Probably a daft question but how accurate is the sat nav when calculating a road trip?
Does it go off the previous w/mile my actual car has achieved?
I’m getting quite a discrepancy between ABRP and the cars own nav when I try and play it safe and add extra passengers, slight headwind, that sort of thing into the ABRP site.
My experience:
ABRP is pretty accurate (I have a 2016 MS70), and especially useful for checking the effect of temperature, extra passengers, headwinds etc. - combined with Google for typical traffic conditions this is the best bet for crystal ball gazing.
The on-board Nav is also extremely accurate but doesn't have the benefit of knowing what the driving conditions will be like before you set off if it's a trip in the future, in that case it also doesn't know what SOC you plan to leave with etc.. It does seem to vary seasonally so my current theory is:
- Nav algorithm doesn't take account of previous driving style (evidence: if I plan a long trip after weeks of short commutes with high Wh/mi consumption it doesn't seem to change its predictions);
- Nav algorithm does take account of prevailing traffic conditions and ambient temperature (evidence: predicted % at arrival / range for long trips changes over the seasons, e.g. more power use predicted in the winter, Nav will re-route for heavy traffic);
- Nav algorithm doesn't take account of reduced charging rate - my peak Supercharging speed is somewhat lower than when new and although this is controlled by the car systems it isn't fed back to the Nav as far as I can see. Evidence: a predicted 30 minute Supercharger stop might take 40-45 minutes for example. Predicted charging time seems to relate to when the car was new. It also depends on sharing with other cars so it's not the end of the world but the time can add up on multi-stop trips.
My car has ~95% of original battery capacity so the overall range loss (~10 miles) isn't really an issue for trip planning.
What the on-board Nav is excellent at doing, though, is adjusting its predictions as you're driving. So if there's a risk you won't have enough charge to reach your destination you'll be warned early on, and really all you need to do is moderate your speed (it tells you to stay below 65/60/50 etc. depending how much power it thinks you need to conserve).
In summary if the Nav says you can make it, you'll be fine, but it might take a bit longer if you have to conserve energy or charging stops take a bit longer. If you want to play with variables for future trip planning/multi-stop journeys I'd use ABRP which is more accurate in terms of energy use and charging times (although it can be a bit optimistic for the point-point travel times).
