Suspension: 850: Switching back from coilovers - parts needed?

[JohnM 855 T5R]

1) Pad area - obviously this determines how much friction material is in contact with the disc.
A: Of course, when all else is equal the larger the pad, the longer it takes to wear out. larger areas also shed heat quicker. You maintain a larger area gives a friction increase, only so far as it stays cool for longer. At the same temperature it doesn't. Incorrect. Firstly, you are presuming linearity of braking response to pad area and force applied. This is not the case. With a larger pad, more friction will generally be obtained at a given force, albeit this will be marginal. A larger pad will, however, enable you to exploit the application of a greater force

2) Friction material - the co-efficient of friction will, in simple terms, determine how well the pad "grips". A high co-efficient however as we all know comes at a price - the pads usually have a narrow optimum operating temperature range and work worse when too cold plus the pressure that needs to be applied to take advantage of high friction material is normally greater which leads to...
A: I am in complete agreement.

3) Clamping pressure (the force that is applied through the pads) - i.e., how hard you shove the pads onto the discs. Apart from the strength of your right foot, the amount of clamping pressure that can be applied is determined by the design of the caliper itself and its hydraulic relationship to the master cylinder (along with the brake booster which makes higher brake pressures possible without having to go to the gym.)
A: Of course, let's call it 'force'.

Having a larger 302mm disc and moving the caliper further out with the required mounting brackets put the pad into contact with a part of the disc which has a higher surface rotational speed. This makes absolutely no difference whatsoever in terms of the basic physics of braking.
A: When you push an object across a table-top, first slowly, and then quicker are you doing the same 'work' in each case? If you wanted the 'table-top' to get hot would the speed you did thsi make a difference? I say, the greater rotational speed will increase heat. You have made a basic error. The TOTAL amount of work and heat generated is the same whether pushed fast or slow across a given distance. When pushed slowly the temperature rise is less at any given point but that temperature rise is for a longer period of time- BASIC PHYSICS and conservation of energy.

If you use the same pads, calipers, master cylinder and brake booster you will get diddy squat improvement on 302's.
A: Not quite, you will see more friction, the Moments of force increase, The pad will now get hot quicker covering more ground than it did on a 280mm disc, we're doing more work. Again, incorrect - see point above. Total work done and heat generated is the same in both cases As above, this argument does not hold up

As I said, the only benefit is in extreme conditions where fade might be delayed due to the increased ability of a larger chunk of metal to soak up generated heat and the higher rotational speed at the rim of the vented disc to dissipate heat in the the airflow.
A: Agreed a bigger chunk of metal will take longer to get hot, and will take longer to cool, outside of race conditions, eg: an emergency stop, that alone is an improvement. It will take more than an emergency stop to reach the point of noticeable fade (unless it's from 125+m.p.h to zero + which I'm sure you never do on the road)

Regards
John

[CNGBiFuel]

Having a larger 302mm disc and moving the caliper further out with the required mounting brackets put the pad into contact with a part of the disc which has a higher surface rotational speed. This makes absolutely no difference whatsoever in terms of the basic physics of braking.
A: When you push an object across a table-top, first slowly, and then quicker are you doing the same 'work' in each case? If you wanted the 'table-top' to get hot would the speed you did thsi make a difference? I say, the greater rotational speed will increase heat. You have made a basic error. The TOTAL amount of work and heat generated is the same whether pushed fast or slow across a given distance. When pushed slowly the temperature rise is less at any given point but that temperature rise is for a longer period of time- BASIC PHYSICS and conservation of energy.

2/10

Oh dear, yes if you did this once, and allowed yourself to take longer for the slow push, than the fast, that would indeed be the case. Same work done in more time. I agree.

If this was repeated for say 10 secs in each case, the faster pushes would cover more diistance in our 10 secs., thus more work would be done. ie a 302mm disc travels further at its perimeter than a 280mm. Hence the pad travels more distance in the same time or one revolution. If the pad is subject to the same force, and in the same time, if I read this correctly, you would have it that no more heat and friction is the result? The grater ditance the pad travels has no bearing on this?

With you correct, save for your comments on heat dissipation and wear, where we agree, we can reduce disc sizes to nothing. As you say there is no mechanical advantage to a 302mm disc over a 280mm. Moments of force can be forgotten too. A short spanner has the same force as a long spanner etc etc.

Thus we can move the caliper closer to the axis. We need a 150mm kit here.

We're learning.

[JohnM 855 T5R]

Another basic error - there is no significant moment of force involved in the vertical plane. Think it through.... the moment of force is in the horizontal plane, i.e. being clamped through the disc.

Regards
John

[CNGBiFuel]

there is no significant moment of force involved in the vertical plane. Think it through.... the moment of force is in the horizontal plane, i.e. being clamped through the disc.

If you can't dazzle 'em with Brilliance, baffle 'em with BS.

