Brake upgrades - is bigger better?

[Kjeld]

Incredible! Do you guys guys use both feet on the brake pedal? I cant understand why everyone can "easily" lock their brakes. Again, I have only driven two Elans, both of them before and after upgrade. Post upgrade showed improvement, but neither offered a consistant and even braking up to lock. Marie's is the other car I have driven, and while she can lock it, it sure didn't seem easy to me.<br><br>Again, using an amatuers sensibility, because the pedal is firm, I am not sure why that means the master cylinder is supplying enough psi to the calipers to get the job done. Seems a question of the pump's abiliiy to transfer pedal pressure to psi. Beginning to wonder about Alan's comment regarding the servo now though.<br><br>I am also a little disappointed to hear the Wilwoods have about the same swept brake area as stock. This means my braking advantage is primarily more efficient (and hopefully more reliable) calipers. Though it is consistant with a secondary mission; one less GM part.<br><br>The irony here is that I do not care about track performance. I just think a tiny car like this with what appears to be more than adaquate brake equipment, ought to stop a lot better than this.

[ESM]

I didn't say could lock easily... I said I could lock<br><br>The master cylinder has to be big enough to displace enough fluid to move the pots the distance required to give good braking effort. Its the servo that gives brake pedal sensitivity - hence the term 'over-servoed brakes'. <br><br>The swept area is largely unrelated to braking torque, remember <br><br>friction force = normal force x coefficient of friction <br><br>there is no area term in there. Swept area does influence the pad surface temperature/heat transfer to the disc but those differences in performance occur at the edge of system performance. The pad will also compress a little less with a bigger pad for a given clamping force causing a slightly longer pedal but this is not a large effect. <br><br>The caliper's pot area does affect the friction/pedal sensitivity <br><br>pot force = hydraulic pressure x pot area<br><br>Since the pots supply the normal force <br>more pot area = more friction (for a given hydraulic pressure) <br><br>However, since you need to displace more fluid to move the pots the pedal will be a bit longer (although since 4 pot calipers are much more rigid than single pots they gain back there). This is why there is a limit to how big a pot area caliper you can put on with the standard master cylinder - the master cylinder can only displace so much fluid.<br><br>As I said check the vacuum pipe to the servo for leaks and that the non return valve in the middle of it is working.

[F1 LOTUS]

[quote author=Kjeld link=board=suspension;num=1116235688;start=15#20 date=05/18/05 at 22:22:30]Incredible! Do you guys guys use both feet on the brake pedal? I cant understand why everyone can "easily" lock their brakes. Again, I have only driven two Elans, both of them before and after upgrade. Post upgrade showed improvement, but neither offered a consistant and even braking up to lock. Marie's is the other car I have driven, and while she can lock it, it sure didn't seem easy to me.<br><br>Again, using an amatuers sensibility, because the pedal is firm, I am not sure why that means the master cylinder is supplying enough psi to the calipers to get the job done. Seems a question of the pump's abiliiy to transfer pedal pressure to psi. Beginning to wonder about Alan's comment regarding the servo now though.<br><br>I am also a little disappointed to hear the Wilwoods have about the same swept brake area as stock. This means my braking advantage is primarily more efficient (and hopefully more reliable) calipers. Though it is consistant with a secondary mission; one less GM part.<br><br>The irony here is that I do not care about track performance. I just think a tiny car like this with what appears to be more than adaquate brake equipment, ought to stop a lot better than this.[/quote]<br><br>Kjeld, sorry to hear that you're disappointed with your brake upgade, given that other people with similar parts are able to lock brakes AND the stock 10" dia brakes are lockable too, your Wilwoods being 20+% larger in diameter should be performing much better than they are :-/<br><br>How were your stock brakes performing?<br><br>Which pad compound did you fit with the upgrade?<br><br>Have you performed this test for the Servo<br><br><br>Hang in there Kjeld, we know this brake set-up does work well

[Kjeld]

I am not really disappointed with the brakes, since the originals did not stop well and there were some sticking issues. And as I said, less GM parts.<br><br>I appreciate the servo blurb, thanks. And while I followed most of Alan's explanation (thank you), I got to thinking that maybe the problem is in the geometry of the pedal itself. I wonder if it just requires an inordinate amount of pedal pressure to get the calipers to grip enough. I'll try two feet. Probably buy an ABS sticker for the dash too.<br><br>I am going to stop whining now.

