“What is the best gear change rpm?”
Knowing the best gear change RPM points (up or down) for your individual racing car, will give you more lap-time, more confidence and a critical advantage over most racing drivers.
This detailed guide will firstly take you through what is really going on during gear selection, the assumptions you’re likely making and why selecting the optimal gear is impossible by feel alone.
I then take you step-by-step through all the calculations so you can work this all 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.
By the end of the guide, you will be able to determine the precisely gear change rpm points for your individual racing car in a way you never thought possible before.
The results may even surprise you (they did for me!)
Goal: Achieving The Fastest Possible Acceleration
In a racing car, the best gear to be in is the one that is going to give you the fastest possible acceleration at any given speed.
If you’re in the wrong gear, you will be going slower than you could be – the equivalent of only pressing the throttle down part way.
Interestingly, by not knowing their best rpm shift points, the majority of racing drivers are possibly giving away seconds of “free” lap-time over a stint as a result.
After all the hundreds and thousands spent developing race engines, not having the racing driver change at the best possible rpm seems crazy.
But it happens all the time.
What you want is absolute certainty on the best gear change RPM. Yet, most racing drivers guess …
In practise it is harder than it looks
Unfortunately (and maybe surprisingly?) racing car drivers rarely change at the best gear change RPM.
The theory is fine but when you start to do it for real determining what gear to be in for fastest acceleration is actually more involved than it first seems.
As always there is plenty “good advice” floating about paddocks and forums on this subject.
For example, you may hear perceived wisdom along the lines of:
“You should change up gear …
- at max revs,
- at the rev limiter,
- at peak horse power,
- at peak torque,
- at some other fixed point in the rev range,
- “when if feels right”,
- “when the car tells you too”,
Whilst well-meaning all this advice is misleading and (sadly) wrong.
Let’s explore this a bit more.
The down shift
Up shifts are one issue. The other is the down shift.
In fact, this is much harder for the race car driver and therefore results in a higher potential impact on lost lap-time.
The situation: You are slowing for a corner.
The question: Do you change down or not?
“So is that a 3rd or 4th gear corner?”said Every Racing Driver EVER …
The issue is that your “feel metrics” can get tricked. This is because one of the main ones, your ears, likes to hear the engine at top revs.
High revs just sound faster. But are they?
The thing is, we race drivers also know that it might actually be faster in a higher gear.
It might not sound as fast but maybe you could get faster acceleration out of the corner in a different gear?
But how can you know?
Unfortunately, as a racing driver you can’t know for sure through driving.
This is because you can only ever be in one gear at a time.
Determining if it is faster in another gear can therefore only ever be an educated guess, done in the heat of the moment.
Typically in these “between gears” corner situations, drivers just experiment.
Over consecutive laps they might try going through the corner in both gears and then (somehow) try to work out (nee convince themselves) which is faster.
Admirable. Common. Expensive? – Yes.
Precise. Optimal. Correct? – Sadly 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 changing gear at the best RPM (both up and down gears) means you are not accelerating the racing car as fast as possible so you are going to be slower than you could be. Period.
Like the Pro’s.
All the professional motor racing teams have teams of engineers working this stuff out. 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 up or down gears in your racing car but 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 would it feel to know you were getting the absolutely maximum on track benefit from all that money spent on engine development?
What about if you were certain that you couldn’t possibly accelerate any quicker?
How would that effect 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 shift targets.
What if you had targets for each gear (hint: they are all different!) and all tailored to your individual race car – not based on some questionable paddock chat, but your exact setup.
And what if you had this information instantly updatable when ever 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 a that lower diff ratio? See how these changes effect everything, instantly.
Whilst your competitors carry on with their old methods, you can be 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 time on the table.
Compared to not doing this right, you will be slower than you could be for something that requires basically no skill – just going in a straight line!!!
Ok. Let’s get into this then.
The Guide: Calculating The Best Gear Change RPM
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 effectively drop back down the torque curve as the higher gear will drop your revs for the same speed.
You then accelerate again through the torque curve. Changing again when you feel the torque dropping away.
The key concept
Here is the point.
To have 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 the rev limiter.
As this is not (typically) the case, there comes a point in the rev band where there is more torque available to thrust the car forward in the next gear than the current one.
For example. 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 to 3rd gear dropped you down from your current 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 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 that makes sense.
As a racing driver it is your job to change gear at the exact point that you could get more torque to the wheels through another gear.
