Figuring out the most effective gear change RPM factors (up or down) to your particular person racing automobile, will provide you with extra lap-time, extra confidence and a important benefit over most racing drivers.

This detailed information will firstly take you thru what is absolutely happening throughout gear choice, the assumptions you’re doubtless making and why deciding on the optimum gear is not possible by really feel alone.

I then take you step-by-step via all of the calculations so you’ll be able to work this all out to your personal automobile. I’ve additionally put collectively an optional spreadsheet that may prevent a while however it’s not at all required. All the data you want is supplied.

By the top of the information, it is possible for you to to decide the exact gear change rpm factors to your particular person racing automobile in a method you by no means thought potential earlier than.

The outcomes might even shock you (they did for me!)

While you’re right here, be happy to take a look at the opposite guides and articles on the positioning — you may particularly like this beast on interpreting racing car tyre temperatures to get complete clarity on your setup direction.

Take pleasure in! 🙂

Sidebar: Subscribers to the Your Data Driven blog get this spreadsheet (and plenty of different motorsports sources) for FREE. For extra info comply with this link.

In a racing automobile, the most effective gear to be in is the one that’s going to provide the quickest potential acceleration at any given velocity.

In case you’re within the mistaken gear, you may be going slower than you may be — the equal of solely urgent the throttle down half method.

Curiously, by not realizing their finest rpm shift factors, the majority of racing drivers are presumably making a gift of seconds of “free” lap-time over a stint because of this.

In spite of everything the a whole bunch and hundreds spent growing race engines, not having the racing driver change at the absolute best rpm appears loopy.

But it surely occurs on a regular basis.

Sadly (and possibly surprisingly?) racing automobile drivers hardly ever change at the most effective gear change RPM.

The speculation is ok however whenever you begin to do it for actual figuring out what gear to be in for quickest acceleration is definitely extra concerned than it first appears.

As all the time there’s lots “good recommendation” floating about paddocks and boards on this topic.

For instance, you could hear perceived knowledge alongside the traces of:

“You need to change up gear …

• at max revs,
• on the rev limiter,
• at peak horse energy,
• at peak torque,
• at another mounted level within the rev vary,
• “when if feels proper”,
• “when the automobile tells you too”,
• and many others.”

While well-meaning all this recommendation is deceptive and (sadly) mistaken.

Eek.

Let’s discover this a bit extra.

Up shifts are one problem. The opposite is the down shift.

In actual fact, that is a lot tougher for the race automobile driver and subsequently ends in the next potential affect on misplaced lap-time.

The scenario: You might be slowing for a nook.

The query: Do you modify down or not?

“So is {that a} third or 4th gear nook?”

stated Each Racing Driver EVER …

The difficulty is that your “really feel metrics” can get tricked. It’s because one of many fundamental ones, your ears, likes to listen to the engine at prime revs.

Excessive revs simply sound quicker. However are they?

The factor is, we race drivers additionally know that it may truly be quicker in the next gear.

It may not sound as quick however possibly you might get quicker acceleration out of the nook in a distinct gear?

However how are you going to know?

It’s because you’ll be able to solely ever be in a single gear at a time.

Figuring out whether it is quicker in one other gear can subsequently solely ever be an informed guess, completed within the warmth of the second.

Usually in these “between gears” nook conditions, drivers simply experiment.

Over consecutive laps they may strive going via the nook in each gears after which (one way or the other) attempt to work out (nee persuade themselves) which is quicker.

Admirable. Frequent. Costly? — Sure.

Exact. Optimum. Right? — Sadly No.

It’s my perception that dangerous recommendation is costing racers seconds of lap-time through the course of races.

All just because they aren’t in the appropriate gear on the proper time.

It’s wonderful if you consider it — racing drivers truly having no clue when one other gear could be quicker!

Not altering gear at the most effective RPM (each up and down gears) means you aren’t accelerating the racing automobile as quick as potential so you’re going to be slower than you might be. Interval.

All of the skilled motor racing groups have groups of engineers working these things out. Nice for them however what about you?

