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[05omegav6]

If a given version of a car does 20mpg, and petrol costs £1.30, I make that 30ppm...

If the same car does 18mpg on lpg, which costs £0.75, I make that 18ppm...

To put it another way, that's the same price as a diesel (£1.38) car doing 35mpg, ie 18ppm, but without a DMF, DPF or stupidly expensive fuel system.

What have I missed

[TheBoy]

Still uses a bit of petrol on the (fuel heavy) startup.

Savings are usually said to be around a third, so your figures aren't far off.

[Entwood]

If a given version of a car does 20mpg, and petrol costs £1.30, I make that 30ppm...

If the same car does 18mpg on lpg, which costs £0.75, I make that 18ppm...

To put it another way, that's the same price as a diesel (£1.38) car doing 35mpg, ie 18ppm, but without a DMF, DPF or stupidly expensive fuel system.

What have I missed

Not a lot ... small amount of petrol on startup, and cost of LPG conversion .. but right ball park

EDIT . must type faster ..

[TheBoy]

On the 3.2, I struggle to exceed 17mpg though. Mrs TB can usually get close to 21mpg.

[TheBoy]

I have my figures for TBE since I got it - petrol and LPG - but it syncs to PC upstairs, and thats switched off.

I could post tomorrow if I remember, if it helps?

[Entwood]

My actual is running at 17.12 pence/mile against an estimated 27.63 pence/mile if I was using petrol , and thats over 60,000 miles, around 10 pence/mile saving

On a far shorter run - yesterday - 190 miles - the saving was 14.82 pence /mile, but it was a sedate motorway cruise at around 60 most of the time, following a mate in his van ..

[05omegav6]

So hypothetically speaking, in fuel terms at least, this...

http://www.autotrader.co.uk/classified/advert/201401130998664/sort/default/usedcars/model/vxr8/postcode/rh202dg/page/1/make/vauxhall/radius/1501/onesearchad/used%2Cnearlynew%2Cnew?logcode=p

Should cost the same to run as this...

http://www.autotrader.co.uk/classified/advert/201401100942774/sort/default/usedcars/radius/1501/engine-size-cars/3l_to_3-9l/body-type/estate/model/vectra/maximum-age/up_to_6_years_old/fuel-type/diesel/page/1/onesearchad/used%2Cnearlynew%2Cnew/make/vauxhall/postcode/rh202dg?logcode=p

Have I missed anything else

[Entwood]

Using the urban cycle figures....

mmmm the Vectra does 28.8 mpg = (1.30 x 4.54)/28.8 = 16.24 pence /mile

The VXR8 does 13.7 mpg on petrol .. approx 10.96 mpg on LPG  (20% less) = (0.72 x 4.54)/10.96 = 29.8 pence / mile  so not quite close ...  (but closer than the VXR8 on petrol (1.3 x 4.54)/13.7 = 43.08 pence /mile  )

Not quite "Should cost the same to run as this.." IMHO ..

[chrisgixer]

I guess, provided the first is not driven above the performance level of the second....

But how likely is that...? .   Although traffic will dictate no doubt.

(The vxr8 will eat tyres though with an LSD, surely? And brakes may have similar intervall, but are 3times the cost. Worth it though, I'd say)

[05omegav6]

Using the urban cycle figures....

mmmm the Vectra does 28.8 mpg = (1.38 x 4.54)/28.8 = 21.75pence /mile

The VXR8 does 13.7 mpg on petrol .. approx 10.96 mpg on LPG  (20% less) = (0.72 x 4.54)/10.96 = 29.8 pence / mile  so not quite close ...  (but closer than the VXR8 on petrol (1.3 x 4.54)/13.7 = 43.08 pence /mile  )

Not quite "Should cost the same to run as this.." IMHO ..

Fixed as the Vectra is diesel... the 20mpg on petrol, 18mpg on gas, is based on a known auto averaging 16 (calculated) on lpg, given the actual car in mind is a manual, (link was for illustration purposes in both cases)

[Sir Tigger KC]

Have I missed anything else

The VXR8 might not be suitable for taxi work?     

[05omegav6]

Have I missed anything else

The VXR8 might not be suitable for taxi work?     

Loads of room in it and a massive boot... what more is required

Besides, it's hypothetical...

[chrisgixer]

Using the urban cycle figures....

mmmm the Vectra does 28.8 mpg = (1.38 x 4.54)/28.8 = 21.75pence /mile

The VXR8 does 13.7 mpg on petrol .. approx 10.96 mpg on LPG  (20% less) = (0.72 x 4.54)/10.96 = 29.8 pence / mile  so not quite close ...  (but closer than the VXR8 on petrol (1.3 x 4.54)/13.7 = 43.08 pence /mile  )

Not quite "Should cost the same to run as this.." IMHO ..

Fixed as the Vectra is diesel... the 20mpg on petrol, 18mpg on gas, is based on a known auto averaging 16 (calculated) on lpg, given the actual car in mind is a manual, (link was for illustration purposes in both cases)

Was going to ask auto or manual. But assumed manual.

[Sir Tigger KC]

Have I missed anything else

The VXR8 might not be suitable for taxi work?     

Loads of room in it and a massive boot... what more is required

Besides, it's hypothetical...

Hypothetically speaking wouldn't the LPG tank take up about 1/3 of the mahooooosive boot?   

[05omegav6]

Have I missed anything else

The VXR8 might not be suitable for taxi work?     

Loads of room in it and a massive boot... what more is required

Besides, it's hypothetical...

Hypothetically speaking wouldn't the LPG tank take up about 1/3 of the mahooooosive boot?   

Not if it's in the spare wheel well where the Full size spare used to sit, silly