How accurate are trip computers?

My mates Corolla 2.0 D4D - Could his Trip comp be overzealous?

The comp says the car is averaging about 52mpg (Average mpg figure)

When he filled up (55l tank he put in 50 and had done 475 miles) I worked it out to be 43.1mpg

My mate says "My diesel should be beating the pants of your petrol Felicia"

And I get 40-42MPG

Trip comps usually over read, but not by 10mpg. What ecomomy you get from each car - petrol or diesel is all down to the type of driving you do and type of driver you are. Heavy right foot = less mpg

I've found the Octy trip comp pretty good so far.

I think the easy answer is yes, a trip computer can be optimistic. A lot comes down to what type of driving he does and also how it calculates the mpg.

Not sure what the books for the Civic state as expected economy, but a) it's a heavy car and it's brand new so economy should improve.

Chris

mine was way out when I first got the car, but now it's over-reading by about 3-4mpg

There's different settings though on the trip comp

MPG what its getting at the current speed

and an "average mpg"

Think he should have got a VW based TDI like a Fabia instead or stop trusting his computer and electronics so much. When he had a 106 he worked out his mpg and cost per mile himself. Think he's going to start doing that again.

His engines done 40,000 miles so it should be running a lot better now. I don't know if any belts have been changed though.

*Edit* - A quick google and I found the Toyota forums

Corolla Mpg Computer, How Accurate? - Toyota Owners Club - UK Toyota Car Club

Looks like it's a common thing for Toyotas and it needs a reset.

His is excessively optomistic; I know the Octy's is optomistic in MPG modes, which seems really bizzare cos it's pretty spot-on in available range mode (based on fuel added), and your mate is using more fuel than I am between fills at similar mileage.

Think he should have got a VW based TDI like a Fabia instead

That's a bit of a drastic solution! My Fabia used to always record around the 50mpg (reset at each fillup) on the computer no matter how I drove it, but actual calculated mpg varied quite a bit with my worst being 43.8mpg.

It amazes me how the computer cannot be accurate as it must know how much fuel is injected and also how many miles have been covered?

Chris

seems like I'm averaging 43mpg at the moment, getting 350 miles to 37 litres, and it's showing 53 on the computer... hmm...

:(

It amazes me how the computer cannot be accurate as it must know how much fuel is injected and also how many miles have been covered?

Chris

I dunno - As far as I can tell it works out the current mpg from the position of your right foot...and I'm always prodding and poking mine trying to find the 'sweetspot' between high mpg on the instant mpg and torque on the road. It's always going to be optimistic because there are times when it doesn't know what's happening i.e. coasting or stuck in traffic. Anyway, I only treat it as an estimate (unless I'm telling colleagues how good my car is, especially the CTR owner ). At today's fillup it read an average of 48mpg - I got 45 litres in and 460 miles done = 46mpg actual.

My Dad on the other hand - his Mondeo GhiaX TDCi automatic is always out by sometimes as much as 5. I've tried explaining to him that it is just using educated guesses to give the figure to which his response is "well what's the point of having it if it isn't accurate?". Also worth mentioning that he's seen real improvements since he started using Millers - I think he's gone from averaging 36-7 to 39-40. I've not seen any MPG improvements at all, but I'm probably enjoying the extra grunt

Don't bother with trip computer - always use brim to brim method.

Hmm, I'll have to work out my real consumption on the Swift and see if it agrees with the computer. Depending on what trips I'm doing, I'll get anything from 32 to 38 average. I reset it's average regularly.

Bear n mind that when working this out, you should fill up at your chosen garage, then re-fill at the same pump before calculating to avoid any measurement error.

Bear n mind that when working this out, you should fill up at your chosen garage, then re-fill at the same pump before calculating to avoid any measurement error.

I usually fill up at the same 'angle' (presume this is partially what you mean) - nonetheless using this method will, over a period of time, produce reasonably accurate figures.

BTW - son has 1.5 Swift - what a good little motor

If you want to get anal about "removing sources of errors", you should alway fill up at the same pump, faced the same way, the same Polar distance from pump to nozzle, and average figures over 6 months or so.

I dunno - As far as I can tell it works out the current mpg from the position of your right foot...

Yes - which is directly related to the amount of fuel going into the engine. And it knows when the car is stationary because the number of miles being covered doesn't change. Bottom line is the ECU should know how much fuel is being injected and because the car records the number of miles covered it must know the distance.

Chris

If you want to get anal about "removing sources of errors", you should alway fill up at the same pump, faced the same way, the same Polar distance from pump to nozzle, and average figures over 6 months or so.

Agreed there are just too many variables (including the pumps being recalibrated!) that are outside human control. Still, who cares aboout mpg

Chris

Yes - which is directly related to the amount of fuel going into the engine. And it knows when the car is stationary because the number of miles being covered doesn't change. Bottom line is the ECU should know how much fuel is being injected and because the car records the number of miles covered it must know the distance.

Chris

And, as I said earlier,, on the Octy the mpg modes are optomistic, but the available range calculation seems about right based on back calculating consumption and available range from amount to fill tank.

Also worth mentioning that he's seen real improvements since he started using Millers

I'm assuming you don't mean Millers the Lager

I'm assuming you don't mean Millers the Lager

Yeah, why, what do you use? :confused: