I do the same journey regularly - every time I do it I get 56mpg, With 18" wheels that figure has decreased. Bigger, wider, heavier wheels and tyres DO have an adverse effect on mpg.
I'm not complaining, simply stating a fact.
Grrr. Missed these wheels
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I do the same journey regularly - every time I do it I get 56mpg, With 18" wheels that figure has decreased. Bigger, wider, heavier wheels and tyres DO have an adverse effect on mpg.
I'm not complaining, simply stating a fact.
freddofrog
won 16.4k on Euro lottery :)
Fair comment about me "agreeing" when originally I didn't "agree", but as Jon says, it's too early to tell.errrr - well you are just agreeing with exactly what I stated. I've already said that the difference is .79%, that's a slight change on the gearing, so the engine does have to work 'slightly' harder.
The tyres are wider, so drag is increased = more fuel being used.
Wider tyres will increase the rolling resistance = more fuel being used.
Weight of larger tyres is increased = more fuel being used.
So as I stated in my original post, the mpg has decreased, I wasnt asking for an explanation to this 'mysterious phenomemen', simply stating that the bigger wheels and tyres have adversely affected the mpg. And just offering up a bit of new Information and knowledge for other owners.
But if there is a difference to that precent change, it is down to odometer difference and rolling resistance change.
"that's a slight change on the gearing, so the engine does have to work 'slightly' harder" is nonsense Alan, and if you believe that, then I'll leave you to that belief.
"The tyres are wider, so drag is increased = more fuel being used" is also nonsense Alan, and if you believe that, then I'll leave you to that belief.
"Wider tyres will increase the rolling resistance = more fuel being used" is also nonsense Alan, and if you believe that, then I'll leave you to that belief.
"Weight of larger tyres is increased = more fuel being used" is also nonsense Alan, and if you believe that, then I'll leave you to that belief.
"simply stating that the bigger wheels and tyres have adversely affected the mpg. And just offering up a bit of new Information and knowledge for other owners"
This is incorrect Alan, you are making a false relationship which should not be passed on without someone pointing out that it is a false relationship.
A driver's perceived MPG changes are affected by:
1. driving style (which you may have changed)
2. drag change (which your tyres have not changed)
3. operating point of the engine i.e. change in BSFC (which your tyres have not changed)
4. odometer readings (which you have not checked)
5. rolling resistance ....you can change brand of tyre and type of tyre within brand and it will affect rolling resistance. Change of wheel size and tyre size may affect rolling resistance poitively, negatively, or not at all.
freddofrog
won 16.4k on Euro lottery :)
We know you're not complaining, but as Jon says it's too early to tell.
And bigger, wider, heavier wheels and tyres DO NOT , repeat DO NOT, necessarily have an adverse effect on mpg. They can improve it. They can have no effect.
Read up about rolling resistance, seriously Alan, please take time to read up before talking cant.
I really don't see why were having this disagreement, apart from you seeming to state that bigger wheels/tyres wil NOT affect mpg, so lets clarify.
1. A Heavier wheel and tye combination WILL affect MPG adversely - it's the law of physics, they are heavier so they require more energy to move.
2. A Wider tyre WILL have an increased rolling resistance, again it's physics.
3. A Wider trye will also decrease the aerodynamic efficiency of a car - the new tyres are 20mm wider, the car is pushing a greater frontal area through the air on all four wheels. It's physics. Thats why 'economy' type cars like the insight have narrow tyres.
Cars attempting the world speed record also go for narrow tyres to minimise the adverse effects of all the above.
My new tyres have a slight increase in circumference, up my 5mm, a 0.79% increase. So my gearing has altered slightly, making my speedo reading slightly out, so the MPG readout will be slightly out, 0.79%, I accept that. So the MPG readout will also be correspondingly skewed. But the calculations are done using the same internal calculation device - ie it is all done on the cars inbuilt 'computer', I'm not using the miles travelled from the odometer, and then using an external method to input the amout of petrol used to make the calculations, I'm using the same method that I used before, nothing has changed.
Now back to what I '***ume' you are making your ***umptions from)).
