What is BS4? Why is it a big deal all of a sudden? | Rushlane
New Cars, Bikes, Latest News, Reviews, Photos

What is BS4? Why is it a big deal all of a sudden?

The question I keep asking myself is, did the manufacturers screw over the dealers?


This reminds me of the whole natak of demonetisation, where the idea behind it was pure brilliance but the execution trumped the whole purpose of it. At least that was a surprise attack. But the case of BSIV was not an impromptu call by the government, the norm was announced well around two years ago and the deadline of implementation was also made public around the same time.

As per the rule, the manufacturers made sure that all new models launched after April 2016 were BS4 compliant, which means they had the know-how and time to tweak the existing models too to be BSIV-ready over the next one year if not right then in 2016. But hey, this is India, even if we are a multinational, multi-billion corporation, we do things only in the last minute.

This was supposed to be a seamless transition not even significant of making the news all of a sudden. Over the whole year, one by one, the models could’ve been upgraded and batches of them could’ve been sent to dealerships without waiting for the very last day. Some automakers did do that. But most of them haven’t. We have heard that a lot of dealers are still waiting for the new batch of vehicles, like the ATMs that waited for the new currency, as if the BSIV norm was announced just yesterday.

This was the situation outside majority of two wheeler dealers. They had to shut shop as scores of people thronged into the showroom.


The manufacturers are hardly incapable of carrying this process out.

Who is affected? Just the dealerships, is what we think. When it comes to sales, the dealerships are just like a store where you buy things from. So they purchase the vehicles from the manufacturers, and once they do they can’t return them just like that. So all the discounts that are announced are borne by the dealers because they are trapped, unless their respective manufacturers agreed to cover the difference (which we haven’t heard of to be the case, yet).

This sudden stir has left an impression in the buyers that the leftover BS3 vehicles are inferior to the BS4, something like an overly ripped banana that can’t be sold or won’t be bought. This has pushed the dealers to spread false information about the vehicles. Some of the propaganda we have witnessed are:

The vehicle has already been BS4 compliant, it is just not certified on paper yet.

Only the silencer is different in the new model, there is no other change. We can replace the silencer for you next month.

Only the headlamp switch is removed, we can remove it and give you.

Our vehicle is already BS6 compliant. Only AHO is not there.

Bring your existing vehicle, we will remove the headlamp switch, connect the headlamp directly and make it BS4.

BS4 is just one more layer in exhaust and AHO, nothing else. If you don’t want AHO in the upcoming version we will install a switch for you after delivery.

And the list goes on.

It seems the OEMs haven’t´educated the dealers, the sales guys haven’t checked to know what BS4 really is, and the people are attempted to be distracted by the hefty discounts.

So here is a quick brief of what Bharat Stage 4 really is. To be blunt, it is a regulation for everything that is emitted from a vehicle. The BS3 norm had only few parameters covered, but the BS4 norm has almost all the criteria defined, taking a peek into the Euro 5 emission standards that was introduced by the European Union in September 2009.

If you think only the exhaust gases are considered as emission from a vehicle, you’d be surprised to see the list below. Apart from the exhaust, there is evaporative emission, light emission, heat emission, electromagnetic radiation emission, noise emission, and tyre gas emission, and perhaps a few more.

Evaporative emission:

After a ride, when the vehicle is halted, the fuel in the tank which has become hot, gets vaporised and collected at the top of the tank. BS3 had gotten this covered, with a leakage limit of around 2g per hour (the value may not be accurate). This had to do with the sealing capability of the fuel tank cap. For four wheelers, even the BS3 norm specified that an evaporative emission canister be installed to collect the evaporate vapour. The BS4 norm insists that the same should be implemented on two wheelers too.

The canister is connected to the tank from a hose that draws out the cloud of vapour in the fuel tank. When the pressure builds up, the vapour tries to find or make a creek and escape through the lid to the atmosphere. This is what is directed to the canister. A pole in the canister absorbs this vapour and stores it in a semi-condensed form, ensuring that the vapour pressure doesn’t become high inside the fuel tank.

BS3 norm mandated an escape valve to let the fume buildup to be released, but at a highly controlled rate. BS4 insists on totally arresting this emission and also recycling this fuel vapour. In the event of the canister getting over loaded, there is a release mechanism in it which allows unusually excess vapour build up. But the charcoal canister is supposed to be designed to never allow for such pressure build up.

