Racing stuff-rear mounting front brake calipers
01-11-2018, 12:05 PM
#41
Team Owner
TC: There was an extensive discussion on this subject a while back. The Wilwoods have the same piston area as the stock system so the brake proportionality is limited. You can't dial in more rear pressure with a proportioning valve, best you could do is manage the front pressure which isn't ideal
PopChevy: Since you are so adept with brackets and such, and your car is a work in process, you might want to think about how you can maximize the braking. The rears typically wouldn't ever lock up on my car (and others) no matter what. One way is different compounds front and rear and I gave that some thought but decided that the time constants would never hold over the operating temperature range. In the end, I fab'd some new brackets and mounted a set of 4 piston fronts (same area as the 6 piston fronts) on the rear, with a proportioning valve. Obviously you never want the rears to lock up first. PaulDana had a different solution with his proportioning valve setup. Take a look at that as well.
PopChevy: Since you are so adept with brackets and such, and your car is a work in process, you might want to think about how you can maximize the braking. The rears typically wouldn't ever lock up on my car (and others) no matter what. One way is different compounds front and rear and I gave that some thought but decided that the time constants would never hold over the operating temperature range. In the end, I fab'd some new brackets and mounted a set of 4 piston fronts (same area as the 6 piston fronts) on the rear, with a proportioning valve. Obviously you never want the rears to lock up first. PaulDana had a different solution with his proportioning valve setup. Take a look at that as well.
No! But I think most here understand the proportioning valve!!!! They do not increase rear brake pressure! What they can do is allow maximum brake pressure of what the system is capable of to that max, or you limit it downward to less from the max, so the rears have less effect, biased to the strength of the front system! Most racers tend to lessen the back, and that gives them better modulation and sensitivity to concentrate on the fronts to dance just enough to pull it down from speed without lockup! That though causes the nose to plow as weight is transferred forward! I rather have max braking and modulate both ends! In testing or evaluation of a course run, I will like I said try to figure out where that happy medium is between front braking and rear pressure between locking up and ineffective essential and no rear braking assist (front brake too dominate)! The weight transfer is a killer front to rear! For side to side and cross weighting checks, I actually ballast for no passenger! Thus I am trying to combat (weight transfer ) that with lowering to the weeds! I also have played with the factory position of the upper front a-arm and the anti-dive angles! I have about 3-1/2 inches of ground clearance in course trim (oil pan and header collectors the two concerns). I have lightened the car substantially! And I am heavy Springs!
Last edited by TCracingCA; 01-11-2018 at 12:50 PM.
01-11-2018, 12:16 PM
#42
Team Owner
I don't really see brake fade with these new racing pads and I use a high boil Grade 4 racing brake fluid! I tried a lot of brands back in the day from Motul to Castro, AP, etc! My go to pads for an endurance run are stock inconel backing plates with Porterfield modern materials! I do think the Corvette without substantial weight reduction is a pig and as such, the stock brakes are marginal for racing basically and so are the J-56s (but these new pads expands the performance envelope greatly).
But in my older age, I am more dropping track stardom fame dreams and past autocross glory days and returning to my roots and passion which are my super spirited Canyon (curvy road assaults) blasts, which are short duration kind of like just doing a qualifying run only! But even when I have trailered them to the actual tracks, I am more of a momentum late apex driver, back early on the gas type, who loves to brake into the turns nutcase, who is hard on the gearbox to aid deceleration and actual due to those habits, fairly easy on the brakes! Thus I tend to have the fresher brakes to get your a$$ for a pass! I developed my bad habit of braking while turning, because of damn Porsche 911s and such! I learned to give them no room, based on being lighter weight and easier on tires and better braking capable to take me up on the inside apex line at entry! Thus braking while turning in slams the door on their area of general advantage, at least until my tires go off prior to theirs! I was out at Willow Springs and saw the actual Can Am cars all were using the same trick on the front straightaway, where they went ***** to the wall and angled toward a tight entry apex into Turn 1, and when they cut the angle they lined up there aim and in a perfectly straight line from maximum attained speed, they clamped it down super super hard and heavy duty to their ideal apex rpm, and then off the brakes totally and back gradually onto the gas prior to and they apex! Thus fully using the entire capability of their brakes! Kind of like a 0-160-0 Magazine test! I just stood there peering through the fence saying to myself, I need to try that and see how it affects lap time! The other classes of cars where essentially all hanging to the outside of the end straight and braking and then lazily picking their apex line compared to those more professional level cars and I assume drivers. I assume because of the terminal velocity capability and the braking capability, when taking slower traffic at the very end of straight-away, A few went off of the standard line to overtake just prior to turn entry and discovered a faster technique and essentially a not natural line of attack to that turn! They also must have major money to burn, as decelerating using the engine through the expensive Hewland while braking could be insanely expensive! Far different than me needing to go get another Corvette appropriate crash box! If I had a Hewland, I would baby talk to it, as grenading one would cost bank! I have been a customer of Andy Porterfield (RIP) for 30 plus years! The last time I looked, I think they offered 19 pad material choices for the Twin Pin Calipers! They also have some torque specs (material to material choice) or braking level and characteristics and suggested usage notes for your educated selection! My opinion, you can essentially throw out the proportioning valve, applying all of this new modern technology!
