- Welcome to ask GMBN Tech.
This is the weekly show where we get to answer your
tech related mountain bike questions.
You can fire your questions into the email address
that's on the screen right now, you can get them to us
via Facebook page on GMBN Tech, and of course in the
comments below.
Now we're gonna get straight to a load of questions
you guys have been asking us from last week.
So first up is from Andrew Brown, it's related to
carbon fiber frames.
So quite a topical thing here.
Carbon frame inspection in particular.
Are there certain things to look for when inspecting
a frame for damage?
I've got a quarter inch wide chip that goes into
the carbon on my frame, for example.
Should I have my local shop look at this or are there
ways I can address cosmetic verses structural damage
on my own?
So the first thing I suggest you look at is take
a good look at it and make sure the chip actually
does go deep into the carbon and it's not just the paint
and the lacquer on there.
Some carbon frames, the lacquer can be quite thick.
If it is just a chip like you said, technically it should
be okay, but I would go with your first instinct and
get it checked just to be safe.
That'd be the same with an alloy frame if you've got
hairline cracks and things, you should have that stuff
checked out.
As far as structurally knowing whether it's damaged or not,
there's a few little telltale signs.
So I've been told by various manufacturers that chips
don't necessarily mean it's gonna crack or fail,
regardless you should still check that.
But cracks in the paint can be a telltale if it's
had some sort of trauma.
And likely if there's a crack in the actual paint
there may well be a crack in the actual carbon where
the resin, the epoxy, has separated underneath.
So you need to find that out.
There are a few specialist places that x-ray frames,
but you've got to bare in mind not a lot of people
actually have this service.
There's one on screen now that I found in the UK
that offered this.
There's a couple more in California that I found and
around the world.
And what they do is they take your frame in,
they inspect it completely, and they basically repair
that damage.
This particular one is certified by Colnago, Trek
and Specialized, so you know it's like the real deal.
I'd be cautious to make sure that if you are gonna
have to get a carbon frame fixed, make sure it is by
someone that's done work for one of the bigger brands,
at the very least.
So interesting, another thing I was told by a few
different carbon specialists is about the sounds that
carbon frames make.
So typically when you flick a carbon frame it should
make quite a crisp sound.
And if it's got a crack in it or if it's got structural
damage, actually the sound doesn't transmit in the
same way and it could be quite a dull sort of thud.
Of course you're gonna notice this more on a traditional
double diamond layout frame, like a road frame or a
hardtail mountain bike than you will with a full
suspension frame.
So there's a lot of other parts of the frame that can
actually mask that sound.
So I think that's one for the experts to tell,
not necessarily you at home.
But like I said initially, if your instinct tells you
to get it checked out, I would definitely get it checked.
Next up is a suspension related question from
Corey Stephenson.
Hi guys, is there a universal front fork lockout.
Currently I'm running a Manitou fork and the lockout
option is unsatisfactory, thanks.
In a word, no basically because there's so many different
elements for suspension forks.
So some forks have externally adjustable damping,
some don't.
Some have the air leg in the left hand side,
some have it in the right hand side.
So for obvious reasons the cap can actually be the
same to fit any old fork.
And of course if the tubing itself is the same size,
still doesn't mean that thread is gonna be the same
pitch on the top.
So fairly unlikely you're gonna get one that's gonna be
compatible with yours.
Now with Manitou forks you can tune them after market.
So a better option might be if the fork isn't performing
as you want it to, go speak to your mechanic at a bike
shop and have a chat with him and see if there's any
sort of little tuning things he can do with that
particular fork.
Or even if you perhaps comment again in the comments
below and tell me what model the fork is,
what year it is I might be able to get a bit more
information for you
But that's about it, I'm afraid, for this one.
Next up is from Rupert S.
I have got a 2016 Rockshox Lyrik RCT3, good fork that,
when I gave it a lower leg service other day I noticed
the rebound damper shaft was wobbly and I'm not sure
if it's a good thing.
For as long as I can remember my forks have made a discreet
sucking sound and I was wondering if the wobbly damper
shaft is the cause?
Okay so bare in mind that when you do a fork lower leg
service you slide those lowers off, exposing the upper legs
with the air shaft and the damping shaft.
Now the air shaft is better sealed than the damping
shaft which only has a single O ring.
So that is a fairly unsupported shaft that's going
into that damper.
That is supported by the bolt into the lower leg,
so it holds the whole thing together and that guides
it in place.
So that's always gonna have a bit of wobble.
As far as the noise goes, to me it just sounds like
that is your rebound working properly.
