run 225/35/18 or 215/35/18 on the 25th ann stock wheels? 5 spoke wheels so what people call them. I know the stock tires are 225 40 18 but I can get both the first two tires for a reasonable price atm. Need some advice

 

if stock is 225 40 18, and youre able to get 225 35 18, the only difference is the tires are going to be 5mm thiner in the sidewall. so youll be ok. a harsher ride (though i dont know if you'd even notice it) but 5mm is nothing

 

Stock is actually 225/45-18 and 245/45-18 , those tires will be almost 2 inches shorter than stock. Perfect size for s civic.

 

If you are uncertain about tire size I suggest that you used the recommended size.

 

Actually, that’s not true.

• The sidewall height on a 225/40-18” tire is 89.9mm and the sidewall height on a 225/35-18” tire is 78.7mm. The difference between sidewall heights on these two tire sizes is not 5mm as you stated. The sidewall height difference is 11.2mm.
  
  
• And, the stock size is not 225/40-18” as you say. The stock size is 225/45-18”. So the sidewall height between the stock tire size (225/45-18) and a 225/35-18” tire is 22.3mm (101mm-78.7mm).

It gets worse when replacing the stock 225/45-18” tire with a 225/35-18” tire when you consider the difference in overall diameter. The stock size has an overall diameter of 25.97”. The overall diameter of a 225/35-18” tire is 24.20”. The difference in overall diameter is 6.82%. That is way too much for normal street driving.

This great a difference would look bad (too much gap), and the car’s electronics would not work properly depending upon its equipment (VDC, TCS, and probably ABS) along with a 7.3% speedometer error.

There seems to be some confusion on the metric tire sizing system, so here’s the deal on this:

The metric tire sizing system represents a tire size as: [section width (mm)] / [aspect ratio] - [rim diameter (inches)]
For example: a tire size 225/45-18 is 225mm wide, has an aspect ratio of 45 and fits an 18" rim (wheel).

The aspect ratio (the second number) is not a measurement. The aspect ratio represents the tire's sidewall height as a percentage of the tires width (section height divided by section width). In the example above, the sidewall height is 101mm (101/225=45).

Hope this is clear and prevents some confusion and inaccuracies.

--Spike