Slime Smart Tube Self-healing inner tube

Slime Smart Tubes are inner-tubes containing a thick liquid which instantly repairs punctures. They work well, and are a very handy option for winter riding, but there is a weight penalty.

This kind of inner-tube is well known in the mountain-bike world, but Slime Smart Tubes are also available for road bikes in two sizes: 700c x 19-25mm and 700c x 28-35mm, both with presta valves.

Here’s the theory: you get a thorn or flint in your tyre and it makes a hole in the inner-tube. As the air starts to escape, a bit of the thick liquid (aka slime) comes out too and then solidifies, instantly sealing the hole.

In practice, these Smart Tubes seem to work. I’ve been testing a pair in my winter training bike for a couple of months and haven’t had a puncture yet.

Fitting is exactly as usual, and you can pump up the tyre to your usual pressure: in my case that's 100psi inside 700x23 tyres.

The Slime Smart Tubes weighed in at 170g each on the road.cc scales, so there is some extra weight to consider (50 to 100g more than usual, depending what you usually use), but this is no problem on a winter training bike.

I didn’t notice a major difference in ride ‘feel’ –  just a tad less lively – but once again no big problem on a winter training bike. If it makes you work harder now, you’ll go even faster in the summer, right?

For the first few hundred miles I was running the tubes inside some reasonably heavy tyres (Bontrager All Weathers) which obviously provided some additional outer protection. Later I tried the tubes inside a lighter pair of tyres (Schwalbe Duranos); still puncture free.

Of course, maybe I would’ve been lucky anyway, so after the road-trials it was time for some further testing.

First test: I deliberately rode over a drawing pin and kept going along the road. I could hear the clicking of the metal on the tarmac as the tyre went round, and there was a slight drop in pressure, but I could keep going without trouble. Back at the road.cc lab, the gauge revealed a fall from 100psi to stabilise at 80psi.  

Second test: Take the pin out, and immediately ride down the road again. There was a sound of escaping air for a few seconds, and there was another drop in pressure, but once again I could keep riding. Back at the lab the gauge showed the pressure had fallen again from 80psi to stabilise at 60psi.

Third test: Drawing pin in, then out straight away, then ride down the road. This time the pressure fell from 100psi to stabilise at 70psi.

(Incidentally, the self-healing does not seem to work if the bike is stationery. I assume the spinning wheel needs to spread the slime around, and centrifugal force may play a part too.)

So, on the road, these tubes seem to work (although maybe I was lucky), and this performance seems to be backed up by my drawing-pin lab tests. It seems that the slime works better if the object causing the puncture stays in the tyre (which is often the case in the real world, as anyone who’s struggled to pull out a thorn from the inner casing at the side of the road will tell you).

If you’re a tourist encountering flints and thorny hedge cuttings, or a commuter dealing with glass and those tiny bits of metal that come off worn car tyres, then these tubes are worth considering. If you’re riding on good roads in clean conditions, and like to keep the weight down, or if you’re happy to ride heavier tyres in the first place, then they’re something you may not need.

On cost, the tubes recommended retail is £9.99 each, though you can find them for a few quid less on-line. Obviously more than a normal tube, but for a better chance of puncture-free cycling this might be a price you’re happy to pay.

Verdict

Inner-tubes to help reduce the chance of punctures. A handy option in winter, but they're not featherlight.