Position of a caliper

f1.redbaron · Post 18 Apr 2006, 01:58

Today, I was at the set of lights when I started looking at the brakes on the car of the guy next to me. I noticed that the position of the calipers on his car are not the same as on mine. So, that made me wonder...does anybody know whether there is an ideal position for the calipers, and do all the F1 cars have them on the same place? Also, if there is an ideal place for them, where would it be?

Thanks

DaveKillens · Post 18 Apr 2006, 02:29

Because of the locations of the upper and lower joints on the steering knuckle, you really are left with two locations, in front of, or behind the axle, usually located almost level with the axle. There's not much room in there, and the places are limited. Also, because most steering linkages attach in front of the knuckle, that really leaves just one place, directly behind the axle. You could fit the caliper in beside the steering joint, but all of a sudden you would have a ball joint very close to a high level of heat, which increases the risk of seizing or failure.
If the brake caliper is for lighter use, it can be smaller and you have more choices for location. But for a large racing caliper, there's not many choices where it can go.

manchild · Post 18 Apr 2006, 02:29

It’s aslo a matter of compromise between cooling and COG. When it matters COG ideal would be horizontally bottom but that would be bad for cooling so they are usually positioned vertically or with certain angle but never horizontally on top or horizontally on bottom. F1 cars have them more-less on same places...

Edit: I typed it while Dave posted his so it sounds stupid a bit now... did my best to fix it up

Ciro Pabón · Post 18 Apr 2006, 11:10

I am thinking aloud (as we say in spanish) so I do not know if this question is a fool one, but I think there is another restriction:

Could it be true that positioning the caliper behind the axle of the wheel reduces the lever (arm for torsion) of the caliper on the COG (as opposed to put the caliper ahead of the axle?

This would mean less tendency to push down on the frontal suspension when you brake. Please, take a look to this lousy picture I made for an article on weight transfer for rookie pilots, but instead of thinking of the effect of the tires of the car, think about the calipers and the body, which is suspended.

Edit: actually, I am not sure if the caliper ahead or behind increase the weight transfer (it has been a long week for me), but you get the idea.

RH1300S · Post 18 Apr 2006, 11:25

I think I understand you Ciro. I am fairly sure the caliper location has an effect on how the loads are sent through the chassis.

The braking loads are transmitted via. the inboard suspension mounts. If viewed from side on these converge towards the CofG (parallel effectively means ground level), you get anti-dive geometry - going through the CofG is 100% anti-dive and a lower converging point is less than 100%, right down to 0% @ ground level. I don't know how much anti-dive is used in F1 cars (or anti-squat for that matter) as too much anti-dive can work to make the suspension "tie up" under braking.

Because the wheels rotate, if the caliper is behind the upright any braking force will try and lift the wheel off the ground (how much effect this has I don't know) - a caliper in front of the upright will try and drive the wheel into the ground. I expect these effects are minimal otherwise I'm sure we would see more calipers in front of the upright.

As it is, for packaging reasons it is probably better to get your steering rack where you want it before the calipers. Also, calipers behind the upright must reduce the MOI of the car.

West · Post 18 Apr 2006, 12:01

There was a Racecar Engineering article a few years ago about this. I think Ciro and RH have the main idea about it tho. The caliper in the rear will create a lifting moment and in front, vice versa. CoG really isn't that important a factor in caliper position these days, although it was novel at the time.

RacingManiac · Post 18 Apr 2006, 15:09

on the upright that I designed for the FSAE car, I placed the front caliper trailing the axle and the rear caliper leading. The reasoning being that underbraking the weight transfer to the front adds load to the front suspension, and to reduce the stress at the lower balljoint you direct the braking moment away from the LBJ. While in the rear weight transfer away from the axle, so adding the braking moment to the LBJ helps "push" down the rear tire to give it more grip under braking....I can't say for sure whether in the end it works out like that as we have nothing to compare it to.....