IF the new 18" tyres were exactly the same weight, and exactly the same width, and exactly the same circumference - then any descrease in mpg would be down to the rolling resistance of the different tyres, and I would be able to state that in all probability, the (new) Falken ZE912's have a higher rolling resistance than Michelin Primacy's (the old 16" tyres), and there would be no 'argument'.
But what I am stating is that the change in wheels and tyres has had a very noticeable effect on mpg, on a route that I regularly drive on, a journey I always use cruise control on, at exactly the same speed that I always set it at, and so it seems reasonable to me that the 3 items I highlighted - have had an effect on the mpg, and this is probably compounded by the Falkens having a higher rolling resistance than the Michelins.
If you wish to believe that heavier, wider tyres, with a bigger circumference that alters the gearing of a car have absolutely no effect on mpg, then you carry on believing it
1. A Heavier wheel and tye combination WILL affect MPG adversely - it's the law of physics, they are heavier so they require more energy to move.
2. A Wider tyre WILL have an increased rolling resistance, again it's physics.
3. A Wider trye will also decrease the aerodynamic efficiency of a car - the new tyres are 20mm wider, the car is pushing a greater frontal area through the air on all four wheels. It's physics. Thats why 'economy' type cars like the insight have narrow tyres.
Cars attempting the world speed record also go for narrow tyres to minimise the adverse effects of all the above.
My new tyres have a slight increase in circumference, up my 5mm, a 0.79% increase. So my gearing has altered slightly, making my speedo reading slightly out, so the MPG readout will be slightly out, 0.79%, I accept that. So the MPG readout will also be correspondingly skewed. But the calculations are done using the same internal calculation device - ie it is all done on the cars inbuilt 'computer', I'm not using the miles travelled from the odometer, and then using an external method to input the amout of petrol used to make the calculations, I'm using the same method that I used before, nothing has changed.
Now back to what I '***ume' you are making your ***umptions from
)).IF the new 18" tyres were exactly the same weight, and exactly the same width, and exactly the same circumference - then any descrease in mpg would be down to the rolling resistance of the different tyres, and I would be able to state that in all probability, the (new) Falken ZE912's have a higher rolling resistance than Michelin Primacy's (the old 16" tyres), and there would be no 'argument'.
But what I am stating is that the change in wheels and tyres has had a very noticeable effect on mpg, on a route that I regularly drive on, a journey I always use cruise control on, at exactly the same speed that I always set it at, and so it seems reasonable to me that the 3 items I highlighted - have had an effect on the mpg, and this is probably compounded by the Falkens having a higher rolling resistance than the Michelins.
If you wish to believe that heavier, wider tyres, with a bigger circumference that alters the gearing of a car have absolutely no effect on mpg, then you carry on believing it
Jon_G
No Longer Active
There's only one way to settle this...
freddofrog
won 16.4k on Euro lottery :)
^ :lol: brilliant Jon .... I give up Alan ..... you win. :lol:
I'm not convinced that there has been a change in your mpg, you believe the wheels make a difference, so you believe there's a change
Trust me, everything you have put reveals a mix-up of concepts, plus a non-deliberate insincere use of jargon ....cant. I can't be bothered with a tennis match on this, and it's not my place to educate you anyway. Father time might help the penny to drop one day ....a few books on the subject will speed the process up.
"a little knowledge can be dangerous"
They do look nice though, if you want to sell them ..... :lol:
I'm not convinced that there has been a change in your mpg, you believe the wheels make a difference, so you believe there's a change
Trust me, everything you have put reveals a mix-up of concepts, plus a non-deliberate insincere use of jargon ....cant. I can't be bothered with a tennis match on this, and it's not my place to educate you anyway. Father time might help the penny to drop one day ....a few books on the subject will speed the process up.
"a little knowledge can be dangerous"
They do look nice though, if you want to sell them ..... :lol:
icewarrior
Members
I'm with Alan on this one. (mostly)
The gearing effect by having the new tyres and wheels, 225/40/18 against 205/55/16 is neglible. less than 1%,
see here http://www.alloywhee...Tyre_Calculator
so where you would have been doing 70mph before, for the same revs you would now be doing 70.7mph, or you would do 70mph with a drop of approx 20rpm. So this really would have next to no difference on the mpg. With 56mpg on the 16s, the difference would be less than 0.5mpg based on the same effort being required to keep the car moving.