[F1 LOTUS]

Kjeld<br>I don't think anybody considers that you are whining, we're just trying to help <br><br>Try the Servo test next time you get in the car.<br><br>If the Servo seems fine then we could try different pads.<br><br>I have a new set of Porterfield RS-4 pads on my desk at work (you should see my desk stop!) which I'll happily send for you to try (that's why I keep asking WHICH PADS DO YOU HAVE???) and you can pay me for them if you decide to keep them <br><br>Let me know

[Doug]

Good offer Brian  :)<br><br>Kjeld, how big are your calves   ::)<br><br>yes you will want pads with a good friction when colder in regular driving.  It's easy to get the wrong end of the spectrum, which is why Brian is asking.<br><br>Brian, what set up do you have on the desk?  8 pots? (I can see the picture in  my mind already)  ::)

[F1 LOTUS]

8 pots? Nah just 2 coffee mugs and someones biro

[Kjeld]

Wow, thank you Brian. Yeah, I would have answered the pad compound question, if I knew. I will find out what pads Marie ordered for me. Given her need for speed, they are probably some sort of racing compound. But that should be good, right? Performance over wear.<br><br>I'll let you know what they are. I will certainly take you up on your offer if it appears it might help. Very generous of you, thanks.<br><br>And lastly, yeah, I like the idea of auto parts on my desk. A lot more interesting (and probably useful) than computer gear and the paper that I am drowning in.....

[jason_h]

I am jumping into this a little late but this is an interesting topic...<br><br>I have converted my car to the willwood set up (which is recommended for competition use only)and have found that the car brakes much "better" than the stock calipers.  However, the stock ones were in need of "adjustment".  I couldn't  lock up the tyres before and now I can.  There is logic to both sides of this issue and in my non tecnical wording I have found that I have more leverage (ie longer pedal travel) and can modulate the braking force more accurately keeping the car right on the edge of lockup.  The "edge" was no where in sight with the stock set up.  I actually have a race track at my disposal and the track is very short about a mile in length with 9 turns.  I got maybe three "hot laps" with the old brakes and they were soaked.  Since the conversion I get soaked before the brakes do.  <br><br>Additionally, I am not a fan of ABS for those of us who do know how to drive...  If you know how to brake your car at the edge of lockup you will be easily outperforming the capabilities of the ABS system in the car.  Oops i'm getting into another topic  so I will just sign off and say that my guess is that you are doing yourself a favor by installing the bigger brakes.  Plus they look cool! <br><br>P.S.<br>Kjeld:  Did you find out what kind of pads you are running?  Also, what does the surface of your rotors look like? Did they have a bluish sheen after bed in? What do they look like now?<br>Jason H

[F1 LOTUS]

Jason<br>Never too late <br>Interesting input and nicely described in that you feel you're in control of a longer more sensitive lever, that's precisely what I like about the assembly <br>If I recall you fitted the Dave Turner kit? Just for interest do you know which size disc, calipers and pads are fitted to your car? Is your set up fine for both track work and daily driving?<br>

[ESM]

A longer AND more sensitive pedal?????? (Stef could have a lot of fun with this). Don't you mean softer and longer (like the toilet roll)? <br><br>I was chatting to the guy who services my car on Tuesday and he was telling me that its not unusual for a new Elan customer to come along with a seized caliper (no shock there) and he sorts it out and then the customer complains that the pedal got longer ::) <br><br>As long as you are used to the feel of your brakes and have confidence in them up to lock, pedal hardness/feel isn't that critical. <br><br>Kjeld,<br>You're not whining, you want to see whining see the thread in problems I started about alternators!

