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Old 21st October 2013, 11:21   #1
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Question Fuel Efficiency: Cars vs Bikes

This may sound like a layman question to some, but would be good to have a clarification .... figure this out:

I have a 2005 Swift (P) and a 2010 Honda Activa. If I take the real world average figures, my swift gives me 14 kmpl and Activa gives me 40 kmpl. A rough comparison of the technical specifications is as under:

Engine Displacement:
Activa: 100 cc, Swift: 1300 CC (13 times)

Power:
Activa: 8 bhp, Swift: 87 bhp (11 times)

Weight:
Active: 100 kg, Swift: 1000 kg (10 times)

Torque:
Activa: 8 Nm, Swift: 114 Nm (14 times)


The question is, if everything in Activa is on an average 12 times lesser than the Swift, why is Activa only 3 times more fuel efficient? I have only given an example above. My query is generalized between a two wheeler & a four wheeler. Good to have a debate..


* Mods, please trash this thread immediately if this is discussed before!

Last edited by akash_m : 21st October 2013 at 11:23.
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Old 21st October 2013, 11:28   #2
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Originally Posted by akash_m View Post
This may sound like a layman question to some, but would be good to have a clarification .... figure this out: I have a 2005 Swift (P) and a 2010 Honda Activa. If I take the real world average figures, my swift gives me 14 kmpl and Activa gives me 40 kmpl. A rough comparison of the technical specifications is as under: Engine Displacement: Activa: 100 cc, Swift: 1300 CC (13 times) Power: Activa: 8 bhp, Swift: 87 bhp (11 times) Weight: Active: 100 kg, Swift: 1000 kg (10 times) Torque: Activa: 8 Nm, Swift: 114 Nm (14 times) The question is, if everything in Activa is on an average 12 times lesser than the Swift, why is Activa only 3 times more fuel efficient? I have only given an example above. My query is generalized between a two wheeler & a four wheeler. Good to have a debate.. * Mods, please trash this thread immediately id this is discussed before!
Your question gives you the answer. Low power and low weight does not necessarily mean good fuel figures. A good amount of power and torque to freely chug the engine without causing much stress would translate good fuel figures. Another thing to note is that the Activa is an automatic whereas other bikes with gear similar power would deliver more mileage.
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Old 21st October 2013, 11:31   #3
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Default re: Fuel Efficiency: Cars vs Bikes

On a lighter vein look at this comparo.

A swift can carry 5 people 40kms on a little less than 3 lits of petrol - which is INR225

that makes it Rs.45 per head for the distance in airconditioned comfort

An Activa can take 2 people the same distance on a liter of petrol=INR 40 per head in desi comfort.

Take a more fuel efficient car like,the Beat diesel or the Altis Diesel and the Activa will be more expensive to run :-)
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Old 21st October 2013, 11:54   #4
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Default re: Fuel Efficiency: Cars vs Bikes

Everything might be 12 times greater on the Swift, but you do want to travel at the same speed at the Swift right?

Has to be a tradeoff somewhere.

PS: I'm in no way implying that travelling at one twelfth of the speed of a Swift will net you the same mileage.
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Old 21st October 2013, 12:16   #5
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Originally Posted by akash_m View Post
This may sound like a layman question to some, but would be good to have a clarification .... figure this out:

I have a 2005 Swift (P) and a 2010 Honda Activa. If I take the real world average figures, my swift gives me 14 kmpl and Activa gives me 40 kmpl.
Hello folks,
Now if we diverge the discussion a bit from only fuel efficiency and take time saving as a parameter too then the two Wheeler makes so much more sense. For example, I use an alto and I go for classes at a distance of about 6km from my place, that's 12km to and fro and I waste around an hour in travelling just that much in any normal busy day. Now my uncle rides an aviator to work and travels a similar distance to a near by place as I do using roughly the same route and he does it in about 20 minutes, that's saving more than half an hour daily. Take 6 days in a week and he saves almost 3 hours hours!
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Old 21st October 2013, 12:17   #6
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Quote:
Originally Posted by akash_m View Post
I have a 2005 Swift (P) and a 2010 Honda Activa. If I take the real world average figures, my swift gives me 14 kmpl and Activa gives me 40 kmpl.

The question is, if everything in Activa is on an average 12 times lesser than the Swift, why is Activa only 3 times more fuel efficient? I have only given an example above. My query is generalized between a two wheeler & a four wheeler. Good to have a debate..
Not fair to compare an automatic and a manual transmission.

In such comparison both the variables musty be same for easy understanding and discussion.

Power to weight ratio plays a major role in stress-free driving. The torque produced also influences. Weight on the vehicle too.

Swift P : 14 kmpl
Spelndor: 60-65 kmpl.


Engine Displacement:
Splendor: 100 cc, Swift: 1300 CC

Power:
Splendour: 10 bhp, Swift: 87 bhp

Weight:
Splendor: 100 kg, Swift: 1000 kg

Torque:
Splendor: 10 Nm, Swift: 114 Nm

Last edited by a4anurag : 21st October 2013 at 12:20.
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Old 21st October 2013, 12:21   #7
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Default re: Fuel Efficiency: Cars vs Bikes

One more aspect is that the smaller engines like that of commuter bikes including the Activa run at a higher RPM and engines with bigger displacements run at lower RPMs; thus saving fuel. A typical bike would have to stress the engine at about 6,000 RPMs to run at about 60-70 kmph; where as a car can touch 100 KMPH in the range of 2000-2500 RPM.
I think along with the gearbox, the length of piston rods is the key here, which is longer in bigger engines as they have to work more in the 'depth' of bigger volume cylinders. Another point, not a brainer, the fuel injection system is much more advanced in cars than most 2 wheelers.

