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Discussion Starter #1
Personally, I have never kept the stock wheels and tires that come with a new car or truck. I have even brought the replacement wheels and tires to the dealer to install. Of course, I negotitated a trade-in value when I purchased the car. This may sound like money foolish. Most new cars come with a wheel/tire configuration intended for maximum mpg, usually at expense of ride comfort. If you think Contiental tires are high quality,.........

Consider changing your stock 15" wheels and tires to 16" with slightly increased offset; not 17" or bigger. The small change will reduce your mpg by an avg. of 0.8 mpg (Scangauge II). Considering how much nicer my Passion rides today, it was worth it.
Wheel Tech - Offset

The slight increase in offset will also help your car track the road better (feel like the tires are grabbing the road better - feel more planted). It is adviseable to maintain the tire aspect ratio as close to stock as possible.
Tire Tech Information - Calculating Tire Dimensions

In lay terms, keep the front wheel smaller than the rear when you change to 16" wheels and tires (like the car is stock). The slightly larger tire size will add a great deal of ride comfort. See My Garage for details.
a.) I sold my Smart 15" stock wheels and tires for almost $700.00. You can get more if you are patient.
b.) A new set of custom 16" wheels will run you about $1200.00 (I said about).
c.) New 16" tires will run about $680.00 (mounted, balanced and installed).

Total: $1200 + 680 = 1880 - 700 (sale of original wheels and tires) = $1180 to greatly improve the ride and handling of your new Smart car. You know, the car you will keep for years while getting 38 mpg, or more.

Are you a racer or a commuter?
How you drive your car has everything to do with after market modifications you consider making. Regarding wheel and tire sizes, a small change is all I recommend. So, if you are a commuter, keep the tire aspect ratios close to stock and don't install bigger than 16" wheels and tires. Anyone driving around with huge wheels and low profile tires lost the dental fillings in the head long ago.

Now, you will get advice to increase the front tire size to the same as the rear to address the Smart's understeer problem.
Understeer - Wikipedia, the free encyclopedia

Unless you plan to race your Smart at the track or drive aggressively, which is quite difficult given the low power of the Smart, I would ignore this suggestion. A bigger front tire will fix understeer. It will also make the car ride harsher in normal driving conditions. AND, it will increase the car's instability in wet road conditions! If you move from 15" to 17" tires, you will lose somewhere around 2-3 mpg.
 

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Can you explain how putting larger wheels on improves the ride? Will making the wheel and tire combo heavier help as well?
Looking forward to your guidance
karl
 

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Can you explain how putting larger wheels on improves the ride? Will making the wheel and tire combo heavier help as well?
Looking forward to your guidance
karl
Tires are part of the suspension, like air springs if you will. I put four equal 185/60-15's on that are 1' larger diameter and the ride is so much better. Wider and larger air springs = better ride. 16" will do about the same, but with a larger rim than the 15", the air springs are smaller volume so not quite as nice as mine and stay away from 17" if you want to fine tune the ride.

I also have put new tires and rims on almost everything I have ever driven since the original equipment is a blend of "what is cheapest for company", what will work for most conditions - but not best for any one and there are always more premium tires on the market than the companies put on AVERAGE cars.
 

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Discussion Starter #6
Same as it is now.

lowndex,
Thanks for the write up. Can I ask you what your original mpg was?:D
Regarding the change to 16" wheels and tires, expect to lose 1.0 mpg (or less). Move to 17" or greater and see the drop increase. Now, my data is based upon a mpg log I keep. My data is not as accurate as a Scangauge II showing real-time mpg. But, moving from 15" to 16" wheels and tires will have minimal mpg impact.

I gained 2.0 mpg with my DTH exhaust system. I lost the mpg gains with my new lead foot. My added driving fun is costing me mpg.
 

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Discussion Starter #7
No, it feel the same.

Sorry, one more thing;
does you Smart feel slower?:D
Changing from 15" to 16" wheels and tires will have a neglible impact on tire rotation - speedometer accuracy and display. I'm sure my speedo is now off by, MAYBE, 1.0 mpg. I kept the tire aspect ratios close from front to rear.

You can use the tire calculator on www.tirerack.com to check for yourself. Else, look up tire size to speedometer calibration on the Internet.
Speedometer Calibration Calculator And Information
 

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Discussion Starter #8
Can you explain how putting larger wheels on improves the ride?
Simple, I have more rubber between me and the road. HOWEVER, there is a fine line between if a little medicine is good for you, then,..........

Be careful making more than a Plus 1 or 2 wheel and tire change:
When I replace the tires on my vehicle, do I have... — Yahoo! Autos

"All this doesn’t mean you can’t change tire and wheel sizes, however. If you maintain the same overall tire diameter as before, you can switch to larger wheels with a shorter aspect ratio tire. This is the basic idea behind "Plus 1, Plus 2" tire and wheel sizing."

Will making the wheel and tire combo heavier help as well?
Remember, weight is mostly your enemy. The main advantage of the Smart car is horsepower to weight ration. Assuming you do nothing to improve the hp, adding weight costs you mpg and slows performance.

