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- Hi, and welcome back
to another Ask GMBN Tech.
This is the weekly Q&A show.
You send your questions in,
and hopefully we get to answer them.
Questions you can fire into
the email address on the screen there.
Use that hashtag #ASKGMBNTECH,
and also you can add them
in the comments below this very video.
So first up is a tire clearance-related
question from Jack Bearnes.
Ask GMBN Tech, what would you
say is the minimum clearance
that I should allow for
on either side of the tire
on the fork or the rear of the bike?
I'd probably say minimum you wanna have
about five millimeters all the way around.
Of course, the more clearance
you can have, the better.
Because of the nature of mountain biking,
you could be riding in mud,
which is gonna clog up.
You could get stones and trail debris
stuck in your tire tread,
which is gonna foul on the frame,
can scratch it, all that sort of stuff.
But something you also
need to factor in is
how stiff your wheels are
and how stiff the frame is.
Now, even though wheels do feel stiff,
they can still flex quite
a lot under hard loads.
So if you're a heavy rider,
or you're heavy on the bike
in the way that you ride,
maybe you like to stuff into those turns,
you're gonna be quite
surprised by the amount of flex
a that rear wheel can have,
even if it feels very stiff.
And under a lot of flex,
it can lead your tire to
buzzing on your frame,
which of course is A, gonna slow you down,
B, is gonna wear out the
paint work on your frame.
Now the same thing can apply to a bike
that's got more flex than one that hasn't.
So, just check those sort of things.
If there's any telltale signs
of any tire rub on your bike,
and if that's the case,
then you definitely wanna go
for a slightly smaller tire.
But rule of thumb, I
reckon, five mil is okay.
I wouldn't wanna have it
any closer than that myself.
Okay, good old oval chainring
pros and cons one here.
So, Emil Jensen wants to know,
I'm riding a 36 tooth regular chainring,
but I have been told that
an oval chainring is good.
Can you please help me with pros and cons?
Okay, so I actually haven't ridden any
of the new breed of oval chainrings,
or certainly not spent enough time on them
to really give you the
best bit of feedback.
So, that's something I need to change soon
and I can feel a video coming on.
But just for the average sort of
pros and cons of what you can
expect from an oval chainring.
So first up, they kinda
maximize on your power output.
So you could argue that they give
a better efficiency for your pedal stroke.
Now, that is assuming
that your pedal stroke
isn't a perfect stroke.
I mean, there's not many people out there
that will have a perfect pedal stroke.
So, arguably, most people
could benefit from this.
Now you could say that they
also will increase traction
by sort of smoothing out
the way that you pedal.
So if you've got an
erratic way of pedaling,
you might find that you stab
at those pedals somewhat,
in which case the torque
of that is gonna help
the tire break loose.
Now, due to the way an
oval chainring works,
you can maximize on the traction on offer
by smoothing out that sort of way
that you apply the
power to the back wheel.
Again, so if you're very good
at spinning a smooth round circle,
it's not actually round,
but if you're good at doing that,
then you might not notice the benefits.
But equally, it's gonna be very beneficial
if you're not so good at that.
I've heard that they're very good
for people with flat pedals
because it's a lot harder
to have an equal sort of pedaling
base when you're pedaling.
And some of the cons, okay,
so I've written myself a bit of a list
here to remind myself.
So, the first up is probably a bit
of a negligible difference.
If they were that good, surely
everyone would be using them.
That's just my speculation
because I don't use them.
I've never felt the need to use them,
but equally, I definitely
want to try them.
So I think I'm on a similar.
I'm kind of on the fence
with you here probably.
Another con is the fact
that, with oval chainrings,
you're gonna be a bit
limited in chain guides.
Now, of course,
people like Absolute Black make
narrow-wide oval chainrings
So, that does get around a lot
of the necessity for having a chain guide.
But as you might have noticed,
a lot of cross-country,
a lot of EXIO, a lot of Endura riders
are still running an upper chain guide
just as an extra form of protection,
just to stop that chain hopping off.
