So I have finally got out with my Panda on the open road with the TMC tuning box and have got some fuel figures. I did a 200km round trip, driving sedately for most of it, and mostly in 100km/h or 110km/h zones.

Half in Eco mode, half in normal mode. On standard wheels (I have sold the 17in alloys).

6.3L/100km on the trip computer.

Yes, I need to re-fuel the car to make sure the TC isn't off with the fairies but so far it has proven very close to tank refuelling checks.

I don't drive the Panda every day, it is a back-up car really, so fuel consumption is not a deal-breaker. Yet I can't help but feel a bit disappointed with the results.

I think, it is not to bad.
I see mostly 7.4L/100km with my standard 85TA. (never use ECO mode)
These are mostly combined commutes with speeds between 50-130 Km/h.

I'm using the 95 octane they supply here - one assumes it actually is

Normal driving for me, which isn't aggressive but I do attack corners and roundabouts (gotta get my jollies ). Basically all around the city and usually in heavy traffic but I do get to play on the Expressway for short periods. Very steep hill I have to climb every day and she gets flogged up that.

Currently 6,600 km on the clock. When I first got her, she was showing 6.4 L/100km but I reset my trip computer every third fill up or so and it's been coming down. Currently it's showing 6.0 L/100 km which I'm pretty happy with.

Standard TA motor and it'll stay that way until I'm out of warranty. Maybe it's the tuning box that's doing the 'damage' to your fuel consumption.,

You need to do a tank to tank test. Most "tuning" boxes mess with the mixture by fudging It's also worth checking the speedometer against a GPS ( at lest 20 seconds constant speed and straight line for most accurate reading) as if it is over reading that will also give "improved" fuel consumption.

Robert G8RPI.

g8rpi said:

You need to do a tank to tank test. Most "tuning" boxes mess with the mixture by fudging It's also worth checking the speedometer against a GPS ( at lest 20 seconds constant speed and straight line for most accurate reading) as if it is over reading that will also give "improved" fuel consumption.

Robert G8RPI.

Click to expand...

Does the speedo over reading mean the odometer will also be over reading?
I thought it didn't.

I'll test with the mile markers on the motorway.

g8rpi said:

You need to do a tank to tank test.......

Robert G8RPI.

Click to expand...

The only way i do it.

deeyup said:

Does the speedo over reading mean the odometer will also be over reading?
I thought it didn't.

I'll test with the mile markers on the motorway.

Click to expand...

Hi,
The spedo and odometer are linked. If the speedo over reads so does the odometer.
In the old mechnical ones the odometer counted the number of turns of the input shaft (linked to wheels) and the pointer showed the rate of rotation using a drag cup and spring. You get speed by integrating distance over time. The electronic units do the same with a microprocessor but fundamentally count a string of pulses generated by the wheels turning. A error or change in wheel size will affect both speed and distance travelled.

Robert G8RPI.

They are linked, but you could put the numbers on the speedo anywhere you like. The resting pin of my old Vespa's speedo was at 5mph, but of course my miles weren't going up whilst it was parked up.

I think a check against known distances is needed.

Okay, i did a little unscientific test on my way to work.

The markers on the hard shoulder of UK motorways show every 100m
I reset my trip at one and counted 16. 1609m is a mile so near as damn it.

I found my odometer to be spot on. Exactly 1 mile clicked over as I passed marker 16.

According to sat nav my speedo is nearly 10% over reading. A good way to check is to set Cruise control at 60mph and time 60 seconds. Even better would be do the same over 5 miles for better accuracy.

I did this in my Nissan Leaf, but will try again in the Panda next time I take it to work to see how that fares, but for sure in the Leaf, the speedo is out, and the odo is correct.

Sorry to highjack the thread btw

deeyup said:

Okay, i did a little unscientific test on my way to work.

The markers on the hard shoulder of UK motorways show every 100m
I reset my trip at one and counted 16. 1609m is a mile so near as damn it.

I found my odometer to be spot on. Exactly 1 mile clicked over as I passed marker 16.

According to sat nav my speedo is nearly 10% over reading. A good way to check is to set Cruise control at 60mph and time 60 seconds. Even better would be do the same over 5 miles for better accuracy.

I did this in my Nissan Leaf, but will try again in the Panda next time I take it to work to see how that fares, but for sure in the Leaf, the speedo is out, and the odo is correct.

Sorry to highjack the thread btw

Click to expand...

This indicates that the basic sensor / gear ratio / wheel size is accurate but it looks like they have programmed the speedometer to over-read. This would be to meet the requirement to not under read given worst torerances of tyre size etc. If you change the tyre size both odometer and spedometer will be affected. For a GPS speed check just use the speed function on the GPS. On some the satellite data screen will give a speed with greater resolution.

Robert G8RPI.

g8rpi said:

This indicates that the basic sensor / gear ratio / wheel size is accurate but it looks like they have programmed the speedometer to over-read. This would be to meet the requirement to not under read given worst torerances of tyre size etc. If you change the tyre size both odometer and spedometer will be affected. For a GPS speed check just use the speed function on the GPS. On some the satellite data screen will give a speed with greater resolution.

Robert G8RPI.

Click to expand...

This is exactly what I was getting at.

g8rpi said:

You need to do a tank to tank test. Most "tuning" boxes mess with the mixture by fudging It's also worth checking the speedometer against a GPS ( at lest 20 seconds constant speed and straight line for most accurate reading) as if it is over reading that will also give "improved" fuel consumption.

Robert G8RPI.

Click to expand...

Yes, this.

I did a tank-to-tank, half the economy run I did at 6.3L/100km showing on the TC, the other half towing my camper. End result? 7.5L/100km on the TC, 6.7L/100km actual.

6.7L/100km is approx. 42mpg, which is thoroughly reasonable I think, all things considered!

g8rpi said:

This indicates that the basic sensor / gear ratio / wheel size is accurate but it looks like they have programmed the speedometer to over-read. This would be to meet the requirement to not under read given worst torerances of tyre size etc. If you change the tyre size both odometer and spedometer will be affected. For a GPS speed check just use the speed function on the GPS. On some the satellite data screen will give a speed with greater resolution.

Robert G8RPI.

Click to expand...

My TomTom live always says I'm doing 66 or 67 when the speedo says 70.....

triumph7 said:

My TomTom live always says I'm doing 66 or 67 when the speedo says 70.....

Click to expand...

Exactly - nearly every production car speedo will over-read by between 5-7%, for all the reasons discussed above. Regardless of what the dash-displayed MPG figure says, you will only ever get a truly accurate economy figure by doing a proper brim-to-brim test and then ideally doing this each and every fill-up. My current TA 4x4 has averaged exactly 40.74mpg over 15,652 miles. Not outstanding, but better than the Audi S4 I had before...

Based on what I've read here, I decided to order a box from TMC. They were very helpful over the phone, even letting me know that there a cheaper option available for the Twinair (its a 2-channel box, found in the Abarth section), so I paid £202 inc VAT instead of the £360 for regular box. The more expensive one has more channels available but as only two are used for the TA, the cheaper box is fine.
I checked with my insurance company (Directlne) and for an "up to 20% increase" they are adding just £15 extra for the remaining 6 months of the policy. As the 10bhp claimed gain is around a 12% increase, I think its a very reasonable increase in premium.
I've only taken it for a quick spin around the block but the results are definitely worth it! I'll report back with the MPG figures later...