Fuel efficiency 4.8TT vs 4.0TT
02-27-2024, 03:18 PM
#16
Intermediate
At sea level, high average temps (mid 80sF and up/30ºC and up), 70% stop & go traffic/ short distances, the other 30% in "highway with a lot of traffic" (average speed of 75km/h = ±45mph), I have averaged 12.71 mpg (18.51 L/100km) over the past 1,900 miles (3,000 kms) on my 2013 GTS. Tires are Michelin Latitude Sport 3 in the stock 295/35/21 size.
My consumption figures are based exclusively on actual distance driven (as measured by the trip odometer in the dash) and the amount of fuel put in at the pump. My onboard trip computer shows a much lower fuel consumption figure than my measured result.
My consumption figures are based exclusively on actual distance driven (as measured by the trip odometer in the dash) and the amount of fuel put in at the pump. My onboard trip computer shows a much lower fuel consumption figure than my measured result.
02-27-2024, 05:29 PM
#17
@Go2GuyTX : You are correct in the sense that the GTS uses a different gear/drive (not sure which) ratio than other 958 models. Will take note of speed/RPM next time traffic conditions allow. Information shared is merely to offer those some quasi-detailed information that my prove to be useful.
Happens to be that I went for a quick errand and took note of the consumption listed (total) in the PCM vs. what I have calculated and the difference turns out to be that my calculations are 12% higher than the PCM claims. Perhaps insignifcant to most, but a curious data point nonetheless.
Happens to be that I went for a quick errand and took note of the consumption listed (total) in the PCM vs. what I have calculated and the difference turns out to be that my calculations are 12% higher than the PCM claims. Perhaps insignifcant to most, but a curious data point nonetheless.
02-27-2024, 06:23 PM
#18
Intermediate
@Go2GuyTX : You are correct in the sense that the GTS uses a different gear/drive (not sure which) ratio than other 958 models. Will take note of speed/RPM next time traffic conditions allow. Information shared is merely to offer those some quasi-detailed information that my prove to be useful.
Happens to be that I went for a quick errand and took note of the consumption listed (total) in the PCM vs. what I have calculated and the difference turns out to be that my calculations are 12% higher than the PCM claims. Perhaps insignifcant to most, but a curious data point nonetheless.
Happens to be that I went for a quick errand and took note of the consumption listed (total) in the PCM vs. what I have calculated and the difference turns out to be that my calculations are 12% higher than the PCM claims. Perhaps insignifcant to most, but a curious data point nonetheless.
For reference, @ 80mph (GPS verified) I'm turning roughly 1900 RPM :-)
02-28-2024, 09:55 AM
#19
Roof box can make a huge difference. I've found our Thule box mostly just increases the negative effects of any wind on the drive with respect to fuel economy. During a road trip to Montana last year, I averaged a hair over 20mpg on the highway in my V6TT S. However when we drove to Texas more recently, trip average was closer to 17mpg. The windiest day of that trip I think netted around 15mpg for the day.
For comparison, I typically get 22-23mpg on my standard daily highway commute, without a roof box of course.
For comparison, I typically get 22-23mpg on my standard daily highway commute, without a roof box of course.
The roofbox in question is the Porsche Performance version. It is designed to roll safely at 200 km/h = 125 mph. I did stab the accelarator a couple times and can report it is stable at 220 km/h. High performance (and silly high price, even with a dealer discount) ... but apparently not low drag. You can read the roofbox's description here:
https://shop.porsche.com/fr/fr-FR/p/...BoC3HAQAvD_BwE
When you think about it, any roof box in profile ressembles an airplane wing, with a smooth bottom and convex top. Now I'm wondering how much lift this one creates at 200 km/h.
02-28-2024, 01:47 PM
#20
Rennlist Member
Here are some more data points for comparison. 2011 Cayenne S - freeway driving averaging ~65-70 mph over 600 miles:
-no roof box, 4 people with luggage: ~22 mpg (10.7 liters/100km)
-Thule Force XT XL roof box (full ~150 lbs), 2 people, fully loaded luggage: 19.0 mpg (12.4 liters/100km)
-same roof box but empty, driver only: 19.6 mpg (12.0 liters/100km)
So the box alone results in approx 10-15% mileage penalty.
-no roof box, 4 people with luggage: ~22 mpg (10.7 liters/100km)
-Thule Force XT XL roof box (full ~150 lbs), 2 people, fully loaded luggage: 19.0 mpg (12.4 liters/100km)
-same roof box but empty, driver only: 19.6 mpg (12.0 liters/100km)
So the box alone results in approx 10-15% mileage penalty.
