Inboard V outboard Brakes

[alfagtv152]

Hi Guys,
How about a bit of discussion over the advantages and disadvantages of each.If you read any discussion like press release on the Alfettas inboard brakes they generally say a reduction in unsprung weight is an advantage yet I read where some say that reducing sprung weight is a good thing by going outboard with the brakes.To me I don't see to much improvement unless you are removing some weight for a start and the unsprung weight is applied directly to the tyre which is not as good as being able to control the sprung weight distribution to an extent through your suspension setup.To me that is what the suspension is all about,controlling how all the moments of force(and weight) in the vehicle motion and loading are applied to the tyre.I have never had any heat issues with my rear brakes and run slotted vented rotors on the rear after tearing the centre out of a solid disc!.
What say YOU!
Cheers
Andrew

[Typhoon90]

The advantages of inboard brakes are somewhat lost with a De Dion setup, as the De Dion linkages etc add considerable mass to unsprung weight compared to a full double wishbone or Chapman strut setup. De Dion also needs the same amount of underfloor space to work as a live axle, so it does impinge on interior space a fair bit compared to a full IRS with gearbox in the conventional spot.
De Dion setups also transmit the suspension/torque forces into the body in a much more component friendly way than Chapman struts or wishbones. If you look at Alfas as an example, it means the front and rear suspension hard points in the body are fairly close together too, meaning the body shell can be made lighter and still carry the loads as the distance front to rear are smaller. I believe this is one reason Alfa went with torsion bars as well, the chassis anchor point is fairly close to the rear suspension points.
De Dion also means the designer can keep the car from the axle hump back nice and light, as there are no loads going into that area, so a bonus for polar moment.
They do make initial assembly of the vehicle quicker though, shove the whole assembly up under the body shell on it's cradle, connect a few wires, lines and cables, whizz in a couple bolts and it's done...especially if the workforce has been bolting in the same rear ends for 10+ years!
So the main advantage is a reduction in unsprung weight, which allows much more rapid wheel/spring and shock response to uneven road surfaces, but again, that is somewhat lost with De Dion, which does transmot loads to the other wheel, not as much as a live axle, but it is there.
The main disadvantags are servicing and brake cooling. More than one Jaguar has been lost to a rear brake fire for example, due to maintenence beng put off, resulting in sticking rear calipers, which is compounded by lack of airflow to the brakes, and a flambe cat. It's also a VERY hard fire to extinguish once it starts.

Regards, Andrew.

[alfagtv152]

Hi Andrew,
Would I be correct in thinking from what you wrote you were in favor of the Alfetta's inboard brakes as opposed to making them outboard?,like me!.
Cheers
Andrew

[Duk]

The argument of unsprung mass is probably relevant, but there are plenty more cars with outboard brakes that handle well than there are inboard braked cars.
I don't normally go for the 'majority rules' argument, but I hate the inboard brakes  .
Maybe if Alfa Romeo had used calipers that were at least self adjusting, but even then.........  .
If it were legal for me to go outboard, I'd do it.

[Typhoon90]

Hi Andrew,
Would I be correct in thinking from what you wrote you were in favor of the Alfetta's inboard brakes as opposed to making them outboard?,like me!.
Cheers
Andrew

Am I in favour? If the car came with outboard brakes but still the transaxle, it wouldn't bother me. They are where they are through deliberate design, I think it's more the fact it was easier for Alfa to keep assembling teh same transaxles the way they were than changing things.
Like the Jaguar rear end, all it would've taken to really improve the brakes is vented rotors and a $5 stamped sheetmetal duct hanging under the transaxle directing air into the whole assembly.
For those that think the Alfa integral handbrake caliper is complex, it's really no worse than a lot of Japanese cars out there, my Skyline had a similar setup and the adjuster was notorius for galling the threads on the pistons.
I'd like to work out a way to adapt those cheapo cable actuated brake calipers for trailers to serve as an independent handbrake caliper and use conventional calipers for the hydraulic system, but that's not going to happen till my car has issues with the calipers.
Handling isn't the primary advantage to inboard brakes, faster wheel response on bumps is. Which is why Jaguar adopted it early on, ride quality.

Regards, Andrew.

[alfagtv152]

Hi Duk,
Good to hear from you,the original callipers are self adjusting if they still work as they should.I find on my race car I have to reset the clearances after each event because they end up a little tighter than I would like,I have experienced this on another car which I reconned the rear brakes on before the last event and checking them after I had 2 that were a little tighter than I set them before the event.
Cheers
Andrew

[Anthony Miller]

I think the main reason for outboard brakes after brake cooling is transmission cooling, transmission acts as giant heatsink and when your rotors are glowing orange your transmission fluid is turning to water.at least that was how it was explained to me by someone who had just had a rather tasty fully adjustable outboard rear end made up.

