“What’s the best RPM to shift gears in racing?”
Knowing the best RPM to shift gears for your racing car is not as straight forward as it first appears. You may have been bombarded by any number of often flawed theories before arriving here. Even once you know the correct answer for the best gear change rpm, you may have been further confused. How do you work out the best RPM to shift gears in your racing car?
What you are after is a simple explanation. Some straight forward answers and some help with the maths. You know that getting your gear changes perfect will gain you free lap-time. It will give you confidence and a clear advantage over your competitors in battle.
By the end of this guide, you will be able to determine the best RPM shift points for YOUR individual racing car.
The results may even surprise you – they did for me!
Introduction To This Guide On The Best RPM To Shift Gears
First you will discover what is going on during gear selection. You will discover the assumptions you’re likely making. You will learn why selecting the optimal gear is impossible by feel alone.
A simple 6 step approach will then show you all the calculations. Everything you need is there so you can work this out for your own car.
I’ve also put together an optional spreadsheet that will save you some time but it is by no means required. All the information you need is provided.
Then, armed with your new knowledge you may then ask “What happens if I change my gear ratios? Say my diff or my gear cluster? Which would be best then?” If you find that that is you, then you will also find some help to answer those questions too.
But, I get ahead of myself.
To start you might be asking yourself – what is “best” anyway? …
Enjoy! ?
Your Goal: The Fastest Possible Acceleration
The best gear is the one that is going to give you the fastest possible acceleration – at your current speed.
If you’re in the wrong gear, you will be going slower than you could be. Equal to pressing the throttle down only part-way.
By not knowing the best RPM to shift gears, the majority of racing drivers are giving away seconds of lap time.
Thousands $$$ are spent developing race engines. To not have the racing driver change at the best possible RPM seems crazy to me!
What you want is certainty on the best RPM to shift gears.
Yet, most racing drivers GUESS …
In Practice It Is Harder Than It Looks
Maybe surprisingly, racing car drivers rarely shift gears at the best RPM.
The fastest possible acceleration theory above is clear enough. But when you start to do it for real, knowing what the best RPM to shift gears is actually more involved than it first seems.
As a result there is plenty “good advice” floating about paddocks on this subject:
“You should change up gear at …
- max revs.
- the rev limiter.
- peak horsepower.
- peak torque.
- some other fixed point in the rev range!
- “when it feels right.”
- “when the car tells you too.”
- etc. ….
Sound familiar?
Whilst well-meaning, ALL these feel metrics are sadly wrong.
Let’s explore this a bit more.
“Is that a 3rd or 4th gear corner?”
… said Every Track Driver … EVER!! ?
.
Problem With Relying On Feel Metrics
Imagine you are slowing for a corner.
Do you shift down gears or not?
How do you know?
How can you know … for sure?
On the slower corners it can be self evident. On other corners you are left wondering …
The issue is that your “feel metrics” can trick you.
Your senses are not good at sensing acceleration. I’m no expert but what your eyes, ears and feel seem to do is combine to work out your acceleration.
You can be effective at sensing big changes in acceleration. What you will struggle with is more subtle differences.
Further more, your ears are particularly dominate. They like to hear the engine at top revs. High revs sound faster. But are they?
Unfortunately, as a racing driver you can’t know for sure through driving alone.
Determining if a corner is faster in different gear resolves to being an educated guess.
In these “between gears” corner situations, drivers experiment. Over consecutive laps, they go through the same corner in different gears. They then try to work out – nee convince themselves – which gear is faster.
Admirable. Common. Expensive? – Yes.
Precise. Optimal. Correct? – No.
Seconds Of Lost Lap Time (For Nothing)
It is my belief that bad advice is costing racers seconds of lap-time during the course of races.
All simply because they are not in the right gear at the right time.
It is amazing if you think about it – racing drivers actually having no clue when another gear would be faster!
Not knowing the best RPM to shift gears means lost acceleration. You are simply going to be slower than you could be.
Shift Gears Like The Pro’s
All professional motor racing teams have teams of engineers working out the best RPM to shift gears. Great for them but what about you?
What if I suggested that with just a few pieces of commonly available data, you could have the same absolute certainty on when to change gears? All without the cost of a team of professional motorsports engineers!
What if you had complete assurance that, no matter what speed, what corner or what circumstance, you would always know which gear to be in?
How good would it feel to know you were getting the absolutely maximum on track benefit from all that money spent on engine development?
How would that affect your ability to qualifying or your confidence in that drag to the finish line with another car?
As well as the performance benefit, what if I told you that you could do all this with decreased engine stress as well? Talk about having your cake and eating it!
