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MG MGB Technical - Braking in the wet
|While returnng from the fantastic MG2006 we ran into a couple of torrential rain storms, lots of water and lots of aqua-planning exciting!!. |
My problem was trying to stop or even slow down.It seems, and this condition is not new, that when there is heavy rainfall ,I loose braking however it does return after stabbing at the pedal to try and dry them off.
Any recomendations on effective brake pads that have good grip when wet?
What type pads do you have? Some of the best pads I haver ever used worked great until you hit heavy rain-- then virtually -0-.
Hawk pads have a high cf and work great. In real wet conditions you lose a little until the disc dries up but it recovers pretty quick.
I've noticed that the problem is in slow driving. Apparently when moving at speed centrifugal force throws the water off and only leaves a thin film that doesn't dramatically affect most pads.
|Also, if your wheel bearings have too much clearance, there will be a lot more water on the discs to start, as the disc will knock the pads back. With correct clearances, the pads normally only allow a very thin film of water on the disc. With the bearings and rear brakes adjusted correctly (and bled well), There should be very little pedal movement before the brakes work; if you have 1" or more, this might be worth checking.|
|I have noticed the Greenstuff pads seem to work well in the wet. I think with wire wheels the discs seem to get wetter. I have had the excitement of not slowing down when applying them at speed on the motorway, the car seems to accelerate and it lasts for ever, in fact you are slowing a bit and it probably takes a few hundred milliseconds. This was with standard pads, I remember that the n/s wheel (RHD car) dried out first and I was grateful for the quick steering and road grip of the B!|
|Are you using high performance tires? Many of the high performance tires are dangerous in the wet. I had Michelins on a new Nissan that wouldn't work well in wet conditions even though the were all season tires. If your tires aren't labeled as All Season that could be the problem. Remember that in the USA we have lots of traffic and if the roads haven't seen rain for several weeks the roads get oil soaked from all the cars and trucks with oil leaks, a sudden quick rain can turn the roads into an oil covered skid pad.|
|We have lots of traffic here too. The most entertainment is to be found at motorway roundabouts at this time of year with lots of oil, diesel and bits of tyre covered with a layer of rainwater. The greenstuff pads seem OK in most conditions here.|
|B D Hird|
|Aquaplaning is where the wheels lock and slide over a film of water (or other lubricant) on the road surface with little or no *vehicle* retardation, which is different to the delay in *wheel* retardation that occurs if the discs/pads are covered in a film of water. On a recent UK 'Top Gear' program they were testing a high-spec Mercedes that detected wet conditions and repeatedly and slightly applied the brakes independantly of the driver to keep the discs and pads clear of water, so as to give 'normal' braking when it *was* required. |
Slotted pads and or discs are reputed to reduce the panic-inducing lack or vehicle retardation when first applying the pedal in extremely wet conditions, although they are more intended to reduce brake fade which occurs in repeated heavy braking in the dry i.e. when a gaseous film develops on the surface of the pads.
But it doesn't matter what pads or discs you have, if the *road surface* is covered in Diesel, rubber and water you ain't going to stop anyway, the wheels will have locked and you are no longer a driver but a passenger, unless you have the presence of mind to lift off or pulse the brakes (cadence braking) and steer instead.
|Paul Hunt 2|
|If you read the specs on various after market hi performance brake pad manufacturers, you will see they point out whether the pads are vulnerable to failure in wet conditions. From my point of view, with a '67 with no vacuum booster, the minor water vulnerability of the Hawk pad is more than made up by the increased "bite" and consequently reduced pedal pressure. The virtual lack of dust and long life are also pluses.|
Modern hi performance tires are amazing on wet roads. Some show 98% traction wet compared to dry. Tires are typically more important in stopping your car than anything else. Modern wheels and tires can transform the handling of the B. Cheap tires can scare the hell out of you in the wet.
|Jon - There is nothing in the world that can make a half a second seem like a lifetime as much as wet brakes in a situation that calls for a quick slow down. Living in the Pacific Northwest and driving a MGB as an everyday car, I became far more familiar with that half second of absolute terror than I ever wanted to be. Wire wheels definitely add to the wet brake disk syndrome when one is on the highway in the rain. I finally purchased the MGOCs club combination of slotted disks and the EBC Greenstuff pads and have found that while they don't completely eliminate the problem, they certainly minimize it to an acceptable level. I no longer leave my finger prints in the steering wheel whenever I have to come down quick and hard on the brakes in the rain. Cheers - Dave|
|Barry, FR,Paul, Stan et al.|
Many thanks for your reponces.
A few more details; this happened with wire wheels shod with 185/70x14 Hercules tires. I use Hercs because with the chrome wires I like to run with white walls and I am only now able to find w/w in this brand.
I used to run Michelins in that size white walls but they are N/A.
The aquaplanning that I experianced was due to flooding of the highway and I experiance the very same effect in my winter beater,a 99 Benz. Loose wheel bearings is a bit of a stretch but I am sure that is not the case, as prior to the Gatlinburg run, they were renewed.
I think the problem is water soaked brake pads. The pads on the car are not new and probably have about 20K on them however this problem has exsisted since they were new and are regular Moss pads. Most of the MG owners around here hide when it rains and only drive about 1500 miles per season so I thought maybe this thread might help. To that end I have heard about greenstuff pads, but not those made by Hawk. Can you elaburate on them. FYI my other set of wheels are minilite Minotars shod with Michelin X-1's. Excellant rain tire, but at 80 mph plus, they do tend to aguaplain and the brakes do get as wet as they do with the wires.
