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Car Forum / Saab Cars / March 20059-5 Aero speed vs. gas mileage
I tried a test with my 9-5 Aero's trip computer last week. On a trip to & from the airport (roughly 70 miles) I got onto the interstate, zeroed out the computer, and tracked the mileage I got while driving at highway speeds. On the way to the airport, I drove 80-85 mph. Highway mileage was just about 29 mpg. That jives with the mileage I've seen on long road trips. On the way back, I drove about 65-70. Highway mileage was over 39 mpg! I don't know how accurate the trip computer is, but I would assume it's consistent from one run to another. I was astonished that an 18% drop in speed would produce a 34% gain in mileage. I guess this is due to air resistance increasing as the square of speed, or something like that? FWIW, the altitude of the start & end points was nearly identical. Temps were maybe 10degF warmer for the return run. I had about 200lbs less passenger & cargo weight on the way back (3 people & luggage vs. 4 people & luggage for the trip to the airport), but I wouldn't think that would make a significant difference on a relatively flat run. I would think the air & rolling resistance would make a much bigger difference. So I could hugely increase my mileage on the road if I'm willing to go slower. Unfortunately I don't know of any way to similarly increase my city mileage, which is probably 80-90% of my driving. I can help it a bit if I always drive like a feeble granny, but then what's the point of owning an Aero!? I've been considering a VW Passat TDI in order to reduce my gas consumption. I get about 22mpg in town driving, 28mpg on road trips. The TDI is rated at 27mpg city, 38 mpg highway. With over 20k miles per year, I'd save something like 200 gallons per year. With diesel running maybe 10-15 cents cheaper than premium, I'd be saving $500 or more per year on fuel. Of course, the Passat is no Aero. I'd be taking a serious hit in performance. And it looks like a 2004 Passat TDI wagon with 20k miles is worth about $4000 more than my 2002 Aero wagon with 60k miles. So maybe it's not worth the change. Unless my mostly-town-driven Aero is a ticking timebomb with the engine problems I keep hearing about... Has Saab USA said anything about a guarantee program for that yet?? Gary Salutations: I don't know much about the later 9-5 engine systems - but I can confirm surprising mileage efficiencies having been recently bagged speeding and subsequently staying at the posted limits with a '93 9000 5 speed Aero over this spring. Basically - I'm averaging about 37-40 miles to the imperial gallon at a steady 60-65mph on the highway and about 25-27mpg (30-35mph) around town. I have tallish winter sidewalls on stock rims currently filled at the upper end of the acceptable range. Now, I burn hi-test exclusively and I know that they change the octane rates as spring turns - so I'm expecting a slight drop in fuel economy as the summer picks up and I turn on the Air-Con every so often. In the end - while the combined expense of the ticket ($215) and the remarkably sizeable insurance hike to come will far outweigh any savings I see in the next three years while I wait for the ticket to come off the record - I am none the less seeing fuel savings that are surprising. As to weight and air resistance - the former plays a *much* larger role than the latter with SAAB's of any vintage and combined with a lower speed on your return trip - would account for the computed report at the dash. Basically you dropped the weight of the car at least 150 pounds by losing one person and the luggage. As to the TDI Passat, nice car - not nearly as much interior room as the 9000 - but not unlike the 9-5 in terms of general amenities I'm told. Cheers and happy motoring. -- Radio Free Dexterdyne Top Tune o'be-do-da-day Joe Cocker - Feeling Alright http://www.dexterdyne.org/888/055.RAM all tunes - no cookies no subscription no weather no ads no news no phone in no sign up required - all the Time > I tried a test with my 9-5 Aero's trip computer last week. On a trip > to & from the airport (roughly 70 miles) I got onto the interstate, [quoted text clipped - 44 lines] > > Gary  SignatureRadio Free Dexterdyne Top Tune o'be-do-da-day Johnny Rivers - Memphis Tennessee http://www.dexterdyne.org/888/050.RAM all tunes - no cookies no subscription no weather no ads no news no phone in no sign up required - all the Time > Basically - I'm averaging about 37-40 miles to the imperial gallon > at a steady 60-65mph on the highway and about 25-27mpg (30-35mph) > around town. Let's see, 37 miles per imperial gallon is just under 31 miles per US gallon. 