The topic of bump stops does not attract much interest. But especially in cars with lowered suspension, and in light-weight cars, bump stops form an important part of the springing system.

A bump stop is the (usually) rubber buffer that is compressed as the suspension reaches full bump. (Some cars also have full droop buffers as well.)

Traditionally, bump stops were impacted only rarely, but more and more often in current cars, the suspension is designed in such a way that the bump stops are frequently contacted.

Let’s look at light weight cars first.

In a light weight car, the variations in possible loads make up a greater proportion of the overall vehicle mass. This means that, to avoid bottoming-out, the suspension must be set up more stiffly to cope with the potential load variation.

Or – and here’s the key point – the bump stops can be designed to be increasing rate (but still relatively progressive) springs that are brought into operation when the car is carrying full loads over bumps. That way, the spring rate of the suspension during ‘normal’ load carrying can be set much softer, giving a better ride.

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Orville and Wilbur Wright were genuine engineering heroes. Despite their relatively humble beginnings, these men were the first to ever to build – and then successfully fly – a powered aircraft.

I’ve often read descriptions of their brilliance that damns them with faint praise: they were ‘just bicycle mechanics’, their work built heavily on the efforts of others, and so on.

In fact, they were simply brilliant engineers, with an astounding work ethic and the ability to both physically make things and also theorise about outcomes.

Unless you think I overstate the brothers’ abilities, consider these points… They built their own wind tunnel and tested in it almost 200 wing sections; they built an internal combustion engine with the then best power/weight ratio of any engine in the world; they made every part of their own aircraft – from that engine through to propellers to wing and control systems; they developed the concept of an aircraft banking into turns – and a lot more. 

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The more you think about turbo boost control, the more implications there are for any given system.

Let’s just refer to a traditional wastegate system.

(That’s where there’s a bypass passage – the wastegate – around the turbine. Open the wastegate and exhaust can bypass the turbine, slowing turbo speed and so dropping boost pressure. Remember – the less open the wastegate, the higher the boost pressure.)

In this discussion it doesn’t matter if it’s an electronically controlled system or a simple pneumatic system.

Let’s say that boost pressure is sensed from the compressor outlet of the turbo. If the maximum desired boost is 10 psi, the maximum outlet pressure of the compressor will also be 10 psi.

But the situation changes if the boost pressure is sensed from the intake manifold. If 10 psi is again desired, the boost pressure at the manifold will be 10 psi, but the boost pressure being developed by the turbo will need to be higher.

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I’ve just returned from a week on the road.

The vehicle of choice was my recumbent pedal trike, a design that you can read more about here and here. (In the pic above I’ve just finished my ride, so explaining the wrong shoes.)

I left Gold Coast and went to Tallebudgera, Pottsville, Byron Bay, Lennox Head, Yamba and then Grafton – mostly in northern NSW. Carrying full camping gear, I stayed each night in local caravan parks, spending one night in each except at Yamba where, because of steady rain, I spent two nights.

My last stop was at Grafton, where I got picked up by car and trailer.

Including diversions, I rode about 350 kilometres.

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