yes... unfortunately it is the mass of the rotor that brings stability, and its overall size will give better heat dissipation...

Having said that, another good option is to have a disc as large as will fit into the wheel, and then have a small annulus. That way you still have a large disc, good disipation and just enoguh mass, but not too much. I have in my shop two front systems, both based on brembo grN calipers.. one is the grN system 355mm, large annulus... other one is a 370 mm, small annulus... 370 mm disc is actually signifficantly lighter... Now, not having tested them I am just making presumptions, but the 370 mm might be a better choice for the track, where speeds are higher than in rally and you can run wheels large enough...

 

I’ve never thought of this aspect of it - but it makes sense

i would imagine it’d have to be a very long straight to cool down detrimentally though …

 

I read some really good paper on brakes and it mentioned teams choosing different brake discs (with different air gaps) to adjust the brakes to a particular track... Or you can block the inlets for brake cooling... that is another way

 

The annulus does play a small role in the braking torque. When calculating braking force it's tempting to put the rotor outer diameter into the equation, but the pads don't act on the outer diameter of the disc. They act on the face of the disc, across the annulus of the brake pad. So the actual braking torque has to be calculated from approximately the middle of the brake pad, not the outer diameter of the disc.

It doesn't make a huge difference in the calculations, but it's worth doing it right.

For braking performance and heat tolerance, the size of the pad is what matters. The annulus alone doesn't tell the whole story because the height and shape matter, too.

For a given rotor diameter, a larger annulus will have more thermal mass and area to dissipate heat, but also more weight.

 

has anyone's evo started understeering on power after installing a front diff? the front end has just been washing wide, seems like for a while now.

 

you also need the gymkhana rear diff or it will push.

 

i have it

 

How stiff are your rear springs?

 

8k f / 12k r

biggest WL rsb. uprights front and rear. we did some snow testing and it just totally washes out the front end wide. I've driven in the snow before with my old cusco 1.5 (you bought) and it was just power oversteer as soon as I touched the gas in the snow.

Now with the front rear cusco 1-ways (and the ATS setup of 1 way / 1.5way) I am power understeering. Wondering if I should just go back to the front helical or wait for the diffs to break in more. Maybe they are too tight to begin with.

I like how the car turns, I don't like how it behaves on power for exit.

 

had that issue since I got wavetrac way way back. been fighting it since. I had a full weekend with Dallas' ACD tune but I still struggled in the wet (had too much front camber for those events tho). Still looking for opportunities to learn its behaviour(s)

 

maybe there's something with the front diff that other guys are doing that we are not. I'm really tempted to swap the helical back in, if I can remember where I left it.

 

the pros left foot brake (earlier) and/or do some foot work and already anticipate the slips and clawing, straighten the wheel so it wont matter which wheel is sliding

 

i don't mean the pros though - in the snow, turn, mash gas, should a front diff be causing power understeer?

 

In the snow, that's probably what's going to happen. You're asking too much from the front with so little grip. The wheels are spinning way to easily on power and locking up the center which is causing the understeer. If you want rotation a little handbrake yoink is what you need to get the shock and break the rear loose.

Which ACD tune are you running? The stock ECU snow programing is pretty amazing in the snow. But only so much magic can be done once in a terminal state.

 

In the snow I would brake, get weight on front and turn while on brakes, get the thing turning and sliding the rear, then mash gas. You want the turning part to be done before the apex.. that way you launch out with front wheel straight..