59 replies to this topic

[elno]

Hello everybody, first time i post.

In the last autosport magazine, there is a very interesting and clear analysis of brawn gp and red bull cars.
But there is one thing i have not really understood: the analysis of location of the caliper at the bottom of the disc, read it:

"the only problem can be brake-pad knock-off with high lateral forces if the bearing assembly lacks stiffness. The conventional
location is about 'three o'clock" - the neutral axis of any potential deflection"

i have misunderstanding with the last part: i would like understand why the neutral axis of any potential deflection is at this location.
I have found nothing on the web.

Thank you for your rsponses !!

Elno.

[Tony Matthews]

"the only problem can be brake-pad knock-off with high lateral forces if the bearing assembly lacks stiffness. The conventional
location is about 'three o'clock" - the neutral axis of any potential deflection"

i have misunderstanding with the last part: i would like understand why the neutral axis of any potential deflection is at this location.
I have found nothing on the web.



Elno.

I too would like to know the reasoning behind this, apart from occasional practical, packaging reasons, or to alter the polar moment of inertia or CoG, I have never understood why the calipers move about from design to design.

[phantom II]

Adrian Newey decides where everything goes. Aero guys rule.

Hello everybody, first time i post.

In the last autosport magazine, there is a very interesting and clear analysis of brawn gp and red bull cars.
But there is one thing i have not really understood: the analysis of location of the caliper at the bottom of the disc, read it:

"the only problem can be brake-pad knock-off with high lateral forces if the bearing assembly lacks stiffness. The conventional
location is about 'three o'clock" - the neutral axis of any potential deflection"

i have misunderstanding with the last part: i would like understand why the neutral axis of any potential deflection is at this location.
I have found nothing on the web.

Thank you for your rsponses !!

Elno.

[Tony Matthews]

Adrian Newey decides where everything goes.

In this house I decide. Ooh! Hello darling, didn't see you there...

[ray b]

the ''neutral axis of any potential deflection ''
wheel will move in or out at top or bottom do to D/F or other loads like weight transfer or bumps/curbs
and as the brake disk will follow wheel moves it can hit the brake pads
but this is less likely at the 3;00 mid position as there is little fore/aft load changes vs high up/down changes

[macoran]

Maybe this little scribble will explain a bit about what Ray has just explained so vividly (to me at least).

the article forgets to say that the 9 o'clock position is as good and stable as the 3 o'clock, but hardly ever used( at the front) because of
steering linkages.

I learnt so much about designing disc brakes for semi-articulated trailers when at Fruehauf, you couldn't imagine
the blunders that were made.
I got so upset one day that I overhauled an old drum brake unit and it out-performed the newest fangled disc brake setup with EBS and all !!

Edited by macoran, 14 July 2009 - 20:25.

[meb58]

I understand the reason, but less clear to me is the cause...why the rotor distorts at 12 and 6 more than at 9 and 3.

Edited by meb58, 14 July 2009 - 20:30.

[macoran]

I understand the reason, but less clear to me is the cause...why the rotor distorts at 12 and 6 more than at 9 and 3.

The rotor doesn't distort. it moves (rocks) due to lack of bearing stiffness/stability.

[wrighty]

The rotor doesn't distort. it moves (rocks) due to lack of bearing stiffness/stability.

if i may.....?

By definition, the centre bearing has a very small amount of 'play' in it, to allow it to turn. If a non-steering hub is straight, square and 'neutral' (i.e. no inbuilt caster or camber in the geometry), there would theoretically be 'slop' movement in all directions, but by bearing the weight on the stub (the tyre touching the ground) the inherent vertical play is already mostly taken, unless the tyre tread is completely flat, the bearing is directly above the tread centre and the road surface is completely flat as well. Therefore the 12 o'clock or 6 o'clock positions are more stable for the caliper position as the play (or 'slop') are already taken up by gravity. Given that the desire for the unsprung parts is to be a) as light as possible and b) as helpful in terms of CofG as possible, 6 o'clock satisfies the criteria of low CofG height and being in the best possible 'neutral' plane to resist the pad knock-off that's so well demonstrated by Macorans sketch.

yeah? i think......


