(logo whooshes)
- Welcome to an Ask GMBN Tech.
Of course this is the first one of 2019,
so happy New Year
- Yay!
- To all you mountain bike
tech lovers out there.
This is our weekly Q and A show,
you get to ask to ask the questions
and hopefully we give you the answers
that you need, if you
want to ask any questions,
get 'em in those comments below,
use that hashtag, #askgmbntech,
or you could forward them
into the email address
right on the screen there.
Kicking off this year, the first one
of the year is from Jack Beames.
What would you say the minimum clearance
should be for either side of a tire
on the fork or rear end of a bike?
To be honest, I would say
probably five millimeters
is about as close as I would like to get
with the biggest tire I'd like to use.
Obviously this is gonna vary
depending on your frame.
If your frame's an older
frame, you're gonna
have more limited clearance
and you're gonna be forced
to use a slightly slimmer
tire, which isn't ideal.
Now you've got to bear in mind,
there's a few different reasons
why you need this clearance.
So the obvious one is mud clearance.
If you live in Europe
or the UK or anywhere
where you're likely to be riding in mud,
depending on the type of mud, if you're
on the sloppy stuff, you
don't need much clearance
but we get the big, thick,
claggy, horrible stuff,
so you need as much
clearance as you can get.
Otherwise you're gonna be
picking out handfuls of mud
out your bike before you can
get the wheels to rotate.
Never a nice situation.
The next one of course, is
if you buckle your wheel
when you're riding and your
wheel can rub on the frame.
So this is gonna take paint off the frame.
Not an ideal situation, you need to allow
for enough room for error, there.
And then finally, and
actually, I think probably
most importantly, is allowing
for frame and wheel flex.
Now, your frame and your wheel will flex
more than you probably realize.
Now I've had this on
several frames in the past,
where my rear tire is
actually buzzing on parts
of the frame when I've been
running a really big tire.
It doesn't happen all the time, of course,
it depends on where you
ride, but those sort
of tight little turns that
you really push the bike into,
they can put a strain and
a stress through the bike
that you probably don't even
really notice it's doing
but you can have a look at
the little tell-tale signs
of paint just missing on the inside
of the chains, the yoke area there.
So you just wanna make
sure you've got room
for a sort of margin of error.
And then hopefully, you'll be all right
but yeah, five millimeters
is what I would suggest.
(mechanical whirring)
All right, next up's a
transmission-related one
from Ben North, Doddy and co.,
I'm currently running
a one by 10 drivetrain
for XCO, so that is
basically the cross-country,
Olympic-level style
riding, 34 tooth up front,
we have 11-34 on the rear.
I always see pro XC
guys like Nino Schurter
running huge front chainrings to make use
of the massive Eagle cassette.
Shouldn't there be a
better and lighter way?
I wouldn't say it's to
make use of that 50 teeth,
'cause I think the 50 teeth enables him
to use an even bigger front sprocket.
So you say you're running a 34,
Nino tends to run around a 38 teeth.
Let's not forget that Nino
is quite a lot stronger,
fitter, and more aggressive
in the way that he rides
so he chooses to use a
big chainring like that 38
because A, it also offers
him, with that 50 teeth
on the back, a low enough gear
that he can get out of jail, basically.
He can get up any climb with that
at any point in a race that he needs to
but also gives him a much bigger gear
than many of his competitors use
and really, he's one of the only riders
that can really, really do
some damage with that gear.
Well-known for putting people
through the Schurt locker
there where he puts the power down
on three or four laps to
go, whenever he chooses,
to be honest, doesn't even
look over his shoulder,
(sputters) goes, you know what he's like.
I don't really think
there's many lighter ways
of doing it because, to
get similar gear range,
straight up beginner need to
do a double chainring setup
up front and that means
having a cable on there,
it means having a front
derailleur, having a front shifter,
all sort of additional
stuff, I actually think
it's the most efficient way,
really for cross-country.
That is, of course, at the top end,
where it's the XX1 Eagle,
they're very expensive,
very high-end stuff.
