17s with 13" brakes or 18s with 14" brakes, is there a benefit in stopping power?

[Henesian]

I've been pondering this for a while. There are better combinations of 17" rim tire sizes than there are of 18" rim tire sizes. The only reason that I can see to going to 18" rims is for the look and 14" brakes over 13" brakes infront.

Is there any performance benefit from the 14" brakes over the 13" brakes, if you take into account the weight increase from the upsize? Or is it just for looks?

The price difference for the brakes is very minimal.

[rjsjea]

I'm not sure there are more 17" tires available over 18"s..........example is the popular Michelin PS2's. Bunch more 18's available than 17's

A whole bunch more billet 2/3 pc wheels available in 18"s.....

[clancj]

many more options in 18" tires/size over 17".

[Derek69SS]

Tire options are better in 18" but they're also more expensive.

I like 17s, but fear they'll be obsolete in a few years.

As for the brake size thing, be honest with yourself... will you ever overheat 13" brakes with track-pads?

[ProdigyCustoms]

Derek started to touch on this with the heat question. A 14 will take longer to heat up then a 13. Realistically a 14" brake MIGHT just add to the MOI (moment of inertia) by making the rotor more heavy / larger diameter. So in reality the brake caliper has to work harder to stop more weight. So technically by going from 17s / 13s to 18s /14s raises the MOI significantly, so braking MIGHT be poorer with the bigger brake kit. Who'd a thunk it?

So why 14s? Because there is more surface area and they take longer to heat up. And they look badd ass.

So unless your running the 24 hours of Daytona, do you need 14s? No.

[ROBS6T8]

Tire options are better in 18" but they're also more expensive.

I like 17s, but fear they'll be obsolete in a few years.

As for the brake size thing, be honest with yourself... will you ever overheat 13" brakes with track-pads?

I fear the same thing! Hopefully I'll be tired of my Rushforth 17's in a few years. Not!!

[DarkoNova]

I wouldn't worry about 17's becoming obsolete.

Look at old BMW CCA racing that restricts tire size to the OEM 14" wheels. There's still plenty of rubber to choose from in that size.

[Derek69SS]

Derek started to touch on this with the heat question. A 14 will take longer to heat up then a 13. Realistically a 14" brake MIGHT just add to the MOI (moment of inertia) by making the rotor more heavy / larger diameter. So in reality the brake caliper has to work harder to stop more weight. So technically by going from 17s / 13s to 18s /14s raises the MOI significantly, so braking MIGHT be poorer with the bigger brake kit. Who'd a thunk it?

So why 14s? Because there is more surface area and they take longer to heat up. And they look badd ass.

So unless your running the 24 hours of Daytona, do you need 14s? No.
I think the mechanical advantage of the caliper being farther from the axle center-line would offset any MOI drawback of larger brakes... but that is still rotating/unsprung weight that will have negative effects on acceleration and handling.


I wouldn't worry about 17's becoming obsolete.

Look at old BMW CCA racing that restricts tire size to the OEM 14" wheels. There's still plenty of rubber to choose from in that size.
Classing restrictions will be what keeps GOOD 17" tires around... Unfortunately, most of them will be 265mm and narrower for SCCA STX class.

[aronhk_md]

[QUOTE=Derek69SS;762054]I think the mechanical advantage of the caliper being farther from the axle center-line would offset any MOI drawback of larger brakes... but that is still rotating/unsprung weight that will have negative effects on acceleration and handling.

QUOTE]

I agree that having the caliper farther from center line outweighs any increase in MOI. Essentially just look at brake upgrades on a C6 vette versus C5. Any time the factory manages to put a larger rotor with the same caliper the net result is faster stopping AND less heat. I imagine too that while a larger wheel weighs a bit more and the MOI is increased due to mass a bit farther out...the tire weighs a drop less because almost invariably a lower profile is used. Dont know what that adds up to though :enguard:

Either way, I'll take the 18 inch wheels with 14 inch brakes over 17's and 13's.

[JRouche]

Is there any performance benefit from the 14" brakes over the 13" brakes,

Not that you will notice unless you are tracking the car regularly and stay on top of the pad changes.

Brake pads WILL show a difference. The rotor size is minor when you are talking about 13 and 14 rotors. Not to mention how the rotors are used. Solid rotor and hat, cast unit? Separate rotor and hat? Size doesent mean ANYTHING!!

The type of brakes mean more. Even more important are the calipers. Single sided calipers, where the pads are forced together with the force of one side (sliding caliper) are less efficient. A decent caliper that forces the pads on both sides of the rotor with hydraulic pressure is better IMO.

