Rear Disc Brakes

[jbcollier]

Cross-drilled rotors are very common in motorcycle applications where they do provide a some of the effect of an internally vented rotor.  There is no room for traditional internal venting such as cars use due to space and weight considerations.  Like a motorcycle, the Europa's stock rotor is too thin for normal internal venting.  I think that careful cross-drilling can provide a benefit.  Others have found it so.  No doubt a a normal vented rotor is better, 100%.  However, space is at a premium if you want to stick with stock wheels.

Track days?  Racing?  Fit traditionally vented rotors, no contest. (regulations permitting).

[JR73]

It’s worth bearing in mind that whatever the 47’s had fitted was relative to the time -1960’s.
Disc brakes where still a fairly new technology back then and things have certainly moved on somewhat since, if vented discs where available (and affordable) then I don’t doubt that they would have been fitted - check out the discs fitted to F1 cars from that time.

The kit that literary has fitted was designed to replace the originals without the need to change wheels, give an improvement in performance whilst maintaining a good balance. - yes all sorts of other options are possible, have seen vented discs and bells with 6 pot AP front and 4 pot AP rears fitted under 15” wheels on a Europa that was running over 350bhp - it was used solely as a race car though and the development of other parts of the car went hand in hand with the brake upgrades.... running slicks it actually bent a set of tubular front lower wishbones under braking - the design and manufacture of these was changed as a result. It also ended up having completely different front uprights because the original trunnions then started to fail......worked fantastically in a race environment but in all honesty would be complete overkill for a road driven Europa. - seriously, how hard can you drive on the road to require that sort of braking setup?!

Like I have mentioned, pretty much the same setup as literary has fitted is on my own Europa with the aluminium front hubs - whilst I was racing it I used a variety of race compound pads (Mintex 1122 and 1144 predominately from memory) and never had any fade, didn’t warp/cook any discs (had temp paint on them to monitor) and certainly didn’t find anything lacking in performance or feel. When I retired it from competition it was then solely used for track days, initially I continued using the race pads but found that good quality road pads where more than up to the job when only at 7 tenths with a passenger (extra weight!) and now run exactly the same on the road (have now connected the handbrake) - they are never close to any sort of track temps but have plenty of stopping power and good initial bite, even without a servo.

As a side note, if you are buying aluminium front hubs then be aware that there are some cheaper ones available that I have seen fail - the outer bearing lands broke into the centre of the hubs...wheels go a bit wobbly when that happens! So buy from a reliable and trusted source.

[BDA]

Speaking of racing brakes, I thought it might be of interest to see documentation on a race prepared Europa back in the ‘70s. The car was prepared for a production category car meaning most modifications were limited to what was available in production cars at the time so the brakes were very similar to stock brakes. Engine mods were allowed but I would guess it produced less than 200 hp. (A very different animal than what JR73 described.) The races were 50 mile sprints.

 http://lotus-europa.com/manuals/misc/jensen.pdf. (See page 11)

[TurboFource]

I inquired about the Jensen rear upgrade previously and no one thought it was worth pursuing....

[jbcollier]

The Jensen document is about building a race car to meet regulations.  They used twin leading shoe rears because regs forbad the changing of brake type.  For their purposes, it worked well.  For street use?  Not a good idea as you would lose your handbrake and the parts to do the conversion are now hard to find.

Also note they changed the rears to match changes at the front.  Important to maintain overall balance when modifying the brake system.

[GavinT]

It’s worth bearing in mind that whatever the 47’s had fitted was relative to the time -1960’s.
Disc brakes where still a fairly new technology back then and things have certainly moved on somewhat since, if vented discs where available (and affordable) then I don’t doubt that they would have been fitted - [...]

Intuitively, I'd agree.
But for the sake of the exercise, the devils advocate may consider what underlies this.

I'd accept that a calliper like the much acclaimed Wilwood would be seen as superior. It's made from billet material so can be lighter and more compact without sacrificing rigidity. It also houses four pistons for more even pad wear and better modulation/feel.

