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Recently I got the Giant Revolt 3 and have been riding it for a few days now. I have lately noticed that there is some rubbing noise when I apply the brakes. If you look at this picture (might be a bit hard to tell), there is a needle or some kind of gauge on top of the brake lever. When I got my bike, I believe they were in the middle, now my left one is all the way to the left, and my right is somewhat off centre. I'm not sure what they necessarily mean, but they have something to do with the brakes.

bike photo looking back over the handlebars

I called the bike shop where I bought this bike and they told me I would have to pay $60 for a tune up, and I don't plan to upfront that much money right now if it is an easy fix. I believe the problem is that since the bike is new, I might have to tighten up my brakes because the wires get stretched?

The brakes that are on my bike are mechanical disk brakes. If someone could tell me what might be wrong I would greatly appreciate it. I fell on my bike once because of a pot hole and scraped one side of the handle bar, but I don't think this is the cause since the needles were starting to get off centre before I fell.

Let me know if you need more information to help me out. Thanks!

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    If you bought the bike within the past month, they really should be doing a tune up for free. Those needles/gauges are gear indicators -- they tell you which gear combination (i.e. front chainring on the left side, rear cog on the right side) you're in, based on which position the needle is in. They are irrelevant to the brakes. – Batman Jul 16 '15 at 13:13
  • @Batman lol Batman to the rescue. I didn't know that those needles are for gears. Just shows how new I am to all these high tech bikes. As far as the shop goes, I called them to ask if I can bring in my bike for checkup and they told me the cost for the tune up which was around $60 for the entire bike. – MB41 Jul 16 '15 at 13:25
  • It's standard practice for bike shops to tune a bike after a month or ~20-50 miles after buying the bike. It could be something related to cabling (you can tune the tension using the little barrel adjusters). You need to check if the rotor is true among other things for a full inspection -- we have a bunch of questions on disc brake rub on this SE, but I'll leave it to someone else to write a proper answer. – Batman Jul 16 '15 at 14:04
  • @Batman I'll call them again and see if they would offer me a tune up for free. I don't think I mentioned that I bought it less than a month ago so that might be why they would charge me. – MB41 Jul 16 '15 at 14:07
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    Just a +1 that a shop who sells a new bike for a retail price should absolutely include a time-up after a period of time. If the bike was used or on a deep discount the situation is different. – jqning Dec 20 '15 at 15:21
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What has probably happened is that when you used the brakes the wheel shifted slightly in the dropouts. The disk brake pads run really close to the rotor, so even a tiny shift can be enough to cause this problem. The solution is to open the front QR lever with the bike upright. As you do that you will probably hear a little "clink" as the wheel settle back into the dropouts. Then tighten the adjustment knob on the other end of the QR axle before closing the lever. More detail here and here with diagrams (and even an animated gif!) or in even more detail at Sheldon Brown's site

The design problem that causes this is serious, and is discussed by people like John Allen and my view is somewhat more forceful than his but otherwise compatible.

You can download the manual for your brakes from the Tektro site and use a 5mm allen key to adjust the fixed pad (the one closest to the spokes) and the barrel adjuster on the brake cable to adjust the other pad.

service diagram for Tektro Mira mechanical disc brake caliper

There are a few descriptions of how to adjust the brakes on this site like this one and on sites like Park Tool (who like to shuffle things round so that link will be broken in a few months)

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