At the conclusion of the Rally Sweden Power Stage, I was tagged in to a conversation about why the Hyundai i20 Coupe lacked the max speed of the Toyota Yaris. One side argued the Hyundai engine must be weaker, the other believed the Toyota aero to be more efficient at high speeds. My belief was it was more to do with gear ratios. Being the Nerd of the Forest that I am, sought what could be pulled from the telemetry.
Fortunately all 3 cars of each team were carrying telemetry on WRC+ and so a basic chart like this showing speed to engine revolutions can be made.
The power output of both engines are equal – 380hp, and both limit at 8400rpm. If one engine is ‘weaker’, surely the perceived line of each gear should be parallel to the other car. If they are further apart at the top than the bottom as would be expected than the ratios are different, even if minuscule. That is my perception. It’s too difficult to tell how the aero influences this but obviously if you took it all off these profiles would change. I would defer to Lluis from https://wrcwings.tech for his input here.
Whilst we’re here, the top speed recorded less than/above the 8400rpm for each car:
- Neuville (H) – 190/194
- Tanak (H) – 192/194
- Breen (H) – 190/195
- Rovanpera – 195/198
- Evans – 188/199
- Ogier – 194/198
The Toyota edges 5-10kph faster at the same rpm and at top speed. On Likenas it must have helped Kalle Rovanpera win at an average speed of 116kph and 3.7s quicker than Neuville. Indeed the splits agree where the faster parts were at the later KMs of the stage. Without engineering diagrams for the engines, gearbox, differentials and running gear, or other expert insight, this didn’t warrant a post from me. This chapter is muddy enough!
An Idle Mind Pottering
During lockdown boredom I realise I never got round to Part 2 of 2019s stage results review (part 1 of 1 is here). Part 2 should have had something to do with the cars results with graphics along these lines. These are the number of stage wins (size of bubble), placed to average speed and distance of those wins.
The time for that post has gone but I began thinking again about speed/rpm ratios and correlations. It makes sense if Hyundai are running shorter gear ratios than Toyota they are at the right ends of the chart for average speeds. Hyundai have better acceleration on slower stages, Toyota higher top speeds on faster stages.
So I went looking for more telemetry from Citroen and M-Sport to see if this speed/rpm graphic, however basic, was telling enough. This was also an adventure to see if any differences between the 18 and 15inch wheels on asphalt and gravel setups were apparent.
But something grabbed my attention when working though the first set of comparisons. Hyundai’s ratios were higher in Finland than in Germany while all other manufacturers were the same.
An Idle Mind in Confusion
If there was a difference between 15 and 18inch wheels why were 3/4 of the teams not bothered to change? Was it a tactical move for Hyundai as Finland is the fastest rally. But the rule book gives no help in clarifying the legality of this. I have found only the following phrase from a Technical document from 2015. I need clarification if this is applicable.
Only the ratios, the housings and final drives homologated in the
WRC extension may be used (without any modification).
ANNEXE J / APPENDIX J – ARTICLE 255A
Even if it is applicable, it’s vague. Does that mean more than one set of ratios can be used? I’ve tried looking but have found no further clarification. All I know is you can’t micro-dial ratios in the real world like you can in Dirt Rally 2. They are physical lumps of metal that need to be manufactured. AFAIK you can’t +/- 0.1 of a tooth on a gear wheel. At this level of world class competition they are highly engineered. It costs money to even think about doing that. Or is it easily done? Please let me know.
A tweak to the differential can change the entire gearbox profile but this wasn’t the case in the Hyundai example where 6th gear hadn’t changed between transmissions. A second or third gear setup is plausible, I thought, but where were the lines. Which events were the teams tactically applying these supposed different gearbox setups? This became the focus of my investigations.
The WRC sporting regulations explain that each car needs to be linked across pre-selected rallies and with engine and transmissions sealed. I don’t fully grasp the depth or purpose of all these regulations but it led me on.
Blessed be eWRC
The very good people at eWRC record which cars take part in each event. This will save me the task of working through every round grabbing telemetry. Here’s a simple matrix for each team showing the events each car took part in.
We know Argentina/Chile and Portugal/Italy were linked events, the same car had to do both events. This checks out for all except Lappi whose car in Argentina was damaged beyond repair for Chile. But it’s amazing how there is absolutely no correlation between the teams in which events they enter cars in.
Hyundai used different cars in Germany and Finland, as did Toyota and Citroen. M-Sport kept the same cars. Only Hyundai ran different transmission ratios.
Meeke did 10 events with the same ratios. (Assumption, not verified). I have checked that Meeke’s Monte ratio is the same as Tanak’s Spain. These are different from Meeke’s Chile ratios, which is a different car.
Neuville’s Chile is the same as Mikkelsen in Finland.
Ogier completed the season in 2 cars, the fewest of any driver. Telemetry from stages in Monte and Turkey suggest the same ratios in the same car. It also appears to be the same ratios in the second car in Finland. That’s not to say the transmissions weren’t changed for another rally.
At this point I invite you dear reader, to tell me what I am missing so I can delete this post. I will probably go no further as there is too much to look at. I would like to know how many different transmission ratios are teams allowed? Does/Could transmissions have a sporting purpose? Why don’t the teams obviously link the faster/slower ratios to the faster/slower rallies? Have I misinterpreted or mis-represented data? Does the difference in tyre size match the difference of wheel size between asphalt and gravel setups?
Some points to consider if you made it this far. In many cases I cut any data where throttle was less than 33% and braking was over 33%. This leaves data points where the engine is mostly under power. There are also other factors at play such as hills, aero, air pressure etc. Before you do insult me may I remind you the key purpose of doing any of this was to fill some lockdown hours and educate me.
Massive thanks to https://www.gpsvisualizer.com and https://www.ewrc.com without whom this noodling wouldn’t be possible and my lockdown wouldn’t be passing quite so fast. Also thanks to WRC+ whose telemetry data is being used for fair comment and critique, and for posting some fantastic historic season reviews lately.
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