Max braking deceleration

[skumdum]

Hi guys,

What is your maximum braking deceleration ever read for a FSAE. (without downforce)

thx a lot,
that will help me for the tire data understanding

[skumdum]

Hi guys,

What is your maximum braking deceleration ever read for a FSAE. (without downforce)

thx a lot,
that will help me for the tire data understanding

[skumdum]

Hi,

seriously, nobody ever read with accelerometer de maximum deceleration of your car??

help me on this one

thx

[VFR750R]

Seriously, would you ask an F1 team that and expect an answer?

Ever seen the trophy competition in Road and track? They post 60-0 times for 5 of the top cars at comp...and the 06 results I'm looking at vary 19%.

[Christopher Catto]

Dude,

what's FSAE got to do with F1? One is a student competition, the other is a money spinning and corrupt sport with team budgets in the $200m.

Like saying "would you ask the US president how often he sleeps with his wife?" Course he would not tell you. F1 teams won't even tell you the weight of their rear brake light.

Can people quietly forget the way F1 teams work or are we gonna hear the same replies over and over again??

Just say, "i'm too worried to give you the answer because I think it would give you a significant advantage" or "do the work and search it on google".

http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[flavorPacket]

Chris,

You're right, but we're all tired of saying that. It's just getting ridiculous.

[C.Zinke]

It depends on the tire, the track, the temps, the concept of the car and its setup. Normally you will have values between 1.2g and 1.7g

[HenningO]

1.2-1.7 sounds a bit high from my experience. You sure your not talking about lateral acceleration, because that sounds more right.

Typical max decel I've seen is around 0.9-1 g with a race setup. You could probably get a tad higher with a "braking" setup.

[Adam L]

HenningO, think about what you just said for a moment though. Your lateral acceleration forces are higher than your deceleration forces using the same contact patch?

You may want to rethink your brake setup or get a better driver.

I would say a proper car should be able to attain 1.3-1.5 +/- 0.1g's of deceleration.

[HenningO]

I reviewed our logged data, and I still haven't seen more then 1.1 g of decel on an autox/endurance race.

Yes, our lateral acceleration is way higher than our longitudinal acceleration. But they are not using the same contact patch...

[Christopher Catto]

I would agree

-1.1G is the average max I've seen and it's remarkably constant for many non aero cars, including big heavy ones. I would go with 1G if you consider an average quality track surface.

With aero you could to better than that (hence why formula cars do so well under braking).

and to put it a bit more directly:

braking and cornerning use the same patch only in principle. unless your car is a square, you will have different track and wheelbase and also the angle between tyre force and tyre centreplane (carcass construction etc) is different.

the contact patch is rarely completely round or square. anyway, too much to go into.

[murpia]

Don't forget, limit straight line braking to a standstill does not appear in any of the competitive events. I would expect a car to be capable of higher peak deceleration than actually shows up in sprint / endurance data.

Generally cars have longer wheelbases than tracks, so they should be capable of greater longitudinal performance than lateral performance (less weight transfer). But, you have to have your brake balance optimised.

Regards, Ian

[C.Zinke]

So our LR07 does 1.2g with 3.5deg camber at the front ant 2.5deg at the rear. When we change camber, the deceleration goes up to 1.45g. In Silverstone this year the overall grip was up to 0.2g higher than in Germany for example. As we use ABS we always have the maximum that all four tires can gernerate, because of the ideal brake balance.

[Brian Evans]

Here is a relevant discussion from the DSR site.

http://p081.ezboard.com/G-Loading-on-the-brakes/fdsrfor...ge?topicID=553.topic (http://p081.ezboard.com/G-Loading-on-the-brakes/fdsrforumtechnicaldiscussion.showMessage?topicID=5 53.topic)

I would hazard a guess that the degree of weight transfer resulting from the short wheelbase and forward biased static weight distribution typical of the FSAE cars overloads the front tires during braking and results in poor (relative to the DSR) performance. They expect about 15% greater G-loading under braking than in cornering.

Brian

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Brian Evans:
forward biased static weight distribution typical of the FSAE cars
Brian </div></BLOCKQUOTE>

I think most FSAE cars carry between 50 and 60% of their mass on the rear tyres.

Ben

[Adam L]

I think you've guys have cleared this up on your own so I don't want to make too much noise.

If your track and wheelbase are nearly square, chances are the forces will be nearly identical. In most cases though, if you take your traction budget into the equation and treat the track and wheelbase as a swingarm (oversimplified for visualization purposes) your roll angle will likely be greater than your dive angle. When braking, hopefully your car has all four wheels on the ground, when cornering some cars will see 1 tire lose contact with the ground reducing your traction budget by 25%. This is of course with all the dynamic loadings taken out of the equation, jacking, track irregularities, etc. etc. but hopefully you get the idea.

My explanation is oversimplified, but I think you guys nailed it on the head in regards to wheelbase/track ratios. However, I don't know how your cornering forces are greater than braking.

Please correct me if I'm wrong.

[HenningO]

I would say one reason why our cornering forces are bigger then our braking is forces, is because the cars are setup to be fast around a track. And as C.Zinke said, decreasing the amount of negative camber increased braking forces.

Of course weight transfer (wheel base/track width) comes in to play, but I'm confident the tires plays a much bigger role then you think. And one tire loosing contact doesn't necessarily mean a drop of 25% traction etc etc.

And yes, England this year was AMAZING when it came to a clean and grippy surface!

[Chris Allbee]

Consistently 1.36 without aero. We've hit 1.92 with aero http://fsae.com/groupee_common/emoticons/icon_smile.gif

[sunil3590]

if we need to stop our 350kg car from a speed of 40kmph, within 1.5 times its overall length.. with its length being 2.4m.. we need to reach 1.75G.. right? can we practically reach this?

[blister]

Without chechking your calculation, with an ordinary FS Car, this is not possible.

For an average estimation, look here:
w w w.fsaustria.at/fileadmin/pdf/Special.pdf

Acceleration is the velocity at the braking line. Keep in mind that teams were allowed to start braking before the "braking line". Nevertheless it was a tire shredding event for teams without ABS.

Also interesting: TU Graz and Karlsruhe hat an ABS built in, either it was switched off, it worked poorly or it was set-up to work poorly ;-)

[RollingCamel]

There was a thread before I started and someone posted 0-100-0 performance from the Australian event.