How wheel & tire size and style affect Mirage fuel economy/mileage

[MetroMPG]

In New Zealand, just two Mirage models are offered: LS (base) and GLS, both with the CVT automatic transmission only.

They both have identical drivetrain/technical specifications, yet the LS has a better fuel economy rating than the GLS, burning 6.1% less fuel. Why? Mitsu points to the wheel/tire spec on the two cars as the culprit.

N.Z. AA explains:

the difference is a result of the variance in wheel sizes. Skinny 14-inch steel wheels are fitted to the LS models while the GLS versions are fitted with 15-inch alloy-wheel rims with slightly wider tyres.

http://mirageforum.com/forum/showthr...e-Association)

(Off-topic... I think it's funny that they call the 165 width tire "skinny", but not the tire that's only 1cm wider. Duh.)

	Mirage LS 1.2 L CVT automatic	Mirage GLS 1.2 L CVT automatic
Combined fuel economy:	4.6 L/100 km 21.7 km/L 51.1 mpg (US)	4.9 L/100 km 20.4 km/L 48 mpg (US)
Wheel & tire	14" Steel w/ Wheel Cover 165/65R14	15" Alloy 175/55R15

How do different wheel /tire size and style cause the GLS to get worse fuel consumption?

• the slightly narrower tire will have a slightly better drag coefficient and smaller frontal area
• that flat plastic 14 inch wheel cover is probably more aerodynamic than the open spoke alloy wheel
• the different tires probably have different rolling resistance coefficients
• the bigger alloy wheels & lower profile tires may have more of their mass concentrated further away from the rotation axis, which would need more power to accelerate

I haven't compared the overall diameter of the 2 tires, but I assume they're very close. If they're not, though, gearing could also be slightly affected.

UPDATE (Jul 11/2013):

Mitsubishi again points at wheel/tire choice and its effect on fuel consumption, this time regarding the new Mirage Sedan G4 / Attrage:

22 KM/LITER. (with 14 inch wheels) Having the lightest body weight, it isn’t surprising that the Mirage G4 has the lowest fuel consumption in its class. [...] Equipped with 15-inch wheels, the Mirage G4’s fuel efficiency is rated at 21 kpl.

source: http://business.inquirer.net/131241/...ry-chapter-two

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FYI: here's a dramatic example of how these wheel size/style issues can affect fuel economy:

• Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)

[rave]

what ET in15" Alloy

in thailand have 14" Alloy Only

[pinky]

I use a Garmin Nuvi 50 [5 inch screen] in speedo mode so if you do change your tire size the sat nav will continue
to provide correct speed and distance. It is mounted in front of the steering wheel which saves me looking down
at the car speedo as well. It cost $90 Aus. no life time maps.
You can also use Phone apps but my sat nat is working the moment I drive.
Phone apps can take 5 minutes to aquire the satalite signal.
I'm a big fan of not getting speed camera photos,

[Flange]

Greetings to all. With my wife having just bought a Mirage a few days back it's interesting to read what others are finding. On the subject of this thread, I will be discarding the OEM wheels and tyres shortly, based on my experience with a broadly similar Suzuki Alto which I bought in 2010.

As with the Mirage the Alto came with skinny (155x65/14) LRR tyres on 4.5 inch steel rims which seemed broadly OK but which certainly couldn't be described as particularly grippy. They would slide noticeably even at relatively modest cornering speed, but never seemed to actually let go - corner faster and they would just slide a bit more. Quite entertaining perhaps. They were shagged by 20,000km at which point I replaced the steel rims with a set of 14x6 inch alloys from a Series 2 Mazda MX5, same stud spacing and offset as the Alto steels but very light and of course suitable for a wider tyre. To the MX5 rims I fitted 185x55/14 Kingstar radials which gave a very slightly greater rolling circumference than the OEM 155x65s giving the side benefit of bringing the speedo closer to correct.