The economy is being affected by the weight of the wheels and it is simple physics. Why else do sportcars have lightweight wheels, it helps them accelerate faster as there is less rotational mass, they are easier to turn. This also means that if if they are easier to turn, if requires less effort to keep them turning at the same speed. Less effort means less fuel being used.
Its the same principle on pushbikes as well. If i take out my bike which has heavier wheels, it requires more effort from me to turn the wheels, whereas if i take out my bike with lightweight race wheels, its a lot easier. it requires less effort from me to go at the same speed. thats why a lot of guys into racing will train using heavy wheels and swap them out on race day, for the same effort they will go faster, or they can go at the same speed with less effort.
The key point i guess i'm making here is rotational mass. Higher rotational mass = more effort = more fuel
There are a number of factors which will affect fuel economy here.
Wheels - Heavier - harder to turn - increased fuel usage
Tyres - Wider - More than likely increased drag which would increase fuel usage - But, tread pattern and compound come into play here. A well designed tyre with a 225 width can have lower rolling resistance than a 205. Given the brands, i would bet that the michelin would have better rolling resistance, but its not a given.
Tyre weight - not necessarily heavier - certainly wider but less sidewall - unknown, possibly heavier, lighter or the same as before
But increased aerodynamic drag from the tyres affecting mpg is almost laughable. Look at the size of the front of the car - An extra 20mm in tyre width is miniscule compared to the size of the front of the car. If it does affect it, you're probably talking about 0.01mpg
The one factor definitely influencing the mpg is the wheels. I have the same wheels which i use in the summer months. When i switch to my 16inch winter wheels, the car accelerates slightly faster (backside dyno), and gains 2-3mpg as it doesnt have to work as hard to keep those wheels moving.
To have better fuel economy with heavier, wider wheels would require a tyre with a good enough rolling resistance to more than offset the increased effort required to turn them.
Another factor to take into account though - what tyre pressures are your 16s at and what pressures are the 18s at?
edit - are you measuring mpg by computer or by filling the tank? brim to brim fills are the only way to tell the true mpg
Actually, rereading my post it would appear that i agree with some elements Alan has said and some that Brian has said.
Also, have you done more than one trip? weather conditions can have an influence as well, wind speed/direction etc.
The gearing effect by having the new tyres and wheels, 225/40/18 against 205/55/16 is neglible. less than 1%,
see here http://www.alloywhee...Tyre_Calculator
so where you would have been doing 70mph before, for the same revs you would now be doing 70.7mph, or you would do 70mph with a drop of approx 20rpm. So this really would have next to no difference on the mpg. With 56mpg on the 16s, the difference would be less than 0.5mpg based on the same effort being required to keep the car moving.
The economy is being affected by the weight of the wheels and it is simple physics. Why else do sportcars have lightweight wheels, it helps them accelerate faster as there is less rotational mass, they are easier to turn. This also means that if if they are easier to turn, if requires less effort to keep them turning at the same speed. Less effort means less fuel being used.
Its the same principle on pushbikes as well. If i take out my bike which has heavier wheels, it requires more effort from me to turn the wheels, whereas if i take out my bike with lightweight race wheels, its a lot easier. it requires less effort from me to go at the same speed. thats why a lot of guys into racing will train using heavy wheels and swap them out on race day, for the same effort they will go faster, or they can go at the same speed with less effort.
The key point i guess i'm making here is rotational mass. Higher rotational mass = more effort = more fuel
There are a number of factors which will affect fuel economy here.
Wheels - Heavier - harder to turn - increased fuel usage
Tyres - Wider - More than likely increased drag which would increase fuel usage - But, tread pattern and compound come into play here. A well designed tyre with a 225 width can have lower rolling resistance than a 205. Given the brands, i would bet that the michelin would have better rolling resistance, but its not a given.
Tyre weight - not necessarily heavier - certainly wider but less sidewall - unknown, possibly heavier, lighter or the same as before
But increased aerodynamic drag from the tyres affecting mpg is almost laughable. Look at the size of the front of the car - An extra 20mm in tyre width is miniscule compared to the size of the front of the car. If it does affect it, you're probably talking about 0.01mpg
The one factor definitely influencing the mpg is the wheels. I have the same wheels which i use in the summer months. When i switch to my 16inch winter wheels, the car accelerates slightly faster (backside dyno), and gains 2-3mpg as it doesnt have to work as hard to keep those wheels moving.
