Tyres to Tarmac
Welcome to part two of trying to make the black rubber doughnuts on your rims more understandable.
Let’s recap briefly…
In part one, we introduced the engineering tyre model, explained how tyres are characterised using slip angle & force, ultimately to conclude that a go-round of Oulton Park by a fresh ACU licensee is not as fast as Shakey Byrne’s recent record lap partially because the Shakester is closer to generating peak grip on his Pirellis.
Sorted. Questions? Feel free to leave a comment.
Part two is all about a principle called tyre load sensitivity, which simply means that tyres are sensitive to the amount of load they have on them, and (more practically) that Dani Pedrosa should be the fastest man (boy) on the MotoGP circuit… technically speaking! Before I’m knifed, howay… technically speaking! Let me explain.
Ever heard the old adage, “forget the trick new pistons, go for a jog”? Well it’s somewhat advisable. The lighter you are, the faster you become. And that doesn’t just apply in a straight line. Of course we know that if you pit a 10 stone rider and a 12 stone rider against each other in a drag race, assuming they have exactly the same reaction, throttle input, all the rest of it, the 10 stone rider will win every time.
What I’m talking about here is purely based on tyre science. Here is what happens when you increase the load on a tyre…
Hopefully you read this part before you try to make ones and twos of the graph. The graph shows the same type of curve from Part I of Tyres to Tarmac, but with different loads being applied to the same tyre. Let’s just say you have (including a rider) a 400lb bike, a 600lb bike, an 800lb bike, and a 1000lb bike…
For 400 pounds of downward force, you get 400 pounds of cornering force (1.0 G). For 600 downward, you get about 575 cornering (.95 G). For 800 downward, you get about 700 cornering (.88 G). For 1000 downward, you get about 800 cornering (.80G).
What’s the pattern? The more downward force you have on a tyre (in this case, weight of the bike/rider), the less G force you make (lateral or cornering force divided by downward force). This is one of the big reasons why weighing less can make you faster.
You might also notice that with an increase in weight (downward force) it takes slightly more slip angle to gain peak grip. Ask yourself, do you know any massive blokes who go quickly and don’t always look like they’re keeping it together? There’s a reason. They have to make up for their lack of straight line speed in the corners, where it takes a bit more sliding to reach the limit. It’s science.
If you were wondering, yes this applies to your Michelins, Pirellis, Dunlops, Avons, Continentals, Yokohamas, Nittos, Toyos, and all the rest of them. It’s a universal principle. The numbers might not be exactly the same for each manufacturer, but the pattern still applies.
This is partially why teams spend hundreds, thousands even tens of thousands at the national level (and even hundreds of thousands in development at the international level) to take every last gram out of the bikes they possibly can. It’s why riders tend to put emphasis on lowering weight when training for motorcycle racing. Yes, it leads to straight-line speed… but we’ve just shown you why weight loss helps your cornering ability as well.
I say all this to say Dani Pedrosa, the lightest rider in the world championship’s blue riband class, should be the fastest man-child in MotoGP. You might not think so, but it’s science… you can’t argue with that.
We wrap up Tyres to Tarmac in Part III next week, so stay tuned…
Main image: Colin Port