DaveKillens · Post 18 Apr 2006, 15:45

I believe that as long as the brake caliper is rigidly attached to the front suspension steering knuckle, the torque transmitted through to the chassis would be the same no matter where the location of the caliper. But if the brake caliper was allowed to float freely relative to the suspension, and an arm located between the caliper and chassis was used to transmit brake force, then you could influence the movement of the chassis relaitive to brake force and torque.
When discussing anti dive geometry on a double wishbone suspension, it is usually done by altering the angle of the locating points on the chassis. But using this method, when you design in anti dive, the front wheels, when they strike a bump, not only move up, but forward. Not a good thing, because when you strike an object, you want the wheel to move away from it, to lessen the impact. That was one of the hidden benefits of active suspension. You could design in a suspension that moved the wheel backwards (and naturally upwards) when it struck a bump, yet the shocks/ springs could generate anti dive.

RH1300S · Post 18 Apr 2006, 16:18

I have trouble fully getting my head around what I wrote about the wheel being moved up/down........

Dave is basically right the forces will get transmitted via the chassisounts. BUT, try and imagine the wheels hanging free (place the car on stands) - spin them fast and heave on the brakes - the wheels are bound to react relative to the chassis.

DaveKillens · Post 18 Apr 2006, 17:38

In the classic double A-arm suspension we currently see in Formula One front ends, the suspension upright is connected by two ball joints, at the top and bottom arms. Those arms are themselves connected to the chassis by joints, or in the case with carbon fiber arms, rigidly, but able to flex up and down. The brake caliper is securely mounted to the suspension upright. So the braking torque and forces are first transmitted to the upright, then through the A-arms before finally going through to the chassis.
Then imagine you instrument the joints on the A-arms where they attach to the upright and chassis, so you can measure the forces transmitted. So if you take a suspended wheel and spin it and apply the brakes, no matter where you locate the caliper, it would transmit the same force to the joints.
If you change the suspension geometry, then you alter the force vectors, and then things are altered. Or as I mentioned, you have the caliper float independant of the upright, and have it connected to the chassis by a rod instead. Then the leverage and distance between the axle and caliper becomes relevant.
The line between where the two A-arms connect to the upright is the center of rotation for the front wheel assembly, and you can alter the moment of inertia by locating the caliper on the top, bottom or sides. This would change the inertia of the wheel assembly, and make it steer lighter or heavier. Of course, the effect is neglible with the gyroscopic effect of the wheels and brake disks being so predominant. And power steering sort of takes this out of the equation as far as driver effort.[/code]

Ciro Pabón · Post 18 Apr 2006, 17:59

West wrote:The caliper in the rear will create a lifting moment and in front, vice versa.

Actually, this is not posible. Anyway you put the caliper the reaction in the car is going to push the front axle downwards, except in reverse. But you get 4 or 5 inches of fictitious "extra-wheel-base". I'll guess this has repercusions in the entire attitude of the car.

It is like the CG: if you get down the COG, a naive person (like me for many years) would think it would improve ONLY the anti-roll tendency of the car, making more difficult to turn it over.

BUT lowering the COG, as you probably know, gives you better braking and acceleration... For example, an effect of SUV getting bigger and higher it is, not only to make them more prone to roll over: they brake and turn worse, because of this weight transfer effect. This is one of the first things you learn in your Basic Racing Course, so I suppose everybody understands me

.

If you do not understand me well, you can read this 1.2 Mb five pages thing I wrote on the subject originally in spanish

Instead of reading my text, you can also read the even longer explanation at Brian Beckman's article that I ripped off (the conclusions about road design in my article is what is mine).

As Manchild says, shoot me, please (well, better shoot MC and then explain to me why)

Actually, if you do not get it, NOW I understand why nobody seems enthusiastic about any posts on car simulation wheel-by-wheel on real tracks at the tires forum. =;

Tom · Post 18 Apr 2006, 18:05

I get it.

The entire car will try to spin about the caliper if it is at the front, while at the back it will try and slice the car in two.

Ciro Pabón · Post 18 Apr 2006, 18:15

Tom wrote:I get it.

The entire car will try to spin about the caliper if it is at the front, while at the back it will try and slice the car in two.

Well, Tom, I think the monocoque can take the rotational forces created by braking...

johny · Post 18 Apr 2006, 18:21

a ver si con tus explicaciones me aclaro

brian beckman's articles are so good to read

Ciro Pabón · Post 18 Apr 2006, 18:26

johny wrote:a ver si con tus explicaciones me aclaro

brian beckman's articles are so good to read

Gracias, viejo Johny. The link I posted is in English (almost in English, you could say) with a little "bogotano" accent.