- Hi, this is ask GMBN Tech, our weekly show
where you get to ask tech related questions
about mountain bikes and we give you, well,
hopefully we give you the answers that you need.
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Right there, it's HELLOTECH@GMBN.COM.
Now first up this week is from Ian Offen.
He says, "Why do hardtail mountain bikes tend
to have a thru axle at the front
but a quick release at the rear.
When it's the rear end that takes more impacts.
I know riders like control of the front end
but every bike I've ever had, the rear axle,
bearings, etc. goes first.
It's the majority of my repairs stroke expenditure."
Okay well firstly let's look at the suspension fork
so the suspension fork really relies on the axle
as part of the structure.
You've got the brace at the top and technically if you look
at the mountain bike suspension fork compared
to a motor bike fork, we're actually inverted.
We call motor bike design inverted
but that's arguably the right way
'cause that was how it was done the first time.
So the motor bike design has twin crowns
and it has the bigger part of the fork at the top,
the smaller part at the bottom and it's clamped together.
But because of the size of the motor bike fork
and materials used in them,
they can't make these clamps industrially sized
to avoid flex whereas if you did that same design
on a mountain bike and some brands have done this,
if you look on screen you can see a Manitou Dorado,
you can also see a Marzocchi Shiver,
and also a nice shiny new single crown fork
called the Intend.
These forks are all fantastic
but they're never gonna be quite as stiff as the other way
which is what we know as the conventional design.
Now way back when everyone was running quick releases,
this was the weak point in the suspension forks,
now you have the brace that helps add a bit of torsion
and stiffness between those two legs
but really it's the axle that does everything
so it's really really important to have that up front.
And now it's universally known as the best way,
even see it as takin' across onto rigid forks
and onto road bikes and gravel bikes now
and the system now effectively
is like an oversized quick release.
It works on the same principle,
it will screw into the actual fork itself
and will have a cam operated lever.
Of course there are some easy options
that just have an Allen key head on.
But out back on the bike you think the bike frame
in particular on a hardtail is the structure,
it's built as a thing, the wheel simply sits in there
and the quick release is there to hold the wheel into it,
it's not there to do anything as such
with the frame rigidity.
It's a little bit different on suspension bikes
because again it can be used for that.
Most suspension bikes these days are warming to the idea
of using or certainly have already been using some sort
of bolt through or a quick release type bolt
through rear end on them.
Now the reason you're getting more problems on the back
of the bike isn't I don't think
because it's got quick release.
I believe it's just because the rear ends
of most bikes take the most amount of abuse.
Now if you ride flat pedals even more abuse out back
but we'll get to that one in another question,
another time.
The whole point I'm saying is you're body weight is based
around the back of the bike when you're descending
and going flat out, the suspension fork out front takes
that shock but the shock still has to go somewhere
and it's gonna hit the back end,
majority of weight is on the back of the bike
and then of course it's what the transmission does.
All of that torque pulling and twisting through everything
so you if think if you do have a bolt through on the back,
you could arguably save yourself some maintenance
that might occur from the twisting of parts of the frame,
they're gonna prematurely wear bearings,
but really it's just the whole thing is gonna take that sort
of abuse and really that's why you're getting that.
Now regular maintenance is obviously gonna help here.
If you're riding with any bearings
that are slightly knocking, slightly loose,
they will certainly get substantially worse by the end
of the ride because all of that driving force,
your body weight, the torque from the pedaling,
all of that stuff going through
that back end is just gonna mash those bearings
to pulp so just keep an eye on your bearings,
make sure you do some overhauls
in fact I think I should probably do a hub overhaul video
on GMBN Tech soon just to make sure everyone's topped up
on that because it's an important one to do and something
that people overlook quite frequently.
All right next up is from Mudkip Man.
And I've just got the new nukeproof scouts
with the brand X Ascend Dropper Post
and it came feeling pretty gritty and had to be pulled apart
by hand to the upper position.
The stanchion was not scratched thankfully.
My Dad recommended using some vaseline under the seal
and now it works magic but is it harmful to the dropper
or any other suspension components
and what might have been wrong with my dropper post
in the first place?
More importantly, can I just use vaseline
as suspension grease?
Well okay first up your Dad did absolutely right thing
in taking the seal back and putting some grease under there
in the first place even if it was vaseline
because you think of the manufacturing process,
thousands and thousands of components like that go
through at some point the grease pot is gonna run out
so it just sounds that your particular seat post
has been unlucky.
I've ridden those before,
and the ones I've ridden have been absolutely fine
so I'm convinced you just had a bit of an anomaly
but thankfully it wasn't scratched and it sounds
like it's working great now.
Just make sure you keep on toppin' up
because just the nature of a suspension fork going up
and down when your dropper post goes up and down.
It can ingest mud and muck under that seal
which of course dries out the grease that's under there
and it can lead to scratches on that stanchion post
or a stanchion jeep so yeah keep doing exactly that
and it'll stay working.
Okay, so vaseline as a suspension grease, right,
so what do we know about vaseline?
Well the first thing a lot of us will have learned
in school is vaseline shouldn't be put near anything rubber.
