keep getting flats at base of tube valve stem!

[NeezyDeezy]

Last time this happened, I assumed I just didn't quite align the tube with the rim, and it pulled the valve stem at a weird angle and caused a tear. But I'm sure the last time I made the alignment 100% perfect. I keep getting little tears at the base of the tube stem valve anyway, and it's especially annoying because it tends to be on the wheel with the hub motor, and I can't even patch holes in that part of the tube. I'm using various brands of "thorn resistant" tubes (thicker rubber), and it doesn't seem to matter which kind I use, this keeps happening.

Any advice? I'd really rather never have to deal with this again! It's making ebiking a chore.

 

[dogman dan]

Been having decent results with the Bell brand stuff, tubes and tires.

 

[liveforphysics]

You need to de-burr the areas of the rim that the stem area contacts.

If you've got tools, use a dremel. If you've got nothing and the rim is aluminum, use a knife.

 

[ambroseliao]

It could be because your tube is slipping inside the tire. Check your tire pressure. If it's low, that could cause it. Also, are you using a high torque motor and gunning it off the line? Just thinking out loud...

I used to have the same problem of tears at the base of the valve stem on my small wheeled scooter. Low tire pressure was the culprit. I could see the stem "leaning" to one side when the tube was slipping inside the tire.

Ambrose

 

[alan]

Rim liner tape usually overlap very close to the stem hole, and I had one that caused tube tears about a quarter inch from the stem repeatedly. When I cut the tape such that the end was about an inch from the hole, the problem went away. That is, I had more tape overlap then I needed, and it was important that the end of the tape was not right near the hole. Just something else to check. My guess is that having too low of air pressure or a burr in the rim is more likely to be your issue.

-- Alan

 

[John in CR]

Any advice? I'd really rather never have to deal with this again! It's making ebiking a chore.

Bike spokes and tires suck. I installed my rear wheel in Dec '08. I added air once, not because it needed it, but to try at higher pressure, which I later let back out. My bike is a very stiff hardtail, so extra pressure was uncomfortable and didn't really change my energy usage anyway. Spoke tightening has been 0 times, even after the several occasions I have started to take off, but got stopped by the chain through the wheel, so I do have a few slightly bent spokes.

My secret is using motorcycle wheels. My 17" rims end up a 23-24" wheel depending on the tire, and my 14" rims end up a 19-20" wheel. Pinch flats and road debris aren't of concern either. Plus I get the benefit of actual testing and ratings for both speed and weight. Bicycle tires are for pedal bikes, but ebikes require something better. Until an in-between wheel comes out, I'm sticking with motorcycle wheels. Oh, did I mention they cost less than all but the cheapest bike tires? Bike tires may be fine for the guys that ride electric assist bicycles, but those of who want low maintenance pedal assist EV's need proper tires.

John

 

[amberwolf]

These things can all do it:
--low tire pressure causing tube movement
--rim tape, if it's a stiff type (not the rubber strips), especially the plastic band types
--cheaply made tubes
--burrs on valve stem hole in rim (this one is really common)
--cracking of cheap rubber stems during inflating if using a direct-connect pump (without a flexible hose); every time you pump you flex the valve stem at the base and can nick it on the rim or just crack it if it's junk.

FWIW, I had a whole bunch of problems for months, maybe 3-4 years ago with tubes bought at pretty much everywhere. Target, Sports Authority, K-Mart, etc. Just by coincidence around the same time I also got some very old but never used still in box ones someone gave me from WalMart and those were bad too, but could've been age. I even had some of them blow the brass valve stem out of the rubber casing entirely, with the bike just sitting there in my living room! Some of them would herniate at the base of the stem, and then rupture from friction on even a carefully deburred and filed rim hole. I went so far as to silicone them in place to prevent that, and I'd still have the herniation rupture eventually.

I went to Slime brand tubes made by Cheng Shin and so far have not had a problem since then. I've also used Cheng Shin brand tubes salvaged from old crappy bikes I get for parts, and even when the tires are sunrotted the tubes still work fine and I don't have the valve stem problems.

 

[Drunkskunk]

Use Better Rim Tape. The good stff is about $1.99 a roll, and thick cotton weaving. I've actualy gotten flats from the plastic liners that some rims use.

Also, take a piece of sandpaper and roll it into a cone, then sand lightly along the edges of the hole for the valve stem. you don't want to make the hole wider, you just want to dull the edge.