Last edited by TCracingCA; 01-11-2018 at 02:17 PM.
01-11-2018, 12:52 PM
#43
Former Vendor
True dat.
No matter how many times we cover this topic there are people out there who still think the prop valve is some magic bullet that increases rear pressure...only your leg does that. And the valve only reduces what you put into it.
That "dial" on it changes the "knee point" which is the point of pressure at which the reduction begins. It's not a set pressure of rear brake. As you dial it up you alter the allowed pressure to get to the rears and then form that point onward it goes up at a slower rate than the front brakes. Up to a common 50% total reduction compared to the total input effecting the fronts.
In a way: the more you put in- the less you get out.
Last edited by Todd TCE; 01-11-2018 at 12:52 PM.
01-11-2018, 01:24 PM
#44
Team Owner
I got it!!! The solution!!!!! Humor coming!
I will choke my seat adjustment forward chest to the steering wheel and as I burn gas, I will move Seat back notch by notch till furthest rear position to aid weight transfer!
I will choke my seat adjustment forward chest to the steering wheel and as I burn gas, I will move Seat back notch by notch till furthest rear position to aid weight transfer!
Last edited by TCracingCA; 01-11-2018 at 02:06 PM.
01-11-2018, 01:49 PM
#45
Team Owner
It's just me but I would think you'd want cooling to the rotor and the caliper to keep the rotor cool and the brake fluid in the caliper cool at the same time. Wouldn't moving the caliper to the back reduce it's ability to remove heat? I don't know, I'm not a racer and am just asking for my own knowledge. Thanks 
01-11-2018, 02:04 PM
#46
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It's just me but I would think you'd want cooling to the rotor and the caliper to keep the rotor cool and the brake fluid in the caliper cool at the same time. Wouldn't moving the caliper to the back reduce it's ability to remove heat? I don't know, I'm not a racer and am just asking for my own knowledge. Thanks
01-11-2018, 02:13 PM
#47
Team Owner
My opinion on changing the location of the brake caliper is on our cars weighing what they do with heavy components, I can't see where it would matter, as they aren't svelte lightweight Formula Cars!
Heck more humor! Let's put it on the bottom of the rotors to pick up the under car draft and lower weight in relation to the ground!
Heck more humor! Let's put it on the bottom of the rotors to pick up the under car draft and lower weight in relation to the ground!
Last edited by TCracingCA; 01-11-2018 at 02:14 PM.
01-11-2018, 02:26 PM
#48
Former Vendor
As the brake is applied it creates a twist on the axle against its natural rotation and spirals up the shafts to the disc. In the case of later model CV joint cars that leads to excess play. The slop in the joints can create some inaccuracies in the true torque being applied to the tire and even go so far as the snap a cage or the axle end.
Also in the case of many platforms today the packaging is now in the air stream under the car whereas the conventional design puts them inside the wheel. For those with real ground effects the tunnel width can then be wider.
I had them on my Pikes Peak car for the first year or two and the "fuzzy feeling" I got from them was sort of a delayed reaction to what I wanted. Moving them outboard was a huge change in response.
01-11-2018, 02:42 PM
#49
Team Owner
I have no splash shields on my vette. They impede cooling especially when you are parked after lapping your car.
I used these NACA air ducts on my vette. They also sell the SS screens and 3 inch hose.
https://www.pegasusautoracing.com/pr...p?Product=3624
01-11-2018, 04:54 PM
#51
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I think this is still 'on-topic'. And I'm willing to be educated here, but since the caliper's force and associated torque only affect the wheel, other than lifting or flattening the tires a bit, I can't see how that would pull the car up or down? The spring still has to bear the weight transfer. Would somebody please explain?
