The Shiny New All-Purpose MTB Thread

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Originally posted by Matthew Robinson:
I have one of these

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Ugh! A piss-pot...

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You're saying it's better to use your chin as a crumple zone?

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Not quite. My concern is that, as can be the case with motorcylce helments, a chin-first strike on the ground might cause neck injuries.

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Most motorbike helmets are full face.

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But are generally signifiantly closer fitting since they qrap around the whole of the head instead of sitting on the top half.

To be fair, I think it looks rather good and, as Matthew points out, the chin guard is removeable.

Notwithstanding Matthew's 'down-with-the-kids' status or its undoubted effectiveness, I'm with Steve on the ugliness of the p1ss pot.

singeltrackworld and bikemagic might be your best bet.

I went to Epping today and arrived with enough reservs of energy for a could of hours pootling about in the woods. I found the jump spot and did some jumps (after a fashion) with the local BMXs. Naturally I fell off. The Kids tried to get me to ride down to Chingford's McDonalds where apparently there is a "massive kicker".

I also found a short but steep downhill track through the woods with some big jumps that I chose to avoid. Next time though.

Matthew

PS Have your tried the DMRs yet?

PS2 I also (probably, fingers crossed) scored a ticket for The Pixies June 2 gig. Woo! Yay!

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Originally posted by Matthew Robinson:
PS2 I also (probably, fingers crossed) scored a ticket for The Pixies June 2 gig. Woo! Yay!

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Hang on a sec, Matthew - are you saying the Pixies have reformed??!

JonR

Have you been living under a rock Jon?

Yes they have reformed (original lineup) and are on tour. Tickets for the London gigs sold out in an hour. Mine comes from a old friend who just broke up with her fella and so happily (at least for me) has a spare.

She paid £150 via eBay for two tickets.

Matthew

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Originally posted by Matthew Robinson:
Have you been living under a rock Jon?

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Obviously, but then again, no change there!

Well, congrats on getting the tickets. I saw them live at Sheffield City Hall 15 years ago and they were fantastic. Let me know what the June gig is like.

Jon

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Originally posted by alexgerrard:
Do any of you MB'ers want to offer a new home for some Titanium Locking Skewers?

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Don't use titanium skewers if your bike has disk brakes.

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Originally posted by alexgerrard:
Steve

The skewers were bought for the Orange which has v-brakes, but I hadn't thought not to use the skewers with discs. Why do you suggest this?

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Titanium skewers don't hold the wheel in as strongly as steel ones. There have been lots of reports of problems on singletrackworld (with some serious injuries) linked to disk brakes and wheels coming out, plus one of the mags did a test a few months back and rated all the titanium skewers very poor. Ironically the best on test where the cheap Shimano Deore ones.

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I still don't know what to do with the Orange. I won't swap parts onto the Cove, so I either sell it or use it as a hack road bike for going to the video shop etc. At the moment it's sitting in the shed doing nowt which seems a shame for such a beautiful bike.

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Unless you really need to cash it's probably not worth selling.

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Originally posted by Matthew Robinson:
PS2 I also (probably, fingers crossed) scored a ticket for The Pixies June 2 gig. Woo! Yay!

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Matthew,

So how was the gig??

JonR

Jon,

It was fucking brilliant.

Matthew

Matthew,

You don't swear often so it must have been good. Do you know if they are they releasing any new material to coincide with their live dates?

JonR

No new material AFAICT but there are all sorts of DVDs, best ofs, concert cds, etc. in teh works.

See http://pitchforkmedia.com/news/04-05/18.shtml

Cheers.

Jon

I spent yesterday dirt jumping and have done something to my chainset. Specifically I can't use the big ring now as the chain rubs against the front mech for part of the rotation.

When I look down as I am pedalling along it appears to be warped. Does this make sense? Can a chainring warp or is something likely bent somewhere? Is it likely I would need to replace the chainring or the whole crankset? To be honest I don't really understand how this can happen.

If I do replace the crankset, can I do this without special tools and/or mechanical aptitude?

And what are these new non-ISIS BBs all about which somewhow have external bearings and a built in BB?