As soon as you get down to
the cheaper level stuff,
the cassette becomes very heavy
and you're right, it
does add excess weight,
doing it this way, so in which case,
you could go lighter with a 2x setup
but that's all about
the 1x for the big boys,
especially if you've
got the power like Nino
to run a 38-teeth chainring.
(bicycle gear whirs)
All right, now it's up to Eric Thatcher.
I'm gonna buy a new bike
this spring and want
to go from a 29er hardtail
to a full suspension bike.
I'm thinking about going to a
27-and-a-half-inch-wheel bike
because the trails I ride
are pretty tight and twisty.
Should I go for it or should I stay
with a 29er with full suspension?
How long is a bit of string, mate?
I really don't know what
to suggest, to be honest.
So, you can be partially right in that
a 27-and-a-half-inch-wheel,
full suspension bike
will certainly feel lively and agile
around that twisty stuff and that's great,
if that's what you're looking
for, but is there any problem
with your current wheel
size on that terrain?
If there's not, then
maybe you should stick
with a wheel size that you know.
Now, a lot of people
compare the two wheel sizes
and they look at what they can roll over.
All right, so arguably, a 29 inch wheel
can go a little bit
faster when it's rougher.
It's a little bit slower
when it's tight and twisty.
But also bear in mind, the
27-and-a-half-inch wheel
will accelerate quicker
and decelerate quicker.
So it's something I've
noticed on a 29-inch wheel
and what I actually think people mistake
for them being quicker
than a 27-and-a-half
is they're slower to
slow down, so you feel
like you're keeping speed more.
And the reason for that,
at least my theory is
when you brake on a
27-and-a-half-inch-wheel bike,
your bottom bracket is higher,
so you put more bias to
dig in that front wheel
into the ground for traction
and for slowing down.
When you brake at high
speed or on chattery terrain
on 29-inch-wheel bike,
you're so low in relation
to the axle that you actually end up
pushing the bike forwards
more than you do down
and therefore, you feel
like you're going faster
more of the time and I
think that's why a lot
of the enduro racers love running the 29s
because they do speed adjustment
rather than braking, so the whole time,
they're just galloping along, really.
I don't really notice
the actual physical speed
between the two, what I
do notice is the position
on the bike and that is everything to me.
It's all about how the bike feels,
not really about what the
bike is doing underneath me.
I have to feel right on the bike.
Now, since I've been riding
almost exclusively 29ers,
every time I go back to 27-and-a-half,
I find them a little bit
unnerving to be honest.
I think I feel too perched
too high on the bike.
This does make them
easier to flick around,
throw around, all that sort of stuff,
but actually, I really like
the position on the 29.
I've not really given you
any sort of answer here.
So if I was you and I liked the 29er
on the typical terrain,
I'd be probably in mind
to stay with that but definitely
try two similar bikes,
one with the bigger wheels,
one with the little wheels.
Either way, there's lots
of options out there
and you might find that you
do prefer the smaller wheels
because they're fun but the big wheels
are also fun in a different way.
Best advice is really to go and try some,
go to a demo and that's really good,
'cause you can change your
mind instantly about stuff.
(bicycle gear whirs)
All right, next up's from Rok Krumpestar.
Doddy, I've got lithium grease
and I don't know if can even use it.
Where can I use it?
Yeah, of course you
can use lithium grease,
it's great, it's really good value,
it's slightly thinner than
a lot of other greases.
You tend to use this stuff
on working components,
things like ball
bearings, so your headsets
and bottom brackets and it's great.
But don't be tempted to use it in places
like suspension forks
because it's not very good
for the bushes and the working surfaces
and the seals and things like that.
Now obviously, there's a lot
of type of greases out there
on the market and they do have
different sort of purposes.
Now you can get some all-purpose greases
that suit a lot of things,
but even then, things
like suspension do require
a slightly dedicated grease.
If you want a complete
breakdown on all greases,
lubricants, threadlocks,
assembly compounds and stuff,
I made a video exactly on that.
I'm gonna put a link to
it in the description
below this and it will tell you, I think,
pretty much everything you need to know
about all the types of greases,
where you can use them,
and more importantly, where
you should not be using them.