A 13" rotor with a superior caliper will out preform a 14" rotor braking system that uses a sliding caliper and stock type calipers.

And toss in some really nice pads and you will be able to control your brakes from full lock up to a feathering of the brakes.

Larger rotors are nice when brake fade becomes an issue. I dont think most of the folks here have a problem with brake fade with their 13" rotors. If they do then its a brake pad problem, not a rotor size issue.

IMO 14" rotors are over kill and a source of unsprung weight, specially if they are a cast hub and rotor. Talk about some weight, thats a heavy unit.

I like an aluminum hat with a bolted on rotor. No reason the hat or hub needs to be cast iron, its just heavy. But its expensive to make a separate a cast rotor that will mount to various hats or hubs. Not so much the cast rotor, but the aluminum hat.

And Id like to see how many of the major castings of rotors integrated with the hubs are out of china. Bet its a large portion. Im talking about the after market products. Cast in china and maybe shipped out here for final machine work. Maybe not even that. Cast and machined in china. Wouldnt surprise me.

A large cast iron rotor is a lil excessive. And if its a cast iron rotor and hat!! Big time excessive. Ive put them on the scale. Some major weight there. JR

[Bryce]

Ok increase in MOI form 13" to 14" brake. everything else is equal, same thickness and material and internal venting, is 25%

Increase in torque form 13" to 14", assuming same clamping force from the caliper is 7.2%

Draw your own conclusions.

[Derek69SS]

Ok increase in MOI form 13" to 14" brake. everything else is equal, same thickness and material and internal venting, is 25%

Increase in torque form 13" to 14", assuming same clamping force from the caliper is 7.2%

Draw your own conclusions.

25% increase in the weight of the rotors alone, vs 7.2% mechanical advantage in braking the weight of the WHOLE CAR. I know which one I'd choose.

[aronhk_md]

25% increase in the weight of the rotors alone, vs 7.2% mechanical advantage in braking the weight of the WHOLE CAR. I know which one I'd choose.

Hmmmm.....I agree with Derek. If your rotors weighed 5lb in a 13, and then 6.25lb in a 14, but you net a 7.2% mechanical advantage in braking a 3500-4000 lb car....I also know I'd choose the larger brakes. Obviously not talking cast rotors here.....and the weight was just an imagined one, but still.

[SIK02SS]

Derek started to touch on this with the heat question. A 14 will take longer to heat up then a 13. Realistically a 14" brake MIGHT just add to the MOI (moment of inertia) by making the rotor more heavy / larger diameter. So in reality the brake caliper has to work harder to stop more weight. So technically by going from 17s / 13s to 18s /14s raises the MOI significantly, so braking MIGHT be poorer with the bigger brake kit. Who'd a thunk it?

So why 14s? Because there is more surface area and they take longer to heat up. And they look badd ass.

So unless your running the 24 hours of Daytona, do you need 14s? No.

Listen to this man. Only way a 14" rotor setup is better than a 13" rotor setup, is if the caliper on the 14" is itself different and better than what's on the 13". Besides, no one wants their over sized brakes slowing them down as a result due to more unsprung weight with rotational mass :)

[SIK02SS]

[QUOTE=Derek69SS;762054]I think the mechanical advantage of the caliper being farther from the axle center-line would offset any MOI drawback of larger brakes... but that is still rotating/unsprung weight that will have negative effects on acceleration and handling.

QUOTE]

I agree that having the caliper farther from center line outweighs any increase in MOI. Essentially just look at brake upgrades on a C6 vette versus C5. Any time the factory manages to put a larger rotor with the same caliper the net result is faster stopping AND less heat. I imagine too that while a larger wheel weighs a bit more and the MOI is increased due to mass a bit farther out...the tire weighs a drop less because almost invariably a lower profile is used. Dont know what that adds up to though :enguard:

Either way, I'll take the 18 inch wheels with 14 inch brakes over 17's and 13's.

The C5 and C6 also have different calipers, the C6 being better..

[aronhk_md]

I disagree...lol. Frank is knowledgeable but not the wizard of performance. Type of caliper is important too. But taking the same piston/type caliper........as long as a cast hub/rotor is NOT being used, there isnt some huge increase in weight or MOI from going to a 14" rotor from 13". Nor is there much increase in unsprung weight. The major increase in unsprung weight is from having to use an 18" wheel over 17". And the increased mechanical advantage the caliper has on the rotor is considerable. Even a 5% increase would be considerable when you are talking about stopping a 4000lb car.