26 per UK gallon is about 21.5 per US gallon. So your town mileage is similar to mine, and your 60-65mph mileage is well under mine. But that's undoubtedly due to the different car, not the speeds. Do you know what you got at higher speeds, before the ticket? (ouch!) > As to weight and air resistance - the former plays a *much* larger > role than the latter with SAAB's of any vintage and combined with > a lower speed on your return trip - would account for the > computed report at the dash. Basically you dropped the weight of > the car at least 150 pounds by losing one person and the luggage. Hm. I'll have to try the experiment again sometime with the same load on both legs. I'd still be surprised if air resistance plays such a small role. > As to the TDI Passat, nice car - not nearly as much interior room > as the 9000 - but not unlike the 9-5 in terms of general > amenities I'm told. I haven't actually checked out a Passat. If it's smaller than the 9-5 (which is a bit smaller than the 9000), it definitely won't work for us. We've got 2 kids, currently 8 and 10, and they're already cramped in the 9-5's back seat. "Tex" <tex@aspam101.org> wrote: > > less passenger & cargo weight on the way back (3 people & luggage > > vs. 4 people & luggage for the trip to the airport), > Sorry...I think this is the funniest part of your post. So you drove > 3 people to the airport. 1 got dropped off with bags. The other > 2 with bags chickened out at the last minute? ;-) No, I drove 4 people (me, wife, 2 kids) + luggage to the airport, and we all went on a vacation. My wife stayed for a business trip, and the kids & I came home. So I had 3 people + luggage on the trip back. Gary Salutations: >> Basically - I'm averaging about 37-40 miles to the imperial gallon >> at a steady 60-65mph on the highway and about 25-27mpg (30-35mph) [quoted text clipped - 6 lines] > speeds. Do you know what you got at higher speeds, before the ticket? > (ouch!) When the officer asked me if I knew I was speeding - I looked him squarely in the eye and said with a smile ".. and how!" .. Lucky for me he saw the humour of the situation as the ticket quoted is *after* he knocked it down 5mph - which could otherwise have seen me charged with reckless. My first in almost 18 years - but around here I might as well have hopped in a time machine and turned 16 again as far as the insurance industry is concerned. The whole business of automobile insurance is legalized fraud as near as I can figure from here in Nova Scotia, Canada. Pay-up - never make a claim for anything, never actually have an accident or get a moving violation - and your rates will only go up 5-10% per year as long as you never move to a competing company or comment to the press about how you think it might all be a little suspect. Arrrgggg - don't get me started. In answer to your question - yes - I was averaging about 35mpg at 70-75mph and about 22mpg at 35-40mph throughout the winter. However, as you will appreciate, the 1993 Aero is a heavier car than the 9-5 Aero overall and the turbo is somewhat less refined than in the 9-5 I gather. >> As to weight and air resistance - the former plays a *much* larger >> role than the latter with SAAB's of any vintage and combined with [quoted text clipped - 5 lines] > on both legs. I'd still be surprised if air resistance plays such a > small role. SAAB has always had a very good aerodynamic package. You might get a little boost in efficiencies with a flat on tail wind in the 9-5 or 9000 or by slip streaming someone. But assuming all other things are equal - you would be hard pressed to see a big change in normal driving I think. >> As to the TDI Passat, nice car - not nearly as much interior room >> as the 9000 - but not unlike the 9-5 in terms of general [quoted text clipped - 4 lines] > us. We've got 2 kids, currently 8 and 10, and they're already cramped > in the 9-5's back seat. Well - you know that was the final factor driving our decision to buy an older 9000. I had always really wanted one and had been very happy with our previous 1989 CD model. The 9000 Aero is really as comfortable as they are made out to be and given that maintenance over the course of it's potential usable lifetime is about what I would spend on a warrentee'd lease - I went for a reasonable deal on a used one with a really clean body that needed/needs a little TLC. The 1993 can be retro-fitted with a pre-DI long block engine and tranny for not much cash if you pick a donor car with the electronics. So when the engine system or tranny dies - I should be able keep her running for several years to come assuming I keep up on the rust-proofing and don't hit anything solid with her along the way. Basically - the 9000 is Tardis (Dr Who) like inside (both for passengers and cargo) and I think offers some real value for the dollar without making some lifestyle statements that I would not otherwise want my friends and neighbours to assume. Yes - it's more than a decade old. However - I feel the design is just as snappy today as it was when it was released in 1993 and we own it outright. Which is nice when you have kids growing up. Be interested in how your second test run goes - I would do it sooner than later as the octane ratings will change in the coming weeks as spring gets here and that will throw off your calculation substantially I think. Cheers and happy motoring. -- Radio Free Dexterdyne Top Tune o'be-do-da-day Stanley Brothers - I'll Fly Away http://www.dexterdyne.org/888/158.RAM all tunes - no cookies no subscription no weather no ads no news no phone in no sign up required - all the Time > "Tex" <tex@aspam101.org> wrote: >> > less passenger & cargo weight on the way back (3 people & luggage [quoted text clipped - 8 lines] > > Gary SignatureRadio Free Dexterdyne Top Tune o'be-do-da-day Johnny Rivers - Memphis Tennessee http://www.dexterdyne.org/888/050.RAM all tunes - no cookies