- Welcome to Ask GMBN Tech this is our weekly Q&A show.
Get your questions in, in the comments below.
Use the hashtag #AskGMBNTech or alternatively,
you can email your questions in
to the email address right there.
First up this week is from James Doyle.
"Hi Doddy, can you explain rear shock sizing
"and can you install a larger travel shock
"on a bike?"
Yeah, there's quite a lot to explain here really.
Well first, I'll look at the shell of a shock.
There's two real measurements on a shock.
There's an auto wide length of the shock.
And then there's the shaft stroke travel.
So you'll often hear of a shock being referred
to as a 200 eye to eye and a 57 stroke.
So the eye to eye refers quite simply by the measurement
between two eyelets, end to end on the shock.
And that refers to if its actually going to fit
in a specified space on a certain type of suspension bike.
The next measurement refers to the actual shaft travel
of that shock and then within those two measurements
that are different variations.
Now depending on the layout of a frame,
you're going to have a certain amount of space
in which you can put that shock and obviously
a certain amount of travel the shock can have
and that directly correlates to my rear wheel travel.
So this is how frame designers decide how they want the bike
to ride and how they wanted to actually feel,
out on the trail.
So often heard hear the term leverage ratio applied
when bikes and manufactures are talking about
the back end and bikes.
So for example, if amount of bikes,
got two to one leverage ratio
for every millimeter that the shock operates,
the real wheel will move twice that.
That is a two to one ratio nice and simple.
Now with that in mind by manufacturers spec,
a variety of different shocks to give their bikes,
different fields and of course it all comes down
to the suspension design of the bike as well.
So there's lots to factor in that.
Now, just for example in ideal world are manufactured
one of us is shock with the most amount of stroke
possible on it because it simply allows for more tuning
and it's going to actually cope with what the,
what is happening in the rear wheel a lot more.
Just for example, if you had a bike that had 200 millimeters
real travels like a downer bike,
if had a little little shocking
and I only had 40 millimeters of stroke,
that shock is going to be working incredibly hard
the oil in there is going to heat up
and as a result of that,
the damping is going to be quite erratic,
it's going to be all over the place.
Whereas if it had a sharp travel of 57 millimeters
or even longer than that,
the longer the shaft is the more oil that's in there,
the better that the shock is going to cope with it.
It's all about finding the best compromise.
Now shock sizing itself.
There's what we now call the metric system
which is pretty much common place on most bikes now
and certainly all bikes going forward.
Once upon a time,
shocks would come in a whole bunch of different variety.
I think it's about nine different options
something like that.
But the point is that they were all unusual lengths
and didn't really correspond to the shaft travel.
It was a bit all over the place.
So the metric system basically what it does
is simplifies this and takes it down to about six options
that's far less options there and within those options
they're actually offers a chance for manufacturers
to spec and more consistent shock
that offers more to the consumer
and obviously to manufacture bike,
to make sure it rides appropriately.
Effectively, It gives the manufacturers bit more freedom
because they do know that whatever shock length they spec
in metric, in theory,
it should perform exactly as well
as any of the other shock sizes.
It's just that picking the size that correctly fits
the bike design have.
As for just checking in a shockwave
longer stroke length into your bike.
Yeah, you can technically do that.
But there's a few things to bear in mind now.
Firstly, is it extends the back end of your bike,
there's a good chance that shock could hit your seat tube
or depending on the design of your bike.
Part of frame could contact that's not supposed to contact
you don't need me to say
that's not a very good thing to happen.
Then of course with having more travel
you might find the wheel strikes the frame your saddle
or even parts of the frame strike each other
there would have been a nominal amount of clearance
to cope with previously.
So if you do want to do that,
just take that into consideration.
Now also if your bike does cope with that
and does allow it longer shocking to get that more travel
it's not going to hamper it
you might find that it twisted geometry
and you're not gonna like the wet right
because it could may have been bracket to high
which in tournaments deepen your head angle
would steepen your see angle.
There is various different effects of doing this.
My recommendation,
stick with the correct length shop for your bike.
Okay, next up. Forgive me if I can't pronounce this.
Bartlomiei Kazmierczak.
I hope that's right or even close to it would be good.
Hello Dolly. Is it worth upgrading aluminum handlebars
and supposed to carbon on an XC hardtail bike.
I am worried about durability when riding in the mountains.
Yes and no you're going to get
not that much more performance.
But for the same post,
there won't really be any performance upgrades.
You might lose a little bit of weight.
But the regards of durability
the hourly post is definitely better.
carbon bar. Again, you might lose some weight.
But actually there are some performance benefits
to running a carbon bar and that's comfort,
lightweight carbon handlebars do absorbs on that buzz.
You get out on the trail.
But of course, if you're crashing
or there's any chances your bikes is going to be
grinding against any rock or anything about that,
then there's a Chartist can get damaged easier,
certainly than aluminum.
Perhaps I would look at doing some upgrades in other areas
of your bike instead using that same money.
All right next to geometry related one,
from the imaginatively named Septem Roptem.
Can you put 27 and a half inch on a 29?
Yeah of course you can.
it's definitely going to have some adverse effects though.
So first up your bottom bracket height.
So on a 29 inch wheel bike,
obviously your bond brackets can be high off the deck.
So by putting 27 half inch wheels In it,
it's going to be slammed
so you're crying so you'll be so close to the ground,
you can be hitting them all the time.
So not good from that respect.
Next up is you're going to have some steering problems.
So there's two things you'll often hear talked about
one of those is offset and the other one is trail.
In fact you'll hear trail referred to less.
So the offset is the distance your fork axle
is based in front of that steering access.
