Author Topic: Yet Another Take on Brakes.....  (Read 1281 times)

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Offline jbcollier

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Re: Yet Another Take on Brakes.....
« Reply #15 on: Wednesday,October 05, 2016, 11:39:57 AM »
Interesting work, well thought out and nicely made.  You are after a lighter pedal with similar, or more, braking retardation.  Certainly going to a larger diameter disc is a good way of doing so.  A larger diameter gives you a longer lever even if the applied force remains the same.

However, I disagree with the statement that the Europa brake system was not properly designed.  They had access to larger discs, wider rear drums and shoes, different pad/shoe compounds and different diameters of wheel cylinders, calipers and master cylinders.  The parts chosen, I would say carefully, work well together and, in 1967 and 1968, provided the greatest stopping power many magazines had tested up to that date.

I find the brakes just as powerful as those on my modern cars but requiring a much greater pedal effort, typical 60's racing practice, and, unlike today's ABS equipped with slam and forget, proper technique.  One needs to apply the brakes gradually at first to allow for "weight" transfer before one can really push hard, pretty much like riding a motorcycle.

Offline 4129R

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Re: Yet Another Take on Brakes.....
« Reply #16 on: Wednesday,October 05, 2016, 12:11:31 PM »
IIRC, the car was originally supplied in the UK on 165/70/13 Dunlop SP Sports front, and 175/70/13 at the rear. There were only 2 cars that had 175/70/13 SP Sports fitted as original equipment, and at that time, I owned both, the Triumph Dolomite Sprint being the other.

Now the car will only stop as well as the tyres grip the road, so there is no point in having huge brakes if it just locks up the tyres. In 1974/5 the SP Sport was a very good tyre with quite long lifespan (30,000 miles normal use), so it was not over-grippy.

I have fitted Yokohama super sticky tyres and big discs all round, so I don't expect long life out of the tyres. I have driven competitively on dry racing tyres, so I know that you can get huge grip from tyres. I drove 350 miles in 5 hours once back from an international rally on Michelin TB20 racers, soft compound treaded intermediate (damp) use. I could go around roundabouts at insane speeds, and stop super quickly.

So, it is not just the discs that count, whether they be larger diameter, ventilated, or stopped by multiple calipers. The black stuff has to make good contact with the other black stuff, without locking up. Tyre choice is equally if not more important in stopping.

Alex in Norfolk

Offline EuropaTC

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Re: Yet Another Take on Brakes.....
« Reply #17 on: Wednesday,October 05, 2016, 11:56:00 PM »
So, it is not just the discs that count, whether they be larger diameter, ventilated, or stopped by multiple calipers. The black stuff has to make good contact with the other black stuff, without locking up. Tyre choice is equally if not more important in stopping.

I'm 100% with you on the tyre grip, it came across very strongly in my researches and made me somewhat cynical about the benefits of simply slapping on a "big brake" kit.

The tyre grip coefficient from Puhn's data ranged from 0.7 to 1.2 but that makes an amazing difference to wheel lock, for example using 0.7 I get front wheel lock at 0.6G, whereas at 1.2 it comes in off scale at over 1.2G.    I used 1.0 in my calcs because that seemed about average for a modern sports tyre but I'm now thinking that might be fractionally low. 

I've no evidence but suspect that in the 60s/70s the tyres were at the lower end which would tie in with my perception of how easy it was to lock the brakes back then. Apparently the police still use 0.7 as the number when evaluating skids.

It's a personal view but I think you need a complete package of suspension, wheel & tyres to get the best out of any brake mods and hence a brake kit alone won't yield optimum results.

Brian