[Jupizire]

THE PROBLEM:
The bikers in India face many problems – like bad road conditions, drenching in rain, risk of getting hit by other vehicles, having to tolerate air pollution etc. Much has been written about these common problems. But I would like to highlight a unique challenge faced by bikers today – increased risk of directly inhaling bike exhaust gas due to badly designed silencer / muffler.
We end up riding bumper to bumper in cities due to congestion. It’s very common for 1 bike to be riding directly behind another. Similarly at a signal, a bike mostly would be directly behind another bike.



Image Credit 1

Image Credit 2

Now a days, most of the bikes have their silencer angling upward, may be to increase the design appeal of the bike. But what this does is that the exhaust gas is pumped upward in the air, as shown by the 2 green dotted lines below.



More often than not, this would gush the exhaust gas directly onto the face of the biker behind him, leading to his suffocation and eventually health problems. Feels very suffocating, like in this tractor exhaust inhalation scene from Dabangg


(Or watch on youtube -- start @ 2:00:42 & watch only for next 15-20 seconds)



I have myself faced this issue many times, and was wondering why bike makers are not conscious of this peril! Hence writing this post.

THE SOLUTION:
I got into analyzing the exhaust angle of a few bikes, in fact all the bikes from the Honda stable. Found an online protractor tool to check the angle of exhaust using which I checked the angle manually for all the Honda bikes. Couple of samples are shown below:

1. Honda SP-160 –> has an angle of exhaust of 154 degrees.



Check the blue line marked on the silencer. Protractor shows the angle of exhaust as 154 deg (from origin, measured in anti-clockwise direction, which is the right way to measure an angle). But for the sake of this post, I would prefer to use smaller numbers which are more intuitive. Hence, I will do 180 deg minus the angle (154 deg) to get it as 26 deg. It actually represents by how much angle the silencer exhaust hole (not the entire silencer in itself, but the projected pipe/hole at the end) is tilted upwards (in clockwise direction).

Zoomed-in view for easier understanding of the angle measurement:


A few more examples:

2. Honda CB 200x –> has an angle of exhaust of 32 deg.


3. Honda Shine 125 -> has the angle of exhaust of 8 deg.


4. Honda Activa 125 -> has the angle of exhaust of (-15 deg). It’s pointing downwards by 15 degrees.


The full list of Honda bikes along with their angle of exhaust is shown below. Let me know if anyone needs the measurement images, and I can share.


So what is the maximum angle of exhaust that should be allowed so that it doesn’t affect fellow bikers on the road? We can find it through simple trigonometry and a few assumptions.




The length (x) depends on the 2 bikes and how distant the rider of backside bike is from the silencer exhaust of the frontside bike.

The length (y) depends on the bike height, rider height, silencer height of the vehicle ahead and road elevation (in case of riding/standing at an incline).

I did some measurements by keeping 2 bikes one behind the other and deployed a rider with a height of 5’ 6”. The measurements I got were:
x = 80 inch
y = 35 inch

So,


This gives the angle as 23.6 deg, which is approximately 24 deg.
Which means, any bike that has a higher angle of exhaust than 24 degrees is likely to cause direct pollution trouble to fellow bikers. For this sole reason, I love the exhaust angles of Royal Enfield Bullet, Yamaha RX 100 (though it’s a different issue that the 2 stroke RS causes more air pollution!) and other such bikes with an absolutely horizontal silencer. Better, the scooter type of vehicles (Activa, Jupiter etc.) have negative angles of exhaust as the silencer let-out pipe at the end is bent downwards.

Applying the above threshold to Honda bikes, we can see which models cross the limit and hence are more damage causing to other bikers on the road.



THE ENFORCEMENT
How to persuade the auto makers to adopt a certain maximum angle of exhaust, which in no way alters the bike’s attractiveness-quotient? The silencer can still be in any direction – fully horizontal like in a RE Bullet to fully vertical like in a tractor if they want . But the small projected pipe at the end of silencer (shown in red circle in the image below) should not exceed the threshold for the betterment of humanity on road.



