermanotorious]

you need a larger driven sprocket which will also sacrifice some top end

 

[Half-breeder]

Driven=axle... For a 12T clutch w/ 15's... IMO, a 72T(at the axle) will put you on the borderline of 'safe' for your clutch(may still be too little... depending on total weight). You 'may' need to fab a JShaft.

1wheel wonders are not good for offroading or anyplace where traction is needed vs the 'drag' of 3 'other' wheels... IMO, Their OK for hard packed n trail type terrain ... but you 'may' wanna invest some time on the advantages of live axle... especially if youre plannin on runnin more off the pavement vs on.

 

[landuse]

Don't increase the engine tooth count. That will just compound the problem. You need to increase the axle sprocket tooth count.

 

[Doc Sprocket]

Larger AXLE sprocket, as already stated. Now... The math looks like this: Everything is a ratio, and everything is relative, sooo-

When you increase (or decrease) tire size, you need to compensate the gearing by the same factor. In your case, you went from 13" to 15". That is an increase in size of about 15%. So in turn, you would increase your gear reduction by the same factor. If, for example, you have a 60T axle sprocket, a 15% increase would work out to 69T. Since 69T is an odd size, move up to the next larger available, generally 72T.

That is the rule of thumb in order to maintain the same performance and speed. Do keep in mind that such a rule of thumb does not account for inertia, mass, rolling resistance etc, so it's better to err on the side of higher reduction, to ensure that the results are acceptable. So you'd go from the 69T mathematical result to the 72T actual, and not 65T for example.

You can also apply the same math to the overall redux ratio and work it that way, if you so desire. Let's suppose that your current ratio is 6:1. Add 15% to that, and you get 6.9:1. Figure out a sprocket combination that gets you 6.9:1 or slightly greater (again, 10T and 69T theoretically) and you're good to go.

 

[firemanjim]

I would just drop to a 10 tooth clutch.... He probably has a 72 tooth driven, giving him 6:1..... Dropping to 10 tooth clutch gives him 7.2:1..... Better for the new tire size..... Just my 2 pesos......

 

[OzFab]

That depends on chain pitch; a 10t clutch for a 3/4" shaft is usually #40/41 pitch, #35 is 12t. If he's using #35 chain, it's not gonna be easy finding a 10t clutch...

 

[firemanjim]

I'm betting he has 40-41.....

 

[Half-breeder]

I'm betting he has 40-41.....

... I saw the word 'betting'... hehe... Im willing to bet he's running #35(because of the 12T clutch)... on a 'norm' 12T=#35 and 10T=#40-41.

'If' he does run a 40-41... not too sure if he'll get a 72T in a 15" diameter(I only have 60T in 40-41 chain... and it's bigger than the #35 72T... so I can only imagine the size of one of those critters).