Caliper choose, 2 piston or 4 piston?

[LSD]

i'm designing next year's brake part. We have use 2 piston caliper for some years, it offers enough brake force, but in harsh braking conditions the car always vertically shake. i think maybe 4 piston caliper will performs better?

4 piston caliper is heavier, what advantage does 4 piston have? Could someone give me some help? http://fsae.com/groupee_common/emoticons/icon_smile.gif

[LSD]

PS. We are now using Wilwood PS1

[Luniz]

What you are describing is certainly not a problem with your brake caliper. It probably comes from lack of stiffness in the suspension system, the whole system resonates because of the stick/slip hysteresis of your tire. A similar effect would be this, just with a much higher frequency: http://www.youtube.com/watch?v=X5Uy7MhFiWA

[LSD]

Originally posted by Luniz:
What you are describing is certainly not a problem with your brake caliper. It probably comes from lack of stiffness in the suspension system, the whole system resonates because of the stick/slip hysteresis of your tire. A similar effect would be this, just with a much higher frequency: http://www.youtube.com/watch?v=X5Uy7MhFiWA

Thank you for your suggestion, i will see the video.
But in china, it's difficult to connect to Youtube.....

[Owen Thomas]

The major difference between a 2-piston and 4-piston caliper of the same total piston area is brake pad area. Subject to design, the 4-piston calipers will typically accomodate larger (longer) pads, which can absorb/shed off more heat before getting too hot. This may or may not be important to you. People will also tell you that 4-piston calipers will have a "softer pedal" compared to 2-pistons, since they tend to displace more fluid. Just looking at piston area you wouldn't guess, but channel design and other black magic make this empirically true (most of the time). More pistons can also mean less deflection, since the clamping force is more distributed across the caliper body. Weight is also a factor, as you mentioned.

The most obvious reason to get more pistons is that you need more area, and a single large diameter piston becomes impractical at a certain point. The larger your effective braking diameter is the more braking torque you can generate as well, so having a "longer" caliper and pad with more pistons is more mechanically efficient than the alternative.

Also, +1 for what Lutz said. The shaking problem probably isn't from your brakes themselves, but a product of the suspension reacting to the braking forces.

TL;DR: They perform roughly the same, FBD solves all questions.

[LSD]

Originally posted by Owen Thomas:
The major difference between a 2-piston and 4-piston caliper of the same total piston area is brake pad area. Subject to design, the 4-piston calipers will typically accomodate larger (longer) pads, which can absorb/shed off more heat before getting too hot. This may or may not be important to you. People will also tell you that 4-piston calipers will have a "softer pedal" compared to 2-pistons, since they tend to displace more fluid. Just looking at piston area you wouldn't guess, but channel design and other black magic make this empirically true (most of the time). More pistons can also mean less deflection, since the clamping force is more distributed across the caliper body. Weight is also a factor, as you mentioned.

The most obvious reason to get more pistons is that you need more area, and a single large diameter piston becomes impractical at a certain point. The larger your effective braking diameter is the more braking torque you can generate as well, so having a "longer" caliper and pad with more pistons is more mechanically efficient than the alternative.

Also, +1 for what Lutz said. The shaking problem probably isn't from your brakes themselves, but a product of the suspension reacting to the braking forces.

TL;DR: They perform roughly the same, FBD solves all questions.

aha, i understand it, i think i will still use 2 piston type, because it lighter and also cheaper.
i will find the reason for shaking in all suspension system.

[MCoach]

Liang,

Just be sure that when you are selecting 2 piston or 4 piston design that you take into consideration that difference in braking balance this will cause. It's likely that you will have to size a master cylinder or brake mechanical gain differently between the two set ups.