[s-cars] G60 Confusion !! (small typo correction)

[Keith Maddock]

OK, I go to the Nürburgring for the afternoon and what a mess I return to!!!

A) I made a mistake reading Jimmy's page - its a little confusing since G60's are only front brakes, not the rears, I interpreted the 45mm and 36mm as the leading/trailing piston sizes.

B) G60's do NOT have dual 45mm pistons - I doubt any sliding 2-piston or any fixed 4-pistons have the same size leading and trailing pistons.

C)  I am 99% certain that G60's have 1 45mm and 1 40mm piston.  Anyone have a spare set they can measure?  This would be the equivalent of one 60.21 mm piston = 2847mm^21
A=Pi*R^2  R = D/2

Pi*(45mm/2)^2+Pi*(40mm/2)^2 = 2877mm = Total Area of 45mm and40mm piston

If you want the diameter of the circle with the same area:

D= 2*SQRT (A/Pi)

SQRT(2847/Pi) = 2847 = 60.21mm diameter.


D) When comparing fixed piston calipers (Brembo/Porsche) to sliding piston calipers, multiply the number of pistons in the sliding caliper  by 2

Why?  Because in a sliding piston caliper, the brake pressure squeezes  the inside pad with the brake piston, however  the brake pressure also pushes equally on the back of the fluid cavity (which is nearly the exact  same size as the piston diameter), which causes the caliper to slide back, squeezing  the outside pad..    This is not the case in a fixed caliper.  The following page explains it better than I can...
http://www.sportcompactcarweb.com/editors/technobabble/0212scc_techno/

So a G60 with 1 40mm and 1 45mm piston would be the equivalent of a brembo with 2 40mm and 2 45mm pistons.

E) Big reds have 2  36mm and 2 44mm pistons, therefore they have LESS effective piston area than a G60. (effictive sliding caliper single piston diameter of 56.85)

F) If you want to comare areas as a "absolute difference in cross sectional area.", then use the following:

[2(44x44)+2(36x36)]/[2(45x45)+2(40*40)] = 0.89

As in.. "Big Reds wtih 36/44mm pistons have 89% of the effective caliper piston area as G60's with 40/45mm pistons"

Even if I'm wrong on point B above, and the G60's have dual 45mm pistons, then it's even worse for the BR's

[2(44x44)+2(36x36)]/4(45x45) = 0.80

As in.."Big Reds wtih 36/44mm pistons have 80% of the effective caliper piston area as G60's if they had dual 45mm pistons"


I'll email a friend back in our Michigan office to find out for sure the G60 piston sizes.  He had a G60 laying around in his office last time I was there.
Business math:  (Lucas+Girling)+(Kelsey-Hayes) = LucasVarity = TRW

Cheers,
Keith





Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474    -   -   keith.maddock at trw.com