Yours ......... Wrighty (hopefully happy to help and incidentally ex-Tinsley>Corus and Montracon )

ps - no wonder drums worked better than EBS discs.....in terms of the pad size there was no comparison....those ZMX hubs were bad boys

[phantom II]

The rotor floats and the only time there is any run out is under hard braking in a high G turn and it doesn't matter where the caliper is located, it will be the same. Braking in a straight line or high G cornering without braking, load on the bearing will be almost equal be it top to bottom or from front to back but less at the 45' positions. The steering is placed in tension because of this load.
The rotor is centered whether there is pressure on the brake pads or not. This is not a street car. If there was any binding to speak of on the slip pads that the rotor rides on, the rotor would shatter. When they do shatter, it is because of a failed wheel bearing.
There is a nice cut away drawing of the wheel bearing and rotor by Matthews in the Ferrari F1 book by Peter Wright.Pg. 147.

[Tony Matthews]

This was obviously about cooling rather than caliper placement... I must admit I am still struggling to understand exactly why the position makes a difference to the function of the disc/caliper set-up. If it is so cut and dried why do the calipers move around from design to design? What about twin, opposing calipers, once used, are these banned now?

[phantom II]

Braking is the creation of heat. Two calipers would be inefficient and heavy. The rotor must cool before the next braking event. The position of them is determined by packaging, cooling and aero and maybe CG location.

This was obviously about cooling rather than caliper placement... I must admit I am still struggling to understand exactly why the position makes a difference to the function of the disc/caliper set-up. If it is so cut and dried why do the calipers move around from design to design? What about twin, opposing calipers, once used, are these banned now?

[Greg Locock]

Braking is the creation of heat. Two calipers would be inefficient and heavy. The rotor must cool before the next braking event. The position of them is determined by packaging, cooling and aero and maybe CG location.

However the pad knock-back issue is real, it's just that your options are very limited in practice, so far as calliper placement goes. This knockback is more obvious on a tall spindle double wishbone, or a MacP, than the short spindle as used in F1 and most circuit cars, as the swan neck/strut is actually quite compliant - effectively reducing the camber stiffness of the suspension. That's one reason why the calliper brackets in a production car's spindle are so heavily braced (the other is that the brakes create huge point loads at the mounting bolts, so the fatigue model tells you to put lots of metal in). There may be additional stiffness requirements driven by squeal and shudder.

[imaginesix]

I understand the reason, but less clear to me is the cause...why the rotor distorts at 12 and 6 more than at 9 and 3.

Because the lateral load, which is what causes deflection, is applied at the contact patch (6 o'clock in the terms we are using). Since the wheel is held in place in the center, the 12 o'clock position gets deflected equally, but in the opposite direction.

[Tony Matthews]

Braking is the creation of heat. Two calipers would be inefficient and heavy. The rotor must cool before the next braking event.

I take your point, but the calipers don't need to be as big if you use two - Williams, amongst others, tried it, but that was really an aside. I know that competition car rotors are a 'loose' fit on the disc bell, and I understand what imaginesix is saying, it's just that, packaging aside, surely that is going to be the result wherever the caliper is situated. Is it worse to have the deflection at 10 past 1, or 11 o'clock? I'm obviously missing something. Possibly brain cells.

[elno]

A Big thanks to all of you. Your responses go beyond my hopes !!

it will take a time to react to each of your responses, because of my poor english.

I would just say it seems this subject is pretty complex, and i note some of you are not agree
(for instance, is there (deflection) distortion or not ?)

Perhaps, some of you could give us any reference (book, article,...) from technical or scientific litterature on this subject ?

thanks.

[mariner]

There are materials limits on F1 calipers ( as with most parts of an F1 car) so as well as aero requireements there is an imperative to make the caliper physically bigger to offset the rules limited low -ish modulus of the caliper. So it may be that the size of the caliper can dictate the location espeically if a fairly large air flow tunnel has to be routed inside the very cramped whelspace as well.


