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I only have experience riding mechanical disc in the middle of winter. I have a set of Magura and SRAM that I can throw on. I'm wondering if there are truly ant noticeable differences in low temp performance? My basic understanding is that DOT should be least-affected by low temps, but is there a real world difference at all?

Thanks.
 

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Elitest thrill junkie
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Yes, a big diff in performance, around teens my mineral oil ones get real stiff and as you get to the single digits and lower, the bite point moves way out (causing your fingers to be way extended) with almost no lever travel, on/off. I have had failures of mineral oil brakes, but i was riding well into the -Fs at the time. They dont all out stop working, but they work much worse than when its warmer and riding downhill/tech gets increasingly more difficult as they work worse. DOT on other hand, working pretty much just like in summer. If you want your brakes to work like summer, DOT. If you dont mind performance being affected and possibly affecting your control, then mineral might be ok, but if you are regularly below -20f i would recommend against. Lastly, i would recommend against shimano mainly because they do not make spare parts available, like seals, which are the parts you should be replacing after a season of winter use. They just want you to buy new brakes (but they will warranty if you have an active warranty).

Again, in the winter my DOT brakes work pretty much exactly like summer, no issues or concerns.
 
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Rippin da fAt
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DOT vs. Mineral oil has been debated to death on the forum.

Low temps will make the mineral oil system sluggish. DOT is unaffected in this regard.

Boiling points are fairly close. Mineral oil cleans up with Dawn detergent while DOT cleans up with plain water.
DOT does absorb air as well as moisture from the air. Both of these facts mean that you MUST use only fresh DOT from a sealed container. You Must degas DOT prior to use.
Degassing DOT is a simple process where you fill a syringe and close the outlet, pull it under vacuum until the champagne appearance subsides. Why would you do this? Because if you don't, you will be bleeding brakes frequently as gas creates bubbles in the system.

Mineral oil and freezing temps... Sluggish application and sluggish lever return.

Otherwise, neither is "better".
 

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Elitest thrill junkie
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Just an addition, all systems will draw in some air and moisture over time, they are not 100% cut off from the environment. The reason that DOT absorbs moisture is to keep it from boiling into water vapor. The “boiling point” is only as good as the lowest common denominator in the system. When something boils, it turns to gas. Thats bad for brakes. The boiling point is probably not the biggest deal for winter cycling, but the idea with DOT is consistent braking, no matter the situation. It is better at cold temps obviously. Theres a lot of hype with DOT too, like itll eat your paint off. Its not that reactive and youd have to leave a bunch of it for a long time. The insides of my DOT brakes are still anodized, so some of this gets blown out of proportion. I clean up with alcohol.
 
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gotta degas mineral oil too or expect to minibleed a bunch later
 
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Rippin da fAt
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Just an addition, all systems will draw in some air and moisture over time, they are not 100% cut off from the environment. The reason that DOT absorbs moisture is to keep it from boiling into water vapor. The “boiling point” is only as good as the lowest common denominator in the system. When something boils, it turns to gas. Thats bad for brakes. The boiling point is probably not the biggest deal for winter cycling, but the idea with DOT is consistent braking, no matter the situation. It is better at cold temps obviously. Theres a lot of hype with DOT too, like itll eat your paint off. Its not that reactive and youd have to leave a bunch of it for a long time. The insides of my DOT brakes are still anodized, so some of this gets blown out of proportion. I clean up with alcohol.
I have heard the bogus claim that ano would be damaged by DOT, this is patently false. I get paid handsomely to deal with DOT systems.
The paint thing... A few minutes of DOT on paint does nothing unless it is inferior paint however, long term, the paint will look like a raised relief map and become rubber like or gooey. Rinse it as soon as possible with water. It is water soluble and isopropyl will do as well.

I see it as humorous on the paranoia of DOT.

The old HS 33's and trials bikes... Yeah, those are still a thing! Dexcool is used in place of mineral oil by trials riders in cold climates for obvious reasons. Foremost being, reduced arm pump during a session.
 

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Any fluid will get more viscous when cold. But this isn't really a problem since you don't move a lot of fluid that the added pressure drop matters. If you look at the caliper and hose, you see the fluid may only travel a few mm or so to move the caliper. It only would matter if it would solidify or get slushy (like glycol does). but we are not talking about such low temps.

I've been riding Shimano in winters down to -20C and never noticed a difference in braking. In fact, at that temp I have Pogies and thicker gloves anyway and braking and all other operations will feel different than in summer.

I'm sure a lab can test if DOT or mineral oil behaves better, but I doubt in practice it matters.

I'm sure if all mineral oil brakes would fail in winter, we would have heard about it. Many of the large manufacturers use mineral oil. I doubt they all have an elaborate conspiracy going to keep that a secret. Like faking the Moon landing conspiracy.
 

