this post was submitted on 21 Aug 2025
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160mm to 180mm disc rotor upgrade query. (lemmy.dbzer0.com)
submitted 2 months ago by theskyisfalling@lemmy.dbzer0.com to c/bikewrench@lemmy.world
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Hi all,

Wondering if anyone can help me with this question before I spend my money on a different mount for this caliper.

I am going to increase my front rotor size but what is printed on the side of my current mount has me confused. It says 160mm or 180mm implying that this mount can be used for both but surely the pads need to be in a different position for each size of rotor? I can't just bang a 180mm rotor on and change nothing else and expect it to work fine can I?

Can anyone clarify for me what this text on the side of the mount is getting at, am I able to use this mount for the bigger rotor somehow? If so how?

I plan on taking it apart this weekend and trying it out for sizing before I order a different mount but in my mind the caliper would need to be pushed further out to make space for the increase in size for the rotor and was hoping someone could enlighten me on what this text actually means whilst I plan the work in my head :D

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[–] JayleneSlide@lemmy.world 5 points 2 months ago (1 children)

The text on the adapter indicates it is for rotors 160 OR 180mm in diameter, depending on the fork design. The flat mount on your fork was designed for 160mm, but there are also flat mounts on other bikes designed for other standard sizes. Contact your fork manufacturer to confirm whether you can fit a 180mm rotor.

Even if a 180mm rotor physically fits, that's only part of the equation. Increasing rotor size increases the moment arm being applied to the fork leg. The fork needs to be designed for the potentially higher forces. YMMV, and be aware that snapping your fork/frame is a real possibility when increasing rotor size. That said, 160—>180 doesn't result in a major increase in moment, but primarily increases cooling area.

[–] theskyisfalling@lemmy.dbzer0.com 2 points 2 months ago (1 children)

Ah I see, I didn't think about the fact the bike could change and then the same mount could be used for a 180mm. That explains that for me, thanks!

Yeh I'm aware that changing it will result in increased load but YOLO, I'm gonna risk it and I'll have faith the forks can take it. Like you say it won't be a drastic increase in braking force, I am more doing it for the cooling element anyway as power wise the 160mm is fine.

I'll get an adapter, cheers for the info!

[–] JayleneSlide@lemmy.world 2 points 2 months ago (1 children)

Enjoy!

I mentioned the increase in moment arm for anyone else thinking about increasing their rotor size. On my own bikes, I would have zero concerns about 160—>180. This is a super common modification, and it is for cooling purposes.

But people being people, someone else would see "put on a larger adapter and rock out!" And then think they could put on a 203 rotor just because it fits. And THAT is absolutely getting into concerning, "you better know what you're doing" territory.

[–] theskyisfalling@lemmy.dbzer0.com 2 points 2 months ago

Yeh I appreciate that. I have been doing all my own bike work, maintenance and upgrading for around 30 years now so I'm fairly confident in my own abilities and knowing what feels safe and what doesn't. It was more the text on what I have that was throwing me and making me wonder if I needed any additional hardware.

Thanks for the input and I definitely won't be slapping on a 203, I'll leave that for the MTB xD

[–] hkwln@lemmy.ml 3 points 2 months ago

as far as i know is the 160/180 adapter you have only a mount four the breaks you have, if you have mtb brakes you don't need any for 160 breaks. what you need is a standart +20mm adapter(160mm to 180mm) front and the adapter is on the top of it. I am mainly using mtb breaks so could be wrong.

[–] plactagonic@sopuli.xyz 3 points 2 months ago (1 children)

I think that the rotor size is more dependent on the frame/fork mounts and configuration.

On my bike the 180mm rotor is just too big and rubs the fork. So this is something to check for first.

[–] limelight79@lemmy.world 2 points 2 months ago

Yeah, on mine, the 160 mm rotor is already extremely close to the fork. I doubt anything larger would fit.

I'd suggest op remove his caliper (just unbolt it), mount a 180 mm rotor to the wheel, and see if it fits.

[–] Diplomjodler3@lemmy.world 3 points 2 months ago

While you can probably fit a 180 mm disc here, you should make sure that the fork and the front wheel are actually designed for it. If you fit an out of spec part, it can have all kinds of undesirable consequences.

[–] teft@piefed.social 2 points 2 months ago

That’s a 160 mount. Just search amazon for 180 flat disc brake mount and you’ll find a bunch that will work for you.

[–] avidamoeba@lemmy.ca 2 points 2 months ago* (last edited 2 months ago) (1 children)

Seconding everyone else's opinions on checking if the fork is rated for 180mm rotors. If it isn't and it fails, the failure would likey occur exactly when you need it most, under hard, emergency braking. If you're trying to brake as fast as possible, having a fork leg buckle would probably go against that goal. 😅

It might be safer to go for a caliper and pads with stronger stopping power. For example a four-piston caliper with metal pads. If there aren't compatible parts from the GRX line, you might be able to use SLX bits. Someone has probably tried it already.

[–] theskyisfalling@lemmy.dbzer0.com 2 points 2 months ago (1 children)

I hear what everyone is saying but in all my years of cycling I've never once seen a fork state a size of rotor it is rated for.

I have looked for specs on this one since people have been saying and again no where does it state a rated up to "x" rotor size. I really think it is very unlikely that a 20mm increase will cause me any issues I'm willing to yolo it. I'm happy for people to mock me and sayi told you so if it snaps and I post the aftermath xD

I more want it for improved cooling, stopping power isn't an issue. I also can't see the difference between adding two pistons and adding a bit of diameter. Both will increase forces exerted on the form so if it is gonna snap either of those options will do so.

Anyway, warnings from everyone heeded, I'll still be going for it xD

[–] avidamoeba@lemmy.ca 2 points 2 months ago* (last edited 2 months ago) (1 children)

Get an Ice Tech Freeza (Shimano) instead of fucking around:

Also, once you wake up in the hospital, come back and reply to this thread so we can mock you. 😄

E: BTW your logic about the load from better calipers and pads being potentially equivalent to larger rotor is sound. Caliper/pads would only be safer if there's a dramatic difference in the moment between the rotor sizes that's larger. Could easily not be large enough. Someone who's studied more physics might have a better idea.

E2: I definitely hope you don't end up in the hospital!

[–] theskyisfalling@lemmy.dbzer0.com 2 points 2 months ago

I'll be sure to check in after failure :p

Nah seriously I appreciate peoples concern and it isn't like it isn't a risk I haven't considered at all but think it is a risk that is fine to take weighing up all sides.