F1 brakes have a praticularly hrad time becuse of the 13" wheel size rule. Most sports car can run 18" wheels or so which gives a bigger clamping radius which partially offsets the bigger braking load ( due to both extra weight and lower drag).

BTW people have played around with calipers etc forever so maybe no one right answer. It was Lola ( I think) in group C who used the inside of the rear uprights as the air channel to the caliper with an air scoop stuck on top sticking up to the airflow over the body.

Louts ( of course ) tried to get really clever on the Lotus 79 by using the diff. side plates as the inside of the caliper with inboard rear brakes. I beleive they forgot about a little detail called differential expansion and used a different material for the caliper outers leading to bad brake problems. In it's first season of the 79 that was not important as it had ground effects and nobody else did. Just to prove even more novelty they had previously mounted the front suspension of the Lotus 77 on twin inboard front calipers so the whole suspension/spring/damper/brake assembly could be moved in/out and back/forewards on little tubular sub frames bolted to a narrow foot box.

The idea was to be able to adjust the cars weight distribution and front rear roll couple between races quickly and at low cost.It was all rapidly replced by a conventional rocker + outboard brake set up but this was the time when Colin Chapman made a the quote " all that matters is how long it is,how wide it is and where the weight is" 30 years later one of the F1 technical directors still re discovers that point every season and builds a lemon.

[elno]

By realizing a new web research and by using key words that i read in your commentaries, i have found a interesting article:

http://www.stoptech....knockback.shtml

So, like ray and macoran told us, it seems that "deflection" (in gary anderson's mind) is a "rigid" displacement of the rotor (so, no distortion due to a flexion constraint )

But, "neutral axis" is a mechanical term related to distorting flexion !

perhaps, it is a misuse of langage ?

[desmo]

If one had a clean sheet in front of you, rather than using a 'spot caliper', surely an aerospace clutch-type design would be worth having a look at. In fact I think one of the F1 teams actually had a serious look at the concept back in the murky past- maybe the nineties before it was made clear that actual new ideas would no longer be tolerated in F1.

[phantom II]

Only good for one landing. http://www.airliners...ead.main/192668

If one had a clean sheet in front of you, rather than using a 'spot caliper', surely an aerospace clutch-type design would be worth having a look at. In fact I think one of the F1 teams actually had a serious look at the concept back in the murky past- maybe the nineties before it was made clear that actual new ideas would no longer be tolerated in F1.

[elno]

@macoran:

the 3 o'clock caliper has not the same dimensions as the 9 o'clock one.
Could you tell us a little bit more on this point ?
thanks.

[doyle]

Caliper placement primarily comes at the compromise position that least affects CoG and polar moment of inertia. Thus, nearly all cars will have the caliper assembly toward the center of the car (rear of the front wheels, front of the rear wheels) 3 O'clock / 9O'clock are relative to the viewer. As the car corners, creating high lateral forces, the contact patch of the tire, as mentioned above, wants to essentially twist the wheel off the car. Picture the inside wheels having their bottoms (at the contact patch) pulled away from the car, twisting about an axis in the hub that runs parallel to the center line of the car, in turn pushing the top of the wheel toward the car. The opposite forces would be realized on the outer wheels. Of course this is simplified, but essentially any movement of the rotor is increased the further away from that axis. Many teams have placed calipers down in the 16:30/19:30 position as, once again, a compromise balance is struck between lowering the CoG and deflection of the carrier/rotor assembly.

[J. Edlund]

If one had a clean sheet in front of you, rather than using a 'spot caliper', surely an aerospace clutch-type design would be worth having a look at. In fact I think one of the F1 teams actually had a serious look at the concept back in the murky past- maybe the nineties before it was made clear that actual new ideas would no longer be tolerated in F1.

I think I have read something about that too, but I seem to recall something about heat issues. To cool a clutch type brake between each turn on a racetrack is probably not without its difficulties. Aircraft brakes on the other hand usually have at least a few hours to cool off between use.