And that does become a little bit harder
with an oval chainring.
Now there are a few
specific ones out there,
like Absolute Black, do make one.
That's one on the screen right there.
But you're very limited
in the market for those.
And now the final one,
is I've heard from some of
you guys actually commenting
that you think that oval
chainrings actually affect
and can wear out the clutch
mechanism on the derailleur.
Now it kind of does make sense
if you think what the chainring is doing.
The chain is actually sort
of stretching slightly
as it is going along,
so you're actually actuating that clutch.
Now I wasn't sure about this,
so I actually asked
someone at Schram just,
have you had this on your radar at all?
And they said, we don't
have anything on our radar
about clutches creaking or
wearing with this sort of use.
In theory, the dampening mechanism will be
activated slightly more cycles
when using an oval chainring,
but this hasn't affected anything to date.
Next up is that good
old fork length question
that always comes up.
A little bit different and
bit more specific though.
So, from Reynald Pader, he says,
hey Doddy, is axle-to-crown more important
when picking a fork than the
suspension travel itself?
I ask this because when
I'm trying to pick a fork
for my bike without drastically
changing the geometry,
it came with an 80 millimeter
Suntour XCT with a 475 fork length.
I assume this is axle-to-crown.
Yeah, generally the length that's quoted
when measuring forks is the
axle-to-crown measurement,
so yeah, you're right there.
I found that the RockShox 30 Gold
with 100 millimeters travel
has a 488 axle-to-crown length.
Will that negatively impact the bike,
or should I go with the 80
mill RockShox with a 468?
Which of course is slightly shorter
than the 475 that you've
actually quoted there.
So yeah, I think actually
most of the time,
fork travel sort of
correlates to axle-to-crown,
but you do get anomalies in there.
And I'd say axle-to-crown
is quite important,
especially on bikes with
slightly less travel,
because it's gonna be more affected
by altering that travel.
Now roughly, for every
10 millimeters traveled,
there's about half a degree
in a head angle difference in that,
so it is affected by how long
the wheel base of the bike is
and a few other features,
but generally, you're
talking about a half degree.
And in your case here,
talking about the 488 over the 475,
that's quite a lot.
You know, you're talking
nearly a full degree there,
so you have to decide if you wanna
actually have that effect on the bike.
Personally, I don't think
a degree is too much
to be worried about,
but if you've got quite a steep head angle
it's very noticeable.
And as well as actually adjusting
the head angle of the bike,
it might be steeper or shallower,
depending if it's a
shorter or longer option,
it also raises and
lowers the bottom bracket
and steepens or shallows
the seat angle as well.
Now, that might sound a
bit negligible to you,
but a bottom bracket height
can be noticed quite a lot,
even if it is a few millimeters
because it really does affect
your position on the bike,
how far you feel like you sit into it,
and you're above the sort
of the fulcrum of your bike.
And again, with the seat angle,
under climbing when you're seated,
you'll notice it if it slackens it,
because you'll feel the need
to sit further forward on the saddle.
And quite often you might want
to run your saddle further forward
to slightly nose-down to compensate
if you are slackening that head angle.
I don't think it's that much
of a problem in your particular bike.
So you said 80 mil RockShox with a 468,
so it's gonna steepen it very slightly.
But the 30 Gold or the 100 mil has 488.
It's not gonna be too
bad if you also factor in
is the 30% sag that you
typically set a bike up with.
Obviously, if it's got more travel,
it's gonna have slightly
more sag in relation,
and you're actually gonna bring those
numbers back closer
again, so it all depends.
If you can put up with it in climbing
where you're naturally gonna be
a slightly slacker seat angle,
I think you'll probably be
all right with a 100 mil fork.
Oh, this is a good one from Dan D,
a chain line friction question.
Loving the tech channel, Doddy.
I wanna ask a tech question
about 1x drivetrains.
I've heard that the 1x
chainring sits so close
to the frame that when you're in your
smallest sprocket out back,
it throws the chain line off
and causes extra friction.