The German designed and made Schmidt 16" wheels I put on are second-to-none in terms of strength, light weight and great looks.
Fog City Performance
Ask for Steve Smith

For now, you can see the many 3 lug wheel choices at:
smart_car_wheels




Looking forward to your guidance
karl
Best advice of all, qualify advice received from me (or others) against a professional wheel and tire dealer in your area.
 

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Discussion Starter #9
You have 37" tires!

Tires are part of the suspension, like air springs if you will. I put four equal 185/60-15's on that are 1' larger diameter and the ride is so much better. Wider and larger air springs = better ride. 16" will do about the same, but with a larger rim than the 15", the air springs are smaller volume so not quite as nice as mine and stay away from 17" if you want to fine tune the ride.

I also have put new tires and rims on almost everything I have ever driven since the original equipment is a blend of "what is cheapest for company", what will work for most conditions - but not best for any one and there are always more premium tires on the market than the companies put on AVERAGE cars.

My God man, you have 37" tires! Sorry, I could not resist.

You are an experienced car owner. Unless one is buying a $75,000 or higher automobile, this rule generallt applies.
 

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Thanks Russ I understand the tires as a spring concept and have no problem with that. how the laws of phisics get repealed for people that spend a lot of money amuses me no end. Even the buyer of a much more modest machine will have the benifit of a lot of development work on the suspension of there car and to make a statement of bigger wheels improve ride is very sad.
how is your experiment working for you still happy with the changes you made.
Thanks karl
 

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Personally, I have never kept the stock wheels and tires that come with a new car or truck. I have even brought the replacement wheels and tires to the dealer to install. Of course, I negotitated a trade-in value when I purchased the car. This may sound like money foolish. Most new cars come with a wheel/tire configuration intended for maximum mpg, usually at expense of ride comfort. If you think Contiental tires are high quality,.........

Consider changing your stock 15" wheels and tires to 16" with slightly increased offset; not 17" or bigger. The small change will reduce your mpg by an avg. of 0.8 mpg (Scangauge II). Considering how much nicer my Passion rides today, it was worth it.
Wheel Tech - Offset

The slight increase in offset will also help your car track the road better (feel like the tires are grabbing the road better - feel more planted). It is adviseable to maintain the tire aspect ratio as close to stock as possible.
Tire Tech Information - Calculating Tire Dimensions

In lay terms, keep the front wheel smaller than the rear when you change to 16" wheels and tires (like the car is stock). The slightly larger tire size will add a great deal of ride comfort. See My Garage for details.
a.) I sold my Smart 15" stock wheels and tires for almost $700.00. You can get more if you are patient.
b.) A new set of custom 16" wheels will run you about $1200.00 (I said about).
c.) New 16" tires will run about $680.00 (mounted, balanced and installed).

Total: $1200 + 680 = 1880 - 700 (sale of original wheels and tires) = $1180 to greatly improve the ride and handling of your new Smart car. You know, the car you will keep for years while getting 38 mpg, or more.

Are you a racer or a commuter?
How you drive your car has everything to do with after market modifications you consider making. Regarding wheel and tire sizes, a small change is all I recommend. So, if you are a commuter, keep the tire aspect ratios close to stock and don't install bigger than 16" wheels and tires. Anyone driving around with huge wheels and low profile tires lost the dental fillings in the head long ago.

Now, you will get advice to increase the front tire size to the same as the rear to address the Smart's understeer problem.
Understeer - Wikipedia, the free encyclopedia

Unless you plan to race your Smart at the track or drive aggressively, which is quite difficult given the low power of the Smart, I would ignore this suggestion. A bigger front tire will fix understeer. It will also make the car ride harsher in normal driving conditions. AND, it will increase the car's instability in wet road conditions! If you move from 15" to 17" tires, you will lose somewhere around 2-3 mpg.

So what exactly were the wheel and tire sizes you changed to? How much were the Schmidts from your recommended source?
 

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Karl,

I have about 1000 miles now on my new tire/wheel combination. And I am very happy with the trememdous ride improvement, cornering at higher speeds and feeling more in control, wet driving, less tire noise than the O.E. tires, the way the car looks and everything but one difference. When I first installed these I didn't have the DT exhaust on. The larger diameter (no lowndex - not 37" but 23.6 INCHES) made the acceleration from a dead stop really weak and my scangauge showed that I was really sucking fuel to get up to speed - and mpg calculations at 39 showed it. Then after installing the exhaust all that improved. However, if I was doing again, even though I really am a Michelin fan, I would look for another premimum tire about that wide, or wider but closer to the O.E. diameter. DON'T use the sidewall marking to calculate diameters, go to their sites to see the diameters. Somewhere in the low to mid 22" diameter range would be better.

My tests on speedometer and odometer have been posted here and now are absolutly correct. But my driving style, interstate driving and use of A.C. does change this car more than others I have owned. Really tender use of "GO" pedal, with A.C. and 100 miles of interstate got me 45 mpg. My former diving style - wife says "agressive" I say "normal" dropped me to 40 mpg, under about the same conditions and highways.
 

