Peter Humphries (GreenV8S) talks us through what hes learnt on upgrading the Brakes on his V8S

Over the past few months I've had a lot of questions from people who want to upgrade the brakes on their TVR but aren't sure about the best way to do it. I seem to have tried most of the popular upgrades on the V8S so I thought I'd share some of the lessons I've learned along the way.

Why upgrade?
The original brakes on the V8S were 240mm single pot calipers/vented discs at the front and single pot calipers/non-vented discs at the rear. These are identical to the brakes fitted to early 4.0 Chimaeras and Griffiths. Newer cars have basically similar brakes but with vented rear discs and slightly bigger calipers. These brakes are perfectly capable of stopping the car, the limiting factor is how quickly they can dissipate the heat i.e. how often you can use them before the pads overheat and fade, or the brake fluid boils in the calipers. In normal use on the road this shouldn't be a problem. But when the car is driven hard on the track, it's all too easy to overheat the brakes. The warning signs are having to push the pedal harder, increased pedal travel or, in extreme cases, a pedal that goes to the floor as the brake fluid boils. The excessive heat may also warp the discs which can cause brake judder. The sensible action at this point is to ease off and give the brakes a chance to cool, and not push quite so hard in future. But once the brakes have been overheated like this they never fully recover, and I find it's usually necessary to replace the pads and fluid. Replacing brake pads, discs and fluid after track days quickly lost its novelty value so a few years ago I started what turned out to be a long succession of brake upgrades.

How far to go?
Brake upgrades can be expensive, and there's no point spending more money than you need to. But if you're going to upgrade the brakes, it's worth deciding how far you're going to go and replacing the brakes once. Doing the upgrade in lots of small steps like I did is very expensive! There seem to be three conventional upgrades:

Stage 1: Fluid/Pads/Discs/Ducts
There are some inexpensive changes which will increase the heat dissipation a little. If your brakes are marginal these changes may be enough to keep you out of trouble.
DOT 5.1 fluid allows your brakes to operate at higher temperatures without boiling. It absorbs water relatively slowly so it doesn't need to be replaced any more frequently than the normal DOT 3 or DOT 4 fluids. Best of all it's fully compatible with the normal fluids so there's no need to flush the system or replace the seals.
You can also fit harder compound brake pads. These can work at higher temperatures without fading, but there's a compromise - the higher temperature rating they provide, the less likely they are to work well from cold. Avoid "race" compounds, "fast road" are the ones to go for. Make sure you follow the correct bedding-in procedure for your particular pads. For example Tarox XF pads have a very high temperature rating and work well from cold, but if you don't put them through the correct heat cycles while they're bedding in they don't work at all well. Mintex 1144 pads are far easier to bed in but don't have such a high temperature rating and don't quite have the grip of the Tarox pads. I've also used Kevlar 'Green Stuff' pads with mixed results. The high-temperature performance is phenomenal and they just seem to work better and better the hotter they get, but they don't work very well for the first few minutes on cold winter mornings, and the disc wear is significantly greater than normal.
You can also fit grooved or drilled discs. These are a direct replacement for the standard items, and they're claimed to disperse gases better during braking, reduce pad glazing and improve heat dissipation. They have the disadvantage that they wear the pads faster, and drilled discs can be prone to cracking if they're severely overheated.
The final change is to fit air ducts to direct cold air to the brakes. On fast circuits these can noticeably improve cooling, on slower circuits I found little benefit.
The uprated components are typically only a little more expensive than the standard ones. On my car I would guess these changes improved heat dissipation by roughly 25%.

Stage 2: Big Brake Upgrade
Because of the forward weight transfer under braking the front brakes do most of the work, almost twice as much as the rears under heavy braking. Although the standard front brakes are bigger than the rears, the fronts are still the limiting factor. Various 'Big Brake' conversions are available, which are essentially spacers to mount the original front calipers further out so that bigger discs can be fitted. The rear brakes are left as standard. The Big Brake upgrade Tower View fitted for me increased the front disc diameter from 240mm to 280mm. This increased the cooling area by roughly 50%, and it seemed the brakes wouldn't overheat however hard I pushed them. Moving the calipers out also increases the amount of braking at the front wheels, which makes the rears less likely to lock up under heavy braking. It was only after I drove the car with these brakes fitted that I noticed that the car had been slightly tail happy under heavy braking, with the original brakes. The effect was barely noticeable, but I'd certainly learned to keep the car absolutely straight under braking. With the modified set-up the car had a slight tendency to straighten up under braking, which meant the car was positively stable even under heavy braking. With care, trail braking into corners was now possible. I felt this improved the handling of the car, but I wouldn't want to move the brake balance any further forward because the car will tend to lock the front brakes. So I wouldn't upgrade the front brakes further than this without taking steps to correct the brake balance.
If you're driving a 4.0 or 4.5 liter car this is probably the most extreme upgrade you'll ever need. It increased the braking capacity substantially. Costs vary depending where you buy from and how much of the work you do yourself, but as a very rough guide you might expect to pay up to around £500 for an upgrade like this. Remember, this is for the front brakes only.

