What yields better fc: Constant speed throughout trip, or mixed fast/slow driving?

**valacirca** · September 17th, 2012 10:30 AM

Consider the following figures:

Trip Time: 3 hours
Trip Distance: 135km

So by simple math, ang average speed is 45kph for the entire trip.

What would yield better fuel economy:

1) Doing 45kph consistently for the entire 3 hours

OR

2) Doing a mix of 10kph for 30 mins then 80kph for 30 mins alternately for 3 hours?

Just asking because I wanted to know how scenario 2 affects my fuel economy.

Kasi I went on a trip from Pasig to Nuvali and back last Saturday, which yielded the following figures:

Trip Time = 3:54
Trip Dist = 92.1 km
Ave Speed = 23.62 kph
Fuel Cons = 13.33 km/L
Car = 2012 Kia Rio 1.4 EX AT Sedan

Considering nag-SLEX ako hitting 100kph at times, mabagal pa din yung average speed because of the very heavy traffic in the Pasig area + moderate traffic in Sta Rosa.

**stickers** · September 17th, 2012 11:02 AM

i dont know if i'm right on this but i think 1st and 2nd gears consume more gas than 3rd, 4th onwards... this is why everytime you get stuck in traffic, you consume more gasoline than the average mix driving.

**niky** · September 17th, 2012 11:55 AM

Try sticking to 80 km/h for the flat portions. Whatever is the lowest speed you can hold in 4th gear (meaning... the transmission doesn't fluctuate between 4th and 3rd and you don't lose speed) is the best on the highway.

SLEX is a challenge because of hills. I try to accelerate going down the gentle slope before the hills at Susana, then semi-coast (on low throttle) to the tops of those hills (hitting as low as 60-70 km/h by the top), then try to regain the momentum on the downhill stretch to Alabang.

**fourtheboys96** · September 17th, 2012 12:39 PM

constant speed will yield better fuel economy.
acceleration consumes more fuel. so if you alternately go from slow to fast driving, you have more instances of acceleration.

but in reality, you seldom drive on constant speed unless you are always on an expressway.

**niky** · September 17th, 2012 01:02 PM

You can use mixed speeds and gain decent economy. The concept is called "Pulse and Glide" by hypermilers. You pulse (accelerate) up to a set speed and glide down to a lower target speed in neutral or... in more extreme cases... with the engine off.

P&G in neutral yields better economy than steady state. P&G with the engine off can give you incredible economy... but this is very difficult to do and very dangerous... and definitely not recommended with an AT.

Still... whether you follow steady state or P&G, the principles for hills remains the same. DO NOT maintain speed up the hill. This is a waste of gas. Let gravity bleed off your speed, then gain it back on the way down.

**valacirca** · September 17th, 2012 02:17 PM

Originally Posted by fourtheboys96

constant speed will yield better fuel economy.
acceleration consumes more fuel. so if you alternately go from slow to fast driving, you have more instances of acceleration.

ok thanks! this is what I wanted to know

**dfopiso** · September 17th, 2012 05:15 PM

^ meron din yatang impact ang rpm

during cruising speed of ~80kph, maintain a max of ~2000rpm. so pitik-pitik lang sa pedal. equivalent yata yan ng p&g

**dfopiso** · September 17th, 2012 05:18 PM

double post

**CVT** · September 17th, 2012 05:30 PM

Originally Posted by niky

Still... whether you follow steady state or P&G, the principles for hills remains the same. DO NOT maintain speed up the hill. This is a waste of gas. Let gravity bleed off your speed, then gain it back on the way down.

That is why driving with autocruise on going uphill is a surreal experience.... The engine RPM compensates (i.e. revs higher) for the 'loss' in speed...

16.9K:spam:

**niky** · September 17th, 2012 05:45 PM

That's why you should only use cruise control on a relatively flat and long stretch of road.

Originally Posted by dfopiso

^ meron din yatang impact ang rpm

during cruising speed of ~80kph, maintain a max of ~2000rpm. so pitik-pitik lang sa pedal. equivalent yata yan ng p&g

Ideally, no need to keep pressing harder to bring speed back up. What you do is let it coast down for a while then pulse once and let off again.

Best is if you can find the sweet spot where the lightest of pedal pressures will allow you to maintain speed on a flat stretch. Very hard to do in practice, because very few roads are completely level. Even on the NLEX, there are portions where you're going slightly uphill or down hill.