Finally, if I have bent it form heavy landings of my 14st 8lb chisled body, I would need something fairly robust. Would these XT Hollowtech do the job or are they more of an XC thing and I would be better off with something like RaceFace NorthShore?

Matthew


The Scene of the Incident

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Originally posted by Matthew Robinson:
I spent yesterday dirt jumping and have done something to my chainset. Specifically I can't use the big ring now as the chain rubs against the front mech for part of the rotation.

When I look down it appears to be warped. Does this make sense? Can a chainring warp or is something likely bent somewhere? Is it likely I would need to replace the chainring or the whole crankset? To be honest I don't really understand how this can happen.

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You should be able to replace the chainring but depending on how warped it is it might not be necessary. Try rotating the front mech slightly to give more clearance.

The big chainring is quite vulnerable though, especially to rocks or logs, so it is quite possible you'll have bent it. Most big rings are fairly soft alloy as well - which doesn't help.

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If I do replace the crankset, can I do this without a special tools and/or mechanical aptitude?

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You'd need a chainset puller but these only cost a few pounds and are easy to use. ISIS and Octalink chainsets require a little adaptor with most tools.

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And what are these new non-ISIS BBs all about which somewhow have external bearings?

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Generally concensus is that current ISIS bottom brackets are very, very bad as the design doesn't allow enough space for decent sized bearings so the BB failure rare is high. Shimano's Octalink BB uses a smaller axle and bigger bearings so it's better, however Shimano came up with the idea of the external bearings as it allows for a very large axle and large bearings to be used. RaceFace also now have a copy of this style of integrated chainset/BB out.

To use these it's necessary to have the BB cups faced on the frame to ensure the bearings sit absolutely square.

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Finally, if I have bent it form heavy landings of my 14st 8lb chisled body, I would need something fairly robust. Would these XT Hollowtech do the job or are they more of an XC thing and I would be better off with something like RaceFace NorthShore?

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Shimano Saint would perhaps be a better option if you really do need to replace the chainset.

What does the bike have fitted at the moment BTW?

"To use these it's necessary to have the BB cups faced on the frame to ensure the bearings sit absolutely square"

That sounds like a non-starter then.

"Shimano Saint would perhaps be a better option if you really do need to replace the chainset"

I thought that was a single chainring DH/FR thing? I need a triple.

"What does the bike have fitted at the moment BTW?"

RaceFace Prodigy which is their cheaper all-round chainset that was replaced this year by the Evolve. It has an ISIS BB.

Thanks.

Matthew

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Originally posted by Matthew Robinson:
"Shimano Saint would perhaps be a better option if you really do need to replace the chainset"

I thought that was a single chainring DH/FR thing? I need a triple.

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There is a triple version of the Saint available.

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"What does the bike have fitted at the moment BTW?"

RaceFace Prodigy which is their cheaper all-round chainset that was replaced this year by the Evolve. It has an ISIS BB.

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The Prodigy is a decent chainset so replacing the bent ring would be the best solution if rotating the front mech slightly doesn't help. RaceFace chainrings are quite cheap I think.

Oh the chain also rubs when in the middle ring with the outer rear gears.

When you say rotate the front mech do you mean rotate it about the seat tube or adjust the H and L limit screws to move it out more?

Matthew

I will be astonished if you have bent the chainset. Haven't you got raceface already? Whatever you have, my guess it is ali, and that the spider is a bit fat lump of ali. IME, they just don't bend that way, and neither do the bottom brackets axles. They just snap, as I have found on a couple of occasions. Also, it takes fairly burly riding over a period to do it. It took my 17st mate a fair few goes at missing a transition from 5 foot up to kill his XT cranks.

My guess is you've clouted the big ring on a log, or it has fallen against something. They are easily replaced, and require nothing more than an allen key and something to hold the female bit (improvise with a screwdriver). That said, if you buy it from your LBS, they may fit it on the spot.

Have to ask the silly question tho'. If it it only slightly warped, it's not just that your front mech cable has slipped, so the indexing is out of whack, is it? If a tweak of the barrel adjuster on the front mech shifter can get rid of the rubbing noise, the job is done.

My sharkbites finally gave up the ghost yesterday, and have been replaced by DMR V8s <yawn>. It turned out the clicking noise I had attributed to a dying BB was actually my pedals letting me know they were going off, so I fixed two things at once.

