[sootyvrs]

I have recently purchased some 17" OEM Flame alloywheels and just put them on my Dooper recently to replace my 15"

Just done my first long run in my LCI Dooper after changing wheels to 17" OEM Flame alloy wheels with 205/45/17 Kumho KU39 non rft tyres and I averaged just 52 mpg compared to the 62 mpg that I have got with my 15" alloys with Michelin Energy 175/65/15 doing a similar journey!

I did a 90 mile return trip using cruise majority of the time at 70 mph (GPS speed) which is indicated 74 mph on 17's and 75 mph on 15's

That's a 10 mpg (16%) drop in economy which is rather significant! It was a windy day today but I averaged the return trip so hopefully the wind didn't change direction.

Will continue to see if there is any improvement with this but it just shows the significance of putting larger (heavier) wheels on and 30mm more tyre footprint on each 4 corners!

17" vs 15"

Positives
Much more sporty looking
Much higher levels of grip
Quieter (surprisingly) than the Michelins
Sharper turn in

Negatives
Greater tram-lining
Much worse economy -10 mpg
Marginally slower accelerating / braking
Less comfort (not much)
More expenses when changing tyres

 

[cjm]

Oh no! I've just changed to those tyres on my 17" Flamies.
A much better ride than 17" r/flats, though...
Tyre pressure is 33psi all around - probably still too soft? What are yours on?
cjm

 

[will&sarah legge]

Very very interesting - i'll be really interested in how it progresses as I specifically didn't buy the 17s on my new car due to the perceved MPG issue - but there were no hard facts.

I've ordered 16s on mine, so hopefully this will be the sweetspot maybe.

 

[sootyvrs]

Oh no! I've just changed to those tyres on my 17" Flamies.
A much better ride than 17" r/flats, though...
Tyre pressure is 33psi all around - probably still too soft? What are yours on?
cjm

The difference might not be a problem with the tyre make/model but due to the extra weight of the wheels and wider footprint (increased rolling resistance) of the tyres in my comparison.

You may find that it makes no difference to your economy if you are already on 17's and 205 rft tyres although I'd be interested to see if you have a negative in this area.

I have pumped mine up to 35 psi all round as per recommendation on the door sticker.

 

[cjm]

Hmm...by keeping the pressure the same you've found that weight and wider footprint increase rolling resistance, linking into wlegge's 'less MPG issue'.
Yes, I suppose extra diameter increases those; I wonder what else is likely to contribute?
I wonder what the secret is behind 'lower energy' tyres that seem to clam to lower rolling resistance?
Thanks, I'll certainly up my tyre pressures to 35psi and get rid of that variable...

 

[dsakko]

Yup. No surprises there. Here's some anecdotal figures from my experience:

2002 Mini Cooper
15" rims and tyres all up 15kg
17" rims and tyres all up 19.5kg (per tyre). More weight = more fuel and sluggish performance. But [email protected] they look good.

1997 Volvo V40 T4
18" wheels with crummy no name tyres: 17.6 MPG (city) 25.6 MPG (country)
17" wheels with nice tyres: 29,1 MPG (city) 36.5 MPG (country)

PS - if you have matched the aspect ratio of the tyre the total rolling diameter will be (near enough) unchanged

 

[will&sarah legge]

What factor do you think the tyre width has on the MPG?

15" wheels = 175
16" = 195
17" = 205

Obviously there will be more rolling resistance but is it the extra wheel weight or the width that is the defining MPG killer?

 

[sootyvrs]

What factor do you think the tyre width has on the MPG?

15" wheels = 175
16" = 195
17" = 205

Obviously there will be more rolling resistance but is it the extra wheel weight or the width that is the defining MPG killer?

I suspect it's a combination of the 2 factors. I guess 16"/195 are perhaps a good compromise between the 15"/175 and 17"/205 but suspect that the loss in mpg might be more towards the 17" end rather than the 15"

It's unfortunate that manufacturers don't provide official economy figures for the larger wheels seeing that they are factory optional extras but suspect that may affect sales as economy is now becoming a very big selling point to most of us.

