Using Brake Pads to Adjust turn-in response
04-28-2010, 08:53 PM
#1
Momentum Keeps Me Going
Thread Starter
Using Brake Pads to Adjust turn-in response
This season I needed new brake pads. I've been happily running Cobalt friction XR2/XR5 combo front/rear for a year and a half. For those unfamiliar with the brand it goes from most agressive XR1, XR2, XR3, XR4, XR5, to least CSR (Club Sport). All are intrended for track use. Grand-Am cars, for example, might run XR1/XR3 combo, or whatever suited them. Link http://www.cobaltfriction.com/compounds/ I noticed that the company had changed their "recommended" pads for the RX-8 to XR3 front/XR5 or CSR rear on their website application guide. So I called and spoke with them about this and learned some other interesting things.
First, their "recommended" pads are not really that...they are more "starter" pads or what a beginning track person might want to try when running street tires, stock suspension, etc. They said they really needed to clarify that, because it looked like they were saying the recommended pad was only what was available. For experienced track users, those with R-comps, and suspension upgrade, he indicated that the XR1 or XR2 might be better front, and then for the rear the advice got more interesting....(at least for me)
The tech person described the choice for the rear going up from CSR could be based on how much rotation during trail braking you wanted to obtain. IOW, the stronger the rear brake bite from the pads choosen, the less the traction remaining for grip in the rear, which would obviously lead to more oversteer in a braking situation. Makes perfect sense, just I'd never looked at pad selection that way.
He said the CSR or XR5 would be "easiest" to drive on track, giving a very planted tail end. Whereas those wishing for a more tail out attitude during turn in could rachet up toward (at most) a one level lower pad than on front. Just something I thought was worth sharing and interesting to keep in mind. And, oh yes, I also learned that each and every order for CF pads is made to order and drop shipped, so as to give the purchaser the very latest pad formulation available. Pretty neat - a custom pad service! So my fresh XR2/XR4 combo should arrive in about 10 days.
cheers, spin
First, their "recommended" pads are not really that...they are more "starter" pads or what a beginning track person might want to try when running street tires, stock suspension, etc. They said they really needed to clarify that, because it looked like they were saying the recommended pad was only what was available. For experienced track users, those with R-comps, and suspension upgrade, he indicated that the XR1 or XR2 might be better front, and then for the rear the advice got more interesting....(at least for me)
The tech person described the choice for the rear going up from CSR could be based on how much rotation during trail braking you wanted to obtain. IOW, the stronger the rear brake bite from the pads choosen, the less the traction remaining for grip in the rear, which would obviously lead to more oversteer in a braking situation. Makes perfect sense, just I'd never looked at pad selection that way.
He said the CSR or XR5 would be "easiest" to drive on track, giving a very planted tail end. Whereas those wishing for a more tail out attitude during turn in could rachet up toward (at most) a one level lower pad than on front. Just something I thought was worth sharing and interesting to keep in mind. And, oh yes, I also learned that each and every order for CF pads is made to order and drop shipped, so as to give the purchaser the very latest pad formulation available. Pretty neat - a custom pad service! So my fresh XR2/XR4 combo should arrive in about 10 days.
cheers, spin
04-29-2010, 06:54 AM
#5
Momentum Keeps Me Going
Thread Starter
If you're in threshold braking Team, of course the ABS is doing what it needs to do, but during trail braking...well - I can't envision doing trail braking in threshold braking mode 
! I always feather the pedal as I'm going from heavy straight line braking to trail braking. ABS would opt out at that point and not be a factor.
I think this is offering a finer braking turn-in balance offset as you feather and trail brake into a corner. For example, already I can do setup a fulltime f/r suspension offset using the ECON adjustment for my Cusco coilovers...1 being soft thru 5 hard. 1 gives more grip (slower shock response) at either end ...to 5 least grip. So a 1f/5r split would give a much more tail happy car that the opposite extreme 5f/1r where the tail is well planted.
I usually drive 5f/5r to 5f/3r on dry track depending....or if it's wet I'll go 3f/1r or play around until I find a good compromise setting. Changing from XR5 to XR4 in the rear 'should' only give an offset toward turn-in brake induced tail happiness
.
! I always feather the pedal as I'm going from heavy straight line braking to trail braking. ABS would opt out at that point and not be a factor.I think this is offering a finer braking turn-in balance offset as you feather and trail brake into a corner. For example, already I can do setup a fulltime f/r suspension offset using the ECON adjustment for my Cusco coilovers...1 being soft thru 5 hard. 1 gives more grip (slower shock response) at either end ...to 5 least grip. So a 1f/5r split would give a much more tail happy car that the opposite extreme 5f/1r where the tail is well planted.
