Exhaust Mods. Worthy or Not?

India being the largest two wheeler market has an immense potential for customisation and modifications. As far as two wheeler's are concerned the most common modification is the switch to an aftermarket free flow exhaust/slip on. The most important point to be made here is that 99% of all the exhaust mods available are not legal. As there are norms to regulate the noise and emission level of any motorcycle/scooter, the noise should not exceed 85 dB and the vehicle should conform to BS IV standards. But until recently the RTO and Traffic Police have been showing a blind eye to the same but there has been a recent crackdown in Bangalore, Karnataka on the most popular bike manufacturer raking the highest number of exhaust mods, it is none other than our very own Royal Enfield. Click on the link to read more about this.

Most of the exhaust mods are meant only for off-road use and are not road worthy, but many users do not realise the same. There is no doubt that Royal Enfield tops the list on exhaust mods, especially because the newer bikes do not come with the same thump which the older Enfield's have but apart from the mods being illegal is it really worth to change the exhaust?

It is not surprising that most after market exhaust manufacturers have extra ordinary claims like a 20% increase in performance. To be very fair most of the exhaust systems rarely increase the engine output by such a huge margin. Like everything the engine is a system and barely modifying one component only puts more strain on the other components rather than being productive. So in our opinion for you to really benefit from the exhaust change you would need to change the intake system, valve timing, valve openings, ecu remap etc. But this would surely burn a hole in your pocket, instead one can opt for a better performing stock motorcycle.

On top of all this there is a lot to be considered while designing an exhaust system, one important factor is backpressure from the exhaust. Although a lot is done to reduce the exhaust back pressure as much as possible the pipe diameter, exhaust length is linked to the valve timing/overlap, valve opening etc. Once an exhaust mod is done this tuning is disrupted resulting in greater losses which allows the fresh charge (air-fuel mixture) to be expelled from engine without getting burnt. This results in a spectacular looking after burn from exhaust in some cases as shown below.

Exhaust flame from Royal Enfield Electra with Short Bottle Exhaust

Although this looks spectacular it is burning off the unused fuel resulting in a loss in economy. Another downside to this is it increases the exhaust temperature which can result in engine damage by warping the exhaust valves which would reduce compression. This can also cause mis-fire because the exhaust valve might ignite the charge before the ignition time. It also reduces fuel economy. To avoid this the mixture needs to be made richer, which is easier on a carbed motorcycle but for EFI bikes it would require a remap or piggyback ECU.

Overheated Bend Pipe of a Motorcycle.

The effects of an exhaust mod is different on various bikes. For example enfield's have low compression and lower rpm's which ensures the engine is not damaged to the extent a high revving short stroke engine such as KTM Duke 390. However engine damage is inevitable with exhaust mods. One needs to understand that motorcycle manufacturers spend a great deal of time and money testing the engine and combinations of exhaust systems, hence if someone claims a miraculous increase its generally not the case.

What if i have improved power as well as FE? An exhaust mod generally changes the power band of an vehicle. This could improve driveability based on the exhaust design like a short bottle silencer would result in a loss of a low end torque which is better in case of a long bottle silencer. So if you are driving in a city a long bottle silencer would be better. Fuel economy may be marginally better but that is because of your driving style and probably because your engine is still pristine but mostly it results in an FE drop unless its perfectly tuned and the newer layout suits your driving style.

To conclude the discussion an exhaust mod is definitely not worth it unless your need is justified (racing/off-roading). There are ample choices but most of the cheaper exhausts are poorly designed and generally affect the engine. More expensive options may cost around 30-35k but however they don't justify their price and as said earlier it would make more sense to invest the money in a better performing bike. Also because most of the exhaust mods remove the catalytic converter it results in more emissions, add to that its illegal and it really doesn't make sense.

Cruiser, Sport, Street and Dual Sport - The Difference Explained

The Indian biking scene has seen a lot of huge changes over the past few years with a lot of manufacturer's stepping into the Indian motorcycle market. Also the choice for a customer has now drastically increased especially those looking for >1 lakh category of motorcycles and so has the confusion. Hopefully you would be a lot more clearer after reading this article.

Let's start with categorising some of the well known bikes into different categories -

Cruiser - Bajaj Avenger, Royal Enfield Thunderbird, Hyosung GV250

Sport - Yamaha R15, KTM RC 390 , Kawasaki Ninja 300

Street - KTM Duke 200, Yamaha FZS, Suzuki Gixxer

Dual Sport - Bajaj Pulsar AS 200, Triumph Tiger 800XCx

So this should help visualise the different categories of bikes. A lot of people buy bikes based on the popular bikes which are hot selling in the market giving little thought to whether that would suffice their particular use. It needs to be understood that every particular bike is built with a purpose in mind and a lot of factors are taken into consideration is given to the class of the motorcycle. But in India it is common to see bikes being used for totally different purposes. The best example for this would be the use of Yamaha R15 as a touring bike.

A Yamaha R15 in Ladakh.

It is not wrong to use a bike for multiple purposes but a bike which has been built for street/track would not perform well in rough terrains and off-road conditions. There are lot of things to consider let us take them one by one.

