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Here are some things to think about for those contemplating brakes and what is behind the R3 single rotor/2 piston caliper - vs. the R6 with dual rotors and 4 piston calipers.

First of all, braking is not about brakes on sport bikes, it's about how much deceleration force the front tire can resist. When the grip of the front tire is exceeded, the braking force becomes zero, (even the R3 single rotor brake can lock that up), so the single largest factor in braking performance is the tire. In this comparison, the R3 110/70 front tire is smaller in contact patch compared to the 120/70 R6 front tire. The 120 size tire with its greater width and larger circumference, producing about 5% more contact patch (depending on tire design - some may not even be that).

Stopping from 60mph (from tests) assumes that braking as at threshold level - meaning the max the front tire is able to stand:
The R3 with 200 lb rider weighs 256kg, stops in 40 meters, indicating a braking force of 2332.8N (the limit of the 110/70 front tire).
The R6 with 200lb rider weights 278kg, stops in 37.8 meters, indicating a braking force of 2641.1N (the limit of the 120/70 front tire).

Other bike tests with similar tire sizes are consistent with this outcome and braking force calculated.

If the R6 brakes and front tire were installed on an R3, stopping distance from 60mph would be reduced by 2.2 meters, or 7.2 feet. The greater mass and larger front tire contact patch produces a 13% shorter 60 to 0 braking distance. Since the rear brakes are the same for the R6 and R3, the contribution for this discussion is negligible. However, some of the added weight of the conversion (tire, wheel, forks, etc..) will eat into this gain to some degree.

At the max speed of the R3:
The R3 top speed of 112mph, would require 138 meters to stop using its 2332.8N of braking force
The R6 top speed of 112mph, would stop in 131 meters to stop using its 2641.1N of braking force

So, with the R6 brakes on the R3, stopping distance from 112mph would be reduced by 7 meters or 22 ft. The difference here is down to 5% between the two at this point - which is basically a factor of the difference in front tire contact patch difference.

At its 165mph top speed, the R6 has to deal with two additional factors. 1.) The extended stopping distance and 2.) the related time it takes to slow the machine down - which builds up brake heat exponentially. This requires greater braking surface area and piston area to dissipate the heat. At that speed, the R6 will take roughly 297 meters to stop, or 2.22 times the distance as it would take to stop from 112mph. This is a long way to go, for an extended period of time, so the brakes must be capable of managing that.

Since tire sizes have an impact on cornering, turn in, lean angles, etc.. the choice of a 110/70 for the R3 is ideal for producing a quick handling bike with less lean required than it would have with the larger front (and paired larger rear) tire. Further, the lighter front wheel and brake assembly is matched to the lower power (20% that of an R3), and somewhat lighter weight (most riders will not be 2000 pounds), the bike is designed to serve. All things considered, it appears that the R3 is delivering equitable performance, within the bounds of its design intent, to the R6 in terms of braking. The R6 simply has much greater braking demands made on it due to its higher top speed, thus, employs a larger front tire and larger total braking system.

The simplest path to increased braking performance on an R3 is to select the grippiest tires possible, preferable radial ply since they provide a wider contact area vs. bias ply.

While moving to a 4 piston caliper on the R3 is an available aftermarket mod, it appears that without increasing front tire (and rear to match) sizes, the gain will be negated by the front tires' grip limits, which the stock braking system is designed around. Since many race bikes utilize the stock brakes (with pads capable of managing increased heat), it appears the stock system is adequate in track use as well. This is predicated by the top speed limit of the bike and reduced weight when trimmed for race use, coupled to use of slicks or other high grip rubber.
 

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2018 R3, 1996 GSXR 750
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Here are some things to think about for those contemplating brakes and what is behind the R3 single rotor/2 piston caliper - vs. the R6 with dual rotors and 4 piston calipers.

First of all, braking is not about brakes on sport bikes, it's about how much deceleration force the front tire can resist. When the grip of the front tire is exceeded, the braking force becomes zero, (even the R3 single rotor brake can lock that up), so the single largest factor in braking performance is the tire. In this comparison, the R3 110/70 front tire is smaller in contact patch compared to the 120/70 R6 front tire. The 120 size tire with its greater width and larger circumference, producing about 5% more contact patch (depending on tire design - some may not even be that).

Stopping from 60mph (from tests) assumes that braking as at threshold level - meaning the max the front tire is able to stand:
The R3 with 200 lb rider weighs 256kg, stops in 40 meters, indicating a braking force of 2332.8N (the limit of the 110/70 front tire).
The R6 with 200lb rider weights 278kg, stops in 37.8 meters, indicating a braking force of 2641.1N (the limit of the 120/70 front tire).

Other bike tests with similar tire sizes are consistent with this outcome and braking force calculated.

If the R6 brakes and front tire were installed on an R3, stopping distance from 60mph would be reduced by 2.2 meters, or 7.2 feet. The greater mass and larger front tire contact patch produces a 13% shorter 60 to 0 braking distance. Since the rear brakes are the same for the R6 and R3, the contribution for this discussion is negligible. However, some of the added weight of the conversion (tire, wheel, forks, etc..) will eat into this gain to some degree.

At the max speed of the R3:
The R3 top speed of 112mph, would require 138 meters to stop using its 2332.8N of braking force
The R6 top speed of 112mph, would stop in 131 meters to stop using its 2641.1N of braking force

So, with the R6 brakes on the R3, stopping distance from 112mph would be reduced by 7 meters or 22 ft. The difference here is down to 5% between the two at this point - which is basically a factor of the difference in front tire contact patch difference.

At its 165mph top speed, the R6 has to deal with two additional factors. 1.) The extended stopping distance and 2.) the related time it takes to slow the machine down - which builds up brake heat exponentially. This requires greater braking surface area and piston area to dissipate the heat. At that speed, the R6 will take roughly 297 meters to stop, or 2.22 times the distance as it would take to stop from 112mph. This is a long way to go, for an extended period of time, so the brakes must be capable of managing that.

Since tire sizes have an impact on cornering, turn in, lean angles, etc.. the choice of a 110/70 for the R3 is ideal for producing a quick handling bike with less lean required than it would have with the larger front (and paired larger rear) tire. Further, the lighter front wheel and brake assembly is matched to the lower power (20% that of an R3), and somewhat lighter weight (most riders will not be 2000 pounds), the bike is designed to serve. All things considered, it appears that the R3 is delivering equitable performance, within the bounds of its design intent, to the R6 in terms of braking. The R6 simply has much greater braking demands made on it due to its higher top speed, thus, employs a larger front tire and larger total braking system.

The simplest path to increased braking performance on an R3 is to select the grippiest tires possible, preferable radial ply since they provide a wider contact area vs. bias ply.

While moving to a 4 piston caliper on the R3 is an available aftermarket mod, it appears that without increasing front tire (and rear to match) sizes, the gain will be negated by the front tires' grip limits, which the stock braking system is designed around. Since many race bikes utilize the stock brakes (with pads capable of managing increased heat), it appears the stock system is adequate in track use as well. This is predicated by the top speed limit of the bike and reduced weight when trimmed for race use, coupled to use of slicks or other high grip rubber.
Thank you Kevin for putting this together. It's always helpful to quantify any potential gains. Your summary makes complete sense to me.
 

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With nicely warmed-up tires on pavement with good grip, another limiting factor is the unloading of the rear wheel (due to the braking torque trying to turn the entire bike forward, loading up the front tire and unloading the rear). When the rear wheel loading reaches zero, any further braking force will lift the rear wheel off the ground ... that's as hard as you can brake, no matter what further braking force your brakes could theoretically generate or how much further grip your tire has.
 
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