BimmerFest BMW Forum banner

1 - 11 of 11 Posts

·
tympj
Joined
·
208 Posts
Discussion Starter #1
Drove over 850 miles over July 4th weekend with no issues. Went from MA to Burlington VT up Rte 89 to Montreal back to Waterville Valley NH back home. Fun driving trip because no encounters with moose or deer. However, we counted 7 dead deer along the way up and back. I averaged 37.4 mpg in EcoPro with moonroof open most of the way and some AC used. Had cruise on 70 to avoid any tickets. Haven't been to Burlington VT since late 70's. First time visit to Montreal but 45 minutes to an hour to get thru border patrol. Nice people in Montreal since someone warned me not to park in a certain area while they were driving by us. Found garage parking so I didn't have to worry about the car. Only regret, visit wasn't long enough but still enjoyed what we experienced.

Here's the trip computer of drive back from Waterville Valley NH to home. No traffic at all on Monday July 4th coming home in the morning which shocked me. This demonstrates the potential mileage with EcoPro that is possible with the right driving conditions.
 

Attachments

·
Registered
Joined
·
10,967 Posts
That's amazing. You wouldn't have done much better with a Prius. (Hybrid's don't have much advantage on the highway.)

EcoPro fiddles with the AC performance. So, I stick with "Sport" here in Florida.

Thanks to that deflector that comes up when you open the sunroof there's dead air there. So, opening the roof doesn't hurt MPG that much.

Keeping you speed down contributed to your exceptional MPG. Aerodynamic drag is roughly proportional to the square of velocity. So, going 80 MPH results in 30% more drag than 70 MPH (80^2/70^2).

BMW's put a lot of effort into fuel economy (VANOS, Valvetronic, turbocharging, direct injection, smart battery charging, electric water pumps, electric power steering, high-efficiency wheel bearings, aluminum body panels, etc., etc., etc.). Mercedes-Benz is slowly catching up. Their pre-2014 gasoline V6's were gas hogs, though.

The higher your MPG, the less is accomplished by further increasing your MPG, "accomplishment" being fuel used for a specific distance. So, going from 20 MPG to 30 MPG accomplishes more than going from 30 MPG to 40 MPG. Here's a graph of Gallons/10k miles vs. MPG. The higher the MPG the flatter the line goes. That's why Priuses (Prei) will never pay for themselves until gas hits about $10/gallon.

My 2014 535i with a manual transmission gets about 29.5 MPG on road trips. But, that's going about 78 MPH. I have DHP, which I turn to Comfort on the interstate to turn off the active suspension's hydraulic pump. When I ditch the RFT's soon, I expect to see a 1 to 2% improvement, hopefully breaking 30 MPG. I have my Excel spreadsheet auto-format to turn my MPG cells' background bright green when I hit 30 MPG.... I am such an Excel geek.
 

Attachments

·
Registered
Joined
·
463 Posts
That's amazing. You wouldn't have done much better with a Prius. (Hybrid's don't have much advantage on the highway.)

EcoPro fiddles with the AC performance. So, I stick with "Sport" here in Florida.

Thanks to that deflector that comes up when you open the sunroof there's dead air there. So, opening the roof doesn't hurt MPG that much.

Keeping you speed down contributed to your exceptional MPG. Aerodynamic drag is roughly proportional to the square of velocity. So, going 80 MPH results in 30% more drag than 70 MPH (80^2/70^2).

BMW's put a lot of effort into fuel economy (VANOS, Valvetronic, turbocharging, direct injection, smart battery charging, electric water pumps, electric power steering, high-efficiency wheel bearings, aluminum body panels, etc., etc., etc.). Mercedes-Benz is slowly catching up. Their pre-2014 gasoline V6's were gas hogs, though.

The higher your MPG, the less is accomplished by further increasing your MPG, "accomplishment" being fuel used for a specific distance. So, going from 20 MPG to 30 MPG accomplishes more than going from 30 MPG to 40 MPG. Here's a graph of Gallons/10k miles vs. MPG. The higher the MPG the flatter the line goes. That's why Priuses (Prei) will never pay for themselves until gas hits about $10/gallon.

My 2014 535i with a manual transmission gets about 29.5 MPG on road trips. But, that's going about 78 MPH. I have DHP, which I turn to Comfort on the interstate to turn off the active suspension's hydraulic pump. When I ditch the RFT's soon, I expect to see a 1 to 2% improvement, hopefully breaking 30 MPG. I have my Excel spreadsheet auto-format to turn my MPG cells' background bright green when I hit 30 MPG.... I am such an Excel geek.
That's a great write up, I wish more posts were like this.
 

·
Registered
Joined
·
9 Posts
That's a great write up, I wish more posts were like this.
+1. As a newly expecting car owner (I feel like an expecting mother), one of my passions lately has been reading up on car performance in general--17'' wheels vs. 18 vs. 19, suspension, handling, etc.--so a detailed analysis about MPG, drag, fuel consumption was an interesting read (it's amazing how little I knew about cars before last month).

Thanks for sharing your trip, OP. Sounds like it was a good one. My wife and I have been traveling by car a lot since we arrived in Germany, but we already have a 1500 mile journey planned once we receive and break in the upcoming 2017 340i--from the base to Salzburg, to Prague, back to the base, though I don't expect to get gas mileage as good as yours when I'm hoping our average speed on the autobahn is 125 mph+ :)
 

·
Registered
Joined
·
13,061 Posts
My 2014 535i with a manual transmission gets about 29.5 MPG on road trips. But, that's going about 78 MPH. I have DHP, which I turn to Comfort on the interstate to turn off the active suspension's hydraulic pump. When I ditch the RFT's soon, I expect to see a 1 to 2% improvement, hopefully breaking 30 MPG. I have my Excel spreadsheet auto-format to turn my MPG cells' background bright green when I hit 30 MPG.... I am such an Excel geek.
Why does RFT hurt mpg? Some RFT's have low rolling resistance and that can help mpg.
 