Pad material and it's composition has also improved over the years.
Similarly, I expect rotor metallurgy has likely improved, too.

But I don't think there's any getting around the physics. The devils advocate might say those improvements have been incremental but not night and day.

350HP Europas?
Sure, but if we're considering a bell curve of braking performance the tails are invariably substantially different from the mean. 350HP Europas are definitely residing on a tail of the bell curve.

Fr'instance, I'd think the Lotus 47 is a reasonable aspirational standard - somewhere to start.
From BDA's previous link:
Lotus 47GT - 565 kilo / 1,246 lbs with 165 bhp / 123 kW @ 7,000 rpm.

I'd suggest there won't be many road going Europas around with a better spec. and most will be heavier.
I've not heard widespread complaints around the braking performance of a 47.
So, in my mind, if we accept the general notion that brakes should be purchased relative to the HP they're attempting to arrest, the question becomes a little easier.

Certainly, a rotor with a higher mass will absorb more heat. A vented rotor will shed heat better than a solid one.
So, how much quicker would a 47 be with vented front rotors given they have no history (as far as I know) of exceeding the performance envelope of the factory spec?
I suspect there'd be very little in it.

As a caveat, there are, of course, other variables and I'm certainly not any sort of brake engineer so would be happy to be educated on all this.

[BDA]

Please understand that I brought up the Jensen race car only for comparison purposes to the race car JR73 described. As I attempted to make clear and JB reiterated, that Jensen car was constrained by the rules. If they were allowed rear discs and vented discs, they certainly would have used them. It was the best method available to skin that cat and they actually did skin the cat.

[jbcollier]

A friend of mine took up vintage racing with a nice Sunbeam Tiger.  By god he was fast out of the blocks!  Holy Doodle, leading by a wide margin only two laps in.  Third lap, approaching the hairpin with limited run-off, the brake pedal hit the floor.  Boiled his brake fluid inside 3 laps and 10 minutes.  He and the car survived but he was never as fast again.  Brakes, particularly thermal capacity, can make a huge difference.

[GavinT]

3rd lap? . . join the club

Other tracks were OK, but at Calder raceway in Melbourne, my brakes would consistently last only three laps till I really had to nurse them. The very long front straight and the longish back straight & not much in between is what I put it down to.

Between heats, I'd have to adjust up the rear shoes each time. Being play racers, I don't have enough data to be 100% sure of things. We used DS11 pads for a long time and when they became rare we changed to something called "Black Flash" front pads and they were fine too.

It's all anecdotal but I recall an event at Sandown raceway. The wife of a club member was running their Elan. Don't be misled, she'd done lots of racing and was a good steerer. The Elan had similar performance so always a fun dual.
Up over the hill we went and down towards the left hand corner. I braked for the corner and she sailed past me on the inside. Dammit . . four wheel disks are impressive, I thought.

[JR73]

47’s did indeed evolve over time, the factory uprated the front brakes whilst they where still in production - the front upright was specially cast in common with the F2 version of Lotus 41 to accommodate a larger Girling brake for the later 47A model and I’m sure you are aware that they had rear discs from the outset along with a balance bar pedal box. - they may look similar to the standard Europa equipment but they aren’t the same.

Pretty much any 47 you see now is likely to be restored back to ‘as was’ spec from when it was new in order to compete in the historic race series’ that they qualify for so anything that may have developed over time would have to have been undone. - I’m not saying that the originals where poor in any way but racers are always looking for small improvements in all areas so it’s likely that vented discs where fitted on some cars as time and technology moved on in order to gain the next small advantage... Historic racers have their hands tied somewhat and have to make the most of what was originally fitted regardless of if it could or needs to be improved.

The reason I mentioned the 350bhp Europa was just to show that anything is possible - and relatively easy to engineer but it then generates the need to further improve other areas as well. Would make for great bar room bragging rights but ultimately it’s unlikely that many (if any) would need anything like that for road use and occasional track days.

