Mpg on 18's

Ic3man · 10-04-2005, 07:48

Since fitting 18's to my Octy Vrs I have noticed a reduction in mpg. I was getting around 31mpg (mixed driving) but I now get around 26mpg for the exact same journey. Obviously the new alloys have come with new tyres Federal SS595ZR 225/45/18 so that would account for some reduction in mpg but I wasn't expecting a 5mpg deficit! Is this normal? Oh and should I have the car tracking re-checked?

Thx in advance.

vRS-vRS · 10-04-2005, 10:02

hmmm, think you might have to take into account that with the bigger wheels the computer is reading the speed differently and thus calculating the MPG wrong. Although it will be a little worse because of the size of the wheels its turning, losing more than 10% economy seems a little "unreal" ?!?!?

devonutopia · 10-04-2005, 10:10

The ne tyre size is 3.61% bigger, so having a 10% drop is a little odd. Do they have stickier tyres on than what you were running originally?

I know going from 185/60 R14 to 205/40 R17, I got quite a drop in economy, in the region of 10-15%, and I had to pin 3% on the bigger size, and the rest on the Toyo Proxes being stickier than conti eco-contact tyres.

Jimmy · 10-04-2005, 11:06

There should be no difference as the rolling radius should be within +/- 2.5% of the original. Why have you gone for 45 section tyres though? I'm running 18's but am using 40 section...

Ic3man · 10-04-2005, 13:16

Sorry, they are 40 section not 45 as stated

. The 'old' tyres were the standard contis on the octy vrs but had about 2mm left when removed so I guess you could say that the new tyres are stickier! I experimented this morning by 'freewheeling' to see if the speed reduction was greater than normal and sure enough it is therefore I would assume I would have to give it more boot (thereby less mpg) to attain the same acceleration as before?

***DGW*** · 10-04-2005, 13:26

Bigger cross-section therefore more drag?

andy_ccr · 11-04-2005, 11:07

Had no problems and no difference when I went to 225/40/18 RS4s over 10,000 miles

Beef · 14-07-2005, 18:55

I too have suffered this since fitting 8x18 RS6 replicas with the 225/40/18 Federal SS595. I have also noticed a slight degredation in acceleration (which is fair enough)

The difference in rolling radius between the 205/50/17 Conti and the 225/40/18 Federal is 0.1%

At the end of the day a 5/6mpg drop from 30mpg is more like 20% which is not practical when you thing about it, as every journey is costing 20% more with these 18s. Therefore I will be selling mine.

I have read on here that these cheap wheels are heavy, and I noticed this when fitting, however I will be weighing them against the standard wheels soon.

I also think that it is this extra weight that has killed my gearbox...

Gandalf · 15-07-2005, 15:12

I have recently fitted a set of 18" OZ vello 5 spokes to my vRS. I have not noticed any reduction in fuel economy - I will see what i get from a full tank next time I fill up.

With regards to acceleration there does seem to be a slight loss, particularly in 1st, but after this things seem to be fine. Maybe a re-map will help? Looking at my speedo now I am able to reach 70mph in 2nd without hitting the rev limiter.

The wheels I have fitted if anything seem lighter than the 17" originals. Was going to get RS4 replicas but was wary about the extra weight.

Gandalf · 15-07-2005, 15:27

I have recently fitted a set of 18" OZ vello 5 spokes to my vRS. I have not noticed any reduction in fuel economy - I will see what i get from a full tank next time I fill up.

With regards to acceleration there does seem to be a slight loss, particularly in 1st, but after this things seem to be fine. Maybe a re-map will help? Looking at my speedo now I am able to reach 70mph in 2nd without hitting the rev limiter.

The wheels I have fitted if anything seem lighter than the 17" originals. Was going to get RS4 replicas but was wary about the extra weight.

logiclee · 15-07-2005, 15:44

I was looking through a Mondeo brochure the other day.

There was around a 5-10% difference in economy between the Zetec and Zetec-S.
Only difference is a slight body kit and the change from 16" to 18" alloys.

Cheers
Lee

Leeboy · 15-07-2005, 18:35

Is this reduction in ecomony not chiefly due to the fact unless you spend loads of pennies, 18" rims are significantly heavier in weight compared to 17" with the small sidewall profile making limited difference in tyre weight saving? Am I not right in thinking that unsprung weight (e.g. wheel, trye and hub/brakes etc) make double the difference in terms of performance deficit compared to sprung weight?