[edit] just seen you most recent post, and I am having trouble visualising it. What is rubbing when in the middle ring?[/edit]

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Originally posted by Matthew Robinson:
Oh the chain also rubs when in the middle ring with the outer rear gears.

When you say rotate the front mech do you mean rotate it about the seat tube or adjust the H and L limit screws to move it out more?

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I mean rotating it around the seat tube. You won't have to move it much - just take a look and see which side is rubbing and then rotate it very slightly out of the way. If it's rubbing on all the chainrings then it's more likely to be either the front mech setup or possibly a knackered BB.

"I will be astonished if you have bent the chainset"

I would be surprised myself but something is defeinitely bent.

"Haven't you got raceface already?"

Yes and it's at the burly end of XC to boot.

"If it it only slightly warped, it's not just that your front mech cable has slipped, so the indexing is out of whack, is it?"

No it rubs only on a part of the ring's rotation and as you look down while pedalling you can see a definite warp of something. I might, as Steve suggests, be able to fudge the front mech placement enough to get it working again but I think it's more than a front mech adjustment thing.

"I am having trouble visualising it. What is rubbing when in the middle ring?"

When in the middle ring and the outer three or four gears at the back the chainline is far enough across to catch the outside of the front mech cage. Again it only catches on part of the rotation.

The fact that both rings appear to be warped kind of implies to me that something axel/BB related is wrong. I think I'd have noticed an impact that bent both middle and big rings.

Matthew

If the axle is bent, wouldn't the allen bolts for the crank be noticeably off centre when you rotate the cranks? That said, looking at mine now, it doesn't seem perfectly centred, so maybe it is not very diagnostic. Like I said, I've never seen a bent BB axle on an MTB, but then I've only seen Shimano UN51s die, and the whole crank/chainset has dropped off. What BB is it?

Still, good show getting enough air to start wrecking stuff.

H4RDC0R3!!!1

It has to be said I am not very good at dirt jumping and it's a lot harder than I expected. There is a little one that I can clear but most times I get the timing wrong somehow and as I try to take off the back wheel hits the jump and it all goes wrong (in the sense that I don't really take off properly).

There is a bigger one with a flat top and a gentle transistion that is easier to time correctly but it's right after a berm and I cannot carry enough speed into it to get more than about a 8" of height off the lip.

At least that's what I though until I saw someone else doing it and he was getting more like 2ft despite going much slower -- again I don't seem to be able to get the timing down and sort lose all my speed going up the bank. I can actually get more height bunny hopping of a curb, all of which surprises me as I assumed getting height was relatively straightforward.

That said, I am of course L33T and ride V. Gnarly.

Matthew

PS I am absolutely gutted that I spent most of my twenties when I was reasonable fit and not prone to injuries and aches and pains (I can barely move today) that I spent ages grinding my way up ridiculously large hills when I could have been doing this sort of stuff. I could really get into it if it wasn't for the fact that I am 20 years older than the people who do this stuff. That and cowardice of course.

Matthew,

Just going on the above, I'd say you've just bent your outer chainring. If a portion of the outer ring has been pushed towards the seat tube then the chain would rub even in the middle ring. Also, the wobble will push the chain into one of the plates in the derailleur when on the big ring. If it were me I'd take a large adjustable spanner/wrench, wrap the ring in a cloth, slide the wrench ove the bent part and lever it straight bit by bit. The outer plate of the front derailleur shouldn't be anywhere near the teeth of the chainrings. It should be barely above them so it just clears. If the teeth rub the outer plate, the front mech has slid down the tube and needs to be raised a little.

I once managed to bend the big sprocket on a rear cluster into the 2nd biggest sprocket. I have no idea how I did it since the force would have had to have come from the spoke side of the wheel. I used a wrench to straighten it out though.

Dan

p.s. why not post an aerial view?

Guys

Maybe one of you may be able to work out what is wrong with my gears....

Last night I was riding through a field (bumpy) with a bit of pace when all of a sudden the chain started slipping through the rear derellieur. I am now stuck in gear and despite up and down shifting I can't change gear. It is a Carerra Vulcan (230) from Halfords, surely I have not killed it...?

Steve