The question seemed to be more about the kit that literary has recently fitted and whether it was a noticeable improvement - I would personally say it is a good upgrade that fits easily, gives a good balance, performs well and the parts are readily available to be sold as a kit. - is it increasing the unsprung weight?

You could fit the 47 brakes but I reckon it would cost you more in time and money to source and then some more of both to fit (a bit of modification required to the front and extensive modification to the rear suspension for certain - questionable as to if it’s even possible?) and once again it’s likely that the unsprung weight will alter from the original - possibly weighing more with the larger calipers and stronger uprights etc...

There are endless options, it really depends on what you are actually after and how you intend to use your car?

[literarymadness]

I called Steve Smith over at Twin Cam Racing in Sarasota who did the install and he told me that in addition to the aluminums hub that the new calipers seemed lighter than the factory ones so those two factors combined should more than offset the weight increase of the vented discs.  He saved my original parts for me and said he would weigh them in the next day or so. His place is about 200 miles from me; otherwise, I would do it myself.  I will post the weight when he gets back to me. Does anyone know the weight of the ones that come in the kit or lives in the UK (to save me an overseas phone call) and could call Richard to find out. The brakes already seem significantly better and that was with driving less aggressively in order to properly break-in the Mintex pads. My TCS is running about 125+ hp at the rear wheels and the weight is about 1450 lb. (sans petrol, spare, or rear tub).

[Chuck Nukem]

Here are the weights of OEM parts in grams - lbs

Cast iron hub (no studs) 2034 - 4.48

Front Brakes      
   Rotor   2546 - 5.60
   Caliper   3140 - 6.91
   Caliper bracket   323 - 0.711

[literarymadness]

Thanks for posting that Chuck! The aluminum hub W/O studs is 2.2 lbs.

[GavinT]

The question seemed to be more about the kit that literary has recently fitted and whether it was a noticeable improvement - I would personally say it is a good upgrade that fits easily, gives a good balance, performs well and the parts are readily available to be sold as a kit. [...]

Oh, no, I'm certainly not looking to criticise Literary's kit nor his (or your) experience with it.
I've already said the kit looks good and both your experiences are appreciated.

My curiosity was to consider a more fundamental point which goes beyond any particular brand of kit.
To reiterate, I expect few would disagree that a larger vented rotor would out perform a smaller solid rotor, but that's beside the point.

The assumption seems to be that the existing Europa front solid rotor is under-performing, but, as far as I can see, there's no broad evidence to support such an assertion.
There's also no broad acceptance that Lotus 47 front brakes under perform and we know they aren't entirely comparable to a stock Europa. My consideration of using the 47 as a reasonable benchmark also accepts that.
I hope that clears up where I'm coming from.

Rear disc conversions are noted on these forums in many shapes and sizes.
Richard's kit seems well regarded all round. There's also many home brew conversions using a variety of different components. The consensus seems to be that converting to rear discs provides a definite improvement.

Based on that, a vented rear rotor should out perform a solid one, right?
I reckon the same logic should be applied to the front rotors but that doesn't seem to happen.

Perhaps it's because we're all human. I expect Chunky would be OK with challenging our own assumptions . . . while adding lightness.

[literarymadness]

Vented brake rotors simply provide better cooling and are less likely to warp and fade. Colin Chapman wasn't worried about the longevity of his cars nor its components. I on the other hand don't have that luxury.  I live in Florida where people drive stupid fast over the Interstate 70 MPH Speed Limits and seem to be overly brake-happy even in semi-dense traffic. I drive occasionally from South Florida to the Smoky Mountains of Tennessee and downhill mountain-driving is murder on your brakes and I will take any advantage I can get.  And the last thing you need is brake fade going downhill. I live in a really flat topography (South Florida) and am not a particularly good mountain driver like some of the guys on this forum who live in those type of regions.  I need my vehicle to occasionally be a better car than I am a driver.  This is something I wanted to do and am not telling anybody to do it. 

Back in the day, I was the guitarist for a band in the '80s that had a number of hits. Those were the days when I really pissed my money away on things I didn't need LOL. 
But it made me happy.