Use your imagination for that one
however it's a little bit different in terms
of suspension components because vaseline isn't that harmful
to the types of o-rings and things that are used
within suspension components
and in fact some dedicated suspension manufactories
that make their own greases, there's a lot out there,
there's Buzzy's, there's Slickoleum, there's Rockshox Butter
or SRAM Butter that's available.
There's loads of options on the market and a lot
of those do have petroleum in them so I looked into this
in a bit more detail just to confirm my suspicions
and you guessed it they pretty much all have petroleum
of some kind in 'em.
Now I was looking into this
because I noticed Slickoleum make greases
for other manufactories but they don't specify
what ingredients are in their actual grease.
Now you look on the safety data sheet,
you'll see that their concoction
if you wanna call it that is a trade secret.
They don't wanna announce what's in it
so I looked into Buzzy's grease which we know is made
by Slickoleum and you guessed it on their safety data sheet,
it actually gives away that there is a petroleum basis
to their grease.
Now this is the same with SRAM Butter which is made
by Maxima Lubricants, again it's a petroleum based grease
so all of them,
all suspension based greases out there really are designed
for use on those sort of seals against bushings, o-rings,
all that sort of stuff and they're perfectly safe
but there are a lot of differences between vaseline
and dedicated suspension greases.
Now vaseline of course is gonna be far thinner
and it's actually gonna just disintegrate a lot quicker
than a dedicated grease.
The dedicated grease is designed to stay there,
designed for that job
and yes okay they're a bit more expensive
but that's what you're payin' for, a dedicated product.
At the same time, smart move on your Dad's part
for knowing that the vaseline would be fine there,
just make sure if you're gonna continue using that,
use more of it more regularly because it will dry up in time
and you wanna monitor that it doesn't damage any
of your suspension components or dropper post components.
Next one's for the tall people.
So this one from Robert Pike.
Doddy, a tip for tall riders please.
I'm just over six foot two, got long legs
and I ride an extra large size 29er hardtail.
My seat is set perfectly height wise
but it's really high compared to my bars.
I want to shorten my stock stem which is really long
and raise my handlebar height
to take some weight off my hands and relieve some
of that pain on my hands and wrists.
Can you tell me again what size stem you use
as I've got pretty straight handlebars and tell me
about the rise you have on your handlebars.
Fingers crossed it will make sense.
So on my Mega which is a size extra large,
I'm just over six (muffled) so we're very similar in height.
It came with a 50 mil stem
but I actually found it a little too long for me
'cause I've got long arms and a bit of a shorter trunk
hence I always go for a shorter stem and a wider bar.
That suits me, it might not suit you, it does vary.
So I've got a 38 millimeter rise bar
and a 35 millimeter stem and on that particular bike
'cause it's exceptionally long I've got I think three
or four spaces under the stem.
Now normally I wouldn't have a front end that high
like on my new Canyon Neuron,
the front end's quite a lot lower.
Bike's a bit shorter so I like to have bit more weight
onto the front tire, if I'm loading it
whereas on the longer Mega I feel like I need to be
in the middle of the bike a bit more
'cause it's such a long bike.
Now you need to experiment with this stuff
and I would say to you one by one
with the stem so let's say you said a long stem,
you haven't said how long, if it's 80 millimeters,
I probably wouldn't go any shorter than 60
because you're changing the extremes of a bike here
and by if you change nothing else, you just change one
of these things like the length of the stem,
it's gonna bring you bolt upright.
You'll feel like you have to put your saddle back
on the rail so then when you're climbing,
you'll have too much weight on the back end of the bike
and not enough on the front so it'll wander around
but you could for example have a shorter stem so go for 60
and then a wider bar so although your position comes back,
your shoulders'll come forwards again
as your handlebars come out slightly.
They're all directly related.
Now make sure you do play around with these things
and if possible ask a friend if they've got I'm sure
between your riding group someone's got
like a slightly longer stem they might not be using anymore.
You could just try the size
or failing that someone will be able to help you
and try a few options on stem's basis for height.
Also bear in mind the higher your stem goes effectively,
the shorter your top tube gets
because you're bringing it back.
If you've got a bolt that goes slack (muffled)
will get even shorter even quicker.
Of course you have to go quite a way for it
to make a massive difference but we're talking five,
10 millimeters, yeah, it does make a difference
in the grand scheme of things.
The best thing to do is experiment with it
and in fact you've given me an idea of,
I'm gonna make a GMBN Tech video on the effects
that these sort of things make.
I'm just gonna accentuate it out on the trail
but in the meantime good luck and I hope you find
what sort of setup suits you.
Ooh, a tricky one from Justin Was In Buffalo.
Doddy, got a good question.
I've got a 2018 Canyon Strive and I have the Rochshox
Monarch Plus R on it but I want
to install a Fox DPX2 upgrade.
Do I need to install it upside down?
Love the show by the way.
Been here to beginning and really appreciate your input.
Thanks, Justin, appreciate that.