What if I urged that with just some items of generally obtainable {data}, you might have the identical absolute certainty on when to vary up or down gears in your racing automobile however with out the fee of a crew {of professional} motorsports engineers?

What when you had full assurance that, it doesn’t matter what velocity, what nook, or what circumstance, you’d all the time know which gear to be in?

How wouldn’t it really feel to know you have been getting the completely most on monitor profit from all that cash spent on engine improvement?

What about when you have been sure that you simply couldn’t presumably speed up any faster?

How would that impact your skill to qualifying or your confidence in that drag to the finish line with one other automobile?

In addition to the efficiency profit, what if I advised you that you might do all this with decreased engine stress as effectively? Discuss having your cake and consuming it!

No extra really feel. No extra guessing. As a substitute, exact gear shift targets.

What when you had targets for every gear ( trace: they’re all completely different!) and all tailor-made to your particular person race automobile — not primarily based on some questionable paddock chat, however your actual setup.

And what when you had this info immediately updatable when ever you made a change to your automobile? Discovered extra energy on the rolling highway or wish to know the impact of a distinct 4th gear? What a couple of that decrease diff ratio? See how these modifications impact every thing, immediately.

While your rivals keep it up with their outdated strategies, you may be assured you understand precisely maximise every thing your engine has to supply.

Driving a racing automobile persistently on the restrict to extract each final 1/tenth is difficult sufficient.

The very last thing anybody desires to do is depart time on the desk.

Okay. Let’s get into this then.

The torque curve of a race engine modifications with rpm; first rising after which usually dropping off at greater revs (see picture under):

As you speed up via the revs the torque obtainable on the wheels additionally peaks after which drops away.

Whenever you change up a gear, you successfully drop again down the torque curve as the upper gear will drop your revs for a similar velocity.

You then speed up once more via the torque curve. Altering once more whenever you really feel the torque dropping away.

Right here is the purpose:

To have quickest acceleration you’ll want to have the utmost torque potential on the wheels for any given highway velocity.

If the torque curve didn’t peak and drop off, however as an alternative continued upwards then you definately would all the time change gear on the rev limiter.

As this isn’t (usually) the case, there comes a degree within the rev band the place there’s extra torque obtainable to thrust the automobile ahead within the subsequent gear than the present one.

For instance. Within the diagram above, let’s say you’re in 2nd gear at about 7000 rpm. The torque from the engine at 7000 rpm is about 100 ft lbs.

The query: Might you get extra torque in one other gear?

The reply: This relies on the gearing. Bear in mind the upper gear will drop us down the rev ranges for the velocity you’re going. In case you drop to some extent on the torque curve that might offer you greater than 100 ft lbs of torque then sure, change gear, in any other case no.

State of affairs 1: Say altering to third gear dropped you down out of your present 7000 to 2000 rpm. The query turns into, is there extra torque at 2000 rpm than 7000 rpm? Trying on the curve on this case, there’s lower than 80 ft lbs of torque obtainable. As 80 is lower than 100 you’d be higher to remain in your present gear.

State of affairs 2: What if altering to third gear dropped you all the way down to 3500 rpm as an alternative? Trying once more on the torque curve there’s about 115 ft lbs of torque obtainable. As 115 is clearly greater than 100, on this scenario you’d be higher off altering to third gear asap.

Hopefully that is smart?

As a racing driver it’s your job to change gear on the actual level that you might get extra torque to the wheels via one other gear.

It may also begin to offer you an perception as to why it’s truly fairly onerous to do that by really feel alone … (trace: how are you going to inform the distinction between just a few ft lbs or Nms?? You may’t …)

Fortunately, really feel is now not require as I’m going to take you thru a calculation you are able to do to seek out the most effective gear to be in, at any velocity (yay!)

Much more fortunately, the calculation applies to (practically) any type of racing automobile (or bike!) and is completely impartial of auto mass or aerodynamics (yay!)