The inclination of the upper and lower control arms form a virtual swing arm towards the rear of the car (visualize the rear suspension trailing arm in a mirror image). When the brakes are applied, a moment arm thing happens between the caliper and the knuckle (through the distance of the rotor radius). The caliper pad friction causes a torque through the bracket into the knuckle, trying to rotate the virtual arm in the direction of the rotor rotation. This rotation of the virtual arm causes a lifting force/anti-dive action, reducing the amount of front suspension compression that would otherwise happen against just the front spring rate. (Trivia: IIRC, the upper A-arm angle in Chevies was changed in 1955. The 54s had parallel UCA and LCA mounts, which allowed a lot of brake dive, while the 55s, with the angled UCA and the resulting virtual arm, had a reduced amount of frontend dive during braking.)
That's my take. I guarantee this info is worth every penny you paid for it.
01-11-2018, 05:26 PM
#52
Former Vendor
01-11-2018, 05:46 PM
#53
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69427 and TC have it right. I been racing cars for 40 some years and see things a little differently. I have a pretty good idea what works, but in this sport you are always learning. So I try to keep an open mind.
The reason for doing what I am demonstrating is to get the caliper in the rear to be able to get more air into the center of the rotor to keep the rotor cooler. I am using the old shield for a mounting point for the duct work from the front air dam. I will probably use very little of it or none , but it is a starting point. Some here "get it" some don't. That's o-k.
The reason for doing what I am demonstrating is to get the caliper in the rear to be able to get more air into the center of the rotor to keep the rotor cooler. I am using the old shield for a mounting point for the duct work from the front air dam. I will probably use very little of it or none , but it is a starting point. Some here "get it" some don't. That's o-k.
Last edited by Pop Chevy; 01-11-2018 at 05:54 PM.
01-11-2018, 07:07 PM
#54
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...The caliper pad friction causes a torque through the bracket into the knuckle, trying to rotate the virtual arm in the direction of the rotor rotation. This rotation of the virtual arm causes a lifting force/anti-dive action, reducing the amount of front suspension compression that would otherwise happen against just the front spring rate.
PopChevy and gkull suggest that moving the calipers to the rear of the rotor changes the dive characteristic. But no matter where the caliper is mounted, the torque is always against the rotation of the wheel and that twisting moment is therefore always the same for either the front-mounted, or rear-mounted caliper against the "virtual arm". A front-mounted caliper pulls down when clamped and a rear-mounted caliper pulls up, I get that. But the twist is the same isn't it?
Thanks for trying to enlighten me. I will look in one of my two suspension books tonite and see if I can come around to your thinking.
01-11-2018, 08:01 PM
#56
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Way to go Ignatz ! You stuck with it long enough to get it. Yes, the twist is the same but are the forces the same ? Hmmmm.
Yes, the NASCAR guy's have some very trick and expensive fans inline for cooling. They also have HUGE budgets to work with. I have always said " I am a thousandaire trying to race with millionaires" Every now and then I beat em !!
Yes, the NASCAR guy's have some very trick and expensive fans inline for cooling. They also have HUGE budgets to work with. I have always said " I am a thousandaire trying to race with millionaires" Every now and then I beat em !!
01-11-2018, 11:27 PM
#57
Race Director
out of curiosity have you been to an SVRA race or the July race at Road America in the past 5 years?
01-12-2018, 07:22 AM
#58
Team Owner
Gee thanks! Actually I am trying to think as to whether I really really want to get into this all super technically!
Essentially the brake torque is going to try to cause the whole car to spin based on the rotational torsion basically thru the upright and force affects thru the suspension components to the chassis and all thru Center of Gravity (CG).
In this thread we have brushed on Brake Dynamics, Suspension dynamics, brake bias, etc etc etc all coming into play, along with weight transfer and inertia, anti-dive, lift, etc etc etc.
Basically we are working on a Production car with the designed in production car weight balance front to rear being biased more front than rear as race cars are more 40/60 or 50/50. And I am not talking about static, but dynamic! Race cars give a lot of design focus on dynamic balance!
