Shimano Plastic Rim Tape

[Valbrona]

Sure someone has mentioned this before, but I am not one for using the search function or for getting up early at the weekend.

Well, the valve hole in this stuff is rather large. So large that I am expecting my tubes to puncture around the valves.

Thanks for any comments.

[reohn2]

I don't worry too much about it,as I always cut a 25mm square of old inner tube make a hole in the middle,put it over the valve stem snug upto the tube.I find this helps prevent the valve tearing out.
I also smooth the edges of the valve hole on new rims with emery cloth or similar which helps prevent it biting into the tube.

[robc02]

I recently suffered a spate of damaged tubes on a wheel with a plastic rim tape with a large valve hole. Strangely, the tape had been in use for several years with no problems, but suddenly I started seeing tubes splitting around the valve seat. Maybe the tape had moved slightly when changing a tyre or tube, or perhaps the new tubes were more delicate than the ones they replaced?

Following this I rounded off the inside of the valve hole and added a piece of rubber to the new tube as per R2s suggestion above. I would add that the rim had a rather large hole on the inside (i.e. the tube side of the rim), but a standard Presta sized hole on the other side. This seemed odd so I made an insert to reduce the size of the hole, only to realise that this stopped the valve from seating properly against the rim, so I opened it out a bit to fix this.- Quite a lot of hassle and not that effective either.

Previously I used sticky backed cloth rim tapes that had only a small hole for the valve. These nicely bridged the large valve hole and provided a soft rounded edge for the tube. i shall be going back to these in future, but with the addition of the loose rubber patch for good measure.

[Brucey]

the (effective, simple, quick, easy) cure for rim inner walls/rim tapes that have big holes in them (Schrader sized) when you are using presta valves is to fit a presta locknut from a recent Schwalbe tube to the valve before fitting the tube to the rim. These locknuts have a shoulder on them and locate into a badly drilled rim. Fitted thusly, this prevents the valve from seeing a major load/chafing where it is unable to resist it.

This of course also forces the valve further above the rim well than normal; however I have yet to see a valve fail as a result of this. The idea that valve stem bases need to disappear into a large hole in the inner wall of a double-walled rim is fallacious; if this were really true valves would fail all the time when fitted to single-wall rims.... In reality valves are extremely unlikely to fail when fitted to (correctly drilled) rims of this type.

cheers

[robc02]

This of course also forces the valve further above the rim well than normal; however I have yet to see a valve fail as a result of this.

After fitting an insert which forced the valve up as you describe, I did suffer another split around the valve seat - albeit it survived for longer than without the insert ( a few weeks rather than a few minutes or hours!). As a result I removed some material from it so that the valve could sit further down and have had no further problems.

As mentioned earlier, I had very few such failures over many years/decades when using cloth tapes that stretched across the valve hole with just a small piercing to let the valve through. I'm thinking "better the devil you know" as the alternative proved to ba an expensive experiment. I have yet to find a way to successfully repair a split so close to the valve.

I suppose the problem could have been due to a problem with the particular tubes, but I don't feel inclined to repeat the experiment with another make.

[Brucey]

this photo shows the shouldered locknut



of course you will need a second locknut if you want one in the usual place.

The extra thickness must put more strain than usual on the valve, (and may expose bad tubes and/or possibly cause some failures directly) but to my mind it is certainly the lesser of two evils if the alternative is to fit a tube to a bad rim. For a valve fitted thusly to come away via peel, the failure ought to start on the inside of the tube, where the joint is most reinforced.

NB most presta valves have a tiny shoulder at the base of the screw thread on the valve stem; this is where the valve should be supported normally. The size of this shoulder is such that the rim/insert drilling cannot be oversize by much more than 0.5mm before the metal part of the valve stem is no longer properly supported.

I've only used the locknut trick a few times myself, preferring to make a proper job of it instead, i.e. use an insert in the rim. I've used many rims that have been correctly drilled and plenty that have an insert in them. If the insert is fitted the valve sits as if the rim had been properly made in the first place. No failures.

cheers

[robc02]

The extra thickness must put more strain than usual on the valve, (and may expose bad tubes and/or possibly cause some failures directly) but to my mind it is certainly the lesser of two evils if the alternative is to fit a tube to a bad rim. For a valve fitted thusly to come away via peel,

I also thought it the lesser of two evils, and I suppose it was - in that the tube lasted a lot longer before failure!

In each case the splits have been two or three millimetres from the edge of the valve, i.e. in the rubber itself, not the rubber peeling away from the metal of the valve. In the first instances, where the valve hole was unaltered, I was sure the cut was due to abrasion on the rim edge. On the last one, after the valve insert had been fitted, it was less clear what had caused the split as the sharp edge had now gone. I put it down to the tube being stretched too much because of the valve being pressed into the tube when inflated.

Now that I have recessed the insert to allow the valve seat to fit inside it, and used a rubber square slipped over the valve, the problem appears to have gone away. I am still a bit puzzled as I have never had such issues in the past despite taking no particular precautions.

A bit of Googling (well, Duck Duck Go-ing actually) showed that other people were sufficiently concerned to use rubber patches.

These were Schwalbe tubes, by the way.

[reohn2]

I've been using the 25mm square of old inner tube over the valve for over 20years in conjunction with both cloth(Jantex) and plastic(Schwalbe or Continental)rim tape,with tyre widths from 25mm to 2.4inch,TP's from 90psi down to as little as 12psi on the 2.4inch knobblies on my MTB,I've yet to have a puncture around the valve seat area.

[Brucey]

a rubber washer helps stop chafing but provides only very limited support (just as a rubber rim tape might). This means with a presta valve in a schrader-drilled rim inner wall, it works OK at low pressures but at high pressures the valve stem ( being unsupported) can still separate from the inner tube.

IMHO, if you want to run high pressures in a presta valved tube especially, you should really aim to support the valve stem directly.

cheers

[reohn2]

a rubber washer helps stop chafing but provides only very limited support (just as a rubber rim tape might). This means with a presta valve in a schrader-drilled rim inner wall, it works OK at low pressures but at high pressures the valve stem ( being unsupported) can still separate from the inner tube.

IMHO, if you want to run high pressures in a presta valved tube especially, you should really aim to support the valve stem directly.

cheers

I agree,and I did fail to address that point,a special rubber gromit(they're available)to reduce the Shrader hole size to Presta on the tube side section of the rim would be my choice along with the 25mm square fix and shrader to Presta locknut on the valve stem on the outside IYSWIM.

[robc02]

I must confess that this is something I have never given much thought to until recently. Having looked at a few rims I see there is quite a bit of variation in the size of the inner hole between manufacturers and models. Am I missing something or would you reasonably expect the manufacturer to drill the right sized holes on both sides of the rim, not just one?

Anyway, weak tubes or not, I will be looking at this more carefully in future, and where necessary will make a metal insert that can be epoxied in place.

[Brucey]

…. Am I missing something or would you reasonably expect the manufacturer to drill the right sized holes on both sides of the rim, not just one?....

you'd think so, wouldn't you...? However things don't always make sense like you might expect them to....

cheers

[landsurfer]

I use black or silver duct tape for my rim tapes ... never have any problems ....