- Right, so I'm back again to answer
your technical problems, questions,
or queries here in the GCN Tech Clinic.
- Konstantin wants to know, "Brake pads.
"I know that carbon rims can wear out
"the non-carbon specific brake pads fast,
"but would it work the other way around?
"Is it safe to train on alloy wheels
"with carbon specific brake pads?"
Right, let's just clarify this for everyone out there.
Brake pads do come in different compounds,
as well as for rim type, also weather types, too.
But let's stick with those carbon specific pads.
So, they work excellent on carbon rims,
because, generally, they've got harder compounds,
so they work better, because generally
you're gonna generate more heat with a carbon rim.
One thing to consider is, if you start to use them on an
alloy rim, you're not gonna get as good braking.
Plus, when you're braking, you're actually gonna pick up
tiny little shards of aluminum into those pads.
Then, if you go back to using your carbon wheels,
those tiny little aluminum shards
can start wearing away at your brake surface.
You might not notice it immediately,
but it will happen over time, so basically
for the small cost of a new set of brake pads,
I would really just use some special pads for the job.
Here's a question from Rob Jones, who asks, "Hi John.
"Currently, I have 52 to 36 with an 11-28 cassette.
"I've got sportives coming up with some steep climbs,
"done them before on a full compact 50 to 34."
Could he fit a 34 front ring instead of the 36,
or is it better to change the cassette?
And he's got Di2.
The good news is, Rob, is that
I've tried this out in the workshop earlier on,
so you can thank me in the comments.
In seriousness, yes you can do it,
so you can have a 52 or a 50 down to a 34.
The shifting, it's not gonna be brilliant,
to be perfectly honest with you, but it is possible
and especially, as like you say,
you've got a Di2 front derailleur on there.
Years ago, when I used to play around sometimes trying
to fit some of those oval tile type chain rings
I was once given.
I ended up clamping and crushing
so many front derailleur cables through playing
around and just moving the front neck up and down,
trying to get it spot on.
In the end, I gave up, but good news is you've got
that Di2 mech, so you can play around, moving up and down
that front mech, to get the perfect,
or as close to perfect shifting as possible.
One thing though to consider, is if you are using
the small chain ring, and one of the smallest sprockets
in the back, so an 11 or a 12,
the chain may be a little bit long.
So, you don't really want that because it's gonna rub,
and it's not really gonna be giving
you optimal performance anyway,
so avoid that combination of gearing.
OK, next up is a question from Toasty Bear, "With regards
"to the Di2 10/11 speed shifter compatibility question,
"I can understand that you would need a new derailleur to go
"to 11 speed, probably a longer cage,
"but the shifters are effectively just buttons,
"and if they have no programming in,
"does that not mean you can just get a new rear mech,
"but can you keep the levers?"
Totally correct, other than on the old Shimano 7970,
I think it was, group set.
That was the first edition of Dura-Ace Di2.
That used a five wire signal, so that
had five little cables inside of that one big cable.
Everything else since has been using a different system,
so it's totally compatible with one another,
and yet you're dead right there.
I at home actually use 11 speed 9150 Dura-Ace Di2
rear derailleur, and that's paired up
to some Ultegra 6770 10 speed shifters,
and it works absolutely fine.
So yeah, you can mix and match.
There are some compatibility issues
with 11 speed rear derailleurs
and 10 speed front, they don't work.
So, if you are gonna start changing things around,
just bear in mind that you will end up basically having
to go to 11 speed front derailleur as well.
Next up is Chris Poyser, "Hi guys, great show as always.
"When buying a new stem for a winter stroke gravel bike,
"how do I work out what degree of drop to get
"to replicate the position on my summer bike?"
Hi Chris, that's a really great question, because generally
your winter bike, or your gravel bike, is going to have
a slightly more relaxed position than that summer bike,
which has probably got an aggressive race position.
So, what you're gonna do, while I'm not
a trigonometry genius, I'm not a genius at all in fact,
but there is a web site which I've used
in the past to actually help with stem angles
and also lengths to provide that reach.
So, the link to it is on screen right now
and also in the description down below,
so have a little look around that
and a little play around, and you should be able
to try and replicate that position.
So next up we've got a question from Nooksak who asks,
"Will using a new chain on an old worn cassette
ruin the chain?"
They want to set up an old wheel as a trainer wheel,
but don't want to ruin their chain.
That's a good idea, actually, to have a different wheel
for your trainer, that way you can actually use
one of those special turbo trainer tires on there.
In the past, I actually bought kind of a trekking rim or
a hybrid type rim, so it's a little bit wider to fit
that tire on, because sometimes they
can be a bit of a pain to get on.
Now, basically yes, if you use a new chain
on an old cassette, it's not gonna work well,
and it is gonna wear out that chain prematurely.
So, what I'd advise basically, is to get yourself
a low-end cassette from the same manufacturer,
so you just use that one on that indoor bike.
So, you're gonna keep those crisp gear shifts,
and basically it doesn't matter
that it's a lower end component
because you're not gonna be using it outdoors,
so there's nothing to be dragging up a hill.
Right next up, Kristinn wants to know, "Could I fit
"Shimano 105 brakes with Sora shifters?
"Or is there actually a difference
"in the pull in the lever?"
That's an interesting one, so some manufacturers,
they use a different amount of pull than the other ones.
In fact, they all do, otherwise
everyone could just mix and match.
So, in essence your Shimano levers will work
with a different Shimano caliper.
Now, they may well pull a little bit different
on the amount of cables actually coming through
the outer cable and to the caliper itself,
but it's not gonna be totally incompatible
and the difference is gonna be pretty small.
