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2005 CBR1000RR, 2018 CBR1000RR SP
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Discussion Starter · #1 ·
REF:

So, I am taking it to say that it is safe to use (or better to use) DOT 5.1 even if Honda specified DOT 4 for their bikes since DOT 5.1 is an improved version of DOT 4?

I know that DOT 5 is not safe since it is silicone-based.

Please confirm.
 

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2017 CBR1000S1
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Please confirm.
Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.
 

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i believe dot 5.1 is a more suitable fuild for cars with ABS otherwise same performance spec as 4.
Over here motul RB600 is what I use. They also do a 5.1 version. They are both synthetic (not silicon).
Interestingly, RB600 has a higher dry & wet boiling point.

I would be interested to know what's special for the ABS application🤔
I notice the low temperature viscocity is different could this be the reason??
 

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Discussion Starter · #5 ·
So, looks like DOT 5.1 should be more suitable for ABS bikes.
 

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So, looks like DOT 5.1 should be more suitable for ABS bikes.
I don't know if it's any better. Honda has offered ABS on the CBR since 2009. DOT 4 is even recommended for the RR-R SP
 

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The technical reason is viscosity. Think tap water vs. honey. DOT5.1 has about 50% the "thickness" of DOT3/4. In anti-lock braking systems, the actuator orfices can be very small so if the system needs to move lots of fluid through that hole quickly it's easier to do with DOT5.1.

For older systems that were originally engineered for DOT3/4 it won't make a difference to use DOT5.1. You do get an extra 40 degrees of boiling protection both wet/dry.
 
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As DOT 5.1 is more hygroscopic than DOT 4 and therefore absorbs more moisture, it will need to be changed more often. However, the benefit of 5.1 with its higher boiling point, is that it can experience higher temperatures than DOT 4 before it starts to affect braking efficiency. Although, a good quality DOT 4 fluid such as the Super DOT4 which has a dry boiling point which exceeds the 5.1 minimum will be able to contend with the temperature levels it would experience on a track day, for example. The Super DOT4, like the DOT 5.1 will need to be changed more often than DOT4 with the obvious budget implications.

DOT 5.1 maintains a lower viscosity in lower temperatures than DOT 4 all the way down to around -40 degrees C, although this is unlikely to be relevant in the UK. For this reason, DOT4 is often an appropriate choice of brake fluid and requires changing less often.
 
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