[MD]

Ah about time we got into some serious gear.

Here's my take on it. For years and years I swallowed the argument about unsprung weight and the value of the inboard brakes. More recently I have been questioning this argument and realised that they have their detractions too.

They pick up all the heat from the engine and exhaust pipe.
They are directly in the path of engine oil if you have an engine oil blow out. Tel me you never had the dispstic pop out and spray oil all under the car. Guess what? No rear brakes. Alfa were also dumb enough to place all the brake lines in the transmission tunnel so when your donuts break and the propshaft flogs around ripping your brake lines apart at the same time have another guess, no rear brakes. Servicing, well I know what to do, but its always a pain in the arse. Size, the callipers are too small to accommodate large enough pads for racing. Heat transfer to the box has already been mentioned.

As for the outboard conversion (which I have on the current race car I am building)well their location negates all the shortcomings of what I have just descibed above. Better cooling.Easier service access. More types to choose from. Less restriction for rotor sizes.Less contaminats that are a hazzard get deposited on them.

Unsprung weight. Yes it is an issue but I think in the case of the DeDion set up, the whole thing in practice is overstated. Try telling an MX5 going doorhandles with you around the corner that you have less unsprung weight or a dog bone live axle Escort. Nah sorry, its a furphy.I am shifting camp.

[alfagtv152]

Hi Mikey,
That's the shot,but I will say again I have never had any heat issues at the rear.I have been running a Temperature sender in my gearbox for a long time and it barely ever gets up!.
Cheers
Andrew

[MD]

Yes tend to agree Andrew regarding the heat during the sort of short track work around the place but say in the case of rally work where the rotors glow red hot or prolonged circuit work, I think the shortfalls would manifest themselves without doubt. But heat is nowhere near the real reason I made the move as I have explained.

I omitted to say that the inboard brakes put an unnecessary wear and tear on the CV's which is not so with conventional outboard brakes.

The transxale car has many advantages but the inboard rear brakes is not one of them in my opinion.

[MD]

Choderboy

I had big (300mm)vented rear rotors inboard that had no heat issues but they had other hassles like I had to cut servicing holes in the boot floor to remove the pads. I also had to modify the DeDion tube so the rotors wouldn't foul on the tube during suspension travel.

Obviously we are in agreemnent about moving them outboard. I am now using the same set up.

[Duk]

Some thing that isn't all together relevant, but the rules for the V8 Supercars has minimum weight for their arse end at 115kg  .
Obviously very different circumstances, but they work.

[Rigi]

A little off topic but a solution to many whining people here. Possible solution to the servicing issues on the inboard brakes, especially on the hastes with initial clearance setup. For those race cars or people who don't need a handbrake, install a set of 105 rear callipers instead.

[MD]

prettyboyalfetta

"....many whining people here..."

I see you are junior member on this Forum. What you should learn is to avoid making comments about anybody making a contribution. Each member has an equal entitlement to agree or disagree with your personal viewpoint. They often do and make it clear that they do. However,the differences of opinion usually revolve around technical perspectives or personal preferences. If you care to read this entire topic set, you will not see anyone making any comment other than technical exchanges.

Open personal attacks between the parties never end and just piss people off.

Now you might care to tell us which 105 rear calipers you have in mind. Ate or Dunlop ?

[Paul Newby]

I am not an engineer so I cannot comment as to whether the Alfetta de Dion rear suspension with the inboard rear brakes is flawed or not.

But I can comment on operating and maintaining the inboard rear brakes in racing conditions as I have been doing this for nine years. My set up is totally standard (calipers and rotors) including an operating handbrake (it is road registered after all.) Only in the last couple of years have I been running a side exhaust which eliminates a heat source and makes maintenance a bit easier.

I have no issues with the rear brakes in racing conditions and that includes hour long races and stints in end. There is more of a limitation with the too small front brakes. In the wet the rears tend to come up to temperature sooner and that can lead to lock up – not nice.

From a maintenance perspective the rear pads don't last as long as the fronts and they are a bitch to change and then set up working clearances. Often when I'm changing pads I have to wind out the pistons so far that they start to leak which is a pain. Setting clearances is very fiddly and putting the retaining clips in is an act of faith. I usually don't bother too much with adjusting the handbrake and I only use it to hold the car on the line for the downhill starting line at Eastern Creek.

Maybe I'm driving hard enough.... 

Oh, and another thing. The Group A 75 Turbo had outboard rear brakes and a fully adjustable (for camber and toe) de Dion.