What is the Actual Power of the i3?

BMW advertises their motor is 125 kW (170 hp). Unfortunately, the math doesn't add up.

• 1 hp = 746 watts
  1 kW = 1.34 hp
  170 hp = 127 kW
  125 kW = 167.5 hp

What's the right answer?

I've seen it given as 167bhp in some publications, I'd imagine the 170bhp is just a rounded up figure.

Zzzoom3 said:

BMW advertises their motor is 125 kW (170 hp). Unfortunately, the math doesn't add up.

Click to expand...

I assume you got that from the "Features & Specs" specification sheet. Did you also notice that the i3 has "2.8-11.8" unit-less cargo volume (and these are highly improbably values for any units)? Also, it has for "Max permissible weight/load" three values of "0.29/2.38/0.69" which are also without units. They have known about these latter two spec errors for at least 5 weeks (since I let BMW know).

Zzzoom3 said:

BMW advertises their motor is 125 kW (170 hp). Unfortunately, the math doesn't add up.

• 1 hp = 746 watts
  1 kW = 1.34 hp
  170 hp = 127 kW
  125 kW = 167.5 hp

What's the right answer?

Click to expand...

Obviously 125kw!

Hp (Ps) is not the same as bhp!
Tahat is why there are differences!

170 European Hp are 167,6 Bhp and that are exactly 125 kW.

DeJay58 said:

Hp (Ps) is not the same as bhp!
Tahat is why there are differences!

170 European Hp are 167,6 Bhp and that are exactly 125 kW.

Click to expand...

I thought BHP was Brake HP measured at the wheels, after passing through the drive train, where (non-B) HP typically refers to the output of the engine.

According to my conversion app, HP is given in three versions: International, Electric, and Metric. It says 170.00 metric HP is 167.61 electric HP, or 167.67 international HP. I would expect BMW to either list which HP standard they are using, or the default should be electric HP for rating an electric motor, at least on the spec sheet delivered to the US and marked for North America.

Is it just me, or have car manufacturers in general significantly reduced both the comprehensiveness and reliability of the specs they provide for their autos in the last decade?

i3Alan said:

DeJay58 said:

Hp (Ps) is not the same as bhp!
Tahat is why there are differences!

170 European Hp are 167,6 Bhp and that are exactly 125 kW.

Click to expand...

I thought BHP was Brake HP measured at the wheels, after passing through the drive train, where (non-B) HP typically refers to the output of the engine.

According to my conversion app, HP is given in three versions: International, Electric, and Metric. It says 170.00 metric HP is 167.61 electric HP, or 167.67 international HP. I would expect BMW to either list which HP standard they are using, or the default should be electric HP for rating an electric motor, at least on the spec sheet delivered to the US and marked for North America.

Is it just me, or have car manufacturers in general significantly reduced both the comprehensiveness and reliability of the specs they provide for their autos in the last decade?

Click to expand...

Accuracy as an engineer I agree, but really is 2.4 HP difference a big deal it is what it is no matter what you call it!

mindmachine said:

i3Alan said:

DeJay58 said:

Hp (Ps) is not the same as bhp!
Tahat is why there are differences!

170 European Hp are 167,6 Bhp and that are exactly 125 kW.

Click to expand...

I thought BHP was Brake HP measured at the wheels, after passing through the drive train, where (non-B) HP typically refers to the output of the engine.

According to my conversion app, HP is given in three versions: International, Electric, and Metric. It says 170.00 metric HP is 167.61 electric HP, or 167.67 international HP. I would expect BMW to either list which HP standard they are using, or the default should be electric HP for rating an electric motor, at least on the spec sheet delivered to the US and marked for North America.

Is it just me, or have car manufacturers in general significantly reduced both the comprehensiveness and reliability of the specs they provide for their autos in the last decade?

Click to expand...

Accuracy as an engineer I agree, but really is 2.4 HP difference a big deal it is what it is no matter what you call it!

Click to expand...

Tell us what it really is not what is deemed appropriate. I'll decide whether it's a big deal. Personally, I'd like to be able to trust in what I'm told not find out it isn't actually completely true. I don't understand the mentality that feels it's OK to tell partial truths. This is a slippery slope IMO ..

