Ultimate brake thread

[EricB]

This question grew out of a discussion with mlytle regarding brakes.  I have owned 320i vented front brakes and 15" wheel big brake kits from Ireland Engineering and Massive Brakes.  mlytle had pointed out the bigger brakes are limited in hard use by the larger rotors(300mm) having too much leverage on the tii wheel bearings.  I have now thoroughly (and expensively) tested this theory and think it is correct.  Has anyone ever made a strut that could fit the geometry of a 2002 and has an E30 wheel bearing?  Are E30 wheel bearings even that much bigger?  It seems like this would be a fantastic way to get brake options that would be the same size, but work better.  I had a brief exchange with Ken from 2002underground.com and it sounds like he is thinking of making such a product.  Does anyone else think this would be a great idea or is there some obvious reason this is a bad idea?  I was also wondering if anyone has pictures of brake ducting that has been installed without a front spoiler on a 2002?  Thanks

 

[Tommy]

Can you or Marshall elaborate some more about the theory? I find it hard to believe that the rotor diameter itself would make a difference. Just quickly thinking through I would say stress caused to bearing by braking is defined by tire diameter, friction, vehicle mass, weight transfer... unless the brakes are so weak that you're not able to lock the wheel, then it would different.

I am using e12 struts, that have same bearing as tii, with some over 300mm rotors but I'm quite sure in my case 17" ET20 wheel and 225mm semi slicks cause more bearing wear than brakes.

[redrumm3]

As Tommy mentioned in his post above, I don't believe bearing size is going to have any effect on the braking. However, I can't directly address your Theory without greater details. Certainly larger brakes can put additional load on the bearing which may in turn affect the longevity and life of the bearing, but ultimately the tires ability to stop the car via tire diameter and width, friction, vehicle mass, and weight transfer will be the main determining factors. I have been running 30mm larger brake rotors and 4-piston Brembo calipers and race pads vs. stock rotors and single piston calipers on the front of my E36 M3 race car with the stock bearings for years without any issues. I do replace the bearings every two seasons as preventative maintenance but that is mainly because the heat generated can cook the grease out of the bearing. I can generate brake temperatures in excess of 800 degrees F depending on the pads. This issue would be the same no matter what size bearing was used.

[AceAndrew]

I am familiar with Marshall's hypothesis.  I've got the experience of dealing with at least a couple hundred of the IE wilwood and volvo kits.

 

Regardless of the cause, there is something to be said for running some larger bearings.  However, the number of those that would actually NEED it over existing options would be very very minute.  Therefore, if the development needs to go beyond some simple parts swapping/welding it might be a challenge to recoup the initial investment time/costs.  I was around a setup several years ago that hybridized the e30 strut housing, unfortunately no pictures remain from that (it would be interesting to explore again though).  

 

Lastly, in regards to your question about brake ducting without a front spoiler.... that is something I'm working on right now and should have sets for sale in the next month or two.  I've spent the last year underneath late model Porsche GT cars (and fancier exotics with not as well thought-out ducting systems), taking inspiration from those cars is yielding some interesting options.

 

Edited August 16, 2017 by AceAndrew

[TobyB]

Quote

the larger rotors(300mm) having too much leverage on the tii wheel bearings.

 

 

???quoi????

 

I need a picture- hopefully with circles, arrows of different colors, force vectors in Greek, and some lengthy equations!

 

Because 'leverage' is, as my high school physics teacher was so fond of repeating, "vague enough to be true"

 

Background:  I've raced the 320 rotors on E30 hubs for something well over a decade, and the ONLY limitation I found was that the 

stock 2002 bearings tended to get pretty warm, requiring regreasing pretty regularly.  

Synthetic grease, used correctly.  As in, fill the hub about 3/4 of the way.

 

The tii sized bearings got grease once a season whether they needed it or not.  Which they never did.

 

And as other boards are so fond of pointing out, I am STUPID hard on brakes compared to most racers.

I hit curbs.  I hit other competitors.  I have been airborne over the t10 curbing in Portland several times.

T5a in Seattle almost all the time.  I brake too hard, too late, too early, too often.  And the bearings survive.

 

And street use doesn't tax ANYTHING in the 2002 half of what a 30 minute sprint race (or an 8 hour enduro) does.