 

[scillyisles]

I also suspect the tyre difference makes a contribution. Michelin Energy tyres are low rolling resistance whereas Kumho tyres are not.

 

[sootyvrs]

With fuel prices ever rising, ultra low rolling resistance tyres are a hot topic. The tyre accounts for approximately 20% of the total fuel consumption of the car, and just a 10% reduction in rolling resistance can reduce total fuel consumption by 1.6%.

Traditionally ultra low rolling resistance tyres are a compromise during development, with low rolling resistance balancing wet performance. As you decrease rolling resistance you also decrease the wet grip, or the safety of the tyre, while increasing the wet performance leaves the tyre requiring more energy to rotate, using more fuel.

I found the above article from tyrereviews.co.uk site relating to Continental tyre which suggests that it would have to be considerably less rolling resistance to have a significant effect.

I would guess that the rolling resistance of a 175mm contact patch and a 205mm contact patch would be 17% increase given the same tyre compound/model.

If economy stays low (relatively to what I was getting before) I will probably try another brand next time around.

I know that reading a lot of the "What mpg are you getting from your Mini" threads it may go some way to explain some of the differences although driving style will obviously be the bigger factor.

I'm glad I've done the test though as there doesn't seem many posting of real world experiences with changing wheel/tyre size changes.

 

[will&sarah legge]

I've found some other useful info.

A study done by a university has shown this:

CD --- Tyre Size / Wheel Type
0.293 --- 155 R 15; 5 1/2 Jx15 St. with wheel covers
0.294 --- 165 R 15; 61 2 Jx15 St. with wheel covers
0.297 --- 175/70 R 15; 6 Jx15 St. with wheel covers
0.305 --- 185/65 R 15; 61 Jx15 St. with wheel covers
0.311 --- 205/60 R 15; 61 2 Jx15 St. with wheel covers
0.314 --- 205/60 R 15; 7 Jx15 Alloy
0.319 --- 225/55 R 15; 7 Jx15 Alloy

If you want to get really into it, take a look at: tire width vs. drag (Cd) - Page 3 - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

WOW, some info in there to dig through.

 

[Angib]

For MPG, I think tyre section width is the only factor that is important, except perhaps to a lesser degree tyre make/model - diameter and weight are largely irrelevant.

Those various Cd factors with tyre width are fascinating - and remember that drag is Cd multiplied by cross sectional area (ie, front view area) so not only do the wider tyres increase the Cd significantly, but then the cross sectional area will also increase a little, so the overall drag increase is worse than shown!

The weight of bigger wheels/tyres is important for acceleration and particularly for roadholding - heavier wheels don't follow the road surface so well, so will slip more on bumps (but wider tyres grip more on billiard table smooth race tracks).

 

[marque]

Hi guys found this you guys may have seen this


Some replace the factory wheels to customize their car or to facilitate plus sizing, while others purchase aftermarket wheels to use on the track. Whatever the reason, a wheel and tire package selected must fit within the wheel well without rubbing on the suspension or fender.

On street cars, it should have an overall diameter that is within ±3% of the factory specification. The ±3% variation is recommended for street cars in order to maintain accurate speed data going into the computer, thus keeping odometer and speedometer changes negligible. While a ±3% diameter increase or reduction in tire diameter may sound very limiting, in most cases it allows approximately a ±3/4" diameter change.

Assuming 24.00" (609.6mm) as the factory specification for overall diameter, any of the following tire sizes may be appropriate:

