Braking distances

[Toad 0]

Afternoon...

 

I was playing with my car the other night and wondered what distance it would cover when braking from 70 to 0.

 

The answer was about 46 yards (Braking distance in the highway code is 75 meters)

 

I was just wondering if anyone else had tried it or knew what distance they covered? Would be quite interesting to compare it to other cars.

 

For the record I've got 280mm front brakes (G60) with EBC Greenstuff pads on the front, standard rear brakes with VW pads, front Goodridge hoses, and I reckon I could have hit the brakes harder, as the fronts didn't lock, but the rears did (I've got a fair bit of rear brake bias)

[Roger Blassberg 0]

I expect that at least some of the difference between your stopping distance and that quoted in the Highway Code is the "thinking distance". I imagine that, in your test, you hit the brakes at a known point and measured from there, whereas the Highway Code takes into account the distance travelled while you are thinking about what to do about a hazard that has just unexpectedly appeared.

 

70 mph is 31.3 metres per second, so if it takes you 0.25 seconds to think and another 0.1 seconds to get the pedal down, you have travelled nearly 11 metres (40 ft.) extra.

 

And I expect that they take into account the slower reactions of the "average " motorist over the whole age range. Ever been in a car with a (cough) "elderly driver"? The time it takes for them to react is bl@@dy frightening. I once sat as a passenger, with my 75 year old father at the wheel at 170mph (Jaguar XKR on an Autobahn). A sure cure for constipation!

 

Best wishes

 

RB

[Toad 0]

Lol. 170mph would frighten me if I was in the drivers seat, let alone riding with someone else!

 

75meters is just the braking distance from the highway code... I've discounted the thinking distance, as I had a marker where I rammed the brakes on...

[mrbeige 0]

Tom, how come your rears locked up? Is your brake bias valve buggered or something??

[Toad 0]

Tom, how come your rears locked up? Is your brake bias valve buggered or something??

 

 

It's cable tied partly open... I know some people will tell me that it's not safe etc, but my rear brakes never used to do anything, the disks stayed rusty, so the front would lock and trees would try to mount my car. I found that by jamming the valve slightly open, the brakes were far more efficient, although the back end could get a bit twitchy when really hitting the brakes hard on rough corners.

 

Now with the bigger brakes up front it's quite nicely balanced, the rears work quite hard, and although there was some lockage(I was pressing the pedal bloody hard), I stopped in a nice very straight line. I'm happy with my setup, and I think I've got a pretty good feel for what happens when the rear wheels do lock up now.

[dinkus 10]

Cool to know - I wonder what it's like with the 312s on :)

 

If your rear brakes lock first I think that might be an MOT failure tho - it's certainlt an SVA failure :s

[jonnyboyo 0]

Jeeze, i wouldn't want to even test the standard pie tins on an early valver :shock:

When i bought my valver they were completely hopeless. Put it down to having a late shape GT4 with mahoosive standard discs previously. But after going back up north and driving the RST, which are synonymous with having horrendously woeful brakes, my humble valver was putting in just as pitiful a performance :(

 

I fitted standard sized drilled & grooved discs front & rear with OMP fast road pads, new rear calipers and new fluid which transformed the braking. Ok, i still have to shove the pedal some to get a reaction, but at least i get one now and they really dig in when pushing the pedal hard.

[dr_mat 0]

The quoted braking distances obviously also vary massively depending on the weather, the condition of your tyres, and the condition of the road surface..

 

Ironically some of the worst places to brake are the ultra-high-grip surfaces just before major junctions where they've screwed it all up by putting regularly spaced big thick rumble strips all the way along 'em. You can't brake effectively when your damn wheels are bouncing off a bloody rumble strip can you, ya bloody idiots??

[Henny 0]

the brakes on J-DUB (305mm 4pot brembos with MKIV rears) pulled her down from 100 to 0 in under 3 seconds at Bruntingthorpe... :shock: They're MUCH, MUCH better than the highway code reckons... :lol:

 

Dunno how good they're gonna be now they're on H-YYU as she's not got ABS, so will probably lock up if I hit 'em REALLY hard... :?