BMW is known for understating the power output of most of its vehicles. I like to look at it as if you got one on the low end of their allowable output range, it would still meet their specs...and, you might get lucky, and get one that has a bunch more. The tolerance on the control circuits is likely such that there is a variance from one to the other coming off of the production line. Going way back to science class, 167 and 170 are essentially the same unless one puts a decimal point at the end - that's less than 2% difference - well within the normal production variances. THen, not knowing the exact control logic, the motor may make more than that 170 for short periods of time, depending on the charge status, motor temp, battery temp, your throttle position, mode, etc. At least you don't have the variables of altitude with an ICE on output to contend with. You might get more than that variance based on the burnishing of the bearing surfaces over the first 1K miles or so.

IMHO, much to do about nothing...

170 European Hp are 167,6 Bhp and that are exactly 125 kW.[/quote]
I thought BHP was Brake HP measured at the wheels, after passing through the drive train, where (non-B) HP typically refers to the output of the engine.

According to my conversion app, HP is given in three versions: International, Electric, and Metric. It says 170.00 metric HP is 167.61 electric HP, or 167.67 international HP. I would expect BMW to either list which HP standard they are using, or the default should be electric HP for rating an electric motor, at least on the spec sheet delivered to the US and marked for North America.

Is it just me, or have car manufacturers in general significantly reduced both the comprehensiveness and reliability of the specs they provide for their autos in the last decade?[/quote]

Accuracy as an engineer I agree, but really is 2.4 HP difference a big deal it is what it is no matter what you call it![/quote]
Tell us what it really is not what is deemed appropriate. I'll decide whether it's a big deal. Personally, I'd like to be able to trust in what I'm told not find out it isn't actually completely true. I don't understand the mentality that feels it's OK to tell partial truths. This is a slippery slope IMO ..[/quote]

1.4% (really)is not a big deal! Heck the manufacturing tolerances will vary the output capacity of the system more than that. Like I said 125 KW is the correct number, you can see what they were doing in their rounding if you peruse the various pieces of information available on the car.

To answer your question about car manufacturers reducing what they tell you I think it is because of nit pickers who want everything spelled out to the nth-degree today and then nit pick the details on the internet blogs for minor variances or rounding strategy differences that amount to basically nothing important. Problem is people get too hung up on the minutiae today.

Expecting marketing folk to bother their heads about accurate copy is like expecting the tabloid press to let the truth get in the way of a good story.

Hi There,

ICE power output is changing with RPM,Temperature,Air pressure, Gasoline Quality etc. etc.
The rated ICE max power is a reliable output each ICE will have (except at >2000m altitude...)

Now it comes to I3 electric motor...
I have seen two diagrams
1. Torque [Nm] over rpm [1/min]. Up to 4000-6000 rpm the engine has max Torque of 250 Nm. (6000@360V, 4000@270V). Higher RPMs are causing losses due to electrical field and magnetic field issues...

2. Power [KW] over rpm [1/min]. max. 125KW (@4500 rpm and 360V). 0-4000 rpm increasing from 0kW to 90-125kW. at higher RPMs (up to 11.000rpm) slowly decreasing.

3. Thermal issue 1: Cooling system and electronics of electric motor / high voltage battery) are able to deliver 40kW permanently.
4. Thermal issue 2: 90kW can be hold for 30secs

Summary: Don't care about power output. You never did on your IPhone as long as graphics are smooth

BMW never used anything else then metric system for engine power out of historic reasons.
Official value is based on SI metrics always (Watt, named after James Watt who introduced HP only as illustration to the brand new electric power unit named after himself

1 metric HP =735,498 Watt. (ISO 1585:1992) (1 metric HP=m*g*v=75kg*9,81m/s²*1m/s=735,498 Watt
1 brake (not british) HP = 745,7 Watt. (higher thus it is measured without any engine losses (1 bhp = 33.000 lbf*ft/min = 550 lbf*ft/s)
1 electric HP = 746 Watt. (close to the british...)
1 SAE HP = 1,014 metric horsepower = 0,7457 kW (SAE J1349).

Got it
Summary: Use Watt from now on! Still based on test specification the output power is different..