It might also start to give you an insight as to why it is actually quite hard to do this by feel alone … (hint: how can you tell the difference between a few ft lbs or Nms?? You can’t …)
Some good news (at last!)
Luckily, feel is no longer require as I’m going to take you through a calculation you can do to find the best gear to be in, at any speed (yay!)
Even more luckily, the calculation applies to (nearly) any kind of racing car (or motorbike!) and is totally independent of vehicle mass or aerodynamics (yay!)
Yes, there are some approximations around the tyre size (fixed), tyre slip (none), nature of torque curve (always same) and driveline losses (none) so just consider that but these are refinements and not (typically) significant.
(Engineers can do excuses too! :-D)
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 forth 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.
Theory Into Practise
On my racing car I happen to have a programmable dashboard with shift lights.
This allows me to specify the light sequence based on the best gear change rpm for each gear. Therefore it is a quick job to update the dash with the latest figures. I then don’t have to think about it again (the challenge actually becomes forcing myself to change on the lights and not the sound!)
If you don’t have shift lights you are going to need to remember the numbers.
As they are all different, try rounding down the best gear change rpm numbers to the nearest 50 or 100. This will make them easier to remember. In my example above you then end up with a table that looks like the image below:
If the table is a nice and compact, you can even print it out and stick it somewhere in the car as a prompt until you learn it. (Do so at your own risk however …)
Either way, once you have these numbers you will be assured that you’re getting the maximum acceleration your racing car has to offer.
Hold on, it is about to get bumpy!
6 Step Calculation Guide for Best Gear Change RPM
I will now take you through each step of the process so you can create a best gear change RPM 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 the time to put something together yourself for free, for the challenge and/or you simply want to know the theory in detail, then read on.
Step 1: Data gathering
All you need to calculate your perfect gear change rpm’s 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 …)
Step 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 (as that is the current setup I have in my racing car.)
We are running the following 5 speeds and final drive ratio:
Next you need the circumference of the tyre. This is because, as we are trying to relate this to road speed, the circumference gives you the distance travelled for one wheel revolution.
The tyre size we are running 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 we 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 our case 112mm sidewall height is 4.37 inches (we are taking the imperial route from here on btw – only as my head thinks in mph …)
Our 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 (in a background workings tab).
Alternatively you can use an online calculator like this one to either get the figures or double check your workings.
We now have everything we need to calculate road speed verse revs for each gear.
With our imperial approach the equation is:
Revs * 60 * Wheel Circumference / 63360 / (Gear ratio * Final drive ratio)
To explain. The 60 is to convert Revs per minute in to Revs per hour. The 63360 is the number if inches in a mile.
The output is therefore miles per hour. Nice!
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 …
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. In 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 also 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 let’s calculate torque verse revs for each gear. Once we have that we can then put them together and see what it tells us.
Step 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 we did in Step 2, the overall gear ratio is the final drive multiplied by the individual gear ratio. In our case we get a table like this:
For each rev point just multiply the torque by this ratio for each gear.
- at 3000 rpm we have 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.
Step 4: Torque at Road Speed in Each Gear
We have revs verse road speed for each gear. We have revs verse torque for each gear. We can now create what we 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:
And it is actually super informative.
Look at this one:
See the (crude!) highlighted line? This line is a “frontier” line. It represents the optimal possibility …
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.
A bit like financial portfolio analysis (humm!) if we are on the frontier line, then there is no better position we could adopt.
To stay on the line, all we need to do is change gear where the lines intersect.
Let’s calculate that too and make our table.
Step 5: Create Best Gear Change RPM 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!
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.
Step 6: Refinements
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 we 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 gear change rpm through each gear.
In our example it is a massive 1330rpm 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, lets just say that all these lower revs will make your engine builder (or your wallet) happier too!
All that is left is to either print the table out to stick in the racing car as a prompt until you remember them, or, program your dashboard shift lights if you have them.
Best of luck!
Bonus Step: Thrust …
It is outside the scope of this post to delve too much into this but you can also use this same information to support your aero tuning / setup / development.
By multiplying the torque at the wheels by the tyre radius you can calculate the forward force at the contact patch.
If you know your car’s mass and drag characteristics, you can start to consider optimising your gearing and aero choices based on the amount of forward thrust you have available at any given speed.
This gets super complicated fast but at least you now have part of the puzzle …
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.
Want to take the guess work 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/