To have better fuel economy with heavier, wider wheels would require a tyre with a good enough rolling resistance to more than offset the increased effort required to turn them.
Another factor to take into account though - what tyre pressures are your 16s at and what pressures are the 18s at?
edit - are you measuring mpg by computer or by filling the tank? brim to brim fills are the only way to tell the true mpg
Actually, rereading my post it would appear that i agree with some elements Alan has said and some that Brian has said.
Also, have you done more than one trip? weather conditions can have an influence as well, wind speed/direction etc.
freddofrog
won 16.4k on Euro lottery :)
^ not you too :lol:
No, no, no ....stop it ....some mix-up of concepts :wacko: ....arrrrghhh help :blink:
EDIT: we won't get anywhere on this unless some basics are understood, and I've got better things to do
No, no, no ....stop it ....some mix-up of concepts :wacko: ....arrrrghhh help :blink:
EDIT: we won't get anywhere on this unless some basics are understood, and I've got better things to do
icewarrior
Members
What you talking about, i agree with some of the stuff you say too :lol:
Rotational mass does make a difference, more so if you are stopping and starting as accelerating is the engine will really notice the extra load. If at a steady speed, it is still there but the extra effort required would be less.
I actually drop from about 45mpg combined to about 42 on my summer wheels. If Alan is getting 56mpg i'm ***uming that is mostly motorway driving at a steady speed, so i would expect a difference of 1-2 mpg due to the extra rotational mass. I think more trips are required doing this route to get a more accurate mpg figure though as 1 trip cant be used for an accurate comparison given weather, temperature etc
and the tyres could be at too low a pressure increasing roling resistance too
Rotational mass does make a difference, more so if you are stopping and starting as accelerating is the engine will really notice the extra load. If at a steady speed, it is still there but the extra effort required would be less.
I actually drop from about 45mpg combined to about 42 on my summer wheels. If Alan is getting 56mpg i'm ***uming that is mostly motorway driving at a steady speed, so i would expect a difference of 1-2 mpg due to the extra rotational mass. I think more trips are required doing this route to get a more accurate mpg figure though as 1 trip cant be used for an accurate comparison given weather, temperature etc
and the tyres could be at too low a pressure increasing roling resistance too
freddofrog
won 16.4k on Euro lottery :)
Sorry , but I'm just not playing on this ........ I've got better things to do B)
:lol: lets FIGHT !!
The increase due to drag should be minimal, and not really worth worrying about.
The older tryes were worn, and newer tyres do have a greater rolling resistance, so that would decrease mpg.
I'm with you in that I'm sure Michelin's are more efficient than Falkens.
The biggest factor has to be the weight of the wheel, they did feel a lot heavier than the 16" when I was changing them over, I'll weigh them both at the weekend to see what the difference is.
A small decrease in MPG I can handle, but the decrease is very noticeable, on a 10 mile rock steady 65mph cruise control motorway run this afternoon, (reset at the start of the run) it never went above 49.2 - that is not what I want, and I don't think bigger wheels etc etc should have had such a dramatic effect.
Tyre pressures, good point Sam, this is something I need to experiment with as I have no Honda reccomended figures for an 18" Tyre. I'm currently running them at 33 front and 30 rear, I reckon I need to increase them by at least 2psi - What pressures do any other 18 inchers (Ooooh Matron) run?
The increase due to drag should be minimal, and not really worth worrying about.
The older tryes were worn, and newer tyres do have a greater rolling resistance, so that would decrease mpg.
I'm with you in that I'm sure Michelin's are more efficient than Falkens.
The biggest factor has to be the weight of the wheel, they did feel a lot heavier than the 16" when I was changing them over, I'll weigh them both at the weekend to see what the difference is.
A small decrease in MPG I can handle, but the decrease is very noticeable, on a 10 mile rock steady 65mph cruise control motorway run this afternoon, (reset at the start of the run) it never went above 49.2 - that is not what I want, and I don't think bigger wheels etc etc should have had such a dramatic effect.
