Britain’s roads are no place for the under-braked. Every year, there are more cars, vans and trucks, travelling faster and less inclined to be tolerant of farm vehicles. Tractors are getting faster, too, with most now equipped with a 40kph (25mph) gearbox and quite a few that will travel at 50kph (31mph).

Trailers with a gross weight of 18t are the norm and trailed equipment like balers, slurry tankers and sprayers are getting bigger.

So it doesn’t take an Einstein or a Newton to work out that having good brakes is very, very important. Yet how many farmers can be truly confident that their tractors and trailers are capable of stopping quickly and without drama?

Awareness of the need to upgrade is growing, according to Mike Erentraut, who has worked with agricultural and truck-braking systems for 40 years. His company Erentek has designed hydraulic and air-braking systems for hundreds of farmers, truckers and machinery makers and also designs air suspension systems.

“Farmers want to know if they can put air brakes on, whether a load-sensing valve would help or whether they can fit ABS braking to their trailers,” he says. Farmers are confident about dealing with hydraulic brake systems, he adds, but pneumatic brakes aren’t something that they’ve grown up with or really understand.

Of course, the simplest way to make sure you have tip-top brakes is to buy a new tractor with an air compressor plus a trailer with high-speed axles (ie with wheel bearings designed to run at high speeds) and pneumatic brakes.

But what if you want to improve the braking performance of an existing tractor and trailer without writing out a big cheque? We asked Mr Erentraut to lay out the options.

What does the law say about trailer brakes on the road?

This is a complex area but here is the gist of it:

• If you stay below 32kph (20mph), ag-spec trailers with standard single-line hydraulic brakes are fine, though they need to be maintained properly (which many aren’t).
• But the moment you go above 32kph, you come under pretty much the same set of rules as an HGV. So you should have two-line pneumatic brakes with a failsafe system, high-speed axles, springs and the correct lights.
• If travelling faster than 32kph (20mph) with a trailer manufactured after 1 May 2002, you should technically have ABS brakes.
• You should have a system that automatically applies the brakes if the tractor and trailer become separated.
• Agricultural trailed appliances (eg, slurry tankers, muckspreaders, balers, trailed sprayers) technically don’t have to have any brakes unless their maximum gross weight is more than twice the unladen weight or if the maximum gross weight is more than 14,230kg, in which case they are categorised as trailers.

So all those tractors running around the roads at 40kph with hydraulically-braked trailers are technically breaking the law?

Well, yes. To be fair to trailer makers, a lot of older trailers were never really designed for lots of road use. The axles are too small and the brake drums and shoes too skinny to stop a heavy load at 40kph quickly. And many farmers genuinely don’t realise they’re technically breaking the law.

But the tractor does most of the braking surely, so why does it matter?

Decent braking involves both tractor and trailer doing their bit. If your trailer brakes are poor, the tractor will have to do all the work and its brakes will wear out frighteningly fast. There’s a growing issue of farmers taking tractors back to the dealer because the brakes aren’t working properly and asking for the work to be done under warranty. Tractor manufacturers are less and less inclined to accept this if they think the wear has come from underperforming trailer brakes.

Equally, says Mr Erentraut, it could be that a well-braked trailer is having to do extra work because the tractor brakes are worn.

What about implements – do they need brakes?

This wasn’t so much of a factor in the past, he says, but as trailed kit gets bigger, the need for brakes increases. Big square balers and trailed sprayers usually come with hydraulic brakes as standard, but it may be worth upgrading those to air-brakes. Some big cultivators and sets of discs can weigh up to 15t, so you need to check they have brakes at the time of purchase. Failure to observe this will inevitably damage tractor brakes.

I don’t want to go to the expense of fitting pneumatic brakes, but are there ways of making my existing hydraulic brakes safer and more effective?

You could fit larger hydraulic brake pipes If you have an older trailer with quarter-inch pipes, they may simply not be allowing the return of oil fast enough. Consider replacing them with bigger 3.8in pipes, though bear in mind that if the brake drums and shoes are worn out/hopelessly corroded/too small it may not make any difference.

You could fit a hydraulic load-sensing valve Unlike car brakes, which are progressive (ie the harder you push the pedal, the more effect it has) tractor hydraulic brakes tend to work in an all-or-nothing fashion. One result of that is wheel lock-up with empty trailers. You push the brake, the wheels lock and then simply skid along.

Too much of that and you’ll have tyre flats – flat areas in the rubber that means the tyres are noisier and run unevenly, which will damage suspension and wheel bearings.