·
Registered
Joined
·
10,967 Posts
Why does RFT hurt mpg? Some RFT's have low rolling resistance and that can help mpg.
The best way to explain this is to first explain how a radial tires works, and then explain how a RFT negates the advantages of a radial tire.

Radial tires have cords (that don't stretch) only in the radial direction in the sidewalls (parallel to the radius line extending from the center of the axle). Having cords only in the radial direction allows the rubber sidewalls to stretch in the tangential direction (90 degrees from the radial direction). This is why a radial tire has a "radial bulge' in the sidewall at the bottom even when properly inflated. The sidewall stretching allows the more rigid tread to deform, forming a flat surface to conform to the flat road surface.

A partially deflated flat soccer or basket ball can be easily deformed. But, the deformed area is not flat. Instead, it is concave, sort of a crater in the surface of the ball. But the total surface area of the ball remains the same. (This deformation without stretching is also why paint-less dent repair works, but only on originally concave surfaces. Hail dents in an F10 concave-surfaced hood or trunk lid would not lend themselves well to paint-less dent repair.)

Bias or "diagonal" ply tires have cords that are in multiple directions in the sidewalls. This prevents the sidewall from significantly stretching or changing the tire's total surface area. Like the partially deflated soccer ball or basketball, the total surface area of the bias-ply tire remains effectively constant. The relatively rigid sidewall causes the area of the tread in contact the road to try to turn inside out, becoming concave, like on the partially inflated ball. This causes the contact patch to squirm (scuff against the road) as it becomes concave. This reduces the tread life of the tire, reduces traction, and increases rolling resistance. It also concentrates the weight of the vehicle and tread wear around the periphery of the contact patch of the tread, especially on the inner and outer edges.

The rigid walls of an RFT, even a radial-ply RFT, diminish the ability of the sidewalls to stretch in the tangential direction and allowing the tread to conform to the road surface, similar to a bias-ply tire.

I have RFT's on my 535i, and even with 18% over-inflation, the outer parts of the tread is wearing about 50% faster than the middle of the tread.

Just for curiosity, I did a tire search on TireRack.com for my F10 535i, filtering "low rolling resistance" and "run-flat." As I suspected, there were zero matches that met both of these requirements.

Here's an article on Edmonds.com where the head of GM's tire engineering group says, almost in passing, that RTF's have increased rolling resistance. He also said that about half of the people with a flat tire and a spare call a roadside assistance, anyway.

http://www.edmunds.com/car-buying/the-disappearing-spare-tire.html

I'm old enough to remember when new cars came with bias-ply tires. Radial tires and front disc brakes were in the optional sport package on my 1976 VW Rabbit. The radial tires increased the top speed from 93 MPH to 100 MPH. So, the additional rolling resistance of bias-ply tires is significant.

I'm having a hard time finding a link that quantifies the additional rolling resistance of RFT's. I remember reading one to two percent somewhere. But, here's a Tire Rack comparison of two non-RFTs to two RFT's. The Bridgestone RFT got 3.37% less MPG than the non-RFT Kumho. The non-RFT Michelin and RFT Pirelli both got 1.1% less MPG than the non-RFT Kumho. This is sort of an apples-to-oranges test, and field testing also has a lot of unknown variables that laboratory testing doesn't.

http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=158

Update: Here's the quote of GM saying RFT's give up one to two percent in fuel economy: http://www.autosafety.org/air-runs-out-run-flat-tires/
 

Attachments

·
Registered
Joined
·
1,002 Posts
Speed is really the biggest factor. Much more so than your tires over the long run though.

Driving from San Diego to Seattle and back I averaged 74.5 mph on the on board computer (cruse control at 80 90% of the time, even through the passes).

Via hand calculation and the on board system I averaged just about 40 mpg in the diesel. If I had been doing 65 for the whole way I would have gotten 50. Those 15 mph cost me 20% fuel economy realistically. But they saved me 10 hours of driving time over the entire round trip :)
 

·
Registered
Joined
·
4,941 Posts
Speed is really the biggest factor. Much more so than your tires over the long run though.

Driving from San Diego to Seattle and back I averaged 74.5 mph on the on board computer (cruse control at 80 90% of the time, even through the passes).

Via hand calculation and the on board system I averaged just about 40 mpg in the diesel. If I had been doing 65 for the whole way I would have gotten 50. Those 15 mph cost me 20% fuel economy realistically. But they saved me 10 hours of driving time over the entire round trip :)
in my 320 I average 37 doing 75, never drove a whole trip doing 80, would be interesting though, but you also have x drive, which would account for less MPG.
 

·
Registered
Joined
·
10,967 Posts
91 AKI is not available where I live. I make my own 91 AKI by blending 1/3 87 AKI an 2/3 93 AKI. The car might run slightly better and might get slightly better MPG with pure 93 AKI. But.... I like savings the money... about $0.18/gallon, about $3.10/17 gallon fill-up. I'm planning on doing a future road trip on 93 AKI to see if the MPG is appreciably better.
 

·
Registered
Joined
·
295 Posts
428xi here. Best I hit was 37.7 mpg driving +75 mph for 300 miles (calculated by gallons filled and distance). Amazed with this and probably would have crushed it with diesel. I'll probably look for a diesel wagon in the next few years (if it is still offered in the US).
 
1 - 11 of 11 Posts
Top