Precision Gear Change Targets
No more feel. No more guessing. Instead, precise gear shifts at the best RPMs.
What if you had RPM targets for each gear – hint: they are all different! – and all tailored to your individual race car?
Gear shift targets not based on some questionable paddock chat, but your exact setup.
And what if you had this information instantly updatable whenever you made a change to your car? Found more power on the rolling road or want to know the effect of a different 4th gear? What about that lower diff ratio?
See how these changes affect your best gear shift RPMs – instantly!
Whilst your competitors carry on with their old methods you can be confident. Confident you know exactly how to maximise everything your engine has to offer.
Driving a racing car consistently on the limit to extract every last 1/10th is challenging enough.
The last thing anyone wants to do is leave lap time on the table.
Ok. Let’s get into this then.
Understanding The Torque Curve
The torque curve of a race engine changes with RPM. First increasing and then typically dropping off at higher revs (see image below):
As you accelerate through the revs the torque available at the wheels also peaks and then drops away.
When you change up a gear, you drop back down the torque curve. This is because the higher gear will drop your revs for the same road speed.
When Should You Shift Gears For Fastest Acceleration?
To have the fastest acceleration you need to have the maximum torque possible at the wheels for any given road speed.
If the torque curve did not peak and drop off, but instead continued upwards then you would always change gear at your rev limit.
That is not typically the case with internal combustion engines. Normally, there comes a point in the rev band where there is more torque available in another gear.
Worked Example – Best RPM To Shift Gears
In the diagram above, let’s say you are in 2nd gear at about 7000 RPM. The torque from the engine at 7000 RPM is about 100 ft lbs.
The question: Could you get more torque in another gear?
The answer: This depends on the gearing. Remember the higher gear will drop us down the rev ranges for the speed you are going. If you drop to a point on the torque curve that would give you more than 100 ft lbs of torque then yes, change gear, otherwise no.
Situation 1: Say changing from 2nd to 3rd gear dropped you down from 7000 to 2000 rpm. The question becomes, is there more torque at 2000 rpm than 7000 rpm? Looking at the curve, in this case, there is less than 80 ft lbs of torque available. As 80 is less than 100 you would be better to stay in your current gear.
Situation 2: What if changing from 2nd to 3rd gear dropped you down to 3500 rpm instead? Looking again at the torque curve there is about 115 ft lbs of torque available. As 115 is clearly more than 100, in this situation you would be better off changing to 3rd gear – ASAP!
Hopefully this starts to give you an insight as to why it is so hard to do this by feel alone. How can you tell the difference between a few ft lbs or Nms rt torque?? You can’t.
As a racing driver, it is your job to shift gears at the exact RPM that you could get more torque to the wheels, in another gear.
From Feel To Precision
Luckily, feel is no longer require. Up next is a calculation you can do to find the best gear to be in, at any speed ?
Even more luckily, the calculation applies to – nearly – any kind of racing car – or even motorbike!
You might also be surprised to learn that the calculations are totally independent of vehicle mass or even aerodynamics!
Yes, there are some approximations. These are
- Tyre size – fixed diameter,
- Tyre slip – none,
- Nature of torque curve – same in each gear, and
- Driveline losses – none.
It is best you know but I see these as refinements and not (typically) significant.
What The Calculations Will Give You
The output you can get is a really useful little table, like the one below:
What this is saying is that in 1st gear I should rev until 7786 RPM before changing to second gear. In second gear I should rev to 7069 RPM and then change to third. In third I should change up to forth at 6794 RPM and from fourth to fifth at 6456 RPM.
Equally, if I am in 5th and the revs drop below 5255 RPM, then I should change to 4th. In 4th when the revs drop below 5108 RPM I would be better off in third. And so on.
Clearly there is time lost in changing gear. It can also unsettle the racing car. It might make no sense to only briefly change down, to then change back up again etc. So you still need to consider your on-track situation but, all things being equal, this little table gives you absolute certainty what gear would be best.
Programme Your Dash Lights
On my racing car I have a programmable dashboard with shift lights.
If you have this too, you can specify the light sequence based on the best RPM to shift gears. If something changes, like a new engine curve – you can update your dash with the latest figures.
The benefit is that in the car you don’t have to think about this again. Your challenge actually becomes forcing yourself to change on the lights and not the sound!!! ?
6 Steps To Calculate The Best RPM To Shift Gears
I will now take you through each step of the process so you can create your best RPM to shift gears table like the images above.