Good information, I
think, check that one out.
(bicycle gear whirs)
All right, next up's from Tipfi CG9.
When I'm racing downhill,
can I go tubeless
without the sealant for the runs
to save less rotational weight?
I know I can't avoid punctures
but it's same with inner tubes.
It's a bit of a mess when I
change tires with the sealant.
No, you can't really do that.
So you can set up a tubeless tire
with no sealant in it and it will inflate
but part of the beauty of the sealant
in the system is if you get any sort
of microscopic holes as you're riding,
it does seal those and
also, more importantly,
when you burp a tire, which is very likely
when you're racing downhill
because you're thinking
about the clock, you're not thinking
about riding conservatively on the bike.
When you burp a tire with sealant in it,
it seals much faster again
and you don't lose too much air pressure.
If you burp a tire with nothing in there,
there's a good chance you can
put it straight off the rim.
So skip that one out completely.
And really, are you gonna
notice much difference
in rotational weight on a downhill bike?
I don't think so.
I'm sure you could notice back-to-back
if you did tests but downhill
bikes weigh 40 pounds.
You're not gonna notice
a bit of tire sealant
slopping around inside the tire.
It doesn't really make
that much difference.
Admittedly, on a cross-country
bike, very lightweight bike
where anything makes a difference
on 'em, you would notice.
But even those guys run
tubers with sealant in them.
Keep the sealant in, does the job,
or get rid of the tubes, your choice.
(bicycle gear whirs)
Okay, next from Fex Bru.
Is it possible to do a
fork lower-leg service
without removing the fork from the frame?
Yeah, 100%.
I pretty much did that in the
winterizing your bike video
where I took the lower
legs off, replaced the oil,
I also greased the seals
up and stuff on those.
When you do this, make sure at the least,
you take the brake pads out or preferably,
take the whole brake caliper
off and let it dangle
somewhere safe where it's not gonna get
any oil contamination and make
sure you have a drip tray,
an old dinner tray,
anything you can underneath
to catch that oil, otherwise
it can go all over your floor
and it's horrible stuff
to clean up, to be honest.
Obviously make sure you dispose
of the oil correctly too.
But nice and simple and
I'm gonna throw a link
to that winterizing your
bike video in the description
below this video so you
can have a look at that.
Super simple process
and yeah, you don't need
to remove your fork from your bike.
(bicycle gear whirs)
Go over to Tomacukor now.
Are master links weaker
than regular links?
If I joined my chain
back to back every time
with one, I would be running four of them.
Do you know what, I don't actually know.
I've ended up running a couple before
and I can't see how
they would be any weaker
than a regular chain when it just comes
to chain forces but because of the fact,
the way they're joined
rather than the pin pushing
through it and staying in
place more like a rivet,
I guess they could potentially be weaker.
That is definitely something I need
to do a test on, but more to the point,
why are you ending up
with four in there anyway?
If you need to split your chain,
maybe to clean some of that out,
why not just split that master link
that's already on there
and replace the master link
unless it's a multi-use one?
I do recommend using the single-use ones
because I feel that
they're safer and stronger
but yeah, why not do that?
Just a thought.
(bicycle gear whirs)
Over to DD410, sounds like
a Star Wars character there.
Help, my brake pistons are not retracting
and one of the pads is
rubbing on the disc.
I tried removing the wheel and brake pads
and pushing the pistons back
in after I put everything back
and I pump the brake
lever, they don't retract.
Brake motor with SRAM Code RSC.
Simple, sounds to me that
you have sticky pistons.
Of course, it could be a bleeding issue
so it is worth doing a full system bleed
on there, just to see.
When you bleed the system, take note
of the color of the fluid coming out.
If it's really dark black and gritty,
then you'll know that that
is one of your issues.
But if you've got a sticky piston,
then you're going to need
to strip your brakes down.
Obviously remove the pads,
keep them somewhere safe
where they can't get covered in oil.
You're gonna need to remove those pistons,
clean them, the insides
of the actual unit itself,
and then you're gonna need to use
some dedicated piston grease.