When the engine is started, the collected vapour is sucked into the intake, thereby making use of the vaporised fuel and clearing the charcoal canister for the next load of vapour when the vehicle is stopped again. There is a solenoid controlled purge valve that controls how much of the vapour is being sent to the engine for utilisation.

Light emission

This defines the minimum and maximum intensity of the various lights used on a vehicle, including the Headlamp – low and high beams, turn indicators, fog lamp, tail lamp, brake light and reverse lamp.

Heat emission

There are regulations for the various heat sources in a vehicle, like the lights, engine and exhaust.

Electromagnetic radiation emission

The various electrical and electronics used in a vehicle emit EMR (Electro-Magnetic Radiation) that is harmful to the human body. Such a radiation is emitted by the alternator/magneto coil, certain sensors in the vehicle and some infotainment devices such as a wireless modem for internet.

Noise emission

Noise is not emitted only by the exhaust system. Noise is emitted from various other sources in a vehicle, such as form the mating parts in the engine, gearbox, horn and even tyre. The BS3 and BS4 norms set limits to the overall noise in different kinds like idle noise and pass by noise. So it is not the case that just the exhaust team works on reducing the noise emitted from the vehicle, almost every component that causes noise has to be optimised to reduce the overall noise emission.

While in case of light emission where the component suppliers and automakers work together in making the part compliant to the standards, some parts like the tyres have a different scenario around them. The homologation for tyres have to be pursued by the tyre manufacturers themselves, without working with the automakers. So the vehicle manufacturers demand lower tyre noise, as they can’t always achieve the noise limit by tuning just the exhaust. This is where RRC (Rolling Resistance Co-efficient) comes into picture. If I’m not wrong, the BS4 standards also mandate lower RRC, like 7.6-7.8, when the previous value was around 12.4.

Lower RRC can be achieved in different ways. If the tyre maker decades to take the easy route, the tyre can just be made harder, which will result in lesser grip and lower mileage of the vehicle. But the advantage would be longer tyre life. Taking the harder route, the tyre will have to be lighter, and formulated with a significant difference to the compound, which is not easy to achieve without compromising on the tyre life. Tyre engineering is the most challenging subject in the field of automobiles. It is an ocean that can’t be swam across.

Tyre gas emission

When tyre gets worn out, kilometre after kilometre, harmful gases are released into the atmosphere. This is another challenge for the manufacturers to be kept in control.

All of the above are regulated differently to different categories of vehicles.

What’s most important in the BS4 norm is the stricter limit of exhaust gas emission, vehicle noise emission and evaporative emission. In detail, BS4 demands lower release of air pollutants (oxides of nitrogen (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matters (PM)), lower decibel levels of idle and pass by noise, and lower release of fuel vapour into the atmosphere. BS3 did set an upper limit for fuel vapour leak, but BS4 demands the EVAP canister be installed for almost nil leak. So it’s not just about the extra layer of coating of palladium and platinum (and the like) on the catalytic converter, and the larger volume of the same, it is about so many other kinds of emission. Ans please be advised, some manufacturers may resort to mildly detuning the engine performance, to reduce the exhaust output and noise.

All this control makes for a much better vehicle in terms of being friendly to the environment.

There is another subject in the BS norms which is the OBD (On-Board Diagnostics) feature. BS3 mandated OBD version 1 and BS4 listed upgrades for OBD 2. The next update of Bharat Stage will talk about the next version of OBD. It is a gateway through which service centres and customers can read the information from ECU (Engine Control Unit) using certain devices. Bharat Stage dictates what are the information that should be made available for customers through the OBD port, and subsequent versions will reveal more information about the car, like the real-time fuel efficiency, various temperatures and emission related data.

Also, AHO has nothing to do with Bharat Stage norms. The confusion arose from the fact that the two were implemented simultaneously.

Then next BS norm is expected to be similar to the Euro 6 norm, and is expected to be termed as BS6 due to its similarity of regulations to the Euro 6. It would enforce a tighter leash on the manufacturers on all the parameters briefed above. For instance, BS3 has pass by noise limit of around 80-82 db, and BS4 has 76-78 db; BS6 might have 74-76 db (the values may not be accurate). And these figures vary for each category of vehicles like CV, passenger cars and two wheelers.