Ahead of the Curve

This week: Your prioritises | Mass effect on Accel | Updated How-to

​

Ever get the feeling your car's job list seems never-ending, Reader?

As soon as you tick off one job, another five appear!

It is so hard to prioritise...

...even worse, when members of your team have different opinions on what is critical (or not)!

Here is how you can make this easier - with Maths!

What is more important... Now?

A team I work with asked me to help add a little objectivity to a "discussion" they were having on this.

Their race car was over the minimum weight for their class.

The debate wasn't about whether that was a bad thing (clearly it is) but about how bad it was – in the context of the infinitely long list of other "to-dos" on the car.

Some felt the weight was a priority, others (strongly!) felt it wasn't.

What would you do?

Ever found yourself in a position like this? What did you do?

With multiple different things on the board, the heated debate isn't normally about the jobs per se, but about how much should be invested in solving them now versus later.

Even working on these on your own is hard.

Below, I'm going to show you the effect of two different masses on acceleration. But don't forget, the actual problem here is prioritisation.

​I'm happy to help you too [link].​

​

Where is a heavier racecar slower?

Perhaps surprisingly, the weight of your car does not affect your potential top speed – in simplistic terms at least. For a given power, your top speed is determined by losses – some mechanical but the majority aero.

I've written more about this in the gearing articles [link].​

Your car's weight becomes an issue in acceleration – i.e., the time it takes you to get to that top speed.

A car that weighs more is going to accelerate slower – I think nearly everyone would agree with that mental model? I hope so.

How much slower? Doing The Maths

For this race team, I built a simple model to show them their car's acceleration profile. I've changed the numbers to my race car so I can share this, but the result is below:

I ran two cars in my model: 650kg and 700kg, with 145hp and a 0.7 Cd. Starting out at 50 mph – as these guys don't do standing starts – you can see a couple of things.

The top speed is the same, and the lighter car is getting to each speed faster.

The thing is, the lines look pretty similar. If you were the guy who said, "don't bother with the weight reduction now," you'd be feeling pretty good.

But look what happens when you look at another view.

Comparison view of the data

I decided to compare the time it took for each car to reach the same speed by calculating the difference.

This chart surprised me.

What it says is that the difference in the time it takes for one car to go from 50 mph to 100 mph is about 0.6 seconds.

Not great, but perhaps not the end of the world. The big difference is at the high speeds.

And thinking that through, it makes sense. As you get closer to your maximum speed, you've got less force available to accelerate the mass. Your top speed is the point where the power available can't accelerate the car anymore.

The Upshot?

Well my feedback to the team was a question: What tracks have you got coming up? If you've lots of slow, twisty tracks park the mass for now.

If its all high speed, then what can you do to take mass out of the car in easy steps, now!

More Power...

When you have models like this, you can't help but play around... so what if you had 5hp more power? Sure:

This is two cars, both 650kg, one with 145bhp and one with 150bhp.

The more powerful car goes about 1mph faster top speed and gets there quicker – in a very similar way to taking 50kg out of the car!

I'll have both please!

Hope you found this interesting? As I say, if you've a study I can help with get in touch [link].​

Good luck staying ahead of the curve,

Samir

p.s. Coming soon, I'll be opening the doors to another cohort of Master Your Tyres [link]. If its a programme you've been thinking of doing then you're not going to want miss this. You'll be first to know.

​

P.P.S. UPDATED Advanced Gear Ratio Optimiser

Changing gear at the right time can gain you meaningful amounts of free lap time. If you can change the ratios or diff in your car, picking the right ones can give you even more of an advantage. My tool to help you doing this is now in iteration 71, so it was about time I updated the how-to guide.

Watch below and grab your copy here [link].

​

​

​