Whaddaya guys think? This seems to be a source of confusion for many people in karting.

Let's say for example that you are on a 12 tooth front sprocket and a 84 tooth rear sprocket.

You now switch the front sprocket to an 11 tooth and the rear sprocket to a 77.

Both sets of gears have the exact same ratio:
84/12 = 7.00
77/11 = 7.00

Will there be any noticeable difference now that you're on 11/77 compared to when you were on 12/84?

There will be differences. How important, that's another question.

The more teeth you have on the driver (and the rear), the less wear on the sprocket and chain because more teeth/links are engaged at any time. That affects reliability.

The larger the rear sprocket, the more likely it is to hit something and end a race. That hurts reliability, offsetting the benefits from having more teeth engaged.

The less teeth you have (total), the shorter the chain can be. That means less mass to accelerate.

Also if you have more teeth on the front sprocket, the chain rolls over the front sprocket easier.

true true....


Something to take note of especially at bumpy tracks and tracks with interesting curbs


And the sprockets will be smaller as well so less mass there too... remaining super-picky the chain will be moving faster if you're running a smaller sprocket combo so it'll experience a minute increase in resistance from aero resistance.

yeh it can become a bit of an issue if you go too small on the front.

Of course all these issues effect performance (in the speed-sense rather than reliability) pretty much in untraceable amounts, for example having the chain in good condition and properly lubed is already far more important for pace than choosing a different sprocket combo with the same ratio.... reliability is by far the more important thing to consider, and the no.1 thing there is rear sprocket size. Any other differences if you run the same ratio with different sprockets?

Performance wise, same ratio, different sprockets = different power range delivery.
high speed track I tend to use bigger front gear. power come smoothly and most time can throttle early too.

drivers with a heavy throttle foot, I'll only give bigger front gear. Smooth drivers have an option to test smaller front gear.

RocK, care to elaborate on why there is a different power range delivery, and how exactly is it different?

I can by verbal with hand signal
but i dont know how to put in text. let me try and hope you get me.

with 84/12 the crankshaft rotate less then 77/11. by rotating less with the same load, it takes more torque to do it. or i should say it waste engine torque. so for driving it is less torquey. so you can apply throttle early without breaking tyre traction.

77/11 = 7.00
84/12 = 7.00

will still have the same top speed/rpm at the end of the straight.
you get me Mikko

But the crankshaft will be rotating the exact same speed and amount won't it - for example like you said:


So say at 107kph you are at 14,000 RPM. The crankshaft is moving at exactly the same speed in both cases (11 or 12 tooth front). Also early on say at 6,000rpm you are at exactly the same speed and RPM in both cases, so how can there be a difference in how the power goes down?

If the power delivery was different surely we would reach a different top speed?


Nope.

Hmm maybe shouldn't say it rotate less or more.
Thing about engine load. Takes more torque to make 1 full rotation with bigger front gear.
meaning less torque available, meaning smoother power delivery.

meaning Im just full of it. forget what i posted before..

I've also been told that different front sprockets (same ratio) can affect pull off of corners.

TJ,

Tht's what Rock is trying to explain....

Put it simply - whilst both ratio gives u the same ending ( top speed ), the manner how u get there differs! The bigger front pinion should give u a better initial response, me thinks.

Do i make sense?

Tell you guys,

Why don't you guys go to the track this weekend and try it out? Then we'll have a consolidated answer by monday.

Can you explain why a bigger drive sprocket would give better initial response?

If it's because of the "leverage" you get on a larger front sprocket which allows it to initially pull harder remember that we aren't accelerating the engine, but the engine is accelerating the kart - any leverage action doesn't work because the chain isn't pulling the engine, the engine is rotating the crankshaft, which has a sprocket attached to it which is attached to the rear axle by another sprocket and the chain. The size of that sprocket within reasonable sizes shouldn't make any difference (other than unmeasurable ones in load from heavier/lighter sprockets+chain and different chain wrap, and the wear differences) if the ratio is kept the same.

The leverage action where torque occurs in an engine is on the down-stroke of the piston, which pushes down the conrod, which rotates the crankshaft. The size of the front front sprocket does not come into play - the engine doesn't take leverage from the outside of the front sprocket, only on the crankshaft when it spins it.

The reason we have sprockets and a chain to connect the engine to the axle is because we need a reduction in the rotation speed - if it was a 1:1 ratio there wouldn't be enough torque to accelerate the kart. With a 7:1 ratio for example we create a torque multiplier giving the engine enough grunt to move the kart forward.

Here's one way to visualize it - say we do use a 1:1 ratio and now both our front and rear sprockets are the same. Now we have a 12 front and a 12 rear... now change that to a 70 front and a 70 rear - why will there be a difference in the way the power is transfered to the rear axle?

I have always thought that a ratio is a ratio and the only reason you change from say a 12 to a 13 is your rear sprocket is getting a bit too big for comfort. I've yet to read anyone explain the theory behind why different sprockets with the same ratio would provide different results, but many feel that it does. I should add that I've also never tried the same ratio with different sets of sprockets back-to-back before, simply because I don't see the point - but I am interested to find out why there would be a difference

Daniel: the only way to make that work would be to make it a blind test.

Mikko,

Not a blind test of course mate. Just tell your mechanic what you want to do and let him surprise you.

Some info from reputable sources:


and