Since the conversion I have done a further 60,000 Km and so have plenty of data to substantiate my claim that on the Alto at least, fitting wider, non-LRR tyres has had NO adverse affect on fuel mileage. For the first 50,000 or so Km I kept a detailed log of fuel in and KM covered and what that has shown is that the Alto started it's life averaging about 52-53 miles per gallon (works best in my head) and as things settled in that gradually improved to the point where it now returns about 57-58 mpg.

Given that the speedo is now slightly less optimistic one would actually have expected an apparent reduction in MPG with the fitment of 185s, but not so, so could it be that LRR tyres are actually a crock ? I wouldn't suggest that, but I have conclusively found that when run at the same pressures as LRR tyres, wider Kingstar directional radials don't sacrifice fuel economy on an Alto. I ran both the LRRs and the Kingstars at 40psi.

Benefits of the wider non-LRR tyres include greatly improved grip (handles like a Kart, stops very quickly indeed) so the wider, non-LRR tyres are much safer, period! And a dramatic reduction in tyre thump on bumps. The Kingstars were directionals and particularly on smooth seal they would howl quite badly but on New Zealand's typically coarse chip seal they were no noisier than the LRRs. Had I stuck with Ecopia LRRs a new set would have cost me $720 at the point when the original set wore out - 20,000km. The Kingstars cost $440 and lasted 55,000km. The MX5 rims cost me $400. That makes it a bit of a no-brainer really, cheaper, safer, nicer to drive on. Kingstar are Hankook's Chinese made line. Not sexy, but they were good tyres.

A couple of months back, with a trip down to the South Island planned and the Kingstars getting close to the wear limit I decided to replace them, particularly given that down south with winter arriving I was likely to (and did) encounter heavy rain and possibly snow/ice. Whilst I was very happy with the Kingstars, this time I fitted another Chinese brand called Green Way. I don't know if they are supposed to be LRR but suspect not. I fitted these because my tyre source said that they had fitted a couple of sets and found them to be good, and they were very cheap indeed, like $260 for a set of four ! Admittedly that's wholesale price with no charge for fitting and balancing - He retails them to the public for under $400. I was a little apprehensive, but figured that for that price if they were no good I could take them off and go back to Kingstars but surprise surprise, they have proven to be good tyres in a very wide range of conditions. They are not directionals or assymetrics, just plain radials, and don't suffer from the howl that directionals sometimes produce. Economy wise, the trip down south saw two bicycles on the back of the Alto, two pax plus a full load of baggage. It also saw a fair bit of time flogging the poor wee thing along at 130km/hr plus so economy suffered, down to a paltry 50 or so MPG. Since I have been back home, things are back to the normal, just under 60mpg so obviously the Green Ways are no less economical than the directional Kingstars.

So the other day I pulled a wheel off the Mirage and offered up one of the MX5 wheels. The stud spacing is correct, the offset LOOKS about right, but the flange on the Mirage's front hub is about a millimetre larger than the corresponding hole in the MX5 rim. It would be no hassle to relieve the hub hole in the rim, but I do suspect that on full lock the steering joint might foul the edge of the rim once the wheel is properly bolted up. For this reason I'm investigating alloys from a Series 1 MX5 which are 5.5 inches (rather than the Series 2's 6 inch) wide.

So there it goes Team, a bit of a lengthy rant but hopefully it documents the real world story of LRR vs non-LRR and wide vs skinny.

If anybody has knowledge of the offset of the standard Mirage steel wheels I would love to know please. Likewise if anybody has actually fitted alloys to their Mirage, please let me know what they are.

Regards to all
Flange



So

[MetroMPG]

Hi Flange - welcome to the forum!

so could it be that LRR tyres are actually a crock ? I wouldn't suggest that, but I have conclusively found that when run at the same pressures as LRR tyres, wider Kingstar directional radials don't sacrifice fuel economy on an Alto. I ran both the LRRs and the Kingstars at 40psi.

