Rear Brake Upgrades. Is bigger really better?
by James Walker, Jr. of scR motorsports
One of the most common questions received from new owners of our front bracken upgrade kits is “ Do I now need to upgrade my rear brakes excessively ? ” To answer this, we need to look at the character of the rise braking system from a few different perspectives. The answer may surprise you, specially hearing this from a company that sells adult brake upgrades !
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REAR BRAKE 101
One of the many purpose factors that goes into the development of a base brake system is the cryptic “ bias “ or “ libra. ” truth be told, it ‘s a pretty elementary concept to grasp : for vehicle constancy under brake, it is required that the rear brakes do NOT lock before the front brakes. Simple, right ? Most of you probably knew that already .
OK, so what governs the ‘lock up ‘ point of the rear brakes ? Drum roll, please :
1. tire tractive capability ( clash )
2. run down convention force ( weight on the tire )
This can be proven from looking that the fundamental relationship for maximal sustainable bore effect : F=µN, where :
F = the lock up point, or extremum force
µ = tire-road coefficient of clash
N = normal load sitting on the tire
then, when the OEM is designing a brake system, they ‘size ‘ the arrangement components ( calipers, dominate cylinder, rotor OD, etc. ) to generate the proper come of torsion at both ends of the fomite so that the battlefront brake storm ( ‘F ‘ above ) exceeds its flower traction first. At this indicate, the front brakes lock and the cable car slides in a decent, stable directly trace. ( note that at STOPTECH, we design our movement brake upgrade kits in the very lapp fashion for the very lapp reasons. )
POTENTIAL IMPACTS OF BIG FRONT BRAKES
fortunately ( from a safety point of view anyhow ), when most big-brake suppliers adapt a mondo rotor and caliper software to a fomite, they end up actually increasing the FRONT bias. How ? By increasing the effective caliper piston area and the rotor effective radius, these two factors work together to increase the ‘mechanical gain ‘ of the front brakes, building more torsion for the same pressure, everything else being equal. so, from a bias perspective we are not pushing the vehicle toward instability, but preferably barely the opposite – we are underbraking the rise axle ! The obvious impact would be an increase in stopping distance – probably the one thing the newly owner was actually hoping to reduce. Ironic. so, say you chose to install these big brakes on the front axle but want to maintain the OEM bias. What ‘s the answer ? Well, one way would be to invest in big buttocks brakes besides which increase the rear mechanical addition to the luff that the system is balanced once again .
SO, WHAT’S THE HARM IN DOING THAT?
well, let ‘s look at why we upgraded the front brakes in the first place. contrary to popular impression, the real number argue sports- and race cars use big brakes is to deal with heat. Period. There has been a crowd of stuff published which will disclaim this, but when you look at the braking system from a design point of view, making them ‘bigger ‘ does n’t basically do anything for stopping distance. It ‘s all about the heat. indeed, you upgraded the front brakes because of thermal concerns but as a hidden surprise got a careen in brake bias. As a band-aid to this circumstance, you now spend thousands more on a rear bracken upgrade because the battlefront system was not sized correctly in the first place. certain, it looks capital, but there is another option …
When upgrading your presence brakes, it is possible to size the caliper pistons and rotor effective radius to maintain the original brake organization ‘s pressure-torque relationship. Yea, it takes more engineer know-how and you ca n’t sell the lapp share to everyone anymore, but you are not altering the basis brake balance from what the OEM intended. This design doctrine stands behind every bracken ascent kit STOPTECH manufactures. now, if you sized the front brakes correctly, why would you need to change the buttocks brakes ? good question. If there are no thermal concerns with the rear brakes ( and on a front-engine street car there rarely are ) then by installing a rise big-brake kit all you are doing is ( a ) spend money and ( boron ) adding unsprung weight. This is not normally viewed as favorable, unless you like driving a heavy, expensive car .
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OH YEA – ONE MORE THING…
finally, under an OEM bias condition, the rise brakes alone lend about 15-20 % of all the braking wedge the vehicle generates, and when you install awkward tires you actually DECREASE the amount of work they need to do. Why ? Because at the higher deceleration levels afforded by slipstream tires, there is more weight transfer taking place, reducing the normal force on the rear tires and increasing it on the front ( remember F=µN from above ? ). If anything, we now want to decrease the raise effectiveness. Ironic once again.
Of naturally, if you decide to upsize your rear brake system components you can besides impact the front-rear torsion relationship, and consequently you can “ bias ” the “ balance ” more toward the rise. Go besides far, and the rise brakes could lock before the fronts. Again, not the end result you were expecting, right ?
It has been said that “ The folks at STOPTECH should consider developing a buttocks kit out to match their battlefront frame-up. They ‘ll be identical happy with the performance improvement if done properly. ” well, since our FRONT systems are designed by rights, we save you the need to spend your money on the back axle .
Let ‘s paraphrase that quote to reflect the STOPTECH doctrine : “ Our competitors should consider developing a FRONT kit to match their stock bias circumstance. They ‘ll be very felicitous with the performance improvement if done by rights, AND will save their customers the monetary value of a buttocks brake upgrade in the march. ”