Sure, there are some approximations across the tyre measurement (mounted), tyre slip (none), nature of torque curve (all the time similar) and driveline losses (none) so simply take into account that however these are refinements and never (usually) vital.

(Engineers can do excuses too! :-D)

The output you may get is a extremely helpful little desk, just like the one under:

What that is saying is that in 1st gear I ought to rev till 7786 RPM earlier than altering to second gear. In second gear I ought to rev to 7069 RPM after which change to 3rd. In third I ought to change as much as forth at 6794 RPM and from forth to fifth at 6456 RPM.

Equally, if I’m in fifth and the revs drop under 5255 RPM, then I ought to change to 4th. In 4th when the revs drop under 5108 RPM I’d be higher off in third. And so forth.

Clearly there’s time misplaced in altering gear. It may possibly additionally unsettle the racing automobile. It’d make no sense to solely briefly change down, to then change again up once more and many others. So you continue to want to think about your on-track scenario however, all issues being equal, this little desk offers you absolute certainty what gear could be finest.

On my racing automobile I occur to have a programmable dashboard with shift lights.

This enables me to specify the sunshine sequence primarily based on the most effective gear change rpm for every gear. Due to this fact it’s a fast job to replace the sprint with the most recent figures. I then don’t have to consider it once more (the problem truly turns into forcing myself to vary on the lights and never the sound!)

In case you don’t have shift lights you’re going to want to recollect the numbers.

As they’re all completely different, strive rounding down the most effective gear change rpm numbers to the closest 50 or 100. It will make them simpler to recollect. In my instance above you then find yourself with a desk that appears just like the picture under:

A lot simpler.

If the desk is a pleasant and compact, you’ll be able to even print it out and stick it someplace within the automobile as a immediate till you study it. (Achieve this at your personal danger nevertheless …)

Both method, after getting these numbers you may be assured that you simply’re getting the utmost acceleration your racing automobile has to supply.

Nice hey!

So how?

Maintain on, it’s about to get bumpy!

I’ll now take you thru every step of the method so you’ll be able to create a finest gear change RPM desk like the photographs above.

In case you are not so comfy implementing these calculations for your self (some bits do require coding expertise) then I’ve put every thing collectively this Pro Grade Race Engineering tool that you could pick up here:

Nonetheless, when you’ve the time to place one thing collectively your self without spending a dime, for the problem and/otherwise you merely wish to know the idea intimately, then learn on.

All you’ll want to calculate your excellent gear change rpm’s is the next {data}:

• Revs v Torque curve
• Gear ratios
• Closing drive ratio
• Tyre measurement

The toughest one among these to get is your Revs v Torque curve, as a result of it requires going to a rolling highway.

Not everybody takes their racing automobile to the rolling highway however a technique or one other, you’ll have to get a consultant torque curve for this to work.

Here’s what you want from my spreadsheet:

You simply have to fill within the rpm and torque columns and the remaining is calculated and charted robotically.

I’d say most severe rivals do have this info although (so simply ensure you get a replica of the rolling highway print out if you end up there …)

The very first thing to do is to calculate a desk of highway velocity verse revs for every gear.

To do that you want your gear ratios and the circumference of your tyre — the pushed one if they’re completely different.

I’m going to take you thru a labored instance primarily based on a rear-wheel drive Mazda MX5 (as that’s the present setup I’ve in my racing automobile.)

We’re operating the next 5 speeds and closing drive ratio:

Subsequent you want the circumference of the tyre. It’s because, as we are attempting to narrate this to highway velocity, the circumference offers you the gap travelled for one wheel revolution.

• 185 is a tyre width of 185mm
• 60 is a share of the width and pertains to sidewall top. So in our case: 185 x 60% = 112mm sidewall top.
• R13 is the wheel rim diameter, in inches.

The tyre measurement we’re operating is: 185/60 R13

To calculate the circumference we merely take the entire tyre diameter and multiply by π (Pi or 3.141592…)

To get the entire wheel diameter you’ll want to add the sidewall top (x2) to the rim diameter.