Lee

Beef · 21-07-2005, 10:22

Quote:

Originally Posted by Leeboy

Am I not right in thinking that unsprung weight (e.g. wheel, trye and hub/brakes etc) make double the difference in terms of performance deficit compared to sprung weight?

Lee

Apparently so, the general concensus is that unsprung has double the effect of sprung weight, and rotational weight is the other killer.

As promised I weighed my wheels when I swopped back to the originals this week:

OEM 'Spider' 7x17 with 205/50 Continental SportContact : 18kgs approx
RS6 Replica 8x18 with 225/40/18 Federal SS595 : 24kgs approx

Thats a massive 6kgs per wheel extra unsprung and rotational weight. since going back to the 17s, the car is feels much more responsive and agile, and the all important mpg is back upto 30ish rather than the low 20s.

Yes you have to pay around £500 extra for lightweight wheels from the likes of OZ etc, but based on my experience of a 20% loss of economy, they could pay for themselves in 25,000 miles, and you would retain the acceleration and agility of the 17" wheels.

E.g. 8x18 OZ Supperleggeras with 225/40/18 would weigh in at around 17kgs a corner, which is lighter than the standard 17s, which may cancel out the wider tyres effect on mpg... I'll let you know...

Leeboy · 21-07-2005, 22:38

So if I were to ditch my 18" Team Dymanic Motorsports in favour of OEM 17" rims, my car too would go like pooh off a shovel (which it does already), erm... so, go like the an extra big dollop of pooh off a shovel?

Ic3man · 22-07-2005, 16:35

Only if you can get the 17 oems (with contis) to stick as well as aftermarket tyres (proxes etc)....there is also cornering to think of. Larger sidewall = less stability.

Must admit I noticed a little decrease on 0-60 performance, just didn't feel as 'brisk', saying that I dont get as much wheel spin (with esp off) with the 18's as I did with the 17s so that will no doubt counter the effects.

I think it was Continental who ironicly said - "Power is nothing without control"! (maybe it was pirelli).

Smithy vRS · 22-07-2005, 19:15

Had my car dyno'd with 18's on and the loss in tranmission was up 6hp

Mil · 23-07-2005, 21:59

Quote:

Originally Posted by Ic3man

Must admit I noticed a little decrease on 0-60 performance, just didn't feel as 'brisk', saying that I dont get as much wheel spin (with esp off) with the 18's as I did with the 17s so that will no doubt counter the effects.

I think it was Continental who ironicly said - "Power is nothing without control"! (maybe it was pirelli).

Obviously..18s have a much larger circumference and therefore need more power to fully rotate the wheel than you would need with smaller wheels.

10-04-2005, 07:48	#1
Ic3man Briskodian Join Date: Sep 2004 Location: High Peak Posts: 348 Thanks: 0 Thanked 1 Time in 1 Post	Mpg on 18's Since fitting 18's to my Octy Vrs I have noticed a reduction in mpg. I was getting around 31mpg (mixed driving) but I now get around 26mpg for the exact same journey. Obviously the new alloys have come with new tyres Federal SS595ZR 225/45/18 so that would account for some reduction in mpg but I wasn't expecting a 5mpg deficit! Is this normal? Oh and should I have the car tracking re-checked? Thx in advance. __________________ '04 Silver Octy vRS - Revo 4bar, Miltek SS, Mitek Downpipe, 100cel CAT, RS6 18" Alloys, Forge 007p, ABD lan pipe/green filter, Samco TIP, Autogauge Boost,Oil temp, Oil Pressure gauges, ESP, Xenons, RS3 upper & lower braces

10-04-2005, 10:02	#2
vRS-vRS Briskodian Join Date: Mar 2005 Location: Newcastle Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts	hmmm, think you might have to take into account that with the bigger wheels the computer is reading the speed differently and thus calculating the MPG wrong. Although it will be a little worse because of the size of the wheels its turning, losing more than 10% economy seems a little "unreal" ?!?!? __________________ Paul, its a Skoda I know

