Lotus Europa Community
Lotus Europa Forums => Technical Articles and DIY tools and tips => Topic started by: EuropaTC on Wednesday,September 21, 2016, 12:40:07 AM
-
Yep, another thread on brakes. I know, I’m like a stuck record at times (for those of us old enough to remember vinyl ;) )
To recap, my car is a TC running standard (232mm) front discs/calipers with a rear disc conversion using 240mm MGF discs & Renault calipers. Mintex 1144 pads up front, EBC Ultimax in the rear, no servo assistance. And it works, I really don’t have any reason to change it.
But….
The trouble with this interweb thing is that you learn new stuff, I noticed some folks commenting about Fred Puhn’s Brake Handbook and eventually tracked down a copy. It’s interesting and although some parts are irrelevant for our cars it does give you a good insight into designing and upgrading brake systems.
And that’s how it all started. So I’m blaming Fred.
Although my brakes are probably better than they’ve ever been, they aren’t “modern” brakes where you get oodles of stopping power simply by brushing the brake pedal with your big toe. I could re-fit a servo to give more system pressure and better clamping force, but decided to try another approach based on overall system design.
I may not know much about designing brake systems but as usual with me, my enthusiasm outweighs any amount of knowledge or common sense.
Right, enough background. The executive summary is that you can stop reading here if you're on 13" wheels, because what I've done won't fit, but if you have 14" or 15" wheels you're in with a chance. Actually, even if you have 13" wheels you can make a slight improvement along the same principles, just not as much.
The project was to fit larger front discs (rotors to you guys over the pond) but retain the OEM front calipers. Sounds odd ? Well, there are sums to explain the "almost" logic but the main driver was that the Elise S1 uses 288mm discs with only 2x44mm pistons in the calipers. 4 pot or larger calipers obviously give more clamping force & bigger brake pads, but not always necessary. I wanted to see how far I could push the type 14 caliper with it's 48mm pistons.
Continuing with the summary, I fitted 265mm front discs, 259mm rear discs. As expected you need new caliper brackets as well, that takes the longest workshop time. Total cost roughly £70 for discs & steel. A cheap project, one you can almost certainly get past your project manager(ess). :)
Does it work ? Yes. Is it noticeable ? Yes. I think you'd be surprised just how much so, or at least I was.
And with my usual 20/20 hindsight, I think the rear brake conversion I did a couple of years ago with 240mm discs might have been better with slightly larger ones.
Enough waffle from me. For those interested I've split it into PDF files in order not to take up too many pages on Joe's forum.....
-
Thank you, Sir, for taking the time to document your mods and sharing the info!
-
You're welcome, and :Welcome:
Don't take the maths as absolute, but I think the principles are sound. More road testing today and now the pads seem to be bedding into the new discs it is becoming more noticeable that the front end really dips, and that's with 250lb front springs. I just wish there was a DIY method of estimating the amount of G it pulls.
:)
-
Aren't there smart phone apps for that? I have seen gizmos you can buy (don't know where or for how much). It wouldn't surprise me if Amazon sells them. They sell everything else!
-
I don't have a smart phone..... :-[
Yes, I know, I really should join the 21st century but phones are just one of those things that don't turn me on. I make calls and that's it really, so we've both got old Samsung things.
But.... you have got me thinking. We do have an android and an Apple tablet so if there's an app about, we should be able to cover it. Good call.
Brian
-
Garages have G thingies to road test brakes for MOT tests when they cannot do it on the rollers because it is 4WD.
Alex in Norfolk.
-
Garages have G thingies to road test brakes for MOT tests when they cannot do it on the rollers because it is 4WD.
Alex in Norfolk.
Thanks Alex, that's interesting. I do remember tapley (?) meters but thought they'd all got thrown away now we had rollers.
On another tack, after BDA's suggestion I went looking round the App store and he's right, everyone and their dog seem to be writing accelerometer apps so I've downloaded one and have another excuse for "road testing"...... an amazing thing this forum.
-
;D
Let us know how what you find out!
-
Got one !
I don't know if it works in the car yet but I downloaded "physics toolbox accelerometer" from Amazon for my Kindle Fire this afternoon. There were several apps in similar vein but this one has graphs, and I like graphs. It certainly moves around if you shake the Kindle so I expect it will do something, but as to whether that something is useful, accurate or just fantasy is something I've yet to find out.
I'm amazed. I had no idea my cheap kindle would do such things, I only bought it to play with when I'm bored on holidays.
And I'm really glad I'm on a forum with friends who keep up to date on such things :)
-
Stick with us, Brian, and you'll go places! :)
-
;D
Let us know how what you find out!
Well, it's been a while now so I thought I'd better post where I'm at. True to form there have been several "dohhh" moments along the way. Having tried a couple of apps now I've settled for trying to learn how to use one of them properly without losing all the data or having to manually scan through massive CSV files to find the braking points.
However.... the Kindle Fire app does appear to give you numbers in the x/y/z planes which are supposed to be the g-force acting on your device. Are those numbers accurate ? well I have no other point of reference so I'll take it as comparative data rather than absolute. It's a real pity that I didn't have this before changing the system because then I'd have a true reference point. (one of the many "dohhh" moments)
What I've found is that testing on dry roads with good grippy surfaces and doing hard stops from between 30 to 50 mph, if I believe the data I can get numbers both above & below the target 1G. This is where I'm suspecting my method or the data sampling is inaccurate because although I've felt close, the fronts haven't locked yet and the calcs said they should at 0.95g. ( on a positive note, neither have the rears :) )
So the data gathering has a way to go yet, but it looks promising.
To end on a positive note I'll say that if you can fit larger discs, then do so. If you're going for a rear disc conversion, fit the largest you can and balance the front to suit. Having now tried it I'd say that this is a massive improvement, far more than fitting GT6 calipers & discs to the Elan. I'd even go so far as to say it's worth junking 13" wheels for, the reduction in pedal effort and stopping distances is, well, just amazing.
-
Interesting, Brian! Who would have thought that bigger rear discs would be the trick after reading so many people say rear drums are perfectly adequate?
-
Hi BDA,
I've no argument with anyone wanting to stay with OEM brakes, all I'd say is to look at it with an open mind. Until Richard on the Yahoo group produced his first spreadsheet my only aim with the brakes was to make sure they were maintained as well as possible. But Richard's approach altered my perception and it was all downhill afterwards ! ;)
His original spreadsheet showed a 74%/26% front/rear split on braking with an S2 using OEM front & rear drum brakes. Changing to 240mm rear discs improved this to 67%/33%. Using TC numbers this came out at 64%/36% and my latest setup has the ratio at 66%/34%. So whichever conversion you go for you're getting more out of the rear brakes.
I always used to think that it was only the front that mattered, but having read up a bit now I can see that the rears are equally important in balancing the car. I'm pretty much convinced the OEM set up wasn't by design but depended on what was in the "cheap parts bin". :)
Brian
-
Very interesting stuff, Brian. I haven't posted in this thread but I have been watching it with keen interest.
-
I'm pretty much convinced the OEM set up wasn't by design but depended on what was in the "cheap parts bin". :)
I think you're right. Lotus built a pretty impressive car from a bunch of pretty unimpressive parts.
-
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.
-
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
-
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