[2fast4u]

As my mechanic guy said.
If your car is RWD then its not a good idea to shift into Top Gear below 60kmph on flat surface / incline as there is too much stress on the Differentials.

A little gain on the FE will burn your pockets to replace a Diff.

Turbosam @ is that right??

[gemithomas]

was just wondering... if we reduce the diameter of the tyres would the F.E increase.

For example my adventure runs of 175/80's . What if i decide to loose some Ground clearance and go for the Petra/Sienna size tyres. I'm asking since i heard that with lower diameter the acceleration increases (though power is same). There by you would not need to press the accelerator as much as you do now. THe car would pull much easier. Thereby shouldnt the F.E figures be better.

[sathya_nars]

Originally Posted by gemithomas

was just wondering... if we reduce the diameter of the tyres would the F.E increase.

For example my adventure runs of 175/80's . What if i decide to loose some Ground clearance and go for the Petra/Sienna size tyres. I'm asking since i heard that with lower diameter the acceleration increases (though power is same). There by you would not need to press the accelerator as much as you do now. THe car would pull much easier. Thereby shouldnt the F.E figures be better.

Flip side is speedo and tacho calculation may be little different due to reduced diameter of tyres, so you may need to switch gears at different RPMs than you would do now. Right?

[moralfibre]

Originally Posted by gemithomas

was just wondering... if we reduce the diameter of the tyres would the F.E increase.

I think it should be vice-versa. Increasing the overall diameter is another way of getting taller gearing.

[kpzen]

Smaller wheels will show + ve error. ie, if you speedo is showing 100kmph, tru speed will be less than that. Bigger wheels will have a tru speed of more than 100 when speedo reads 100kmph. Hence smaller wheels will show more FE.


Lower overall diameter (OD) will give you shorter gearing.
Higher OD will give you longer/taller gearing.

[TURBOSAM]

Originally Posted by 2fast4u

As my mechanic guy said.
If your car is RWD then its not a good idea to shift into Top Gear below 60kmph on flat surface / incline as there is too much stress on the Differentials.

A little gain on the FE will burn your pockets to replace a Diff.

Turbosam @ is that right??

thats not true... unless your car has screw type diff used in log movers and very heavy trucks or a sliding mesh gear box < and your car is not having it ha ha ha !>
and for added info .. all cars have some kind of a differential ..
u can de clutch the engine for the same effect though ...
just raise the rpm leavel to the corresponding rerquired rpm when releasing the clutch ..

[TURBOSAM]

Originally Posted by kpzen

Smaller wheels will show + ve error. ie, if you speedo is showing 100kmph, tru speed will be less than that. Bigger wheels will have a tru speed of more than 100 when speedo reads 100kmph. Hence smaller wheels will show more FE.


Lower overall diameter (OD) will give you shorter gearing.
Higher OD will give you longer/taller gearing.

if u use same od and thinner tyres u will get better F.E.

[TURBOSAM]

Originally Posted by moralfibre

I think it should be vice-versa. Increasing the overall diameter is another way of getting taller gearing.

yes you are absolutely correct..

[gemithomas]

With a taller gearing could you get more F.E.

Just one scenario. Imagine we reduce the overall diameter of the adventure tyres. Thereby the acceleration increases. In this case if we still drive sedately as we used to do earlier wouldnt we be getting better F.E figures. Or is it that since the gearing has got short we end up changing gears more frequently and thereby getting lower or almost same F.E Figures.

How exacly is
1.Overall Diameter of tyre
2.Profile of tyre
related to F.E figures.

[TURBOSAM]

Originally Posted by gemithomas

With a taller gearing could you get more F.E.

Just one scenario. Imagine we reduce the overall diameter of the adventure tyres. Thereby the acceleration increases. In this case if we still drive sedately as we used to do earlier wouldnt we be getting better F.E figures. Or is it that since the gearing has got short we end up changing gears more frequently and thereby getting lower or almost same F.E Figures.

How exacly is
1.Overall Diameter of tyre
2.Profile of tyre
related to F.E figures.

its simple mathematics..at present your adventure is doing lets say, @117 kmph at 3000rpm of engine.
if u reduce the outer dia of the tyre, then it will reduce the circumference of the tyre,ok? now with reduced circumference u will travel lesser distence for every revolution of the wheel! at the same engine rpm ..
in short lesser circumference of the wheel means equivalent of lower gear..

[humyum]

I have 145/80/r12s in my carburated 1998 800 and the original size of the tyres was 145/70/R12 so I increased the aspect ratio of the tyre.
This in turn leads to getting an error of 5.7 % on the speedo.
So when i cover 100 km on the odo i have actually covered 105.7 km.
The flip side is the pickup has increased a tad bit and initially to get the same pull out of the car i used to rev it a bit more than what i used to normally rev it with the 70 aspect tyres.So that negated the affect of the 80 ratio tyres and i used to get the same mileage.
But since now i have got used to the 80 aspects tyres and a little less pickup i change the gears smartly and have noticed an increase of about 1 to 1.5 increase in FE.
So as turbosam said with this tyres if the engine rpm is 3000 at 100 kmph on the speedo with the 80 aspect tyres its 105.7 in actual at 3000 rpm.

[manish7]

Useful information indeed. Thanks!

[Vinaygv]

Hi, with regard to additives in fuel and driving styles, this is something that I came across on the net while researching acetone. Please check this link. Makes some interesting while validating most of the ideas discussed on this thread.

Acetone In Fuel Said to Increase Mileage

[wmax]

Hi all,

Please let me knw at what RPM should i change my grars to get the maximum FE(for a getz). ALso please tell me how is FE related to RPM??

Changing gears properly is very important to get a good FE and to maintain ur engine in a good condition.

Thanks

[sathya_nars]

Originally Posted by wmax

Hi all,

Please let me knw at what RPM should i change my grars to get the maximum FE(for a getz). ALso please tell me how is FE related to RPM??

This is my opinion, others please correct me if I am wrong. For many cars, 1500 RPM is good to shift gear. This balances FE as well as engine's proper usage.

RPM tells how hard or soft engine is being worked at. Balancing it in right RPM optimizes the energy engine supposed to produce Vs actual. More strain put onto engine wastes fuel and hence FE reduces.