[Bill S]

Aircraft brakes on the other hand usually have at least a few hours to cool off between use.

As little as 30 minutes on some domestic turn-arounds, usually a maximum of 1:30 on international flight. An aeroplane on the ground = lost revenue, so they're kept working as much as possible.
There are some types that have in-built brake fans in the landing gear assembly to help cool the brakes between landing and takeoff.

This is one unit we used to use when I flew 747's ...



It wasn't unusual to arrive in places like Dubai, where the temperature could easily be in the mid 40's and so stinking hot, and at maximum landing weight so the energy absorbed by the 16 brakes was huge. In such cases we'd call for brake cooling as without it there was a distinct chance of the tyres over-temping and we'd get a fuseable plug blow-out. If we didn't need the extra cooling then we'd often still have to wait a good hour or so to get the temps down to the point were we could go.

</thread hijack>

[cheapracer]

Obviously not a 2009 picture Bill 'cause everyone knows that it's slicks this year.

[RDV]

If one had a clean sheet in front of you, rather than using a 'spot caliper', surely an aerospace clutch-type design would be worth having a look at. In fact I think one of the F1 teams actually had a serious look at the concept back in the murky past- maybe the nineties before it was made clear that actual new ideas would no longer be tolerated in F1.

Ligier tested this type brakes in conjunction with Carbone Industries in 1989.
Was interesting, but gave no clear advantage, and cooling was a bit of a problem on the multi-disc pack, not being homogeneous, also slightly heavier than the standard mono-disk

[Tony Matthews]

Obviously not a 2009 picture Bill 'cause everyone knows that it's slicks this year.

Still on a roll I see, Cheapy!

Right, so we have a situation where, apart from the sheer practicality of mounting the caliper, and taking into account PMI, the effect of clamping the rotor is the same wherever it is positioned untill yopu introduce the significant effect of the load induced by the tyre through the contact patch, and this determines that in fact the ideal position of the caliper is restricted to a small angular range. Have I got that right?


I will accept no comment as 'yes'.

[gruntguru]

Still on a roll I see, Cheapy!

Right, so we have a situation where, apart from the sheer practicality of mounting the caliper, and taking into account PMI, the effect of clamping the rotor is the same wherever it is positioned untill yopu introduce the significant effect of the load induced by the tyre through the contact patch, and this determines that in fact the ideal position of the caliper is restricted to a small angular range. Have I got that right?


I will accept no comment as 'yes'.

No comment.

[Tony Matthews]

No comment.

Ta

[Tony Matthews]

Lotus 87 front and rear brakes - twins all round.

Edited by Tony Matthews, 18 July 2009 - 10:44.

[Tony Matthews]

Lotus 91 front - single caliper, rear - still twins. And wait for it...

Edited by Tony Matthews, 18 July 2009 - 10:48.

[Tony Matthews]

Lotus 97 front and rear - single calipers! I am possibly the only person to find that interesting... Williams seem the most consistent, the FW07C had twin rears, but later models didn't vary much, at least up to the FW22, which was the last one I saw in detail.

Edited by Tony Matthews, 18 July 2009 - 10:55.

[cheapracer]

Can't see a thing Tony and I haven't been drinking or doing the 'other thing' either!

[Tony Matthews]

Perhaps your vertical hold has gone...

Anyone else who can't see anything, put your hand up - one, two... hang on, one hand's just gone down again...

Edited by Tony Matthews, 17 July 2009 - 14:49.

[OfficeLinebacker]

Dammit cheapy stole my joke about those tyres being grooved.

[Tony Matthews]

Dammit cheapy stole my joke about those tyres being grooved.

Ay, he's like that, ay.

[RDV]

The reason for the rash of twin calipers was the additional capacity for heavy braking with improved tire grip, which in turn needed increased pad area, which brought on severe pad wedging as the longer pad "tilted" on the single piston, as constrained in 13" dia. rims, not to mention caliper flex as the "bridge" got longer...eventualy twin piston calipers (now even three piston...)with different size bores on the leading and trailing edge of pads and better engineered calipers (FEA helped there..) solved the problem, and voila...