In turn, causing a loss in power.
What are your thoughts?
Well, firstly, it doesn't
sit that close to the frame.
It's sat basically to give it
the best chain line through all the gears.
So it sits about halfway
through the cassette,
so it's not too extreme on either side.
Now as long as you've got
your chain line correct,
actually I don't think there
is that much friction in there.
However, there is always
gonna be more friction
on the smaller sprockets
than on the high friction,
regardless of the derailleur
here for a second.
If you think about the chain
just wrapping around the sprocket,
when it wraps around the biggest sprocket,
there's not as much wrap,
so there's less friction in the chain.
When it's wrapped around
a smaller sprocket
and it's almost all the way around it,
the chain has to move a lot more.
So, each chain link is doing more,
so there is naturally gonna
be slightly more friction.
But in honesty, I'd actually
need to put it on a machine
to feel the difference,
because I don't think
a rider can feel the difference between
that and running it halfway
up the transmission,
regardless of the actual
gear that you're in.
I still think it's that
possible in a mountain bike
when there's so many
other factors in there
like the tire pressure you run,
the suspension you're running,
how much grease you may or
may not have in your bearings,
the surface you're riding on.
Like if you're riding on grass, obviously,
it's a lot of friction, quite tiring
compared to riding on Tarmac.
I'd actually really like to try some
sort of friction-based testing
and spend a couple of days just trying
a whole number of different situations
I wanna try and find out for real.
But I don't think, in this case,
that you can actually
know where you stand.
If it was, you wouldn't
see so many companies
dedicating themselves to 1x transmission,
and especially with that new
Shimano XTR transmission.
We've got a video dropping,
a bit of a geek edition,
looking at all the facts
and figures to doing that,
and it's pretty impressive stuff.
And you know what Shimano are like,
I really can't believe they'd get involved
with a little 10 tooth if they
didn't think it was worth it
and it had additional friction.
So, shifting issues from New
Zealand, or NZ, Mountain Bike.
GMBN Tech, I've got a Trek Roscoe 8 with
a Sram NX one by 11, and in
the middle range of gears,
it won't always shift, and when it
does shift, it skips gears.
At the lower and upper range
of gears, it shifts fine.
How can I fix it?
All right, so first, you just need to
identify what the problems are,
and with gear shifting,
if you've got issues,
firstly do a visual inspection.
Actually check those sprockets.
Check your chain.
Make sure there's no sort of stiff links
or any damage with a link that's maybe
split and it could break.
Then you wanna look at the
alignment of your derailleur.
So, obviously, you wanna
make sure it works smoothly,
the cable is working smoothly
inside the outer housing.
See, if there's any sort
of unwanted friction
or any gunk inside there, it's gonna cause
the cable to stick and it's
never gonna shift correctly.
But in theory, if you have
your limit screw set correctly,
either lower limit screw
for the bigger sprocket
and the higher limit screw
for the smaller sprocket,
and the derailleur completely
correlates to those,
then, in theory, the
only thing you need to do
is to let out your cable tension with
a barrel adjuster to get perfect shifting.
If yours is suffering, it's
gonna be out of alignment,
or it's gonna be suffering
from stickiness somewhere.
So, you just need to factor all those in.
I'm just gonna throw you
quickly to some clips
from a perfecting your shifting video.
The link to that is gonna be in
the description below this video,
and that will answer all
of those individual things.
So, I promise you, if you
run through all of those,
you will find your
issue, even if you think
that it's working well at
either end at the moment.
Good luck with that.
Whistler Bike has got some
10 to seven speed problems.
Got a question about setting
up a 10 speed to seven speed.
I have an Atomlab DHR Rear Hub,
and it only fits seven cogs.
So I took a Shimano Ultegra 6700
Road Cassette and removed three cogs.
My question is shifter set up.
I don't like having three dead shifts.
Within there, obviously, 'cause it's
designed for 10 speed rather than seven.