Last edited by saket77 : 21st October 2013 at 12:23.
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Old 21st October 2013, 12:22   #8
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Default re: Fuel Efficiency: Cars vs Bikes

Ok, to keep the discussion within the same boundaries, let me swap the Activa with a Hayabusa.

So, we have "2" 1300 cc engines now. (Busa is 1340, but more or less, it can be rounded off)

Power:
Swift - 87 bhp
Busa - 197 bhp

Weight:
Swift - 1 ton
Busa - 250 kg

Need I say more?

Ok, mileage?
Swift - 14-18 kmpl
Busa - 14-18 kmpl.

Same to same!
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Old 21st October 2013, 12:26   #9
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Default re: Fuel Efficiency: Cars vs Bikes

Two wheelers are for two people! So,take that as a base and calculate the per KM cost for moving two people for X KMs in both the vehicles! Don't bring in other considerations like extra seating capacity, AC etc! Then you will have to throw in the cost of the vehicles, depreciation, maintenance costs, insurance etc and then calculate the per KM cost!

My Splendor returns ~ 63 KMPL on the highway. So, if I and my wife go to Pondy - 300 km round trip - by Splendor (we never do! Just for comparison!), we will spend Rs 380.00 for fuel. We always take the Alto and it consumes ~ 14.5 litres for the same distance, which is Rs 1160.00. So, theoretically, even if four people take two Splendors, it would still be cheaper by Rs 400.00!

My 100cc Splendor makes 7.7 bhp. Whereas my 800cc Alto makes 47 bhp! If it is 8 times bigger, should it not make 61.6 bhp?!

Applying your logic, is the Splendor engine more powerful than the Alto engine?

Last edited by Gansan : 21st October 2013 at 12:30.
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Old 21st October 2013, 13:01   #10
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Default re: Fuel Efficiency: Cars vs Bikes

Guys,

Thanks for the responses but I was expecting a technical answer to a layman question.... maybe in terms of engine efficiency or something!

Last edited by akash_m : 21st October 2013 at 13:03.
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Old 21st October 2013, 14:41   #11
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Default Re: Fuel Efficiency: Cars vs Bikes

Fuel efficiency depends on a LOT of other factors and not just on engine size.

Please go through this thread: http://www.team-bhp.com/forum/techni...fficiency.html (Engine size inversely proportional to Fuel efficiency?) . You will get an idea why the activa isn't giving 140kmpl.
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Old 22nd October 2013, 04:47   #12
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Default Re: Fuel Efficiency: Cars vs Bikes

Air drag !

People sitting on a 2 wheeler act like a wall, so the vehicle has to work much harder to overcome the drag resistance. Cars are designed to reduce air drag.

Plus, modern cars shut off a few cylinders when cruising to reduce fuel consumption.

Also, the additional weight of the car allows it to coast easily whereas a 2 wheeler slows down faster due to lesser weight and, again, air drag.
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Old 22nd October 2013, 13:41   #13
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Default Re: Fuel Efficiency: Cars vs Bikes

In my mind it is very simple; Its displacement..

Lets assume there are two engine both single cylinders.. One 100 cc and the other 350cc; Lets also assume the following

- Both have the same stroke ratio [Piston diameter to Stroke]
- Both have no gearbox attached; so free reeving.. no load
-Lets assume that its on a dyno; so no air drag and all the other element
- Also naturally aspirated
- Same timing in respect to degree @ TDC [4 stroke]
- Same compression

Now look at this way.. the amount of fuel+air mixture required to fill up the dome on the cylinder head under full / peak compression is going to much lesser in the 100cc than 350cc... which means all other factors kept the same you need to put in more fuel to get your peak power which inturn will only turn the Crank once


So keeping the above in mind.. remove all the assumption and the additional fuel air mixture required to turn the crank once at peak power goes up..


So as you add more CC the fuel consumption to turn the crank goes up.. as you add cylinders it goes up..and so on and so forth..

In simple a bike is a small cylinder moving a small object requires much less fuel to get the bang strong enough to move the crank and which in turn moves the wheel.. wheras a bigger cylinder which has more surface area requires more fuel to move a heavier crank which in turn will move a heavier object..


Cant be anymore simple that this..
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Old 23rd October 2013, 22:35   #14
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Default Re: Fuel Efficiency: Cars vs Bikes

Two reasons mainly :

1. Aerodynamic drag : two wheelers, or more precisely, their riders , are aerodynamically very inefficient. I surmise, sealed two wheeler cocoons would be very fuel efficient.

2. Small engines but revving higher : 2000rpm vs 4000rpm , that's twice as many combustion cycles which no doubt eat into the energy efficiency of lower displacement engines.

Re : that comparison between 1300cc Swift and 1300cc Hayabusa , again the efficiency-losing factor is RPM. The Hayabusa makes peak power at 9800RPM, the Swift at 6000. Even cruising at 100km/h, the Swift is revving lower than the 'busa by a few 100rpm.
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Old 24th October 2013, 00:38   #15
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Default Re: Fuel Efficiency: Cars vs Bikes

splendor vs swift petrol

1. Weight
100+80(1 person) = 180, 1080 = 1:6

2.Single cylinder vs 4 cylinders
Has to idle at higher rpm.

Also splendor revs at higher rpm during normal operation.

3. Carb vs MPFI
MPFI has optimum fuel air mixture control.

4. No fuel saving measures like fuel cut off while coasting in gear.

5. Not sure if splendor has a inlet manifold vacuum based timing advance for spark ignition, if not then timing is never optimal like the swift which has ecu controlled timing.
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