Ask Fatdoc - the MTB technical thread (Read 81285 times)

nic mullin · July 31, 2009, 12:18:20 am

Got a weird problem with my bike - the valves keep partially pulling out of my inner tubes. I'm using prestas in rims drilled for schrader (never had a problem with this before). Only happens in my back wheel (mavic D521 rim, panaracer cinder tyre). Tyres kept at around 40psi, mostly light riding, valves don't go through the hole at a funny angle or anything but don't seem to last more than a few weeks before the tyre goes flat because the valve has started to part company with the tube. Happens with different makes of tube and regardless of whether I screw the little retaining ring onto the valve stem.

Any ideas? Ta.

Norton Sharley · July 31, 2009, 08:13:48 am

Does it happen with Schrader tubes too?

tlr · July 31, 2009, 09:41:12 am

I've had this with some tyre/rim combinations. One was so bad that it would rip the valve out after a few hundred yards, luckily it was on my wife's bike...She got through 5 tubes between Les Gets and Morzine, just rolling down the road. I think that it happens when the tyre is loose and baggy on the rim, and the tube sticks a bit to the inside of the tyre. Everytime you brake the tube and tyre get dragged a bit round the rim eventually pulling the valve out.

Either swap tyres, talc up the tube, or stop braking.

If you have a narrowish Cinder on a 521 then that might be quite a loose combination as the rim is fairly wide.

Yossarian · July 31, 2009, 10:28:21 am

Quote from: fatdoc on July 30, 2009, 06:54:57 pm

take the schrader valves off ( on for the air pressure) mist likely got dirt round it, impinging on the blue dial that adjusts the travel, may need needle nosed pliers if your stuck in long travel

it turns fine (the adjuster), it just doesn't have any effect on the travel.

fatdoc · July 31, 2009, 12:01:20 pm

Mojo.

sorry.

nic mullin · July 31, 2009, 03:03:19 pm

Nice one - reckon I'll get my talc on and report back.

Not tried schrader valves, but only because my front wheel is drilled for presta and needing to keep 2 different types of tube around is a pain. I could always just drill out the valve hole on my front wheel though if it keeps being a problem - schrader valves seemed to be fixed into the tube more sturdily so I guess should they should be less likely to pull out.

Cheers.

Norton Sharley · August 03, 2009, 09:57:20 am

Daft question, but you are using the right sized tube for tyre combo. i.e. don't expect a 2.1 tube to work well, especially at low pressures in a 2.3 or bigger tyre. Also don't buy Specialized tubes, they're crap

Bubba · August 03, 2009, 11:50:48 am

Quote from: nic mullin on July 31, 2009, 03:03:19 pm

Not tried schrader valves, but only because my front wheel is drilled for presta and needing to keep 2 different types of tube around is a pain. I could always just drill out the valve hole on my front wheel though if it keeps being a problem

I've used the drill method and it seems to work pretty well, ie no catastrophic failures any nasties so far.

Joepicalli · August 04, 2009, 08:28:48 pm

Big up to Norton for bike help tonight, waddage your way (though I suspect the promised beer will touch the cockles of his heart more).

fatdoc · August 04, 2009, 08:49:07 pm

grease, cones.. getting it tight.. that must be near nivarna for the pair of you.

nic mullin · August 04, 2009, 11:10:10 pm

Maybe not such a daft question, I think they're 1.75's in a 2.2 tyre. This might explain things.

Have had panaracer and no-name tubes and they all seem to fail equally quickly.

Not ridden since talcing my pneus so don't know if that has done the trick, but i reckon that in combination with buying the right size tubes next time and maybe getting my drill on I should be sorted.

Cheers guys.

Norton Sharley · August 11, 2009, 12:23:29 pm

Quote from: nic mullin on August 04, 2009, 11:10:10 pm

Not ridden since talcing my pneus

.. which I skim read as talcing your penis. Does that help your valve from ripping too?

SA Chris · August 11, 2009, 01:16:30 pm

Are Maxxis High Rollers of a particularly soft compund? I had some generic old tyres on my hardtail which lasted about 5 years before a sidewall looked like it was about to fail. Had the new Full suss for about a year, and the tyre are already lookign noticably worn down. Not bothered if they are, just wondering.

Bubba · August 11, 2009, 01:38:28 pm

Quote from: SA Chris on August 11, 2009, 01:16:30 pm

Are Maxxis High Rollers of a particularly soft compund?

They are offered in several compounds.:

60a - Maxxpro - XC use
42a - Super Tacky - sticky for general use
40a - Slow Reezay - very sticky (I've used for DH)

Some tyres come with mixed compounds, for example 70a centre (extra hard wearing) with softer sidewalls and not all compounds are available for all sub-types/sizes.

SA Chris · August 11, 2009, 01:48:45 pm

Hmm, not sure which ones they are will need a closer look. Nothing is simple is it.

nic mullin · August 11, 2009, 07:18:28 pm

Quote from: Norton Sharley on August 11, 2009, 12:23:29 pm

Quote from: nic mullin on August 04, 2009, 11:10:10 pm

Not ridden since talcing my pneus

.. which I skim read as talcing your penis. Does that help your valve from ripping too?

I hoped somebody would.

I once spent the best part of a fortnight in font sn**gering at the 26" pneus and pneus junior signs I'd seen in the bike section of decathlon. Simple minds...

Talc does seem to help though, cheers for the knowledge guys.

fatboySlimfast · August 12, 2009, 08:52:24 am

Quote from: SA Chris on August 11, 2009, 01:16:30 pm

Are Maxxis High Rollers of a particularly soft compund? I had some generic old tyres on my hardtail which lasted about 5 years before a sidewall looked like it was about to fail. Had the new Full suss for about a year, and the tyre are already lookign noticably worn down. Not bothered if they are, just wondering.

Bout right for a bike being used for lots of cross discipline stuff, my rear high roller lasted about 6 days in Morzine(you have been this year I just remembered!) outside lugs were fine however the middle lugs looked like someone had bitten them off!

SA Chris · August 12, 2009, 09:19:29 am

That's what mine look like. Didn't take bike to Morzine tho'. Been using it a bit too much on tar lately, probably bad for them. Need to get some road slicks.

Bubba · August 12, 2009, 12:16:33 pm

I've got 60a's on my XC/messing about hardtail and they've lasted quite well, rear is only just starting to look suspect. Will buy the same again, though a bit skinnier this time.

I echo Fatboyslimfast's comments about Morzine - my 40a's were more destroyed a week. The rear was gone after about 5 days really.

chappers · August 13, 2009, 11:10:56 am

ha ha, my surly project started this morning. bought myself a canecreek S8 headset, chainset, and a new flat handlebar. just have to wait for stock of a long haul trucker frameset!

Joepicalli · August 30, 2009, 03:27:49 pm

HELP Trying to fit a new rear cassette aqnd drive train un-aided by a compatent adult could anyone give advice help. Will pay in beer.

tlr · August 30, 2009, 04:53:03 pm

Whats the problem? I've got time and tools.

fatdoc · August 30, 2009, 07:15:10 pm

more details..

or just tap up me, TLR, Norton, FBSF or me to fix it for you...

DONT YOU DARE take it in to *that* shop... or you'll find your windows broken in...

tomorrow eve OK for me..

BTW.. you'll need a nu chain an all..

Joepicalli · August 30, 2009, 08:26:19 pm

I love you all and want to have your children. I'll call you tomorrow Fatdoc.

Norton Sharley · September 02, 2009, 12:59:59 pm

FD, you need to go and break his windows. I heard that he went into the shop that shouldn't be named at least 5 times yesterday and reported that they were helpful!