That is the oil being pulled back through the shims.
Now, you could do a little experiment to test this
out for yourself.
Dial on a few more clicks of rebound so as to make
the forks slower and go and jump off a couple of things
and you should hear that sort of squelching,
that (sucking in) noise as the fork extends.
Now try it with less clicks on there, so it's faster,
and you'll find the noise will still be there,
but be a far more subtle (sucking in quickly).
So if that's the cause then that's fine,
if not then there is a slight chance that your damper
might need bleeding or just needs a little overhaul.
But more than likely it is just the noise of the oil
flowing through the shims and the ports inside the fork.
Next up is for Neil Waudby.
Hi Doddy, can you do something on how to keep internal
cable routing from rattling?
It's driving me crazy out on rides.
Yeah, actually I've got a frame that's doing the very
same to me at the moment.
that gravel frame I borrowed off the guys,
it wasn't a production one and it hasn't got the internal
sort of mounts to hold the cables so the cables do
rattle on that.
So yeah I'm gonna do something to show you how to
do that, but there are a few different ways you can
do this yourself.
The easy option is try and eliminate the cable rattle
from the outside.
So normally from the outside of the frame there's one
or two cables go in.
If you can tie them together with cable ties or a bit
of electrical tape, you do both ends you can actually
put a bit of compression on there,
that can help stop things.
The really neat one that I've seen people do,
and this applies with cables just on their own on the
inside of the frame and they're rattling around
is get some tiny zip ties, you tie them round the cable
and you push it in through that cable hole and then
push it along the cable.
Basically what happens is the tail of that zip tie
springs out and sits against the frame,
pushing cable against one side of the frame on the
inside to help stop it coming out of position and
rattling around.
So I will actually make a video on silencing internal
cable rattle, and also some other creaks, groans,
and noises that bikes makes.
There's a whole bunch of tips I can share with you there.
Next up is from Fernando Fojo, I have a 2013 specialized
Hardrock and, being an older model Hardtail XC bike,
it has a three by eight transmission.
I'm not a fan, I see the advantage of one by systems.
I'm currently saving for a new full sus bike,
but my question is are there one by transmissions which
would be compatible with my bike?
I'd like to keep it and have it as I can, basically,
seeing as there isn't anything wrong with it.
First up, all sort of one by transmissions would be
compatible with your bike, it's just the extent of
how far you want to go.
So, for example, you could buy a Shimano SLX setup,
so that would be a crank that comes with a chain ring,
chain, cassette, rear derailleur, and a shifter,
that's a full one by setup.
Crank will also come with a bottom bracket on there
so you'd have everything new.
Of course, that is the expensive way of doing it.
Now, in your case, if you want to do this the cheapest
and fastest way, what you need to do is get a dedicated
one by specific chain ring.
So that's a narrow wide chain ring, remove your current
chain rings, or three of them, remove the front (mumbles),
and remove the shifter and then mount this new chain ring
in place of the middle chain ring.
Then you've got a one by setup.
It'd be one by eight so you obviously one have as much
gear range, you won't have as low or as high a gear
as you currently have.
And you do need to factor in the size chain ring
you need for that bike.
For example, I'm running a 34 and I think the average
seems to be between 30 and a 36 depending on conditions
and spread of gears available at the back.
Bare in mind that if you do just want to put bigger
cassette on there, as well, you will need a new chain
to go with that and you're also gonna need new
rear derailleur and a shifter.
So obviously the cheapest option is just to buy
a chain ring.
You can have a one by setup.
Next one is another suspension related question from
Patrik Marcinek.
Hi Doddy, I'm a big fan of GMBN Tech and I'd like to ask
you if you have any experience with MRP ramp control.
I like the idea of tool free and quick change of
suspension progressivity whenever I want.
Is it worth the money?
Do you know what?
MRP ramp control, like this one here,
is a really really nice bit of kit.
So in case you don't know, on air suspension forks
you can change the volume adjustment on them by
placing these volume adjusting spacers inside.
Obviously when you put it in a confined space it's
naturally progressive, so it ramps up.
So it gets a lot harder to compress the last bit
of travel.
Depending on how many you put in each fork,
so whether it's a Fox or Rockshox, etc,
you can change the characteristics of the fork.
So if I put three of these in a fork and I had it against
a fork with none in, I'd be running the same pressure,
but with the one with three of these in it'd be
a little bit more supple initially, then it'd be a lot
firmer and the fork would sit in the middle of the
travel bit better and it'd be really, really hard
to bottom it out.
