StopTech ST-40's

[gan1hck]

Does the front kit use the same pads as the rear kits?

Bimmerworld only sells the front pads.

[Richbot]

Yes

[gan1hck]

thank you

[///Mobbin]

The end.

[dozaiya]

finito

[Datka]

[gan1hck]

so another question.

The ST-40 rotors are 355 mm.....so smaller than stock?

I thought BBK's are supposed to have bigger rotors for better performance?

[dparm]

Originally Posted by gan1hck

so another question.

The ST-40 rotors are 355 mm.....so smaller than stock?

I thought BBK's are supposed to have bigger rotors for better performance?

Larger rotors do not mean better stopping. Friction and surface area are not related. Between two rotors, all else being equal, the larger diameter rotor will stop better because it has more MASS to dissipate the heat, not because the friction surface is larger.

The concept of friction and surface area being unrelated is tough for people to grasp. Here's an easy way to prove it: take a non-square box and put a bunch of stuff in it. Try pushing the box across the floor and feel how much effort it takes. Now, rotate the box to a different side (either smaller or larger) and push it again. It will take the same amount! This is because the friction is exactly the same.


The reason the BBKs can be smaller but work better is because they are far more efficient at bleeding off the heat than an OEM rotor. They're able to do this because the cooling veins are more efficient, more plentiful, spaced better, etc. Also, it's a true two-piece rotor.

[M3 Number 86]

Originally Posted by dparm

Larger rotors do not mean better stopping. Friction and surface area are not related. Between two rotors, all else being equal, the larger diameter rotor will stop better because it has more MASS to dissipate the heat, not because the friction surface is larger.

The concept of friction and surface area being unrelated is tough for people to grasp. Here's an easy way to prove it: take a non-square box and put a bunch of stuff in it. Try pushing the box across the floor and feel how much effort it takes. Now, rotate the box to a different side (either smaller or larger) and push it again. It will take the same amount! This is because the friction is exactly the same.


The reason the BBKs can be smaller but work better is because they are far more efficient at bleeding off the heat than an OEM rotor. They're able to do this because the cooling veins are more efficient, more plentiful, spaced better, etc. Also, it's a true two-piece rotor.

St40 I assume also have more contact area on the pads than stock right? So more clamping strength and two additional pistons.

I just today that st40 are now $1700.

[///Mobbin]

Originally Posted by M3 Number 86

St40 I assume also have more contact area on the pads than stock right? So more clamping strength and two additional pistons.

I just today that st40 are now $1700.

For that price I might have to pick up a rear set!

[gan1hck]

I've been looking at Turner's site.

I'm going have to call them and ask, but the pricing is seems very variable.

Just changing the color changes the price by almost 500 dollars????

[roastbeef]

Originally Posted by dparm

Larger rotors do not mean better stopping. Friction and surface area are not related. Between two rotors, all else being equal, the larger diameter rotor will stop better because it has more MASS to dissipate the heat, not because the friction surface is larger.

The concept of friction and surface area being unrelated is tough for people to grasp. Here's an easy way to prove it: take a non-square box and put a bunch of stuff in it. Try pushing the box across the floor and feel how much effort it takes. Now, rotate the box to a different side (either smaller or larger) and push it again. It will take the same amount! This is because the friction is exactly the same.


The reason the BBKs can be smaller but work better is because they are far more efficient at bleeding off the heat than an OEM rotor. They're able to do this because the cooling veins are more efficient, more plentiful, spaced better, etc. Also, it's a true two-piece rotor.

this.

op, scroll past the product on this site to view a pretty thorough info blog on brakes. it sort of explains how they can get away with using a smaller rotor. (not stoptech, but the concept is the same)
https://www.essexparts.com/essex-des...p5060355mm-e92

[M3 Number 86]

Originally Posted by gan1hck

I've been looking at Turner's site.

I'm going have to call them and ask, but the pricing is seems very variable.

Just changing the color changes the price by almost 500 dollars????

Well it is an extra step or a "custom" build but black works just as good as (enter color) lol

[///Mobbin]

Originally Posted by gan1hck

I've been looking at Turner's site.

I'm going have to call them and ask, but the pricing is seems very variable.

Just changing the color changes the price by almost 500 dollars????

Originally Posted by M3 Number 86

Well it is an extra step or a "custom" build but black works just as good as (enter color) lol

PM Joe at Trinity Autosport, purchased my ST-40 front kit from him for a great price, LINK.

[gan1hck]

thanks

[gan1hck]

Anyone know why there is such a huge variation in prices?

Bimmerworld has the identical kit of $2,900....That's $1,200 more than what Turner charges.

Am I missing something here?

[Richbot]

St40 front rotor is 35mm thick vs 30 stock. It's a larger rotor overall. A 355x32mm rotor is also the OEM front rotor used on the Viper for a number of years which is capable of achieving about 20mph more on a given straight than these cars.

[gan1hck]

Originally Posted by Richbot

St40 front rotor is 35mm thick vs 30 stock. It's a larger rotor overall. A 355x32mm rotor is also the OEM front rotor used on the Viper for a number of years which is capable of achieving about 20mph more on a given straight than these cars.

for some reason I thought that stock m3 rotors were 355 mm

[Richbot]

They're 360x30 front 350x24 rear

[dparm]

Originally Posted by gan1hck

Just changing the color changes the price by almost 500 dollars????

Silver, black, and red are all the same price. You are probably looking at a different kit (such as the larger ST60 or a Trophy).

I went for black because it never looks dirty and is stealthy. My only gripe is that the white StopTech logo has turned beige from the heat, haha.

[dparm]

Originally Posted by M3 Number 86

St40 I assume also have more contact area on the pads than stock right? So more clamping strength and two additional pistons.

Larger pads mean they can take more heat and will wear slower.

[gan1hck]

Originally Posted by dparm

Silver, black, and red are all the same price. You are probably looking at a different kit (such as the larger ST60 or a Trophy).

I went for black because it never looks dirty and is stealthy. My only gripe is that the white StopTech logo has turned beige from the heat, haha.

They had one Trophy rear kit left for $1,700....discounted...that's what I was seeing.