Passat has solid discs on the rear, I can apparently fit vented ones. Now of course I wouldn’t consider this for any kind of sporty reason since I don’t drive anywhere near fast enough for that, but when towing the brakes have to work a fair bit harder. So would it help performance?

I might end up somewhere mountainous this summer with the caravan, so it might help..? Cost increase is pretty small.

Doesn’t the towed vehicle has an inertia brake and take most of the load?

Doesn’t the towed vehicle has an inertia brake and take most of the load?

Depends on the caravan, but you’d think so, it still puts a load on the car’s rear brakes though as the spring in the tow hitch is pretty stiff. And if you brake hard the ABS will cut the front brakes first as the rear’s have much more grip than usual.

As for whether it needs vented disks, I’d probably conisder them (but my trailers aren’t braked and probably weigh <300kg), it’s not like standard brake pads need any heat to start working so you’re not going to suffer with them being too cold.

Have you noticed any brake fade before?

Doesn’t the towed vehicle has an inertia brake and take most of the load?

Yes but the force applying the brakes is dependent on the difference between caravan brakes and car brakes – if they were both equally good, the caravan brakes wouldn’t work and so the van would run on there by putting more load on the car.. and so on.

The brakes definitely have to work significantly harder when towing, and you can’t slow as quickly.

I haven’t noticed brake fade before, but I haven’t been to the Alps or Norway before with a caravan!

You do realise that you can’t just fit vented discs in place of solid ?

You will have to change callipers & mounting brackets also .

Hmm. I’d assumed that since they were both listed for my car they would both fit and that they’d adjust due to being fancy electronic handbrake calipers. Of course, there are to other possibilities – either Eurocarparts’ database is rubbish or vented rears were a factory option.

10mm difference in thickness.

Yes but the force applying the brakes is dependent on the difference between caravan brakes and car brakes – if they were both equally good, the caravan brakes wouldn’t work and so the van would run on there by putting more load on the car..

I don’t see what your trying to explain. The caravan brakes will operate when the coupling is compressed, if the brakes are less powerful than the car, the coupling will simply compress a bit further to apply more brake pressure until the caravan is slowing at the same rate as the car. On a descent using engine braking and no footbrake, the brakes on the caravan will still be operating as the caravan is compressing the coupling against the car.

The only time this doesn’t apply is when you’ve panic braked and the coupling has compressed the whole way and bottomed out, the caravan wheels have locked and therefore aren’t doing their fair share of the braking. Or, the caravan brakes have overheated, in this instance your vented discs may help you out.

Eurocarparts database isn’t rubbish, different vehicles come with different options, not every option is deducable from a VIN number or they don’t have access to the data that makes it the case.

They won’t fit straight on, as the caliper won’t be wide enough, neither will the caliper carrier. The rears do very little work, and if there is a load sensing valve in there, that will alter the brake bias automatically. The brakes on your vehicle have already been deemed appropriate for the gross train weight that is quoted on it’s plate. So if your caravan/trailer combined with car is over that weight, then you are overloaded and infringement of traffic laws.

It is pointless. Modern cars are massively over braked anyway and the use of modern Dot 4/5 fluid means brake fade is not really an issue especilly if, on steep hills, you are effectively using low gears to control your descent rate.

the coupling will simply compress a bit further to apply more brake pressure until the caravan is slowing at the same rate as the car.

Yes but a) the brakes on the van are rubbish so they can only do so much and b) the reaction to the force activating them is pushing the car forwards still.

Thikning about it, b) is pretty small, but a) seems to have a big effect because you can’t slow down as quickly with the van on – this is a fact.

However – good points about the discs well made. Not worth pursuing.

And if you brake hard the ABS will cut the front brakes first as the rear’s have much more grip than usual.

Eh? Possibly wrong way around…

Also, another Moly overthinking things thread.

It is pointless. Modern cars are massively over braked anyway and the use of modern Dot 4/5 fluid means brake fade

Brake fade is different to boiling the fluid, when the pads/disks get too hot the coeficient of friction falls off a cliff.

