568bhp per tonne is an absurd figure. It’s something that needs to be put in context to be properly understood since power-to-weight ratios aren’t something we quote all that much. But once it’s pointed out that this number exceeds what two of the ‘Holy Trinity’ of hypercars from a few of years ago manage, you get the picture.
It’s more than you’ll get from any mainstream supercar and a figure that bests the original Bugatti Veyron. And yet, it’s made possible in this Radical SR10 by a reasonably humble powerplant: a Ford inline-four.
Specifically, it’s a 2.3-litre Ecoboost inline-four. It’s had a bit of work done to it, including the addition of forged pistons and con-rods, a dry-sump lubrication system and a Garrett G-Series turbocharger. This means you get 425bhp and 380lb ft of torque to play with, with those outputs only having to shift a measly 725kg of car.
It’s that light because there’s precious little of it. The SR10’s footprint is similar to that of a supermini and there are no doors, roof or windscreen. FIA LMP-inspired composite bodywork clads a tubular space frame chassis, and there’s no real cabin to speak of - merely a couple of seats, a small array of buttons and a steering wheel. Exactly what you need to belt around a track chasing lap times, and nothing more.
Peterborough-based Radical is known primarily for its bike-engined track beasts, so it was useful to have a go in the high-revving, Suzuki inline-four-powered SR3XX as a primer. Partly to understand Radical’s core product (it’s sold over 1000 SR3s), but also to see where the SR10 differs. Primarily, that’s in the latter’s brutality.
The revvy, naturally-aspirated SR3XX feels quick so long as you rev it out, but you quickly get on terms with its level of straight-line pace. The SR10? That takes a little more getting used to. From the boosty mid-range all the way up to the redline, it offers eye-widening, breathtaking acceleration, interrupted for only the briefest of moments as the Formula 2-spec Hewland sequential gearbox aggressively bangs-in another cog.
It’s not the best match for cold tyres, as I find out via a clumsy, awkward sideways moment exiting the tightest corner of Bedford Autodrome’s west circuit at only partial throttle. Once the tyres are up to temperature, though, the rear slick tyres are untroubled by the fat wad of torque being sent their way.
That’s probably for the best, as it’s difficult to module the throttle on corner exits. I’m finding myself skirting around the boost threshold point, and even in the middle ground fifth throttle setting, the power delivery is astonishingly aggressive.
It’s noticeably quieter than the SR3XX, which becomes painfully loud as you near the redline. Over a certain point, all you can hear is wind noise, meaning my shifts from third to fourth and fourth to fifth are often short. The manically flashing LEDs of the shift light system help, but with my eyes glued to the track ahead, I’m not always noticing what they’re up to.
Playing around with the seating position to give a better view might help, but in any case, it’s not much of an issue. There’s so much torque propelling such a light car that you can easily get away with being a gear higher than you need to be on all parts of the circuit.
Although you can play about with the throttle mapping there are no traction control settings to fiddle with. Because it doesn’t have traction control. Or ABS. Which sounds scary in a near-600bhp-per-tonne car, but in reality, it isn’t.
The brake pedal has plenty of travel and feedback, making for easy modulation. And if you get ambitious with your corner entry, the SR10 seems to respond with mild understeer before anything more tricky arises to threaten a trip into the kitty litter. The suspension is highly adjustable, though, so it’s presumably possible to go for a more oversteer-prone setup.
That’s not to say I’m finding this easy. The way I’m being belted out of corners means my feeble, slow-paced mind is struggling to keep up as the next bend arrives much sooner than expected. I’m scrubbing off more speed than I need to and making up for it by riding the SR10’s boosty wave in the middle part of the corner, my head pushed against the roll hoop from the G-forces. If you’re more talented than I (which isn’t hard), it’s possible to pull 2.3 lateral G in this thing.
Whatever Gs I’m managing, it’s causing me actual pain. And what I don’t realise at the time is that it’ll still hurt the next day. You also feel everything from the uncompromisingly firm double-wishbone suspension setup. Every little bump in the track shudders through the frame and your body, and each greedy clip of Bedford’s weird dipped kerbs damn near knocks the wind out of you. The steering is, as you’d expect, very direct, and also unassisted. It is possible to spec an optional power-assisted setup, but I’d be happy leaving it as is.
In the end, it turns out I’ve only bettered my best time in the SR3XX by a second or two. But that’s probably the way it should be - it’ll take time to unlock the 10’s full potential. It’s something that needs working up to, and among the rewards on your way there are thrilling adrenaline spikes on a magnitude that a conventional track-focused sports car just can’t deliver.
The engine doesn’t make the most soul-stirring soundtrack, but it’s hard to argue with its hilarious clout. It gives similar performance to the SR8’s V8s (which, brilliantly, is two bike engines stuck together), but with a far longer life between rebuilds - the modified Ecoboost unit can endure 80 hours of abuse before needing any work, outlasting the rebuild interval of the gearbox. So really, it’s quite sensible. Ish.
The SR3XX is the sweeter of the two I’ve just driven, and the SR10 does have the feeling of a sledgehammer in comparison. But it’s the latter that leaves me striving to be a better driver - to chip away at those lap times while the cornering forces destroy my weak neck muscles. As a weekend track toy or club racer, it’s superb. The only downside is the cost of entry - with a starting price of £126,000, this one’s for wealthy track day types and, according to Radical, “motorsport country club members”. Any suitable volunteers?