Load-sensing valves can be fitted to any trailer with springs. They measure roughly how much weight is in the trailer by gauging how compressed the springs are. Then they adjust the oil flow accordingly.

So instead of giving 120bar of oil pressure irrespective of whether the trailer is empty or full, they will allow, say, the full 120bar when it’s full and just 70bar when it’s empty.

It’s a simple, mechanical system that’s easy to fit and costs about £250. It also helps prevent an unloaded trailer “stepping out” (ie trying to move sideways) when you brake.

You could fit a failsafe system If the tractor-trailer coupling fails (typically caused by the trailer eye jumping off a worn tractor hook) you have a potential catastrophe on your hands. If the hydraulic pipe is a non push-fit sort, the departing trailer will probably wreck the tractor spool valve before heading off and could hit another road user.

A simple way to limit the potential damage, points out Mr Erentraut, is to fit a hydraulic failsafe system. One non-electric (and reusable) system that costs around £250 system consists of a valve block on the front of the trailer connected by a cable to the back of the tractor, plus a hydraulic accumulator underneath the trailer.

If tractor and trailer part company, the cable tightens and then pulls a pin out of the valve block. With the shaft rotated and the pin out, this prompts the valve to open the accumulator, pressurising the brake circuit and bringing the trailer to a smart stop.

You could do a bit of maintenance Despite their importance, most trailers don’t get a lot of attention. Mr Erentraut says they should be serviced every six or even three months. Brake shoe and drum wear should be checked, pins greased (but not over-greased) and the ram travel adjusted correctly: 30-40mm of ram travel is about right.

I’m thinking about upgrading to air brakes. Why are they better than hydraulic brakes?

Two reasons:

• If you have a hydraulic leak and lose fluid, you have no brakes. If you have an air leak, the compressor will replace the loss
• A two-line failsafe air system will apply the brakes automatically if there’s a loss of pneumatic pressure from the emergency line (red).

So what are my options?

• You could buy a new trailer.
• You could get the maker of your existing trailer to upgrade it or ask your tractor dealer if it can retro-fit air brakes.
• You could do it yourself. Suppliers like Erentek provide a full set of components, plus brackets and Airfix-model style system drawings that show exactly what goes where.

Can I fit air brakes to older trailers?

An old trailer with ag-spec axles, no springs and small (typically 300mm diameter x 90mm width) brake drums would need to be upgraded first to bigger-diameter, high-speed axles and 420mm x 180mm brakes. But there’s no point in fitting air brakes to trailers that have seen better days, says Mr Erentraut.

What about newer models?

This shouldn’t be a problem and Mr Erentraut says it’s an increasingly popular option. You can buy a kit for DIY conversion of a two-axle trailer for about £620 that includes components, brackets and drawings. The job takes about a day.

Or, if you don’t fancy doing it yourself, your local tractor dealer or sprayer maker may well be able to do the job

Also available from some suppliers is a combined hydraulic/pneumatic brake system that can be hooked up to tractors with both pneumatic and hydraulic brake systems.

Can you fit your own compressor to the tractor, too?

Yes, DIY kits for most models are available. Mr Erentraut says that some tractors have so little spare space under the bonnet that the compressor has to poke 100-120mm (4-5in) proud of the side of the bonnet. But you can get a painted grille that fits over it and neatens things up. Price is about £1375 plus fitting and the job takes about two days.

Is it true that you can fit ABS to farm trailers?

Technically, any trailer built after 1 May 2002 and travelling on the road at more than 32kph should have ABS brakes. A pneumatic ABS kit for DIY fitting costs about £1250. But you would require ABS-compatible axles (about £600) or a sensor package (about £150).

It will stop the brakes locking and prevent flat patches on tyres developing from skids, so tends to be used by those doing large amounts of road-work. You still need to have load sensing, though. If you are buying an ABS system, make sure it’s a 12v ag system rather than a 24v HGV one.

Do air brakes take much looking after?

They do need regular maintenance, but it’s nothing too complicated, says Mr Erentraut. Shunt valves need using once a week, water needs draining from the system daily and laden and unladen pressures need to be measured during regular maintenance checks.

Which air coil should be uncoupled first, the red or the yellow?

It’s critical that the red is disconnected first and reconnected last, otherwise an already-applied handbrake can be deactivated and the tractor and trailer start to roll.

Farmers generally have low levels of knowledge about pneumatic brake technology, so it’s worth finding a firm that specialises in tractor and trailer braking systems to assist in any modifications.

Erentek, for instance, has produced a driver/owner handbook that explains the different components involved, how you operate an air-brake system and what maintenance is needed.