Gearing Discussion

Based on some of the conversation over in another tread, was very curious to see how others approach gearing?

• Do you use detailed Mychron data to validate this?
• Do you have a specific math formula or use the histogram?
• Specific datapoints your looking for?
• Going to a new/existing track, where do you start?
• Just by asking around and then fall back to the first point of data evaluation?
• Do you run some simulation software?
• Is there a mathematical formula to get you in the range on a new track based on key items such as overall length, length of front strait, amount of slow/fast corners… May create a specific ratio to look for?
• Do you chance your gearing between practice, qualifying, and race?
• Maybe gear differently depending where you qualify in the field?

I’d like to add a bit more data analysis behind my decisions which is why I’m asking. I’ve usually asked around to get the range of gears that people are in, seems to very +/- 2 teeth. And from there I run laps, determine if I need more drive out of the corners or more down the front strait. Usually keep the gearing the same once I get in the range regardless of session or placement, usually in top 6 or 7 with that extra 0.200-0.400 to 1st delta. Depending on the engine im running the only data I use on Mychron is, laptime, high/low rpm (aim to bring the low up as much as possible) and EGT.

Honestly lap time it the only data that actually matters.

Is it? I used to tune solely on lap times. This is great for qualifying. But what about passing? If the track has 1 very long straight maybe it’s better to tune for passing on the straight. Or protect from someone passing you. I will admit we only have few years experience but I’m finding there is not usually an easy answer…

I stand by my statement, it’s worked for me for a very long time and resulted in a ton of championships and race wins.

Great to hear your current methodology is working. can you expand on what you used as a starting point? im assuming you just didn’t show up with whatever gear you had on the kart when you bought it. is there a known ratio your track runs? when testing for fastest lap time, do you do six runs and then change the gear +/- 3 teeth to see if you in the range, then dial it in to +/- 1 or 2 teeth to get that last tenth/hundredth?

For new tracks that I’ve never been to, if I know someone that has been there, I will ask them where they are geared. If I don’t have someone that I can ask, Google maps becomes my friend. I look at the track and see how many tight corners there are, and how long the straight is. I compare that to tracks I have been to to get a starting point.

Once on the track, I look primarily at the low RPMs to make sure she is above the minimum I want her at. If she is above, and the motor is not revving higher than I want, we’ll leave it alone. No special formula, It’s mostly about making sure she is in the range I want her at.

No need to overthink it. Ask someone where you should start and work from there, keeping an eye on minimum and maximum RPM. I use MyChron data to make notes of how much I’m gaining off the corner vs. how much I’m gaining on the straights. When I set up my splits I am trying to isolate sections of the track, so I’ll usually have a split that consists of the longest straight and a split that consists of the tightest infield section. That way I can quickly and easily see what my times are through each section and then compare.

If I know I’m going to have to race and work through traffic I might throw a tooth on, knowing I’ll get bottled up in corners and need some oomph to not get mobbed by the pack.

I disagree with Greg that lap time is the only important thing. I think you need to consider how well you can race or battle with each gear. @CourterZT recently mentioned in another thread how he did some testing with drastically different gearing, and they all ran within the same tenth of a second on lap time. One of those gears is going to be easier to pass in the infield with, one of those gears will be easier to pass on the straights. So even though they give the same lap time, one might be a better choice for a heavy traffic situation vs. a qualifying situation where you’re on your own. Also need to consider if you are going to be drafting. The ideal gearing might cost you time at the end of the straight if you’re in a pack and you’re topped out in the draft.


You can tune the gearing for passing on the straight,but you may have some problems out of the turn.What you can do is check out if there are easy overtaking turns,if so don’t use the long gearing,if it is hard to overtake in the infield you can use the long gearing.

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There are so many right answers. Mainly, because there are several factors that go into the decision. 2 stroke or 4 stroke? Rev limiter or not? Close to minimum weight? Track layout, tight or flowing?

Like Gerard said, if there is a lot of passing opportunity in the corners, then gear slightly for the corners.

