Brake rotors

Hey there, cycling crew... 😁
So, I'm riding a Trek 820 disc setup right now. It came stock with 160mm hydraulic discs, and I’ve got a question for the group. Can I just swap out the rotors for bigger ones, or am I looking at replacing the entire braking system? I was thinking about bumping things up to 185mm rotors. Also, how often are you guys actually topping off the fluid in those reservoirs on the handlebars, and what kind of brake fluid are you using?? 🙄

If you want a bigger rotor, obviously you’ve gotta buy a larger one... plus an adapter to fit your brake caliper to it, yeah...

The oil depends on what brakes you're running—some take mineral oil, others use DOT fluid... honestly, don't mess with it if they're working fine. But if they fail and you don't know how to bleed them, just take them to a shop... My Shimano 525s have been biting perfectly for three years without a single bleed, just swapped pads... it's definitely not something you need to do every week...

If you really want to tinker with them yourself, just download the manual online for your specific brakes and see what they recommend...

Jacob Fisher6 said:First off, a quick hello to everyone in the cycling community. 😁
I’ve got a Trek 820 disc setup that came stock with 160mm hydraulic rotors. I was wondering if I could just swap in larger discs—maybe go up to 185mm—without having to overhaul the entire braking system? Also, how often are you guys topping off the reservoir at the lever, and what kind of fluid are you using? 🙄

Don't go messing around with the derailleur adjustment yourself; you should probably just take it into a shop, because it isn't as simple as just popping it open and draining the oil.

@Jacob Fisher6/">@@Jacob Fisher6 - Regarding those larger rotors, you're going to need the right adapters, just like analogseal72 mentioned. Your best bet is to head down to a local bike shop and ask; the adapters themselves shouldn't break the bank.

As for the brake fluid, you really ought to swap it out about once a year (your mechanic will give you the rundown on that too).
I personally run DOT 4, though I haven't touched mine in two and a half years. Everything seems fine for the most part, except for that one time I lost pressure in my front brake.
I’d estimate the bleeding process takes about 70-$33.

analogseal72 said:if you want a bigger rotor, you obviously have to buy a bigger rotor. Plus, you'll need an adapter for whatever size you pick so the caliper actually fits on there, I guess...

oil depends on which brakes you're running. some take mineral oil, others use DOT fluid. maybe don't mess around with it too much while everything is working fine, but if things go south and you aren't comfortable bleeding disc brakes, just take it to a shop... my Shimano 525s have been going strong for three years without a single bleed , just swapping pads, so it’s not exactly a weekly chore...

It might be smarter to just change the fluid. It eventually loses its properties and instead of absorbing moisture—whatever the science is there, it evaporates or something, I don't really know—moisture builds up in the system. That can cause internal corrosion, which might lead to a hose bursting right when you need it most.

electricotter9 said:Don't mess with bleeding them yourself. Take it to a mechanic, because it isn't as simple as just opening it up and pouring fluid in.

Bleeding brakes isn't rocket science. If you look up the process online, you'll probably get the hang of it without too much trouble—though I suppose you do need a clear head and a decent amount of patience to pull it off.

Thanks for all the input, everyone... I definitely agree that getting it looked at by a pro at the local bike shop is probably the smartest move here.
So, here’s what’s on my mind: right now, this ride is rocking an RST Gila 100mm fork. If I decide to upgrade to those beefier disc rotors, am I going to need to swap out the whole fork for something more heavy-duty? I keep seeing guys online who upgrade to bigger rotors and immediately jump to a much beefier suspension setup, so now I'm sitting here wondering if that's actually a necessity or if I'm just overthinking things...??

You don't need a second fork. Honestly, the real question is whether buying another rotor and adapter is even worth the money. Maybe just take it to a shop or grab a buddy who actually knows their way around a wrench to see if those brakes are even biting properly? Or maybe they just need to be bled so you can finally get some actual stopping power.

My Avid rotors are sitting at about $90 185mm each.. does anyone know what kind of damage I'm looking at for adapters, and has anyone actually pulled this off before?

So, I finally picked up some $27 Avid adapters... now I’m just sitting here wondering if anyone has actually messed around with these before? Like, has anyone gone down this rabbit hole? I’m looking for the real deal—give me the good, the bad, and the ugly.

Forget the extra luggage; just swap in a bigger drive and get the right adapter. Problem solved.
Yeah, we’ve been doing that for ages.
Most of us have.

Totally worth it...

Could this actually wreck a fork? Say, if you’ve got a budget fork paired with a massive rotor. From what I've gathered, some forks have a specific limit on the max rotor size they can handle.

Patrick King7 said:Could that actually wreck the fork? Like, if you have a weaker setup paired with a massive rotor? From what I've gathered, some forks have a hard limit on the rotor size they can handle.

It definitely can. I remember riding an old Trek where the limit was 185mm, but on my Fox Revelation, it goes up to 210mm.

First off, that caliper is total junk, but you're lucky the hydraulics aren't quite as bad.
Basically, nothing's gonna happen.

A Formula or XT setup with a 160mm rotor is going to outbrake a 486 (which is more like an entry-level Shimano level, if I recall) even with an 180mm rotor.
Bottom line: don't sweat it.
Actually, I'd say go for the upgrade.

silentpanther15 said:RST forks are absolute garbage, but you're lucky that the hydraulics aren't quite as bad.
Basically, nothing's going to break.

