Mpg Drop

[BIKERBOY]

hi everyone, new member!

IS220D

I have just changed my wheels from the OEM 205/55/16 to 225/40/18 unfortunatley my fuel consuption has dropped from averaging 40mpg to 32mpg

CAN THIS BE RIGHT?

my dealer in Liverpool says its the new wheels thats causing the drop in mpg as they are different ratio,circumference etc

but when I priced the wheels the calculator said there would be less than 1% difference in circumference

I have had the 5th injector replaced 3 times and have done 37000 miles

any comments chaps

Alan

[Tango]

I have just changed my wheels from the OEM 205/55/16 to 225/40/18 unfortunatley my fuel consuption has dropped from averaging 40mpg to 32mpg

CAN THIS BE RIGHT?

my dealer in Liverpool says its the new wheels thats causing the drop in mpg as they are different ratio,circumference etc

but when I priced the wheels the calculator said there would be less than 1% difference in circumference

Sounds like BS to me....

[Tony-Bones]

Welcome to the club.....

The wider tyre adds more drag laterally.... The toe positions need to be changed since the Geometry positions where written for a tyre rolling resistance of 205mm and a contact patch of around 40mm.

[boddamloon]

Welcome to the club mate

[BIKERBOY]

Welcome to the club.....

The wider tyre adds more drag laterally.... The toe positions need to be changed since the Geometry positions where written for a tyre rolling resistance of 205mm and a contact patch of around 40mm.

hi, thanks for the info'

speak to me in english, can i get it altered at a tyre bay?

will it make 8mpg difference?

[Sagitar]

It sounds like a very extreme change. I agree with Tony about changes in rolling resistance, but I would expect them to be marginal.

Over what period did you check the new average consumption?

Measurements over short periods are susceptible to all sort of variations - weather, different road conditions, the weight of your right foot etc. I can get apparent differences of 4 or 5 m.p.g. from one tankful to the next without any changes to the vehicle. At the extremes I have had as low as 25 m.p.g and as high as 38 m.p.g.

So I would give it long enough to get a well smoothed average figure before drawing conclusions.

[spikes]

hi welcome to loc :)

[ibby]

I always think along the lines of..

= Bigger tyres = heavier to move = more transmition loss.

[Tony-Bones]

Welcome to the club.....

The wider tyre adds more drag laterally.... The toe positions need to be changed since the Geometry positions where written for a tyre rolling resistance of 205mm and a contact patch of around 40mm.

hi, thanks for the info'

speak to me in english, can i get it altered at a tyre bay?

will it make 8mpg difference?

That was English

[Tango]

I always think along the lines of..

= Bigger tyres = heavier to move = more transmition loss.

Weight wouldn't be a deciding factor as with bigger rims and therefore a lower profile, the actual tyre mass could be less. I'd also be surprised if the contact patch has changed enough to be a consideration in the mpg loss stated....as Sagitar suggests the mpg needs monitoring over a reasonable time. May be worth checking the tyre pressures too as I found my bigger rims/the wider tyres required a 2 psi increase to maintain an even contact patch.

[BIKERBOY]

It sounds like a very extreme change. I agree with Tony about changes in rolling resistance, but I would expect them to be marginal.

Over what period did you check the new average consumption?

Measurements over short periods are susceptible to all sort of variations - weather, different road conditions, the weight of your right foot etc. I can get apparent differences of 4 or 5 m.p.g. from one tankful to the next without any changes to the vehicle. At the extremes I have had as low as 25 m.p.g and as high as 38 m.p.g.

So I would give it long enough to get a well smoothed average figure before drawing conclusions.