If you are not so comfortable implementing these calculations for yourself (some bits do require coding skills) then I’ve put everything together this Pro Grade Race Engineering tool that you can pick up here:
However, if you’ve got the time to put something together yourself and you want to know the theory’s then read on:
1 – Data Gathering
All you need to calculate your perfect gear change RPMs is the following data:
- Revs v Torque curve
- Gear ratios
- Final drive ratio
- Tyre size
The hardest one of these to get is your Revs v Torque curve because it requires going to a rolling road.
Not everyone takes their racing car to the rolling road but one way or another, you’ll need to get a representative torque curve for this to work.
Here is what you need from my spreadsheet:
You just need to fill in the RPM and torque columns and the rest is calculated and charted automatically.
I’d say most serious competitors do have this information though (so just make sure you get a copy of the rolling road print out when you are there …)
2 – Speed In Each Gear
The first thing to do is to calculate a table of road speed verse revs for each gear.
To do this you need your gear ratios and the circumference of your tyre – the driven one if they are different.
I’m going to take you through a worked example based on a rear-wheel-drive Mazda MX5. That is the current setup I have in my racing car.
Gear Ratios
We are running the following 5 speeds and final drive ratio:
Tyre Size
Next, you need the circumference of your tyre. As you are trying to relate this to road speed, the circumference gives you the distance travelled for one wheel revolution.
The tyre size for the example is: 185/60 R13
- 185 is a tyre width of 185mm
- 60 is a percentage of the width and relates to sidewall height. So in our case: 185 x 60% = 112mm sidewall height.
- R13 is the wheel rim diameter, in inches.
To calculate the circumference you simply take the whole tyre diameter and multiply by π (Pi or 3.141592…)
To get the whole wheel diameter you need to add the sidewall height (x2) to the rim diameter.
In this case, 112mm sidewall height is 4.37 inches. The example is in imperial from here on – as my head thinks in mph.
The rim is 13 inches so the tyre diameter is: 13 + 4.37 + 4.37 = 21.7 inches.
This makes our tyre circumference: 21.7 * π = 68.3 inches.
I have no idea why tyre sizes are this odd combination of metric and imperial measurements. It does make things a bit more fiddly … anyhow … ?♂️
In the spreadsheet, I’ve calculated all the tyre info for you. You simply enter the tyre size you have and it generates this little table:
Alternatively, you can use an online calculator to get the figures or double-check your workings.
Road Speed V Revs
You now have everything needed to calculate road speed verse revs for each gear.
The equation is:
Revs * 60 * Wheel Circumference / 63360 / (Gear ratio * Final drive ratio)
To explain this. The 60 is to convert Revs per minute into Revs per hour. The 63360 is the number if inches in a mile. The output is miles per hour.
Again in the spreadsheet, I’ve done this for you. See below. You even get a nice little chart, which will come in handy later…
Rev Drops
What you can also see in this chart (zoomed-in below) is what I’ve discussed about the RPM drop between gears:
Pick a speed, say 40mph. In first gear that would be 7000 rpm. In second gear that would be 4500 rpm. Third gear, 3000 rpm. In forth, 2300 rpm and in fifth, just below 2000 rpm.
Can you see? If you knew these rev drops, and you knew your torque curve (really well) you could work this all out as you went round…
Why this is basically impossible to do in your head is because you will also see that the amount the revs drop between each gear changes with speed.
If all the lines were parallel then you’d have half a chance as the drop would be the same but they diverge.
It is clearly amazing you’ve done as well as you have! ?
Ok. Now you calculate torque verse revs for each gear. Once you have that you can then put them together and see what it tells you.
3 – Torque In Each Gear
To calculate the torque in each gear is a bit more straight forward.
All you need to do is take your torque curve and multiply by your overall gear ratio in each gear.
As you did in Step 2, the overall gear ratio is the final drive multiplied by the individual gear ratio. In this case you get a table like this:
For each rev point multiply the torque by this ratio for each gear.
For example:
- at 3000 rpm we have a torque of 115 ft lb.
- In first gear that means 12.2304 x 115 = 1406 ft lbs at the wheels.
Do that for each point on the rev curve and for each gear.
Again in the spreadsheet this is done for you but it is easy to do if you are doing this yourself.
You want to end up with the following table (and chart).
What you can really see the effect of the gearing here. The higher the gearing the flatter the curve. Look at the big difference between first and second.
If you look at the slope of that first gear torque curve past the peak, you can see it is quite steeply downwards. Much steeper than all the others.
In the car this feels like you are not accelerating as quickly, even slowing down.
Racing drivers often short shift here thinking they will get more acceleration from the next gear.
As you will see below, despite how it feels, the best option in our example is actually to run 1st nearly to the redline…
Feel is history!
Let’s start pulling this all together.
4 – Torque At Road Speed In Each Gear
You have revs verse road speed for each gear. You have revs verse torque for each gear. Now you create what you are really after – road speed verse torque for each gear.