[Kevin Bacon 5]

Really? So your car gets from 100 - 0 in about the same time as an F1 car then :lol:

 

Imagine 100mph, now count in your head 2 and a bit seconds. Your car comes to a complete halt from 100 in that time does it? Hmmmmm

 

Mate, my 330mm APs don't even come close to that retardation speed. Care to reevaluate your estimate? :lol:

[Toad 0]

Cool to know - I wonder what it's like with the 312s on :)

 

If your rear brakes lock first I think that might be an MOT failure tho - it's certainlt an SVA failure :s

 

Yeah.. I'd like to see/feel the difference...

 

The brakes have been in the same state for the last 2 MOTs and it's passed fine... They won't lock so easily on the test stations rollers as there isn't the weight transfer from the rear to the front of the car I believe.

 

Id have thoughtthat other people would have gone and had a go at this by now... Someone must have some distances to compare mine too....

[dr_mat 0]

Apparently an F1 car " .. can decelerate from 185mph to a standstill in 3.5 seconds". I think 100-0 is probably easily dispatched inside 1.5 or 2 seconds then..

 

** disclaimer - since this information was gleaned from the WEB, it might very well be bullshit.

[Kevin Bacon 5]

LOL, no need to add a disclaimer, no one would openly admit to knowing that precise peice of information from the top of their head :lol:

 

Maybe it's 0 - 100 - 0 they in 5 or 6 secs or something. I remember a demo on TV ages ago, but half of that time was braking back to zero again IIRC.

 

Not doubting Henny's car brakes quickly, but 100-0 in under 3 seconds is a little far fetched for a 1200 Kg car with relatively small discs.....but I'm willing to be corrected!

[dinkus 10]

I reckon you should go find a nice bit of straight, flat (*cough* private) road and give it a try Kev... ;)

[Roger Blassberg 0]

Don't care how big the discs are, the maximum retardation you can get, relying on friction between the road and the tyres and without ground effect or similar tricks, is 1.0g. That's 9.81m/sec/sec (approximately!!). So from 100 mph, (or 45m/sec,) it will take at least 4.6 seconds.

 

Elementary my dear Newton.

 

Best wishes

 

RB

[dr_mat 0]

Ah yes, but you are neglecting wind resistance and downforce.. ;)

 

The aforementioned F1 car actually pulls MORE braking power between 200 and about 150 mph (about 5G), because of the extra downforce from the *huge* wings, combined with the enormous amount of drag (after all, it requires 700-800 horsepower to *maintain* 200 mph - lift off completely and you're losing 500 kJ of inertia every second just due to wind resistance).

 

Your personal car has a similar, if greatly reduced downforce, but also has a crap Cd so the same applies. If it requires 100bhp to maintain 100mph..

Sticky tyres would also allow you to exceed 1G on their own. After all, if you had a perfect grip to the ground, you would be able to achieve infinite G forces under braking.

[Roger Blassberg 0]

Talking about a Corrado, not an F1 car, I accept your argument for wind resistance, although the loss of say 75kJ/sec. at 100mph rapidly drops away under braking , since drag is not directly proportional to velocity. By the time you are down to 50mph the drag is relatively negligible, maybe 10kJ/sec.

 

A 1250kg Corrado travelling at 45m/s has 1265kJ to get rid of, so even the drag associated with 45m/s over the whole deceleration would take nearly 17 seconds to dissipate all that kinetic energy.

 

Don't know about downforce though with a Corrado. If anything there is likely to be uplift - look at the shape of the thing in logitudinal section. It's not low enough to have any serious ground affect and is a good approximation to an aerofoil, even with the trademark spoiler deployed. (which is accepted to be there to reduce lift at the tail.)

 

Do we have any tyre experts? What sort of frictional coefficients can be assumed for "normal" tyres and surfaces? And how much energy is given up to rolling resistance?

 

 

 

Best wishes

 

RB

[DanVW 0]

Mine appears to stop quick enough, I do wish I could turn off the ABS sometimes though as it does get annoying

on Southampton's shockingly poor roads!! I have driven in 3rd world countries with better roads :-(

 

might rig up a switch to the ABS ECU at some point.

[Toad 0]

Anyway. Hasn't anyone else measured their distances yet??

[DanVW 0]

Not doing anything lunch time, lets try mine in the car park ;-)

[Toad 0]

Not doing anything lunch time, lets try mine in the car park ;-)

 

Yay!

 

[in joke]Would that be considered worse than smoking outside the front door??[/in joke]

[DanVW 0]

Am sure we can make enough smoke to keem them happy :lol: