legacycentral bbs

Since I can never leave anything alone. Is it worth my time to swap my turbo legacy rear brakes to my WRX and the WRX rear to the legacy? Is the vented rotor the only difference?

Which one do you want to stop better? The turbo legacy rear brakes are better in every way.

you won't notice a damn difference!

The only difference is the rear rotor on the t-legacy is vented........however the newer wrx caliper may be slightly stiffer.....in which case.....I'd keep the stiffer caliper.

But like I said.....I wouldn't bother.

go to a road course and you would. there is a reason every front rotor made now is vented. take that same principal and multiply it in a performance situation and you will get usuable braking out of the sport sedan rears much longer than little solid discs.

so it depends on what you are doing. if the car is strictly for the street... then either is a toss-up (but rear vented is still a badge of honor). any sort of endurance racing will beg for the sport sedan rears.

So I would just swap the rotors or do I need to swap the caliper as well?

I autox...so maybe it's worth it?

I don't think Auto-X would make a big difference - you usually don't get to the kind of speeds that the vented rears would be such an improvement, but that's a guess. If you notice them fading, then you might want to go with the vented.

Steve

even at a road course.....I doubt you'd notice any difference. The rears don't do that much braking. All you'd need to do is run good pads, and it'd be fine.

For auto-x.....it will gain you nothing.

But if you wanted to swap them, yes, you'd have to swap the calipers.

Not to get this topic off course, but Josh you might be underestimating rear brakes just a wee bit. For example, Subaru cars all got rear drums (back in the day). Yet, every turbo model had rear discs. Fast forward some and every turbo model of course has rear discs and all turbo Legacies have rear vented.

Therefore I discern from this that Subaru engineers feel that vastly increased speeds (ex: turbo) and increased weight (Legacy) = the need for rear vented rotors. Now of course, money dictates what gets put on cars even safety-wise and the now quite porky WRX's end up with rear solids (but Legacy's still get vented, though).

Also remember that I'm not always braking in a straight line , ie all weight transferred to the front. I never had brake fade with my current setup. Fade is one thing but consistency is another. If the vented rear gave me a consistant feel, more than the stockers then I would switch them out.

After one of my autox runs I dare you to touch one of my rear rotors. Then tell me that don't do much:)


autox run:

gas...gas..gas...BRAKE....................turn/gas. My ABS chatters all day long at autox.

WRXdan wrote: autox run:

gas...gas..gas...BRAKE....................turn/gas. My ABS chatters all day long at autox.

You should try bypassing the ABS for autox.

I'm not really underestimating the rear braking system. You need to really understand that between the WRX & turbo legacy rear brakes, the ONLY difference between them is the vented rotor, & caliper design, assuming pad type and pad surface area is exactly the same.

Everything else is the exact same, same brake lines, same caliper piston diameter, etc. Now look at those things that are different, and what differences they can have on the overall braking of the car.

Vented rear rotor. The ONLY thing the vented rotor adds to the braking system is the ability to sink more heat into the brake system. ie. you can spread the same amount of heat throughout the vented rotor as you can with the solid rotor and the overall temperature of the rotor should be lower. The question you need to ask is how much lower, and is it negligible under normal driving situations. If so, does the lower temperature at more extreme limits warrant the added unsprung weight. AND....can the added temperature be combated with a slightly better brake pad material so that it can cope with the elevated temperatures.

Lastly, caliper & bracket design. The caliper & bracket design has changed. We can only assume that it's for the better, and that the stiffness of the caliper has increased. That increase in caliper stifness will result in better brake pedal feel and modulation at the edge of the "operating curve".


So like I said......the difference is going to be pretty negligible IMO, and without detailed information it'd be a little hard to tell whether there is an actual benefit.

One thing I guess you could do is weigh a non-turbo solid rear rotor, and then weight a turbo vented rear rotor. See what their difference is in weight, try to get that back to a mass, and then try and determine how much actual heat capacity the vented rotor gives you.

If someone can get weights, I'll try and workup the calcs. Ideally it'd be best to use new rotors, but at the very least, they should be rotors that have not been cut.

also speaking of mass, wouldnt the vented rear weight more as well, thus negating some of the stopping power and also accelleration?

That was the unsprung weight comment Hardy. The heavier rotors incerase unsprung weight.

oh , well we can pretty much gaurantee that it affects accelleration rgiht?

Yea, but it would likely be unnoticed.

i dont think my abs works

See that's the point I was trying to really make.....the differences we're talking are probably very minimal.....increase/decrease in unsprung weight, more mass for heat to absorb into, etc.

Without doing some calcs, you really can't say for sure whether it amounts to an increase/decrease in performance, and in what area.

Legacy777 wrote:The ONLY thing the vented rotor adds to the braking system is the ability to sink more heat into the brake system.

Well, it also provides a higher ratio of surface area to volume, which allows the rotors to shed heat faster.

vrg3 wrote:

Legacy777 wrote:The ONLY thing the vented rotor adds to the braking system is the ability to sink more heat into the brake system.

Well, it also provides a higher ratio of surface area to volume, which allows the rotors to shed heat faster.

Yes....this is true......guess you can lump that in with the rotor's ability to sink/reject heat, or its heat capacity.

Sorry, I didnt explain what i meant before. I had meant that the rotor would also be more rotational mass aswell as unsprung weight.

I have decided not to swap due to the caliper. I don't know if my stainless line or pads will work with the Leg calipers.

The lines will work. The pads may not.