2017 REx's surprisingly low range increase

Although there are several errors in this InsideEV's article about the 2017 REx, it does point out the surprisingly low all electric and gasoline range increases for the 2017 REx.

The 94aH battery pack's 45% increase in usable capacity results in a 2017 BEV's range increase of 41% (114 mi / 81 mi). Maybe the slightly heavier weight of the 2017 i3 explains the 4% discrepancy. However, the REx's all-electric range increases only 35% (97 mi / 72 mi) for a 10% discrepancy.

Despite the usable gasoline tank's 26% size increase (2.4 gal / 1.9 gal), the REx's gasoline range increases only 6% for a whopping 20% discrepancy.

These E.P.A. range ratings make the 2017 REx look like a pretty disappointing upgrade.

Anyone have any explanations for these REx range discrepancies?

Just a hypothesis: on both sides of the Atlantic car manufacturers have recently been busted for cheating and fudging the emissions and efficiency regulations. It also appears that the numbers advertised are more on the corporate honor system, rather than after real-world independant testing. So rather than risk joining this parade of infamy, maybe just maybe BMW has now decided to get out ahead and declare more realistic numbers up front.

But wouldn't BMW have declared a similar very conservative range for the 2017 BEV? The range rating for the 2017 BEV seems a bit conservative, but the range rating for the 2017 REx seems very low.

I'm sure we'll understand as soon as we learn more about the 2017 North American REx.

I read somewhere that the 2017 version of the REx increased power from a max of 34 to 38Hp. The REx does not operate at full speed all of the time, it adjusts somewhat. But, for those people that insist on driving it at highway speeds, uphill, with everything on, those extra 4Hp might give it enough extra capacity to keep going...you don't get something for nothing. That might account for the difference in reported REx range add-on. THen, again, until officially released in the USA, hard to tell exactly what the specs are. As in most any vehicle, how you drive it will affect your maximum range and efficiency.

jadnashuanh said:

THen, again, until officially released in the USA, hard to tell exactly what the specs are.

Click to expand...

It has been officially released in the U.S. with the first cars now in dealer hands. Below is a photo of the Monroney sticker on a 2017 REx. Also note the incredibly poor fuel economy, greenhouse gas, and smog ratings which certainly must be a mistake.

Does it say anything about max power output...in a quick scan, did not see anything. Unlike a conventional ICE, the output of the REx is not directly controlled by road speed...it's load related. If you assume a higher load, and because it is potentially capable of a higher output, one could expect the MPG on the REx to go down with a power increase. Real world, verses test conditions could easily differ significantly - depends on how you drive it. Sort of like running at 50mph verses 80mph on an ICE...the EPA ratings do not take that into account.

alohart said:

jadnashuanh said:

THen, again, until officially released in the USA, hard to tell exactly what the specs are.

Click to expand...

It has been officially released in the U.S. with the first cars now in dealer hands. Below is a photo of the Monroney sticker on a 2017 REx. Also note the incredibly poor fuel economy, greenhouse gas, and smog ratings which certainly must be a mistake.

Click to expand...

Thankfully I scored my 2014 before the 2017 showed up.

Bob Wilson

In thinking about this a bit more, and this is just speculation, in response to those that filed a lawsuit regarding the 'unsafe loss of power' when the REx is running under high load and the SOC drops too low, it is also possible that BMW chose to raise the amount of normally unavailable power in the battery, to allow it's use in those stressed situations as outlined above. As a result, you won't be able to use as much of the battery as in the BEV. Throw in that at least some reports indicated that the output of the REx was increased to 38Hp, and your mileage results will drop. If you disregard all of the indications and warnings, though, you can still get into that situation, so (IMHO), the majority of people buying the car will have it somewhat compromised for those that refused to read and understand the operators manual. Those that do understand their cars may now be inconvenienced by the lower improvements provided to the others. I wonder if this is similar to the vehicles provided to other, less litigious markets?

The moderate increase in REX range from 2016 -> 2017 can be explained by the additional power BMW bestowed upon the REX engine. The old REX got 40MPG, while the new REX is rated at 35MPG (due to the higher engine output now avail), presumably due to the lawsuits brought by customers over the REX losing power when climbing hills.

My approach is to get the roll down coefficients for any car and the make a spreadsheet showing the drag HP vs mph. I'd already done that for our 2014 and the only thing that jumps out is the low thermodynamic efficiency of the engine. Driving benchmarks have also suggested the control laws are buggered.

The first thing I would do is modify the control laws so the engine always runs at peak efficiency and banks excess charge into the battery. That alone would be a step up. So the engine would have: warm-up; peak efficiency, and; off.

My next speculation is to tap the exhaust just after the muffler; cool it, and; meter it into the intake manifold. This will have the effect of letting the throttle plate open up further, reducing pumping losses. WARNING: carbon monoxide gas is deadly! Do not do this too casually.

I don't know if it has Adkinson valve timing but that would help too. In effect it pushes part of the fuel-air charge back into the manifold for the next cylinder but it also means the throttle plate can be further opened, again reducing pumping losses. But there are low-hanging fruit including doubling the gas tank capacity to 4 gallons. This would cut the number of fuel stops in half and significantly improve the block-to-block time.

Then there are the aerodynamic tweaks but we can chat about them another day.

Bob Wilson

FWIW, I'm pretty certain that BMW adjusts the REx speed to minimize cabin noises. I do not know if tweaking the range hold would allow it to recharge more verses holding. ON some of their other hybrids, they give you the option to use the ICE to fully recharge the battery pack so that, say, when you get to the city or other area where you want or need EV power...you've got the max. But, those have significantly larger ICE engines and aren't serial hybrids, but parallel ones.