I just picked up my Passion last Friday and drove it home 400 miles at 75-85mph. As you can guess the MPG wasn't too good. The last 100 miles before home I refuelled and babied it between 55-65mph and got about 42MPG.
Anyway, on to the subject of my thread. I've been interested in high MPG cars for a while, owning a gaggle of Chevy Sprints and later Geo Metros in the 80's and 90's. In particular, the first Sprint I owned I bought new in 1986. It had 12" tires on it. I averaged about 47MPG around town and about 53MPG on the highway with that car. That is until I changed the wheels and tires. About a year and a half after I bought it I put on 13" wheels and lower profile tires that equalled the original diameter of the 12" stock tires. The new 13's were wider, probably about 1.5" or so, but again the same diameter. My fuel economy dropped to about 37MPG around town with that single change. I assume it was rolling resistance that caused it. In 1995 I bought a Geo Metro with the same motor (the 3 cyl 1000cc) but this time it was fuel injected instead of carburated and the Metro had 13" tires and slightly wider. I got about 37-38MPG around town with that car. I wonder what the effect of different tires on the smart would be...
Low roll resistance tires (like those on hybrids) would surely help to some degree at the expense of handling and ride comfort. Wider, heavier, wheels and tires will take some toll in the city, but the smart's wheels/tires are already pretty tiny.
I upgraded to 15x6 wheels with 195/50 all-season tires front and rear and didn't really see any noticeable change in mileage, but I have virtually no city driving and I made the change early while the car was still breaking in, so it's probably not the best comparison.
However, if you do decide to make changes, be careful. All of the safety systems on the car (traction control, stability control, etc.) are tied into sensors that monitor wheel speed front/rear. Any change must keep the diameter of the front/rear tires very close to avoid throwing the car into limp home mode due to "faulty" signals received from the wheel speed sensors.
And, let us know if you make changes and what the results are!
I'm a former tire sop manager and pizza delivery driver and wannabe hypermiler as well as a former owner of the ultimate US MPG champ, the original Honda Insight with a 5spd manual.
Anyway, some observations...
Heavier rims/wider tires: They will have a detriment to fuel econ. But, the real loss comes from the added weight of the rims/tires in city driving. If highway driving, there may be very little to no effect. In city driving (such as all pizza delivery) I lost 3mpg (25 to 22) when I went from worn 185/60/15's on my turbo Jetta that weighed 35lbs to 225/45/17's on heavy factory replica wheels (51lbs). On the highway however...I noticed almost no difference.
I considered this recently when I purchased my Smart as I liked the idea of the wider wheels for handling purposes. Also, the 195/50/15 size is a fairly common size making replacement about $50 each for those 2 tires, while the smaller 175/55/15 rear size is closer to $100 per tire. So, I figured whatever I lose in MPG I gain back in lower tire cost, and I have the benefit of the gain in performance. Both front sizes though are about equally as expensive due to their rare sizes that only fit Smarts.
When possible, I try to select the lighter tire available. Tire Rack lists tire weights in their "specs" on their site. I've seen 215/45/17's for my old Civic range from 18-24lbs. Tire weight is even more improtant than rim weight since it's further from the axis of rotation. One of these days when I get bored, I'll pull off the wheel form the car and weigh it just to see. I haven't looked for rims that much for my car yet...but the few sites I did look on (US sites) had very little.
As a sidenote, I peeled up the passenger floor to get a look at the OEM battery and it's HUGE!!! Prob weighs 40-45lbs or so. I have an 11lb AGM battery in my WRX that cost only $60 shipped. On the Smart, I'm a little worried that the heavy battery is there to provide stability, rollover resistance, or better weight distribution. So, not as eager to change that out for the weight savings. Although, it would make parking lot steering ever so slightly easier =P
Last edited by pointlomadave; 04-13-2012 at 11:47 AM.
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^^^I'm thinking mostly in terms of roll resistance. That much weight placed that low in the car would play a significant part in helping the car resist roll-over in an extreme situation...may buy you an extra degree of lean or two! Now, the chances of encountering a situation that would roll the car either way is doubtful.
Larger batteries are basically a convenience item in most cars so that one can leave lights on for long periods of time with the engine off, or keep oneself busy with the stereo or whatever. But hauling around an extra 30 lbs is pretty unnecessary IMO for the small benefits mentioned that a larger battery provides...which is why I usually swap them out for tiny ones on most of my vehicles.
This one I have in my 2010 Subaru WRX right now. Works just fine =)
I have said it before and I'll say it again.... Mobil 1 oil is extra slippery which delays the engine break-in by about 12,000 miles. I did not start getting better mileage until almost 30,000 miles. Before that I was getting around 35-38mpg mostly highway miles. Once I passed the 30K mark I saw a gradual improvement and since around 45K I have been getting 42-48mpg driving the exact same roads.
Give it time and it will get better.
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^^^Too funny! But yeah, the physics of rotating vs. static weight and rolling resistance are well documented. I wish these stupid car mags would do more articles on real world stuff than testing $200k cars that normal people don't buy.
But come to think of it, I did read an article on wider/heavier rims & tires some years ago that some magazine or online mag did. I think they only lost 1.5mpg or so mpg on a 25mpg car or so. But, again, if just rolling down the highway at steady speed, they'll be less detrimental than stop and go driving in hilly terrain which would have the greatest effect.
Did the math...at $4.50 a gallon, the difference is $1,800 over 100k miles on the car in the article. Not too mention the additional initial cost of the rims and the wider, more expensive tires.
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