A thought has to be given on our heavy cars as to the over riding factor that is having the most prominent affect, as under braking, you cause the tires to push forward against the ground and they will inherently have a lifting force as weight transfer and I mentioned taking a set comes into play! Essentially due to traction, the ground force and friction from tire rotation, traction, force of lifting from essentially the ground, lifts or compresses the suspension and thus forces are applied to the chassis. It is important for the Corvette to have the shocks/Springs tuned in very precisely, as that is a prominent area needing special focus for getting us to having handling! In my opinion moving that caliper around on the upright or in relation to the spindle is irrelevant in our cars, as what I just mentioned and the overall weight transfer are major in regards to force based on the caliper positioning being such a low in relationship area of effect! ! The brake bias and control of weight transfer is so overriding also!
I am an advocate generally of smooth, precise, deliberate control! But sometimes a track characteristic will cause me to look for a trick to set the chassis set for a turn entry or quicken putting the car to a set! Basically if the car is still shifting its weight transfer based on throttle, braking and steering input, then your traction will not be predictable and the car will ill handle! I believe in getting to that point of max weight transfer as predictably as possible and once there, you have yeah so much traction available and thus predictability. It is known that you in like a race car can shift oversteer and understeer with throttle manipulation, braking and steering! I am a Porsche guy as well as a Corvette guy, and I even have a 1969 F2 car in the garage that is getting built back up! Like in a Porsche never lift in a turn, no if anything,apply more throttle!
Essentially braking shifts weight right to the front and can induce oversteer, because of unweighting the rear and essentially the tire traction, and acceleration shifts weight to the rear and can induce understeer! But then traction loss can turn that all on it's head! And many can get confused, from going from oversteer to understeer and vice versa, through the operation of racing, so fast that it causes one's thoughts and brain to spin and subsequently too, their car!
Lower traction can cause or reduce reduce weight transfer, like if the front is trying to slip out from under the chassis weight wanting to shift over and force plow or understeer! Basically you are taking a set or driving using controls to set the chassis set for a section of track, and in a turn your priority is looking for neutral a balance between understeer and oversteer. You achieve neutral when the weight transfer hits it limits and you still have a set amount of traction! But in real life, you are modulating the controls and steering, braking force, and gauging throttle, not even getting into drivetrain torques or inertia forces as designed by suspension characteristics!
Wow! I am up at 4am writing this! I will need to reread when not fighting to go back to sleep tomorrow! I am sure I could delve even deeper into the topic. A Formula car is an entirely different creature and the weights and. CEnter of gravity, etc all play to something with far less weight transfer, and a far lower CG! It will handle so much flatter on a track while we sway like pigs, based on mostly weight transfer effects! But basically braking forces cause a rotating tenancy or torque about the CG, and torque basically wants to put our cars as designed on its nose, so you actually need lift force productively to counteract that! Or go more into Formula car characteristics like me on your car build! I have gone lower, lighter, more suspension sophistication, addressing weight transfer thru things like brake bias or static weight changes shifting to the rear with like my aluminum block and heads and heavy springs! I have two cars that ride down the road like trucks, but are super flat on an actual race track!
Essentially the brake torque is going to try to cause the whole car to spin based on the rotational torsion basically thru the upright and force affects thru the suspension components to the chassis and all thru Center of Gravity (CG).
In this thread we have brushed on Brake Dynamics, Suspension dynamics, brake bias, etc etc etc all coming into play, along with weight transfer and inertia, anti-dive, lift, etc etc etc.
Basically we are working on a Production car with the designed in production car weight balance front to rear being biased more front than rear as race cars are more 40/60 or 50/50. And I am not talking about static, but dynamic! Race cars give a lot of design focus on dynamic balance!
A thought has to be given on our heavy cars as to the over riding factor that is having the most prominent affect, as under braking, you cause the tires to push forward against the ground and they will inherently have a lifting force as weight transfer and I mentioned taking a set comes into play! Essentially due to traction, the ground force and friction from tire rotation, traction, force of lifting from essentially the ground, lifts or compresses the suspension and thus forces are applied to the chassis. It is important for the Corvette to have the shocks/Springs tuned in very precisely, as that is a prominent area needing special focus for getting us to having handling! In my opinion moving that caliper around on the upright or in relation to the spindle is irrelevant in our cars, as what I just mentioned and the overall weight transfer are major in regards to force based on the caliper positioning being such a low in relationship area of effect! ! The brake bias and control of weight transfer is so overriding also!
