Cobra Linear Inner Tubes

[Aushiker]

These tubes look pretty interesting as allow for a tube change without removing the wheel. They got mention on Velomobiles but as they come in 20" they are of course suitable for BMX bikes as well. It would be cool if they extended to other sizes. For those interested the Cobra Linear inner tubes are sold by flybikes.

There is a video of tubes available on Vimeo.

Andrew

[reohn2]

For low pressure big volume tyres ie;MTB,roadsters with hub gears(especially Shimano ),BMX,etc, I think they're a boon if the quality is good .
For high pressure small section tyres they need a bit developement where the ends meet,with a joint needing to be as "seemless" as possible.

BTW,in the video,he used a SCREWDRIVER to get the tyre on!!!!!!!!!!!!!!!!!!

[BigG]

They work wel lon 28 and 32 mm tyres (both 27" and 700C) without any feel of an overlap. This is as I would expect as the air preassure is constant all the way round whether there is an overlap or not. Unfortunately, my original supplier (Halfords) no longer sells them and I cannot get replacements.

[reohn2]

They work wel lon 28 and 32 mm tyres (both 27" and 700C) without any feel of an overlap. This is as I would expect as the air preassure is constant all the way round whether there is an overlap or not.

That's good news.

Unfortunately, my original supplier (Halfords) no longer sells them and I cannot get replacements

I'm surprised they aren't more popular,if they work as well as you say.Perhaps it's a marketing issue
It's certainly a great Idea

[Brucey]

in a LBS to me they would surely use these with some enthusiasm since they do a lot of repairs on bikes with IGH/chaincase/hub brake etc.

However when I asked about them they commented that they had tried this style of tube and found the ones they could obtain at the time (which may or may not have been this brand) were prone to failure at the ends, and did not constitute a reliable repair.

I think that if they made them (at some expense) in a mould with 'ends' to it they'd be better; as it is, they pretty much seem to make a tube, cut it, then bond the ends in the ones I have seen. This strains the tube very greatly near the ends when it is inflated, and (I think) leaves an edge that might chafe.

cheers

[mig]

i wonder how much more puncture resistant an inner tube can be made and still retain the elasticity? all concentration in the area is on tyres. does that mean it's nigh on impossible or that way given price constraints?

[BigG]

I think that if they made them (at some expense) in a mould with 'ends' to it they'd be better; as it is, they pretty much seem to make a tube, cut it, then bond the ends in the ones I have seen. This strains the tube very greatly near the ends when it is inflated, and (I think) leaves an edge that might chafe.

cheers

I don't think that the end seal is under much pressure as it is held closed by the pressure of the overlapping tube.

[Brucey]

if indeed there is an overlap; I am not convinced that this is always the case.

Also I would assume that if the tube is slightly skinny for the cover (which you can usually run happily with a normal tube) this might well be more likely to cause trouble with these tubes.

If the ends of the tube are trying to move lengthwise (circumferentially) as the tube is inflated, this leaves potential for all kinds of tube-folding antics that normally don't occur, too.

cheers

[jb]

It looked to me like there is a hole in the other end that fits over the valve which would keep it in the right position.

[RickH]

It looked to me like there is a hole in the other end that fits over the valve which would keep it in the right position.

You mean like this?

(from here)

Rick.

[reohn2]

At about three times the price of ordinary good quality tubes it's a bit steep IMO

[Barrenfluffit]

It strikes me that it should be possible to make these from an ordinary tube and some rubber cement. Might want a clamp to hold the ends firmly together for a few days and to check for an airtight seal but nothing too onerous.

[Malaconotus]

in a LBS to me they would surely use these with some enthusiasm since they do a lot of repairs on bikes with IGH/chaincase/hub brake etc.

I would too, subject to some user testimony on reliability. I've the same concerns as Brucey about overlap, fraying, and the sealing of the tube ends.

Perhaps worse than the IGHs and chaincases are the BMX kids who no longer seem able to fix their own punctures. It's always the back wheel, with stunt pegs, and when you put the wheel back in you always have to set the brake up from scratch because the wheel wasn't straight and chain taut in the first place.

The £5 flat charge just about covers shop floor staff changing a tube on a disc or v-braked wheel with a q/r hub, but it's the owners of nutted axles, IGHs, chain cases, BMXs who are most likely to rely on the LBS to get a puncture fixed, and it can easily be a half-hour job for a mechanic.

[Brucey]

It looked to me like there is a hole in the other end that fits over the valve which would keep it in the right position.

You mean like this?

(from here)

Rick.

that is different from some of the others that I have seen, and does look like a somewhat better arrangement. I wonder how reliable it will be though?

I can't help but think of all the many daft things I have seen which have eventually caused 'a spontaneous lack of air retention' in the past....

cheers

[Barrenfluffit]

It strikes me that it should be possible to make these from an ordinary tube and some rubber cement. Might want a clamp to hold the ends firmly together for a few days and to check for an airtight seal but nothing too onerous.

Ok I had a go with an old tube.
1, rolling back the cut ends to evenly apply the glue is a given. Thereafter they need to be rolled back straight away to give a chance of lying flat and making a seal (i.e before the glue becomes tacky)
2, The length to be sealed needs to be much more than 1 cm. I left then for about 7 hours but it wasn't enough.
3, Something(s) metal and smooth (a nail?) needs to lie across the sealed ends in the vice/clamp to create a proper crimped seal
4, Tying the ends may be more effective but then overall tube length becomes an issue.