Gearing for KZ: help plz (KartKraft)

It appears that I must change gearing on the KZ for Amp. My s2 time is always exactly the same despite my overall laptime getting lower and lower. Since s2 is basically a full throttle straight, I’m guessing I’m spending too long on limiter.
Here’s lap so u can listen. https://youtu.be/cS-J3EuYT-c

How do I change gearing in the KZ? What should I do to start? I am guessing mess with rear sprocket? What am I shooting for? Hit limiter at EOS?

goal is to be 0.0000001 RPM from the limiter on the fastest speed portion in question - as long as that doesn’t hinder your pace elsewhere.

start with the rear sprocket, then play with the front if that doesn’t get you what you need.

Thanks Matt,

So, I’d be removing teeth, correct? Start with rear and take 2 teeth out?

Two teeth is a huge change for a gearbox engine. I normally only go one tooth or less by using a different combo of front and rear sprockets. How long are you tapped out in 6th before braking? A gear change will also change your shift points on the rest of the track. The best way to find the right gear is getting your hands dirty and trying different combinations based on your needs. There will always be some give and take with gearing. Also, make sure you are getting the proper revs out of the engine before making a gear change if the only issue you are having is one straightaway.

Ha! I just realized this is for a game. No need to worry about the revs :wink:

What gear ratio are you running now? In the 4:1 range, one tooth on the axle (+/-) is worth about 100 RPM on the top. So if you’re hitting the limiter right at the end of the straight, you’re going to hit the limiter a little sooner by adding one tooth.
Something to try. Hitting the limiter before the end of the straight might be good. Having that lower gear throughout the rest of the track might be the ticket? You going to get onto the straight quicker and accelerate quicker, that’s got to be good.

Thanks Al,
So the deal is that the second sector is basically a straight. My sector time remains unchanged despite dramatic decrease in overall lap times.
Ergo, my assumption of incorrect gearing.

“Having that lower gear throughout the rest of the track might be the ticket?”

Maybe but I think not. I am currently 4th USA but my s1 time is world #3. My s3 time is consistent with my leaderboard peers. My s2 time is off pace and it has been pegged in exactly the same speed to the hundredth since I was 8th USA.

In order to answer your question about ratio, I will look when I get home. I am guessing I will need to know how many teeth front and back to calculate this?

Thanks Al.

Thanks Scott,
Why not worry about revs? Don’t follow. I appear to be at max rpm.

How long are you tapped out in 6th before braking?

I think 3-5s.

I’ll try 1 tooth rear to start thanks!

That’s about right with a 219 pitch chain.

However the 428 pitch chain with number total of teeth in 20-30 range is a lot different. One tooth is a much bigger jump.

Al,
So I went ahead and changed it from 16 front 25 back to 16/24. It feels like it has a lot more top end.

I am guessing that I could do a half step of some sort by messing with front next? 17/24?
Or does the front make massive changes?

Matt,
So I went ahead and dropped a tooth. It changes things pretty dramatically in terms of flow. I guess that’s the shift points changing.

How do you ascertain wether the change is good?

In absolute terms I lost a tenth as far as optimal is concerned. I was struggling to make the same pace through sector 1 with this different gearing.

But the few times I did make a “decent” s1, the extra oomph down the straight paid dividends. The optimal wasn’t far off.

Bit confused. Accept the slower overall pace and figure out the new rhythm?

1 Like

7/28 = 4.0
8/32 = 4.0
So you’re right, the RPM changes are different with a one tooth change on the axle. Don’t know what I was thinking, I must’ve missed the part about the 430 chain.

I have trouble adjusting from 219 as well. I have some shifter gear Calc sheet that I’ll dig up.

@Bimodal_Rocket you can hold me accountable to this too

Send me a request for "nine sheets"an the Excel spreadsheet at [email protected]
42 pages of karting related utilities. It’s free!

Al, can you walk me through what the spreadsheet says?
Thanks.

:grinning: Nope. Enjoy Ireland. @alvinnunley Al’s got this.

I’m afraid not, it’s 42 pages long, just send a request and see for yourself, it is free you know! I keep no mailing list if you’re wondering about that. lol

@alvinnunley I meant the bit you posted above. Not the full worksheet. I’m not sure how to understand this.

https://forums.kartpulse.com/uploads/default/original/2X/1/123a8fccbda4f938eee73f6eb1c5c9d58484e40c.jpeg

This is less relevant to KartKraft really, but nonetheless… Here’s the folder of gear calc sheets I have for various shifter motors.

Based on sheets John Denman originally made for the CR125 and CR80, I’ve created sheets reflecting the individual input and internal gear ratios of various KZ engines and the CR250.

One tab lists gear ratios sorted by numerical value, so you can see what the next “increment” in gearing looks like.
Second tab you input your overrev and shift RPMs along with the sporcket gear ratio to get a sense of how it might look in terms of speed in each gear, top speed etc etc.

Naturally the very top speeds (115MPH+) are not attainable without a laydown body or a significant draft.

https://drive.google.com/drive/u/0/folders/0B5O3efMkqXjzTks3dzlHbFVEWTg

Thanks James. Modena MKZ is the KZ?