16:64 or 20:80

knighty

Member
Hi Folks, about 2 years ago we used to run 20:80, then I migrated over to running 16:64, this is using the 219 style chain, my main logic was it made the rear sprocket much smaller and the reduced inertia would allow the rear axle to spin up quicker - theoretically.......we back-to-back tested in detail at our local circuit, and I really couldn't deduce much difference in lap-times, but one nice benefit was the smaller 64 axle sprocket was now above the chassis rails, so it would not hit the kerbs or cause damage or scrubb of speed when kerbing.......so we ran 16 drivers ever since......3 race wins, 1 championship, 6 poles and 15 podiums later I'm re-questioning my sanity, as others have achieved more.......as the dyno is saying a 20:80 accelerates the dyno-flywheel quicker than a 16:64......by about 0.05 seconds in a 3 second pull from 2600-6100rpm.

We race on very start-stop type kart circuits, not ovals........based on your experience whats your feeling, 16 or 20?

Admittedly when we tested it my son was 9 years old, not bad, but not great either......now he is 11 and slowly becoming a bit of a driving weapon, as we won last week (see link below, kart 88 in the 2nd feature down) .......I will test both again on track, but any opinions welcome in the meantime.

http://www.buckmoreparkkartclub.co.uk/results-reports/race-reports/bpkc-summer-champs-r7/

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Oman

Member
The larger gears themselves should have a larger moment of inertia so should be slower on the dyno so rule them out. I would be looking into the chain as the source of the difference if it is repeatable. Either the physics of the chain accelleration around the smaller sprockets or the friction is greater when the chain is turning tighter radii. my 2c
 

Kart43

Member
"by about 0.05 seconds in a 3 second pull from 2600-6100rpm." How many pulls on the Dyno to arrive at this data?
 

95 shaw

Premium User
There were several gearing threads over the last year on this subject. Several theories are discussed. If your dyno sampling rate is quick enough, might be interesting which part of the rpm range was the time picked up. Was some lost elsewhere in the pull? Will that translate to ontrack performance?

All interesting questions. Some were beat nearly to death in the threads.
 
166 views and no replies!........any opinions welcome.
One possible reason is because your results on the dyno are the OPPOSITE of what is preached by most in the karting world. Most all will tell you that the smaller driver will "accelerate" quicker. Your results show this not to be the case. Your results are similar to mine. Other variables such as clutch used and chain length and others seem to be a factor more so than driver size in my experience. I am in the minority however. Keep up the testing. Good luck.
 

knighty

Member
Im starting to think that less driver teeth logically means more contact pressure per tooth, therefore more friction for smaller drivers.......considering half is wrapped by chain, we are comparing 8 with 10, so its in the order of approx 20% more friction for the 16T driver.

The angular acelleration of the flywheel is noticably higher with the 20T driver compared to the 16T........but the upside is the axle sprocket inertia is greatly reduced......i will continue my testing......most people here all use a 19T driver......it certainly works.
 

manyfunnies

New member
Post all ramp times. Your data could be statistically inconclusive. Also you are finding a situation where an inertia dyno has a weakness and inaccuracy. You are changing the system inertia and thus power wont be represented accordingly.

You will never get an answer though. No one here knows anything about this. They all have their theories but know nothing about what they are talking about. I believe in science and physics not theories.
 

flattop1

Dawg 89
Wow Mannie way to build everyone up.(no one here knows) Not just some , everyone , but you.
I'm sure I don't know the answer except .05 in three seconds does not correlate to .05 every three seconds on the track.
I also know there are some here who do know the answer.
Looking forward to the highly scientific answer.
 
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Kart43

Member
Post all ramp times. Your data could be statistically inconclusive. Also you are finding a situation where an inertia dyno has a weakness and inaccuracy. You are changing the system inertia and thus power wont be represented accordingly.

You will never get an answer though. No one here knows anything about this. They all have their theories but know nothing about what they are talking about. I believe in science and physics not theories.
We know you are going to tell us the answer because you are a believer .....
 

Mr angery

New member
Are you basing your results of this off of engine rpm or wheel speed ?
Looks like engine rpm to me. For acceleration I would thank wheel speed changes with a min 4x resolution would work better.

Based off of engine rpm
2600 rpm = 43.333 rpm per second .1 of a second is 4.3 .05 is 2.15 rpm

6100 rpm =101.666 rpm per second .1of a second is 10.16 .05 is 5.08 rpm


Now how accurately are you measuring your rpm start stop points ?
Or how is your software calculating them and to what accuracy

How about some clutch slippage added in on the bigger driver vs smaller . any slippage will rpm faster this giving you false acceleration based off of engine rpm.
We only need to slip the clutch 2.15 revolutions to pick up .05 of a second during the entire pull.And

For a minimum I would want direct drive with at least 4x on the wheel for more like 15 seconds with wheel coast down ### pre and post.

But in the end I don't need any of this info as I already know how drivers work in racing based off of track results.
When this comes up with people ,I say hay you put a 20 foot diameter rear sprocket on your kart with the same ratio as my 1 foot sprocket and tell me who's going to accelerate faster
 

manyfunnies

New member
Wow Mannie way to build everyone up.(no one here knows) Not just some , everyone , but you.
I'm sure I don't know the answer except .05 in three seconds does not correlate to .05 every three seconds on the track.
I also know there are some here who do know the answer.
Looking forward to the highly scientific answer.
find someone who knows why bigger drivers/smaller drivers are better in certain situations. i have never seen anyone here come up with a solid reason why other than they just are.
 

Kart43

Member
find someone who knows why bigger drivers/smaller drivers are better in certain situations. i have never seen anyone here come up with a solid reason why other than they just are.
You have the floor, many await your statements, as so many before you have been incorrect.
 

flattop1

Dawg 89
I am saying this with a smile.
we don't race dyno's.
We need more data.
now along with what Mr. Angry posted.
I wonder has the moment of inertia been recalculated to add the difference of sprocket and chain length as a weight change could affect data acquired.
 

knighty

Member
Oman - the chain, yes - I think you have a good point there.......I read the article on the maxtorque site about boiling the chain in 30wt oil mixed with paraffin wax, I will give that a try and dyno it, as it will cost peanuts to do........apparently the was seals the oil in between the pin and roller.......makes sense to me

Manyfunnies - I believe the data is from wheel speed.

Flattop1, the inertia was certainly not re-calculated to allow for the bigger sprockets, but you do raise a very valid point. I cant post every minuscule bit of data, the acceleration time was recorded via setting the SportDevices software average HP boundaries, so it automatically records the acceleration duration, for me its more than accurate enough.....this is also my favorite saying: "there is not a chequered flag in the dyno".....a dyno is for indication only......seat-of-the-pants dyno has the final say.

With that in mind I am going to take a sabbatical from the 16T drivers for a while, and use 19T drivers.......I have also spoken to a few well informed friends that previously tried 16T and said it lacked the edge an 18T or 19T driver gave them, but a 16T is well worth using on a really tight & twisty track, I suspect as the chassis flexes, it warps the chain less, which is not such a problem on faster tracks.......which I think is why we go well on a tight & twisty track, but struggle a bit on faster tracks, whereby we get blasted on the straight, and I have had enough of it!........so probably 16T for slower tracks and 19T for faster tracks.

I will give it a go and report back......stay calm everyone!
 
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