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Exterior guides and mods

Axle Caps

A decorative item to add some style to the ends of the suspension tube.

Modification Details

I don't want to seem like I am trying to teach people to 'fit stalk caps' here, yes the axle caps
are easy to fit but the main reason for this page is to show that they also fit the new smart
fortwo. Axle caps are quite an old mod so may have been lost to the new owners.

Axle Caps?

Don't blame me for the incorrect name. Some nob-head had already coined the phrase and the name stuck.
They are De Dion tube decorative end finishers. It's not as catchy or easily remembered.

Especially as people don't know what a De Dion tube is.

Types Of Axle Caps

The original design axle cap, usually comes with 6 or 8 holes around the outside.

Axle rings where quite rare in the UK, most people went for caps (above).

These are the new smartmods ones in black plastic.

Where Can I Buy Them?

There are various types and designs, from various suppliers, they come in aluminum versions,
to newly released superior plastic ones over at

What Do They Fit?

Axle caps and axle rings will fit all smarts except the 454 Forfour. Here's the proof.

Smart Fortwo 450

Smart Fortwo 451

Smart Roadster 452

All the axle caps shown above are exactly the same size and type from the same supplier.

Fitting The Axle Caps.

Clean up the inside of each tube, push the decorative addition in place and tighten the
allen headed grub screws up nice and tight. Usually there are 3 grub screws to tighten.

Most axle ends will come with the correct allen key.

Are They Going To Cause Problems?

Some people worry that water is going to be able to collect in the tube, this won't happen.
They are a fairly loose fit and they stand slightly away from the axle tube.
This allows water to drain right out. The only problem I can see is they don't tend to look very new
for long and the metal ones tarnish quite badly. Once you have fitted them they are staying there.

It is a good idea to laquer them or paint them before fitting. As standard they are raw aluminium with no
protective coating. Bi-metal corrosion can occur between the cap and the grub screw as they are dissimilar metals.
Copper grease on the grub screws will reduce this effect.  This isn't a problem with the smartmods ones.

Corroded caps can be improved with a wire brush and some emery paper.

Some people have experimented with putting lights and LEDs in the caps, have a go yourself.

What About Covered Caps?

Around 2010, some genius decided that cheap plastic tube end caps were a good finishing piece.
They were about £1 and were resold for a lot more. No one really questioned the idea of blocking the tube.

I can tell you now, it's a bad idea. Why? Because people don't notice things like a big hole further back.

We all know that water has an uncanny ability to get anywhere if given any opportunity.
A hole big enough to put your finger in is definitely large enough for water.

The hole is there to allow air flow to come in to relieve the low pressure that would occur in the tube.
Remember that the open end of the tube is in a low pressure area of the car when it's driving.

Water isn't the only problem. Water vapour is in the air and will condense as the tube changes temperature.
The tube will heat up from heat radiated from the engine and the road. When it cools, condensation can occur.

If the condensation is trapped in the tube due to a decorative cap, the water will sit and rust everything it touches.

That is why axle caps have holes in. Not just for water draining but to allow an air flow through the tube.


Blocked tube photo by Frankie A

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