[John Brundage]

I remember seeing twin front calipers on a late Lola 332---The Boraxo car.

[cheapracer]

Ay, he's like that, ay.

'ey, I'd agree with yar there Mate if I was a Kiwi,'ey!

'ey, not the 'ey's but the thieving part,'ey.

[Tony Matthews]

'ey, not the 'ey's but the thieving part,'ey.

ey, contentious, ey!

[cheapracer]

I was serious Tony, for once, your pics are not displaying - I can see all other pictures.

[Tony Matthews]

Well, they're not massive files, and I don't think it would be appreciated if I re-posted them, I'm not sure what to do - and you're not missing much! I could try deleting them and substituting smaller files...

[Tony Matthews]

Job done - they were unnesecssarily big, hope they show now.

[phantom II]

Loud and clear, 5 * 5. Have you got permission to use this copy written material?

Perhaps your vertical hold has gone...

Anyone else who can't see anything, put your hand up - one, two... hang on, one hand's just gone down again...

Edited by phantom II, 18 July 2009 - 12:37.

[OfficeLinebacker]

Loud and clear, 5 * 5. Have you got permission to use this copy written material?

[Tony Matthews]

Loud and clear, 5 * 5. Have you got permission to use this copy written material?

No, I'm a rebel! Whatever happened to Duane Eddy...?

[desmo]

Still twanging!

[cheapracer]

Loud and clear, 5 * 5. Have you got permission to use this copy written material?

The Guy has already admitted elsewhere a few days ago he's not the real Tony Mathews!

[Tony Matthews]

The Guy has already admitted elsewhere a few days ago he's not the real Tony Mathews!

Well, that may not be the real Duane Eddy... And wot I said was, whoever thought I was the real TM was in for a surprise, I didn't admit anything, Your Honour, I wasn't even there, ask my wife, I was watching the telly all evening...

Edited by Tony Matthews, 19 July 2009 - 09:27.

[Bonde]

Hi there Tony,

Lunch break!

I've bitten the bullit and ventured into the Technical Forum, this being, IIRC, my first post here (haven't posted earlier for fear of publicly displaying my profound ignorance of current racing car technology in general and current F1 technology in particular).

Anyroads, I thought I might contribute a bit to the caliper placement discussion, mostly from a Formula Ford perspective though.

We've tried running calipers either in front of or behind the upright at either end of the car (on Vectors), but found no measurable difference in lap times or 'feel'. There's a sentiment in some circles that forward location of the caliper would tend to pull the wheel downward and aft location would pull it upward the moment the brakes are applied, but we haven't in practise been able to determine the effect, although I would like to repeat the experiment sometime with instrumentation.

IIRC, one of the arguments put forward for using twin calipers in the late seventies and early eighties (apart form the pad area and pad wear issues) was to balance the reaction couple from the calipers, but irrespective of how many calipers you arrange and how, braking will always try to rotate the upright, so the raction at the suspension attachments won't differ. As others have said, practical implications such as steering arms, cooling ducts and centering of mass will probably decide caliper location more than anything.

On our Formula Ford, we've located the caliper horizontally at the bottom of the upright. For us it enabled the most compact installation with the lowest centre of gravity using a non-handed (symmetrical) upright with the rear suspension geometry we've got. Our lower wishbone sits quite high in order to clear our horizontal floor-level spring damper, and as we like to spread the higher loads on the lower suspension link over more members, we've also got our trackrod in the lower plane, making the upright wide at the bottom and narrow at the top - thus the caliper simply fitted well at the bottom. The only drawback to the arrangement is that since we're compelled to using affordable off-the-shelf AP Racing calipers, you have to remove one of the attachment bolts and swing the caliper into a more upright position when bleeding the rear brakes in order to ensure no air is left behind, but we've become fully accustomed to doing so, so it's only a minor snag. And, oh, it looks rather fancy, too...