I usually drive 5f/5r to 5f/3r on dry track depending....or if it's wet I'll go 3f/1r or play around until I find a good compromise setting. Changing from XR5 to XR4 in the rear 'should' only give an offset toward turn-in brake induced tail happiness
.
04-29-2010, 09:30 AM
#6
This fine tuning is real. For an extreme but more easily understood example imagine driving a car with front wheels braking only. Got it?
It does get complicated.
Staggered pads can cause the fronts to wear faster and to build a good bit more heat.
The suspension you have also has to be brought into play. etc etc.
Also you may NOT want tail out on trail braking that is helped by the pads. I rather use the steering wheel myself
We already have a very front biased car.
I ran staggered pads for a while --carbotech xp8 on front and carbo tech bobcats on the back. I recently switched to a balanced set up after attending a braking tech class at Road Atlanta.
Good info though --appreciate the post.
OD
It does get complicated.
Staggered pads can cause the fronts to wear faster and to build a good bit more heat.
The suspension you have also has to be brought into play. etc etc.
Also you may NOT want tail out on trail braking that is helped by the pads. I rather use the steering wheel myself
We already have a very front biased car.I ran staggered pads for a while --carbotech xp8 on front and carbo tech bobcats on the back. I recently switched to a balanced set up after attending a braking tech class at Road Atlanta.
Good info though --appreciate the post.
OD
04-29-2010, 06:41 PM
#7
Except by going to a more aggressive rear pad you lower the rear wheel lockup threshhold. You typically only feel the ABS when the front brakes start to lockup, not the rear. So yes, if you are using light braking the effect will be there, but if you push the car with the ABS on the braking will effects will vary and not be consistent
04-29-2010, 08:41 PM
#8
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All my cars have a little bit of rear bias in regards to brakes.
4 channel/3 channel/amount of skid allowed in the abs programming etc plays into what you do. Then you start changing bars/spring/damping etc and watch out.
I'm surprised you don't see more ABS computer reprogramming at the race track.
There is some pretty good ABS programming from the programming.
ZOK Solstice NA will smoke tires under threshold braking.
Cobalt SS/TC will do the same.
My TTRXR1 will not though.
I like ABS that lets the tire skid enough to create liquid rubber. Most don't though.
FM
4 channel/3 channel/amount of skid allowed in the abs programming etc plays into what you do. Then you start changing bars/spring/damping etc and watch out.
I'm surprised you don't see more ABS computer reprogramming at the race track.
There is some pretty good ABS programming from the programming.
ZOK Solstice NA will smoke tires under threshold braking.
Cobalt SS/TC will do the same.
My TTRXR1 will not though.
I like ABS that lets the tire skid enough to create liquid rubber. Most don't though.
FM
04-30-2010, 02:18 AM
#9
Registered
I'll suggest to everyone (especially the new and learning guys who might read this thread in the future) that the biggest issue influencing braking on these cars is grip and weight transfer.
I've driven a few students cars at local HPDE/Open track days and here is what I generally see: Stock suspension with larger and better performing tires will allow for better front grip in hard braking which leads to larger weight transfer which leads to the rear end getting light which can lead to easier (possibly undesirable) rear end rotation with some or very little steering input. In these cases it is easier to feel and experience what too much or too little rear brake pad is doing.
The real issue IMO is the too huge of forward weight transfer allowed by the increased front grip. The first weakness that gets exposed on these cars at the track is the low front spring rate if you ask me-----especially when more and larger front grip has been added.
New drivers should understand that this may reveal itself ON PARTICULAR CORNERS and not on others. Typically you'd see this on a high speed straight leading to significant braking followed by some type of kink or higher speed corner.
Be careful to understand and work on the correct end of the problem.
I've driven a few students cars at local HPDE/Open track days and here is what I generally see: Stock suspension with larger and better performing tires will allow for better front grip in hard braking which leads to larger weight transfer which leads to the rear end getting light which can lead to easier (possibly undesirable) rear end rotation with some or very little steering input. In these cases it is easier to feel and experience what too much or too little rear brake pad is doing.
The real issue IMO is the too huge of forward weight transfer allowed by the increased front grip. The first weakness that gets exposed on these cars at the track is the low front spring rate if you ask me-----especially when more and larger front grip has been added.
New drivers should understand that this may reveal itself ON PARTICULAR CORNERS and not on others. Typically you'd see this on a high speed straight leading to significant braking followed by some type of kink or higher speed corner.
Be careful to understand and work on the correct end of the problem.