I am an advocate generally of smooth, precise, deliberate control! But sometimes a track characteristic will cause me to look for a trick to set the chassis set for a turn entry or quicken putting the car to a set! Basically if the car is still shifting its weight transfer based on throttle, braking and steering input, then your traction will not be predictable and the car will ill handle! I believe in getting to that point of max weight transfer as predictably as possible and once there, you have yeah so much traction available and thus predictability. It is known that you in like a race car can shift oversteer and understeer with throttle manipulation, braking and steering! I am a Porsche guy as well as a Corvette guy, and I even have a 1969 F2 car in the garage that is getting built back up! Like in a Porsche never lift in a turn, no if anything,apply more throttle!
Essentially braking shifts weight right to the front and can induce oversteer, because of unweighting the rear and essentially the tire traction, and acceleration shifts weight to the rear and can induce understeer! But then traction loss can turn that all on it's head! And many can get confused, from going from oversteer to understeer and vice versa, through the operation of racing, so fast that it causes one's thoughts and brain to spin and subsequently too, their car!
Lower traction can cause or reduce reduce weight transfer, like if the front is trying to slip out from under the chassis weight wanting to shift over and force plow or understeer! Basically you are taking a set or driving using controls to set the chassis set for a section of track, and in a turn your priority is looking for neutral a balance between understeer and oversteer. You achieve neutral when the weight transfer hits it limits and you still have a set amount of traction! But in real life, you are modulating the controls and steering, braking force, and gauging throttle, not even getting into drivetrain torques or inertia forces as designed by suspension characteristics!
Wow! I am up at 4am writing this! I will need to reread when not fighting to go back to sleep tomorrow! I am sure I could delve even deeper into the topic. A Formula car is an entirely different creature and the weights and. CEnter of gravity, etc all play to something with far less weight transfer, and a far lower CG! It will handle so much flatter on a track while we sway like pigs, based on mostly weight transfer effects! But basically braking forces cause a rotating tenancy or torque about the CG, and torque basically wants to put our cars as designed on its nose, so you actually need lift force productively to counteract that! Or go more into Formula car characteristics like me on your car build! I have gone lower, lighter, more suspension sophistication, addressing weight transfer thru things like brake bias or static weight changes shifting to the rear with like my aluminum block and heads and heavy springs! I have two cars that ride down the road like trucks, but are super flat on an actual race track!
And to be honest, the Corvette is so frustrating, that the heavy springs just pure bandages it's flaws! Essentially overpowering and controlling the car's characteristics very heavy handed! But it suits me! But ideally on especially rough road handling, would you gain traction from brute force heavy springs, or from a light sprung car and faster reacting suspension to gain traction as the tire is better tracking road irregularities! Basically when operating my race suspensions cars on the street, I have street rubber on, so instant understeer! As those tires instantly get blown off fast! But god help the guy in his new Porsche GT3 RS if I have rubber mounted appropriate to my car's set up! I will dial back especially my camber, and go less radical on toe for street ops, as everything on two cars is adjustable! thoTherefore study and setup for the road is essential! There is no one magic setup! Either direction we go in causes a compromise! And therefore on a given day, one car setup with an opposite approach may be the quick setup! I firmly believe on most days I can out set up and drive a Corvette better than most guys racing them, but I don't have their budgets for tires! I generally am driving on tires that are past their prime, still trying to get results! A new set of tires can be such an important factor to turn a pig into a prince! I hate to get beat by the wallet, and a no talent individual, and an inferior car, because they put fresh rubber on , that can negate all of my work to setup my car for handling! !Back in the day, some of my Family was the first C3 guys in the Country to mount 315/335 rubber for autocrossing! They got disqualified most weekends, but prior to being scratched from the result sheets, they had like 60 something event FTDs of any year Corvette out here in the SoCal club racing SCCA world! And If they got beat, someone had new tires usually! I actually within my own family, am far from being the family suspension expert! One other of my brothers holds that distinction! But hearing him get into the technical and engineering has led to me holding my own in conversations, on such topics!
Last edited by TCracingCA; 01-13-2018 at 05:18 AM.
01-12-2018, 10:50 AM
#59
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Redvet- SVRA ? I have held an SVRA competition license for the last 5 yrs. I've raced at Indy twice, Homestead, Pocono, Summit Point, Nelsons, and have run hundreds of laps at PIRC. I had to quit 2 yrs ago because of cancer treatment and I foolishly sold the fastest car I ever drove. I made it, now my strength is coming back and I am itching to get back behind the wheel. Now I'm curious, have you raced in the last 5 yrs??
TC, that was a good read on vehicle dynamics. Well put.
TC, that was a good read on vehicle dynamics. Well put.