Yes, I know the calipers are different C6 to Z06......thats what I meant. Sorry for the confusion. C5-C6 is the same. But I was referring to the Kore brakes for example.......where one can choose the C6 brake AND caliper, or choose the C6 caliper with a Z06 rotor.

P.S. - I've driven the newer Z06. I dont really think the big wheels and big brakes slow it down or make it less responsive in any measureable way over the base C6. Not going to compare braking because I know its a different caliper.

[Derek69SS]

Way too many variables to say one is going to make you faster than the other.

Type of course:
Average autocross, even 13" brakes are overkill... I've made 30+ autocross runs in one day in 90+deg weather at a test-n-tune, and never experienced ANY fade in my C5 brakes. Tires got greasy, but brakes never faded. Advantage - Smaller brakes
Put the same car on a big roadcourse with some speed and some really heavy braking zones to get the rotor temps up... Advantage - Bigger brakes

Horsepower:
300hp car - MOI is really going to effect your acceleration. Advantage - smaller brakes.
600hp car - MOI isn't going to matter so much, you can only accelerate as much as the tires will let you anyway. Draw.

Weight of car:
1800lb Lotus - doesn't need big brakes and an increase in unsprung weight would be easily felt.
3700lb Chevelle - more weight to stop, and the weight increase would be a smaller percentage of its total weight, so it would be less noticeable.

As with any part of your suspension combination, it's all about sacrificing one aspect to gain in another, and balancing those sacrifices to get the best possible combination for your usage.

If all I have to do is stop, I want the biggest ones possible. :bananna2:

[aronhk_md]

Very well put Derek.......and well thought out. I do tend to think of things from my perspective. I will be seeing higher speeds than some, and I do have a heavier type car. Thanks for putting that out there....I think it does the most to really qualify why one might want the larger brakes.....or the smaller.

[SLO_Z28]

Autocrossing ive never even come close to fading out my 10 inch brakes, and my braking is tire limited. I am switching to a 12 inch setup with a SL4 caliper on a aluminum hat but thats mostly to lose weight while maintaining pad size and increasing PSA. Derek is dead on a few posts up, the reason my brakes work for me are correct pad choice and usage.

[ProdigyCustoms]

So in summary, 14" over 13", brake package MOI and unsprung weight rise slightly, slight mechanical advantage. 18" wheel and tire package, MOI of the wheel / tire package increases slightly, unsprung weight increases slightly, no mechanical advantage. In summary, probably a unmeasurable difference.

I call for a test! A magazine needs to do this. It would be really simple with Wilwoods. The 13" kit is converted to a 14" kit with a rotor and a couple caliper spacers, could be done in less then a hour. Get 2 sets of tires and wheels, same brand / style wheel / tire. Swap the rotors, tires. My bet is there are within feet of one another, if not inches.

Steve?

[aronhk_md]

To do a test properly one would need to have several kinds of cars. First would be the heavier higher horsepower vehicle. Next would be the heavy lower horsepower vehicle. Then you'd need at least one lighter type vehicle, but again, preferably 2.....one with higher, one with lower horsepower.

Then you'd need to run them over 2 kinds of test courses. A longer higher speed course, and a shorter lower speed course. This is to determine if the larger rotors, bigger wheels and increased MOI and unsprung weight really slow down a car.

Then you can do pure stopping distance tests to see if the larger rotor really gives greater stopping power.

If you only do a stopping distance test you are only testing part of the equation/theory. Same with vehicle type.

......theoretically as Derek pointed out a low weight vehicle like a Lotus might not get enough braking benefit to offset the larger percentage of unsprung weight it is carrying by going to a larger rotor. You might see this as some slight stopping advantage to larger rotors, but slower times around a course due to the extra weight.

On a heavier more powerful vehicle though as he pointed out the percentage of unsprung weight with the change is not as much. Acceleration on this vehicle might be barely affected, if at all, especially on a faster course where the increased mechanical advantage of the larger rotor allows one to maintain a higher speed longer before having to slow for a corner.

Theoretically that is.......

[Derek69SS]

A cool test for a magazine would be to do timed & data-logged 0-100-0 runs with each rotor size, several times back to back, using a pyrometer to take rotor temps after each run. It would also be cool to do the test using "street" and "track" pads

List the best 0-100 time and average G-force for each rotor size, then list separately the braking times

Brake size/pad type: run #, 100-0 time, average 100-0 G-force, and front rotor temps after stopping

Do 8-10 runs on each combination to show how rotor size effects heating, and how heat effects braking performance. It would really be cool to show people how street pads start strong and fall off quickly, and how track pads suck at first, and take a few runs to get enough heat in them to work well.