+-----------+-------------------+
| TIRE SIZE | DIAMETER |
+-----------+-------------------+
| 195/55-15 | 23.44in (595.5mm) |
| 205/40-17 | 23.46in (595.8mm) |
| 215/50-15 | 23.46in (596.0mm) |
| 215/45-16 | 23.62in (599.9mm) |
| 195/50-16 | 23.68in (601.4mm) |
| 185/60-15 | 23.74in (603.0mm) |
| 215/40-17 | 23.77in (603.8mm) |
| 205/55-15 | 23.88in (606.5mm) |
| 215/35-18 | 23.93in (607.7mm) |
| 175/65-15 | 23.96in (608.5mm) |
| 225/45-16 | 23.97in (608.9mm) |
| 205/50-16 | 24.07in (611.4mm) |
| 225/40-17 | 24.09in (611.8mm) |
| 225/35-18 | 24.20in (614.7mm) |
| 195/60-15 | 24.21in (615.0mm) |
| 205/45-17 | 24.26in (616.3mm) |
| 215/55-15 | 24.31in (617.5mm) |
| 195/55-16 | 24.44in (620.9mm) |
| 205/40-18 | 24.46in (621.2mm) |
| 215/50-16 | 24.46in (621.4mm) |
| 185/65-15 | 24.47in (621.5mm) |
| 215/45-17 | 24.62in (625.3mm) |
+-----------+-------------------+

NOTES:
Stock fitments are highlighted
Fitment dependent on wheel offset and suspension setup
Tires availabilty may be limited in certain sizes

There are performance benefits from wider tires, in that there is more rubber gripping the road. Increasing tire width or increasing wheel diameter means lowering the sidewall of tire. While a shorter sidewall, gives quicker steering response and better lateral stability, it may make for a "harsher" ride and leave wheels more susceptible to damage from encounters with curbs or pot-holes.

Increasing wheel size is not always required to fit wider tires. For example, 205/50 tires fit 16" wheels providing the same tire print as the factory 17" wheel/tire package and 0.40" (10.3mm) additional sidewall cushioning.

When selecting wheels, bear in mind that larger diameter wheels mean more expensive tires, and heavier wheels mean more unsprung weight, thus poorer handling.

When selecting tires, make sure that they have an appropriate speed rating and load index:
Speed Rating
H minimum - Cooper and One
V minimum - Cooper S
Load Index
84 minimum

The Tire Rack - technical pages


Contact FAQ Custodian

 

[sootyvrs]

Thought I'd give an update.

I travelled 250 miles today on a return trip that I do on a regular basis and I'm pleased to say I managed 58 mpg on the 17" wheels above which is much better. So that means it's only 4 mpg short of what I average on this trip on 15's.

I can only assume that the really windy conditions we had over the weekend had a big effect on the mpg from before. Perhaps the wind direction changed in both directions. I think the weather forecast said it was up to 60-70mph winds!

Will keep this updated if any more changes

 

[will&sarah legge]

thanks for the update. 4mpg is still significant but slightly less worrying.

 

[KiwiRob]

Very very interesting - i'll be really interested in how it progresses as I specifically didn't buy the 17s on my new car due to the perceved MPG issue - but there were no hard facts.

I've ordered 16s on mine, so hopefully this will be the sweetspot maybe.

I had 16 and 17 inch wheels on my old Clubman, I never noticed any significant difference in MPG between either size.

 

[gary.lawlor]

I have recently purchased some 17" OEM Flame alloywheels and just put them on my Dooper recently to replace my 15" Just done my first long run in my LCI Dooper after changing wheels to 17" OEM Flame alloy wheels with 205/45/17 Kumho KU39 non rft tyres and I averaged just 52 mpg compared to the 62 mpg that I have got with my 15" alloys with Michelin Energy 175/65/15 doing a similar journey! I did a 90 mile return trip using cruise majority of the time at 70 mph (GPS speed) which is indicated 74 mph on 17's and 75 mph on 15's That's a 10 mpg (16%) drop in economy which is rather significant! It was a windy day today but I averaged the return trip so hopefully the wind didn't change direction. Will continue to see if there is any improvement with this but it just shows the significance of putting larger (heavier) wheels on and 30mm more tyre footprint on each 4 corners! 17" vs 15" Positives Much more sporty looking Much higher levels of grip Quieter (surprisingly) than the Michelins Sharper turn in Negatives Greater tram-lining Much worse economy -10 mpg Marginally slower accelerating / braking Less comfort (not much) More expenses when changing tyres

I’m wanting to fit 17s to my 08 cooper D will I have to get the odometer recalibrated and can I fit the new alloys with stock suspension?