(mechanical grinding)
- Welcome back to another episode of the GCN Tech Clinic
where I solve your bike-related problems
that you either submit using the hashtag on screen
right now on all forms of social media,
or you leave down there in the comments section below.
So if you've got a bike-related problem,
make sure you let me know about it.
So the first question this week
comes in from Steven Reeves who says there's a nice
Shimano Dura-Ace r9000 dual power meter on sale online,
however, it's 180mm crank lengths.
They're kind of putting them off, really,
because he's normally used 175 mil length cranks.
193 centimeters tall and wears a size 50 shoe.
What would he need to consider
before changing crank arm lengths?
Right, then, Steven.
That's a pretty big shoe you've got,
I must say, first of all.
Now, there are a few different theories
and calculations that people do find out there
on the Internet as well as with bike fitters.
But something also worth considering
is that Adam Hansen, a pro rider,
he's a few inches shorter than you
and he uses 180 millimeter cranks.
Now, he has got his own theories around all of that,
but I can't really help without knowing
what sort of rider you are,
and also what bike you're fitted on at the moment
and how it could affect the actual handling of it.
Now, without knowing your leg length,
or the type of riding that you do,
it is very hard to give a definite answer.
But one definite answer I can give
is don't be tempted to buy something because
it's cheap or it appears like a bargain.
Make sure you buy the right thing the first time.
Next question this week comes in from Samuel
who says I'm planning on replacing the bottom bracket
on my bike because it's creaky and doesn't feel smooth.
It's a 68 millimeters by 110.5,
and it's a sealed cartridge unit.
Now, the replacement bottom brackets they're looking at
only come in 110, 113 and 115 mill.
Should they go for the bottom bracket
closest to the original one,
or go for one with a slightly longer spindle?
Right, first up,
sorry to hear about that creaky bottom bracket
and those sealed cartridge bearing ones.
They went on for quite some time, didn't they?
Now, if I were you,
I would go for the 110 millimeter length one.
Because unless your chainrings or cranks
are dangerously close to your chain stays at the moment,
you're actually gonna be bringing them in
just by naught .25 millimeters on each side.
So you are gonna get a little bit
better in terms of power transfer
'cause it's gonna be marginally stiffer, I imagine.
And if you were to go wider, well, in turn,
you could well get extra flex
as well as actually messing around
with the Q factor slightly
and nobody likes that.
And a little final tip here is just to actually
grease up the bottom bracket shell
as well as the cups before you install it
so that many years down the line
you can remove it a lot easier.
Okay, the next question comes in from GauGaut,
and they say hi John, thanks for your videos,
which have always been of great help.
You're welcome.
I was wondering about the best way to clean headset
and bottom bracket bearings.
Should the old, dirty grease be simply wiped away
and some new stuff applied?
Or is it better to spray the bearings with degreaser,
rinse it off with dish liquid
and water then apply new grease?
Thanks in advance.
Absolutely love a bearing question.
Now if those bearings are not rough, are not gritty,
nothing like that, then simply wipe away the old grease
which generally goes quite mucky.
Apply some fresh stuff,
and then put it back into place.
Now, if those bearings are a little bit rough,
you could temporarily save them,
but you are gonna need to replace them in the long run.
So to temporarily save them, you could pop off those seals,
flush out all of the bad grease
and all the muck that's in there,
and then carefully, you want about a third capacity
of greasing inside of that bearing,
and then re-pop the seals on.
Of course, greasing up the bearings before reinserting them
into the component or the frame
and you should be good for probably
about another week to two weeks worth of riding,
but ultimately, if they are feeling bad, get some new ones.
Next question comes in from Aubert,
and Aubert says hi Jon,
is it possible to run a non-round outer chainring,
like a Q-ring, Osymetric, et cetera,
with a round inner chainring?
Does it cause any problem for the shifting or chain drop?
Would it be okay on my TT bike?
Because they barely use the inner chainring.
Right, I had to consult with a good friend
of mine for this one because
he has used that exact same setup
and I've had good reports back for you, Aubert.
And it does, in fact, work okay.
Now, one thing certainly to consider here
with those chainrings, when you're using them,
kind of use your legs almost in a clutch mechanism.
So kind of back off the power a little bit
when you're changing between the two chainrings
so that it does help the shifting of those gears
because sometimes I have found
when I experimented using them
they are a little bit temperamental.
However, it may well have just
been the set up that I was given,
but yeah, just bear that in mind.
Next up is Niklas Eckert who says,
is it possible to fit a 32-tooth cassette
with a mid-compact 52-36 chainset on my bike?
Right then, Niklas, I don't see why not.
Now, it does obviously depend on what rear derailleur
you currently have fitted on the bike,
so if you've got a short cage one,
it's very, very unlikely it's gonna work.
Alternatively, get yourself a medium cage one,
and it probably will work,
but better still, get yourself a derailleur hanger extender.