[aronhk_md]

That would be good Derek. But I would also like to see the lap times with different types of cars, on a short slow course and a higher speed course. After all, there is a group of people claiming the extra MOI and unsprung weight of larger wheels/rotors will be slower in general, and running it around a course along WITH a 0-100-0 run would tell the whole story.

[ProdigyCustoms]

Lets not forget this will take days and to be a true test the temperature, density altitude, barometric pressure, track temp, position of the sun, what the driver ate the night before must all be the same.

I guess what I am saying in being a smart ass is we are really over thinking all this and taking this beyond a reasonable "achievable" test. We are not building Space Shuttles, we are building Pro Touring cars that drive on the street and go to Goodguys autocross or a "Run To" event once in a while. This is not class racing professionally where 1000ths count. And in the end we all know the test results will be a almost unmeasurable difference.

Could someone find a 69 Camaro and do a easy brake test swapping a couple sets of wheels and brakes, probably. Can we get Obama to let us in on some of that loose money that builds bridges to no where to put 12 scientist on this, most likely not.

[High Plains Mopars]

Tire options are better in 18" but they're also more expensive.

I like 17s, but fear they'll be obsolete in a few years.

As for the brake size thing, be honest with yourself... will you ever overheat 13" brakes with track-pads?

If you pick out 17 sizes that were heavily used by OEMs, then tire selection will continue to be available for some time to come. I'd think that 255, 275, and 335 will be the larger sizes that will continue to be widely produced because they were used extensively on Camaros, Mustangs, Vettes, and Vipers. Selection among manufacturers may shrink, but the sizes will continue to be available.

[aronhk_md]

I agree......I was just trying to add to the "ideal" scenario. Its quite obvious that getting multiple cars to try these tests out most likely wont happen. BUT, its reasonable to expect that 1 car as you suggested could do more than just a stopping distance test. As Derek mentioned......a 0-100-0. This will tell if acceleration is really slowed by the extra weight and MOI, AND whether stopping distance was measurably decreased. Run it around a course 3 times before, and 3 times after the swap to get an average speed for course completion. This will tell you if the unsprung weight difference really slows the car's handling measurably. If its a decent course one could at least take a hand held IR thermometer and check disk temps after each run.

All of this is reasonable in a days testing.

[Derek69SS]

Testing as I described would be easy and repeatable enough to be reasonably scientific, and able to be done in an afternoon... Maybe 15 minutes of actual testing per combination, and a 30-45 minutes of work to swap parts and cool things down.

If I had a location to do the testing, and the parts to make it work I could pull off a test like that... a couple volunteers to record temps and spray tires to keep them consistent, and borrow a datalogger from any number of local autocrossers to record the rest... finding a location to do it safely would be the hard part.

Adding road-course/autocross laptimes into it would definitely not be repeatable enough IMHO... too many variables just in driver skill alone.

[Jim Nilsen]

Anyone wanting to try this out and pay for all the parts I am more than willing to try the test. I know my stock Z51 vette brakes are good but they can go bigger and the pads can be better.

The one thing that always gets me is that everyone always seems to think that all rotors weigh the same when they talk about going to larger diameter rotors. You can go to a larger diameter and go thinner and be less in weight or the same, you do lose the mass to transfer the heat but they should heat up slower disapate it faster if they are larger because of the same force in less rotations.

The whole part of the game is based on the wheels that fit over bigger brakes that look cool because there are really nice wheels to show them off.

[aronhk_md]

One fairly experienced driver is all it would take. 3 trials with each setup to account for issues on any one circuit. The reason being that if the times are fairly close then I think you can throw out the window the idea that increased unsprung weight is the huge factor that some say it is going from 17 to 18 with bigger brakes. Without some form of test for this.....only part of the question of 17 vs 18 is answered. People can decide for themselves afterwards if the road course portion is more qualitative than quantitative.

Your acceleration test takes care of part of the MOI question, and then the stopping test answers the rest of the MOI question and throws in the answers to whether the increased braking force overcomes any MOI concern.

Keep in mind the test vehicle needs to have tires BIG enough to theoretically take advantage of increased braking effort.