In our case 112mm sidewall top is 4.37 inches (we’re taking the imperial route from right here on btw — solely 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 do not know why tyre sizes are this odd mixture of metric and imperial measurements. It does make issues a bit extra fiddly. Anyhow …

In the spreadsheet I’ve calculated all of the tyre information for you. You merely enter the tyre measurement you have got and it generates this little desk (in a background workings tab).

Alternatively you need to use a web-based calculator like this one to both get the figures or double verify your workings.

We now have every thing we have to calculate highway velocity verse revs for every gear.

With our imperial strategy the equation is:

Revs * 60 * Wheel Circumference / 63360 / (Gear ratio * Closing drive ratio)

To clarify: The 60 is to transform Revs per minute in to Revs per hour. The 63360 is the quantity if inches in a mile.

The output is subsequently miles per hour. Good!

Once more in the spreadsheet I’ve completed this for you. See under. You even get a pleasant little chart, which can turn out to be useful later …

What you can even see on this chart (zoomed in under) is what I’ve mentioned in regards to the RPM drop between gears:

Decide a velocity, say 40mph. In first gear that might be 7000 rpm. In second gear that might be 4500 rpm. In third gear, 3000 rpm. In forth, 2300 rpm and in fifth, just under 2000 rpm.

Are you able to see. In case you knew these rev drops, and also you knew your torque curve (very well) you might work this all out as you went spherical …

Why that is principally not possible to do in your head is as a result of additionally, you will see that the quantity the revs drop between every gear additionally modifications with velocity.

If all of the traces have been parallel then you definately’d have half an opportunity because the drop could be the identical however they diverge.

It’s clearly wonderful you’ve completed in addition to you have got! 😀

Okay. Now let’s calculate torque verse revs for every gear. As soon as we have now that we will then put them collectively and see what it tells us.

To calculate the torque in every gear is a little more straight ahead.

All you’ll want to do is take your torque curve and multiply by your total gear ratio in every gear.

As we did in Step 2, the general gear ratio is the ultimate drive multiplied by the person gear ratio. In our case we get a desk like this:

For every rev level simply multiply the torque by this ratio for every gear.

• at 3000 rpm we have now torque of 115 ft lb.
• In first gear which means 12.2304 x 115 = 1406 ft lbs on the wheels.

For instance:

Try this for every level on the rev curve and for every gear.

Once more in the spreadsheet that is completed for you however it’s simple to do if you’re doing this your self.

You wish to find yourself with the next desk (and chart.)

What you’ll be able to actually see the impact of the gearing right here. The upper the gearing the flatter the curve. Take a look at the large distinction between first and second.

In case you take a look at the slope of that first gear torque curve previous the height, you’ll be able to see it’s fairly steeply downwards. A lot steeper than all of the others.

Within the automobile this appears like you aren’t accelerating as shortly, even slowing down.

Racing drivers usually quick shift right here pondering they may get extra acceleration from the following gear.

As you will notice under, regardless of the way it feels, the best choice in our instance is definitely to run 1st practically to the redline …

Really feel is historical past!

Let’s begin pulling this all collectively.

We’ve revs verse highway velocity for every gear. We’ve revs verse torque for every gear. We will now create what we’re actually after, highway velocity verse torque for every gear.

Relying on the way you’ve completed this you’ll be able to merely copy the related figures over. In my spreadsheet I’ve simply referenced the cells and lined them up robotically make this desk:

And from this you’ll be able to generate my favorite chart of this complete train:

Cool hey!

And it’s truly tremendous informative.

Take a look at this one:

See the (crude!) highlighted line? This line is a “frontier” line. It represents the optimum chance …

The quickest acceleration will come from getting essentially the most torque to the wheels at any given automobile velocity. And that’s the yellow line.

We merely want to remain on the yellow line to have the quickest potential acceleration at any velocity.

Growth!

A bit like monetary portfolio evaluation (humm!) if we’re on the frontier line, then there is no such thing as a higher {position} we may undertake.

To remain on the road, all we have to do is change gear the place the traces intersect.