"LRR" is only a label, and the rolling resistance properties of various tires lie across a spectrum. So that Alto tire may have been labelled "LRR" but could conceivably have been at the low end of the scale in terms of rolling properties -- not much different from a non-LRR tire at the upper end of its spectrum.

Also, not sure about NZ, but they're still sorting out LRR labelling/evaluation/comparison issues here in North America, and at the moment, it's a bit of the wild west (in other words, not all "LRR" claims are made equal).

The effect of wider tires is well understood to adversely affect aerodynamics and decrease efficiency at higher speeds. Wider tires increase both drag coefficient and frontal area. By any chance does your Alto generally spend more time in the city or on the open road? EG: see http://ecomodder.com/forum/showthrea...g-cd-7475.html

Last year, for kicks (I lead an exciting life), I compared various tires fitted to the same car. Rather than looking at fuel consumption, I directly compared each tire's "roll out distance" down a very small hill. Results were interesting. Here's an image that showed the "spread" from the worst to the best tire (in terms of rolling ability), all at the same pressure:



From: http://ecomodder.com/forum/showthrea...e92-19126.html

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Aside from all that ...Thanks for posting your experience!

And the big question: How are you liking the Mirage ??

If anybody has knowledge of the offset of the standard Mirage steel wheels I would love to know please. Likewise if anybody has actually fitted alloys to their Mirage, please let me know what they are.

Best results for getting a response to those questions is if you start a new thread with a descriptive title.

cheers!
Darin

[Polkiuj]

Hi!

I'm working in the tire industry (so maybe I'm a little biased, haha) but LRR does make a difference in rolling resistance (lol). It increases the distance (and hence speed) that you can roll (whether in gear, neutral or engine off). Any hypermiler will tell you that more rolling = better FE.

The only time it won't make a difference is when you don't roll (coast). If ever slowdown is by braking then it won't make the slightest difference to your FE.

[Flange]

Cheers for that Mr Admin. This looks like a good site in the making. Being a "world" car we should certainly get a wide variety of owners and attitudes towards the car. Thanks for your efforts in administering the site, much appreciated.

Apart from a ten km drive down the main road I haven't been granted driving privileges in the Mirage yet but Jocelyn is very pleased with it, and viewed of course in the context of what the car is - economical and comforftable transport from A to B, it seems nice. Jocelyn's previous car was a 2006 Colt Sport 1.5. She did just under 200,000 very trouble-free km in that including many trips around NZ, sometimes carrying four adults which the Colt carried out with aplomb. If the Mirage does as well then we will be very happy indeed.

Looking at the old OEM tyres from the Alto still sitting on the OEM rims in the garage, I see that they are Goodyear GT ECO tyres. As you say, probably not all LRR are created equal, and I have long since abandoned judging quality by brand and price so who knows what the real difference in rolling resistance is between a Goodyear GT ECO and a Kingstar K108 ? I do suspect that rolling resistance is more to do with tyre pressure than it is with carcass construction, except perhaps where tyres are run at low pressure (say around 25psi) when I could see a more rigid carcass having less rolling resistance than a more flexy one. But then I look at your roll out test.......

The Alto is my work hack and bicycle transport (can't be too many Altos claiming that !) and I live rural but work mainly in town areas so my running is a very mixed bag of rural and urban with a fair few three or four hundred KM trips thrown in. Shortly the Mirage will become the bicycle transport once my friend has fabricated a bike rack to attach to the tow bar mounting points which Mitsubishi so thoughtfully provided on the chassis rails. It will be a bike rack only, not a towbar as I feel towing even a very light trailer with something like the Mirage, particularly CVT equipped, is asking for trouble. According to our dealer Mitsubishi NZ do not offer a towbar as an option, but as imtimated there are three captive-nutted holes on each of the chassis rails and I can't see any purpose for those other than towbar.

