Braking Pedal Force

[Ianthegypo]

I am currently sorting out the pedal box for our car, and wondered if anyone had a realistic number for the amount of force a driver can put onto the brake pedal? I was guessing around 20kg worth, but could do with something a bit more accurate. Cheers

[SH]

A real simple way to get this number is take a bathroom scale set it up against a wall and push on it with your foot as you would pushing on the brake pedal on your car...

[terra_dactile]

ian,
hi in a book i have called brake design and safety,by Rudolf Limpert, they recommend that the maximum pedal force be no more than 445-489 Newtons(100-110lbs) , That is what we used oin our last car and the pedal feel is great, its a little hard at low speeds but once the G's kick in the braking feel is excellent.

Jude Berthault
ETS Formula SAE (2003-Present)

[Igor]

The previous answers regard normal braking force.
Also think about how much force a scared driver can put on the pedal when driving towards large concrete objects etc.. You don't want the pedal to break in those situations.
So as one can put about 100kg of force on the pedal when relaxed, I would calculate for about 200kg for an adrenaline pumped driver.

Igor

[Cement Legs]

Originally posted by Igor:
Also think about how much force a scared driver can put on the pedal when driving towards large concrete objects etc.. You don't want the pedal to break in those situations.
So as one can put about 100kg of force on the pedal when relaxed, I would calculate for about 200kg for an adrenaline pumped driver.

Igor

hmmmm .... i think you mean pounds. 200kg - 440 lbs - one leg ? what do you squat?

[kwancho]

even so, 200lbs is a lot. I'm designing around 100 lbs, and even that's on the high end of normal values. You don't want to tire out the driver's leg.

[terra_dactile]

i believe thiers a difference between the force needed to brake at the pedal and the safety factors you would put for the strentgh of the pedal assembly itself,
the value of 100-110 pounds is the force required to stop and not what a driver could possibly put in an amergency, the brake pedal should be able to withstand at least 3 times more that the comfortable pedal force of 100 lbs

Jude Berthault
ETS Formula SAE

[kwancho]

Excellent point. He's right.

[CMURacing - Prometheus]

i can prolly max out the leg press at around 500lbs. my buddy (a biker of the roadie variety) can max 500lbs with EACH LEG.

so 200kg can be done, but you gotta get your driver in shape.

[kwancho]

This may or may not be related, but I'm thinking we're gonna go with a hand clutch and have 2 pedals, which means left-foot braking, go-kart style. Means we better start working out our LEFT legs.

[Agent4573]

this topic has been brought up in quite a few threads before. I believe the acceptable answer was between 90 and 100 pounds from the driver. If you design for anything more than this the drivers leg will get fatigued in endurance, anything less and you get more into a brake by position situation. Of course, you can do whatever you want, but I'm pretty sure this is how the typical car is designed.

[markocosic]

2000N/200kgs/400lbs is about right for your averagely fit and healthy 95th percentile male in a 'blind panic' situation.

200N/20kgs is fine for a motorwayhighway cruiser but far too soggy to control when you're being thrown about in a racecar IMO

[paddy]

I cant help but think 400lbs is a bit much. Most of the braking is done by the foot rather than using the whole leg. After all there is hardly that much room in these cars for exagerated leg movements.

[Buckingham]

400 lbs is a bit much, even for a 'blind panic'. Besides, you would like to think that your driver has enough nerve not to "panic" when he see's an obstacle. It is almost always easier to go around an object than to try and stop in front of it, especially by locking 'em up.

[James Waltman]

We did a test where we put a scale in a door jamb. The scale was on one side and we pressed our backs against the other side. The left column was everyone's agreeing that 120lbs of force was not too high. The right column was the max force for each person for one leg. The picture was taken before Jason tried. He was a thrower for our school's Track & Field team and got well over 600lbs with one leg.
We have broken pedals that were not up to the task.
http://dot.etec.wwu.edu/fsae/HostedPics/James/Pedal_Forces.JPG

[Z]

So who can't hop on one leg!!!???

If you weigh around 100kg and can get any sort of "air", then you are pushing down with a force of about 200kg! (in round numbers). Now think about sprinting up a hill...


James, so what's up with Jack? Too much time in front of a computer screen?? http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

[CMURacing - Prometheus]

Originally posted by Z:
So who can't hop on one leg!!!???

If you weigh around 100kg and can get any sort of "air", then you are pushing down with a force of about 200kg! (in round numbers). Now think about sprinting up a hill...


used that argument freshman year when all the seniors doubted 100lbs of pedal effort was physically possible.

james, while putting your back against a doorjamb gave you a constraint, i would think it also allows you to put some of your lower back (and gluteal) muscles to use. z's experiment is much more "pure"...you could even get really scientific and get a high speed camera to measure how high everyone jumps, weigh them, etc., and figure out the force they exert. you can also use a more realistic range of motion, by constraining how much the knee is bent at the start.

