On the subject of gearing

Let’s discuss gearing for a sec. I have been experimenting with different gear ratios at the tracks I drive in sim.

Generally, I start by looking for a ratio that hits limiter near-ish the end of straight. However, I find myself walking my gear ratios back. These days I have been running shorter ratios that aren’t correct (conventional wisdom).

What I have found is that gearing effects how you drive. Shorter ratios change how the kart responds in that it feels tighter and more on “boil”. So, I have been trying to find the ratios that feel very torquey (but manageable) but doesn’t fall flat on its face EOS.

What’s odd is that I have been able to set fast times with a too short ratio (I think). There’s something about how much more responsive and on edge the kart feels. It’s different in how you drive it. Or at least, that’s what I am seeing/feeling.

I guess my question is, is there always a “correct” gearing or is it somewhat open to interpretation? Shorter is faster through the twisties but obviously gives up top end.

While I know diddly about sim racing I’ve been racing karts successfully for a very long time. Since I own and run a kart shop I get gearing questions constantly. Usually the questions involve a magical rpm figure in the question.
The answer is the best ratio is the one that turns the best lap times PERIOD.

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Walk up and down the grid of any big event, and you’ll probably see a range of gears within 2-3 teeth on the fastest guys.

Pegging the limiter just at the end of the straight isn’t always the goal. Even before you get to the limiter, the kart is running out of power on the top end.

The reality is, as with most things in karting, “it depends”. A longer, more flowing track might allow you to run well below the limiter, as you are able to lug the engine and keep it in the mid-range power for longer. A track with really tight hairpins and long straights might require you to stack rear gear to deal with the corners, and then you just have to sit on the limiter halfway down the straight.

Similarly, you might have a different line or chassis setup or driving style that will change how you gear the kart. If you drive very smoothly, you may be able to roll through the corner easier than some guys, and run a lower gear to drive by them on the straight. If you have a more aggressive driving style, maybe you can make up time on the entry to the corner by driving in harder, and then add rear gear to help dig yourself off the corner easier. You also need to consider changing grip levels. Once the track starts to rubber in, you might find you can keep dropping teeth as you are carrying more corner speed.

Also, you need to consider whether you’re going to be racing in traffic or out front of the pack. A driver out front might be able to run less gear for more top end because they aren’t battling or getting held up in the infield at all. If we are going to be running in traffic, we usually consider adding a tooth so that we can battle and have a little extra torque for pulling off a corner after a pass or for defending.

So I would say there’s a range of gears per track that will give you a good lap time. Then it’s up to you to figure out which in that range suits your driving style and will allow you to race effectively.

Don’t overthink it. Find a gear you think is right, then test within a range of 1-2 teeth down and 1-2 teeth up and see what the lap times look like. Then pick a gear for your racing situation.

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I learned a lot about gearing this year some of it by mistake. I am sure Greg and TJ know a ton more than I do but here is what I look for:

  • track layout – how tight is the tightest turn and how important is it for the overall lap; how long is the straight and can you actually pass at the end of it; where are the best places to pass on the track

  • minimum RPM & max RPM. For a Leopard, I try to start with minimum revs at 7800-8100 and see how it goes. If the lap times are competitive and I have good speed the last 1/4 of the main straight / passing area, I stay where I am. If I am catching other karts right as it is time to hit the brakes, then I add teeth. If I am getting killed off the slowest corner, I add teeth.

I don’t obsess on max RPM. As an example with a Leopard on the following tracks here is my max RPM

  • NJMP 17,100
  • New York Race Complex - 15,400 & it was very fast.
  • Pitt Race, 16,400
  • E-town high 16,900
  • X1 Boston - 16,800

And of course how the chassis is handling has a ton to do with it. I won Homestead FWT many years ago with 3-4 fewer teeth than the guys in the lead pack. My tuner AJ Whisler had the kart so hooked up that it was like going out for a Sunday drive.

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When you ask even builders for RPM targets they give you the top end figure. I’ve been paying a lot of attention to the low number as the more critical number and the top end over-rev kinda is what it is.

I believe people are inadvertently getting to the same point but I feel like the focus on low was more important for me finding the right gearing recently.

I’m all new to low stall clutches though? On yahama the low rpm was wherever you set the clutch (500 rpm below peak torque).

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I’m with Greg 100%. IAME has a nice graph which will get you to the ball park, then you need to tweak it up or down to strike the best balance between hauling ass outta the turns and gunning it along the straights.

All terrific thoughts, thank you all.

Most of my driving is at a mid-range track and running Rotax, X30 and KA100. For this track, the taller the faster but driving and kart has to be spot on to roll the turns. As the grip came up, the taller the gearing.