Does anyone ever put them the same side of the axle, in side view, as the rack?

 

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Greg Locock

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Greg

You would not suggest that there is more room for the steering arm and caliper if they are on opposite sides of the axle are you  

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Pat
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Sure, I think (1) covers it, just wondering if there was some masochist who had tried, in particular, front mounted callipers and front rack.

If nothing else the poor old outer tie rod's grease would melt.

 

Cheers

Greg Locock

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@Greg, surely the back plate and some ducting would get around that if they were near each other, ill have a think of the different cars and see if any do.
Is that the only reason or am I over thinking this?

Thanks.

I think your reason (2) is of little real impact, and although I've seen a few attempts at explaining (3) they haven't convinced me, at least as to whether 3 o'clock would be better than 9 o'clock.

I did see something convincing as to why 12 o'clock would be a bad thing other than packaging, but can't remember the story.

So it would be interesting if you can find any examples, but even then we wouldn't know why they did it that way.



    

Cheers

Greg Locock

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I guess you could argue that rear placement will cancel some of the forces on the spindle. The tyres push up on the pin while the brakes create a force which pushes down on the pin...

But then, the simplest explanation is usually the most likely. Most vehicles use the advantages of front steer which leaves the rear of the rotor open for a caliper.
 

I wouldn't say that "most" vehicles nowadays use front steer (rack ahead of the front wheel centerline). Every modern vehicle with transverse engine and front drive has the steering mechanism behind the front wheel axis, for the simple reason that the steering mechanism can't go through the engine and transmission (which nowadays are always ahead of the front wheel axis). This pretty much dictates that the caliper is going to be on the front. The mechanical design is just a whole lot easier to deal with if the tie-rod and the caliper bracket are on opposite sides of the hub.

If there is a modern transverse-engine front-drive vehicle that has it otherwise, I haven't seen it.

If you go back to the 1930's, you can find examples of front-drive vehicles that had the powertrain behind the front-wheel axis (example: Cord), and Saab and Renault have had some oddball front-drive layouts in later years, but have long since reverted to the norm.

Say we go away from the front axle and onto the back where nothing really defines position, I guess Im pulling straws now, they probably just run with what they have been at for years with regards position.

Thanks to all for the above reply s.

Brian.

With respect to bearing forces... You can take some load off the spindle/bearings with the caliper placement perhaps hoping to increase service life.  However, I read somewhere that in racing applications this is not desirable as the driver can feel the bearing being unloaded and the resulting play in the assembly.

Brian Bobyk - Hoerbiger Canada

The Cord had inboard drum brakes.  

TOP
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"Node news is good news."

No automotive connection, but motorcycles almost always put the calipers behind the fork legs, and the rumor was for low steering inertia.
http://static.blogo.it/twowheelsblog/honda-2009-01/honda_dn01_2009_01.jpg

There were exceptions, like ROKON, but they ignored any number of "rules"
http://rokonworld.com/brochures/c5.jpg

"Say we go away from the front axle and onto the back where nothing really defines position"

Still Item #1.  One might think that toe control links for independent rear suspensions and shocks and trailing lower links for stick axles should get first crack at available space.


Norm

Brian - you are right, there are a number of FWD cars with rear steer. The design is mostly due to packaging.

As for the rear, on my C5, the uprights are common on diagonal corners so the front design dictated the position of the rear caliper.

On a lot of other cars, it seems they are just put opposite of the fronts. Around here, it seems a lot of cars have front calipers to the back side of the rotor and rear calipers to the front side of the rotor. The ones with front calipers to the front of the rotor have the rears to the back of the rotor. Aesthetics?
 

I go outside and look at my Mazda, which has rear-steer and rear mounted calipers.

I've never heard of tie rod problems, brake heat related or no, but servicing the brakes is difficult because of the location of the steering arm.

 

Back brakes normally do not get as hot as fronts.

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Pat
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Izzmus what mazda do you have? I have not seen any with the TRE on the same side as the caliper.

Pat anyway evidence to back this up? You'd need to do some extensive testing with a moveable caliper to get any worthwhile evidence. Not saying your right or wrong just interested to see if there have been any studies/experiments on it.

As for vertical force exerted by the hub on the bearing, i.e. climbing in the 3 o'clock position, some could argue that the disc will try and pivot from the pad contact area, however thats another argument!

As far as I know front or rear placement is due to the steering arm placement, as has already been said.

BrianPeterson summed up very well the fwd caliper placement.

Cooling can be created quite easily, via ducting, wheel tub design and to an extent wheel design.

Placement other than 9 or 3 (roughly positions) like 12 or 6 is pretty much unheard of. 12 o'clock there will be interference issues with the struts or wishbones, also some would argue that more weight higher up will have a negative effect on handling but tbh it wouldn't be that much of an issue unless its a heavy cast iron component.

6 o'clock, interference with lower wishbones, more exposed to damage from debris, water ingress and so on, but ideal placement for the weight purists, but not practical.

Ideal position of course would be inboard, reducing unsprung mass greatly, but its poor for cooling, maintenance etc. Anyone who has worked on certain Jag's and Alfa's and some other euro stuff will know what I mean.

Citroen had inboard discs in 1955 I think.

Problem with inboard is a drive shaft or CV failure is also a brake failure.

Also braking forces are applied to CVs and drive shafts.

My evidence of rears not being so hot are unscientific and varied ans sometimes indirect, being:-

There is normally considerably more weight over front axle, especially when weight transfers forward during braking.

Faster build up of dust on front wheels.

Faster wear on front pads.

Front pads normally about twice as big.

Front rotors are normally bigger or ventilated vs non ventilated.

But most of all, when I place my hand on the wheels after a very hard stop, the front wheels are uncomfortably hot while the rears are only noticably warm.