Let’s calculate that too and make our desk.

The very best gear change rpm factors are the place the traces intersect.

Choice 1: Learn off the charts

The simplest method to do that is solely to learn the factors off the chart.

First: Check out the zoomed in torque verses velocity chart above.

You may see the primary and second gear traces cross at about 42 mph.

Second: Now return to the Revs verse Street velocity chart (see under).

Learn alongside the X-axis till you get to 42 mph.

Then learn up till you hit the primary gear line.

Then learn throughout to the Y-axis for the revs.

You get about possibly 7600 rpm? Or thereabouts.

Merely do that for all intersections alongside the frontier and bingo you’ve bought your desk.

For a 5 velocity gearbox, there are 8 shift factors to exercise (4 up and 4 down).

That is simple and can get you actually shut.

Nonetheless, in spite of everything the hassle to get this far it appears a disgrace to estimate the important thing outputs by eye, so …

Choice 2: Optionally available Modelling strategy

Alternatively you’ll be able to attempt to code this up in order that it’s automated, extra correct and quicker to replace. You flip this from a one off to a mannequin you’ll be able to experiment with. Rather more helpful.

Creating all this as an immediately changeable mannequin is absolutely the principle bit I’ve completed this for you in my spreadsheet.

In case you are doing this your self, it’d assist to know I ended up utilizing an incredible piece of open source VBA code for the intersection. You may then merely code a linear interpolation to seek out the exact Revs from the intersection mph.

It took me fairly some time to determine all of it out to be sincere. Nonetheless, in my workings ended up with a structure like under that might offer you some inspiration.

I’m positive smarter folks than me can determine different methods / higher methods — so let me know!

Anyhow, both method we’re there!

You need to now have just a little desk like mine to your particular person racing automobile. {Data} you’ve by no means had earlier than. Intelligence over your rivals. The data of extract the quickest potential acceleration out of your racing automobile. The very best gear change rpm factors to your racing automobile.

Properly completed!

What I additionally did in the spreadsheet was spend a little bit of time dashboarding out the outcomes.

Along with the desk I’ve additionally created this chart which you may additionally wish to take into account.

This chart is successfully an adaption of the revs verse highway velocity chart we noticed already however exhibiting the frontier.

I believed it summarised every thing properly. You may see the most effective gear change rpm factors, up and down, and what velocity we must be travelling at.

It’s also possible to see how the optimum factors change relative to one another, which I feel is beneficial.

The one factor that basically bought me when placing this all collectively, was how a lot distinction there’s in the most effective gear change rpm via every gear.

In our instance it’s a huge 1330rpm distinction between the most effective shift level in first gear and the most effective in fourth.

That’s definitely by no means one thing I’d have thought of earlier than.

What about reliability? Properly, lets simply say that every one these decrease revs will make your engine builder (or your pockets) happier too!

All that’s left is to both print the desk out to stay within the racing automobile as a immediate till you bear in mind them, or, program your dashboard shift lights when you have them.

Better of luck!

It’s outdoors the scope of this publish to delve an excessive amount of into this however you can even use this similar info to help your aero tuning / setup / improvement.

By multiplying the torque on the wheels by the tyre radius you’ll be able to calculate the ahead pressure on the contact patch.

If you understand your automobile’s mass and drag traits, you can begin to think about optimising your gearing and aero decisions primarily based on the quantity of ahead thrust you have got obtainable at any given velocity.

This will get tremendous difficult quick however no less than you now have a part of the puzzle …

In case you are curiosity in utilizing the spreadsheet I’ve put collectively to help this text right here is a few extra details about it.

In case you take a look at the picture above. All you’ll want to do is present the data in Step 1, within the three little bins — circled within the picture.

All of the charts, tables and graphs this immediately replace along with your {data}.

• one other diff,
• completely different gearing in as much as 5 gears
• a distinct tyre measurement, or
• even the impact of modifications to the torque curve.

You may immediately see the results of:

I’ve additionally included the rounded desk of finest gear change rpm values if you’re going the print out route.