[Chris Boyden]

What about repitition? How many times can you exert 150 lbs force over 1" of motion? An inclined leg press with your back against the ground is just about the same incline as many FSAE seats. I imagine this varies quite a bit depending on how far one's legs are extended. If your knees are bent too much, that sure makes it a lot harder. If your legs are almost fully extended then things get a lot easier. It would be a pretty quick test at the gym.

[Cement Legs]

Originally posted by CMURacing - Prometheus:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
So who can't hop on one leg!!!???

If you weigh around 100kg and can get any sort of "air", then you are pushing down with a force of about 200kg! (in round numbers). Now think about sprinting up a hill...


used that argument freshman year when all the seniors doubted 100lbs of pedal effort was physically possible.

james, while putting your back against a doorjamb gave you a constraint, i would think it also allows you to put some of your lower back (and gluteal) muscles to use. z's experiment is much more "pure"...you could even get really scientific and get a high speed camera to measure how high everyone jumps, weigh them, etc., and figure out the force they exert. you can also use a more realistic range of motion, by constraining how much the knee is bent at the start. </div></BLOCKQUOTE>

I would agree... put the scale in your car against a block mounted at the same angle as your pedal. Do your experiment again pushing against the incline plane of your seat and not a solid door jam. Then post your new picture.

[James Waltman]

Z,
Jack is a pretty small guy. To be fair to him though, he went first. He didn't realize that this was also a contest to prove one's manhood.

I know our test was not entirely representative. We were just trying to get a baseline. I put it up here to counter comments like – ˜A pedal that can handle 3 times 100 pounds should be strong enough' and ˜400 pounds seems too high'.

The best test would be to strap your driver into your car and rig up some kind of sensor on the actual pedal. Then you can post your data.

[Agent4573]

heres an amazingly simply and dead on balls accurate way to get everyone to shut up. Someone go buy a pressure sensor, put it in your brake lines, and work through the two or 3 simple equations to figure out how much pedal force it takes you to lock up your tires. That way everyone can stop guessing and doing experiments that aren't good estimations.

[Buckingham]

A force transducer placed on the pedal would give a better result for this test than a pressure sensor. There would be a lot of uncertainty propogation through pressure losses, the bias bar, and the assumed pedal ratio. A force transducer doesn't require equations. Force transducers are also easier to self-calibrate by using a known mass.

[Homemade WRX]

Originally posted by Agent4573:
heres an amazingly simply and dead on balls accurate way to get everyone to shut up. Someone go buy a pressure sensor, put it in your brake lines, and work through the two or 3 simple equations to figure out how much pedal force it takes you to lock up your tires. That way everyone can stop guessing and doing experiments that aren't good estimations.
this would be good...I think we have one on the Legends car...I'll see I get when I drive it next week...so long as we do have the sensor.
-Micah

[McFly]

You will never get the exact number for the force applied to the pedal for getting the brakes to lock up. It will change with multiple factors, like road surface condition, weight bias, brake bias.....etc. Along with that each car has a different design for the brakes and each required pedal force is going to be different. Doing the calculations will mostly get you in the ball park, but most importantly it will get you the right front to rear bias. Then you can be sure you have enough adjustment in your brake bias to accommodate for dry and wet driving conditions.

my 2 cents:
The "maximum" possible applied force shoud be taken into consideration. The design should focus more on the maximum deflection under maximum braking. Having a lot of brake pedal movement is usually undersirable to the drivers. Our 2005 car for maximum braking had a little over a 1/2 inch of travel at the point of contact for the drivers foot. Though just under a 1/4 inch of that was from the brake pedal deflecting, so that is why we are looking at the maximum deflection of the pedal this year.

Carroll Smith recommends about 100 lbs of force that the driver should have to apply to get the car to lock up the wheels.

Our team can attest to this, last year I ran the calcs for our 2004 car and it took about 160-180 lbs of force to stop the car. When driving the car, it seemed like you had stomp on the pedal and throw your whole leg into it. Where in 2005 I designed it for under a 100 lbs and it made a world of difference.

[Alan S.]

im pretty sure this there are two things to consider in this thread
a) the break pedal should probably be designed to take at least 600 lbs of force
b) when calculating for the breaking system itself use a "safe number" 100lbs seems to be a middle range guess

[drivetrainUW-Platt]

hey guys, good to see our new brake guy Allen is gettin comfortable with the forum and also that a few Madtown boys are chiming in. Donavan, what is this force transducer you are talking about? some sort of strain guage or dial indicator scale or something?