205/50R17 vs 225/40R18
225/40R18 is 0.1% taller (+0.02 in) and 0.79 in wider than 205/50R17.
225/40R18 is 0.1% taller than 205/50R17. That is inside the ±3% most shops treat as a straight swap.
Real speed on 225/40R18.
Change in height under the axle.
On the same wheel, split inboard and outboard.
Shop 225/40R18 tires
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205/50R17 or 225/40R18?
Can I use 225/40R18 instead of 205/50R17?
225/40R18 is 0.1% taller than 205/50R17. That is inside the ±3% most shops treat as a straight swap. Also match or beat the original load index and speed rating, and check that the wheel width suits the new tire.
Will my speedometer be off?
At an indicated 60 mph on 225/40R18 you are really doing 60.0 mph if the speedometer was set up for 205/50R17. Going the other way, 205/50R17 would make it read 60.0 mph at a real 60.
How much ground clearance does it change?
Half the diameter difference: +0.01 in (+0 mm) under the axle.