new wheels r beautiful BUT, mpg!

[Phil_beeza]

has gone from 45, to 41, i got them installed only saturday

f%&k. is the pd160+green cotton likely to put this back up a bit?

or is this purely due to larger wheels and wider tyres?

in which case i need a re think!

any other suggestions !?

 

[vwpologti]

are you joking? you may have lost 4mpg so you mite change your rims?

 

[Viking]

Yep, the bigger wheels and wider tires will be losing you mpg. More rolling resistance.

 

[Phil_beeza]

well 10% is quite a few litres of diesel over a few years...poss thinking of going to 205, instead of 215....depends what the main cause of the mpg change is...weight of the rims or the amount of tyre contact on the road

this is just something you gotta live with for nice wheels i guess ?

 

[Dyscontinued]

I'd guess it's the contact area as opposed to the weight.

Is this ever factored in when people compare the Ibiza/Leon mpg difference? I've noticed weight mentioned a lot but never wheel size.

 

[Viking]

Mostly it's the larger diameter rims. You've moved the wheel weight further away from the centre of rotataion, so it requires more power to turn them. Putting narrower tires on will help somewhat by reducing the contact patch on the road, but minimal compared to reducing the rim diameter again. Lightweight wheels are very expensive and manufacturers tend to make their wheels cheap and look nice, and keep quiet about the mpg factor.

 

[Phil_beeza]

how would you rate the following in terms of difference?

7j vs 6j
215 vs 205 - would this make more difference in sustained motorway driving?

17 isn't an issue, i like the size

 

[Viking]

I honestly don't know. I've never gone in for aftermarket wheels etc. once I discovered that mileage takes a hit. I drive anywhere up to 50k miles a year, so I like to keep my economy as good as poss. There's also the insurers wanting extra for non standard wheels aswell, so I've never changed any and just stayed with stock.

There'll be a benefit I'm sure, but how much I don't know.

 

[sssstew]

put the old wheels back on to see.

 

[jonjay]

Are the aftermarket wheels heavier? If they are quite a bit heavier that will effect the mpg.

 

[muddyboots]

Mostly it's the larger diameter rims. You've moved the wheel weight further away from the centre of rotataion, so it requires more power to turn them.

I'd tend to agree, the biggest factor will be the wheel diameter, I doubt a small reduction in tyre width will have any noticeable effect.

Because the weight is further from the centre of the wheel, it will take more effort to rotate them - in other words the difference will occur during acceleration.
In which case, reducing the number of times you slow down & accelerate again should help - to this end, improving your anticipation and therefore smoothing out your driving style may pay dividends - a good way to do this would be to go on an advanced driving course such as IAM or RoSPA.

Just a thought

 

[Phil_beeza]

any ideas if 6j/7j would make a diff? i like 17"

the only way to go down to 6j would be new wheels which isn't a viable option so having that info would just be for 'peace of mind'

mainly having the info about if 205 width would make any difference because i could change that on my next tyre set.

 

[silver surfer]

i run 18" on my toledo and compared with the dam ugly steels with wheel trims 4 mpg loss i wouldent be bothered and anyway on steady crusing the larger diameter wheels increases your gearing so you use lower revs for same speed so you should get your fuel back and mines chipped which gives me more torque and better fuel consumption

 

[Viking]

Larger wheels only increase your gearing if you put larger diameter tires on them. Generally, tire & wheel packages are designed to keep the original rolling diameter so that the speedo and odometer aren't compromised.

A 205/55/16 wheel & tire package has a diameter of 632mm whereas a 245/35/18 wheel & tire package has a diameter of 629mm. Small enough to be insignificant.

But increase the tire profile from 35 to 45 and the difference is 46mm. This could come close to fouling the wheel arches.

 

[Phil_beeza]

please let me off the hook for another post on this, but i also thought just now....

regarding the tyre/wheel width, bigger wheels also have more "angular momentum?" (ive watched too many scrap heap challenges ) , so even tho wider, bigger wheels would help keep themselves rotating once started because theyre heavier, so the engine would have to do less work once they are going round

i dunno. maybe

 

[Viking]

To a certain degree, yes. But in practice, you never get up to speed and back off until you come to a halt. You'll use more energy getting started, then have to brake more to slow down again. It's only minimal, admittedly, but over the course of a tankfull, it all adds up.

Look at it like this. If you have to travel 1 mile in distance. The most economical way to do this is to acceleralte until you reach just enough speed to coast to your destination without braking. Smaller wheels mean you use less fuel reaching that critical speed, and then coast to a halt. Larger wheels will mean that you use more fuel, although the critical speed will be slightly less as there's more kinetic (stored) energy once you're moving and you'll coast for longer. However, once you have to brake, all the saving of being able to coast further is lost, and the extra fuel used to get you up to speed is wasted.

Now ask yourself, how often do you drive like this?

 

[Sisson]

4mpg is 40 miles per tankish...

so roughly 1 gallon per tank.

1 gallon is roughly £4.20.

So for every full tank it costs £4.20. Not really worth it IMO.

40mpg is low for a derv anyway, do you nail it everywhere or sit in traffic lots?

 

[Phil_beeza]

ps i don't know what derv stands for.

my car use is more or less opposite ideal for a diesel, it's to work (2x10 miles per day), with occasional long trips. i have a diesel because that's what was available second hand - my dads got a skoda vrs and had good things to say about it, altho he does long journeys. i wanted an ibiza, with a fairly big engine

i'll keep an eye on my ave fuel. on my way home yesterday it was 42.2, down from 44.8 but up from <41 which is what i had on thursday

 

[muddyboots]

4mpg is 40 miles per tankish...

so roughly 1 gallon per tank.

1 gallon is roughly £4.20.

So for every full tank it costs £4.20. Not really worth it IMO.

40mpg is low for a derv anyway, do you nail it everywhere or sit in traffic lots?

Not really worth it if you don't do many miles. But if like me you travel 500-550 miles a week, which means filling up weekly, it does add up....

DERV = Diesel Engined Road Vehicle (I think...).

Which begs the question, should petrols be called PERVs ?

 

[rice-c87]

i dont see your problem i have a tdi 90 leon on a 02 plate and i get about 40 all the time and i dont do a lot of motorway miles about 20 miles a week and i cover about 3-400 miles a week,

just drive it dont worry about what it drinks coz if you had a petrol with the same power you would get about 25 round the doors and about 35 on the motorway