[intro] Speaker: Welcome to another GCN Tech Clinic
where we aim to answer your bike and tech-related questions. You can submit your questions using
the hashtag #AskGCNTech down in the comments below on this video and on other videos as well.
We'll do our best to answer them. Without further ado, let's crack into this week's first question,
which comes from Zach Benjamin. Well, he's actually asked two questions. First, why don't
disc brake rotors have a bigger diameter as they will be more efficient if they did due to greater
angular moment? Question two, what is the only country in the world that tends in the letter, H?
Well, to answer your second question first, I happen to know that it's Bangladesh because I'm
a cricket fan. Bangladesh are one of the only Test-playing nations.
Yes, nice try to catch me out on that one, but I also, if I didn't know the answer to that, have
the power of Google at my fingertips. In terms of your disc brake rotor question, they do in fact
come in different sizes. On mountain bikes, you will see much, much bigger rotors. Some downhill
mountain bikes have 220-millimeter rotors, whereas the biggest you get on road bikes at the moment
is usually 160s and that's usually on the front. The UCI standard in their spare wheels that they
have on the back of service cars is now 160 front, 140 rear. The simple reason why we don't
put bigger rotors on road bikes is because they're not required. They're a surplus to requirements.
The 160 rotor provides more than enough braking power and contact patch on the rotor
for what you will encounter in road situations for most weight road riders. You just simply don't
need it. It's very difficult to actually cook a disc brake rotor on a road bike.
It is something I'd like to do in a future video, where we just try and drag the brakes
down a really steep climb. Load up the rider with loads of weight and see if we can actually just
destroy the disc brake. Watch this space, but we'll try to do that in the future.
Next question is from Ahif Zaheed. He says, "If I'm straightening a bent derailleur hanger, can it
damage the carbon bike frame?" Well, I would say, providing you do this with the wheel in place,
you should have no problem. Normally, the way you do it is you use the derailleur straightening tool
and you remove your rear mech and screw that into where the rear mech goes on the hanger.
Then there's a big lever arm that you can use it to bend it into position. Then you do this
against the wheel. You're trying to get the hanger straight against the wheel the whole way around.
However, one thing to be aware of when straightening a bent hanger is that,
once a hanger has been badly bent and then bent back into shape, it's usually not quite as strong
as a fresh one that's never been bent. It can be a bit structurally weak and they're more prone to
bending again in the future. The best advice and we say this all the time, is always have a spare
derailleur hanger, just at home in your workshop. If you ever travel with your bike, take it as
well, because it can be hard to source one at short notice. Always just have a
spare and you should be fine. You shouldn't damage your frame when you straighten it.
Next, we have a question from Joe, who says, "How often should you get your wheels trued?"
Truing a wheel, [chuckles] I think it's that thing of, "Well, when it needs to be." If your
wheel has become bent and is then rubbing against your brake pads as it goes round,
or rubbing against your frame, yes, you need to get it trued. Some wheels can be very,
very slightly out of true, just a touch. At which point you might not need to get it trued,
it might not be causing issues when you ride and it should be all right. In my experience, wheel
truing is something that happens very rarely now. Most modern wheels are very strong and don't often
buckle and don't often require truing. It was something I found myself having to do a lot more
maybe 8, 10 years ago. Now, it's something that doesn't really happen too often. Of course,
if you're a heavier rider, then you might find that you're bending wheels a bit more often.
The short answer, "True them when they need truing," but it shouldn't happen too often.
G B has said, "Should you get a bike fit before or after buying a new bike?" Well,
if you're unsure of the size that you need on a new bike, I would say, "Absolutely.
Get a bike fit before you get one." The thing that really springs to mind on this question is the
Selle Italia idmatch that we did recently. An amazing tool. Using that, you can get a bike fit,
but it can also then, using their vast database of all different frame sizes,
tell you exactly what frame size you would want in any brand of bike. Then what sort of
accessories you'd want with that frame as well. How many spaces you'd want below the stem?
How high you'd want the seat post? What size seat post? What size stem? What size handlebars?
All those things, which are just really useful. That means that when you buy
your new bike, you get it completely the right size. In the past, people have got bikes and then
fitted the bike to them. Whereas I think, it's a much more sensible way and will probably
save you money in the long run and improve your riding experience. If you fit yourself
and then get the bike that's your fit. I would advise doing that if you can. Next question is
from Siddharth Doshi. He says, "Hi guys, I have an Ultegra 11 Speed R8000 mechanical groupset.
I'd like to upgrade it to electronic shifting sometime in the future. Can a Shimano drivetrain
and disc brakes work with SRAM eTAP front and rear derailleurs and shifters, as it seems
cleaner to upgrade to eTAP as you don't have all the wires and things that you have with the DI2.
Right. Quick answer, no, won't work. The parts that you could use and transfer over if you were
interchanging SRAM and Shimano would be the cassette and the disc brake rotors. Although,
both of the brands would recommend that this is sub-optimal and they wouldn't recommend it.
The reason why you can't use SRAM shifters and Shimano hydraulic calipers,
and the same applies on rim brakes, actually, as well. Is because along the same lines, but
the amount of hydraulic fluid and the way that the hydraulic pistons work in the shifter,
is directly corresponding and proportional to the way that the caliper is designed.
It won't work properly. It's the same with the cable pull ratio on the mechanical rim brakes.
The amount of cable pull is different from Shimano to SRAM. Therefore, you have issues if you try and
mix and match those brake systems as well. Basically, just stick with either or,
whichever you decide to go to get the complete groupset of that particular brand.
Unfortunately, that's all we've got time for this week. I hope you've enjoyed the show.
Keep your questions coming in. It's always a pleasure answering them using the hashtag
#AskGCNTech. Still not too late, to get some last minute Christmas shopping in for the cyclists in
your lives or you could treat yourself. GCN Ass Savers also available in GCN Shop. Look at these.
You saw this,when you see mine's been saving my ass recently. There you go. Anyway,
see you in the next one. Bye. [00:07:57] [END OF AUDIO]