Can you record in MPH ?

Pinseeker · Post by **Pinseeker** » Sun Nov 23, 2014 5:03 pm

Is there a way to record in MPH ?

Post by **Harry** » Sun Nov 23, 2014 8:10 pm

Yes, certainly. LapTimer switches between Imperial and Metric units based in the system settings (language/country, check Settings app). In case you do not agree with your country's settings, you can override unit selections in LapTimer / Settings / Display / Units.

Harry

gplracerx · Post by **gplracerx** » Sun Nov 23, 2014 8:49 pm

Unfortunately, 1 Imperial gallon is 1.20095 US gallons. Mentally adding 20% to the gal reading in the OBDII output is slightly annoying. I'm assuming that value is calculated, as it goes to INF when the car isn't moving but the engine is running. If it were a simple fuel flow rate, it shouldn't do that.

Post by **Harry** » Sun Nov 23, 2014 10:59 pm

The gallons shown in LapTimer are US gallons - just to clarify. LapTimer uses the terms "Metric" and "Imperial" to categorize the sets of units used, in this case it is not consistent. I have no plans to further differentiate that topic, neither to introduce another gallon. For the majority it is fine. For U.K. there is a special issue. Most users expect imperial units, while the UK seems to have adopted the metric system formally. This seems to be the reason iOS selects "metric" for the UK and users need to switch manually in case they prefer the imperial system.

Gallons are used in two situations: fuel tank volume (new feature in v19) and miles per gallon. The later is calculated from MAF - which means it is based on flow rate. But: to calculate mpg, one needs to add speed to the formula. "Driving" with zero speed results in an infinit (INF) consumption per mile.

Anecdotal: I remember the times when mpg gauges were introduced to cars (some 20 to 30 years ago). While most cars switched to zero consumption when standing in front of a traffic light - and nobody asked if this is correct, BMW did it the other way around. This in turn has been often perceived as "wrong" - although it is correct.

- Harry

gplracerx · Post by **gplracerx** » Mon Nov 24, 2014 3:36 am

OK.

But the box label just says gal and the number is too small to be mpg. In normal driving I see numbers in the range of 1-4;, which would be about right for gallons/hour. Does that mean you calculate gallons/hour from MAF and an air/fuel ratio, calculate mpg by dividing speed by gallons/hour, and then convert back to gallons/hour by dividing speed by mpg? The result at 0 speed would then be zero/zero, which is undefined and could have any value.

Post by **Harry** » Mon Nov 24, 2014 8:24 am

Interesting enough I have never received a question on this (and haven't thought about either)... Natively, LapTimer calculates liter/100km - which is the standard for Europe. The value is converted to gal/100km by the unit system, but that's certainly not mpg and will go towards infinity if you make no km

mpg should be zero when not driving. Forget about the story above - that's an European story too. I will add the missing conversion to mpg to the next major release.

Harry

Pinseeker · Post by **Pinseeker** » Mon Nov 24, 2014 10:02 am

Thanks for the reply. I was looking for a specific setting for MPH so no wonder I couldn't find it lol.

Post by **Harry** » Mon Nov 24, 2014 10:53 am

Pinseeker wrote:Thanks for the reply. I was looking for a specific setting for MPH so no wonder I couldn't find it lol.

LapTimer's engine is quite a complex beast and has unit handling deeply integrated into everything. Sometimes I need to laugh out load when apps are advertise to really really support metric and imperial units - and provide a manual settings. An anachronism from my point of view. The remaining issue is the one with the two systems in the U.K.

- Harry