A change to 16" wheels & tires really improves the ride

[lowndex]

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.

[16d @ 4]

lowndex,
Thanks for the write up. Can I ask you what your original mpg was?

[16d @ 4]

Sorry, one more thing;
does you Smart feel slower?

[Karl Roth]

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

[RussBarnes]

Originally Posted by Karl Roth

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.

[lowndex]

Originally Posted by 16d @ 4

lowndex,
Thanks for the write up. Can I ask you what your original mpg was?

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.

[lowndex]

Originally Posted by 16d @ 4

Sorry, one more thing;
does you Smart feel slower?

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

[lowndex]

Originally Posted by Karl Roth

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.

[lowndex]

Originally Posted by RussBarnes

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.

[Karl Roth]

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