10-04-2005, 10:10	#3
devonutopia Mongreller Join Date: Apr 2003 Location: Exeter / Devon Posts: 30,079 Images: 5 Thanks: 76 Thanked 347 Times in 290 Posts	The ne tyre size is 3.61% bigger, so having a 10% drop is a little odd. Do they have stickier tyres on than what you were running originally? I know going from 185/60 R14 to 205/40 R17, I got quite a drop in economy, in the region of 10-15%, and I had to pin 3% on the bigger size, and the rest on the Toyo Proxes being stickier than conti eco-contact tyres. __________________ Jason - Mongrel owner! WOOOOF! Grrrrr Custom Fabia Bonnet Lifter Kits - £45! Click Me. Cheesy bonnet lifter video to "raise me up" http://www.youtube.com/watch?v=hMnGECEi5Oc See the mongrel's 260bhp Dyno Video!

10-04-2005, 13:16	#5
Ic3man Briskodian Join Date: Sep 2004 Location: High Peak Posts: 348 Thanks: 0 Thanked 1 Time in 1 Post	Sorry, they are 40 section not 45 as stated . The 'old' tyres were the standard contis on the octy vrs but had about 2mm left when removed so I guess you could say that the new tyres are stickier! I experimented this morning by 'freewheeling' to see if the speed reduction was greater than normal and sure enough it is therefore I would assume I would have to give it more boot (thereby less mpg) to attain the same acceleration as before? __________________ '04 Silver Octy vRS - Revo 4bar, Miltek SS, Mitek Downpipe, 100cel CAT, RS6 18" Alloys, Forge 007p, ABD lan pipe/green filter, Samco TIP, Autogauge Boost,Oil temp, Oil Pressure gauges, ESP, Xenons, RS3 upper & lower braces

10-04-2005, 13:26	#6
*DGW* BRISKODA Staff Join Date: Oct 2002 Location: Cambridgeshire Posts: 17,259 Thanks: 51 Thanked 197 Times in 149 Posts	Bigger cross-section therefore more drag? __________________ Denis 2002 Octavia 1.8T 4X4 turbo Estate - rebreathed on by Jabba ... 31.93mpg 2007 Fabia vRS - CC, ESP and full leather trim by Seat Surgeons ...48.57 mpg...

10-04-2005, 11:06	#4
Jimmy Briskodian Join Date: May 2003 Location: North East Posts: 2,446 Thanks: 0 Thanked 0 Times in 0 Posts	There should be no difference as the rolling radius should be within +/- 2.5% of the original. Why have you gone for 45 section tyres though? I'm running 18's but am using 40 section...

11-04-2005, 11:07	#7
andy_ccr Briskodian Join Date: Aug 2003 Location: Essex Posts: 407 Thanks: 0 Thanked 0 Times in 0 Posts	Had no problems and no difference when I went to 225/40/18 RS4s over 10,000 miles __________________ Black '53' Octy vRS - 18inch RS4 in Graphite Grey - Colour coded front grill - Samco TIP - Carbonio filter - OBD Remap by Mike @ Impossible Performance Forge FMIC SuperSprint cat back exhaust. Coming soon - Rear ARB, better suspension, better brakes.... Damn that bloody Nurburgring ! Coming before the end of Jan 2007 - Audi A4 Cabriolet - Ebony Black- 18inch RS4 Wheels - Red Knappa leather

14-07-2005, 18:55	#8
Beef Briskodian Join Date: Mar 2005 Location: South Wales Posts: 56 Thanks: 0 Thanked 0 Times in 0 Posts	I too have suffered this since fitting 8x18 RS6 replicas with the 225/40/18 Federal SS595. I have also noticed a slight degredation in acceleration (which is fair enough) The difference in rolling radius between the 205/50/17 Conti and the 225/40/18 Federal is 0.1% At the end of the day a 5/6mpg drop from 30mpg is more like 20% which is not practical when you thing about it, as every journey is costing 20% more with these 18s. Therefore I will be selling mine. I have read on here that these cheap wheels are heavy, and I noticed this when fitting, however I will be weighing them against the standard wheels soon. I also think that it is this extra weight that has killed my gearbox...

