Readers reply: Why are cars designed to be capable of going much faster than the speed limit?

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Why are cars designed to be capable of going much faster than the speed limit? (Don’t tell me they’re made with the Autobahn in mind.) Andy Crosby, north Wales

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Readers reply

Because for mechanical reasons a car that can reach 100 is going to perform better at 70 than a car that can only reach 70. Also, an engine that can only achieve 70mph on the level may struggle on hills. I had a 1.2 Clio that needed me to anticipate hills and drop a gear so it didn’t get out of breath. My Golf diesel would take those same hills in its stride with no complaint. Of course you can fit speed limiters to vehicles (I frequently drive a limited minibus). Consider however the problem that arises when one speed-limited lorry tries to overtake another and slowly grinds past in the middle lane of the motorway and the chaos and congestion that ensues. YorkshireExPat

I believe the Germans call it “elephant racing”. Socialismnow

Because men are too embarrassed to buy Viagra, of course. GregKZ

Because it sells them? Motoring journalists like to include acceleration and top-speed performance in their reviews as a positive thing so presumably car buyers want faster cars even though they can’t (at least in theory) use that performance. reggiepurrin

I bought a 2015 Audi A5 3.0TDi Quattro five years ago. With 245bhp it will see 60mph in under 6sec. When you need that oomph to pass a dawdler doing 40mph on an open highway, then it means overtaking is quick and effortless, thanks also to the bags of torque.

Its top speed is a limited 155mph – I’ve never seen it. In France I’ve done 82mph on the autoroutes where it’s the legal maximum.

The best part is that, despite engine size, it’s literally ticking over at 70mph at 1,600rpm and means it will get over 50mpg on long runs. Hence, it’s a good grand tourer, with ability to waft along, have a decent slug of power and grunt when you need it. It called having flexibility. I’m looking forward to my next road trip to France already! chilledgibbo

You are Jeremy Clarkson and I claim my £5! Tattie_Bogle

It disappoints me that the move to electric power has not been taken as an opportunity to end the obsession with higher and higher power motor vehicles. We see adverts boasting of insane acceleration rates and high figure power outputs, the consequence is a need for bigger and bigger batteries, more and more mass and so with it much greater environmental impact, in manufacture and use. The opposite of the potential of electric vehicles to reduce the impact of personal mobility. Bring on properly enforced lowered speed limits and aggressively punitive taxation of over large and powerful personal vehicles. Evan1

Best efficiency point. Designed for 70mph it would be operating flat out. Imagine sprinting endlessly every journey. Designed for a top speed of 100mph, then 70mph is a cruise. Comfortably running along. senoj1

Quite a few EVs are bucking the trend in that while they have very quick acceleration their top speed is relatively low. For example mine allegedly gets to 60 in under 7sec, an acceleration that would have been associated with a top speed of 130-140. In fact its top speed is about 108, which is more than adequate allowing a comfortable margin of reduced stress at legal speeds. It’s also true that some EVs will hit 60 in 3sec or less, which begs the question how many drivers can handle this without hitting something more solid. seedysolipsist

Fuel efficiency – if the car is capable of going 240kph while red lining in fifth, it probably hits 120kph revving much lower and burning less fuel. Macknight

Because speeding fines are a valuable source of revenue? EddieChorepost

Margin of error (AKA safety). You want to be using mechanical devices that are not running at stress points all the time, because you will occasionally need to swerve (at legal speed) to avoid an accident, and having to the wheels fall off isn’t good. speedy95060

A car with an engine with a “design” speed of 130mph, can be fitted with a carburettor that is “undersize” for the engine, thus limiting power and speed accordingly, but with all the advantages of less stress on the engine and moving parts. Of course, this will cost very near as much as the “unrestricted” version, so I guess manufacturers go with the higher speed version to increase sales as boy racers like to go over the speed limit!

balanceandreason

Cars are sold as toys, only incidentally as transport. lochaber1

I hope this is the answer they put in as the “final word”. Dorkalicious