1) Motorcycle Ergonomics - Motorcycle Ergonomics has got to be the most ignored thing while deciding on which bike to buy atleast in India although on the contrary it is one of the most important factors to be considered. Let us take 4 bikes belonging to different segments in order to compare.

 

Ref: http://cycle-ergo.com/

The above 4 bikes belong to different classes and there is a huge difference in their seating positions and postures. If we see in the cruiser segment we have the thunderbird it has a very comfortable seating position designed for longer trips rather than sharp maneuvers. The seat height is low at just 30 inches and foot pegs are placed forward allowing for a comfortable seating position and the position is upright which helps in reducing fatigue over long distances. The purpose of this bikes is to cruise comfortable on long straights.

If we have a look at the R15 it is exactly opposite of the Thunderbird the seating position is low and the foot pegs are swept backwards and the rider leans over the front handle bars. This forward crouched position is needed for track riding as it increases maneuverability of the bike but it can be a pain for long rides as the seating position causes back, neck and wrist pain.

The KTM on the other hand is meant for short rides in and out of city it has an almost upright position it also has back swept foot pegs the seating and handle bars are both positioned relatively higher which allows fast direction changes. It is good for normal city use where maneuvering a cruiser or sport bike would be relatively tough.

The dual sport bikes are almost new to India market and they are basically bikes which can be used for touring and in both tarmaced surface and on dirt as well. They have much higher seating positions and the handlebar is kept higher with respect to the seat to help the rider reach easily even whilst standing on the foot pegs again the seating is almost vertical. The foot pegs are almost exactly below the rider's seat allowing the rider to stand upon them for steering.

So this said even in a particular class a bike need not suit your proportions. R15 is more suited to people with short and medium heights and Ninja 300 is more suited for medium and tall people. You can visit the above link and verify the ergonomics of the particular bike by giving your height as input.

2) Motorcyle Dynamics - Motorcycle dynamics refers to the geometry of the motorcycle and more specifically its steering and suspension components. One of the most important factor which decides the steering effort and agility of the bikes is the rake angle of the motorcycle. 

It is the angle of the steering axis from the vertical and it can be observed as the inclination of the front forks in most motorcycles. As the angle increases the bike becomes more stable in the straight line and the steering effort increases while lower the angle the greater the agility of the bike and also the maneuverability increases. In case of cruisers generally the rake angle is quite high as they are more oriented towards straight line driving than cornering. It is the least for sport and street bikes while the dual sport bikes rate in between.

The next most important system would be the suspension of the motorcycle. There are a lot of different suspension systems like upside down forks for front suspension and monoshock for the rear suspension but honestly they dont make all that much of a difference. What really makes the difference is the stiffness of the suspension and travel which the suspension provides. Let us talk about the front forks first. Most of the track/street bikes have very less travel to offer as a stiff suspension would help them in better handling than a soft suspension but this can be a pain on long rides as this might increase the vibrations and cause fatigue to the rider. However the suspension is generally soft and has good travel on both the cruiser and dual sport bikes but this makes them harder to handle as well. In the rear the primary advantage of monoshock is that it gives very good wheel travel and most of the modern bikes are equipped with monoshocks and very few bikes have very stiff setup in the rear as it directly affects the rider comfort. KTM Duke has a very stiff suspension setup which is a big turn off while doing longer trips. Another big advantage is that most of the bikes have adjustable pre-load which also affects the suspension stiffness.

Pre-Load Adjustment on Rear Suspension

For track riding generally the preload is kept at the highest position with maximum compression of the spring for road use its best to keep preload on the lowest possible setting. as shown in the picture above.

3) Engine Power & Characteristics - The engine power is the last thing which matter while selecting a right motorcycle. It is always better to have more power but the downside is that higher displacement motorcycles generally cost more and also the mileage is lower. However for the Indian road conditions there is any use for motorcycles >250cc exceptions being the enfields as they have comparatively lesser out put for displacement.

While most people look at engine power they dont consider the driveability and characteristics of the engine. If you have a highly peaked power band which would deliver the peak power at 9000-10000 rpm your motorcycle would be extremely sluggish at the mid range which would be mostly used. A peaked power and torque band is again only useful in the track and not on road so most sport bikes tend to have such characteristics. Also it has to be remembered that faster revving engines develop more problems and give lesser efficiency than lower revving engines. So for cruisers it would be preferable to have an engine which produces torque at lower rpm Enfields are good for this to put it in perspective an Enfield 350cc does 80kmph at 3100 rpm in 5th gear while a CBR 250r does that at 5000 rpm in 6th gear. For street bikes a peppy fast revving engine would greatly increase the driveability suitably with a flat torque curve,

Hopfully this article has highlighted the important factors of choosing the right bike for the right purpose and why its important. Also there are some bikes which fall into both the categories like CBR 250r comes under a category called Sports Tourer which ensures its seating position is not too agressive and it can be used for touring as well and even the suspension is setup relatively soft. Whatever the bike you choose be certain about the riding style you want and decide based on where the bike would mostly be used.