To the degree that it can feel quite harsh on your wrists.
The fork running with none of those in,
the fork again will feel supple, but I'm gonna use a lot
more travel all the time, and when it goes to the end
of the stroke it can be quite an impact as the fork
bottoms out.
Now what MRP ramp control does, this goes in in place
of the air cap on your fork and replaces what these
would do to an extent.
So basically when you have a ramp control in there,
if you hit a bit impact the air has to pass through
the ports in here and it restricts the amount of
air that can get through them,
so the fork ramps up and it feels like a much firmer
fork in that situation.
But as soon as you go back to normal impacts the ports
open again and it becomes a lot more supple like
a fork with no volume spacers in there.
So it's quite the best of both worlds, if you want.
Really nice bit of kit, it is pricey though.
Another suspension related question, this time from
Rowan Connolly.
Please help me.
When I removed my lower legs on my fork to do a lower
leg service the oils were different colors.
Red in the drive side leg and a weird creamy, cloudy oil
in the non-drive side leg.
Which oils do I buy or which leg?
First you haven't said what fork it is,
so I'm sort of unaware there.
Bare in mind that the oil that's in the lower legs of
virtually every fork on the market is just lubricating oil,
it's nothing to do with the damping and therefore
it should be the same oil in both legs.
So it does sound to me that it's just contaminated.
That could happy from dirt or muck that's ingressed
into the fork leg itself, or it could be from greases
elsewhere in the fork.
So if you do a lower leg service, you've taken those legs
off, cleaned them, and replaced them with some nice new
fresh lube in there, you should be fine.
Obviously you need to make sure you put the correct
amount of lubricating oil in a fork 'cause you put
too much and you can actually damage the seals
on those forks.
And it does say on all the major manufacturer's how much
you should put in them.
And if it's a Rockshox, on the actual little bolts
on the bottom it should say like five cc or 15 cc,
tells you how much you need to put in there.
And next up this is transmission one, this is good,
this is from Ari Nathan.
I have a weird shifting problem.
When I pedal backwards in the first gear it switches down
to a third gear.
The cables are new and my limit screws are adjusted
correctly, thank you.
Okay Ari, well you've got to bare in mind that the
transmission on bikes are, especially bikes with
derailleurs like this one, they're designed to work in
one direction.
You only need to sort of freewheel, you don't really need
to back pedal at any point on a bike.
If it's the case if you're going through a turn
you want to lower your next crank, just do half a crank
forward at each time.
Don't need to pedal backwards to do that.
However, most bikes shouldn't be skipping gears when you're
pedaling backwards.
So assuming your derailleur is correctly adjusted,
there's a few things it could be.
Now, assuming that your transmission is working correctly,
it's changing gear the right way,
there's a number of little things here.
When you're pedaling forwards on the rear derailleur,
the upper guide wheel, that is the one that keeps the
chain in line.
When you're pedaling backwards there isn't anything
to do that so you're subject to the chain line.
So firstly if you've got a poor chain line on your bike,
that's gonna have a significant effect.
So when you said you were in first gear,
you haven't said if that was first gear just on the
rear cassette or if you mean first gear and one of three
at the front, or just a single one.
So if you're in an extreme gear,
let's just say middle or big at the front and you're
in the big at the back, then your chain is crossing over
at such an angle it's naturally not gonna want to sit
onto that upper sprocket.
Also there are ramps on your cassette which are designed
for a chain to hop up.
They also have the opposite effect when you're pedaling
backwards, they want the chain to hop back down.
So you've got to bare these things in mind.
Now, if your chain is old it's gonna have more sort of
lateral flex to it so it's less likely to do this.
With a newer chain it's gonna have way less flex.
So again, even a perfectly setup bike,
there is a chance that a gear could skip and come
down one.
Finally, if this happens across all of your gears,
I mean I know you said between first and third,
if this happens across all your gears it could be
a stiff link, it could be a stiff jockey wheel,
or even a bent derailleur.
So number of things it could be.
But don't be too alarmed, as long as your gears are
working correctly running forwards.
Alright this is kind of a retro related question
from Mainz Man.
Given the motorbikes have been using upside down forks
for over 30 years, it seems strange they never caught
on with mountain bikes.
I assume there must be a good reason.
They've been pretty much standard on dirk bikes for years.
What's stopping them on mountain bikes.
Yeah, you're right, there's not many on the market,
there are a few modern ones these days.
There's a DVO Emerald downhill fork,
which is a flipping good fork and it's basically
addressed a lot of the issues that have plagued
upside down forks.
