Gearbox tuning: how does it work?

4,969
United Kingdom
Druids Bend
Z4E_Midnight85
Hey all. I've been playing a while and I've got my head around suspension, diff, and aero tuning, but the one thing I still can't work out is gearbox tuning. I often fit a fully customizable gearbox then just adjust using the top-level "speed" adjustment. I've seen loads of tunes where people set a "speed" adjustment, then go into the gears and fine tune them all individually and then use a final gear adjustment to tune all the above. But my simple mind can't comprehend how it all works and how best to approach it to get the best outcome.

Can any of you pros provide any insight as to how you go about tuning the gearboxes for the optimal acceleration/speeds you require??

Many thanks in advance!!
 
Simplified:
throw your car around a track and see in which corners you find yourself shifting too much.
Either set your gears so you dont need to downshift too many times, or set your gears so you can upshift close after leaving a corner that leads to a high speed part.
Helps with speed, stability and fuel efficiency if done correctly.
 
Slightly less simplified:

wheel torque = engine torque x gear ratio (- frictional losses)

wheel speed = engine speed / gear ratio

You get the best acceleration when you run the engine close to peak power (check the power curve of your engine to learn where that is)

Engines with peaky power curves benefit a lot from closely spaced gear ratios, because it allows the engine to operate close to peak power for long durations. With widely spaced gears the engine drops far below peak power when you shift and your performance will drop.

You can optimise your gear ratios by reducing the space between the gears in the speed intervals where you think you will be spending most time during the race, but also keep in mind that acceleration is more valuable at low speed than at high speed (going quickly from 100 to 120 will save you more time than going quickly from 200 to 220). It’s also a good idea to consider the time it takes to shift gears, so don’t space the gears too closely either.
 
Last edited:
Slightly less simplified:

wheel torque = engine torque x gear ratio (- frictional losses)

wheel speed = engine speed / gear ratio

You get the best acceleration when you run the engine close to peak power (check the power curve of your engine to learn where that is)

Engines with peaky power curves benefit a lot from closely spaced gear ratios, because it allows the engine to operate close to peak power for long durations. With widely spaced gears the engine drops far below peak power when you shift and your performance will drop.

You can optimise your gear ratios by reducing the space between the gears in the speed intervals where you think you will be spending most time during the race, but also keep in mind that acceleration is more valuable at low speed than at high speed (going quickly from 100 to 120 will save you more time than going quickly from 200 to 220). It’s also a good idea to consider the time it takes to shift gears, so don’t space the gears too closely either.
That's a brilliant description, thank you!

Thinking back to your first two verbal equations. I've had a few occasions where I've set a car up with massive power, gone to do a high speed run and rolled the gears all the way up to say, 450 kph (on the top-level adjustment) only to find its getting up to around 370 kph in 5th and 6th even starts losing speed. Would that mean you want to:

a. Shorten the last two gears so they have more acceleration.

b. Shorten the "final drive" ratio so the speeds all come down across the range.

c. Neither.

Because that's where I get a little bit lost usually...

Regarding the term "peaky", is that meaning the power curve is really steep with a big drop after peak power? And would a flatter power curve mean your gears would want to be spaced further apart?

Another question, as a general rule. Is it best to space the ratios evenly, make them get progressively closer as you go up the gears, or progressively further apart as you go up the gears?

Sorry for all the questions. It's just an area I've never been able to get my head around properly to get the most out of my tunes.
 
Last edited:
That's a brilliant description, thank you!

Thinking back to your first two verbal equations. I've had a few occasions where I've set a car up with massive power, gone to do a high speed run and rolled the gears all the way up to say, 450 kph (on the top-level adjustment) only to find its getting up to around 370 kph in 5th and 6th even starts losing speed. Would that mean you want to:

a. Shorten the last two gears so they have more acceleration.

b. Shorten the "final drive" ratio so the speeds all come down across the range.

c. Neither.

Because that's where I get a little bit lost usually...

Regarding the term "peaky", is that meaning the power curve is really steep with a big drop after peak power? And would a flatter power curve mean your gears would want to be spaced further apart?

Another question, as a general rule. Is it best to space the ratios evenly, make them get progressively closer as you go up the gears, or progressively further apart as you go up the gears?

Sorry for all the questions. It's just an area I've never been able to get my head around properly to get the most out of my tunes.

For maximum top speed you should reach the top speed at the same time as your engine is producing the maximum power. If you do that then it’s physically impossible to go any faster. So check the engine speed on your next top speed run and see how it compares to the power curve of the car. If you have gone past max power then you need to make the gear a little taller. If you haven’t reached max power yet, then you have to make it a little shorter.