Tyre pressures, good point Sam, this is something I need to experiment with as I have no Honda reccomended figures for an 18" Tyre. I'm currently running them at 33 front and 30 rear, I reckon I need to increase them by at least 2psi - What pressures do any other 18 inchers (Ooooh Matron) run?
icewarrior
Members
damn, there's your problem
somewhere between 35 and 38 is what you want for 18s
somewhere between 35 and 38 is what you want for 18s
freddofrog
won 16.4k on Euro lottery :)
Lesson 1
The power to overcome rolling resistence = mass of car x g x coeff of rolling resistance x velocity of car
The whole car weighs 1500 kg (Tourer). It's the total weight that affects rolling resistance, I fail to see how 4 slightly heavier wheels can make such a difference to a weight of 1500 kg.
Following examples coeff of rolling resistance
steel wheel on steel rail ...........up to 0.002
car tyre on concrete ................0.010
car tyre on concrete asphalt ....0.015
car tyre on rolled gravel ...........0.020
car tyre on Tarmacadam .........0.025
car tyre on dry farm land .........0.1 to 0.35
Note also that the coeff itself does actually vary a bit with speed.
The coeff varies with tyre pressure. The coeff varies with rubber compund. The coeff varies with temperature to a lesser degree.
Generally, the coeff is greater the smaller the wheel radius.
As for "rotational mass", there is no such thin involved in rolling resitance.
As for "rotational mass" affecting the amount of fuel required to move accelerate the car, well the engine is trying to accelerate 1500 kg, so again I fail to see how 4 slightly heavier wheels affect mpg in this case.
Sam and Alan ....your "science" is "pseudo-science".
freddofrog
won 16.4k on Euro lottery :)
end of Lesson 1.
I'm off to the pub with my lad now :lol:
I'm off to the pub with my lad now :lol:
icewarrior
Members
Lesson 2:
http://en.wikipedia....ment_of_inertia
angular acceleration of the wheel
(edit - like i said, a constant speed will not be affected much, but the moment you include acceleration into the equation then rotational mass does have an effect on effort required)
end of lesson 2
http://en.wikipedia....ment_of_inertia
angular acceleration of the wheel
(edit - like i said, a constant speed will not be affected much, but the moment you include acceleration into the equation then rotational mass does have an effect on effort required)
end of lesson 2
Jon_G
No Longer Active
Brian is correct... the tread rolling radius has increased, therefore the apparent MPG has decreased.
Alan is correct... the new wheels/tyres are heavier and create more drag, so the real MPG has decreased.
It will be very hard to calculate which has the dominant effect.
While it may nevertheless be relatively indicative, I doubt the accuracy of the MPG figures quoted. 56MPG is ridiculously optimistic. Pump volumes and distances recorded by GPS technology are the only way to get the real figure.
Alan is correct... the new wheels/tyres are heavier and create more drag, so the real MPG has decreased.
It will be very hard to calculate which has the dominant effect.
While it may nevertheless be relatively indicative, I doubt the accuracy of the MPG figures quoted. 56MPG is ridiculously optimistic. Pump volumes and distances recorded by GPS technology are the only way to get the real figure.
icewarrior
Members
Anyway, to stop any arguments, have a look at this
http://www.topgear.com/uk/photos/new-hennessey-venom-gt2-2012-11-27
get yourself one of these and you wont care about mpg :lol:
http://www.topgear.com/uk/photos/new-hennessey-venom-gt2-2012-11-27
get yourself one of these and you wont care about mpg :lol:
Jon_G
No Longer Active
icewarrior
Members
Jon_G
No Longer Active
I stand corrected.
icewarrior
Members
Back on topic (again). Alan, pump your tyres up and do a couple of runs to eliminate the possibility of driving into a headwind on a single run and let us know how you get on
Jon, don't be corrected, it was the only vid i could find lol
Jon, don't be corrected, it was the only vid i could find lol
freddofrog
won 16.4k on Euro lottery :)
no Sam, it has no relevance compared with change of momentum of 1500 kg. Please stop the pseudoscience and get real.
