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SUVs Acura RDX Acura RDX Real World MPG
189 messages, Last post on Nov 08, 2009 at 3:44 PM
You are in the Acura RDX Forum. Your Hosts are steve_ & tidester
| Just to throw out some mixed info -- my last car was a turbo-4, 250HP, AWD, and weighed 350-400 lbs less than the RDX. It did a little worse than the RDX on highway MPG, and a little worse yet on average/mixed MPG. But it appeared less draggy to the eye. I don't think it's easy to figure out what/why goes into overall MPG, there are just too many factors. I think the largest one is the fuel/rpm consumption and the rpm at cruise. The RDX does cruise at a rather low RPM in 5th gear on the highway, perhaps 600-700 rpm lower than my last car. | |
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I wasn't comparing the V6 Rav4. If the turbo isn't providing much of anything at cruise, the engine should be comparable to another 4 cylinder like the Rav 4's 4-banger version. That's where I got the mpg from. "the RDX is also wider (73.6" vs 71.5") and has wider tires, resulting in more aerodynamic drag." Umm, no. Drag is figured by surface AREA, but it is also figured by drag coefficient. For arguments sake I took the two as boxes and just figured out their general area based on specs given on this site, the Rav is 32.92 sq ft, the RDX is 33.32. Only .4 sq ft of difference. The Acura is also shorter and sits lower to the ground which also has an effect on drag. Now you can argue the tires are wider as well, but with these numbers, can you really tell me there is that much of a difference? The drag coefficient of the Rav 4 is .33, I doubt the RDX's is worse than that which should makeup for the slightly larger area(it's not listed anywhere I can find). These two vehicles are as close as you can get in terms of overall dimensions. The only glaring difference is that the RDX weighs 456 lbs more(#'s from this site). You may have a point on the tire tread, but I don't know nearly enough to comment on that. Yea, I know it's a crapshoot trying to find the losses. The more you dig the better you make the car though, right? It still just seems that the RDX is a bit heavier and just needs a finer touch if driving for mpg. If they can lighten it, I'm sure that will make up the difference in MPG. |
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My wife and I have a RDX w/TECH Package that is currently getting 20.5mpg in city driving. The RDX currently has 13,xxx miles since we got it in Sept. 2006 (We made a few trips from South Florida to Georgia). Highway mpg at the time we took the last trip was 22  75mph not using the cruise control. That's 12mpg less than the 2004 TSX w/NAV we traded. The primary reason for trading the TSX was lack of power. It was a fun car to drive but it just didn't have enough power. We enjoy driving the RDX 
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Here are my thoughts on the RDX's less than ideal fuel consumption: 1.Weight (it weights close to 4,000lbs)  2.AWD (all wheels driving the vehicle)  3.Tires (18" High Performance All Season) and 4.Gear Ratio (4.533-Great for acceleration not for crusin') 
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Replying to: wkrd09 (May 12, 2007 9:05 pm)
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Replying to: oncrank (May 14, 2007 2:48 am) |
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You guys need to go drive an RDX on the highway. In 5th gear on the highway, it's turning lower RPMs than any recent 4-cyl vehicle I have owned, in fact it's pretty much loping along. At 70mph it's turning 1900rpm. That's lower than many 4-cyl vehicles turn at 60mph! 5th gear has a tall 0.612 ratio, which combines with the 4.533 final drive ratio to net a 2.77 gear ratio. It's not enough to look at the final drive ratio, as the overall gearing also depends on tire/wheel size and the transmission gearing. For the RDX, the overall result is 27rpm per mph in 5th gear. As for the number of gears, 6-spd transmissions don't always use the 6th gear as a high speed cruising gear -- in fact they normally increase the number of gears to result in tighter gear spacings, not a taller cruise gear. Whether it's a 4,5,6,7 speed is not directly relevant to the rpm/mph at highway cruise -- the overall ratio in top gear is what matters. I have a 6-speed sports car and it actually turns around 4000rpm at 75mph.
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Replying to: c_hunter (May 14, 2007 8:07 am) The reason the RDX can pull 1,900 rpms at 70 mph is because of all the low end torque it has. It has a flatter torque curve then just about any production honda engine. I think it is the first time honda has had an engine make more torque then horsepower. A little bit of tweaking might even allow a slightly lower, numericaly speaking, 6th gear as well. By using a 6 speed tranny though could tighten the gear ratios up some giving a slightly lower rpm in each gear and smoother shifting. |
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Replying to: c_hunter (May 14, 2007 8:07 am) |
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We're looking for ways to improve the mileage for people who obviously aren't as adept at driving for mileage. You know how the car works and clearly are able to use that to your advantage to get decent mpg, others aren't so lucky. That's why we're here nitpicking ideas. Yes, a 6 speed is often used just for shifting performance. It COULD be used to provide a better gear ratio for cruising on the highway while not sacrificing smooth performance in the other gears. While it is already low, it could be lower. Acura 4.533 and 0.612 X3 Man. 3.73 and 0.85 X3 Auto 4.44 and 0.67 The BMW does come standard with 17's as opposed to Acura's 18's, but has an option for them. Now I get confused with how this works out in terms of best gear ratio for low rpm highway cruise. If I figure this right, the X3 has a smaller tire which doesn't help gearing yet it still gets 26mpg. This would effectively be the gearing if I understand the numbers correctly doin most of the work for mpg. If you compare the RDX's with the Auto gearing as the manual doesn't really apply here, the numbers are close but there is still room. If a sixth gear was put in that dropped it a hair above/below(not sure which way the #'s need to go) what the bmw's is, that would probably make for a pretty good cruisin suv mileage wise. Trimmin some body weight to boot, and you have something very sweet for both worlds. Lemme know if I'm way off on this cuz I always had trouble understanding gearing principles.
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