Ceramic or Semi-Metallic Brake Pads: Which Suits How You Drive

Somebody brings their car in because the front wheels are black with dust two days after a wash, or because the brakes squeal every time they roll up to a junction. Nine times out of ten the pads are fine. They are just the wrong kind of pad for the way that person drives, chosen because they were the cheapest box on the shelf or because a forum said they were "the best".

When I ran the shop, the pad compound question came up more than almost anything else on the parts counter. People would read "ceramic" on one box and "semi-metallic" on another and assume one was simply better. It is not that simple, and choosing badly costs you in discs, noise or stopping distance rather than in the price of the pads themselves.

What is actually in the box

Brake pads are a steel backing plate with a block of friction material bonded or riveted to it. The friction material is a recipe, and every manufacturer guards theirs, but they fall into rough families:

• Organic, sometimes sold as NAO (non-asbestos organic). Fibres, rubber and resins. Soft, quiet and kind to discs, but they wear quickly and fade when they get hot.
• Low-metallic. An organic base with some steel or copper mixed in. This is what a lot of European cars wear from the factory. Good bite, moderate dust.
• Semi-metallic. A large share of steel fibre, often somewhere between a third and two thirds by weight. Strong bite, handles heat well, dusty and noisier.
• Ceramic. Ceramic fibres and fillers with a little copper or none. Quiet, low dust, long life, with a gentler initial bite.

The labels are loose. One brand's "ceramic" can contain more metal than another brand's "low-metallic", and nobody is policing the word. That is why I pay more attention to two markings on the pad itself than to the name on the box, which I will come to.

The "ceramic is always the upgrade" advice

Online, ceramic pads have a reputation as the premium choice for every car. For a lot of drivers they are a good choice. But "premium" and "right for you" are different questions.

Ceramic compounds tend to need a bit of temperature before they bite their hardest. On a commuter car that does short runs in town, that is rarely noticeable. On a car that tows a caravan down a long hill, or a heavy van loaded to the roof, a pad that likes heat more is often the safer choice, and that tends to be a semi-metallic or a low-metallic. They also cost more: a typical front axle set of ceramics runs maybe £40 to £70 for a common hatchback, against £15 to £35 for an ordinary low-metallic set. You are paying for clean wheels and quiet, which is a fine thing to pay for, as long as you know that is what you are buying.

Semi-metallics have the opposite reputation, as loud, dusty and hard on discs. All three are often true. They also hold up when brakes get properly hot, which is why you find them on police cars, taxis in hilly cities and plenty of vans. A semi-metallic pad will wear the discs faster, so budget for discs sooner if you choose them.

The question is not which pad is best. It is which kind of heat your brakes actually see.

Matching the pad to how you drive

This is the rough guide I used at the counter. It is a starting point, not a rule, and the car's own handbook or the original part number should always win if it says something specific.

One more thing I always said at the counter: do not mix compounds on the same axle. Left and right should match, or the car will pull. Front and rear can be different, and often are from the factory.

Two markings worth reading before you pay

The R90 approval

In the UK and Europe, replacement pads sold for road use should carry ECE R90 approval, printed on the box and usually on the backing plate as a code starting with "E" and a number, followed by "90R". It means the pad was tested against the original equipment and performed within a set margin, roughly 15 percent, of the factory pad's friction. It does not tell you the compound. It does tell you the pad was tested, which is worth more than the word ceramic on the box. Pads without it are either for off-road use or not something I would fit.

The two-letter edge code

On many pads you will find a pair of letters stamped on the edge of the friction block, such as FF or EF. That is the SAE edge code. The first letter describes friction when cold, the second when hot, on a scale that runs roughly from C (low) through D, E, F and G to H (high). An E sits around 0.25 to 0.35 and an F around 0.35 to 0.45. A pad marked FF keeps similar bite cold and hot. One marked EF bites harder once warm.

The code comes from a fairly crude test and two brands with the same letters can still feel different, so I would never choose on it alone. But if the pad you took off was FF and the new one is DE, you will feel the difference in your right foot, and now you know why.

Fitting is half the result

Most complaints about new pads, whatever the compound, come from the job around them rather than the pad. Glazed or lipped discs, seized slider pins, no grease on the contact points, or skipping the bedding-in all cause noise, judder or weak braking that gets blamed on the pad.

Bedding in matters most with a change of compound, because the new pad has to lay down its own thin layer on the disc. The usual approach is a series of moderate stops from around 40 mph down to 10 mph, without stopping fully, then a few miles of gentle driving to let things cool. The pad maker's instructions win if they say something different.

If you are not sure the pads need changing yet, start with when to replace brake pads and when to wait. If you are weighing a branded pad against the dealer one, the notes on OEM versus aftermarket costs and what "genuine" really means on a parts box are worth ten minutes before you order.

Before your next brake job

Next time the car is parked, take a torch and look through the wheel spokes at the old pad. If you can see the edge of the friction block, note the two-letter code, and photograph the box or invoice from the last job if you still have it. Then write one sentence about how you actually use the car: towing, school runs, motorway. Take that sentence and the code to whoever sells you the next set. You will get a better pad than the one that happened to be on offer, and probably cleaner wheels as well.