I have monitored this over the last month including a 270 mile run to Maidstone and back!

currently today its at 32mpg which is terrible

i am going to put my old wheels on at the weekend and see what happens?

if it is the wheels I will be selling them! I cant afford to lose £10 per tankfull as I do 25k per year!!!!

so I may be selling a 1 month old set of Lenso elegance 18" alloys with tyres if anyone is interested

Alan

[Tango]

I have monitored this over the last month including a 270 mile run to Maidstone and back!

currently today its at 32mpg which is terrible

It certainly is...with careful driving on a similar run my IS250 SE-L with 225/25/19 x 8.5" and 275/30/19 x 9.5" easily returned over 40 mpg. Even stonking it on short runs it averages around 28 mpg.

Something doesn't appear to be right with your 220D and I don't think it's your new rims.

[Tel]

Twice due to a set of circumstances I have changed from 17" to 18" &,if anything,the MPG has risen as the car has "run-in".I do not drive slow in the UK yet my Auto returns c. 32mpg.

Suggest your car needs more mods!

Tel

[BIKERBOY]

HI GUYS

I have put the original wheels back today Saturday so I will see what happens with the mpg?

as a matter of interest when I put the wheels back to back the new alloys were very slightly bigger!

anyway lets see what happens, I'll let you know soon as

Alan

[Matus]

I run 205/55/16 as winter tires and 225/245 17" as sommer tires and there is no change in the consumption.

Did you alter the tirepressure according to the tire size?

[BIKERBOY]

HI GUYS

I have put the original wheels back today Saturday so I will see what happens with the mpg?

as a matter of interest when I put the wheels back to back the new alloys were very slightly bigger!

anyway lets see what happens, I'll let you know soon as

Alan

UPDATE

drove to Oldtrafford to watch the mighty reds thrash Newcastle 6 - 0 yesterday average mpg 40.8

I am guttted it must be the wheels!!! I cant believe there would be so much difference!

anyway they will have to go as I do approx 25k per year and get paid by the mile so mpg is king

the Lexus dealer must have been right - as I have the basic 220d with 16" wheels you can only go up to 17"

from 17 to 18" is ok but not 16 to 18???

the problem is they look fantastic on the car! but I cant afford to lose 2 pence per mile so they have to go!

anyone interested adundon@fsmail.net

Edited January 13, 2008 by BIKERBOY
Only GOLD members can sell on the forums

[3 MSF]

HI GUYS

I have put the original wheels back today Saturday so I will see what happens with the mpg?

as a matter of interest when I put the wheels back to back the new alloys were very slightly bigger!

anyway lets see what happens, I'll let you know soon as

Alan

UPDATE

drove to Oldtrafford to watch the mighty reds thrash Newcastle 6 - 0 yesterday average mpg 40.8

I am guttted it must be the wheels!!! I cant believe there would be so much difference!

anyway they will have to go as I do approx 25k per year and get paid by the mile so mpg is king

the Lexus dealer must have been right - as I have the basic 220d with 16" wheels you can only go up to 17"

from 17 to 18" is ok but not 16 to 18???

the problem is they look fantastic on the car! but I cant afford to lose 2 pence per mile so they have to go!

anyone interested adundon@fsmail.net

Hi mate - this might be a bit left-field, but as you said your new wheel diameter was slightly greater than your originals, this means that you're travelling further per wheel rotation than your odometer will suggest. You're also, therefore, travelling slightly faster than your speedometer suggests too, so don't hover up against 70mph, as you may be closer to a speeding ticket than you think!

Regards - Mark.

[Tango]

Hi mate - this might be a bit left-field, but as you said your new wheel diameter was slightly greater than your originals, this means that you're travelling further per wheel rotation than your odometer will suggest. You're also, therefore, travelling slightly faster than your speedometer suggests too, so don't hover up against 70mph, as you may be closer to a speeding ticket than you think!

Regards - Mark.

No way....for the tyre and rim change he's only +0.84% on rolling diameter so when the speedo is reading 70 mph he'll be doing a theoretical 70.59 mph. As speedos can be anything up to 10% optimistic I don't think a speeding ticket will result . The recommended tolerance when switching tyres/rims is to keep the change within 2.5%, so it's well within this range.

However, if the system hasn't been recalibrated to the new rolling diameter it does explain some of the mpg difference.