All calipers flex. Some more than others. Just seeing a caliper flex while bleeding doesn't mean much by itself. If it was flexing enough to cause uneven pad wear or odd breaking characteristics, then you are onto a potential reason for changing them out. Also, Wilwood (and most caliper manufacturers) has various different types of calipers - some more street oriented and some more track oriented. Each will behave differently in flex and other attributes.
Only stopping distance data I ever saw was from the prototype kits for the Stoptech BBK. Braking distances increased. But I never saw any data from the released versions of the BBK. I think it has to do with proportioning more than the brake kits themselves. On the newere cars no one is installing adjustable proprtioning valves so as the front/rear bias shifts, the rear brakes may not be doing as much as they can. For panic stops it's all up to the ABS system anyway so that's not as much of an issue. Personally, I'd be willing to give up a little distance via non-optimal proportioning if I eliminate the pucker factor of fading brakes at the end of a track session! Fade going into a sharp turn at the end of a high speed section is no fun at all! Matt
I know all calipers flex. But caliper flex should not be visible to the eye. The flex should be under HARD LOAD and fractions of an inch. If a caliper is flexing from bleeding the brakes then the structural integrity of the caliper is not very strong. From what I have seen Wilwood produces a limited number of calipers and merely changes the brackets to fit specific vehicles without giving consideration to caliper piston size. I can guarantee if you bleed the Brembo brakes or Stoptech brakes you will not see the caliper flex.
I believe that's due to newer cars having EBD (Electronic Brake-Force Distribution) which leaves room for some adjustments to the brake system. The point of a balanced brake system is for it to be properly proportioned. From brake torque values to rotor size to piston size.
That and even in cars without that they typically have a 4-channel ABS system that, while not as advanced, hinders the installation of a method to adjust the bias. I figure with EBD that the biasing is really taken care of in panic situations so maybe the increase in stopping distance is more from environmental and testing variables. Truthfully the limit to most vehicles stopping ability is the absolute grip of the tires. The most powerful brakes in the world won't do much good if only a tiny fraction of the force can be put to the pavement without causing a lockup.
I guess that's an explanation, not an excuse! Anyway, if one does some math it's not that hard to come up with a larger brake kit that maintains factory proportioning so should keep the braking distances minimized. It's just that no one does it. And FWIW, if you look through Wilwoods (or pretty much everyones) caliper catalogs, you'll find that there are a variety of calipers and for each caliper there is a mix of piston sizes available. A good brake person can go through the catalog and select the correct mix of piston sizes for a given caliper to get the right front rear bias for a given rotor diameter. Anyway, for street cars, most BBKs (even if they have floppy calipers) are overkill. Matt
I always knew your stopping distance is only as good as your tires. That's why I went with stock diameter slotted rotors and performance pads, ss lines, and high temp fluid when I had my brakes done years ago. My enemy was brake fade, not lack of braking power. The stock system was more than capable of locking the tires causing ABS to kick in. Since I don't track my car, the only time I've seen brake fade was after about 6 runs back and forth a twisty Appalachian road this past summer in an undisclosed location.
Why not? I don't really see a huge difference between squeezing the rotor at a stop while bleeding to squeezing the rotor at speed. The only difference is that the rotor is rotating - which is why you'll see pad taper on a caliper that is deflecting too much. Define limited? There are 13 different calipers for the front brakes here: Caliper You are probably correct about the StopTech calipers. They are known for having a caliper that flexes less than most. Its also bigger and heavier than most. I don't have any experience with Brembo calipers so no comment. There are some interesting articles in Race Car Engineering on brake caliper and brake system design. Ever read them? If not, do so. Its quite interesting. I'm not trying to bust your chops. Just posting my thoughts and some info and a difference of opinion to some of your comments.
I think a lot comes down to preference... One of the Koni Challenge racers I talked to preferred the regidity of the iron JCW caliper over the lighter aluminum calipers because of what he percieved as reduced flex. I'm sure it also comes down to the type of driving that is done as well. Matt
It may be reduced pad knock instead of perceived flex. Sliding calipers have less of a tendency to induce pad knock, from what I have learned. Still, I have a lot of respect for AP Racing and find it hard to believe it has more flex than the stock iron calipers. I have read through many technical papers regarding caliper design, and have also had the pleasure of talking to master technicians at Brembo, Endless, and Project Mu. The difference between squeezing the rotor at a stop and while it's rotating is everything when it comes to caliper flex. Think about the amount of rotating mass the caliper has to stop while the rotor is in motion. Essentially the rotor will try to move the caliper from it's bolted position, and the fight that goes on between caliper and rotor in this sense is called caliper flex. The bridge in the caliper has to maintain it's rigidity so the caliper can maintain pedal feel and stopping power. While they make many different style calipers, if you look through them you'll find that the piston sizings are similar on almost every one. The difference being one design may be standard bore and the other being differential bore.