Thus from your comments we conclude:

1) The distance we place the caliper from the axis has no effect. It follows that a short spanner has the same leverage as a long one. This because it is in the vertical/horizontal plane. Think it through?
2) The greater distance the pad travels (per revolution) - this on the larger disc - has no effect.
3) Friction is a factor of area. Bigger pads, bigger friction. The Laws of Friction ... "Friction is independent of the area of contact as long as there is an area of contact." Don't apply. Think it through. Amonton was an idiot.

In short, all this time we've been fooled. The 302mm set-up offers no advantage other thatn greater cooling /heatsink etc, this because the pad remains unchanged, and what we are changing, the distance from the axis is has no effect. To work, the pad would have to be bigger?

We've thought it through, and had our fun. Thank you.

[Shinsplintz 101]

You're both right .....and you're both wrong. :

Have a read - apologies it's an American site - but since I can't be arsed to type out war & peace myself it'll have to do as the most straight forward write up I could find of vehicular hydraulic braking at short notice.

https://www.brakes-shop.com/brakeped...rade-selection

In summary:

Increasing brake radius (for the same caliper/pad/ master cylinder) does provide a benefit to braking - an increased torque on the braking wheel for the same amount of force applied at the pedal.

Larger disks = better thermal performance under repeated heavy breaking

For best results change oem pads for a type/brand that suit your diving style - going harder ( read as more expensive) for heavy breaking types of driving.

All in all it's a dark art - like most car modifications. Best left to the experts or intrepid amateurs with deep pockets. Like everything in life. Buy cheap, buy twice.

In terms of earlier comments on this thread - lowering a car, i.e. decreasing it's centre of gravity - also aids in braking as it decreases the moment of force towards the front axle under braking load, improving stability and grip.

Back in the day Volvo struck a balance- like all manufacturers - between practicality and performance. To imply that improvements can't be to handling & braking over a stock set up using modern aftermarket parts and skilful modern mechanics is simply ludicrous and totally without merit. Sorry if I've burst anyone's bubble there.

Cheers, Morgan

[foggyjames]

As I understand it, greater pad area gives three primary benefits:
1) Better pad cooling
2) Better service life
3) The potential for larger caliper pistons (and hence greater clamping force)...but the pad alone won't have that effect.

Oh, and do try to keep it polite, all. You can politely disagree without likening someone else's post with testicles...

cheers

James

[CNGBiFuel]

I think we'll park Amontons' Laws, anything we were taught in school re: simple levers and er... dangly bits etc. It's got boring.

In terms of earlier comments on this thread - lowering a car, i.e. decreasing it's centre of gravity - also aids in braking as it decreases the moment of force towards the front axle under braking load, improving stability and grip.

Back in the day Volvo struck a balance- like all manufacturers - between practicality and performance. To imply that improvements can't be to handling & braking over a stock set up using modern aftermarket parts and skilful modern mechanics is simply ludicrous and totally without merit. Sorry if I've burst anyone's bubble there.

I don't think any of us imply it's not possible to improve the stock set-up with the right amount of work. Yet in practice, a bloke with a £1000 odd to spend on 'race parts' isn't set to get far. To get a decent compromise between height and comfort took development engineers more time and money than any of us can spend. The geometry was set for the car at stock levels, a compromsie in itself. The reality for our 'bloke with a box of spanners' is more probably going to be a mess. All we'll have access to is an after-market kit with elements made adaptable to many cars. These parts will no doubt offer adjustments, which will be sold as an 'actual' advantage, but therein is the BIG clue... if it was actually 'for the job' NO adjustment would be required? When did you last ask for P80 air-filter that was adjustbale? You want one for the job. If a £10 oil filter was sold as 'adjustable' we'd ask why? Yet when spending £1000 on 'race parts' we don't?

If parts are correct for the application, these won't require adjustment. Then again, we're back to a set of stock Nivomats at our 'luvverlee Nivomat ouch price'.

It seems the OP's car has already been thru' stage one of this cycle, and it doesn't sound successful. Yes, lowering a car is all fine, the theory sounds right. It is right.

And, this can all be achieved, however in reality, not by most of us... 'sides, nothing is more reassuring than the soundtrack of the ritual "clonk" as the nightly 'congregation' crosses McDonalds' speed-bumps on the diagonal.

[Rich850R]

Have i just read that 280's and 302's are more than up to the job?? wow

Should bin my AP's with 328mm J-hook Rotors then and saved a shed load of money in the process

[CNGBiFuel]

Should bin my AP's with 328mm J-hook Rotors then and saved a shed load of money in the process

If you're going to put them my way for £50 - such that I can do the needless willy-waving with these instead of you, then yes. Agreed, I'd have no more need for these at legal speeds than a set of 302mm, only... they shine, and I paid £50 for 'em. Some things you have to hang on your car even if it makes no sense whatsoever. Complete tosh, and I want them anyway.

Bring it on.

[Rich850R]

Originally Posted by CNGBiFuel

If you're going to put them my way for £50 - such that I can do the needless willy-waving with these instead of you, then yes. Agreed, I'd have no more need for these at legal speeds than a set of 302mm, only they shine, and I paid £50 for 'em. Bring it on.

even at legal speeds these are far superior than 302's, so you assume i have Aps for willy waving purposes?

Have you ever driven an 850 with Aps?