The aerodynamic thing is fairly incontrovertible in a naked environment (like on an open wheel racer), an 18.5cm wide block of rubber of given height will take more energy to push it through the air than will a 16.5cm wide block the same height, but I do wonder what happens when you introduce the aerodynamic effects of bodywork. Could it be that the modest difference in frontal area between say 165s and 185s pales to insignificance when three quarters shrouded by bodywork which is already deflecting most of the wind blast ?

As for the offset, to answer my own question the offset of both 14" steel and 15" alloy Mirage wheels (in NZ anyway) is 46mm. Marvellous what one finds when one reads the manual.

Regards to all
Flange

[Polkiuj]

Hi

The LRR in the tire actually is actually mostly to do with the compound. The carcass also do play a role (especially in the reinforcing textile materials) but most improvement still comes from the compound. So does the tread patterns (plays a role as well), again most difference comes from the compound.

Old tires used a material called carbon black to reinforce the compound of the tires. What manufacturers do is to add silica to this mix to make LRR tires. As you mention earlier, not all LRR tires are created equal. The % of silica vs carbon black definitely plays a huge role (Some more advanced tires are now made with 100% silica). When the tires roll, energy is wasted from friction with the road and also internal friction of the rubber. When silica is added to the mix (or it being the main reinforcement), it reduces the internal friction (yes, LRR runs cooler).

Silica advantages:
Lower rolling resistance
Better wet traction

Silica disadvantages:
Lower tread life

If you've ridden mountain bikes long enough you would have lived to see through this change. When LRRs were introduced (remember red and green tires?) back then, speeds at Xcountry races increased and times were reduced. If you read that and tried them, you'd soon realize that your tires wore much more quickly than carbon black based tires.

You would also notice some high end sport tires with dual compounds (silica on inside for LRR and wet traction, carbon black on outside for durability).

Hope my explanations could be understood.

[Flange]

Hi there Polkiuj

Thanks kindly for your explanations which do help greatly to understand the science behind LRR tyres. It's a very imprecise question but when considering the rolling resistance of a tyre, what percentage of the resistance would you feel is due to pressure (or lack thereof), and how much is due to tread and carcass deformation ? To put the question in a different way, can most of the rolling resistance of any given tyre be overcome by increasing the tyre pressure ?

I don't have much experience on mountain bikes, most of our cycling is on road and good quality hard packed trails. On those surfaces my legs tell me that it is much harder to pedal the bike if the tyres are down around 50 psi than up at 80 psi. What is really noticeable is if I am coasting my hybrid downhill alongside somebody on a mountain bike with fat knobbly tyres the mountain bike soon drops behind. I put this down to the lower pressure usually used in such tyres along with the widely spaced tread blocks.

Cheers
Flange

[MetroMPG]

The aerodynamic thing is fairly incontrovertible in a naked environment (like on an open wheel racer), an 18.5cm wide block of rubber of given height will take more energy to push it through the air than will a 16.5cm wide block the same height, but I do wonder what happens when you introduce the aerodynamic effects of bodywork. Could it be that the modest difference in frontal area between say 165s and 185s pales to insignificance when three quarters shrouded by bodywork which is already deflecting most of the wind blast ?

Even with closed wheel (ie. conventional) bodywork, the drag effect of wider tires is significant:

From: Influence of the tire width on drag, lift, and yawing moment, after H Kerschbaum Fig 5.72



CD --- tire & rim size (for a 1991 BMW 318i)

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 LM
0.319 --- 225/55 R 15; 7 Jx15 LM

Keep in mind the increase in Cd comes with an (admittedly small) increase in A (frontal/projected area) too, so you're getting a double whammy.

Data for other vehicles (source):

• 1986, wind tunnel development work for Subaru XT show a drag increase of 5.1 % when tire size is increased from 155 to 185 series radials.

• 1984-1987 HONDA CRX shows jump from 165 to 185 series radials increase drag 9.3 %.

This is all complicated by the fact that if you hold everything else constant (tire construction & materials properties), RR apparently decreases as width increases. So the net impact on efficiency by going with a wider tire will depend on whether you primarily drive fast or slow.