FYI I got an ABS light for some reason the other day, and so I tested it out. The fronts locked up and the rears did not.

 

Sometimes I wonder if I'm just not sensitive enough to what my car is doing. :P

I never noticed my Cooper being unstable under hard braking (in a straight line). Yes, add some steering in while braking hard and things got interesting. But, that goes back to car setup again - front camber plates, small-ish front bar, large-ish rear bar.

I wouldn't be surprised if someone else drove my Cooper (well, once it's drivable again) and told me it was unstable under braking. But, it's not something that sticks out in my brain.

 

thanks! You running the same pads all the way around? and which ones?

ive been trying to think back, i remember a while ago i was quite disturbed at how wild my rearend got under straight line braking. And ive been trying to figure out what i did to fix it. And just right now it occured to me. I got my car in dec, and winter tires went on the next day. Once spring rolled around i was used to the car and really starting to push it, and thats when i really noticed how wild it got. When i put my performance (albeit runflats...) tires back on, the squirrellyness went away. I dont know what the info is worth to anyone, but with my car, it was the tires that was causing the wild back end. FWIW

Beecher

 

regarding brake bias in this situation: i have a TCE/Willwood 13" kit up front and the TCE rotors w/ relocated stock calipers in the rear. i have tried the following combinations with no significant difference: 1. BP-20's front/ stock rear, 2. BP-20's front/ Porterfield R4 rear, 3. Poly H's front/ Porterfield R4 rear and 4. Poly H's front/ stock rear. this represents a pretty wide spread of Cf's front and rear. still unsettled under all combos. Snid: if you have this situation, you would notice!

i thought that things got better when i initially switched from RA-1's to Hoosier R6's. that was until i approached the new limits of the R6's. same as before.

i have tried to methodically analyze this problem......no luck yet.

a few additional thoughts.....i need to order my third set of rotors before my next track weekend (22k miles on the clock), so i know that i am hard on brakes (but i like braking late and hard). a friend of mine (LgEnf) has this same problem now that he has gone to track only pads in an otherwise stock system (except fluid). this didn't happen to him w/ two different Hawk compounds that he previously used. i'm not positive what he last ran at Daytona (HT10's from Satisfied Brakes i think), but he now knows what he saw my car doing.

 

you want to do some work? I dont know your situation or if you still have the parts, but would you be willing to try putting the stock fronts back on (and leave the big rears) to see if that makes any difference? Of course the relocation of the rear caliper might not be enough, especially with your 13incher, but if you try the fronts, and it gets better, you could try the bigger claiper tce now offers for the rear, or just upgrade the stock fronts. Maybe this summer i will get around to doing some brake stuff, and imight start with the rear end, just to play around. Oh, heres another though, see if you leave your street tires on the front, and put your Rs on the back, and see if that changes anything. Thats free and easy to try. That way, your front brakes should lock before the Rs will loose traction. i will try that as soon as weather permeits me to pull he Rs out of my basement and take them out into the weather. The results of that should help us chase down a cure for this problem.

Beecher

 

I don't think the brass bushings or SS lines will do anything for you, I still have these. They simply make brake feel a little better and a little more firm.

What speed are we discussing? I feel the braking instability above 120mph - on a track.

ABS is always working over-time at the track...in fact, I feel it is way too sensitive.

...maybe we're all experiencing a lack of bound control...which can have a fairly major affect on braking stability.

 

My car has the original pads on it (15k miles). JCW factory installed front brakes.

 

bound control eh? how would we change that? turn up the bound on the coilovers if possible (it is on mine, but they arnt even on yet). Or would turning it down actually be the appropriate action?

When i was on my snow tires, it was at a mere 50mph. Once i put the runflats on, i dont really remeber, but i know it went from scary to just a bit twitchey, and nothing to worry about. I was testing this out on a service road, so straight flat and smooth. Honestly, im rarely braking that hard in a stright line tho, im usualy braking to slow down, and im usualy braking well in to the corner, so i havnt done any true stright line hard braking in some time. I now have r comps only (besides my blad runflats 3 of which are scrap, but i have 2 that will work for a mix and match test)

Anyway, how does bound control influence braking?

