McLaren 720S vs Mazda MX-5: Which is the most fun?

What percentage, I wonder, can one get out of a McLaren 720S on the public road? I was pondering on this while driving the GT in France and realised there is a way that question could be answered. What if we drove the car on one of our favourite stretches of road, keeping to the national speed limit as far as possible, and then afterwards plugged a laptop into the car’s on-board diagnostic system that, among other things, logs throttle position?

Better still, we could take that most usable of sports cars – the Mazda MX-5 – and do exactly the same. We would then be able to compare the data from both cars and even overlay them over each other to see the difference in percentage throttle used. We know that driving a car like the MX-5 to its limit is just about the most fun you can have but it would be interesting to put some numbers to it.

So that is why I am heading down the M3 in the McLaren. The destination is Crickhowell and the roads that I’ve been driving on for the past 30 years. But before that, I’m stopping off at Litchfield Motors in Tewkesbury. I have known Iain Litchfield since he started his eponymous business at the age of 19.

Iain and his staff of boffins forget before breakfast more about software and engine management electronics than I will ever know. Put simply, if Goodwin was to start mucking about with either cars’ brains with a laptop, it would be a disaster. The poor car would probably end up thinking it was a Suffolk Punch lawn mower and run on just the one cylinder.

The reason for stopping off at Litchfield Motors was to check that it will be possible to extract the data, and in particular the throttle position. Iain knew that it was possible with the MX-5 but wasn’t 100% sure about the McLaren. It turned out there was no problem. Better still, Iain is sending technical manager Dan Cook along to help us with gathering the data.

The next day, Matt Saunders, Cook and photographer Luc Lacey are in a car park on the B4560 above Crickhowell. It’s a bit miserable with showers coming and going. Saunders has brought with him the MX-5. We’ve chosen a 1.5-litre version because its 130bhp will better illustrate the point we’re making.

We plan to make three different runs. The first is the run up from Llangattock (a small village just outside Crickhowell) up to a T-junction where it meets the B4560. Once you’re out of the village, it’s national speed limit the rest of the way. We reckoned that the best plan was to drive up in a pair with the lead car setting the pace and the one behind it being the one whose data was being captured. For consistency, Saunders is to drive the McLaren on all the runs and me the MX-5. Cook will ride shotgun in whichever car is being ‘data captured’.

The second and third runs we will make along the B4560 in each direction. Our first run is between fields and trees but the others are much less hemmed in and across open moorland. The first run is entirely uphill, the others mostly so. No point using long stretches of downhill because both cars will spend time coasting with closed throttles.

So here we go. Saunders in the 720S on run one with me following in the Mazda with Cook. He’s not even using a laptop, just his mobile phone, which receives the data via Bluetooth from a widget that he’s plugged into the car’s OBD port. It’s that simple.

On these damp roads, it’s amazing how much effort I have to put into keeping up with the McLaren. Also, it’s much easier to keep myself from going over 60mph than I expected it to be. Mostly I’m in third and fourth gear, only briefly into fifth.

With the run done, Cook slips into the 720S and it’s their turn to follow me as I drive as near as possible at the same speed as before. I suspect Saunders is having less trouble keeping up with me than I did following him. Now to what we call the top road. Our first run on this route works perfectly and we later discover that we’ve managed to keep within two seconds of each other over a run that took 140 seconds. Unfortunately, on the run in the opposite direction we’re baulked by traffic, but no matter because the results from our first run up from the village and then our first across the open moorland are excellent.

Saunders reports that he’s been using hardly any throttle but I can’t wait to see what the data says. Cook produces a graph that tells the story perfectly. For long stretches, the MX-5 used about 93% throttle (actually, the maximum opening possible), while in contrast the 720S only for one brief instant used 70% but averaged nearer 25%. Our speeds, as you can also see from the graph, were very similar – and more or less within the limit.