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An interlock example

MG X-Power SV-R

It’s been a while since I posted about an architecture of control designed to assist/protect the user rather than to frustrate or intimidate, but just reading a great article about the MG SV-R supercar formerly produced by MG Sports & Racing*, a very simple interlock example (more discussion of interlocks and forcing functions here and here) was mentioned:

“So, behind the wheel… pressing the clutch all the way down (a US requirement to avoid starting in gear) the starter button brings the V8 to life….”

Can any US readers confirm if this really is a requirement for all manual gearbox cars – presumably because the dominance of automatics makes it more likely that a driver will accidentally start a manual car in gear?

I know in the UK quite a lot of people do, in practice, start manual cars with their foot on the clutch, often simultaneously putting the car into first gear while turning the ignition key, but never having been the owner of a car that didn’t need substantial warming up/choke adjustment to prevent it stalling as it pulled away, it’s not an automotive design issue I’d considered before!

*The UK registered design for the car has now been transferred to Nanjing, but it seems unlikely it will be reintroduced in its original form.


  1. Part of me is glad that Nanjing has the car, since I was unimpressed with Shanghai’s bullying tactics. After all, they already have the MG TF and numerous other designs. But you are right: the SV is unlikely to return, even if Sport & Racing itself was making a bit of money for the troubled MG Rover Group.

  2. I can confirm that in both the US and Canada, you must push the clutch all the way down to the ground before you can start the motor. I feel a little naive after reading this post, because although I’ve been to the UK before, I’ve never driven there and it’s never even crossed my mind that one wouldn’t have to do that!

  3. Dan

    Thanks Lindsay! Much appreciated. I guess little differences like that are the kind of thing that rarely gets mentioned, as everyone assumes that it’s like that for everyone else. It’s a good example though to introduce the idea of an ‘interlock’ through something people are familiar with every day.

  4. Jason

    I’ve driven older manual shift cars in the US that had no such requirement. Starting the car in gear with the clutch up resulted in wild bucking. I now drive a 2001 Kia, and it requires the clutch to be depressed before the car will start.

  5. Tom

    Not all US cars have it…

    I was always taught to automatically press the clutch regardless of the gear position as it reduces drag on the cold gearbox and more chance of the engine starting -mindyou I have always had old cars. It is all part of driving technique – along with checking the mirrors – before pulling out in front of a lorry!

    There are a number of times it is useful to start in gear –
    If the clutch release mechanism fails – you can successfully start the car and get home… If the clutch sticks on from lack if use it can freed in a similar method, and if the engine won’t start the car can be succesfuly moved off the road using the starter.

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