04-30-2010, 07:13 AM
#10
Momentum Keeps Me Going
Thread Starter
^ +1 So very true and esp. as Eric says to new/stock 8 drivers. Stock setup is soft and will result in excessive rear lift under braking, transitions, turns and esp. with better grip and track pads. I've seen others spin out and have myself (DSC off). Not fun... and potentially dangerous. Which led me to using Cobalt pads (XR5 in the rear), designed specifically to help address the braking instability issue.
By no means consider this the solution... but rather as part of a well thought out plan of changes to holistically reduce/eliminate this trait including suspension, lowering, spring rates, chassis stiffening, etc. Use patience making changes to gauge results. When correctly adjusted, your car won't be stock anymore, but it WILL BE your friend and a car you can depend on.
"XR5 is a highly specialized low-medium torque compound designed for rear-axle applications in vehicles exhibiting rapid and high levels of weight transfer under braking (e.g. front wheel drive touring cars). Solid initial bite and a flat torque profile which transitions to a slightly negative slope during the last 60-75% of a brake zone eliminates rear lock-up."
Last edited by Spin9k; 04-30-2010 at 07:22 AM.
04-30-2010, 09:31 AM
#11
well said Spin. Its all about being familur with your car also. You can have a set up for a particular driving style and all of a sudden a different scenario will present itself.
Example--- few weeks ago i was making a pass on the long straight at roebling Road approaching turn 1. I wanted to enter that turn a certain way and in order to do that i had to move more outside (after my pass on the inside) just before braking. When i did and hit the brakes the car didnt like it. I didnt have the chassis settled and the inside of the car was still a little light. My brake pads --carbo techs xp 8's-- have a strong initial bite and I didnt need a strong bite right then! So end result --i messed up my entry on that turn and by corner exit the car i had just passed was ready to pass me. If i had had a stagged pad set up in that scenario i think my tail end would have came around on me.
Good discussions/points.
OD
Example--- few weeks ago i was making a pass on the long straight at roebling Road approaching turn 1. I wanted to enter that turn a certain way and in order to do that i had to move more outside (after my pass on the inside) just before braking. When i did and hit the brakes the car didnt like it. I didnt have the chassis settled and the inside of the car was still a little light. My brake pads --carbo techs xp 8's-- have a strong initial bite and I didnt need a strong bite right then! So end result --i messed up my entry on that turn and by corner exit the car i had just passed was ready to pass me. If i had had a stagged pad set up in that scenario i think my tail end would have came around on me.
Good discussions/points.
OD
04-30-2010, 01:33 PM
#12
justjim
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I agree with what Eric Meyer said. I have been running my RX-8 with stock OEM springs and shocks, Progress sways (which don't affect this issue), and R-compound tires at Sebring. I used to use the Cobalt XR2f and XR5r combo. When I went to reorder once they only had the XR1s in stock no XR2s. So I got the XR1s for the front and I felt that the car was a little more stable on turn in for the reasons Eric has pointed out.
I have a LOT of weight transfer under heavy braking because of the soft suspension and sticky tires. This throws more weight on the front than the ABS would normally expect on the street with street tires. Increasing the front bias (or decreasing the rear) with the pad helps keep things balanced I believe. That's my story and I'm sticking to it.
I have a LOT of weight transfer under heavy braking because of the soft suspension and sticky tires. This throws more weight on the front than the ABS would normally expect on the street with street tires. Increasing the front bias (or decreasing the rear) with the pad helps keep things balanced I believe. That's my story and I'm sticking to it.
05-09-2010, 03:45 PM
#13
Registered
I agree with what Eric Meyer said. I have been running my RX-8 with stock OEM springs and shocks, Progress sways (which don't affect this issue), and R-compound tires at Sebring. I used to use the Cobalt XR2f and XR5r combo. When I went to reorder once they only had the XR1s in stock no XR2s. So I got the XR1s for the front and I felt that the car was a little more stable on turn in for the reasons Eric has pointed out.
I have a LOT of weight transfer under heavy braking because of the soft suspension and sticky tires. This throws more weight on the front than the ABS would normally expect on the street with street tires. Increasing the front bias (or decreasing the rear) with the pad helps keep things balanced I believe. That's my story and I'm sticking to it.
I have a LOT of weight transfer under heavy braking because of the soft suspension and sticky tires. This throws more weight on the front than the ABS would normally expect on the street with street tires. Increasing the front bias (or decreasing the rear) with the pad helps keep things balanced I believe. That's my story and I'm sticking to it.
05-12-2010, 12:35 AM
#14
I'm on Cobalt XR2/XR5 and a big fan - looking forward to Spin report on switching Cobalt compounds.
