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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.
2021 Toyota Venza Limited Hybrid, 2022 Ram 2500 Laramie 6.4 Hemi, 2007 Mazda MX-5 Miata PRHT
http://en.wikipedia.org/wiki/Gear_ratio
Their equations at the end are somewhat misleading because they don't note a lot of unit conversion is needed to make it work. Here's the equation I follow:
V = C*RPM / (Gt*Gd*1056)
V = vehicle speed in mph
C = tire rolling circumference in inches
RPM = engine RPM
Gt = gear ratio of a particular gear in transmission
Gd = gear ratio of differential
You can estimate the rolling circumference as:
C = 2 * Pi * (D/2 + W*AR/25.4)
D = rim diameter in inches (ie, 18)
W = tire width in mm (ie, 235)
AR = tire aspect ratio (ie, 0.55)
To get an accurate circumference you really need to measure one full revolution of the tire on the ground, but I think the estimation (which uses a nominal tire size) is OK for comparison.
I am sure the BMW 17" and 18" options have the same (or nearly the same) outer diameter (and hence circumference) so there is not likely a gearing difference there. You can compare the BMW and RDX nominal tire sizes with the equations to get a real comparison of the overall gearing.
The only thing I can say relative to gas mileage is that I tend to drive with a light foot on the throttle, rarely mashing it. Even when traveling at 70-75mph on the highway, I am pretty easy on the throttle. That gives me 25mpg on trips, or 21-23mpg in mixed driving. I am sure I would be in the teens with more city driving.
When considering the RDX, I was alarmed by low MPG reports and paid attention to the trip meter during test drives. What I found was numbers of 14-16mpg when driving on city streets around the dealership with a reset trip meter. That climbed into the upper 20s on the highway, and settled out around 22-23mpg over a 12 mile test drive. If I only looked at the 14-16 aspect, I would have been turned off.
I also repeated the same test loop with my old car, also with a reset trip meter, and noticed very similar trends. It too got MPG in the mid teens in the city and then climbed into the 20s on the highway. That car never made it higher than the low to mid 20s and settled out around 20mpg.
I think I mentioned earlier that my previous car was very similar to the RDX in power and also had a turbo 4. But it weighed about 350 lbs less. Considering that, I think the RDX is doing pretty good if it returns similar or slightly better MPG under the same driving conditions.
Thanks for the link hunter, thats good info. Yea, I think alot of people just dont feather the throttle enough on the highway. I live in a hilly area so I might have more of a hard time getting decent mileage combined everyday. Part of the reason why I'm so adamant about suggestions for improvements. I'll be in the market for a new car within the year and I REEEEEEALLY like this suv, but some improvement in mpg aside from some minor interior improvements would be great and really put me over the edge in getting it. Right now, I'm still on the fence.
I would say that you should worry about MPG if you did a lot of city driving , or all city driving. If you do highway driving or back road driving, the RDX should be OK. At 45-55mph on country roads, the MPG soars into the mid 20s -- that seems to be the sweet spot..
I was really on the fence about the RDX, in fact if you look at some of my posts from last fall, I was not too thrilled with the RDX. But it gradually grew on me; I love the interior and handling, and I felt better about the MPG after many test drives. Finally, the drop in street price to invoice or lower (I paid $30300 for my base RDX) sealed the deal. After 5 months of ownership and about 6800 miles, I am real pleased with the RDX. It's a very comfortable ride for my commute and on the many ski trips I take.
This has nothing to do with our discussion, but I agree with some of the complaints listed in the shorter reviews. For $30,000, your passenger seat should move for you. My wife and I ride together alot so it would see alot of use. All other base Acura's have bluetooth standard on them. I was told by the dealership I test drove at that first year outs dont get that. Huh?! If you want a car to sell, you hit it out of the ballpark the first time. You dont nitpick stupid crap like that.
Anyway, back to the topic. Well, it does seem if you pay attention to what you're doing and adjust your driving habits a little bit, you can do well with this suv. For the sake of people that have a little trouble changing, an extra gear and a little less weight would go a looooong way in making this suv the exception and not the rule.
Thanks for your inputs c_hunter, really appreciated the responses.
I gradually have seen the accuracy of the reported MPG improving. (I kept detailed records at fill-ups). The 1st month the onboard computer overstated MPG by 4.8%, the second month by 4.1%, and by the 4th month by only 3.4%.
My overall MPG is now around 18. This is all good news.
In my tests I have reached up to 25 mpg in freeway driving at 65 mph at 2000 rpm, with no AC, no load, and without invoking the turbo like when passing other cars. I guess it's the downtown traffic that brings down my average.
After 2500 miles of mostly driving in country settings with LOTS of rolling hills and average mpg of 22.7
We are traveling from Md to NMB South Carolina in a few weeks and I am looking forward to see how it does once we get past Wash DC traffic.
Problem is we are leaving at 2pm and should be lucky enough to hit rush hour. Oh the joy. Maybe the real time traffic will help.