So, by and large, it's good to go.
What you don't want to do though,
is start mixing SHRM calipers with Shimano levers,
or Campagnolo calipers with SHRM levers and vice versa.
All those things, it's not gonna give you great braking.
So, try and stick to just that one manufacturer,
and you'll be okay.
Another tire question, I get plagued
with tire questions for some reason.
Now Humberto Leandro wants to know, "When the pros have a
"puncture on their tubular tires,
"are they thrown away after one puncture,
"or is it possible to fix and use them again?"
Right, it's an interesting one.
Generally, they just throw them away.
The reason being is that the sponsor provides enough
so that they can just keep using new ones.
It's not particularly good for the environment, possibly,
but I guess that the team are just thinking
about race wins and results.
Now, it is possible to just patch them up,
and I reckon in years gone by, the team would get them
and then patch them up and then give them to a rider,
and they could use them in training.
However, these days most pros don't train on tubular tires,
because clincher tires have come on so much.
Now, like I just said, it is possible to repair them.
It's not particularly easy or time-effective though,
because you have to peel back the base tape
of the tubular tire, unpick the stitching of the carcass
of the tire, repair the inner tube,
sew it all back together, and then relay that base tape.
Not the sort of thing you really want to do
at the side of the road, I'm sure you agree.
Asy Threlfall wants to know, "Hi Jon.
"Really a big fan of the show."
That's kind of you.
"I was wondering if there are any pros or cons
"to multi shifting with Di2, thanks."
Hi Asy, well I'm a big fan of Shimano's Di2,
right back since I saw prototypes of it in 2007,
and the Di2 multi shift function, basically
that means that you can press one of the shift buttons,
and in doing so, have multiple gear shifts at once.
Now I can't really actually think of
any massive pros for it, because it's not often
you're gonna to want to change
so many gears all at one time.
The only sort of instance I could think about it would be
if you were literally riding on a roller coaster,
so down and then up really, really steep,
and then suddenly down really, really steep,
so to go all the way back into a higher gear.
So, it's not really any pros out there for it.
Cons, I can think of a couple.
One would be that if you leave your finger too long
on the button, you could shift more gears
than what you wanted, so leaving you
in not the ideal gear at the time,
but you know it's easy enough to try around,
so plug your bike into the YouTube software
and have a play around.
If you don't like it, you can just
go back to the standard shifting.
OK next up, Hamish McDonald, he's got some new wheels,
and basically rode them for the first time in heavy rain,
and noticed they were holding water.
"Is it common, is there anything to be concerned about?"
I'll tell you what, Hamish, those new wheels
of yours getting treated to heavy rain
on their first outing, that's not very kind of you,
but however, most deep section wheels,
they do tend to gather a little bit of water in them.
It does disappear, though, I don't know where.
You could put the bike on top of some newspaper
to actually, you know, put your mind at rest
to make sure that the water does leave.
Some rims do actually have little drainage holes,
so have a look around and you may find them.
Now, if you've got clincher tires
and you're still really concerned about getting
that water out, just take off the tires,
remove the rim tape, and pour it out.
Or you could put the bike near a radiator,
that could absorb it.
Garry Street wants to know, "Jon, please help.
"I have a 2017 specialized Roubaix
"with a slipping seat post."
He's removed it, cleaned it, and reapplied
the grip compound without success.
He doesn't want to over torque the bolts,
as this is the Roubaix frame where the seat clamp
is mounted lower to give more compliance.
"Any ideas?"
All right, first up, great that you're using both
that grip compound, as well as a torque wrench,
because quite a few people out there don't,
and I can't emphasize how important it is to do that.
Now, if possible, try and actually measure
with some calipers, the exact diameter of both
the seat post, as well as the frame.
They do go in 0.2 millimeter increments,
and it wouldn't be the first time that I've known someone
to have the wrong size seat post in their frame,
and 0.2 millimeters can actually make a huge difference
in their interface, so actually check that out.
Something else you could try, is a bit of a hack,
or is it a botch, seen it done in the past before,
even on a professional's bike,
was a bit of aluminum drinks can.
They carefully cut it, and they wrapped it around
the seat post, put it in, did up
the seat clamp bolt, everything was good.
Bit of a hack, bit of a botch.
Final result, take it down to your local shop,
and get them to check it out, as there possibly could
be something actually with the frame
that's causing this issue.
Final question this week is from Max Grass, who asks,
"Do pros use sealant in their tubular tires?"
And also, he wants to know, "Are there any pros using
"a tubeless setup, or is it all tubular?"
Right, okay so just to recap to everyone,
you can actually put a sealant into an inner tube,
a tire, or a tubular tire, and the idea behind that is
if you do puncture, this sealant actually forms a seal
in the hole, so you're not gonna lose
any tire pressure, or a very small amount.
As for pros using it, not as far as I'm aware.
The reason being, they're gonna start
adding rolling resistance to a wheel
by adding in that extra weight,
when they don't really need it because generally,
they have a team car pretty close by
they can just radio to and get a spare wheel pretty quick.
Now, a race where it could be very, very useful
is Paris-Roubaix, so in that race, you don't really have
a team car that close to you a lot of the time,
because the race tends to get split over quite
a large space of time because of its terrain.
So, that can be an ideal race, actually where a rider
could use that in their tubular tire.
As for riders actually using tubular setups,
not as far as I'm aware.
I think a team did use them a few years back.
I think there were some Hutchinson tires, not sure,
but I will keep my eyes peeled
and I will let you know if I see any.
That is it, we're here at the end of the show.
Now, do remember to leave your technical questions,
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