Fuel Economy On 33's

[The Lang-Shankit Scunner]

Did quite alot of driving around this evening, and used a fair amount of fuel as always, and i thought about the mpg's, and tried to work it out. Then i thought, im actually doing more km's than the counter is telling me, due to the circumferance of the tyres.
So I got the satnav out and worked out litres to gallons and km's to miles, and miles to gallon, and i found that my mpg hasnt changed over a 150 mile trip! That was 240 km's and i'd put in 27 litres of fuel veg mix.

So was wondering if mpg droppage on 33's is due to the counter being thrown out cos of tyres, or whether im just fortunate to have one that dont mind em.

[KERRSURF]

you think too much.

[The Lang-Shankit Scunner]

Not usually

[dee]

you think too much.

lol


light comes on, put fuel in, light comes on, put fuel in.... ain't gonna stop you driving the thing is it?

[The Lang-Shankit Scunner]

Not now it aint

[white akita]

i have no idea about mpg, ive not noticed it using anymore since fitting 33s but as soon as i have half a tank left i fill it up.

[The Lang-Shankit Scunner]

i fill it when i worry about getting to next port of call

[white akita]

im probably only getting about 20mpg so i like lots of fuel in the tank

[The Lang-Shankit Scunner]

im not doing too bad at 26mpg then

[PDR]

Fuel light? What’s that then?... never seen mine lit in 16 months of ownership because I always fill up once I get down between ½ or a ¼ of a tank.

Carl, more importantly I think you ought to be checking how the indicated speed shown on your speedo relates to that on your GPS.

I know mine is out by 5 mph right across the range compared to my GPS and those roadside signs. I guess the needle was not put back correctly when they changed the dial to MPH upon import to the UK.

[Snorkel]

I'm replying to this without thinking too much, as it seems obvious, but do tell me if I'm wrong (I'm gonna use the 'sleepy' excuse again anyway).

Why would the circumferance of the tyre make a difference to the mileage count? both tyre edge and rim edge do same distance, just one edge travels faster than the other. Perhaps think of a penny farthing bike = the 'axle' (whatever it's called) turns just as many times as the wheel as they are fixed together. The clock will count how many times the bit near the 'axle'/ bearings turn right?

(sorry for any painful thoughts/cringes at lack of part's terminology.

[Antshiel]

Tyre edge and rim edge don't do the same distance, they do the same revolutions. If they travelled the same distance they'd be the same size. The same way gears work. The smaller the gear the less distance it travels the bigger= more distance.

If you took the tyres off the rims and drove only on the rim then you wouldn't travel as far as you would with the tyre on. This is why when you fit mahoosive tyres (Rod leach stylee) your diffs need regearing.

[Snorkel]

erm - yeah - not going to use a sleepy excuse there (you'll just have to trust me when I say I did know that, and don't know why I wrote they do the same 'distance'. I think I had in my mind that over 10 miles, both rim and tyre of course therfore do 10 miles each, but the 'mile-ometer' is surely callibrated/set to that of what the rims are attached to, so unless you change THAT size, the correct mileage work be calculated no?

[Karma Supra]

Your Logic hurts my brains

Circumference is calculated by 2*Pi*r, so increasing the tire wall increases the radius (r) and therefore by definition increases the circumference.

By definition the circumference is the distance covered by a fixed point on the outside of a circle during one total revolution. So increasing the circumference increases the distance covered in one revolution.

Soooooooo as the speedo works by translating revolutions per minute of the axle, and each revolution is covering more distance then it did before... the speedo is out :P

[PDR]

Your Logic hurts my brains

Circumference is calculated by 2*Pi*r, so increasing the tire wall increases the radius (r) and therefore by definition increases the circumference.

By definition the circumference is the distance covered by a fixed point on the outside of a circle during one total revolution. So increasing the circumference increases the distance covered in one revolution.

Soooooooo as the speedo works by translating revolutions per minute of the axle, and each revolution is covering more distance then it did before... the speedo is out :P

Which is why I suggested that you check your speedo against your GPS.. you may find (like me) that you are traveling faster than what your speedo says