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Rippin da fAt
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Any fluid will get more viscous when cold. But this isn't really a problem since you don't move a lot of fluid that the added pressure drop matters. If you look at the caliper and hose, you see the fluid may only travel a few mm or so to move the caliper. It only would matter if it would solidify or get slushy (like glycol does). but we are not talking about such low temps.

I've been riding Shimano in winters down to -20C and never noticed a difference in braking. In fact, at that temp I have Pogies and thicker gloves anyway and braking and all other operations will feel different than in summer.

I'm sure a lab can test if DOT or mineral oil behaves better, but I doubt in practice it matters.

I'm sure if all mineral oil brakes would fail in winter, we would have heard about it. Many of the large manufacturers use mineral oil. I doubt they all have an elaborate conspiracy going to keep that a secret. Like faking the Moon landing conspiracy.
This is laughable...

Yus, we are moving a very small amount of fluid and not thinking about the resistance that increased viscosity causes with pistons and seals.
There is a reason SAE chose DOT as a standard in the auto industry. Simply works!
Do mineral oil systems fail in winter? Not necessarily however, they suffer in terms of operation due to sluggish return.
There is also a large number of folks that have removed the baby oil and replaced it with coolant, since it works well and suffers no adverse affects in cold weather.
 

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In my experience with Shimano SLX brakes (Shimano mineral oil) - in cold temps (below..20F-ish) there is fluid expansion in the system which takes up some or all of the slack in the lever -I guess depending on how cold - and in some cases sometimes seem to even push the pistons towards the rotors a tiny bit so they might rub a little bit. I don't recall riding below 0F. I've never used brakes with DOT so cannot compare first hand.
That said - it sounds worse than it is. It hasn't been a big deal.

COBikeman
 

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Elitest thrill junkie
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Fluid expansion as it gets colder? That seems to go against thermal expansion principles and common physics.
Yeah, the lever engagement moves out and during consecutive braking efforts, it goes further and further. It makes it "seem" like the fluid is expanding, but I believe it's largely due to the fact that the fluid is too thick to move through the replenishment port freely, thereby you get the bad moving engagement point (further out).
 

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Any fluid will get more viscous when cold. But this isn't really a problem since you don't move a lot of fluid that the added pressure drop matters. If you look at the caliper and hose, you see the fluid may only travel a few mm or so to move the caliper. It only would matter if it would solidify or get slushy (like glycol does). but we are not talking about such low temps.

I've been riding Shimano in winters down to -20C and never noticed a difference in braking. In fact, at that temp I have Pogies and thicker gloves anyway and braking and all other operations will feel different than in summer.

I'm sure a lab can test if DOT or mineral oil behaves better, but I doubt in practice it matters.

I'm sure if all mineral oil brakes would fail in winter, we would have heard about it. Many of the large manufacturers use mineral oil. I doubt they all have an elaborate conspiracy going to keep that a secret. Like faking the Moon landing conspiracy.

It seems you never tire of being wrong, and proud of it.

If you never go colder than -20C, then you might never notice a difference.

If you spend a lot of time there, or go much colder, you'll have the opportunity to learn the error in your logic.

Mineral oil hasn't been kicked to the curb because not enough people ride in real cold.
 

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Rippin da fAt
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In my experience with Shimano SLX brakes (Shimano mineral oil) - in cold temps (below..20F-ish) there is fluid expansion in the system which takes up some or all of the slack in the lever -I guess depending on how cold - and in some cases sometimes seem to even push the pistons towards the rotors a tiny bit so they might rub a little bit. I don't recall riding below 0F. I've never used brakes with DOT so cannot compare first hand.
That said - it sounds worse than it is. It hasn't been a big deal.

COBikeman
Jump in a motor vehicle in the dead of winter and take a drive.

As for cold and "expansion", there is no expansion however, contraction, yus. The return port in a bicycle sized master cylinder is very minute and the chilled oil will not readily return. This give the illusion of expansion.

An example... Check automatic transmission fluid level before driving a car, check it at operating temperature. Note the difference in level reading. Hot oil expands considerably but contracts when cold.
 

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Elitest thrill junkie
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I've been riding Shimano in winters down to -20C and never noticed a difference in braking. In fact, at that temp I have Pogies and thicker gloves anyway and braking and all other operations will feel different than in summer.
But that doesn't really make sense. You say you don't notice any difference...but the operations, including braking, feel different in winter. Isn't that a direct change in performance? You are saying the brakes work exactly the same at -20C as +20C or not? Although -20C may not be the coldest I've ride, I have definitely ridden mineral oil extensively in that temp and the difference in performance, even at that temp, is significant. Modulation and control are significantly affected. More-so on any steep slope or tech riding. Just riding on endless flat stuff where you don't even need brakes...well yeah, not going to affect the riding performance much. Not to knock that kind of riding, that is definitely a big part of winter riding for some places. But it's still risking a failure/accelerating wear for a system not designed for the temps.
 
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