- Welcome to another weekly Ask GMBN Tech Q&A Clinic.
Get your questions in to us
at the email address on the screen
or you can add them in the comments below.
Alright, so first up this week is from Freddy Dembrey.
Freddie asked GMBM Tech, "Can you run SRAM brakes
"(levers and calipers) on Shimano rotors? Thanks."
Yeah, is the answer to that.
Bearing in mind that some disc sizes are slightly different.
For example, you get the 200 versus the 203
with the SRAM Shimano thing there.
And disc rotors, actually some of them
are a little thinner than others
although, your brakes will compensate for that.
In case you wanted to know, Shimano rotors are
1.8 mil thick as standard and obviously
they get thinner as they wear.
If they start getting beyond, I think it's 1.5
then you want to sack them off because
they start losing their strength and their integrity.
With SRAM ones I think it's 1.85
so they're very, very, fractionally bigger
and I think Formulas are fractionally smaller.
But that doesn't really make too much difference,
as I say, your pistons will compensate for that.
As long as you have the hardware correct
where your brake is mounted, so if it's mounted
on a direct mount, you might need some of those cone washers
to compensate for the 200 or the 203 rotor
depending on which way round your brakes are
and, of course, if you've got the correct adapter.
Always make sure that your brake pads
sit completely onto the actual disc rotor braking surface
and make sure the disc rotor can't foul
the inside of the caliper as it passes through.
And if that's all good, then you're good to go.
Okay, nice punchy one from Daylight Sensor IMA.
Asked GMBN Tech, "Is it normal to blow through
"160 millimeters of rear travel on a two foot drop?
"I have a 2013 Canyon Strive AL 8.0."
No, it's not normal, but that does
depend on a lot of things.
It depends on how you like your suspension,
how you ride, the way you even approach that drop.
Let's just talk about the actual drop
from physical riding point of view.
If you're going off a drop really fast
you can actually meet with the ground a bit
and you can actually lessen the impact.
Whereas if you're just popping off something
you get all that down force in one hit.
Now, of course, if it's a wheelie drop
you can lower that back wheel if you just pop it off
you have more impact.
So, it does affect you slightly differently.
And, of course, your ability as a rider
to use your body to absorb that impact.
But just the physicality on the bike,
it sounds like to me either your rear suspension
is slightly too linear for the way that you want to ride
if you want to be doing drops like this
or perhaps it's set up slightly under sprung.
So, the first thing you want to do
is check the spring on your bike
whether it's a coil spring or an air spring
is basically giving you enough or not too much sag.
So, you're looking between 20 and 30 percent
of the available travel to sag when you sit on a bike.
If you've got an air shock, you can measure this
with the O ring on the actual shock shaft.
If it's not, if you've got a coil shock
the best way to do that is to measure
with you not sat on the bike
the distance between the saddle and the tire
and then by subtracting the amount
of suspension travel you have on the bike
you can work out your 20 or 30 percent sag
when you sit on it and that gap will obviously close.
So, get that set up and if it's not correct
then, if it's an air shock then you can adjust
the air volume in that shock.
Sometimes you can do that with air volume spacers.
Sometimes, it has to be done in different ways internally.
But that's basically your solution to that.
So, hopefully you can get that done.
Alright, next up is from Herby.
"Is there any disadvantage of overspending grease
"in a headset?
"I normally put grease between the spacers,
"and between stem and steerer tube.
"I just got a new Canyon Spectral AL 6.0"
nice bike, dude, "and I took the forks off
"just to have a look how it works
"in there and I noticed that there is
"much less grease inside than I would put in, thanks."
Bearing in mind that when bikes are put together
in big production lines, they put in
what's an efficient amount of grease.
So, cartridge bearings themselves
they all have grease inside them
the whole point of them is they're a contained unit
you pop into the bicycle, you pop into the headset
and it works.
The advantage of having more grease in there, really
is an extra barrier against corrosion and water
and getting water into that bearing in the first place.
Of course, any water getting into
the actual cartridge bearing, that is where
the problems start arising so
the more you can ward that off, the better, in my eyes.