 

wouldn't the first thing just make the rears lock first, increasing instability?

and isn't braking and turning a big no-no? cuz u can't use maximum braking or turning, cuz of the traction ellipse thingy?

i might be wrong, but this is what i was taught

 

i have no idea on your first question at all.

as for the second, depends on what your trying to achive i guess. I drive my car fast and loose, so im usually 4 wheel drifting most corners, is it the fastest way around a track, no i wouldnt say so, but it is the most fun, and i can run with most of the locals that way, so i do it. i use the brakes to get the rear end out, thats why i brake really late and keep braking relativly deep into the trun, then as soon as im off the brakes, im on the gas. I guess what im saying is that when im on the track, at least the tracks i run, and the style of autox i like, i dont brake long enough to unsettle the back end, its all highspeed, or gradual decreasing speed, so your never really that hard on the brakes for a long period of time, usualy just a hard jab than chuck it around the corner, and im usually turning in around the same time as the braking. Ive got a whole new suspension for this year, so my driving style will probably change now that i have a suspension that will offer alot more grip than stock. Ive only done one event with the r comps, so that should make a big differnce, and force me to drive properly instead of just inducing snap oversteer with the runflats. I will pay more attention to the braking behaviour soon, driving and racing seasin is almost here. My mini should be put back together in 3 weeks at the most, so we will start evaluting things then.

talk to you later

Beecher

 

Ah, well that explains why I haven't felt it. My poor little Cooper tops out around 105-110mph on the track around here.

 

of course i'm willing to do some work! (and have done some already). my stock front brakes have gone to the big landfill in the sky, so that's not an option. the new TCE rear caliper is a cosmetic upgrade, not a performance upgrade. this is directly from todd, not my opinion. my street tires are 215.35.18's mounted on HRE wheels. my HRE's aren't going on the track. even so, one of my above mentioned trials, BP-20's front with Porterfield R4 rear, gives the rear more brake torque potential than the front. didn't help.

as far as speeds.....i've never noticed a problem on the street. on the track, it is a function of THRESHOLD braking. 115- 45 at turn 7 (hairpin) at Sebring or 105-75 at turn 2 (quickly at Homestead). i can go from 125 to 90 (at less than threshold pressure) entering turn 1 at Sebring with no problem. it just occurred to me that some of those that don't know to what i'm referring may never have actually threshold braking! find a deserted stretch of road (or better yet, a closed course) and try somede braking exercises. seriously. stock MINI brakes are good and may surprise you. you aren't at (or near) the limit if you can't get the ABS to intervene. sticky track-only tires take this to another level. then back off a bit and learn to modulate. it takes more time to learn to brake effectively than it does to mash the GO pedal.....lecture over

bottom line: i don't think that the problem is a brake bias issue. i've tried multiple combinations with no notable difference...

maybe threshold braking in a short wheel-based front wheel drive car is inherently "unstable". here is a short vid of how i like to brake....
http://s166.photobucket.com/albums/u...t=d1ab6770.pbr

 

What happened to the original poster? Think he's been scared away by all the suggestions/questions?

I was curious to see a solution to his problem...

 

do you think that the pad differnce alone would offer enough of a bias change to truely alter things tho? I just dont know enough about everything to make an educated guess my self. I just thought of something else. My stock brakes used to be able to squeel (not lock up, just hear them complain) my runflats from about 60 all the way to a stop with out the abs comming on, but all this year, they wouldnt do that, abs came on all the time, then i put race pads on, and they still wouldnt squeel the tires. I wonder if some of the instability disppeared due to some kind of braking deficiency my car developed, but why would that change anyway. not that that really has anything to do with anything.

How could the rear kit be totally looks. it must offer some increase in braking, the shear physics dictate that. Not much tho probably. Probably not enough to really notice, which could be said of the pads as well. track pad to another shouldnt make that big of a difference. Starting throwing stock pads in the mix and you might be able to see something, but you would need them on the front i would think, with better ones on the rear. Someone really needs to try putting r comps on one end only, and normal tires on the other, then switch them, so see what effect that has on anything. I can in a few weeks if no one else has before, but at present my car doesnt seem to be doing it, at least not as bad as it was before, so i wouldnt be able to say if it cured the instability or not.


OV- as for his problem, i would still probably say hes bump stopping, especially since he says hes slammed. Most of the rest of these posts are getting into track territory with fixes that probably wont be for the weak of heart (or pocket book probably, unfortunatly).

 

of course, theroretically, anyone with this problem could be bumpstopping as well, has everyone checked that avenue out. I remember reading posts about it on here a while ago, and it sounds like this problem.

I may be over analysing the problem like i usually do and start dragging brake bias in, when its just bumpstopping. Is there a correlation here between people running coilovers vs lowering springs vs stock?