Eh? Possibly wrong way around…

No, you’ve put ~50kg of nose weight on the towbar, which works to lift the front wheels off the ground, and push the rear wheels down*. So when braking they will be able to do more of the work, either if the car has some fancy electronics to work this out in advance or by the ABS cutting the braking effort from the front brakes as they become overloaded.

Moot point anyway if they don’t fit.

*say for the sake of argument the wheelbase is hald the length of the car and the overhangs ar a quater each, you’d take 25kg off the fronts and add 75kg to the rear, if the car weighs a ton then that’s 5% off the front and 15% more weight on the rear axles.

I agree on the rear wheels having more grip, the nose weight plus the caravan nosediving during hard braking puts a huge load on the rear axle, and this opens the load sensing valve putting more braking effort into the rear wheels.

You can see it here!
[video]https://www.youtube.com/watch?v=pR9rVALw5ck[/video]

VAG brakes are pretty straight forward.

Unless you have a top end sports model with a Brembo upgrade then all the brakes are single piston floating caliper designs made by ATE. They just spec different sized calipers and discs for different applications.

Fitting vented to the rear which will be thicker might involve a new caliper or you could get away with a different pad carrier to accommodate the thicker disc but I’ve no idea if the pad carriers are available as a seperate part.

Alternatively just upgrade your pads – EBC Red and Yellow Stuff are a good upgrades and deal with heat build up better than a lot of OEM pads

Brake fade due to overheating? Absolutely no chance on a normal road car on the road even towing a caravan. the main reason for brake fade historically is due to boiling brake fluid – no problem there these days and though theoretically it is possible to overheat the brake lining material and the coefficient of friction will fall off a cliff the reality is that it is practically impossible even if you were trying your best. Even back in the day when I had an old Porsche on std brakes and did loads of track day’s the brake temps never got even close to causing a drop off in brake performance. And i’m talking about a 20 yr old Porsche, so not a modern one with top spec brakes or even carbon brakes.

Standard brakes are more than adequate. the majority of braking is done by the front brakes anyway even when towing. Most cars don’t have active brake distribution and even with active brake distribution you’re not going to get much more than 30% of braking carried out by the rear wheels even if you’re towing. And EBC red or yellow stuff and other aftermarket “peformance’ brakes are crap for day to day normal driving – really crap cold performance (which 99.9% of your braking is) and often squeal like a stuck pig. I’d say don’t even go there you’re wasting your time – the real car designers know what they’re doing and often do a proper job with the standard stuff. Seriously, save your money.

No chance of brake fade? Tell that to my old 1997 Citroen ZX Diesel, heavily loaded with camping gear and attempting to keep up with the spirited driving of the in inlaws along twisty roads. We weren’t even going downhill, but to press the brake pedal and suddenly find that there is suddenly a significant loss in brake effort, and the harder you push, the more you realise that you can’t actually stop is a bit of a shock. They dropped us at thisn point so we carried on at a more sedate pace 🙂

The pedal didn’t go mushy so it would have been the discs/pads that overheated – your Porsche’s standard brakes would still be in a different class in terms of outright power and cooling capability.

I never bothered changing anything on either of my 530d sport Tourings when I was towing 30ft yachts around Europe, no need.

How fast do you expect to drive exactly whilst towing ?

as above, best case it would be a new yoke but that depends on design. Worst case is it needs a new caliper also due to the design of how the pads are retained and also it might be a completely different pad design, larger piston etc etc.

Yes but the force applying the brakes is dependent on the difference between caravan brakes and car brakes – if they were both equally good, the caravan brakes wouldn’t work and so the van would run on there by putting more load on the car..

Don’t get this either. Not sure you’ve considered the brake coupling properly there but that is an old post that has already been commented on.

All my advice would be just make sure all your brakes are in good working order and have plenty of pad material left before a trip. Do pay particular attention to the back but mainly due them normally coming with less pad material to begin with and generally being checked less often as the fronts take priority most of the time. Also any weakness in your handbrake will be much worse with a trailer hanging off the back and make sure you don’t have any dragging brakes (sticking sliders, grubby pad slides etc) as it will just add to fuel consumption and could very easily eat a new set of pads on a long trip when towing and kill the discs as well.

oh and use a decent brand of pads.