I actually had to look at this just to check
because it's very unusual for a bike owner
to have the shock upside down when it's clearly a lot
of room in the frame, there's no obvious reason
and I think you do have to run this upside down
because of the fact that the top of the DPX2 shock
if you're to run it the correct way up
with the piggy back and the shock and adjusters
at the top there essentially the shape shifter system
where the top shock now is I think it fouls it very slightly
when the whole system moves.
I run the compression where the shape shifter brings it back
in and under compression.
I don't think it's actually compatible that way
which is why Canyon speck it upside down.
A little bit annoying granted because the fact
that you're access to the climb switch
if that particular model has a climb switch
on it means it's further down but the thing
that you all probably know that I've discovered is
on the Strive when you actually put it
in uphill mode actually the climb switch is less relevant
because the position you are in on the bike,
it's up to you though.
DPX2 is a very fine shock, it just does mean you'll need
to run upside down but you could run it with a lockout
and have the lockout remote on the bars.
That would mean having a lot of remotes on your bars though
which would be unfortunate.
All right next one is a shock related question
from Aaron Ashmole.
Hi, Doddy, I've got a Fox float CTD shock.
Can I run it in trail mode on less bumpy descents
or will it still damage it?
No, it'll be absolutely fine so the CTD stands
for Climb Trail and Descent so Trail basically means
you can use it when you're out on the trail.
The idea from Fox was you use it
on the more undulating terrain and you have it
in descend first flat out bits where there's no sort
of charge, you gonna pedal, it's all about descending.
The shock's gonna be completely open
and then you can flick it onto the climb mode
when you're goin' back up that climb to get to the top
and basically your bike's just gonna react a lot less.
Now you're not gonna damage anything by running in this
so don't worry about that.
I'm just gonna explain to you a little bit
about how the system works so you've got the dial
on the top here with a lever, a three position lever.
This one actually doesn't have three positions
because the one's been cut away.
This drives the cam at the top, then there's a little pin
like a shaft that goes all the way down here
and you can just about see here some shims,
basically with this you have three different positions
allowing different amounts of oil to flow through
with different amounts of resistance to go through
that circuit that's built on the inside here.
Now by closin' that,
you're effectively stopping the oil come through there
which means it's effectively locked out.
However in the big impact, the shims will simply move
and allow the oil to pass.
You're not gonna damage anything.
In time if you were to run it let's say for example
in a fully locked out mode and you ran it
in that all the time and you're goin' out,
you're jumpin' off flights of stairs and doin' that sort
of stuff, you can basically get an oil leak on the inside.
You can damage the oil seals
and you can probably just bend those shims a little bit
just through misuse but it's no biggie
because the shims don't cost a lot
and at the end of the day, you'll be lookin' at service.
It's nothin' crazy so don't worry about it,
continue using your lockout lever
for exactly what you're usin' it for.
You'll not damage it.
And last one is from Harvey Lakey.
I've got 2018 specialized pitch comp 27.5 hardtail.
The drivetrain is Shimano Acera rear derailleur and altus
from derailleur.
It's a three by nine cassette.
Now I've been wondering is it worth converting it
to one by 10, one by 11, or one by 12
as I'm jealous of my Dad, his mates and friends.
The area I ride is not very flat and hills are quite common
so I need a really big and a really little gear.
Yeah okay well firstly try not to be jealous
of anyone else's bikes and their gear,
just love your own bike, get to know it,
and get ridin' it basically.
You will toughen to it, you'll have to ride anything
on it regardless of however many
or however few gears you have.
That said, if you wanna upgrade, yes,
of course you can do this but it will cost you money
to do it so my recommendation firstly is wear out
that transmission that's oilin' your bike.
If you're to take it off now and sell it,
you wouldn't get that much money for it so you may
as well use it to the best so ride it until it's worn out.
I'd recommend you get yourself a chain checker
because then you can monitor the wear on it
and then when it's finally worn out,
then hopefully at that point,
you'll have saved up enough money
to get yourself a one bike transmission.
Now I don't think you need to go as hard as goin'
for a one by 12 and it will cost you more by doin' that.
I reckon you'd be quite fine goin' for a one by 11
or a one by 10.
It's no problem, you'll need a cassette.
You might possibly say got a three by nine
as you say could go one by 10 on there on yours no problem.
You might need a different rear hub
if you wanna go any bigger
because the free hub body itself is slightly wider.
That's when it starts costing money
so back to my original point is start saving now
and just get on with your riding for the time being.
Don't worry too much about them.
In fact, just get really thin, perhaps you'll destroy 'em
on those climbs and in doing so,
you're gonna wear out your transmission anyway
which means hopefully at that point,
you'll have enough money, you can upgrade your wheels
at the same time get yourself a new chain, a new cassette,
a rear derailleur and then you can just get one bike
on your existing cranks at the front.
Nice and simple.
And there we go, there's another weekly ask GMBN Tech
in the back.
For any questions, let us know in those comments
or hit us up on email at HELLOTECH@GMBN.COM.
And for a couple more videos,
if you wanna see that brand new 29er Whyte (muffled)
downhill bike, click right down there
and if you wanna learn a bit more about body position,
particularly helpful if you're super tall or super short
and you're a mountain biker, click down here.
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