no subscription no weather no ads no news no phone in no sign up required - all the Time >>> Basically - I'm averaging about 37-40 miles to the imperial >>> gallon at a steady 60-65mph on the highway and about 25-27mpg >>> (30-35mph) around town. > > In answer to your question - yes - I was averaging about 35mpg at > 70-75mph and about 22mpg at 35-40mph throughout the winter. So you had somewhat lower mpg at 70-75mph. But you also had significantly lower in-town mpg during the same time. So it's hard to say what caused what. > Be interested in how your second test run goes - I would do it > sooner than later as the octane ratings will change in the coming > weeks as spring gets here and that will throw off your > calculation substantially I think. Actually I don't recall ever seeing the octane levels change around here. But our winters (in Colorado but not in the mountains) are a lot milder than yours. In any case, I'll do both the high- & low-speed tests at about the same time, probably on the same tank like I did last week, so the gas formulation shouldn't be an issue. Gary Salutations: >>>> Basically - I'm averaging about 37-40 miles to the imperial >>>> gallon at a steady 60-65mph on the highway and about 25-27mpg [quoted text clipped - 6 lines] > significantly lower in-town mpg during the same time. So it's hard to > say what caused what. It was particularly chilly this winter here and that will consume more fuel on short hops on it's own account. I also tend to use lower gears around town given potentially slippery conditions. The TCS system operates as advertised (I'm using a 5 speed model), but I still like a little range to work with going around corners. The highway figures do not surprise me. You are not winding up the turbo accelerating and decelerating as much for the total miles covered and the hop from 60-75mph isn't much more than a couple of hundred rpm overall. Moreover, the electrical defrosters and blowers are not working as hard between starts/over time as they would in city use. That said, as evidenced by the speed recorded by the officer, I would tend to kick it down pretty deeply when an available passing lane was at hand. I have been recording the figures and resetting since the fall at fuelling. I have some odd gremlins that I want to sort out and while it is not definitive information - following average fuel consumption over given periods of time can provide some feedback on work performed. >> Be interested in how your second test run goes - I would do it >> sooner than later as the octane ratings will change in the coming [quoted text clipped - 10 lines] > > Gary Standing by and interested in your report. Hey - I wonder if smaller changes in altitude at higher altitudes would impact your figures? Never been out your way, is there a climb to the Airport? -- Radio Free Dexterdyne Top Tune o'be-do-da-day Stanley Brothers - I'll Fly Away http://www.dexterdyne.org/888/158.RAM all tunes - no cookies no subscription no weather no ads no news no phone in no sign up required - all the Time > Standing by and interested in your report. Hey - I wonder if > smaller changes in altitude at higher altitudes would impact your > figures? Never been out your way, is there a climb to the > Airport? It's long rolling hills all the way. The airport is at 5431' (hmm, higher than I thought), and our house is at about 5000'. So there is a bit of a net climb to the airport. > less passenger & cargo weight on the way back (3 people & luggage vs. 4 > people & luggage for the trip to the airport), but I wouldn't think Sorry...I think this is the funniest part of your post. So you drove 3 people to the airport. 1 got dropped off with bags. The other 2 with bags chickened out at the last minute? ;-) [I suppose you could be running an airport car service] As for your MPG issue, I have also noticed significant increases in MPG at slightly slower speeds ('04 9-3). But is this really surprising? Fuel efficiency advocates have espoused for years that decreasing your speed by even just 5 mph makes a big difference in fuel economy. So a speed drop from 85 down to 65 is bound to have a sizeable effect on MPG. While I make no claim to know the mathematical aspects of vehicle aerodynamics and road resistance, the overall effect of the speed drop is obvious (as evidenced by your 9-5's trip computer). - tex Hey Gary - Reminds me of something that happened to me the other day... I woke up early and the sun was rising in a cloudless sky, so I decided to take the old 9000 for a quick spin. The roads were quiet, the sunrise was amazing and I had the CD player pumping - even had the roof open (with the heater on). Anyway, someways on up the road, I came across a 9-5 Aero (black) doing about 70... I took the chance to slow down, back off and change the soundtrack. After a while I put my foot down, and as I passed a fellow Saaber on this glorious morning, I looked over to give him a little nod of recognition...... but he didn't even see me... seemed he was too busy staring at his fuel gauge or something!...... > I tried a test with my 9-5 Aero's trip computer last week. On a trip > to & from the airport (roughly 70 miles) I got onto the interstate, [quoted text clipped - 44 lines] > > Gary
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