Stage 3: Monster Brake Upgrade
The Big Brake upgrade was great. But various tweaks which followed increased the power of the car, culminating in the installation of a mildly tuned 4.6 liter V8 from V8 Developments. With worked heads and an ACT induction system, this puts out nearly 40% more power than the original engine. Obviously with the extra power (yahoo!) I was using the brakes much more, and now I found that on some circuits the brakes would overheat when I started pushing it.
Once again Tower View had the answer: a 'Monster Brake' conversion. This involves replacing the discs and calipers all round. When I was talking through the options with Dave at Tower View I explained that I wanted the biggest brakes I could get - there was no way I was going to buy a whole new set of brakes and then find they were still marginal. Dave took me at my word. The rear discs and calipers are bigger than the front brakes were after the 'Big Brake' conversion. They are huge! The front brakes are even bigger, they completely fill the 15" wheels and the new four-pot calipers barely clear the wheel. We even had to move the balance weights to make room for them. Despite this extra size, the new brake components actually weigh less than the originals, keeping the all-important un-sprung weight to a minimum.
The first chance I had to try the monster brakes in anger was at a MaxTrack track day at Bedford. This was an excellent track day with plenty of track time and very little traffic, so I could concentrate on testing the new brakes. (If you were following me round and wandering why I was braking in strange places, this was why!) I came to the conclusion that on the limit the bias was a little too far forward. After another brief trip to Tower View to fit an adjustable hydraulic brake regulator, I guessed at a rough balance and then headed off to the TVRCC track day at Cadwell Park for more testing. The rough setting was about right, but I found I could move the bias rearwards a fraction without destabilising the car. It was interesting to see how far I could move the adjuster before the effects were really noticeable, it seems you can have the brakes a long way out of balance and the effects will only be noticeable if you brake hard when the car is unbalanced. I suspect there are quite a few cars out there with uprated brakes which are out of balance, waiting to catch somebody out on a wet motorway.
A few weeks later I entered a sprint at Goodwood, which gave me a chance to test the new brakes on a track I knew fairly well. There are a couple of corners at Goodwood which are approached absolutely flat out at speeds approaching 150 MPH, with braking left to the last possible moment. At places like this you tend to note your braking points very carefully indeed; hit the brakes a couple of yards too late and you can be in real trouble. It is also vitally important to be able to brake near the limit of grip without locking a wheel - a locked wheel has much less grip than a rotating one and can mean you don't slow down in time for the corner. Obviously, at these speeds we all leave a safety margin, but the more controllable, balanced and predictable the brakes are, the less margin you need and the harder and later you can brake. This translates directly to quicker lap times and a happy driver!
The new brakes behaved impeccably. The pedal pressure is slightly lighter than before, but the balance is spot on and they're so progressive that I could confidently brake hard enough to squeal all four tyres from 140 + down to about 70, without locking a wheel. This was the first time I ever broke the 100 second barrier for a lap from a standing start. This isn't the first time the barrier has been broken by a roadgoing TVR - Sean Hayes achieved this some months ago in his 420 SEAC - but it was a first for me, and for a change I came back without having scared myself silly. Although I said at the beginning that the standard brakes are OK, the uprated ones are distinctly better. This must be just about the ultimate brake upgrade for a roadgoing car. But be warned, it doesn't come cheap.

Do-It-Yourself Brake Upgrades
Given the relatively high price of this sort of upgrade, the idea of getting the components yourself to save money has obvious attractions. But there are quite a few pitfalls for the unwary.

The first, obvious, problem is getting everything to fit and line up. You usually need to fit an adapter plate between the upright and the calipers to space the caliper the right distance away from the hub and with the correct offset for the bells you're using. With 15" wheels or bigger, and discs under 290 mm, this shouldn't be a problem. But if you're trying to squeeze bigger discs into standard size wheels you may find you need to choose the offset carefully so the caliper clears the rim, while still clearing the suspension through the full range of suspension and steering travel. If the brakes are a really tight fit, make sure you've left enough space between the disc and the caliper to allow for expansion as the disc heats up, and enough space between the caliper and the wheel to allow for flex in the bearings. The caliper really needs a good 2mm clearance all round.