[Kjeld]

Longer and more sensitive pedal.... yeah, I guess walked into that one. I meant the force applied by the pedal assembly to the pump. You are the engineer, but the pedal is just a lever, right (please, no brit puns here)? Depending on where pedal arm pivots, more or less pressure is applied at the pump. My new theory is that if it takes two feet to apply enough force to stop the rotors, and if as you guys keep telling me, the pump is adaquate, then the problem must be the force into the pump.<br><br>Not only will I stop whining now, I think I will start riding my bike to work more often. It stops better and I can build up my legs enough to stop my Elan.

[jason_h]

Brian<br><br>I have the Dave Turner 12" rotors installed...  The pad/rotor ctr. line is 5 1/4" away from the hub center.  Lots of leverage.  The calipers a dynalites.  Won't work with the 16s from what I remember.  My car currently has "bling"18s (that that weigh in at 25lbs each ) so they at least clear easily.  Actually I am looking to go to light weight 17s.   I am going to have to have a look in the tyre/wheel section and see what people have to say about wheels.  <br><br>Good luck on the Brakes Kjeld... just keep investigating<br><br>jason out

[Dico]

If you think that a 'big brake' upgrade will make the car stop faster under normal driving conditions then you're mistaken - this is only true if your stock brakes were faulty.

I drove Montys car today with the Wilwood setup - 310mm discs/ 4 pot calipers/dot 5.1 fluid/stainless hoses. amazing! As i see it theres no way the standard setup, even when working perfectly can match this upgrade. And i'm talking from cold here. Infact it made me wonder if they were just too good as it was so easy to lock up the front wheels.
Montys had his suspension stiffened but it still dipped down severely when braking.

Just need to pull my finger out now and fit mine

[Dave M]

To revive an older thread, I've got some thoughts after the last outing with my car to the track. My car has the AP front brake conversion along with an air ducting system that should provide a nice stream of fresh air to the inside of the rotor. Therefore one would think I'd have no issues on the racetrack, right? Wrong. I continue to have fade issues after some heavy lapping. If you let things cool down, the brakes come right back and are solid, but they will fade. Here's my guess:

When you put the big brake kit on the front, you've effectively changed the amount of braking force you get when you step on the pedal. Most who've done an upgrade will attest to the better "feel" you get. For me that means not having to mash the pedal to get adequate braking. Since there is less pedal pressure, there is less pressure in the lines to reach the rear brakes. If you look at the way the proportioning/limiting valves work, it is equal pressure until 15 psi, then a ratio of pressure (for my car at least it uses the 20% valves) up to a max psi rating (65 or 70, depending on when built). By changing the front brakes to provide more grip at a given pressure (even by just changing pads), already you've biased the car more to the front. Now with less pedal pressure to make the fronts work, there is even less work done by the rears.

I'll continue this later as I'm looking into adjustable proportioning valves to bring the rears up to "operating" status (my rear pads still look brand new after 4 track days since the rebuilt calipers were put on), but just wanted to get some thoughts and provide some warning on this. I'm still a big fan of the kits, but wanted folks to understand that to once again balance the car for track work and get true, maximum braking abilities out of the car, more work may need to be done.

[ESM]

Yeah big front brake replacements do put more energy through the fronts and will actually increase stopping distance a little, as well as fading a little sooner than they would if the balance was spot on. While adjusting the front/rear balance would be good to optimise braking performance (minimise stopping distance) I doubt the rears would take enough energy out to delay front fade by much. If you take the fronts almost to lock they will get the same 'power' put through them regardless of rear braking - the extra rear brakes will help by making the braking event a little shorter and taking some of the energy burden but your are talking about a 5% difference (under heavy braking a standard has around 11% of the total braking effort at the rear compared to the front, in a HiSpec front brake equipped car - I've already done the numbers for that system - its about 6% at the rear).