And yes, peaky means that the power rises (and drops) relatively quickly. Typically you will see this in engines with low torque and high power. Engines with high torque have less peaky power curves generally speaking. Less peaky engines also benefit from more closely spaced gears, but they don’t benefit as much as the peaky engines. Basically, the flatter the power curve, the less they will benefit. I think it was in GT6 where you could use the power limiter to create engines with completely flat power curves. The interesting thing about that is that then you could set whatever gear ratios you wanted and it wouldn’t make any difference to the lap times, because the engine would pretty much always operate at peak power no matter what you did to the gearbox.

As a general rule it’s better to have the gears get progressively closer as you go up the gears. There are two reasons why your car accelerates faster at low speeds than at high speeds. The first reason is that aerodynamic drag increases, the second reason is that force = power/speed, so the faster you go the less force can be produced at the wheels.

Do a lap around a track you want to tune your car for and see what kind of speeds you’re mostly running at. If you spend most time between 150 and 250 km/h, then the optimal gearbox is the one where the gears are closely spaced within that range of speeds (but not too close, because it takes time to shift gears…)
 
For maximum top speed you should reach the top speed at the same time as your engine is producing the maximum power. If you do that then it’s physically impossible to go any faster. So check the engine speed on your next top speed run and see how it compares to the power curve of the car. If you have gone past max power then you need to make the gear a little taller. If you haven’t reached max power yet, then you have to make it a little shorter.

And yes, peaky means that the power rises (and drops) relatively quickly. Typically you will see this in engines with low torque and high power. Engines with high torque have less peaky power curves generally speaking. Less peaky engines also benefit from more closely spaced gears, but they don’t benefit as much as the peaky engines. Basically, the flatter the power curve, the less they will benefit. I think it was in GT6 where you could use the power limiter to create engines with completely flat power curves. The interesting thing about that is that then you could set whatever gear ratios you wanted and it wouldn’t make any difference to the lap times, because the engine would pretty much always operate at peak power no matter what you did to the gearbox.

As a general rule it’s better to have the gears get progressively closer as you go up the gears. There are two reasons why your car accelerates faster at low speeds than at high speeds. The first reason is that aerodynamic drag increases, the second reason is that force = power/speed, so the faster you go the less force can be produced at the wheels.

Do a lap around a track you want to tune your car for and see what kind of speeds you’re mostly running at. If you spend most time between 150 and 250 km/h, then the optimal gearbox is the one where the gears are closely spaced within that range of speeds (but not too close, because it takes time to shift gears…)
Thanks for your help on this. I've followed your advice and I think I'm starting to get the hang of it, little by little.

Another question: when fine tuning the gear ratios, there's a speed indicated in brackets at the end. Is that the top speed possible in that gear considering power x ratio? Or is that the speed the car will reach at peak power/RPM? The reason I ask is power drops off after the peak power, so is the gear ratio able to keep the car accelerating (under slipstream or downhill) past the peak power point to max out at the speed indicated? And if so, I'm assuming I'd be best to have that number a bit higher than the speed I actually anticipate reaching... Eg. if the 6th gear shows 346 kph I'd probably expect something around 300 kph from the car on a flat track at max pace. In any case, I don't think I've ever reached the top speed indicated by those ratios when the gearbox is set for a big top speed...
 
Thanks for your help on this. I've followed your advice and I think I'm starting to get the hang of it, little by little.

Another question: when fine tuning the gear ratios, there's a speed indicated in brackets at the end. Is that the top speed possible in that gear considering power x ratio? Or is that the speed the car will reach at peak power/RPM? The reason I ask is power drops off after the peak power, so is the gear ratio able to keep the car accelerating (under slipstream or downhill) past the peak power point to max out at the speed indicated? And if so, I'm assuming I'd be best to have that number a bit higher than the speed I actually anticipate reaching... Eg. if the 6th gear shows 346 kph I'd probably expect something around 300 kph from the car on a flat track at max pace. In any case, I don't think I've ever reached the top speed indicated by those ratios when the gearbox is set for a big top speed...

Sorry for the late reply, I saw the notification and then forgot about it.

I’m not sure about the speed, but I assume that the indicated speed is the wheel speed when the engine reach its maximum rpm. So it’s probably good to keep that figure a bit higher than the speed you actually want to go. As you said, the power drops off as you approach the rev limiter, and there’s also a bit of wheelspin to take into account, so the wheel speed is usually a little higher than the speed of the car.
 
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