I would always prefer to have a bit more grease
especially coming from the UK, we have a lot of wet weather.
So, I tend to put a bit more grease in there
when I put stuff together and afterwards
you can just wipe it down on the outside.
And then, periodically after, I don't know
two or three months or however bad your weather
may or may not be, have a little inspect
make sure that it's basically still in there.
If it's gone this sort of a brown-y sludgy color,
it's a good idea to wipe it all clean
and check the bearings are good and then replace that.
But bearing in mind the bearings themselves
are only good if they're running nice and smooth
and have grease in them in the first place.
The minute that they are actually all gritty in there
no amount of grease being applied to them
is going to repair them.
So, just take that into account.
So yeah, just treat it as a waterproof barrier.
- Okay, Frank Town wants to know, "What is the purpose
"of the star fangled nut?"
"You said that with the top cap it helps
"align and tighten everything
"but I don't get how that works exactly."
Okay so, parts of the headset right,
so if you look at the fork itself
you have the steerer tube on there.
Then on the steerer tube you have the lower crown races
on the crown of the fork you have
bottom part of the races sits into the bearing
the bearing sits into the cup in the frame
steerer tube passes through that
the upper cup sits on the frame,
steerer tube passes through that
bearing sits into that, then you have
the selection of washers that sit into that
like a compression ring, then you have
the stem, you have the top cap.
On the inside of that steerer tube
you have the star fangled mount which is
wedged in, it's like a bob so it can't move.
When you adjust or tighten the bolt on the top
it basically pulls the steerer tube up through the stem.
That's why you have to leave that gap at the top there.
When I say, pull this, I'm making quite a big movement
you're actually talking like less than half a millimeter
or so when it moves.
And the idea is, you're pulling everything taut
or you're pre-loading the bearing.
So, it's not actually doing anything
to the bearing itself, it's just making sure
that all the components of the headset
are all taut and they're in place
against each other so there's no movement.
As in, any sort of movement that's not
just a physical turning of the headset bearing itself.
Because any movement you get, any sort of rattling in there
that, with the amount of leverage that you have
at the wheel end and the handlebar end
is going to start slowly destroying those bearings
which, of course, can lead to other problems.
So, it's essentially just a way of pre-loading the system
making sure everything is nice and tight
and doing its job correctly.
If you ride a bike with a loose headset
or if you try and basically put the system together
without having that top cap on there
you will never get it tight and the headset
will always be slightly loose.
That's all it is.
Alright, so Sumner Bob is next.
"Doddy, I've got a specialized FSR downhill
from the nineties" oh dude, trick bike
got a friend who's got one of them, at Shrewsbury actually
and he's got a Palmer replica.
"And the suspension linkage bolts keep loosening
"after every ride, even though
"it's been torqued up properly.
"It uses bushings instead of bearings,
"will Loctite fix this?"
In theory, yes, so Threadlock does a great job
of stopping bolts coming undone,
however, if the reason they're coming undone
is because of movement coming elsewhere,
and the bolts are starting to unwind
rather than rattle loose then
they won't help, they will always unwind basically
however much you put on.
And if that's happening, that would suggest
that the bushes are worn.
So, my advice would be to, with all the bolts tight,
check to see if there's any play or any movement
in the back end of that bike,
you should still be able to track down
the relevant bushing kits for it.
Get a fresh bushing kit in there if that is the problem
then, when you put it back together,
use the relevant greases, assembly compounds
and Threadlock of course and use your torque wrench on there
then hopefully, you'll have no problems.
Basically, it sounds like movement is happening
from somewhere, but Threadlock on the bolts
is your first point of call if everything works
because it's designed there to lock those threads
and stop it rattling loose.
Okay, next up from Kenny Minigun.
"Are straight pull spokes stroke hubs suitable
"for abusive riding like downhill and enduro?
"Are they any better than traditional
"J-bend spokes and hubs?"
Yeah, they're absolutely fine, to be honest.
It's more down to how they're built
and laced up and tensioned as is the case
with any sort of wheel.