SRAM make one, they're
very similar to the ones
on the market, especially
a DOT-friendly grease,
so the grease is not gonna break down
with the DOT fluid in there,
it helps pistons slide
in and out, retract properly,
and then you'll need
to do a full system re-bleed.
I'm not sure I've actually done this
as a video, so this is
actually a good idea.
So I'm gonna do a piston retract,
re-bleed, clean type video soon, I think.
If you can wait, watch
that, and I'll show you
how to do it, if not, just get involved.
It's nothing to be afraid of.
It's a fairly simple
process, there's just a lot
of steps to it and if you're
happy bleeding brakes,
then it's just the next step from that.
But just make sure you
get the correct grease,
the DOT-friendly grease
like this one on the screen.
All right, now to Sean P.
If a rim was bent but trued, how long
before you need the rim with a new one?
Can you get away with riding the same way
on a once-bent rim or not that rough
and recommend getting a new one?
Totally depends on how
you ride, to be honest.
Despite being quite big and heavy,
I'm actually fairly light on
a bike and I've ridden rims
with really messed up spoke tension
and stuff for quite a while.
Obviously, it's entirely
up to you, really.
If you are like Blake and
you sort of go through wheels
like you do breakfasts, then, well,
you're answering your own question there.
As soon as the wheel
collapses, sort it out.
I don't think there's any rush to do it.
Just keep an eye on your spokes,
make sure no nipples
are ridiculously loose
and if they are, just keep them
nipped up when you see fit.
But keep an eye on the rim for
any actual structural damage.
Keep an eye out for cracks, any creases
that look like they could
lead to the rims splitting,
things like that, use
your common sense, really.
If it ends up being that badly buckled,
you're never gonna be able to return it
to a completely true
wheel and then it is time
for a new rim and pretty much every time,
you're gonna need a new set of spokes
to go with that as well,
it's not a problem.
It doesn't cost a lot of money
and it's well worth doing because you get
effectively, a brand new wheel again
and whilst you're at it,
do a hub service too,
just to make sure all your
internals are working and nice.
But really, it's kind of
using your common sense.
There's no right and wrong with this.
It's pretty much up to
you with how you ride.
(bicycle gear whirs)
Okay, so Griffin Taylor wants to know,
the Kashima coating on FOX shocks,
is it a functional
piece or just marketing?
If it's functional, do
you notice a difference
between a shock with it
and a shock without it?
No, it's 100% functional
but it's a marginal thing.
So let's just say a FOX 36
or 34 with the performance,
so that's the black coating and then
there's the same equivalent with Kashima.
Now, they'll fill out
the box, so obviously
you'll need to bed in a bit,
but they'll both feel very, very good
and they'll continue feeling that
after service, they'll both
feel very, very similar.
The difference is the longevity to it.
So the black ones, the regular
stanchion tubes, that is,
they basically need more servicing
and more TLC to continue
feeling that good,
whereas Kashima-coated
ones work a lot longer.
They feel a lot better for a lot longer.
And arguably, if you were
someone like a Greg Minnaar
and you're really, really
tuned into the mechanics
of a bike, you would be
able to feel the difference
between them but for most normal people,
myself included, they
basically feel the same.
But essentially, what
it is, is you're paying
for a higher quality coating
that feels better for a lot longer.
(bicycle gear whirs)
And there we go, that's our weekly
Ask GMBN Tech rounding up.
If you've got any questions
or you wanna know anything,
let us know in those comments below
and definitely, you can email
us at hellotech@gmbn.com.
For a couple more videos,
tech-related of course,
click down here for confusing tech terms.
There's a lot of confusing
names but actually,
they're all fairly simple if you
just deconstruct them a bit.
And click down here if you wanna see me
do a bit of trailside
setup on my own bike.
We always talk about doing
stuff in the workshops,
getting it set up, but nothing
beats getting out there
and actually making those
fine tweaks on the trail.
As always, give us a huge thumbs up
if you love GMBN Tech and let us know
what you wanna see in the
future as well in those comments
and don't forget to subscribe.