right on the moving vs stopped but with three piston sizes, and multiple pistons per caliper, that's a huge number of combinations. They all do it that way, some with more and some with less, but they all step through a range of piston sizes. It just doesn't make sense economically to do it any differently. Rotor diameters are all over the place, pretty much a continuum of diamterers. So you step through the piston sizes and the like to get the bias you want. What other way is there? I went to the brembo site. You have to get into the race calipers, then they do have a larger range of piston sizes.. Starts at about 24mm diameter up to 44mm diamter, but some are skipped, it's not every 2 mm. I think there are about 8 sizes. If you do select kits for the Mini, I didn't even see the piston size listed! Matt
I understand what you are trying to say, but the idea that Brembo and Stoptech actually manufacture kits based on the OEM bias with a caliper that minimizes flex is a lot more than what I can say for Wilwood. I've heard a lot of good things from people that have owned Wilwood brakes, but then I have heard the other side from people who have switched from Wilwood to a different name brand. This goes back my original comment about caliper flex. It's not too common for manufacturer's to post piston sizing of their calipers, I guess you can chalk it up to "intellectual property." But then again I guess that's where the price comes into play. The money spent on research and development for a vehicle versus leaving it to the customer to determine whether or not they are happy with what they purchased. Since the public doesn't actually do any testing for stopping distance it's easy to produce a kit with an oversized rotor and call it a a big brake upgrade kit.
This relates to something that came up in another conversation about suspenion stuff. it's easier to sell someone what they want than to educate them about what they really need. But really, most assume that brake kit providers know something about what they're doing, and will take care of these types of details. Matt
FWIW, most people won't understand piston sizes. I know I didn't until a bunch of us RX7 guys worked with RacingBrake.com to build a custom 4 corner BBK for our cars. Listing that info as part of the marketing material is immaterial for most people and will probably just wind up confusing the issue and would require them to try and educate people as Dr. O said. Some people won't understand no matter what so they'll just waste time educating. StopTech is one of the only companies that actually do on car testing of their BBK adjusting piston sizes based upon the results of their tests. Most companies that offer BB kits do the math and and some research and call it done. That is the main problem I have with most after market brake kits. Most will tell you piston sizes when asked - in my experience researching brake kits. In the end, the results and budget are what matter for the given application/goal. If a Wilwood does the job in one's application, goodie. If not, move onto something else.
Guess I should have stopped by sooner....Please allow me to clear up some confusion and misconceptions in this thread. 1. The two piece hat and rotor kit is not a Wilwood product. It's a TCE product only. Rotors can be replaced for about $100ea btw. They are not limited to TCE hats however and can be had with Wilwood matching style hats upon request. 2. The rear kit at 11.75" is intended to compliment the TCE 13" front kits. They have been shared with some Wilwood 12.2" kits at time also however I do not push them here nor do I believe they should be paired with an 11.75" front kit ever. 3. The intent of the rear kit is both visual and functional. You can get the visual I'm sure. The functional is both proper brake balance (when paired with the 13") and the added MASS of the rear rotor (the friction surface, as the total weight is probably a wash) for track use. The car when used on track see elevated rear temps that have been shown to cause the rear calipers to run hot and both boil fluid as well as overheat pads. The larger rotor offers a greater efficiency in that regard and allows the pads and caliper to run cooler and lessen the need for high temp track worthy pads to keep up. Tested? Hard data; no. But with many, many, and a few more 13" kits in service with and without this rear design it's been found that even running oe pads on the 11.75 rear has proven more effective than high-zoot pads on a stock rotor. 4. Pad wear, bias and torque. A reduction in pad wear for Nathan would tell me that the removal of this has reduced the effectiveness on the rears and placed greater duty on the fronts. That being said, the fit of the 11.75 with another suppliers front kit can bring into question how these kits functioned with one another. From outward appearances the results were an excessive amount of rear brake wear leading me to believe that there were balance issues that were not correct. This does not make one set up better or worse than the other- like running two brands of injectors perhaps; both are good when fit with their mates in a full and proper set up. 5. While I have no real issues with other brands, I've been a Wilwood dealer for over 17yrs and seen a vast assortment of product in service by both them and other builder such as myself. I'll easily give a positive nod to ST for the claimed stiffness of their calipers- but don't overlook the massive nature, both weight and wheel fit required based upon the caliper size and rotor size used. I'll certainly agree that the smaller, lighter and more compact the caliper the more prone to flex and distortion will be evident. Regardless somewhere in the middle is where the sweet spot is for many. Remember to chalk a certain amount of what you read and hear up to marketing before drawing too many conclusions...any company's primary goal is to sell product. (even me! lol)