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.

And in cars with lowered suspension? In these cars, the amount of bump travel is decreased. Even with the stiffer springs that are used, the bump stops are likely to be hit much more often than with the unmodified suspension.

This pic shows two very different rear suspension bump stops. Both are from front-wheel drive cars with torsion beam rear suspensions. The bump stop on the right is from a Honda Insight and the one on the left is from a Daewoo Matiz. Both are tiny, light weight cars.

The two-seater Insight has a short travel rear suspension – the designers get away with it by specifying a small load carrying capacity.

On the other hand, the Matiz is a four seater – its potential load variation is much greater than in the Honda. So the Matiz designers have done two things differently to the Honda. They use stiffer rear springs – and a much better design of bump rubber.

Both the Honda and Daweoo bump rubbers are progressive – that is, their spring rate (measured in pounds/inch or Nm/mm) increases as they are compressed. This increasing rate is achieved in two ways – the shape of the bump stops and also the fact that they are made of rubber, a substance that naturally has an increasing spring rate.

But as the pic shows, the Daewoo bump rubber is far more progressive – the thinner parts of the rubber initially compress more easily, bringing together the thicker, stiffer parts. Not visible in the pic is the fact that the Daweoo bump rubber also has a hole through the middle into which the compressed rubber can expand.

If carrying loads in the Honda, the rear suspension can easily bottom-out with a jarring thump. To overcome this, I originally fitted Daewoo Matiz springs to the Honda (they go straight in), a swap that gives a stiffer rear suspension. However, the standard Honda rear dampers are then a bit soft – to get best results, they should also be upgraded, something I didn’t do.

I ran with the Daweo rear springs and standard dampers for about a year, but then recently wondered what would happen if I went back to the original soft Honda springs – but also fitted the Daweoo bump rubbers.

And the result? It’s very good – a softer rear suspension but without the jarring bottoming-out over big bumps when carrying a load. In fact, it’s rather hard to tell when the suspension is hitting the bump rubbers – exactly what is desirable.

Especially in cars where the springs are easily removable, it makes sense to explore different bump rubber options. After all, there’s nothing to stop you – for example – fitting much longer than standard bump rubbers, so giving you a more rapidly rising rate spring. (In a front-wheel drive, doing this to the back suspension is likely to reduce understeer as rear roll stiffness increases.)

Or, as I have done, simply fitting a better design bump rubber to give improved full travel behaviour.

At my wrecker, bump rubbers are just a few dollars each – well worth exploring!