Zach, I appreciate the thought process behind this and would love to hear as you have more data to analyze.
Like you, on faster flowing tracks (New Castle) I found that gear changes had very little effect on overall lap time once I’m ballpark on gearing, but my home track, in the right conditions I can change 1 tooth and benefit .2 in lap time. That track is much tighter and the low end RPM range becomes a bigger thing to stay away from.
I’m just trying to make sense of it all. I have pretty good handle on chassis setup (I think ha), but my weak point is definitely engine/carb setup. I don’t quite have that “feel” for what makes it happy. But if I have data that shows something good/bad then I have something to reference off of and bridge the gap until the “feel” comes to me.
I might be off in left field with the theory. But I can’t help but to be curious on if I’m onto something or not. I guess time will tell.
What’s your home track? With MCC it seems to be pretty easy to get in the ball park. But I’d be curious to see what’s causing your home track to be so knife edge.
Here’s the math channel. Scaling is just what RPM range your motor works in. But make sure the Sampling, Filter, Decimal are all set to those parameters.
Under the Channels Report page, add the channel to see the average for every lap in the session. Make sure you select “Average if not zero” otherwise the number will be way off in left field because it’ll sample when not on throttle.
Another little trick is you can use it to tell when on throttle and off throttle. It’s not perfect, bumps can sometimes make it go crazy, but it’s pretty accurate to see when picking up the throttle through corners.
(Mods, if you want to move this to the Data subforum that’s fine. It’s sort of going on a tangent to KA’s)
Please define your terms. I am pretty decent with math. Took Physics in college.
IF = if (data fits parameters)
(GE = What does this equal
times (
GPS_LonAcc,0 - I get Longitudinal Acceleration, what is the “,0”, does that mean the function ignores values of zero?
,RPM,0) - does this mean that the function ignores values of zero in its calculation?
I still think taking an average is the wrong approach. A better approach might be how much time is spent at a given RPM. That way you can toss the data at extreme high and low and focus on where you spend the most time at. For example, if you you stay in the power band for 80% of the track, then who cares if 10% is below and 10% is above such that you sacrifice one slow corner and the end of a high speed straight to gain an advantage on 80% of the track?
I didn’t write the channel, I was given it by a friend. Someone smarter than I am ha. I basically told him what my idea was and this is what he came up with and told me to try it.
The approach is similar. The idea is to spend the most time in the most power possible. The method of figuring out what that ideal ratio is completely open for debate and options. I’m mostly trying to get my thought process out there and bounce around ideas for how to A) make it work, and B) if there’s better options.
question…
Assuming we can arrive at the same final ratio is there an advantage / disadvantage to using a larger or smaller sprocket? Say 10/70 vs 11/77 or 12/84, both are 7.0 final?
Some things to consider are that a larger rear sprocket means more susceptible to having chain knocked off from contact with curbs or road surface if you should drop a wheel off he edge of the track. You can remedy that with chain guards on either side of the rear sprocket. Secondly, although not as impactful as losing a chain is going with a smaller gear set reduces rotating mass. A larger rotating mass takes more power to spool up and may slightly reduce acceleration. More of an impact in lower horsepower classes.
The formula IF(GE(GPS_Lon,0),RPM,0) translates to:
if the longitudinal acceleration is greater than zero (positive acceleration), display RPM.
If the acceleration is less than zero or negative ( deacceleration/braking), do not display RPM.
There really is no effect in the rotating mass, at least not from what most of us would be able to tell. I have gone both ways on my daughter’s kart. Two things that I remember reading before between the smaller or larger size sprockets is if using the smaller sprockets, you end up with the chain in contact longer with the sprockets, which could create more drag (possibly reason why no difference with the rotating mass). However, I think the more important aspect is the angle of pull on the chain, and having a better torque for pulling the chain. I will have to see if I can find that and post it here.
Of course, I can be way off base and remember it wrong.
you’re correct, you always want to run the largest possible front sprocket as the tighter the radius the chain needs to turn around that front sprocket the more loss of energy.
Thanks for confirmation.
I think there’s also less wear on the chain and bearing with the larger sprocket.
To Tony,
Thank you for the breakdown of the math channel. It makes more sense now, but still ignores where most of you the RPM range is spent. Sure, it influences the average, but does not tell you where the meat of your power is being used. Gear too low and your average spikes, gear too high and your average plummets. Knowing how much time you spend in the power band tells you that you are extracting every last bit of energy from your engine.
To Michael and Andy,
How is that a loss of energy? I can agree it may wear the chain faster, but the only energy lost could be friction. The chain has to bend around a smaller radius, but that is what chain lube is for. To reduce friction. In either case, I think the loss from friction or rotating mass is extremely minimal compared to the risk of derailing your sprocket because you nicked a curb, because your driven sprocket was too close to the tire’s diameter. I would say that a 10 or 11 is about as far as you would want to go on a 2 stroke. 4 Strokes have a different torque range, so a larger drive sprocket is acceptable, because the gear ratio is shorter.
A ratio is a ratio. Any drivetrain loss from smaller front sprockets, longer or shorter chains, or whatever is all negligible.
Use the histogram plot in RSA to see what rpm range you spend the most time in.
My main concern when gearing is clearing curbs and the size of the rear sprocket being too large. I only use a 10 or 11 tooth on our KA, and it’s typically track dependent. The rotating mass between possible rear sprocket sizes is negligible because there isn’t much difference between the weights, such as the loss on the front sprocket between a 10 and 11 isn’t different enough. Typically, the tracks that we run on (NTK, HCKC, GCKI) we use the 10 tooth because the rear sprocket would be too big on the 11 tooth. I run the 11 tooth mostly at Speedsportz, but have ran the 10 there without any loss of lap time.
Between a 10 tooth and an 11 tooth front sprocket, you won’t see any of the potential negatives. You probably won’t see them until you have a much bigger size difference in the front sprocket.
Does anyone run a 9 tooth sprocket? I just ordered one to throw on my sons micro swift. They normally run a 10/85-88. I run a 10/84 on my ka and have thought about dropping to a 9 as well to shrink the rear sprocket and gain some clearance at the chain guard.
Do they make a 9-tooth for the KA?
I haven’t seen one made. The homologation only states 10 through 13.
Are we talking #35 or 219 chain? They make a #35 9 tooth sprocket but not a 88 tooth. They make a 88 tooth 219 sprocket but not a 9 tooth for the engine.
I need some clarity on the chain size.
It looks like they do make One for x30/ka. It requires a special Starter nut and washer to clear the chain.
#219 (20 characters)