I think ducting improvements are the way to go to kill fade.... If kuching's still about he's probably the man to ask about that. Also look for pad compounds that hold friction at high temps.

you'll find it hard to match the stock brake proportioning I'm afraid.. Unless you get a 15" wheel Wilwood front kit

[Dave M]

Thanks for the info, Alan! How do you come up with the % figures you mention? Though I think I can see how the rear would be close to 11% in a standard Elan: since the valves send 20% of the braking force to the rear (and assuming you do not go over the max pressure threshold of 65/70 psi), you start at a 20% figure. Assuming pad compound is identical, the torque applied to the fronts would be slightly greater because of the rotor size (the front caliper is further out from center than the rear) - therefore lower the 20% a bit more. Maybe there is also an adjustment made due to the weight bias front/rear? Though that may limit braking ability, it wouldn't change the actual force applied to the rotor. I may be misunderstanding what you mean by "effort", however.

To help increase the ultimate work the rears are able to do relative to the fronts, I can:

1) increase the line pressure to the rear calipers
2) install a grippier rear pad
3) increase the size of the rear rotor
4) install stiffer springs in front to prevent dive and weight transfer
5) lighten the front of the car

Sound right?

All this said, Alan is right concerning a standard car with standard-spec tires. You will have a hard time matching the stock brake proportioning if you go to a big brake setup in front. However you may never use them repeatedly hard enough for it to become an issue. My issues are first, I never liked the stock brakes on a racetrack, and second, my car isn't "standard" any longer - including the tires. The stickier tires alone have made handling and braking aspects of the car change, and probably not all for the good, hence why I'm chasing brake bias at the moment.

One last note - the adjustable proportioning valves I've found so far have a max pressure reduction of ~60%, so that would send more force to the rear than stock. In a standard car, this could be too much. If you applied enough pressure to the pedal to put 85 psi to the front brakes in a stock car, the rears would see 29 psi (see table in the Service Manual, section JE page 21). With the adj valves I'm considering, the min pressure the rears would see would be 34 psi, and you could always increase that if needed.

[johnbenk]

Hi

I beleive HI SPEC (dont laugh) sell these.

Beware loging on to their web site though you WILL SEE a warning from a
dissatisfied customer before their web page.

[Dave M]

Glad to see they didn't just discriminate against us Elan owners!

Some more info to ponder:

http://www.stoptech.com/tech_info/wp_pr ... lves.shtml

[ESM]

I like stoptech - they know what they're talking about.

I got the numbers for front/rear 'effort' by taking the brake proportioning diagram from the manual (which is plotted in brake line pressure) and deriving the equivalent front rear braking torque graph for a few brake setups. The torque is calculated based on the effective braking radius - which is derived from disc radius and pad depth - the caliper pot area and a typical pad coeficient of friction. The maximum stopping effort will be proportional to Front torque (just before lock) + rear torque, assuming front lock always occurs before rear lock. I gave my figures under the 'under heavy braking' proviso because I selected a point well after the rear effort is proportioned downwards. I admit I picked an arbitary brakeline pressure to represent 'heavy braking' and this skewed the figures a bit, I should have selected a common front torque but it was late and I couldn't be bothered I just did it properly and the difference is more like 3% (at the same front braking torque this time).

Redressing the frontward proportioning changes caused by front disc size and pot area increases is tricky. You want essentially the same front brake torque vs rear brake torque the Lotus set up (because they CAN set up a car to handle well). The problem is that the transition in the slope of the brake bias graph occurs at a certain brake line pressure not a braking torque - the braking torque of the transition is determined by the size of calipers & discs and you've been and gone and changed them. So if you up the rear efficiency in proprtion to the front you delay the transition - relative to stock - and move the bias much further to the rear than standard after the initial proportional slope. I've stuck a graph on that shows a stock setup, a Hi-Spec setup and a couple of hypothetical front & rear upgrades to show what can happen to the brake balance if you're not careful.

On your other ideas: the weight distrubution will effect the locking point (mostly of the rear) adding rear weight simply allows you to put more bias rearward before you get rear lockup - that problem you don't got. Ditto I wouldn't go for stiffer springs. I think a grippier rear pad is a good starting point and, if I were you, I'd see if Stoptech would supply proportioning valves that would match the stock behaviour on your modified brake system.