Sorry to say Jon, but no, the wheels do not increase drag, as they are only 2cm wider, whereas the cross-sectional area of the main car body is 175 cm wide by 130cm deep, so again Sam and Alan are talking pseudoscience.
And the weight of the wheels have no effect either, because the car itself (Tourer) weighs 1500 kg. You;d need to add a lot of weight to make a difference to the weight that affects rolling resistance, and to the wieght that affects the torque required by the engine.
Finally, Alan has not confirmed the tyre sizes .....waiting .............waiting .........
icewarrior
Members
at what point did i say wheels being wider increase aerodymanic drag??? I did actually say that aerodynamic drag from wheels was almost laughable.
There is more to mpg than just rolling resistance from the tyres. So less of this pseudo science nonsense that you keep spouting and come back when you learn some simple physics. I tried offering an olive branch and just cant be bothered with you now.
(and if he is using the recommended tyre sizes for the 16s and 18s then i have already given you them)
so lets just agree to disagree
There is more to mpg than just rolling resistance from the tyres. So less of this pseudo science nonsense that you keep spouting and come back when you learn some simple physics. I tried offering an olive branch and just cant be bothered with you now.
(and if he is using the recommended tyre sizes for the 16s and 18s then i have already given you them)
so lets just agree to disagree
freddofrog
won 16.4k on Euro lottery :)
Lesson 2a
If you take a slightly heavier wheel of the same size, and swap the tyres to it, how much does this affect power rrequired at 70 mph ?
***ume car weight = 1500 kg. ***ume extra additional weight of each wheel = 10 kg. ***ume tyre coeff of rolling resistance = 0.015
New car weight = 1540 kg.
old power to overcome rolling resistance = 6,868 Watts
new power to overcome rolling resistance = 7,051 Watts
i.e. at 70 mph, the required power has gone up by 183 Watts (your rear windscreen heater and headlights would affect mpg more than this)
Lesson 2b
tyre A has coeff of rolling resisttance = 0.015 and tyre B has coeff of rolling resistance = 0.016, how much extra power is required at 70 mph ?
***ume car weight = 1500 kg.
power to overcome rolling resistance for tyre A = 6,868 Watts
power to overcome rolling resistance for tyre B = 7,326 Watts
i.e. at 70 mph, the required power has gone up by 458 Watts. QED.
End of Lesson 2.
If you take a slightly heavier wheel of the same size, and swap the tyres to it, how much does this affect power rrequired at 70 mph ?
***ume car weight = 1500 kg. ***ume extra additional weight of each wheel = 10 kg. ***ume tyre coeff of rolling resistance = 0.015
New car weight = 1540 kg.
old power to overcome rolling resistance = 6,868 Watts
new power to overcome rolling resistance = 7,051 Watts
i.e. at 70 mph, the required power has gone up by 183 Watts (your rear windscreen heater and headlights would affect mpg more than this)
Lesson 2b
tyre A has coeff of rolling resisttance = 0.015 and tyre B has coeff of rolling resistance = 0.016, how much extra power is required at 70 mph ?
***ume car weight = 1500 kg.
power to overcome rolling resistance for tyre A = 6,868 Watts
power to overcome rolling resistance for tyre B = 7,326 Watts
i.e. at 70 mph, the required power has gone up by 458 Watts. QED.
End of Lesson 2.
freddofrog
won 16.4k on Euro lottery :)
are you talking to me or Jon ??? He ***ociated you with that, not me.
no I listed the tyre sizes first, you obviously didn't read my post before yours, which included a similar link to the link that you gave.
You are mixing up simple physics, I am using books on the subject of automotive engineering.
Good, clear off :lol: :lol:
icewarrior
Members
freddofrog said:
you mean those tyre sizes, you couldn't even get those right, so why should I have any faith in your ability to read a couple of booksfreddofrog said:
and physics applies to everything, it is never irrelevant.
and clear off? no one likes a keyboard warrior
This thread is hilarious :lol: . I'm loving the polite arguments.
But let me get this straight. Your MPG has gone down significantly since you've replaced 16s with 18s right? If you choose the correct tyres, the outer diameter of the tyre should be the same and therefore, no difference. You've got slightly incorrect size tyres, but it's likely to result in less than 1% difference overall, so no big deal.