Can I modify my saint shifter
to make it seven speed,
or have I seen a block that fits
on the cable to limit
the shift cable movement?
I don't think so.
I've not seen it.
You're saying that it sounds like
something that should exist.
The only thing I've seen
for shifter modification
is from E13 to modify your 11 speed
shifter to take 12 speed shifting.
That is by including a proper ratchet.
You actually take apart your shift
and put that inside in
place of the 11 speed one
to give yourself the extra click.
I've not heard of something
to convert a 10 speed,
or any other shifter,
backwards down to a seven.
The new XTR has it from 12 to 11,
but it's only compatible with 12 speed
just for taking off the extra there.
No, I don't think so, but I'd love to know
if there is something
out there that does exist
because if it does, we'll
look at doing a video
on how to hack a drivetrain like that.
In the meantime, I'll try and find out,
but I don't think so.
I think you're gonna have to put up with
those extra clicks, unfortunately.
Okay, so next one is bike
fit from Andy Ginther.
Doddy, I'm impressed and amazed with how
thorough and articulate you are.
It's just research, mate, and in fact,
I'm a bit of a bike geek.
I love this stuff.
Excellent work, man.
I'm currently riding
an 09 Nomad size Medium
and hoping to upgrade soon.
I've struggled finding
a stable body position,
especially downhill, due to small reach.
Yep, it's always a big problem,
especially for taller riders.
I have my eye on a new Nomad size Large.
I'm five-foot 10, and I like a short stem.
Any thoughts on bike size,
or ways to find my triangle ratio?
I love the fact that you say that
'cause I do completely believe in that
basically is the argument for
getting the ultimate bike fit.
I had to look online at the 09 one
versus the current one,
so the one in the office
we have for bike build is a size Large.
So the reach on the size Large now is 460
and it's got a 690 top due.
And on your 09 one, it's 405 and 609,
so it's absolutely tiny by comparison.
So no wonder you're struggling.
So at 5'10, I mean Santa Cruz
recommend a size Large
anyway for your fit,
so I think that's a no-brainer because
it is a nice roomy bike.
You're about to put a
30, 40 mil stem on there.
You're gonna get that nice roomy cockpit,
all the control that you
want, aggressive geometry.
I mean, you know already
if you're looking at
a Nomad, know what you're
dealing with there.
I always tell people to size
up on bikes if they can,
or at least try and pick the right size
as opposed to picking a smaller size
in the theory that you're
gonna get to throw it around
because all that's gonna
happen is yeah, all right,
if you're really into jumping,
a small bike can be very beneficial,
but if you wanted to go fast off-road,
a nice long bike that you
sit into the frame properly
is always gonna be better
than a short wheel base bike
that doesn't fit you or
your weight is all up top,
and a bit of weeble-wobble.
It's almost like a big pendulum
that wants to take you off the bike,
and accordingly, you're
leaning too far back
and too far forwards the entire
time to get that balance.
Definitely go for the Large.
I would still try and get a
demo on it if I was you though,
but good luck and I hope you enjoy it.
So that's another Q&A session in the bag.
Hopefully, it's answered some questions.
If you've got any, add
'em in the comments below,
or fire 'em into the email address
at the beginning of the show.
For a couple more tech-related videos,
click down the bottom
there for the bike fit one.
So this is answering a lot
of problems a lot of you
ask all the time about
having hand pain when riding,
not being able to manual,
all that sort of stuff,
so click down there and
hopefully it gives you a better
idea of how to set your bike up
and to understand the effects of what
those things do to other
things on the bike.
And if you wanna find out a
bit about what a chain does
to actually affect suspension,
click up here where Neil basically set up
an idle wheel system on his bike
so the chain passes over it,
to see how the bike felt
with isolated suspension.
Pretty tech, pretty geeky.
We've all known that
people have been using
this sort of stuff for a while,
but Neil's put it to the test.
It's quite cool.
So, as always, click on the round globe
to subscribe to the channel,
'cause we've got new content
for you every single week here.
At GMBN Tech, we love having you around,
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