So imagine drawing a line all the way through your head
all the way down to the to the axle,
you'll find quite often the axle is stepped forward,
that is your offset and you can get different offsets
on different forks
and that tends to happen
by getting a different crown steer unit assess
where the offset actually happens,
as opposed to happening at the actual bottom
of The fork there.
Now there's also measurement called trail.
Now trail is a distance between the tire contact patch
on the ground and that virtual line
going all the way through your head tube
where it meets the ground there.
One of the problems you have with 29 is we'll biases
as your actual get high off the ground,
the trail measurement basically increases
so what they used to do is change the offset
in order to bring it back again.
So by putting smaller wheels on your bike
your hardly is going to go all over the shop.
next up your chain stay length is going to feel pretty wacky
by putting a smaller wheel in there
defect is basically by having a bigger wheel in there
It makes the chain feel shorter
by putting a smaller wheel and it makes you feel longer.
The longer chain stay is
the more weight you have to pull back on the bars
in order to lift a finger off the ground.
As a benefit though,
it does bring body weight further in the middle
of the two axles of the bike.
I personally quite like a long chain state,
but it's definitely going to change the way your bike feels.
Now back in 2014.
There's a couple of writers at the Meg avalanche
both writing on the commerce ad team,
one of them is Nico quaint
and the other was Pierre Charles George.
Now they were both running 650b commerce
our bikes at the time,
but the mud that year was so bad
that they both swap to 26 inch wheels
in order to get through the frame
but you've also got bear in mind,
the difference between 26 inch wheels 650 B is a lot closer
than 650 B to 29 inch wheels.
So I don't think you want to be messing around with that
when your bike but by all means
put in some of your friends wheels
and have little play around.
Next steps from SB.
Is it bad practice to be sitting on the seat
when the dropper is fully down?
sometimes I like peddling around with the seat down
maybe when session features for an hour or so
but I'm concerned that it might damage the dropper
since It was designed for dissent
when you're not when you're supposed to be stood up.
No it's absolutely fine basically drop a post.
what they do is they move oil from one chamber into another
and I have air basically that when you Open,
the portal allows all to flow back in
and the air basically helps extent
so pretty simple system of course there are intricate parts
on the inside but when it's lower and slam down
You are absolutely fine to use it in that position
in fact you are ok to use it in other positions
as well within there don't feel confined to using it fully
extended all the time.
So job done it's a drop the post enjoy being dropped
Next steps from Mick gearing.
Hey Doddy thanks to you and the team
for providing us with great content,
I love tuning in and learning new things every week.
Thank you. Thanks Mick. I really appreciate that.
And my question is about volume spaces in forks
and rear suspension cans.
I'm on a slightly heavier side
but not too out of shape body wise thanks to riding
frankly again at the moment
I find myself on the upper limits of
the fox 36 performance elite
and a DPX2 float evol pressure charts for my bike.
will adding volume spaces to my suspension
helping reducing?
How much psi is needed for my targeted sag range
between 25 and 30%
or a primary designed
for getting the suspensions to ramp up quicker
Do I need to look into suspension products
that cater for higher psi requirements
my bike is a 2018 giant rain advanced one.
I'm riding as much as possible
to continue reducing my weight to come down
in required psi for Fox gear on my bike.
Okay so there's there's a lot to this.
So first let's look at the air pressure recommendations
for your fox and shocks.
So looking on the fox site,
they say evolve equipped DPS and DPS two shocks,
they've got maximum pressure of 350 psi.
So that's quite significant amount of pressure
people need shock
but something that you really need to take into account this
is the amount damping that you're putting on that as well.
So with more pressure put in a shock
you think is stored energy you really need to control that
as much as possible.
That can have an effect on how the bike feels
even if it is slightly over the sect.
now also take into,
account now this is foxes recommendation here
that the pressure measure in ambient temperature
of 70 to 75 degrees Fahrenheit
normal operating temperature range of Fox products
is 20 to 140 degrees Fahrenheit.
now Fox I've got a pretty helpful way of checking
the maximum volume spaces which will definitely help
with your ride because they do of course affect the end
of the stroke and how it ramps up
but they do have a slight overall feel
and you do tend to have to run slightly less pressure
with the I'm talking maybe like five psi
it can be enough to make a difference
so if I should definitely try a ramp them up
with as many volumes basis as you can have a product.
So I'm just throwing you a link on the screen
now is a link to the right folks website
and you'll fall your forks and your shocks
will have a little four digit ID code on them.
So if you put that into the search product information,
bet it will bring up all the information about your
particular focus shock.
I'm guessing you probably know this
because you had referred to the pressure charts
so it's the next step up from that.
But also the other things to take into account
the suspension design on bikes.
Now your bike is a linkage bike.
So for example, a single pivot bio code orange,
you're gonna need to be slightly lighter rider
in order to use out over a linkage bike
just because the amount of pressure
you end up using in those shocks.
I don't quite know what the max is on yours.
But the truth is,
is something you're going to need to play with yourself
to get exactly right on there.
I'm almost certain whatever your weight
you can get the bike chained in to feel just right for you,
but it might require a little phone call for some tips
to a dedicated suspension tuner,
someone like videFoxUK or TF chewed or sprung over
enforce a thing and there are a number of those in Europe,
in Asia in America wherever your base as well
I hope you can get that figured out.
Sorry. It's a bit of a vague answer on air
like the volume spaces will definitely make a difference.
But its Definitely something you can need to play with
to see how they feel.
She might also not like the way that
they change the characteristics of your body.
And then we go there's another Ask GMBN tech in the back.
We've got any questions add them in the comments below,
it's going to comments at them and in below as well.
Please don't forget to subscribe to GNBN tech
and tell everyone about us.
And we're going to be launching some really,
really cool new content soon on the channel.
So keep your eyes open for that
and don't forget to give us a thumbs up
and if you want another great GNBn tech related video
right down there.