| Author | Message | ||
| Rob Baylor (Baylor308)
New member Username: Baylor308 Post Number: 27 Registered: 11-2002 |
Cooling of the calipers is important but for real performance gains cool the rotor and the caliper. It's kind of like if somethings on fire don't shoot at the flames, shoot at what's on fire. The heat generated from braking is produced at the pad/rotor interface. The caliper gets hot as a result of the heat generated by the pad/rotor. One way, possibly the best way, to cool the rotor is with a clamshell housing that goes over the inner and outer face of the rotor just after the caliper. Kind of like a mini caliper that's hollow. On the inner clamshell a hole is provided for a cool air supply. This usually comes from the front spoiler by means of an air duct. The only hitch is keeping water away from the rotor when it's raining. This is usually accomplished with a water trap in the air duct. Regarding caliper placement, when I was involved with Indy cars we always placed the front calipers to the rear and the rear calipers to the front to minimized the car's polar moment (concentrate as much of the mass of the car as close to the geometric center of the car as possible). Rob Baylor www.ultimatepedals.com [email protected] | ||
| Charles I Claussen (Atlantaman)
Junior Member Username: Atlantaman Post Number: 163 Registered: 3-2002 |
Steve is correct in that the rear of the front rotor and the front of the rear rotor are the best places. If you look at most indy, gtp, or f1 cars that is where you will find them. | ||
| Giang Hoang (Spidersense)
New member Username: Spidersense Post Number: 46 Registered: 10-2002 |
what about cooling? would rearward mounting get more air to the calipers? or brake ducts work better with front mounted calipers? how about more equal or even cooling with rear mounted, but ducted cooling? | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 681 Registered: 4-2002 |
"The caliper is stopping the car! This means that it's mounting must transfer several hundred pounds of force on the caliper to some part of the front suspension that's strong enough to transfer it to the main body of the car." Yes, but the force transfered into the suspension (pure braking) is not different with the caliper in front or behind! It is still a torque (rotating force). When this force pushes on the top ball joint, and pulls on the bottom ball joint, it gets translated into compressile and tensile forces in the suspension arms. Since the point of leverage at the caliper is about 1/2 the rolling radius of the tire, the force at teh caliper is about 2X the force on the contract patch. At 1 Gs of braking, and 30% weight transfer, the front wheels on an F355 are delivering about 1000 lbs of force at the tire contact patches, so the caliper has to be developing about 2000 lb of force due to its smaller radius of operation. Split evenly top and bottom, each ball joint feels 500 lb of force. | ||
| Verell Boaen (Verell)
Member Username: Verell Post Number: 778 Registered: 5-2001 |
I think Steve's hit on one of the key factors. The caliper is stopping the car! This means that it's mounting must transfer several hundred pounds of force on the caliper to some part of the front suspension that's strong enough to transfer it to the main body of the car. I'm being sloppy, but when you sketch out the force vectors things will be more understandable. | ||
| Jack Habits (Ferraristuff)
Member Username: Ferraristuff Post Number: 701 Registered: 4-2003 |
>>>>At what RPM do you get peak acceleration Hahahahaha! that was NOT the intention behind the question. It was purely my own curiosity. I'll start looking for "front mounted" jpegs. Jack | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1807 Registered: 1-2001 |
Jack -- I would have to say "no" since both 308s and TRs have the steering arm connected at the frontside and the caliper at the rearside  (I almost hate to start this since it's like asking "At what RPM do you get peak acceleration?", but IMO) The moment required to (dynamically) pivot the front spindle about the king-pin axis is only dependent on the perpendicular distance to the brake caliper mass from the pivot axis (whether it's on the same side or the opposite side as the steering arm connection). I would concede that generally you've got to beef things up both where the steering arm attaches and where the brake caliper mounts so it might make some sense to try to "combine" the mountings on the same side of the front spindle to minimize the "beefing" -- but I'd still like to hear about/see a jpeg of an application that does have a frontside front caliper. | ||
| Jack Habits (Ferraristuff)
Member Username: Ferraristuff Post Number: 693 Registered: 4-2003 |
Just had a discussion on this topic with a friend (who took 7 years to get his automotive engineering degree which normally takes 4 years....) and his remarks are that you want the biggest mass as close to the point where the steering arm hooks up to the hub. The shorter that distance, the less power it takes to move that mass and the less power you will need to put "into" the steering wheel. We had no time to verify this but basically this would mean that cars where the steering arm hooks up to the front of the hub will have front mounted calipers and vv. Makes sense? Jack | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 595 Registered: 11-2002 |
I think you guys are giving too much credit toward optimizing performance of either the brakes and/or vehicle dynamics. Those characteristics are certainly important, though, what tops most every design engineers list of parameters he/she must conform to is: COST to manufacture. How their system (brakes) interacts with other suspension components. So, ultimately, it's a compromise with cost to build, suspension performance goals, brake system performance goals. This is for a road car. Race car design goals are skewed toward ultimate performance, cost is less of a factor. A brake component manufacturer will tell you that as far as they're concerned, placement makes no difference. A vehicle dynamicist may prefer to have the calipers contained within the wheelbase (polar moment). Bottom line for traditional auto manufactures: cost. | ||
| Sean F (Agracer)
Junior Member Username: Agracer Post Number: 148 Registered: 2-2003 |
Manufactures, in general, mount them where ever is cheapest for the guy on the line to bolt them in, without getting in anyone elses way. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1805 Registered: 1-2001 |
One could also argue that mounting them at the rear side of the front hubs and the front side of the rear hubs would minimize the vertical polar moment of inertia, but for a road car don't they usually mount them at the rear side of both to minimize showering the caliper assembly in it's own debris? Anybody got a front side/front hub example? I don't think you're overlooking anything Jack -- it's an axis-symmetric situation for the braking forces regardless of placement so not part of the decision for frontside/rearside IMO. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1516 Registered: 11-2002 |
>>But how these influence the decision on front vs rear mounted? << laws of physiscs... Sorry Jack but I don't have a link to Brake System Dynamics Physics to provide (might try a google search)...I'm sure some articles are out there in cyberspace somewhere. Who knows...maybe the physics will suggest it doesn't matter? or that maybe the top or bottom are better and so location is simply an arbitrary choice? ;-) ps: what I really want to know is how big is outerspace and how long a piece of string is...if you run across those links send me a private ;-) | ||
| Jack Habits (Ferraristuff)
Member Username: Ferraristuff Post Number: 690 Registered: 4-2003 |
>>>brake system pressure, clamping force, wieght of vehicle, tire size, ladden wieght, rear size, suspension type and design...uhhhh But how these influence the decision on front vs rear mounted? Jack | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1515 Registered: 11-2002 |
>>What am I overlooking? << brake system pressure, clamping force, wieght of vehicle, tire size, ladden wieght, rear size, suspension type and design...uhhhh ;-) | ||
| Bob Campen (Bob308gts)
Member Username: Bob308gts Post Number: 573 Registered: 9-2001 |
From what I have read on this they are mounted front/rear where the space allows, I always thought there was a magic to the mountings also. One F1 team has them mounted at the bottom, to lower CG | ||
| Jack Habits (Ferraristuff)
Member Username: Ferraristuff Post Number: 689 Registered: 4-2003 |
I was wondering about the pros and cons of front mounted calipers vs. rear mounted ones. What are the choices of car makers based upon? The only differences I can think about is the direction from which the disc "comes in" between the pads (front mounted from the top, rear mounted from the bottom) and a marginal difference in center of gravity. What am I overlooking? Jack |