A Formula or XT setup with a 160mm rotor is going to outperform a 486 (which I think is about Alivio level gear) running an 180mm rotor by a mile.
Bottom line, don't sweat it.
In fact, I'd actually suggest making that upgrade.

I'm mostly on board with the bold take, though those forks are decent enough if you're just doing cross-country riding.
A buddy of mine has a Wheeler (pretty sure it's a PRO 39 from 2007) with some RST fork on it—can't remember the specific model—and it holds up fine, except for those times it feels like there's way too much oil in the stanchions.

As for the larger rotors, I was thinking about stepping up to something like 180-185mm since I'm sitting at 160mm right now, but finding compatible adapters for my brakes (Giant MPH) is proving to be a massive pain.

By the way, does anyone here have any leads, or know roughly what I should expect to pay for some affordable Deore 525 brakes?
I've always liked those, but nobody in my neighborhood who rides actually sells them.

So, from what I can gather, I don't actually *need* to swap out my fork, but hey, if I find myself with some extra cash burning a hole in my pocket... maybe I will. Hahaha... alright, fine, whatever. 🙂 Yippee!

ruggedharbor77 said:It’d be smarter to just swap the fluid, honestly. It loses its chemical properties over time... instead of pulling moisture out of the system—I think it evaporates or something, I don't know, but it matters—moisture just builds up inside. That causes internal rust, which could crack a caliper and leave you without brakes right when you need them most.

That shouldn't be an issue with Shimano hydraulics since they use mineral oil, whereas DOT absorbs water from the air... and I'm running Shimano 😉

Here's some stuff I found on a US bike forum...

"Did a little digging on Wikipedia—DOT 3, 4, and 5.1 are the fluids used by Hayes and Avid. DO NOT MIX them with DOT 5 fluid. DOT 5 is likely that silicone-based "mineral" type, while the others are polyethylene glycol based."

"Also, watch out for water. Polyethylene glycol-based fluids absorb moisture from the air, which REALLY drops their boiling point. Don't leave them in open containers, otherwise your brakes will boil way sooner when you actually ride them.

Brakes that use DOT fluid have to be serviced regularly (meaning, change the fluid) specifically because of that property you mentioned. But with mineral oil, it's different... you just top it off and ride until the brakes fail.
"

Here’s the lowdown from the Formula website:

Only use DOT 4 Super hydraulic brake fluid straight from a sealed container. Don't let those bottles of
DOT fluid sit open for too long—this stuff sucks moisture right out of the air, which messes with
the physical properties and can seriously tank your braking performance. Make sure you swap out
the brake fluid every two years at the absolute most.

I agree with what I quoted earlier, DOT 4 isn't mineral-based...

Got a new bike now with Hayes brakes, so I'll have to deal with all that in about a year...😁

analogseal72 said:it lines up with what I quoted earlier—DOT 4 isn't mineral oil...

So, my new bike has Hayes brakes, which means I'll probably have to deal with all this in about a year or so, I guess.😁

I don't know why you're overthinking this, man.

God forbid you end up without brakes just because of something as trivial as switching out the fluid for $33.🤷

ruggedharbor77 said:Man, I don't know why you're overthinking this...

God forbid you end up without brakes just because of something as minor as changing the oil for your $33.🤷

I'll probably swap the oil during the Black Friday sales, mostly because my old bike is going up for sale soon and I want to service it first... it's pretty filthy and greasy 😁 ..

And about the "overthinking" part... I really don't think I am. Because regarding mineral oils, what you're saying just isn't right—unless we're all just blindly following Wikipedia 😉 ..

Here's the link, and the important part from the Wiki:

"Most automotive professionals agree that glycol based brake fluid, (DOT 3, DOT 4, DOT 5.1) should be flushed, or changed, every 1-2 years.[1] Many manufacturers also require periodic fluid changes to ensure reliability and safety. Once installed, moisture diffuses into the fluid through brake hoses and rubber seals and eventually the fluid will have to be replaced when the water content becomes too high. Electronic testers and test strips are commercially available to measure moisture content. The corrosion inhibitors also degrade over time. New fluid should always be stored in a sealed container to avoid moisture intrusion.

DOT 5 is silicone fluid and the above does not apply. Ideally, silicone fluid should be used only to fill non-ABS systems that have not been previously filled with glycol based fluid. Any system that has used glycol based fluid will contain moisture, glycol fluid disperses the moisture throughout the system and contains corrosion inhibitors. Silicone fluid does not allow moisture to enter the system, but does not disperse any that is already there either. A system filled from dry with silicone fluid, does not require the fluid to be changed at intervals, only when the system has been disturbed for a component repair or renewal. The United States armed forces have standardised on silicone brake fluid since the 1990s."

http://en.wikipedia.org/wiki/Brake_fluid

Oh, and I found another interesting difference between mineral and DOT fluids

Shimano uses mineral oil, and besides the OEM stuff, you can use Magurin, and from what I hear, it works great for Citroen setups. I had amazing results using Magurin on my Shimano brakes, so give that a shot. Definitely stay away from DOT. Mineral oils have additives to swell the seals, but DOT doesn't. DOT is aggressive and eats through rubber that isn't a high-grade NBR designed to resist DOT fluids. Every brake system has seals designed specifically for the type of fluid it uses, so it makes sense why mixing them is a bad idea.