I don't do alot of stop and go driving, no quick accelerations, and I haven't used the paddle shifters.
Rich
People that are getting 15mpg must be doing lots of cold starts and stop-and-go driving. No gasoline engine is efficient in those situations (though maybe electric might be). I think the RDX's MPG is great (for a 2 ton vehicle) on the open road.
143/9.11 = 15.7mpg (Trip Computer Show 15.8mpg)
Location, 95% local drive 5% highway in the Bay area CA.
I drive it very easy and slow since it's still breaking in..... but 15.7 doesn't sounds good. what do you think ?
80% highway and 20% city in varied terrain of pacific northwest. I think 20mpg is probably the average depends on the driving habit. I don't hammer the gas and use cruise control on highway. And open window/roof instead of AC in local.
Result" I got 25+ out of the first tank and 26.5 out of the second. Pumping the tires to about 40psi was the only thing I really did for trip prep. This might be the point where I really started to love the RDX again.
Since most of the time you spend driving the RDX you are off-boost you are sacrificing a serious level of FE improvement for the rare and brief periods of "on-boost" acceleration.
Mill the engine head to raise the CR to the "standard" of 10:1 and "wire" the turbo wastegate fully open and you will likely see an FE improvement in the range of 30-50%
Or even better use VVT-i to dynamically change the CR from Atkinson cycle mode for cruising but into the Miller cycle as boost rises.
So much for TURBOCHARGING...!!
The traditional ease the pedal acceleration won't save gas?
330.7 miles/14.966 gallons = 22.1 miles/gallon
Love the boost when you need to merge and pass. The handling is phenomenal on the twisty mountain climbs and descents! I admit that I went pretty easy on the gas pedal as the engine is still breaking in, but I still has numerous full-on accelerations to merge and pass on the freeways. Gas mileage was probably improved as descending from the mountains was most engine braking and little to no throttle.
The only negative so far is that the navi got lost in the heavy tree cover of the SF mountains.
720 miles/35.196 gallons = ~20.5mpg
Not bad considering we were rolling through high elevations so the boost was kicking in even while descending.
The drive down CA-1 was a BLAST! I finally got to really test the SH-AWD. I'm not sure, but I think the VSC kicked in on one corner that I overcooked. It was both downright terrifying and thrilling at the same time. There was no way I was going to take my eyes off the road and glance down to check how many bars I was up to, but on one sweeping corner I saw the meter go up to 3 bars.
We also had a huge scare and almost ran out of gas on N101. The low fuel indicator had gone off, but I thought I could go another 50 miles before it got serious and we'd have to look for a gas station. The low fuel light had gone off on me before. That time I went 40 miles and found out that I still had 4+ gallons left in the tank when I filled up. Luckily, my GF is from the area so she knew that there was a 24 hr gas station near Garberville. When we filled up I was surprised that we put in 17.3 gallons! I thought we'd have ~3 gallons left! I'm not sure if we would have made it to Garberville. We'll fill up when it gets down to 1/4 tank next time.
This brings up an issue I have with the navi system. Little towns with little to no services show up (Leggett, Piercy), but bigger towns with (ie., Cloverdale) don't unless you zoom all the way in. I don't think that gas station showed up on the RDX navi system, either. My Garmin handheld GPS is much better and more reliable. If I didn't have a "local" with me I could have been in serious trouble.
Why..?
Most of the time the RDX runs in detuned/"derated" mode. During "cruise" mode the compression ratio is significantly reduced from the Otto mode standard.
I am "breaking" her in, about 500 miles, and drive 10% city, 90% highway, averaging about 22.5-23.5 on the trip computer.
Average speed is 69 mph acc to computer.
I floor it here and there, but largely feather, stay out of boost, and my range is close to 350 miles to a tank so far. . .I should hit 400. . .will keep everyone posted. . .the new DFI def should improve mileage. . .
Remember EPA revised all mileage estimates in 2009 because of the "cash for clunker" program, so estimates are off in FAVOR of more mpg apparently now. . .
oddly enough, I'm getting the same mileage as my 2005 Evolution VIII which was 800lbs lighter. . .go figure, technology. . .
First tank averaged 24-25.9 MPG in stop and go construction traffic on the highyway.
Second was about 23
Third has a little more around town driving and was about 21
and now on my 4th I am at 19.5.
On the highway, I'm pretty much 70mpg or lower 15 miles each way then local roads with stop and go for the other 5-6.
I try not to step on it and use the turbo as much on local roads, but occasionally I do have to use it. Same on the highway. I'm at about 800 or so miles so the engine is not totally broken in.
Shouldn't the average MPG go up as the car gets broken in? I'm not looking for 28mpg but 21-22 would be nice.
2014 Accord Touring
2014 Accord Touring
10:1 with certainty and maybe even as low as 7-8:1 if the turbo is to spin up really quickly and substantually raise the effective CR. So you can expect hwy FE about 20% lower than an equivalent displacement volume DFI engine.