David, you installed slotted rotors with greenstuff pads. Have you been in a real deluge with them as yet?
|Jon - "David, you installed slotted rotors with greenstuff pads. Have you been in a real deluge with them as yet?" You have obviously never been to Seattle druing the months of October through June. While we selcdom have real deluges, we get a pretty constant rain (we don't have webbed feet for nothing) and the freeways, with groves worn by studded tires, maintain a goodly amount of water on them. After driving for several miles at freeway speeds in these conditons, the front disks are well coated with water. It always took, what seemed like 15 minutes (actually probably only a half a second) for the pads to wipe the water from the rotors and actually start slowing the car. Since putting the slotted rotors on, I have not had that problem. I was told that the slotted rotors get rid of water on them much faster than plain ones and I am now a believer. I still get a small amount of time lag from hitting the brakes and their taking hold, but is no longer a rectum puckering experience.|
|Paul's contribution is spot on. I was intellectually aware of the effect of rain after a long dry spell, but after a lurid slide in nearly 2 tonnes of company Merc exiting a motorway some years ago I am now also viscerially alerted. Some opposite lock a little bit of luck a power steering pump with all the grunt you needed and those hours and hours on the Stuttgart test track saved my bacon thanks for asking.|
|Interesting about Mercedes work with a system to keep the brakes dry. That is the same technique that e all used in southern California when it rained and all of the surfaces streets were running curb deep in water. One always kept the left foot on the brake pedal (even if you had a manual transmission) to keep the brake drums dry incase you needed to stop suddenly. One lady didn't do that in her late 50s Buick on Christmas eve afternoon in 1959 and wound up using my TD to stop her at an intersection - wiped out the whole right side of the TD and I think it also broke her parking light!|
Paul - I have also read about the slotted disks being intended to reduce brake fade by channeling the gaseous film away from the disk/pads on hard braking, but it also does a great job with the water film on wet roads. The problem is not apparent if one has disk wheels, but with wires and to lesser extent with alloys, is is rathere disconcerting. Cheers - Dave
No never been to Seattle but I have been to Vancouver where they say it only rains twice a year,-once from January to June and the other from July to December....
I have seen 2 types of modified rotors, one type has many holes cross drilled in them, for cooling I suspect, and the other from Moss ,cross drilled with holes and 4 diagonal groves cut into them. Which of these are the rotors tthat you seem to be having good luck with.ie: keeping your pants dry!!!
|green stuff the rotors from the MGOC accessories at: http://www.mgocaccessories.co.uk/acatalog/ they are a 6 slot rotor but no cross dirlled holes. When I purchased them, it was|
|No one has mentioned the age of the tyre. I have found that old tyres do not grip as well as newer ones, irrespective of tread depth. This problem effects both wet and dry grip.|
|I'm finding this discussion a bit puzzling. I drove my '58 MGA and a '64 MGB on various Michelins (Xs, XASs, ZXs) as daily drivers in the 1960s and early 70s in all the weather that Southern Ontario can have. I don't remember ever running out of brakes and I drove a lot faster and harder, then. The MGA acquired 1600 disc brakes in '67 and had no problem with them, either. I wonder if the older OEM-type brake pads were better? It can't be just the Michelins.|
|A mini Cooper I aquired once came fitted with Michelin Xs, all I can say is if you were able to handle a car in the wet shod with them you are a better driver than I am.|
|To add to the wet road braking story: the first rain is the worst. All of the rubber and oil creates viscous hydroplaning --- and it happens just where you need to brake: intersections,sharp curves and the like. A hard rain will wash these materials away and then braking becomes more predictable. People forget to drive more cautiously during that first rain . . . any pay the price.|
The transportation agency in California (CalTrans) grooves the roads at some locations, but not enough of them. Cities appear ignorant of grooving at chronic trouble spots. Grooving drains away the water and provides a roughened surface to aid braking. A "popcorn" surface also works well. airport using airport transfers sevenoaks runways which are re-paved and not yet grooved require the a Notice (NOTAM) be sent out.
High-speed hydroplaning occurs at 9 x (tire pressure) and so is seldom encountered. The worst situation is water on ice near freezing temperatures.
|Oops! Make that 9 x (square root of tire pressure)|
|An example of the "first rain" phenomena. Way back when TR3s were not that old and my college suite mate had one he was driving down the Arroyo Seco Parkway (now Pasadena Freeway I think) during the first rain of the season and slid off the road at 30 mph on a curve. This was usually good for well over 50 on that curve.|
Just a bit of trivia.
A comment on the Caltrans grooving of the concrete roadways. It is often done parallel to traffic direction and with the old biased ply tires would sometimes result in a bit of a lack of directional stability at speed. Not a comforting feeling in a 49 MG YT at freeway speeds!
|Southern Ontario got a lot of rain the other day. I took my 58 MGA, disc brakes, on 35 year old Michelin XASs out. Found some long, deep puddles and got the brakes thoroughly wet. Tried panic stops--I could get the wheels to lock up and the XASs to slide. No sign of brake fade; no pulling, no excitement. The A stopped in nearly the same distance as it would in the dry (and it stops very well, thanks!). The old Michelins wanted to slide on hard corners but that's to be expected from ancient tires. I'm surprised they handled as well as they did.|
So, I don't think there's anything inherently wrong with MGA/B brakes if they're working properly and set up correctly.
As for the Michelin Xs: I rallied my '61 VW fairly hard on them in '62/63, then transferred the SAME tires to the MGA. Seemed just fine in the rain.
This thread was discussed between 07/07/2006 and 14/07/2006
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