But surely with denser air, it requires more energy to make a sound travel because of the molecules banging into each other dissipating the energy quicker. As the air thins, each molecule can travel further (for the same energy). I agree in a vacuum you can't hear anything because there's no molecules .... but when the air thins there are :P

For comparison, try shouting on a clear summers night (when the air is dry and less dense) or in the rain. Which sounds travels further

Chris

The "molecules" dont actually travel very far, they just rub against each other causing the vibration/sound.

Less molecules = less chance it'll hit another and pass the sound on.

If the molecules traveled with the sound you could suffocate someone by making a loud noise

yes but are you comparing like for like??

are you comparing a brand new set of groovies against a set of part worm oe discs??

No, I went from brand new oem 312's and oem pads on knockhill to Tarox G88's and Pagid Pads on the same circuit within a month.

EDIT: Both sets were worn in before track use

yes i agree that pads do give off vapour and groovy discs will dissipate this, but a lotus elise is a fast car and may benefit from grooved discs, however for any road application plain disc should be adequate for anything you throw at them.

can anybody here actually prove that grooved discs reduce their braking distance??

oh we could be here a while

i dont think mercs put them on their road cars just for the sake of it surely?

oh we could be here a while

i dont think mercs put them on their road cars just for the sake of it surely?

mercs have drilled discs, which is another thing i really hate!!!

but then when you look at the service schedule of such a merc, it specifies they are changed frequently regardless of condition

they surely must have them for a reason tho?

they surely must have them for a reason tho?

i'm just an old cynic!!! probably just to bump the price of servicing up!

The "molecules" dont actually travel very far, they just rub against each other causing the vibration/sound.

Less molecules = less chance it'll hit another and pass the sound on.

If the molecules traveled with the sound you could suffocate someone by making a loud noise

i've known bengie to choke/gag after i've farted. is this the same thing?

you're using the wrong brake fluid then. i'm sorry but grooved discs and 'black widow' pads or whatever they are called:rolleyes: are just gimmickey rubbish, and if you ever were to go on the track you'd be better off using sintered metal based pads because they have a higher coeffiecient of friction at high temperatures.

if you find your brakes are fading it's normally because the fluid is boiling and the best thing to do is err.... go slower

Ok, I'll write off everything that every qualified automotive engineer and competition car designer has ever told me about braking systems then.

Oh and my own practical experience.

As I said, the guy from Lotus I spoke to should be sacked.

you might be right Phil

my own practical experience of using grooved discs on hill climb rallying is that they are just a waste of money, BUT if you can stretch to the diamond cut ceramic ones porsche / merc /lotus use then go for it

my own practical experience of using grooved discs on hill climb rallying is that they are just a waste of money, BUT if you can stretch to the diamond cut ceramic ones porsche / merc /lotus use then go for it

Isa anyone else thinking what I'm thinking - about the brakes on a car for going up hills quickly

:orb_lol:

yeah i know uphill!

i've done grass track/gravel circuit rallying

and tarmac sprints too!

when i was doing sprints in one of my mk4 polos i actually had at one stage 280mm front brakes on with all the grooved discs and everything...... but after a while i realised it wasn't worth it so i went back to the 256mm plain discs/calipers. and it makes no difference to the lap times at all........

anywho i'm getting boared of argueing this point now

sounds like you weren't driving hard enough then tom :P

Come on guys it is simple basic stuff. Cross drilling allows fade gases to escape more easily. Fade gases are emitted from the pads when the temperature gets high. Higher temperature equals more gas volume. On a given drive, the pads have to warm through fully, as do the discs, before fade gases will be at maximum level. Cross drilling allows you to prolong or avoid the onset of fade.

So arye your brakes fading because the pad compound is vapourising or because you brake fluid, or the moisture in it is boiling or the air is being released from the fluid resulting in cavitiating? Easy to tell. If the pads are fading, you get grumbling as the pads wobble about a bit and intermittently penetrate the fade gas cushion.

If your fluid is fooked, the brakes just dont get pressed against the discs hard enough, no grumbling.

Fast road driving can induce pad related fade. I have cross drilled a vented front / solid rear setup successfully and it worked very well, completely eliminating fade, however, the backs of the venteds developed cracking within 10,000 miles. About 120 holes at 3mm dia, countersunk front and rear at 45 deg. The cracking started when the countersinking wore down, but having said that, the non drilled set before them cracked on the rear surfaces as well.

If you can lock the wheels or trigger the ABS (when the system is very hot), no amount of fancy pad material or drilling will makle you stop quicker. If you cannot lock the wheels, then cross drilling may help.

Chris

If you can lock the wheels or trigger the ABS (when the system is very hot), no amount of fancy pad material or drilling will makle you stop quicker. If you cannot lock the wheels, then cross drilling may help.

i couldn't have put that better myself.......

don't agree with that completely really, i can lock the wheels in swmbo's hyndai accent 1.3 Si super easy but it won't stop anywhere near as well as my octavia which doesn't lock up very often at all, its called modulation

from years on bikes i had some magura discs for about 18months and thought they were fine, i could stop well and lock the front wheel pretty much at will but i have since changed to some larger better discs(hope, 6 pot ti at the front and 4 pot at the rear) and the braking is much more controlled so can stop a hell of a lot better and quicker.

Just read in Evo magazine they have changed from drilled discs to grooved one on their long term lambo due to cracked discs.

don't agree with that completely really, i can lock the wheels in swmbo's hyndai accent 1.3 Si super easy but it won't stop anywhere near as well as my octavia which doesn't lock up very often at all, its called modulation

Hi Bengie

Yes, I agree thatmodualtion is important as well, but the fact remains that if you rcar has ABS and you consistently get the system triggered when the brakes are as hot as they will get, your stopping didtances wont improve much if at all by improving brakes. Brake feel can be better, brake balance can be better, tyres can be better, but if the stoppers are not the weak link in the system then there is little or no benfit in upgrading.

Of course if the disc pad combo make modualtion difficult, then upgrading will help. Hoses can help with this as well. I suspect you Octy has much more mechanical grip than the Accent as well. There are many factors that affect stopping distance. The MR2 has small disks but stops as well or better than anything else I have driven. Modulation is extrememly good as well.

Chris

Ok Chris, so now explain how a change of friction material (same discs, claipers, fluid and control tyres) gave the Ginetta challenge cars typically 0.3g higher stopping loads!

Ok Chris, so now explain how a change of friction material (same discs, claipers, fluid and control tyres) gave the Ginetta challenge cars typically 0.3g higher stopping loads!

i think that will be something to do with the different temperature ranges at which the pads work, normal road brake pads are effiecient at upto about 300 degrees farenhiet, whereas semi-metalalics have a higher coefficient or friction at upto 500 fahenheit..... the point is this.... for the majority of road applications semi-metalics would never reach thier optimum temperature so normal asbestos type brake linings are more suitable.

Ok, so having conceeded that different pad constructions and chemistries can make a difference on track, will you accept that there's no reason why a suitable selection won't do so on a road car?

Ok, so having conceeded that different pad constructions and chemistries can make a difference on track, will you accept that there's no reason why a suitable selection won't do so on a road car?

yes, but it depends on what material they are made from, i would use normal asbestos linings, or if i was feeling really rich i would use kevlar based ones, trouble is with kevlar ones is that they **** up the discs more quickly

Key word "asbestos" I think - there is no such thing as a new asbestos-based brake pad any more!

Key word "asbestos" I think - there is no such thing as a new asbestos-based brake pad any more!

yeah when i say asbestos i mean the organic substitute stuff they use....

asbestos hasn't been fitted to road car brakes since about 1990 (cossie's had them)