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Discussion Starter · #1 ·
Just had Les Schwab put new tires on my ‘08 Cabrio. I thought the car looked a little different and it turns out they put the same size tires on the front as on the rear! They’re 175/55R-15 all the way around. The fronts are supposed to be 155's. So, my question is, does anyone know why the tire sizes are different from the factory? The larger tires clear the wheel wells just fine and I don’t notice any difference in handling. Should I just keep them the way they are? Thanks for any input you have.
 

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There's apparently a reason, but plenty of guys have done the same size tires mod with no apparent issues....I wouldn't worry about it.
 

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Discussion Starter · #3 ·
I just got to thinking (maybe bad thing to do!), aren’t the rim sizes different? I think I read the fronts are 4.5” and the rears are 5.5”. Don’t know much about tire sizing and wondering if it’s okay to have the larger tires on the smaller rims?
 

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The reason for staggered tire sizes on the smart between front and back:

“Staggered tire setups with smaller width tires at the front axle generally produce understeer near the handling limit. Understeer, or a vehicle’s tendency to “push” through a corner, is considered a safer limit handling characteristic than oversteer, which is when the rear of the car breaks traction and moves around during aggressive cornering.”
 

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I read that originally SMART was designed with all four wider rear tires, but during Hard Cornering Test the car was tipping and rolling over, because wider tires have. more frictional resistance no wiggle room for sliding. The only way SMART was able to pass the Hard Cornering Test was narrow tires on the front. Just be aware and carefully during sharp sudden steering maneuvers.
 

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Discussion Starter · #6 ·
Thanks for the replies! And you’re right on! I talked with a MB guy and he confirmed that the tire sizes are to create the understeer that you refer to. He also said that it could screw up the stability control computer and that the front rims are too narrow for the larger tires. I managed to confirm all this by researching old posts on this site. Bottom line is, I took the car back to Les Schwab and had the correct size tires installed. They were great about it and even refunded me $20 because the smaller tires are cheaper!
 

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...I talked with a MB guy...the front rims are too narrow for the larger tires...
A MB guy isn't going to recommend any non-factory approved modifications.

155/60R15 is not the largest tire size that you can fit to the front 4.5J rims.

Toyo give a range of 4.5J to 6J rim widths for the fitment of 165/60R15 tires


175/55R15 is not the largest tire size that you can fit to the rear 5.5J rims.

Toyo give a range of 5" to 6.5" rim widths for the fitment of 185/55R15 tires

 
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