Depending on how you’ve done this you can simply copy the relevant figures over. In my spreadsheet I have just referenced the cells and lined them up automatically make this table:
And from this you can generate my favourite chart of this whole exercise:
Cool, hey!?
And it is actually super informative.
Look at this one:
See the highlighted line? This line is a “frontier” line. It represents the optimal possibility for acceleration …
The fastest acceleration will come from getting the most torque to the wheels at any given vehicle speed. And that is the yellow line.
We simply need to stay on the yellow line to have the fastest possible acceleration at any speed.
Boom!
If you are on the frontier line, then there is no better position you could adopt.
To stay on the line, all we need to do is shift gears where the lines intersect.
Let’s calculate that too and make your table.
5 – Create The Best RPM To Shift Gears Table
The best gear change RPM points are where the lines intersect.
Option 1: Read off the charts
The easiest way to do this is simply to read the points off the chart.
First: Take a look at the zoomed in torque verses speed chart above.
You can see the first and second gear lines cross at about 42 mph.
Second: Now go back to the Revs verse Road speed chart (see below).
Read along the X-axis until you get to 42 mph.
Then read up until you hit the first gear line.
Then read across to the Y-axis for the revs.
You get about maybe 7600 rpm? Or thereabouts.
Simply do this for all intersections along the frontier and bingo you’ve got your table.
For a 5 speed gearbox, there are 8 shift points to workout (4 up and 4 down).
This is easy and will get you really close.
However, after all the effort to get this far it seems a shame to estimate the key outputs by eye, so…
Option 2: Optional Modelling approach
Alternatively, you can try to code this up so that it is automated, more accurate and faster to update. You turn this from a one-off to a model you can experiment with. Much more useful.
Creating all this as an instantly changeable model is really the main bit I’ve done this for you in my spreadsheet.
If you are doing this yourself, it might help to know I ended up using a great piece of open-source VBA code for the intersection. You can then simply code a linear interpolation to find the precise Revs from the intersection mph.
It took me quite a while to figure it all out to be honest. However, in my workings ended up with a layout like below that could give you some inspiration.
I’m sure smarter people than me can figure out other ways / better ways – so let me know!
Anyhow, either way we are there!
Success! – You Now Know The Best RPM To Shift Gears!!
You should now have a little table like mine for your individual racing car. Data you’ve never had before. Intelligence over your competitors. The knowledge of how to extract the fastest possible acceleration from your racing car. The best possible gear change rpm points for your racing car.
Well done!
6 – Refinements – Best RPM To Shift Gears
What I also did in the spreadsheet was spend a bit of time dashboarding out the results.
In addition to the table I’ve also created this chart which you might also want to consider.
This chart is effectively an adaption of the revs verse road speed chart you saw already but showing the frontier.
I thought it summarised everything nicely. You can see the best gear change RPM points, up and down, and what speed we should be travelling at.
You can also see how the optimum points change relative to each other, which I think is useful.
The one thing that really got me when putting this all together, was how much difference there is in the best RPM to shift gears in different gears.
In this example, it is a massive 1330 rpm difference between the best shift point in first gear and the best in fourth.
That is certainly never something I’d have considered before.
What about reliability? Well, let’s just say that all these lower revs will make your engine builder happier too!
All that is left is to either print the table out to stick in the racing car as a prompt. Or you can program your dashboard shift lights if you have them.
Best of luck!
Race Car Gear Shift Calculator In-Detail
If you are interest in using the spreadsheet I’ve put together to support this article here is some more information about it.
If you look at the image above. All you need to do is provide the information in Step 1, in the three little boxes – circled in the image.
All the charts, tables and graphs this instantly update with your data.
You can instantly see the effects of:
- another diff,
- different gearing in up to 5 gears
- a different tyre size, or
- even the effect of changes to the torque curve.
I’ve also included the rounded table of best gear change rpm values if you are going the print out route.
Further Reading …
You now know when to shift but how do you choose the BEST RATIOS for a particular track?
If you have the option to change your gear ratios take a look at the advanced 6 speed version. This goes further into the background to help you select precisely the right gear sets for any track you visit. If you prefer a video explanation then this post on choosing the best diff has a free walkthrough to accompany everything.
There is more to racing than gearing …
Want to take the guesswork out of setting your tyre pressures? Try this article including a free calculator: https://www.yourdatadriven.com/how-to-set-your-racing-car-tyre-pressures-perfectly-every-time/
Wondering what the tyres are actually doing? This article should help your visualisation:https://www.yourdatadriven.com/tyre-slip-angle-explained/