Cheers
05-12-2010, 07:32 AM
#15
Momentum Keeps Me Going
Thread Starter
^ ...good point! ... sticky tires allow better braking, and better brakes encourage stronger braking, increasing the possibility of more weight transfer actually occuring.
The concept people with stock suspensions can consider is that although springs, shocks, etc. cannot change the amount of weight transfer, it is entirely possible to change the affects of weight transfer on the car.... i.e., the rate of that weight transfer, and the impact of weight transfer on the suspension geometry and handling stability. Minimizing dive (braking) and squat (accelerating), and body roll (cornering) thru stiffer springs/shocks/sway-bars helps keep the CG stable during weight transfer.... vs. the changing CG/geometery of a soft stock suspension's exaggerated movements of first it's flat, then it's rear up, front down, or perhaps bowed over to the side during cornering.
One great side benefit of a 'tighter' suspension, less upset by the effects of weight transfer is that you can more easily decern the effects of any changes made anywhere in the car (e.g. brake pads), rather than having them masked by other unintended chassis dynamics occuring at the same time
The concept people with stock suspensions can consider is that although springs, shocks, etc. cannot change the amount of weight transfer, it is entirely possible to change the affects of weight transfer on the car.... i.e., the rate of that weight transfer, and the impact of weight transfer on the suspension geometry and handling stability. Minimizing dive (braking) and squat (accelerating), and body roll (cornering) thru stiffer springs/shocks/sway-bars helps keep the CG stable during weight transfer.... vs. the changing CG/geometery of a soft stock suspension's exaggerated movements of first it's flat, then it's rear up, front down, or perhaps bowed over to the side during cornering.
One great side benefit of a 'tighter' suspension, less upset by the effects of weight transfer is that you can more easily decern the effects of any changes made anywhere in the car (e.g. brake pads), rather than having them masked by other unintended chassis dynamics occuring at the same time
05-20-2010, 07:03 PM
#16
Momentum Keeps Me Going
Thread Starter
...follow-up on my brake upgrade including the rear XR4 track pads.
The XR2 Front/XR4 Rear pad change were part of my winter brake maintenance including new slotted RB rotors all around, 2p in front.
Spent 280 miles & 3.5 hrs hours @ Lightning NJMP. The result? Nothing noticeable trail braking w/new pads. Maybe some more time on different tracks will tell more where more TB comes more into play, but so far nothing.
Trip notes...
- Best lap 1:21.682
- 900 mile trip - hwy 22+mpg/on track ~8mpg
Track notes...
- skill+mindset+track familiarity is a huge plus to pass higher HP cars. Extreme illustration - the slowest car at the event was a 2010 GT3 with ceramic brakes something like http://jalopnik.com/5141807/2010-por...ed-from-112200 ... the fellow said he was building up his skill with the car a little at a time...which is probably prudent in an $125K purchase!
- very sticky tires are a huge advantage... There are not many things you can quickly change on a car that will enhance track performance more the Super Glue rubber. In so many ways, my BFG R1s 255/40/17 tires are superior to the NT-01s I used previously.
- raw power is a huge and decisive advantage when used effectively...otherwise, it doesn't help that much.
Overall the refreshed brakes and race rubber worked as planned and expected. Excellent 'right now' progressive experience with complete control. Front/rear balance was fine, I did settle on softer rear shocks setting. Maybe that was some compensation, but overall the car offered amazing braking confidence.
The XR2 Front/XR4 Rear pad change were part of my winter brake maintenance including new slotted RB rotors all around, 2p in front.
Spent 280 miles & 3.5 hrs hours @ Lightning NJMP. The result? Nothing noticeable trail braking w/new pads. Maybe some more time on different tracks will tell more where more TB comes more into play, but so far nothing.
Trip notes...
- Best lap 1:21.682
- 900 mile trip - hwy 22+mpg/on track ~8mpg
Track notes...
- skill+mindset+track familiarity is a huge plus to pass higher HP cars. Extreme illustration - the slowest car at the event was a 2010 GT3 with ceramic brakes something like http://jalopnik.com/5141807/2010-por...ed-from-112200 ... the fellow said he was building up his skill with the car a little at a time...which is probably prudent in an $125K purchase!
- very sticky tires are a huge advantage...
There are not many things you can quickly change on a car that will enhance track performance more the Super Glue rubber. In so many ways, my BFG R1s 255/40/17 tires are superior to the NT-01s I used previously.- raw power is a huge and decisive advantage when used effectively...otherwise, it doesn't help that much.
Overall the refreshed brakes and race rubber worked as planned and expected. Excellent 'right now' progressive experience with complete control. Front/rear balance was fine, I did settle on softer rear shocks setting. Maybe that was some compensation, but overall the car offered amazing braking confidence.
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