Like TJ said, if you are bouncing off the rev limiter in the draft, then gear slightly for the straights.

The track I run changes very little throughout the day, so my Qualifying gear typically ends up being my Final gear and I just adjust my driving slightly to make the most of it. From race to race however, I may go up or down after practice to adjust for grip. Newer tracks are harder to read than familiar ones. If someone in your group gives you a range, look at how much weight they have on the Kart and adjust your choice accordingly. I am over minimum, so if a driver with 20lbs of lead says its a range of 10/76 to 10/80, I would likely start with a 10/79 and adjust from there. At NTK (tight and twisty) I will run a 10/81 when its super green and a 10/79 when its gripped up, because I can carry more speed through the corners.

TJ, I’m not convinced you are actually disagreeing with me. I don’t see how there’s any question that meeting your lap time target is priority number one. Having said that there are plenty of times when varying +/-1 tooth or at the most +/- 2 teeth can improve raceability.
Over thinking this variable can be headache inducing.

After I posted my comment I read your comment about playing with the gearing long straight/infield.
My comment is basically the same…oops,looks a bit silly,sorry for that.

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I watch lap times, and how our kart performs relative to our competitors. Are they gaining out of a corner, are they faster on the straight? Some tracks want the engine to scream, others to lug.

I have noticed some competitors at the track will fiddle with gearing on a regular basis. Since I primarily race at one track I have pretty much gone with the set it and forget it method.

So, am I missing something? Is there an advantage or necessity to change gearing based on the variables we encounter?

In my somewhat limited experience, the “correct” gearing varies by a couple teeth. Back when I was doing lots of TT I could do a top time with a couple different ratios. Small differences in ratio changes how the kart feels, aggression wise, personally. More corner exit feels less momentum-y and requires really great timing on throttle, since it’s so tight.

I could see a situation IRL that someone might change gearing due to atmospheric and track conditions. For most though, it’s probably sett and forget.

If you’re racing at just one track, you should be within a couple teeth most of the time. Especially humid weather might require an extra tooth as you’re making less power, and if it’s cold and dry maybe you can take a tooth off. The track might also have a higher or lower grip level throughout the year, which might change your gearing choice one or two teeth.

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All my experience is low hp, so take it how you want:

Grip level, draft, wind direction/speed, racing situations… all taken into account when choosing gear ratio for a low hp 4 stroke (206 in this case).

Reasons for dropping a tooth:

  1. Track grips up and you can carry more corner exit speed
  2. Race conditions involve more drafting so you expect to be in a pack (vs qualifying or practice)
  3. Need to create passing opportunities (be able to pass at the end of the straightaway).

Reasons for adding a tooth:

  1. Track gripped up so much the field is fighting tight (boggy) condition
  2. headwind on the front stretch (think a 15 second straightaway at New Castle in a 206)
  3. Qualified on the pole and dont plan on drafting/passing anyone. Just want to try to set fastest lap times and stay out front.

Now that we talking about gearing, is this exclusively the domain of karts? (Swapping sprockets). Do cars (with gears) need changes to final drive or anything depending upon track?

Derek is pretty spot on, but I’ll add that there are some times when I get a bad pill draw on a tight track and I’ll add teeth to make my passes off corners instead of into corners on a too end run.

That part comes down to preference and knowing the competition and the track.

And there’s plenty of times that me and Derek can be on completely different ratios and be the same same speed. We seem to get stuck together a lot. :joy:

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Same, I have ran with Derek on similar and different gearing and his comments are almost always spot on.

Also, Derek always runs clean but hard and thats alot of fun to drive with! Now you just need to start coming out to a few of those races.

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I can liken this to my experience crewing with my Dad in his H Prod Civic. He has two five speed gear boxes. One is geared tall (Si box), the other slightly shorter (Standard box). Based on his engine’s power band, the track layout will determine which box he uses. More often he goes with the taller box as it give better corner exit acceleration and he rarely maxes revs at the end of the long straights in either box. However, if the track is very flowing, there is an advantage with the shorter box. (shorter = lower final drive ratio/slightly higher top speed)