 

beecher: yes, i think that the pad "experiments" that i have gone through adequatly address the bias issue. i'll ask todd to give his impressions on this thread. i hope that the OP isn't scared off by this informative discussion. i authored a similar thread some time ago....no resolotion, but much food for thought....

upon further review.....the TCE rear brake kit that i have does offer an increase in braking peformance over OEM. this is due to the fact that the same friction coeffiicient applied with a greater moment arm will result in a greater braking force. however, i stand by my earlier comment that the new TCE rear brake kit will not improve upon the brake capabilites that i have.

 

I would expect additional braking power in the rear to exaserbate this problem.

There are so many possible causes. The multicellular jounce dampers - bumpstops, bound control, swing arm movements, wheelbase, tire type, and a host of other items. Unless we begin with a baseline car, we're simply engaging in nice conversation - no problem with that. But a solution is not easy when we consider the different modifications and tire type between us...and perhaps driving style and ability.

Jasen, you still get going fast enough, trust me

 

Since it's moved from suspension to braking conversations...I'll toss my .02 in the ring as well.
1. Wheelbase. As stated; it's short. There's simply no way you're ever going to get a strong braking response from the rear end of this car. As I often say; the Wow factor is never the same out back with any change to it over a good front brake kit. The wheelbase simply won't allow for the rear brakes to keep enough load on the wheels to be of significant value. So can we make it better?

2. Rear alignments. I'm reading a lot about all these control arms and such. Great but has any one really plotted the bump curves on these? If you have your car on lowering springs now you've put it in bump before you even set any rear toe. Under hard braking the car rises and you move to a droop position. Anyone put some toe plates on this and see what happens with 3" of travel? This is just too easy to do and not do it.

3. Rear kits. While I offer them and they do represent a properly biased package when paired with the 13" front kit they won't make a huge change one way or the other as bean has pointed out. The bigger gains here are more mass for less possible fade issues. It's probably only a couple % one way or the other over stock and when installed with a big front kit it really negates any rear brake "improvements".

4. Alternate calipers. Putting the new "rear caliper kit" on the back that I offer won't change anything. The parking brake caliper is nearly the same piston size as what you have now. It's still a single pot floater. It's all show and no go.

5. But I want less rear brake~! Ok, then put in some real crappy pads and give it a go.

6. But I want more rear brake~! Ok, then put two big sand bags behind the back seat for a session and see what happens. I can promise you more rear brake function- more weight over the rear wheels means more rear grip.

I'm all for making things better. And I've been wrong at times too, but we need more real world testing with documented results than just saying "I installed, I bought, I purchased, Race Suspension says, and such. Get out there and run the same tires, same pads, base line it and make on change at a time. Including those sand bags.

 

Todd! You are alive!!! Thank you for you thoughts!!!

Way up above I wrote about toe compliance. I had this 'problem' with a stock mini and with a mildy set up mini - 1/8" toe-in in each case. But I did not experiment enough with each setup to garner anything useful.

Another thought...in 03 or 04, Mini changed the rear trailing arm bushing. Are we having this instability across the the life cycle or just pre or post 03/04?

 

oh ok. I was just thinking the more rear brake would have a tendency to pull the front down rather than having the front brake lift the rear end. Of course the front would still be lifting the rear, but i though if there was more rear brake, it would do it less.

so yup, way out of my league here than. But im still willing to experiment with stuff, and see what can be done.

Beecher

 

More rear brake will want to make the rear "hunker down" more- in the rear. But...only to the point you can keep weight on it long enough to exploit it. You can't change the weight transfer to the front but maybe slow it down some with some suspension changes. Reverse rake might be worth looking at? Problems here are that you may well trade some great braking improvements for very poor handling characteristics elsewhere. 1.5" of reverse rake might be good under braking but I bet it pushes like nobodies business in a high speed sweeper...

Reality; it's all just a bunch of words on a forum here, get out there and try some changes! Get into a local club, do 3 laps, pit and make a change, go out, do three more and do another....doc it all and see what shakes out.

 

haha, a taildraggin mini. dont tempt me! I have to make a taildragger out of one of my other cars yet this year, hahaha.

 

Has anybody mentioned the factory weight bias of 63% front to 37% rear? The sandbags are an interesting idea. I wonder how much 100 or 200 pounds of weight sitting back there would affect lap times or overall "feel."

 

There are a bunch of things to try, but a lot of options come with a cost someplace else; make the rear track wider...that'l lower the static rollcenter and increase the swing arm length...which may also reduce toe changes, along with reduced camber compensation.