The second problem is to get the static brake balance right. As you push on the pedal, the amount of braking force at each wheel depends on the geometry of the brakes (see figure 1). If you replace the calipers or move them further out from the axle center line you change the amount of braking at that wheel. Figure 1 shows how to estimate the braking effect for each wheel. If you work this out for the old and new setup you can see how much the braking effect has changed. Its best to ensure the front and rear change by similar amounts if you can, although you can increase the front a little bit more than the rear without problems. However, I'd be very cautious about increasing the braking at the rear more than the front as this reduces the car's stability under braking. How much is significant? Well I found that changing from 240mm discs to 280mm was very noticeable, an increase in braking force of just 20%.

A is the total piston area of the calipers. The area of each piston is proportional to the square of the piston diameter. If the calipers are the single-sided floating design (like the calipers that TVR fit to the Griffith and Chimaera), the effective piston area is doubled because the same piston clamps both sides of the disc. B is the distance from the center of the brake pad to the axle center line. C is the distance from the road surface to the axle center line. The total braking force is proportional to (A * B / C).

The third problem is to get the dynamic brake balance right. This means that the amount of braking at each wheel is exactly proportional to the weight on the wheel regardless of how hard you brake. Under very gentle braking the braking distribution will be the same as the weight distribution of the car, almost exactly 50:50. As you brake harder and harder the weight on the front wheels increases. At about 1G braking the weight distribution is around 65:35 - the front wheels have almost twice as much weight on as the back wheels. Figure 2 shows how the amount of braking at the back tapers off as you brake harder and harder. The standard brakes use a small inertial regulator valve in the rear brake line that restricts the fluid going to the rear brakes under heavy braking. But this is set up to work at a particular hydraulic pressure. If you've changed or moved the calipers the brakes will be working at a different line pressure, and you'll have to change the brake regulator to match. On my V8S the standard regulator was completely unsuitable for the new brakes and I used an adjustable Tilton regulator to get the right cut-off characteristics. If you've uprated the front brakes a lot and messed up the static balance you may find it difficult to get enough braking at the rear under heavy braking. You may even be tempted to take the regulator out altogether to get something like the right balance under heavy braking. This is not a safe approach. The problem is that the balance may feel fine under heavy braking in a straight line, but gentle braking round a corner in the wet will show that you have far too much braking at the front. As soon as you dab the brakes the fronts will lock up and you are off into the scenery. Admittedly braking round corners in the rain is a pretty bad idea at the best of times, but brake systems are designed to make this as safe as possible. If the dynamic balance is wrong it can be positively dangerous. You really need to get the static brake balance right and then use a regulator to establish the right dynamic balance.

fig 2

The fourth and final problem is to match the cooling characteristics of the front and rear brakes. There is really no point fitting dustbin lids on the front if those old drums you've got on the rear overheat on the second corner. You need to make sure you're addressing the weaknesses in the braking system, and the problem may not be with the front brakes.
So there you have it. None of these problems are insurmountable but there's more to it than simply picking parts from a mail order catalog. If you buy your new brakes from an expert you are buying peace of mind.

Insurance
Obviously, you need to notify your insurers of any changes you make to the car. My insurers made a nominal administrative charge to cover the brake upgrade, but didn't increase the premium and in fact offset the uprated brakes against some of the other performance modifications.
And finally …
Was it worth it? For me, absolutely. Although the green V8S does 20,000 miles a year on the road, it also competes in sprint and hillclimb competitions most weekends, and does a dozen or so track days a year. The original brakes were a real problem on track days. In race cars you may be able to work around this problem with high temperature pads but for sprinting and road use I need to have brakes that work well from cold. Given the performance of the car and the use (and abuse) it gets, the upgrade was the sensible way to go.

Griffth Owners Brake Modifications

Richard Olssen's big brake kit from Rally design, fits with 15” standard wheels.

Simon Roper's beautiful beast with 17" Technomagnesis Detroit's with Toyo Proxes F 215/40/17 and R 255/40/17 with Brake upgrade F 4 pot AP/ Hi Spec 315mm disc R 300mm + existing calipers.

Antony Pattisons 4.2 ltr Griffith with 16" Spider conversion, engineered by Himself.(Couldn't wait for the factory)

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