I think the answer is no b/c there is either not enough clearance and/or the brakes are physically different.

But does anyone know if you can put the optional R Performance red brake calipers on an XF Supercharged?

 

The calipers are painted. You can have your stock calipers painted red which would be cheaper.

The R calipers should also fit though why you would want to add them is a mystery. The brake rotors on the R may be larger and the pads would then not be optimized for the SC disc size.

Braking performance is mainly affected by the tires anyway. Larger brakes and calipers cannot improve stopping performance except in extreme conditions where heat is the issue. The bigger brakes will feel different but unless you are not already at the limit of the tire performance your bigger brakes will not improve braking.

 

Are you saying I have no increase in stopping distance with the Alcon calipers & 410mm rotors that I now have over the stock brakes fitted to my 2000 XKR ? If that were the case why don't cars come with small inexpensive brakes & big wide tires ?? That would be much cheaper.

 

Heat. The kinetic energy of the car is transformed into heat by the friction of the pads against the rotors. Smaller or even undersized rotors/pads might stop the car once or maybe a few times, but then would be too hot to be effective. They would fade and possibly boil the brake fluid. And btw, I know what you're saying, but when it comes to brakes, "decrease" in stopping distance is what you want, not "increase"! For brakes that are already sufficient, going bigger might result in shorter stopping distances, but more likely the advantage is repeated stops with no fade or increase in stopping distances, as the bigger rotors and pads can absorb and dissipate more heat.

 

If ABS can be engaged on dry pavement then you need stickier tires before you bother with "bigger" brakes.

Yes, I am saying you wasted your money buying "bigger" brakes for the XKR. Unless, as I say, you were routinely unable to engage the ABS on dry pavement.

Heat is not a problem for modern all disc equipped road cars. No decently engineered road car suffers from brake fade. If you track the car it would be more effective to put track biased pads on for the track session than to put bigger brakes on.

And cars that are designed solely from an engineering perspective for performance use on the road do not have big brakes or big rims or extremely low profile tires. None of those things is useful for fast road driving. Marketing men and the suppliers of brakes, wheels and tires are all laughing all the way to the bank.....

 

I respectfully disagree. Track biased pads help, but can only do so much (they have a higher MOT, so can continue to perform at elevated temps). In track driving (been there, done that, but not with my XFR ... yet), the heavy repeated use can use up the ability of the brakes to absorb and dissipate enough heat to keep the pads from exceeding their MOT and/or boiling the fluid. That's what big brake kits are for. I agree that big brake kits don't necessarily stop the car in any shorter distance. Read here for interesting info: StopTech : Balanced Brake Upgrades

 

Jagular I have to ask why if the size of the brakes make no difference then why is it that cars are not fitted with small brakes & large tires? It seems like high performance cars are fitted with larger brakes not smaller. Are you saying that bigger brakes are for show only? I wonder at times what qualifies you as such an expert on these cars.

 

I am no expert but I do read a lot of expert stuff. Some of what I say is just physics and not a matter of opinion.

Manufacturers will try to fit the cheapest brakes that will do the job. If buyers think bigger brakes are better then manufacturers will fit bigger brakes than are necessary and charge accordingly.

F1 cars have to use tiny brakes because wheel size is regulated, which is why the tires are still so tall. The tires are in fact 90% of the suspension on an F1 car (and 100% on a Kart).

As for peak temperatures boiling the brake fluid then the solution is to install higher temperature brake fluid, if possible. However, I do agree that if tracking the car raises the brake temperature to fluid boiling levels the pads are not relevant, you need bigger rotors to hold the heat without raising the temperature to fluid boiling point. That's just simple physics. It is also a reason not to track the road car, rather than modify it for track use but, people are odd. Buy a track car if you are really serious about track.

Why anyone would use that criterion to select brakes for his road car is beyond me. Road cars make craptastic track cars for very good engineering reasons. Good track cars are absolutely hopeless for ordinary road use.

For road cars you need "appropriate" sized calipers and rotors equipped with relatively soft pads. Period. Oh, yes, and "big tires" do not necessarily stop better than regular sized tires. Lower profile tires do not brake better than taller tires, they corner better. Bigger tires often corner less well than stock sized tires, it depends on a anumber of factors, suspesnion geometry being most important.

The grip available at the contact patch is not affected by tire profile. Grip is a function of rubber compound. Period. Tire structure allows the grip to be exploited more effectively, with profile affecting cornering positively so long as the suspension geometry can handle it. Profile does not increase or decrease grip. Profile does not affect braking or acceleration in any meaningful way on a road car(there are effects from profile but lower profile isn't "better" for grip in braking or acceleration).

 

So far the comments have been interesting but one sided. I have installed a "big Brake" kit on one of my Volvos and the results contradict what is being said in this set of posts.

From a logic standpoint, braking is the function of applying friction in order to overcome motion. The larger the contact point between the two points the greater the friction and therefore the faster the reduction in movement. There is a point of diminishing returns however, putting 14" brakes on a 2000 lb car will not help it stop faster but putting them on a 5000 lb car would. Likewise upgrading the tire width to increase the contact area will reduce the tires tendency to loose traction.

Finally tire size. Low profile tires vs std profile etc. Come on guys it is not all about looks. Do your research about the need to reduce the amount of unsprung weight. Alum. or Mag wheels are a lot lighter that the rubber in the respective tire. If a tire has a rolling profile compatible with a 20" tire, you could reduce its weight by half or more by using low profile tires and light rims.

 

I don't know how one can say bigger brakes won't improve stopping distance. That's a very false statement to make.

The stopping power difference between 2010 premium XF and 09 premium is night and day due the larger brakes on the 2010 premium. It's so much better that it's not even comparable.

 

By the way, do you know why the F1 cars have small brakes and pads? They only weigh about 1300 lbs which is a far cry from the 4000+ of a XKR.

 

I have the XFR and attended the performance academy, where they beat the crap out of the cars. One of the interesting points was that there was little to no brake fade even after repeated extreme braking. Also, talking with the instructors that was one of the interesting things they found was that they would have expected fade but really never experienced any with these cars. Not sure how the XFR compares to SC models re brake set-up, but doubt that any upgrade over the XFR set up would bring any advantages.