[SIK02SS]

I disagree...lol. Frank is knowledgeable but not the wizard of performance. Type of caliper is important too. But taking the same piston/type caliper........as long as a cast hub/rotor is NOT being used, there isnt some huge increase in weight or MOI from going to a 14" rotor from 13". Nor is there much increase in unsprung weight. The major increase in unsprung weight is from having to use an 18" wheel over 17". And the increased mechanical advantage the caliper has on the rotor is considerable. Even a 5% increase would be considerable when you are talking about stopping a 4000lb car.

Yes, I know the calipers are different C6 to Z06......thats what I meant. Sorry for the confusion. C5-C6 is the same. But I was referring to the Kore brakes for example.......where one can choose the C6 brake AND caliper, or choose the C6 caliper with a Z06 rotor.

P.S. - I've driven the newer Z06. I dont really think the big wheels and big brakes slow it down or make it less responsive in any measureable way over the base C6. Not going to compare braking because I know its a different caliper.

C5 and C6 calipers are different. The GS and Z06 calipers are useless junk..but better than the C5/C6 calipers.

For reference of why I agree with Frank, is that NASCAR Cup cars (among many other racecars) don't use the same size rotors for every track for good reason. Some tracks they need all the rotor they can fit to help with cooling since they are so hard on the brakes at those tracks (and the cars aren't light). Other tracks where brakes aren't used to that extent they drop to almost the smallest sized rotor they can fit. Why? because it's less weight and not needed. I've been through all these discussions with a brake engineer for my Corvette that I race. I could run a 14" front rotor, but have no need with the extra weight it adds vs. the 13" rotor I'm currently running (same rotor the Corvette C6R team and typically the top 5 Cup cars and many more use). But unless you're running a 12 hour + enduro race, the extra surface will not make a difference in stopping power/heat expulsion if using the same caliper (assuming it's a good caliper, not a factory C5/6/Z06 pos). The rotor doesn't give you the stopping power, the clamping force of the caliper and pads gives you the stopping power, the rotor just lets you do it over and over again by being both the friction source (along with your tires) and providing heat expulsion so as to not overheat the pads/calipers/fluid.

But hey, it's your money. I'm just trying to help :)

[aronhk_md]

As was mentioned above a larger rotor doesnt even necessarily weigh more, but lets say in this case we compare a light 13 with a light 14. The weight difference and MOI is not that large....especially when talking about a car near 4000 lbs as opposed to a 3400 lb nascar car. Also, that nascar car doesnt regularly scrub off speed from over 100 mph to take a curve that requires 40 mph or less. If as you said the brakes arent going to be used much.....SURE, why not use smaller brakes? That may apply to nascar cup races.

I never claimed a larger rotor gives you more stopping power. Its the mechanical advantage the caliper has being located further from center. Take the SAME caliper mounted on a 13....mount it outward another 1/2" (14" rotor) and the mechanical advantage is increased. This is a separate issue from the heat dissipation afforded by the larger rotor.

[SIK02SS]

So in summary, 14" over 13", brake package MOI and unsprung weight rise slightly, slight mechanical advantage. 18" wheel and tire package, MOI of the wheel / tire package increases slightly, unsprung weight increases slightly, no mechanical advantage. In summary, probably a unmeasurable difference.

I call for a test! A magazine needs to do this. It would be really simple with Wilwoods. The 13" kit is converted to a 14" kit with a rotor and a couple caliper spacers, could be done in less then a hour. Get 2 sets of tires and wheels, same brand / style wheel / tire. Swap the rotors, tires. My bet is there are within feet of one another, if not inches.

Steve?

I'll offer myself as driver :)

[SIK02SS]

As was mentioned above a larger rotor doesnt even necessarily weigh more, but lets say in this case we compare a light 13 with a light 14. The weight difference and MOI is not that large....especially when talking about a car near 4000 lbs as opposed to a 3400 lb nascar car. Also, that nascar car doesnt regularly scrub off speed from over 100 mph to take a curve that requires 40 mph or less. If as you said the brakes arent going to be used much.....SURE, why not use smaller brakes? That may apply to nascar cup races.

I never claimed a larger rotor gives you more stopping power. Its the mechanical advantage the caliper has being located further from center. Take the SAME caliper mounted on a 13....mount it outward another 1/2" (14" rotor) and the mechanical advantage is increased. This is a separate issue from the heat dissipation afforded by the larger rotor.

