Team-BHP (https://www.team-bhp.com/forum/)

-   Technical Stuff (https://www.team-bhp.com/forum/technical-stuff/)

-   -   Car not rolling freely (https://www.team-bhp.com/forum/technical-stuff/107437-car-not-rolling-freely.html)

My driving style includes a lot of engine braking than actual braking in the city.

Also when on downward slopes I seldom slot the car in neutral. I know the risks but its only once in a blue moon.

Now I have found that my Jazz rolls well in gear or in neutral compared to my lancer. What can the reason be?

For e.g. if I am cruising @40kmph on both and let the engine braking play, Jazz will cover more distance compared to lancer. The same will also be the case in neutral.

Lancer runs on Xm1+ and Jazz runs on XM1. Lancer has 14 inch Mitsubishi alloys while Jazz has Honda 15 inch alloys.

if you are talking about the engine braking, every engine has different characteristics and this difference will be evident with every car even ALto F8 and Alto K10 have this difference, you cannot compare Jazz and Lancer based on same aspect.

whats the cross section on the tyres?

How old is the lancer? Engine braking (or free rolling with powered engine) depends on lot of things including the characteristic of the engine and transmission.
Very difficult to compare 2 different cars and expect to have a similar characteristic.


HC

Of the three cars that I have owned, I find that the City has this effect the most. The other cars (i10 Kappa and Swift 1.3), not so much. Perhaps this effect is lesser on more modern engine for some reason?

one of the variables in engine braking is engine size. the bigger the engine, the more it will be able to protest. jazz has a smaller engine as compared to lancer hence less protesting more rolling.

when rolling in neutral a new car will probably roll more than an old one because everthing is more shiney and greasy. plus, in your case xm1+ is a sporty tyre (as advertised by michellin) so it is bound to have a compound which is more sticky as compared to xm1 (which is not advertised as sport tyre).

True! Just too many parameters are different to do a apple-to-apple comparison. Besides the parameters mentioned above, it would also depend on the weight of the car, the size and condition of tyres etc.

Jazz is lighter, has thinner wheels, less friction

Mitsu is heavier, thicker wheels, more friction

Short answer...

When in gear:
Any kind of resistance (friction), all the way from the rolling resistance of the tyres - including every single moving component up and through the drive-train - right up to the friction of the pistons against their sleeves will slow your car down.

When the car is in neutral:
Its the same deal, but includes only the components in the drive-train between the tyres and the gearbox. (No engine friction is counted here, since its disconnected from the drive-train since you're in neutral).


As parts get worn beyond a certain point, sludged up, or less well lubricated - their ability to work as efficiently (ie with minimal friction) decreases. Some of these parts could be :
- Wheel hubs (get em lubed up)
- Tyres (run the correct pressure. On the higher side if you want less rolling resistance)
- Differential oil (change if possible / reccomended)
- Gearbox oil (change it)
- Engine oil (change it - consider synthetic -- we have a thread on this)
- Check that your brake calipers are not jammed (though nothing hints to this)


Also, its a momentum vs friction fight. If both cars suffer from the same friction, in a coasting drag race from the same speed down -- the one with more mass (ie more momentum) will go further.

cya
R

The Jazz in your case is showing lesser engine braking than the lancer. To test if it is the engine or the drive train.
. Put the cars in neutral when at around 40 kmph, and note the distance travelled
. Take your foot off the accelerator at around 40 and note the distance.

In neutral - if both cars cover the same distance in neutral, then it is the engine braking that is different, if Lancer rolls less then there is problem in the drive train/brakes of the Lancer, if the Jazz rolls less then again it is engine braking of Jazz that is less.

One of the reasons for lesser rolling in gear, everything being equal, is the amount of fuel injected when the accelerator is not depressed. If the ECU injects the fuel assuming you are idling, you roll farther, if the ECU detects motion along with accelerator not depressed it may reduce the fuel to an absolute minimum and the engine braking will be more effective.

Another reason for better engine braking (lower rolling distance) is higher compression. An engine with higher compression ratio will brake better than an engine with lower compression engine.

Actually if I recollect, it is the air resistance and not momentum (as demonstrated by Galileo?). So if both cars have same aerodynamic coefficient, they will roll the same distance. Any way the air drag is negligible at or below 40 kmph.

What Galileo demonstrated applies to bodies in vertical free fall on which the only force applicable its the "g" force at 9.8 m/s^2.

In this case the momentum will be the deciding factor.

Cheers,
R_S

The eight of the car plays a role here. The frictional loss due to tyres between different makes, would be negligible. The part quote- Now I have found that my Jazz rolls well in gear or in neutral compared to my lancer.-unquote is not clear. Please clarify. Do you mean rolling on deceleration by rolls well in gear.

Assuming the Jazz to be a new car, transmission losses are much less. Also, being a Honda helps. Where as, Lancer comparatively old, should have higher transmission losses.

Also, IMO, the more the car weighs, the more frictional losses. Clearly the lancer weighs more.

So, transmission efficiency + weight, works out in favor of the Jazz, and hence the end result.

At speeds below 40kmph, Aerodynamic effect is negligeble, and I have assumed that Jazz is 175 R15 and Lancer is 175 R14. If Lancer is 185, then add this factor too.