So that simply drops down
the rear mech by about two centimeters,
and I've used it myself using a short cage rear derailleur
and I even managed to fit a 36-tooth sprocket on there.
So that's a certain solution for you.
Next question this week comes in from Michl Madl.
Hi Jon, I love your videos and find them really helpful.
Thanks.
Ah, you're welcome.
I'm currently running 23mm tires on my wheels.
Do I think 25mm tires would work and be better?
Any problems with aerodynamics?
Right then, Michi.
Thanks for those kind words.
Now I'm pretty sure,
in fact, I'm 100% confident that you can
put 25mm tires onto those wheels.
Now, as for aerodynamic differences,
it's very, very, very unlikely you're
gonna notice anything because by using that
slightly wider tire you can have a slightly lower pressure
and in turn have better comfort,
and basically a better quality of riding.
And in turn, you're gonna be able to ride faster,
because you're gonna be happier,
and you're not gonna be bouncing around such like.
Nearly everybody I know who's gone from
23 to 25mm tires has absolutely loved it
and they've kind of endorsed it in their own way.
The only time where a narrower tire
is really gonna be better is if
you've got a perfectly smooth road
or if you're riding on a velodrome.
So make the change and I am so,
so confident that it's gonna be the one for you.
Next up is a question from Martin who has
a Tiagra compact chainset, a 50-34,
and they spin in the highest gear,
so they wanna go up to a 52 big ring.
And is it possible to just change the 50 to a 52?
And is the difference noticeable,
or should they go to a 53 and higher?
Right then.
It's quite unusual to be spinning out in those gears,
but let's tackle the problem and the dilemma
that you find yourself in here.
So currently you've got a difference of 16 teeth
between the two chainrings,
and you're looking to go into 18,
possibly 19 tooth difference.
So most manufacturers out there,
they will say it's not really possible
or certainly shouldn't be done to get good gear change
between the two rings, however,
there's a company out there called WickWerks
who actually make a pair of chainrings in 34 to 53
and they claim that they shift better
than a standard compact chainset.
So there we are.
Maybe that's an option for you.
So it actually shows it can be done as well.
And I don't reckon you'll be then spinning out
in 53 x 12, because, well, most professionals would never
find themselves in that sort of situation.
Let me know how you get on and which decision you go for.
Next question this week comes in from Caillou who who says
hi John, here's my question.
I run an Ultegra compact chainset with 50-34
and an 11-27 10-speed cassette in the rear.
I noticed when calculating the gear ratios
that two combinations, 50-19 and 34-13
and 50-21 and 34-14 yield almost identical results
in terms of how far the bike's gonna go, basically,
when you turn a revolution of the cranks.
Should I prefer a combination over the other?
At the same cadence, the results of the speed
and power requirement will be the same, right?
Or am I missing something?
Right then, Caillou, very true.
Many bikes in there do tend to
double up on the actual gear ratios.
But as far preferring a certain combination over another,
well, that's quite personal, I guess,
because if you're riding in a small chainring
and you're having to use
a bigger cadence or a higher cadence
you do tend to start bouncing a little bit.
And ultimately your peddling isn't gonna be as efficient.
There is also a bit of a placebo effect, I guess.
Because if you're in the big ring,
you're gonna feel like you're going faster.
But there is also a bit of science
or methodology behind this all because
a big chainring and a big sprocket tend to roll better
because the angle or the shape of the chain
isn't as extreme as it is if you're
in a small chainring and a small sprocket.
The chain there has a lot of
curvature to actually deal with.
So, yeah, I would always tend to go for the big chainring
and the bigger sprocket, but that's just me.
Final question this week comes in from Brian Ritter
who says they have a SRAM 1x Apex system on their bike
and they're having problems where the rear derailleur
won't shift back onto the smaller cogs.
They've changed the housing, adjusted the B screw
and installed a Teflon-coated cable.
The local SRAM rep even changed the routing
under the handlebar tape slightly
and still having issues.
Any ideas?
Right then, the only ones I can think of here are
either one, sprockets on your cassette,
or rear derailleur hanger alignment.
And then really extreme is that the spring
in the rear mech is worn, basically.
Or it's been overstretched,
so it's not springing back into place.
However, those things are quite extreme,
so I don't know the exact answer to your question.
I'm gonna put this one out to the viewers then.
Does any viewer out there know of
the solution to Brian Ritter's problem?
Let us know down there in the comments section.
Right, that is it for this week's GCN Tech Clinic.
But as ever, make sure you leave me
your bike-related problems
down there in the comments section
so I can try and tackle them
to get you riding again quickly.
And also, remember to give it a like, a share,
a thumbs up, share it with a friend of yours
who's got one of these problems
so that they can ride in, well, harmony, I guess.
Now, remember as well to check out
the GCN shop at shop.globalcyclingnetwork.com
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