100 km/h vs 120 fuel consumption

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100 km/h vs 120 fuel consumption

Post by Khiba »

Will I be able to see a difference?
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Re: 100 km/h vs 120 fuel consumption

Post by Tman21 »

Driving from JHB to Durban the most noticeable difference would be that at 100 you will be in everyone's way!
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

You should see a difference, assuming no other changes or differences.
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Re: 100 km/h vs 120 fuel consumption

Post by panic-mechanic »

air resistance rises by the square of speed. So there is a significant increase in drag between 100 and 120. Some sites will tell you as much a 1 L per km but it really depends on what car and what engine size.
But going from JHb to durban you will see a measurable difference.
Many of the fuel consumption numbers quote on makers sites are at either 80 or 100km/h and that is often why people can't understand why they just are not getting what the pamphlet said
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Re: 100 km/h vs 120 fuel consumption

Post by Stu »

flip I would struggle driving anywhere at 100km/h just cant do it
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Re: 100 km/h vs 120 fuel consumption

Post by DIKKIES »

Yes , you will see a big difference in fuel saving , while the guy on 120-will be before you only by maybe a half a hour and a empty tank of fuel and bigger risk of making a accident ...!!!

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Re: 100 km/h vs 120 fuel consumption

Post by VAG Fan »

With the car that's listed in the OP's signature, there will be a marked difference - I would wager, easily 10%, quite possibly closer to 20%.
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Re: 100 km/h vs 120 fuel consumption

Post by OettingerTDi »

Following from Panic's post above...

The increase in wind resistance from 100km/h to 120km/h is about 40%, so you will definetely see a difference.

Also remember that if you compensate for speedo reading versus GPS speed, and use GPS speed, the difference could even be more.
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

Tman21 wrote:Driving from JHB to Durban the most noticeable difference would be that at 100 you will be in everyone's way!
Try getting out of the fast lane if you find this is the case.
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

DIKKIES wrote:Yes , you will see a big difference in fuel saving , while the guy on 120-will be before you only by maybe a half a hour and a empty tank of fuel and bigger risk of making a accident ...!!!

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Are you also one of those that believe that people have accidents only because of speed?
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Re: 100 km/h vs 120 fuel consumption

Post by amstel18 »

spanner in the works.

I know the wind resistance is greater at higher speeds, but depending on the car and the gear ratios. Wouldn't some be more efficient higher in the rev range?

I've noted on my Audi, that if I set the CC to 155, the ave km/l is lower than on 128. The OBC is not too accurate, but just trying to test my theory?
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Re: 100 km/h vs 120 fuel consumption

Post by Tman21 »

Neuk wrote:
Try getting out of the fast lane if you find this is the case.

Neuk I actually think with some slower traffic like trucks that speed and people who tow caravans that go 80-110kmph you will probably end up breaking for slower traffic trying to stay out of the way of fast lane drivers and then have to speed up again. Consumption and momentum goes hand in hand.

Guy thats going slower might also cause and accident, as you mentioned not only speed causes accidents.
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

Tman21 wrote:
Neuk wrote:
Try getting out of the fast lane if you find this is the case.

Neuk I actually think with some slower traffic like trucks that speed and people who tow caravans that go 80-110kmph you will probably end up breaking for slower traffic trying to stay out of the way of fast lane drivers and then have to speed up again. Consumption and momentum goes hand in hand.

Guy thats going slower might also cause and accident, as you mentioned not only speed causes accidents.
I was being flippant but you are right, our recent trip to Cape Town and back was broken up a lot by slow traffic overtaking slower traffic, even though I was taking it easy in a Fortuner at around the national speed limit. I didn't mind the slower drivers at all, not everyone is able to drive at the speed limit but what did get annoying was the impatient tonsils overtaking out of turn, endangering other motorists at times.
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Re: 100 km/h vs 120 fuel consumption

Post by OettingerTDi »

amstel18 wrote:spanner in the works.

I know the wind resistance is greater at higher speeds, but depending on the car and the gear ratios. Wouldn't some be more efficient higher in the rev range?

I've noted on my Audi, that if I set the CC to 155, the ave km/l is lower than on 128. The OBC is not too accurate, but just trying to test my theory?
I found this too, but in a different way. Towing an off road trailer with the Caddy, I got better fuel consumption going faster (125km/h indicated versus 110km/h indicated) due to the Caddy pushing away more air so that the trailer was running in a sort of air pocket behind it.

I think every car has a sweet spot, where power, torque and wind resistance work in some kind of harmony for an optimal result.
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

amstel18 wrote:spanner in the works.

I know the wind resistance is greater at higher speeds, but depending on the car and the gear ratios. Wouldn't some be more efficient higher in the rev range?

I've noted on my Audi, that if I set the CC to 155, the ave km/l is lower than on 128. The OBC is not too accurate, but just trying to test my theory?
Gearing and torque will have an impact but as panic says, the increase in resistance due to drag is exponential as speed increases so the faster you go the more and more power you need to overcome drag. I am sure you can find examples where the gearing and torque have such an impact that you will get better fuel consumption at a higher speed.
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Re: 100 km/h vs 120 fuel consumption

Post by madracer21 »

Neuk wrote:
Try getting out of the fast lane if you find this is the case.

Which lane is the fast lane?
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Re: 100 km/h vs 120 fuel consumption

Post by Neuk »

madracer21 wrote:
Neuk wrote:Try getting out of the fast lane if you find this is the case.
Which lane is the fast lane?
The one next to the slow lane.
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Re: 100 km/h vs 120 fuel consumption

Post by panic-mechanic »

yes the v10 touareg is lighter on fuel at 160 than at 120 but I'm sure it will be lighter at 100. I struggle to go anywhere at that speed though.
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Re: 100 km/h vs 120 fuel consumption

Post by ICE King »

depends on the vehicle , the idea is not to load the motor.
My consumption is more at 100 than 120 in highest gear.
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Re: 100 km/h vs 120 fuel consumption

Post by playback »

Speak to your parents.
When there was fuel shortages many many moons back.
You were only allocated a certain amount of fuel.
You had to drive economically and max speed limits were reduced nationally to enforce better economy.
Long story short.
Generally 100km/h should use less fuel than at 120km/h.

The less aerodynamic a veichle the more you notice.
My Wrangler unlimited Rubicon is heavier on fuel at 120 vs 100 and considerably more so at 140.
On a car like that you easily see the diff as it’s large.



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