The weight in my opinion is not significant. We're talking the equivalent of having a small person (40-60kg) as a passenger on a relatively large engine, fairly powerful car. It can't make that much difference. Tyre design/brand will have far more impact, as will incorrect tyre pressure.
Buy tyres known for good MPG and run them in the high 30s PSI and it should be fine in my opinion. I'm no expert, but there's no other reason I can think of for a significant MPG drop when changing wheels/tyres.
Alternatively, have you considered that maybe, coincidentally, something else has gone wrong at the same time as you changing your wheels? When is your car due a service and/or filter change? Fuel filter, air filter, spark plugs/glow plugs, engine oil etc, can all have significantly detrimental effects on MPG if they need changing.
Also, consider in the last two weeks the weather has gotten significantly colder and wetter. MPG is always poorer in cold/wet weather as the air is much denser and therefore the MAF sensor orders the engine to put more fuel through the pistons for a bigger bang to compensate for the colder, denser air.
I think there is more here than meets the eye the problem doesn't lie solely in the wheels.
Just my 2 pence .
But let me get this straight. Your MPG has gone down significantly since you've replaced 16s with 18s right? If you choose the correct tyres, the outer diameter of the tyre should be the same and therefore, no difference. You've got slightly incorrect size tyres, but it's likely to result in less than 1% difference overall, so no big deal.
The weight in my opinion is not significant. We're talking the equivalent of having a small person (40-60kg) as a passenger on a relatively large engine, fairly powerful car. It can't make that much difference. Tyre design/brand will have far more impact, as will incorrect tyre pressure.
Buy tyres known for good MPG and run them in the high 30s PSI and it should be fine in my opinion. I'm no expert, but there's no other reason I can think of for a significant MPG drop when changing wheels/tyres.
Alternatively, have you considered that maybe, coincidentally, something else has gone wrong at the same time as you changing your wheels? When is your car due a service and/or filter change? Fuel filter, air filter, spark plugs/glow plugs, engine oil etc, can all have significantly detrimental effects on MPG if they need changing.
Also, consider in the last two weeks the weather has gotten significantly colder and wetter. MPG is always poorer in cold/wet weather as the air is much denser and therefore the MAF sensor orders the engine to put more fuel through the pistons for a bigger bang to compensate for the colder, denser air.
I think there is more here than meets the eye the problem doesn't lie solely in the wheels.
Just my 2 pence
.
freddofrog
won 16.4k on Euro lottery :)
^ Steve, that was absolutely spot on dude
icewarrior
Members
Steve, it was only a single run so wind could've been a factor, but the biggest factor appear to be that the tyres are a bit soft 30psi rear and 33 front, which you covered in incorrect pressures. I think we'll have more insight once Alan has pumped up the tyres a bit and done a few runs.
it could be tricky to tell in the immediate future though as the temps are due to plummet over the next week, well, up here anyway
it could be tricky to tell in the immediate future though as the temps are due to plummet over the next week, well, up here anyway
Oh, and this isn't F1! The kind of tiny tolerances you guys are talking about with weight, rolling mass etc... We're talking a large, heavy daily driver on very changeable road and weather conditions. I mean, just driving into strong winds for an hour will have an impact. The fuel in your tank. Possibly a duff batch of supermarket petrol, anything.
I think there's an aspect of not seeing the forrest for the trees here boys.
Everyone calm down, keep things clean and look at this in a simpler light. There's probably a much more grounded solution than the minutia of a percentages with rolling mass and aerodynamics.
:lol: honestly, for those of us, like me, who aren't in the bowels of this dispute, it is very funny. I don't understand much of it, but there's some very technical, heated discussion here. Careful it doesn't unnecessarily spiral out of control .
I think there's an aspect of not seeing the forrest for the trees here boys.
Everyone calm down, keep things clean and look at this in a simpler light. There's probably a much more grounded solution than the minutia of a percentages with rolling mass and aerodynamics.
:lol: honestly, for those of us, like me, who aren't in the bowels of this dispute, it is very funny. I don't understand much of it, but there's some very technical, heated discussion here. Careful it doesn't unnecessarily spiral out of control
.- Status