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Karl,

I have about 1000 miles now on my new tire/wheel combination. And I am very happy with the trememdous ride improvement, cornering at higher speeds and feeling more in control, wet driving, less tire noise than the O.E. tires, the way the car looks and everything but one difference. When I first installed these I didn't have the DT exhaust on. The larger diameter (no lowndex - not 37" but 23.6 INCHES) made the acceleration from a dead stop really weak and my scangauge showed that I was really sucking fuel to get up to speed - and mpg calculations at 39 showed it. Then after installing the exhaust all that improved. However, if I was doing again, even though I really am a Michelin fan, I would look for another premimum tire about that wide, or wider but closer to the O.E. diameter. DON'T use the sidewall marking to calculate diameters, go to their sites to see the diameters. Somewhere in the low to mid 22" diameter range would be better.

My tests on speedometer and odometer have been posted here and now are absolutly correct. But my driving style, interstate driving and use of A.C. does change this car more than others I have owned. Really tender use of "GO" pedal, with A.C. and 100 miles of interstate got me 45 mpg. My former diving style - wife says "agressive" I say "normal" dropped me to 40 mpg, under about the same conditions and highways.
Thanks Russ sounds like you found the sweet spot for you without spending 75K premium is a word I have trouble with in ice cream it tells me there is more milkfat... So premium low fat ice cream is... tires like cars are a compromise no matter how much you spend. The difference is the direction of compromise. The more grip the less tire wear so on glad your choice is working for you.
karl
 

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My data is not as accurate as a Scangauge II showing real-time mpg..
Sorry to change the subject for a moment, but I've seen this line before concerning scangauge and "real time" mpg....how does that work - does scangauge actually measure the amount of fuel going to the engine/unit distance? (which is to me, the only definition of real time mpg!)
 

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Do you think this is something I could ask a tire shop do and they would know what I was talking about? Like Merchant's Tire? Or would the dealer have to do it? I'm nowhere near owning a Smart yet, but I would definitely be interested in doing this. Alas, I am no tire expert. :eek: Thanks!
 

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Sorry to change the subject for a moment, but I've seen this line before concerning scangauge and "real time" mpg....how does that work - does scangauge actually measure the amount of fuel going to the engine/unit distance? (which is to me, the only definition of real time mpg!)
The ScanGauge reads the car computer. Therefore is can "see" the amount of fuel used and the mph so it can calculate mpg and can display gph. Not that there isn't a slight delay, but it is close to "real time". I notice when it shifts or when I slow there is a very, very slight lag to the display and knowing what is going on.
 

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Do you think this is something I could ask a tire shop do and they would know what I was talking about? Like Merchant's Tire? Or would the dealer have to do it? I'm nowhere near owning a Smart yet, but I would definitely be interested in doing this. Alas, I am no tire expert. :eek: Thanks!
I seriously doubt any smart dealer would make these tire/wheel changes because if they do then you could go back for warranty repairs and if the larger tires/wheels caused a suspension, brake, transmission, steering failure there will probably be NO warranty. And if they installed them then they have approved it and granted warranty. Just like they noted I have a Scangauge and IF I erased a code then they would have a way out of giving warranty - say over reving or over speed or overheat, etc.

So you can go to an independent dealer but there are less and less tire dealers that will be creative. With the scare in manufacturers from the FORD/Firestone deal they have become so paranoid about everything that it is getting harder and harder to be creative. I went to one Firestone dealer locally that wouldn't put the tires I wanted on my Excursion, so I went to WalMart and had it done.
 

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Mileage and performance are not impacted by size. But they are greatly impacted by rotational mass! The weight of the wheels/tires will determine the actual impact. (within reason, like here with a 1 inch change in rim size)
One other long term benefit is increased tire life. On my track cars, the initial question is "how much does it weigh?" if it spins in any function of the drive line. Carbon fiber drives shafts, 7 pound aluminum flywheels, lighter clutches etc. all have a trememdous impact on performance and fuel mileage. And wheels, since there are FOUR of them, can be an incredible gain in the battle against rotational mass. It is easy with most cars to shave 100 pounds with the right wheel/tire choice.
 

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...It is easy with most cars to shave 100 pounds with the right wheel/tire choice.
You're right! But with the Smart car, it is not so easy cause the stockers are pretty light weight already. Also, the companies that do make lighter 15" wheels don't make them in 3-lugs, and the only adpoter / spacer that's currently available is 3 to 5x112. Needlesstosay, there are very little light weight, in-expensive 5x112's out there (maybe BBS or OZ).

The waiting game continues...:mad:
 

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Discussion Starter #20
Who needs 5x112 mm?

You're right! But with the Smart car, it is not so easy cause the stockers are pretty light weight already. Also, the companies that do make lighter 15" wheels don't make them in 3-lugs, and the only adpoter / spacer that's currently available is 3 to 5x112. Needlesstosay, there are very little light weight, in-expensive 5x112's out there (maybe BBS or OZ).

The waiting game continues...:mad:
When there are plenty of 3x112 mm wheels to choose from:
smart_car_wheels
 
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