Regards
Pat
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Pat I miss read your comment., I thought you were referring to front and rear placement on the front wheels. My apologies.

I agree with the rear axles brakes are always cooler than the fronts and the rest of your description.

Citroen were using inboards a lot later than 1955's. Also the handbrake on the front wheels etc, awesome cars. If you have ever re-piped a BX or Xantia you would know what a joy they are to work on..

Some things like H1's still have inboard brakes due to the portal gears.

My 1955 ref was meant to be as early as, not as late as.

The D series was the most advanced compared to its peers as any car in history I think. Every so often Toyota launch an add campaign claiming to invent a feature that was on the D series. Steering and self leveling headlights spring to mind.

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Pat
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Some Porsche models might be exceptions to the front brakes always hotter rule, maybe?

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Pat
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I concur, pretty much anything new on cars citroen done sometimes well years ago. The first decent fwd car was the Traction Avant, beating the mini by 13 or so years if I recall correctly.

Sadly since the PSA group took over Citroen became a shadow of their former selves. They are just Peugeots now and I don't like Peugeots, although some are easy money spinners for poor design faults.

As for Porsches, the rule of front hotter still applies, weight transfer still occurs but I see your thinking. But you would be right in assuming the temps are closer end to end than say a fwd's. Thankfully these days they don't like to swap ends as easily but if you provoke them they will spin.

You have to admire their persistence in engineering a wrong design right, or at least trying to

I always thought you could increase braking by using something similar to a clutch pack with carbon/carbon and actuate it with a hydraulic clutch ring. I know there would be release problems and such, but nothing unsolvable,  with no need to hang a caliper.

We went through this when they started hanging big Lockheed calipers on the Norton motorcycle,and one of the things we looked at was the polar moment on the steering axis. I don't know if that is a consideration on a car or not, but that seem it would put them on the top or bottom.

Cheers

I don't know anything but the people that do.

chammyman - all Mazda RX-7 had rear mounted calipers in the front, but the first generation (models before MY1986) had rear-steer recirc-ball steering.  The engine is too wide and low to fit a rack beneath it, and most of the front suspension is carryover from sedan models.  Presumably, they didn't want to spend much money on the car.

Now that I think of it, the earlier models may also be rear steer/rear caliper, but I'm unfamiliar with them.

I recall an article in the SAE Journal back in the '80's when I belonged that had an in-depth analysis of the forces with 3-o'clock and 9-o'clock calipers (I think on a MacPherson suspension specifically).  There was an advantage to one or the other, but not huge.  No longer a member so I can't search their archives.

Didn't Chrysler have an option fro a  multi disc/stationary disc "something similar to a clutch pack" on their cars back in the early '50's?

@Ross, was bearing loading the issue? Or can you remember?
Thanks to all for the replys, youve all answered many of my questions.
Brian.  

I honestly don't remember, sorry Brian

Quote:

I always thought you could increase braking by using something similar to a clutch pack with carbon/carbon and actuate it with a hydraulic clutch ring. I know there would be release problems and such, but nothing unsolvable,  with no need to hang a caliper.

Most airplane brakes are like this. Four, five or six cylinders, a hollow tube with spines for the stationary disks and bolt on splines inside the wheel.

Aircraft have several criteria that automobiles don't have. One is an aborted takeoff in which case the brake is designed to become incandescent with out self destructing till after the aircraft is stopped. Another is a landing with a full load. Another is parking after a hot landing without the metal softening with a loss of pedal. Because aircraft brakes don't have to dissipate heat and drop down in temperature immediately after a stop they can be designed like this. But a "clutch" like brake would not dissipate heat well for automotive because the braking material is compact with little room for circulation and convective heat transfer.

 

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probably why we don't see them on cars - also they make a terrible rattling noise when the wheel rolls.

I was hoping the carbon carbon would handle the heat but you are right about the noise as my Ducati makes more clutch noise in the mornings then the exhaust.

Well....I didn't mean to high jack this thread with my interjection.

 

I don't know anything but the people that do.

Automatic transmissions seem to operate without waking the dead, but they do have the ATF to cool them and damp any noise. I thought motor bike clutches were mainly multi plate wet clutches like an automatic.

I think it would be extremely heavy and quite expensive to build a multi stack fluid cooled brake system.

Without the fluid a multi stack will take to long to cool between applications.

Regards
Pat
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izzmus gen 1 rx7's did indeed have recirc ball steering but they had front mounted calipers, the later gens had rear mounted calipers and track arms that went overt he wishbone to the front of the hub carrier. So again we are waiting for a car with rear calipers and rear track arm mounts.

Speaking as someone who has owned, modified, and raced them since 1998, as well as running up approximately 25,000 miles per year driving them daily and performing all of the regular maintenance that ensues from it - they are definitely rear mounted.  The easiest way to unbolt the calipers is to first unbolt the strut/spindle housing from the steering arm to get it out of the way.

Of course, you don't have to take my word for it, when there are images available - http://c4.ac-images.myspacecdn.com/images01/52/l_b676217ddb6563e3652faf7e2f51b923.jpg details just how cramped it is there.  As well as the lengths one will go to in the quest to save money on dampers...

Damn that is tight!

"I always thought you could increase braking by using something similar to a clutch pack with carbon/carbon and actuate it with a hydraulic clutch ring. I know there would be release problems and such, but nothing unsolvable,  with no need to hang a caliper."
"Most airplane brakes are like this. Four, five or six cylinders, a hollow tube with spines for the stationary disks and bolt on splines inside the wheel."

Many off-road vehicles use inboard multi-disc wet brakes. Many of them are spring applied and hydraulically released, this way if the hydraulics go out the vehicle comes to a stop.

ISZ