Okay, then here's some more to think about:

Did you ever play with a gyroscope when you were a kid? The bigger the gyro the harder it is to control.
Unsprung weight IS an issue but rotating unsprung weight is a bigger issue. Add to that, the further out in the radius that weight is the more it adds to the gyro effect! Rotor mass can be good but you want to keep it as close to the rotational axis as possible. Hence the 5 1/2" dual and triple disc clutches. The leverage difference between a 13 and 14" rotor isn't worth any of the other trade-offs...unless you are endurance racing. Again, I don't think you would gain any stopping performance from a 14" rotor over the 13 rotor. BUT you will lose some very important things that will have a noticeable affect on the cars handling. At least 6lbs increase in unsprung AND rotating mass. A 1" difference in diameter is a big difference weight wise no matter how you look at it. This goes for cast 1 piece rotors and 2 piece full floating rotors.

Fuel to the fire? :D

The reason I mentioned stopping power above is yours and others concerns is looking for being able to stop. Figured I'd break down what stopping power is really from.
Increased gyro effect which will affect steering feel and turn in precision.

[Bryce]

Ok increase in MOI form 13" to 14" brake. everything else is equal, same thickness and material and internal venting, is 25%

Increase in torque form 13" to 14", assuming same clamping force from the caliper is 7.2%

Draw your own conclusions.


Just to reemphasize the numbers behind the discussion

[aronhk_md]

I understand physics quite well, and the gyro effect you are referring to I am aware of, however the steering geometry used in our cars makes it difficult to notice, and our wheels are not spinning at 10,000 rpm. Again......go from a C6 to a Z06 vette and you are not going to notice some strange new feel to the steering because the rotors are bigger. You also arent going to notice the slight increase in unsprung weight.

But if you used the same caliper on the car with first 13" rotors and then 14" rotors......you are going to notice an increase in stopping power. A 1" increase is a BIG increase in stopping power.

Again, we'd need to see test results to lay this issue to rest.

[SIK02SS]

I disagree :) Changing cars is an apples to oranges comparison and won't show you anything the way you are comparing them (C6 has different rotors, calipers, wheel sizes, tires, shocks, springs, curb weight, etc from a C6Z). There's no way to accurately measure anything related to rotor sizes unless you're trying to get an average..but even then prep levels can vary. If someone wants to buy me a set of AP racing full floating 14" rotors from HardbarUSA I'd be more than happy to give an apples to apples comparison and track results with data aquisition :)

Hell, I could apply some of my data aq onto my '67 and I have a wilwood setup with 13" rotors, again if 14" are provided (I'm pretty sure I have the space under my 17s) I can test both cars, same track, same day.

[aronhk_md]

There are differences between the C6 and Z06 I agree.....but if you look at the parts that contribute to unsprung weight and MOI I would almost guarantee the Z06 is heavier in both cases with greater MOI. The steering geometry is the same, and as mentioned it does not have a heavier feel, nor does it take more time to "turn in". Curb weight is not that different, and springs/shocks affect the "gyro" effect and MOI little, if at all. Not really an apples to oranges comparison........but I agree, not as close as we could get with 1 car and a change of wheels/rotor.

So I think it would be great if some magazine funded ALL the PT guys to try both on their cars! lol

[SIK02SS]

There are differences between the C6 and Z06 I agree.....but if you look at the parts that contribute to unsprung weight and MOI I would almost guarantee the Z06 is heavier in both cases with greater MOI. The steering geometry is the same, and as mentioned it does not have a heavier feel, nor does it take more time to "turn in". Curb weight is not that different, and springs/shocks affect the "gyro" effect and MOI little, if at all. Not really an apples to oranges comparison........but I agree, not as close as we could get with 1 car and a change of wheels/rotor.

So I think it would be great if some magazine funded ALL the PT guys to try both on their cars! lol

Similar yes, but still too many differences that will affect a direct comparison :)

Where's Steve!!!?? :lol:

[Cannon]

If you guys are looking to save in weight on ur street car, there are much better places to save than brakes! I wouldnt even bother thinking of what is going to be better in performance in brakes, because they will be so close if u get the same kind of caliper/pads, that it wont matter. What you should be looking at is what tire/wheel sizes, choices, and pricing are going to be best for you and then let that make the decision on brakes.

[aronhk_md]

Its not just weight thats a concern here. Its unsprung weight, which CAN affect handling to a great degree. And the further out that weight is on the spinning assemble affects MOI. But I agree in that the weight of a 14" rotor vs a 13" rotor is minimal, especially when you add the increased braking force into the equation. :smoke:

Oh, and these arent just street cars......if they were we'd be more concerned with whether the calipers were chromed or powder coated. LOL