I feel the influential forums and communities like Team-BHP can put in a word to the auto companies. And they can also recommend to SIAM to enforce this as a rule that all 2-weheeler companies must adhere to. Thus we can bring about a positive change in the society. Else, we run the risk of status-quo, which usually only worsens over time and increases the health issues owing to the direct-inhalation of polluted air.

Comments and reactions are welcome.

[deep_bang]

This is definitely a problem in the metros where jams are common and two wheelers are very close to each other. I have faced this many times and realise that the sportier bikes have this issue more than the normal commuter two wheelers - which is kind of the summary of your table too.

I am wholeheartedly in for a regulation to not-direct the flow towards the vehicle at the back.

Well, I cannot help but wonder if this will automatically get solved with EVs. But the fact is there is not a single EV in the sports bike segment as of today - so I think there is still value in fixing this problem now for the next decade or so.

[am1m]

Originally Posted by Jupizire

For this sole reason, I love the exhaust angles of Royal Enfield Bullet, Yamaha RX 100 (though it’s a different issue that the 2 stroke RS causes more air pollution!)

I think this is the pertinent point. I'd be more worried about the age of the bike and how well-maintained it is rather than the angle of exhaust because that will have a greater bearing on the degree of pollution. I think I'd rather be stuck behind a BS-VI compliant bike with up-swept exhaust than an old or badly-maintained bike with a straight exhaust.

I've experienced the direct puff of exhaust while behind bikes with up-swept exhaust pipes, and yes it's very irritating! (Especially since more often than not the idiot on the 'racer' bike needs to keep revving to show how 'MotoGP' he is...in Bangalore 6kmph average speed crawl traffic!) But from a 'pollution inhaled' point of view, does it make much difference? Even from a straight exhaust, the exhaust gases are going to expand and spread in all directions and you can't escape them. So am not sure how much of a difference this makes.

(Not to mention the number of diesel cabs, cars, and buses that will be in the same traffic jam and causing bikers to inhale considerably more pollution!)

[tharian]

In my opinion, if you are behind a motorcycle with an upswept exhaust with the gases pointed at your face or close by, shut the visor of the helmet. Of course you need a full face helmet which is also safer.

On the other hand, with so much pollution around when in traffic and the bs6 or even bs4 bikes with their cat-convertors, the exhaust will hardly reach you especially from a sub 300cc bike. Gone are the days when you are sure to get a punch on your face from a Bullet's exhaust when behind it.

This is how I got a free flow muffler designed for my old Bullet 500. If it was facing up, it was sure to cause issues on the road.

[V0rtex]

A few months ago, I was waiting in traffic and saw a ZX-10R. It had a stock exhaust with the catalytic converter removed (I could tell because the bike was running quite loud with the stock pipes). Since it was quite hot outside, I decided to lift my visor but couldn't bear the foul smell of the exhaust gas coming from the bike, which was several feet in front of me.

[Rehaan]

Fantastic research, data & presentation!

Loved the Dabangg reference.


However, I think there might be one small issue that is being overlooked: Which is that we are dealing with gasses, and hence the mystical world of fluid-dynamics.

Ever ridden behind a Bullet and you suddenly feel that sudden thump of air on your face? That's despite their exhausts being horizontal:


Expelling exhaust isn't quite like shooting a shell out of a canon - where it follows the angle of the pipe:

img source

I guess it's more like breathing, where as soon as the air leaves your mouth-pipe it begins to expand, slow down and swirl around:

img source

I guess this would be more-so the case at idle due to the lower exit velocity of exhaust gas; which would be the situation in your 'stuck in traffic' scenario.


Now I'm not at all saying that an exhaust pipe pointing straight at your face from a distance of 4 feet away on a 42-degree day in the midst of May isn't adding to the problem. But perhaps just saying it's not so much of an issue that most manufacturers would take note.


On the flip side...

