Hexsense

Nah, my road bike use 140mm rotors.

They would, but how? 29" wheels aren't going to shrink its diameter down. The head tube is as short as they can do without compromising strength. The fork though, can shrink by 1-2cm but doing so means they break compatibility with all the current frames. Basically, the front tire will rub on the bike down tube on deep compression. Unless the frame are redesigned with big offset/recess downtube to avoid contact with the tire.

160 watt would be 0.214564 horse power. Are you sure your car have less than quarter a horse power?

Freestroke (Bite point adjustment) is already set closest possible from the factory and it's just a tiny grub screw. So, just leave it alone and don't touch it. Instead, use lever reach adjustment (another screw) to adjust lever position. Which, Hayes lever maintain leverage ratio no matter how close or far the lever is set.

@gabriel-mission9: Other example ways to get toe in pads without different size pistons are: 1) Piston bore is angled (so that it has to move a longer distance than another straight pair). This isn't common. 2) Square seal used behind different pair of pistons are different. If a set of square seal behind the piston is flexier/firmer (not just just physically bigger) than another pair. Then the piston would retract and advance at the different rate. Re: "no braking force at all is exerted until all 4 pistons are fully activated". Did you assume square seal bending force to be 0? Hayes Dominion A4 has 7.011x hydraulic leverage ratio and 5.909 mechanical leverage ratio. Combined, the light lever force at the lever (which is light, but isn't zero) is multiplied by 41x at the caliper. During partial pad contact (one set of piston is in, another pair isn't contact yet) you already have some noticeable braking force. The lever feel remain light until both set of pistons are fully engaged then lever firm up. That lever travel between when the braking start to apply to when the lever firm up is what give lower initial bite.

@vinay: Hayes Dominion A4 has hydraulic leverage of 7.011, Hayes Dominion A2 has hydraulic leverage of 6.986. So, technically yes. A4 has a tiny bit more leverage ratio than A2. But not much at all. On Shimano camp, we are looking at the leverage ratio of 4.8 vs 5.1 for 2 and 4 piston respectively. Which is more noticeable than difference between Hayes 2 and 4 calipers. I'd say the offset pair of piston @thenotoriousmic mention is the bigger differentiator between 2 and 4 piston than difference in leverage ratio for Hayes.