 

[NeezyDeezy]

thanks everybody, I bought a rat tail file and will smooth out the rim hole, I'll let you know if this works

 

[Gordon]

Are you using tubes with Presta or Schrader valves? Well, it doesn't matter, but it's more common on presta valves.
Is the stem is threaded all the way to the tube and have a knurled locking nut like this pic ??

The locking nut is only used to keep the tube in position while you are getting the tire onto the rim.
After the tire is all in place and you are sure you haven't pinched the tube under the tire bead you have to loosen that nut a couple full turns.
What happens if you have the nut tight when you inflate the tire is that it will put a lot of strain on the base of the stem like it is trying to pull your tube through the hole in the rim. You'll end up with a flat every time.

 

[jateureka]

I agree with what amberwolf has listed about flats caused by valve stem failures.

You'd be surprised how much the tyre pressures can drop over a day but still some people only check them once a week.

I also had two instances where the brass valve stem was not sealed to the tube properly.

I like to use the thornproof tubes or regular tubes with Zefal tyre liners.

 

[Ypedal]

I do the canadian thing and use hockey tape as rim liners !! :wink: ( woven, fairly thick, and lay on about 4 layers, then exacto knife an X across the valve hole, push the valve thru )

Metal stems also rule..

I use the thickest tubes the bike shop has to offer, along with wide tires for comfort ( considering the weight of the ebike a fatter tire helps smoothen things out )

I get a few flats per year but never at the valve stem.

as LFP already mentioned, de-burr the hole if it has sharp edges, ditch plastic rim liners, and all should be good.

how wide is your rim and what size tire are you using ? ( also, make sure you get a tube capable of inflating big enough for the width of tire used.. )

 

[jateureka]

, ditch plastic rim liners, and all should be good.

how wide is your rim and what size tire are you using ? ( also, make sure you get a tube capable of inflating big enough for the width of tire used.. )

Interesting you should say that about tube/tyre/rim width size - I had a thornproof tube split where the thick section meets the thiner inner section because it was designed for 1.95 and it was run in a 2.125 width tyre.

I haven't had any issues with the soft edge tyre liners, but the others can cause pinch flats if you run your pressures low.

 

[amberwolf]

What happens if you have the nut tight when you inflate the tire is that it will put a lot of strain on the base of the stem like it is trying to pull your tube through the hole in the rim. You'll end up with a flat every time.

Somewhere around here I may still have the Bell Presta tube box I got that doesn't explain that--it just shows tightening the nut down finger-tight, and inflating everything. The instruction sheet inside is identical to the box, down to the spelling mistakes, except it doesn't have Bell's name on it anywhere. :lol:

I suspect that kind of problem might be common because of bad instructions like that. I didn't even think of it, as AFAICR I've only twice used a threaded Presta valve like that, once by mistake and once because there were no other tubes in the only store within walking distance of my flat.

 

[jateureka]

Because this is happening on your hub motor wheel, I'm wondering if the torque from the motor may be causing the tyre to move slightly on the rim, thus pushing the side of the valve stem into the rim?

Do you apply throttle gradually?

 

[02jze]

if that was the case how would you stop that ? fill the tyre with glue? Or use one of those tyre stays off a pitt bike or similar ?

 

[Ypedal]

The layers of Hockey Tape ooze a bit of sticky glue and keep the tube in place, along with 40+ PSI tire pressue, but unless you are pulling megawatts i doubt torque is your problem, and even then you'd break loose and spin before having tire slippage ( assuming you have a proper tire/rim combo ).

 

[jateureka]

You don't need 'megawatts' to make a tyre move enough on a rim to cause the tube stem to press into the rim.

I have seen it happen on a trike with a little 250W hub geared motor (like a Bafang) in a 20" wheel running 2.125 tyres. There is so little weight on the front it can spin the front wheel easily if you are not gradual with the throttle.

 

[jateureka]

if that was the case how would you stop that ? fill the tyre with glue? Or use one of those tyre stays off a pitt bike or similar ?

I don't know what a tyre stay is/does. Could you elaborate?

 

[Ypedal]

http://www.motorcycle-superstore.com/productimages/OG/0000-Neutech-The-TUbliss-Core.jpg

common on MX bikes.. can't imagine it on an ebike tho..

 

[Whiplash]

I do the canadian thing and use hockey tape as rim liners !! :wink: ( woven, fairly thick, and lay on about 4 layers, then exacto knife an X across the valve hole, push the valve thru )

Haha! I had a flat from the holes in the rim to tighten up the spokes on mine when I got it, and I just put about 5 layers of electrical tape (thought that was appropriate for an E bike, and it worked like a charm, wheelies and all I am good to go now...