Direct 'Dear Dave' tech letters to dave@eyesoreracing.com. Coleman will share mind-numbing details, earth-shattering revelations, and technical nerdisms in this space each month.
Q More stopping or more going?
I have a base 350Z and I've been wanting to upgrade the brakes as my first modification. Since I read Sport Compact Car, not Sport Luxury Car, you can probably guess I'm on a budget. The planned set-up is a 13-inch, four-piston front with StopTechs and Racing Brake's 13-inch OE upgrade for the back.
The only problem is that the rears will still be the stock sliding calipers instead of a fixed, opposed-piston set-up like the front. Would this numb the feel on the front brakes because I didn't change the rear calipers?
My driving skill is good enough to feel and understand a vehicle's dynamics. I go to at least four HPDE events a year and do a lot of spirited driving. The guys I run with all say I should go opposed-piston all around, but they can afford cars that come with good brakes stock.
I guess I could try the Racing Brake upgrade and if I don't like it, eBay it. But skipping it altogether would save about $1,500 for that Quaife ATB differential I'm considering. I think I just answered my own question... but I would still appreciate your input.
Oh, and don't tell people to cut their springs, seriously.
Frank Monserrate
Alameda, CA
A.You should be very cautious mixing unrelated brake kits. Odds are good that not only will braking performance be hurt by your arbitrary rear upgrade, but the opposed-piston rear calipers might even make pedal feel worse.
First, braking performance. A properly engineered brake kit like StopTech's will be tuned to provide the correct brake bias. Most factory systems are a little too front-biased for maximum stopping power. In spite of their larger size, the front brakes in a StopTech Z kit actually exert less brake torque for a given line pressure than the stock brakes. This forces the rears to work proportionally harder and should get all four tires to the point of lock-up (or to the ABS threshold) at the same time.
Advantages of a big brake kit come not from increased brake torque, but from maximizing the stopping potential of the tires through brake bias optimization, improved modulation through more rigid calipers, and from better consistency through improved heat capacity and cooling.
Trusting that StopTech did its homework right on brake bias (and there are few companies who get gold stars on their papers more consistently), fitting bigger brakes on the rear is probably going to throw that bias off. While the exact brake torque available from a given brake kit is hard to calculate, it's reasonably easy to guess which way things will go when parts are changed.
Torque is a force times the lever arm it's applied with. When tightening a bolt, yanking on the end of a one-foot wrench with 50 pounds of grunt will get 50 ft-lbs. Same goes for brakes. The force is a function of the surface area and coefficient of friction of the pads, how hard they're clamped against the rotor, and how fast the rotor is moving. The lever arm is simply how far the caliper is from center of the rotor.
With the Racing Brake 13-inch OE upgrade, the OE calipers are used with larger-diameter rotors (this is made possible by Racing Brake's clever caliper bracket that re-aligns the factory caliper with its larger rotor). On the force side of the torque equation, the surface of a larger rotor will slide past the pads a little faster, slightly increasing the force applied by the pads. On the lever arm side, the caliper is further from the center of the rotor, so the arm is longer. More force times a longer lever arm equals more rear brake torque. To maintain proper brake balance, this stronger rear brake should only be used with a stronger front brake.