Ok,

I can't believe I'm asking this question but here goes...

I've got a gorgeous, but old, KHS mountain bike, circa 1992. It's taken me all over including 3000ks through south east asia without a single flat tyre. Never punctured in a race, hardly ever on a ride - and it was usually easy to find the thorn, nail, piece of glass that caused them when it did.

Now, all of a sudden I'm not getting normal old, patch em up, punctures but the valves are getting cut through from rims (bontrager narrow). I've changed the tape, only ever use a track pump etc and still it happens. And not when I'm riding either, it's when it's standing in the garage, or in the back of the car en route. Very odd.

So, can anyone tell me what little gremlin is at work here? and the solution

thanks

Sarah

Do you powder your tubes?

I was having the same problem, and was told to try talc - something along the lines of so the tube doesn't stick to the tyre, so if there's movement the valve doesn't get ripped off.
[hope this makes sense, someone please correct me if I'm wrong]

Anyway, it worked for me. Give it a try.......

yep, talc

so this is happening while the bike is standing still? or are you noticing it only after you have left the bike for a while after a ride? maybe its happening on the ride, but the leak is initially slow enough that you dont notice it till the bike is left for a bit.


have you checked the actual hole in the rim? it might have developed a sharp edge somehow, or a piece of glass or a flake of chrome got in there and happily slicing away with the pressure of riding.

Talc it is!
Don't use the stuff for anything anyway and now I can say "Oh joy, talc!" at Xmas time

As for the tubes, the brands have been many and varied and recently purchased.
The tyres are smoke lites, circa '92 or maybe even '93

We've had to bin lots of the tyres because the walls were perishing but the plain rubber ones have lasted well.

This is the year of the hot new bike, fingers crossed!

I don't understand where the valves are being sliced...I'm guessing at the base of the stem?

I'd personally take the wheels off, take the tires off, pull off the rim tape, scrub the rim with a bristle brush, soap and water. Then look for anything unusual on the rim...spokes sticking up, burrs or cuts of any kind. File them down if there are any; I'd expect to find something that's causing the problem. The rim, if it's as old as the bike, might have sidewalls caving in or something, too. Might be new rim and spoke time, or just live with it until hot new bike day.

If I was keeping the rim, I'd then put a new Velox rim tape in with a new tube and tire, and hope it works. (You're seriously running tires that are over 10 years old??!! You deserve some new ones, even if they're not your problem!!)

MD

MikeD wrote: (You're seriously running tires that are over 10 years old??!! You deserve some new ones, even if they're not your problem!!)

Thanks Mike I'll do that too. And yes, the slice is at the base of the stem. You look closely and it's a weak point in the tube anyway. Makes sense that if the tyre is sticky that it's stressing that point. And yeah, I have presta, can't run shrader tubes on bontrager rims)

And I'd like to say I've been riding those tyres hard for over 10 years but I've been doing the career thing and the baby thing in that time too. Plus I got the bike and tyres on my OE and one had to have one's sand tyres, clay tyres, summer tyres, winter tyres, back wheel, front wheel so I came home with quite a selection to slowly work my way through

Sarah

you can with the help of the trusty drill

Also - tyres move around at low pressure.
Some DH'ers use tubular glue (from road bikes) and put three drops around the tyre / rim to stop it from slipping and taking the tube with it.

Hey everyone,

I'm really impressed with the response from this forum. I'll let you know how I get on.

thanks

Sarah

if you've got old tires, they're highly likely ot be slipping on the rims, so, if you do use talc, make sure you don't get it between the tire bead and the rim. it can even be worth a little touch of sandpaper on the top of the rim wall if it's been polished by the tire slipping past it.

i had same thing happen many years ago it was the rims hole get new rims

KONAMAN wrote:i had same thing happen many years ago it was the rims hole get new rims

I suspect that this is actually the "right" answer

but the solution I ended up with was to put an extra little nut on the inside of the rim. Y'know how with presta tubes you have the nut thingy for the outside of the tube to hold it in place. Well I've got on on the inside as well acting as a washer. That way the rims are only touching the metal of the valve, not the rubber on the tube. So far so good.

Sarah