12 replies to this topic

[kayemod]

I've just had to have new front discs on my car, apparently I've worn out the originals in not much over 20,000 fairly gentle road miles, and I was astonished at the weight of the things. The discs are drilled and ventilated and 340mm in diameter, and each one weighs no less than 10kg, so that's 20kg of sprung weight at the front of the car. How much would the discs weigh on something like a Lotus 49 or 72? it's easy to see why Colin Chapman wanted to put the things inboard, all that mass on the ends of long and fairly spindly suspension arms, too spindly in the opinion of some drivers of course, but has anyone got some idea of the kind of weights involved? I can remember Williams going back to metal discs from carbon on Zanardi's car in 1999 in a vain attempt to get some speed out of him, but given the probable weight difference, unless the metal discs were lightweight, I'd have thought that the car's handling characteristics would have been altered, as well as braking performance and feel.

Edited by kayemod, 30 May 2013 - 17:58.

[PeterElleray]

has anyone got some idea of the kind of weights involved?

Yes - an 11" diameter by 1" thick vented disc of the type used in F1 around 1980 weighs around 4kg.

Peter

[Peter Morley]

Rob
A 330mm ventilated disc for a Subaru Impreza weighs around 4kg and mine are still ok at nearly 100,000km!
The discs on your car are extremely heavy and wear out surprisingly quickly.
Peter

[kayemod]

Yes - an 11" diameter by 1" thick vented disc of the type used in F1 around 1980 weighs around 4kg.

Thanks for that info Peter, I'd imagine that 1970s ones would be much the same weight and dimensions, carbon discs maybe less than half that?

On Peter M's post I agree on both points, the weight of the discs and wear rates, but my discs wore a lip around the edge, and they told me they couldn't fit new pads to replace worn-out ones with the discs in that state. The car is a Mercedes C Class AMG coupé, 'only' the 205hp 2.2 diesel, not the full-fat Jeremy Clarkson one, but all the suspension, wheels, tyres, brakes etc are the same, so maybe that's what it takes to stop the 6.2 litre 457hp version. It still doesn't explain the wear rate of mine though, first time in my life I've worn out a set of pads.

Edited by kayemod, 31 May 2013 - 22:12.

[arttidesco]

Back in the day when I was working for a Volvo dealer it was not uncommon to change front brake discs from around 24,000 miles because of the lip you mention, not sure why some vehicles develop this lip while others do not, IIRC the discs on my Golf were replaced after 60,000, retired parental, miles I wonder if some pad materials are simply more abrasive than others and if the abrasiveness varies greatly between sets even when they are 'genuine' dealer authorised parts ?

[PeterElleray]

Thanks for that info Peter, I'd imagine that 1970s ones would be much the same weight and dimensions, carbon discs maybe less than half that?

The 11" (actually just under) were fitted inside a 13" wheel with the twin caliper balanced braking setup. In the mid 70's on a standard AP or Girling twin pot single caliper they tended to be around 10.4-10.5" x 1" or even 13/16 " but the thinner disc was marginal in F1.

carbon in similar size generally under 1kg each (reducing to zero when you you wear completely through them).

Peter

[xj13v12]

The basic question asked here is quite correct but in the end there was still compromise. Something has to hang out there. As time has gone on improved materials and inboard suspension removed much of the unsprung weight. On a road car I recently changed front calipers to alloy and saved 3.5 Kgs. My wheels are 3 Kgs lighter than original etc. A good race car builds this in to start with. The old style APs on most of my cars from period are 4 pot which may have been heavier than the 2 pot that preceded them but brake efficiency was gained. The open back calipers are lighter. 17mm thick pads are heavier than 15mm pads so provided they will last the race they might be chosen. Everything that can save weight has a benefit unless it creates a greater problem elsewhere. Rocker arm suspension saves weight but early examples flexed so much the suspension geometry was compromised and so on.
Discs on a F5000 might be 10 1/8" x 1" but on a Can Am (with 15" rather than 13" front wheels) are 12" x 1.1". The 15" wheels carrying 23" o.d. tyres are heavier than the 13" x 20" o.d. tyres. More weight, more rotating mass etc.
If you want to try to get an understanding of the effect of extra weight try this. Stand holding a 5Kg weight straight out to one side. Move your arm up and down a few inches either way as fast as you can. Now do the same using a 2Kg weight. Obviously you have more control over the lighter weight and you can move it much more quickly. Same on the suspension which would have been carrying wheel, disc, caliper and upright. Would you like the shock/spring to control 15 Kgs or 10 Kgs?

I am sure someone here who has experience with a typical 1980s car can now supply some detail on what improvements were made over a decade.

[xj13v12]

By the way. Modern cars have discs from the factory that do wear out quickly and aftermarket discs often last much longer. We have that problem a lot in Australia especially on European cars. In many cases it seems that the discs wear out much faster than the pads. The truth is that the steel often used is quite soft which gives good feel but poor wear rate. However the cost of new discs is so low that the old way of skimming discs 30 thou a few times over their life is barely economical given labour rates. However putting harder discs on rather than the soft factory ones may well save you over the life of the car.

[kayemod]

If you want to try to get an understanding of the effect of extra weight try this. Stand holding a 5Kg weight straight out to one side. Move your arm up and down a few inches either way as fast as you can. Now do the same using a 2Kg weight. Obviously you have more control over the lighter weight and you can move it much more quickly. Same on the suspension which would have been carrying wheel, disc, caliper and upright. Would you like the shock/spring to control 15 Kgs or 10 Kgs?

All thought-provoking stuff, which brings us back to the Zanardi question, even with changed spring rates etc, three or four kgs taken off the sprung weight on each front corner, must have had more effect than the supposed aim of restoring brake feel, surely more would have been lost than it was possible to gain?

[xj13v12]

All thought-provoking stuff, which brings us back to the Zanardi question, even with changed spring rates etc, three or four kgs taken off the sprung weight on each front corner, must have had more effect than the supposed aim of restoring brake feel, surely more would have been lost than it was possible to gain?

In theory yes but never underestimate the value of driver confidence. Few things have the benefit of better lap times than a set-up or feel that gives the driver confidence. That's also why team set-up from one car to another is such a personal driver related issue. What works is whatever produces the best lap times. I am not familiar with the example you are citing but it seems the team was trying to get more out if a good driver by making him more at home. A computer model might say the change cost .2 per lap but if added confidence gave .5 per lap than the answer is clear. All of this is a good example of the why the squishy bit behind the wheel can never be replaced. Go back to the Porsche 917 at the 'Ring stories. "Ze computer says 9" wheels at ze rear are adequate". "The bloody computer's not trying to drive the bastard around the 'Ring in the wet!". Or words to that effect with apologies to Frank Gardner.

Enter the anorak with the correct quote, just don't flail me with it.

[Roger Clark]

Rocker arm suspension saves weight

Is that correct?

[Roger Clark]

Am I correct in thinking that Ferrari had inboard rear brakes on all his Grand Prix cars from the first 1960 rear-engined prototypes to the last of the flat12s almost 20 years later?

Some Lotus 18s had inboard rear brakes, but I don't think anybody else followed Ferrari's lead (always the innovator!) until the 1969 Matra MS80. The rear of the field followed fairly quickly after that and outboard rears only came back into fashion following the Lotus 79 and the need for aerodynamically clean space alongside the gearbox.

Were there exceptions?

Edited by Roger Clark, 01 June 2013 - 13:34.

[Macca]

The exception was the 1970 312B, then they reverted to inboard again from the 312b2.

Paul M