Exhibit A:


Exhibit B:

img source

[hikozaru]

Originally Posted by Rehaan

Ever ridden behind a Bullet and you suddenly feel that sudden thump of air on your face? That's despite their exhausts being horizontal:

Expelling exhaust isn't quite like shooting a shell out of a canon - where it follows the angle of the pipe:

Gets PTSD of being stuck behind a 411 two days ago. It is not at all like a japanese firebreather which is polite. What feels like mechanical heartbeat to the rider, to a person behind the exhaust it feels like a semiautomatic gun where each shot was clicked with deliberation and making peace with the fact that it reaps death with each click. Truly living up to their tag line of made like a gun.

[saket77]

We are overlooking the fact that even with some 'swept-up' designs, the actual opening of the exhaust muffler is facing downwards or not at the expected angle which can solve this issue without altering the looks of such designs. Also, the method by which the angles of exhaust you have measured can be misleading for such designs.

Eg. check this image:





But yes, this is a problem for 2 wheeler commuters.
I have faced most issues when I was behind any RE.

[Jupizire]

Originally Posted by Rehaan

Fantastic research, data & presentation!
Loved the Dabangg reference.

Thanks @Rehaan. Glad you liked it. And thanks for converting the relevant portion of the video to GIF.

Yes, gas disperses faster compared to other forms. There is always passive inhalation of the pollution already present in the air. I was just trying to focus on better silencer design to reduce active, direct inhalation.

Originally Posted by saket77

We are overlooking the fact that even with some 'swept-up' designs, the actual opening of the exhaust muffler is facing downwards or not at the expected angle which can solve this issue without altering the looks of such designs. Also, the method by which the angles of exhaust you have measured can be misleading for such designs.

Hi Saket - I am actually measuring the angle of the actual opening of the exhaust. And that's what I have mentioned in my post as well.
Another proof is - Activa has a swept up design, but the angle quoted is -15 deg., which is the angle of of the tail end pipe/hole. Another example is that of Africa Twin which again has swept up design, but the angle is quite low at 7 deg.

[kiranknair]

Hot air rises up. Changing the position of the exhaust pipe would not help. Even if we keep the exhaust pipe parallel, the fumes from the bikes in front (not necessarily the immediate front) would finally find a way into the nose.

[srini1785]

I don't know if you can find a solution to this problem using trigonometric functions. Its oversimplifying a lot of things. Two things come to my mind.

1. Will this work for TVS50 as well.
2. Are angled exhausts just cosmetics or do they serve a purpose.

Having said that I must confess I have been rendered breathless when a bullet goes in front of me even with a normal exhaust. It has something to do with the internal construction of an exhaust (which is assume members know) and less to do with angle. For example what is the velocity of the exhaust gases and their pressure?.

[jagdish_ker]

I happened to be behind a Continental GT 650 at a traffic signal. I am not being rude. The genius riding it was cranking it for no reason. It was like pulsating strong jets which I could feel in my eyes (the helmet visor was open). I wondered how these bikes and riders are even allowed on the road.

[doga]

Upswept exhausts allow them to be longer without protruding too much behind the bike. The length and width of the exhaust decides the final escape velocity and temperature of the gases thereby affecting back pressure. On high performance machines this has significant bearing on the low rpm grunt.
However, given the amount of polluted air majority of Indians breath in even sitting at home, an upswept exhaust shouldnt result in a significant reduction from the overall life expectancy!

Btw The gen1 dukes should be your favourite bikes op then. Now each time someone says its a chhapri machine I can counter saying this doesnt pump in carbon down your throat

[DustyWanderer]

The Bajaj Pulsar NS and AS series have underbelly exhausts, and I myself own a Pulsar AS 200. I hope more manufacturers come up with this concept.

[Joe367]

Originally Posted by deep_bang

Well, I cannot help but wonder if this will automatically get solved with EVs. But the fact is there is not a single EV in the sports bike segment as of today - so I think there is still value in fixing this problem now for the next decade or so.

Correct me if I'm wrong, Can't ultraviolet f77 be considered a sports bike? We defenitly need electric bikes, even if it won't save the world or anything, it can reduce pollution in cities. I wonder why we haven't got any entry level bikes when there are a lot of electric scooters available already.