Now, one of the reasons mountain bikes don't tend to
use upside down forks is A, to make them is very
expensive and the reason for that is they have to
make them immensely stiff.
To make them stiff you tend to make something very
heavy or you have to make a very expensive workaround,
like DVO have done.
They've got a carbon lower arch,
which kind of makes them feel like they're a regular
Way up fork, but they've got the advantage of the
seals being looped all the time.
Now, over the years there have been a lot of different
people have tried this.
So for you people who haven't seen this,
one of the earliest ones was from Mountain Cycles,
you came out with a fork with suspenders,
so that was an upside down inverted single crown fork.
And that was seen on the Mountain Cycle San Andres
which has the pressed up dish brakes and a whole bunch
of other things.
And there was one in rewind a couple of GMBN Tech shows back
so if you have another look on the screen now you'll
see that fork.
And absolute stunning piece of kit and it worked
really well.
Following that came the Halson inversion fork.
Again, inverted, single crown, except this one has
a brace that operated in two slots in the upper legs.
So this thing was great when it was dry,
never too good when it's wet.
It had these crazy rubber boots that covered the
whole fork.
Kind of nice, I do like one just as a retro bit of kit,
that's a really different way of thinking.
Now Manitou have got the Dorado, the fork is still
produced just about, and it's one of the nicest looking
forks of all time, I think.
Full carbon, it's got a lovely aluminum cnc'd crowns,
works really well, but it is known as being quite flexy.
Now some people don't mind that because there's an
element of flex in riding that's actually quite good.
It's good for comfort and it's good for traction.
Sometimes you can have a front end that's too stiff
on a bike and you actually end up with a front wheel
that's sort of scratching for grip a bit more.
So I think a lot of people have ridden Manitou over
the years have actually loved that fork,
but it's definitely sort of a marmite thing.
And another bendy one was the Marzocchi Shiver.
I had a set of these back in the day and it was so nice
to ride, so plush, but they were bendy as anything.
Again, they look so moto that you kind of forgave
them for their looks.
Then there's a few other sort of random ones on
the market.
There was the Mr. Dirt Fork which was absolutely
enormous.
I can't find out much information about this online,
but I do know a guy who's still got a pair of these
so I'm gonna try and go have a look at those and see
if I could bring them in to have a look at in the show.
There's also White Brothers, they used to do the UD 150.
White Brothers used to be a sort of sister company
or part of MRP back in the day.
And that was a really, really good fork from what
I remember.
And then yet again there's another one,
there's Foes Fabrications F1 fork.
So Brent Foes was doing his thing with inverted forks
and long travel bikes long before anyone else was.
Coming from an off road background of motocross bikes
and all-terrain vehicles, Brent also brought in the
Curnutt shock technology, which has got a massive
stable platform on it so it enabled you to have
a long travel shock and these were used originally
on sort of the big desert racing trucks.
If you can imagine having a truck with all that
suspension trying to go around a turn,
the whole thing would be wallowing.
So it'd have an inertia valve on there so the forces
of the body roll that should be counted,
so it'd keep it quite stable.
And you had that on his early bikes,
so that was a really cool thing.
Then of course there's the Rockshok's RS1 which is
a fairly modern fork.
So that's not talking about the original one,
which came out in the late 80s,
talking about the inverted one, carbon fiber,
cross country super fork.
That's a pretty special bit of kit, but very expensive
to produce.
Now, finally of course there's the Cannondale Lefty.
So as well as being an inverted fork,
it's a single leg fork as well.
And that works because it's four sided and it's got
needle barrings, so roller barrings on each of
those sides.
And, I mean, most people don't tend to love the Lefty.
Personally, I love them.
I love the fact that it's such a bizarre thing and
Cannondale insisted on producing it for so long.
So the problem, really, has always been the stiffness
to weight ratio, and of course getting the costing down
not only in production but how much it costs the consumer.
So you think with mass production on regular way up forks,
they're so common now and a lot of them share the
same sort of chassis between models.
Now you're pretty limited with upside down forks
in the way you do this.
So that was the end of this week's Ask GMBN Tech.
Hopefully my answers have helped enlighten some of you.
If not, let us know in the comments below if there's
stuff you want me to expand on even further or maybe
even turn into other videos.
If you've got suggestions let me know in the comments
and of course you can fire in your questions to the email
address on the screen.
For a couple more useful videos, if you want to find out
how to repair tire wall slashes,
if you fancy getting handy with a needle and thread,
click down here.
And if you want to find out how to pick the right
mountain bike for you, click up there.
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