 

Ducting?  there are lots of possibilities, from behind the headlights (SCCA legal) to a lip under the chin to pulling air from beside the radiator.

To a hose zip- tied along the 'frame rail' that is just open to a high- pressure zone under the car.

It's something you do as the temperatures require it.  And a thermometer with a remote thermistor is really helpful here, as is temperature sensing paint-

it's surprising how inlet temperatures vary around the front of a 2002.  

As is a differential pressure gauge (used for commercial HVAC testing)

When I got the 2002 I now race, it had rear drums with some of the least- inspiring  looking ducts under it I'd seen-

and yet, those $4 worth of shop-vac hose parts worked at least as well as anything I came up with afterwards.

 

t

Edited August 16, 2017 by TobyB

[NickVyse]

[EricB]

In a previous post mlytle posted:

 

"have you used the massive/IE 11.75in brake system yet?

as probably the one who tracks an M2 harder and more often most, i would not put that system on another track car. the wheel bearings on the 2002 (tii) are not strong enough to support it. they flex enough in hard corners to allow the huge rotors to push the caliper pistons back in their bores...resulting in the need to double pump the brakes at every corner to slow. these symptoms are not evident in mild or street use, but when you really push it on R-comps it is bad.

the smaller e21 rotors, real track pads, and cooling ducts is a much better solution. that is the solution i was using with no issues until i mistakenly "upgraded".

Just my experience. ...yours probably varies! :-)"

 

I have not had the same experience with the calipers pushing the caliper back, but I have had warping of the rotors with both kits.  The Ireland kit had to be shimmed to get the caliper lined up with the rotor and the pads never wore flat.  The fit and finish on the Massive kit is notably better, but I have still managed to warp rotors on the track.  I am running a 2.5 liter s14 and 205/50/15 Bridgestone RE-71 tires.  Anything works n the street, but on the track at COTA and ORP I seem to be able to kill brakes pretty handily.  Fade has not been a big issue, but I am disappointed in the durability and it seems like they could be a little easier to modulate.  I am going to take his advice about the ducting and I think it may be better to go with the smaller brakes which is a little surprising to me.  I am not sure if this confirms the theory about the bigger rotors, but I wondered if they would work better with a larger bearing.

 

Sorry to disappoint, but my vectors and greek are both a little weak.  Thanks for the input on the brake issue.

Edited August 27, 2017 by EricB

[Tommy]

Alright now I got the theory and related issues. There may be a point but there's many other things related than just the bearings. Light springs are sometimes used under pistons to hold them closer to rotor. 

 

Really optimized system has as small rotors that are just big enough with effective cooling. However generally my experience is that bigger brakes are easier to make work without issues.

Pads wearing unevenly is a problem with all the "cheap" calipers that have equal sized pistons. Another is how rigid the calipers and their mounts are. For example the old Wilwood Superiltes that I have are giving up a lot under pressure. The race shop owner nearby calls them lumps of clay (selling Alcon). If the money wasn't an issue...

[TobyB]

mmm, darn, I was all geared up for thetas and omegas...

 

heh.

 

But yeah, with the rotor so far inboard of the center of rotation of the hub,

and all the spindle overhung on that, it's going to flex.  I'm not sure I agree it's

the bearings' fault so much as just the overall design, which was driven by 4- pot fixed calipers.

On a light, 100bhp sedan, with 4.5" wide tires.  The 10" wide gumballs we run now just don't enter into the original design calculations!

And inexperience, too- in 1966, there were few cars with disc brakes, and most were having teething problems...

The E30, tho, stock, doesn't leave room for a 4- pot, trading better geometry for an inferior caliper...

 

Ducts.  They are important.  I'd try that first for warping rotors. How much ducting do you have now?

 

And yes, knockback with 300mm rotors, I could see that.

I've never been allowed anything

over the 320 vented rotors and iron calipers, so that has not yet been a problem.  Plus, road car

calipers are designed to reduce it, too, whereas Wilwood et al are expecting

modern levels of suspension stiffness.