15-07-2005, 15:12	#9
Gandalf Briskodian Join Date: Jun 2005 Location: North East UK Posts: 64 Thanks: 0 Thanked 0 Times in 0 Posts	I have recently fitted a set of 18" OZ vello 5 spokes to my vRS. I have not noticed any reduction in fuel economy - I will see what i get from a full tank next time I fill up. With regards to acceleration there does seem to be a slight loss, particularly in 1st, but after this things seem to be fine. Maybe a re-map will help? Looking at my speedo now I am able to reach 70mph in 2nd without hitting the rev limiter. The wheels I have fitted if anything seem lighter than the 17" originals. Was going to get RS4 replicas but was wary about the extra weight.

15-07-2005, 15:27	#10
Gandalf Briskodian Join Date: Jun 2005 Location: North East UK Posts: 64 Thanks: 0 Thanked 0 Times in 0 Posts	I have recently fitted a set of 18" OZ vello 5 spokes to my vRS. I have not noticed any reduction in fuel economy - I will see what i get from a full tank next time I fill up. With regards to acceleration there does seem to be a slight loss, particularly in 1st, but after this things seem to be fine. Maybe a re-map will help? Looking at my speedo now I am able to reach 70mph in 2nd without hitting the rev limiter. The wheels I have fitted if anything seem lighter than the 17" originals. Was going to get RS4 replicas but was wary about the extra weight.

15-07-2005, 15:44	#11
logiclee Briskodian Join Date: Nov 2003 Location: Notts, UK Posts: 787 Thanks: 0 Thanked 1 Time in 1 Post	I was looking through a Mondeo brochure the other day. There was around a 5-10% difference in economy between the Zetec and Zetec-S. Only difference is a slight body kit and the change from 16" to 18" alloys. Cheers Lee __________________ Another Ex-Scooby owner. Mondeo TDCi 130 6 Speed Ghia, Octavia 1.9TDi Elegance (Now Sold), Fabia 1.9TDi Comfort and Felicia 1.9D GLi

15-07-2005, 18:35	#12
Leeboy Briskodian Join Date: Nov 2003 Location: Hampshire Posts: 1,178 Thanks: 11 Thanked 11 Times in 11 Posts	Is this reduction in ecomony not chiefly due to the fact unless you spend loads of pennies, 18" rims are significantly heavier in weight compared to 17" with the small sidewall profile making limited difference in tyre weight saving? Am I not right in thinking that unsprung weight (e.g. wheel, trye and hub/brakes etc) make double the difference in terms of performance deficit compared to sprung weight? Lee __________________ Lee Want to be carbon-neutral while driving? Hold your breath!

21-07-2005, 22:38	#14
Leeboy Briskodian Join Date: Nov 2003 Location: Hampshire Posts: 1,178 Thanks: 11 Thanked 11 Times in 11 Posts	So if I were to ditch my 18" Team Dymanic Motorsports in favour of OEM 17" rims, my car too would go like pooh off a shovel (which it does already), erm... so, go like the an extra big dollop of pooh off a shovel? __________________ Lee Want to be carbon-neutral while driving? Hold your breath!

22-07-2005, 16:35	#15
Ic3man Briskodian Join Date: Sep 2004 Location: High Peak Posts: 348 Thanks: 0 Thanked 1 Time in 1 Post	Only if you can get the 17 oems (with contis) to stick as well as aftermarket tyres (proxes etc)....there is also cornering to think of. Larger sidewall = less stability. Must admit I noticed a little decrease on 0-60 performance, just didn't feel as 'brisk', saying that I dont get as much wheel spin (with esp off) with the 18's as I did with the 17s so that will no doubt counter the effects. I think it was Continental who ironicly said - "Power is nothing without control"! (maybe it was pirelli). __________________ '04 Silver Octy vRS - Revo 4bar, Miltek SS, Mitek Downpipe, 100cel CAT, RS6 18" Alloys, Forge 007p, ABD lan pipe/green filter, Samco TIP, Autogauge Boost,Oil temp, Oil Pressure gauges, ESP, Xenons, RS3 upper & lower braces

22-07-2005, 19:15	#16
Smithy vRS Briskodian Join Date: Mar 2004 Location: Republic of Ireland Posts: 290 Thanks: 0 Thanked 0 Times in 0 Posts	Had my car dyno'd with 18's on and the loss in tranmission was up 6hp

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