If you look on screen now, we're just going to look at
the J-bend pros and cons and we'll do the same
for the straight pull afterwards.
So first up, J-bend pros, they're easily available
to suit any hub, basically any sort of standard hub that is
with a flange and drill holes, they've always
been made this way and been made so long
that companies make excellent spokes like this.
They can be laced in any cross-pattern like this as well.
You're not sort of confined to have to build
hubs in a two cross or whatever pattern
you can build them two cross, you can build them
radial with three cross, four cross even
or if you're daft you can build them
in a snowflake patter if you really wanted to.
There's no limits to what you can do
with a regular J-bend spoke.
Arguably though, they are slower to lace up.
So, whether that's a good thing or not
that is just one of the facts because
they take a little bit more time to intricately
put them into the hub itself.
One other cons is they can break at the elbow
and although DT do say that their spokes pretty much
versus each other are about as strong as each other
it's basically down to how they're built
and the quality of the hub that they're put into
that affects this with the J-bend spoke.
So, for example, if the holes in the hub
where you put the spoke into are slightly bigger than
the actual size of the spoke going through that
that can create a sort of amount of movement
and of course, that could stress the elbow itself
and it could crack at the elbow and break.
Now also, if the wheels are under-tensioned
it enables too much flex and the flex has to go somewhere
in the spoke and it's going to basically
fatigue that elbow which eventually will break.
And, of course, there's slightly more material.
We're talking a marginal amount here, so you could argue
that you've got a slightly heavier wheel
with J-bend spokes as well.
But if you look at straight pulls, right,
so the straight pull chart is on the screen now.
The pros are, they're slightly shorter spokes
so you can build a slightly lighter wheel.
We're talking like a minute amount here
but in some cases, that's a really, really important thing.
Arguably, they're easier to lace as well
because you just drop them straight into the hub
so that's a great thing too.
And they can arguably be stronger as well
because they don't have a bend.
So, this isn't really a physical problem of the spoke
it's more the fact that you can drop the spoke
into a hub and it's going to be as strong as it can be
because it can only do a certain job in a certain way
it's not subject to the quality control of a hub
or the way it's built to sacrifice the strength of that.
The cons are, you have different straight pull spokes
for different hubs, they're not all the same.
There are some standardized version,
but Mavic have their own slightly thinner ones at the head
they also have some slightly thicker ones
and different brands do that as well.
So, it's just not a standardized item like a J-bend spoke
which you can get literally in any bike shop.
The advantage again of a J-bends is you could buy one
for a 29 inch wheel and you can have it cut down
and re-threaded and it will fit
a 27 1/2 or 26 or anything.
Really convenient if you're doing any sort of traveling
or globe-trotting, to have J-bends for that
sort of reason.
Another con is that they can only be laced
in the orientation that the hub allows.
So, if you've got a straight pull hub
and it's set up for two cross you can only ever
lace your hub wheels up two cross.
You're not going to be able to take advantage
of having a three cross design for example.
It simply will not allow that.
And also, if not tensioned correctly,
this is very rare and this used to happen on older designs,
the head of the spokes can actually become unhooked
which is I think is probably one of your concerns.
But let's not forget that a wheel works
on even tension, it's not pushing, it's a pulling thing
that basically enables a wheel to be strong
and tensioned, so really, they'll be absolutely fine for you
and hopefully you've just seen a little bit of detail,
pros and cons for both styles.
For the record, I think think straight pulls
look way cooler on a bike,
they look so futuristic and purposeful.
But, I think I prefer traditional J-bends
for all of the obvious reason.
So, there we go, there's another weekly
GMBN Tech Clinic in the bag.
If you've got any questions, let us know
in those comments or you can just
email them direct to us.
For a couple more cool videos if you want to learn
how to fix a chain when you're out on the trail in the rain
check this video out that's just down here.
That's fixing a chain three ways there, that's really cool.
And if you want to win some insane Syncros wheels,
super, super ridiculously light ones,
click down here.
All good stuff there.
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