 

t

[tzei]

I'm running 345 mm rotors at front. Tii bearings in Al-hubs. Just few races with these rotors. All good so far. Before i had 328 mm Alcon discs for years. Only issue was calipers. Binned Wilwood superlite II's that i used and went for AP calipers. Totally different and better feel! Wilwoods flexes in bleeding process quite a bit even with bridge bolt. Can't really recommend those for anything - sorry. Maybe for modest street use but then again wouldn't one want decent calipers even for that use?

[EricB]

OK, now I am even more confused.  TobyB, you have been using E30 hubs with 320i rotors?  I thought the common big brake setup was e21 haps with 320i rotors.  Can you use E30 hubs on a tie spindle?  tzei, you are using 345mm rotors?  Are Al hubs aluminum hubs?  The Massive setup has 300x32mm rotors and barely fits under a 15" wheel.  Are you using 16" wheels.  If I wanted to switch to a smaller rotor with AP racing calipers does anyone make a kit?  AceAndrew, I look forward to your brake ducting kit.  I am currently not running any ducting and will integrate this into my next brake setup.  Thanks

[TobyB]

No, sorry, you were talking in your op about an e30 swap.  The e30

geometry is better, but that comes with a tradeoff to a less- desirable caliper type, due to space restrictions.

 

If you have no ducting on a track car, you'll run into trouble with anything over a tii engine

on many tracks.  Stock, there is little airflow.  If you look at anything after the E21, you'll see that BMW changed

the way they moved air around- the backing plates change, the valences work differently...

Again, the 2002 was a cheap 100 hp car meant as a sedan.

 

Even a huge rotor will eventually heat soak with no airflow.  Anything that ducts flow to the eye of the rotor will

do it- the rotor's a powerful fan at 120mph.  But it needs a source of cool, relatively non- turbulent air.

Under the chin works, next to the radiator, crap, probably just a scoop placed in the right part of the wheelwell.

Again, the hvac manometer that reads in inches of water is a godsend- put one tube at the eye,

one tube where you want to put a duct inlet, hit 75mph, and see if it reads positive by more than a few inches.

 

As I posted above, $4 of shop- vac hose is often all it takes.  If it's in the right places...

 

t

 

[tzei]

EricB. Yes rotors are 345 mm 32 thick. Hubs are made of 7075 aluminium. I'm using 17" wheels. Air ducts (76mm/ 3") comes from front air dam. One per wheel.

Edited August 28, 2017 by tzei

[Rodolfo Alcocer]

In a previous post mlytle posted:
 

"have you used the massive/IE 11.75in brake system yet?

as probably the one who tracks an M2 harder and more often most, i would not put that system on another track car. the wheel bearings on the 2002 (tii) are not strong enough to support it. they flex enough in hard corners to allow the huge rotors to push the caliper pistons back in their bores...resulting in the need to double pump the brakes at every corner to slow. these symptoms are not evident in mild or street use, but when you really push it on R-comps it is bad.

the smaller e21 rotors, real track pads, and cooling ducts is a much better solution. that is the solution i was using with no issues until i mistakenly "upgraded".

Just my experience. ...yours probably varies! :-)"

 

I have not had the same experience with the calipers pushing the caliper back, but I have had warping of the rotors with both kits.  The Ireland kit had to be shimmed to get the caliper lined up with the rotor and the pads never wore flat.  The fit and finish on the Massive kit is notably better, but I have still managed to warp rotors on the track.  I am running a 2.5 liter s14 and 205/50/15 Bridgestone RE-71 tires.  Anything works n the street, but on the track at COTA and ORP I seem to be able to kill brakes pretty handily.  Fade has not been a big issue, but I am disappointed in the durability and it seems like they could be a little easier to modulate.  I am going to take his advice about the ducting and I think it may be better to go with the smaller brakes which is a little surprising to me.  I am not sure if this confirms the theory about the bigger rotors, but I wondered if they would work better with a larger bearing.

 

Sorry to disappoint, but my vectors and greek are both a little weak.  Thanks for the input on the brake issue.

You can replace the wilwood discs with PFC discs. Much better in every way.
Bolt circle is the same.



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[tzei]

One thing comes to mind that i think is worth mentioning... when choosing calibers do check what pads you need. Friction materials that are available (one's you want to run) and prices. Your newly purchased hipo cheapa$$ calibers might use (thin) pads that costs as much as those calibers did. At that point people are usually a bit disappointed.