Downsizing rim diameter, what is the optimal tire size?
 

Hi, so I'm downsizing from a r14 rim size to a r13. Current tire size is 155/65/r14 and that is the oem size. My current rims are 14x5.5 rota alloys (so what I got is wider than oem spec. Oem rim size is 4.5).

I have two option for tire sizes:
1.) 155/80/13 (taller sidewall).
2.) 165/70/13 (wider but same as oem diameter. Accurate speedometer)

I found cheap alloy 13x4.5 et45 rims that match up to my car's oem specs (Suzuki celerio / alto 2010 model).

Now the reason for the downsizing is because I am not satisfied with the current tire's ability to absorb potholes, I recently changed front struts (from old busted ones) and it seems that the tires are really just not pleasant to use on bad roads like the ones in my country.

Do take note that in India (where the Celerio is made) the oem tire size there is 155/80/13. The roads there are pretty bad too, potholes galore.

What is the optimal tire size? Should I go for a taller tire or maintain the oem diameter? Would the slightly wider tire negate any efficiency benefits I get from downsizing?

Ideal pot hole tire appears to be largest over all diameter, as wide as practice with a large aspect ratio for lots of side wall.

Right, so this is a vote for 155/80/r13 I assume? Thank you for your advise. Its the tallest sidewall tire I can find for the 13" rim size

The only downsides I see to it is incorrect speedometer reading and slightly less acceleration due to a wider diameter over OEM spec.

I think you will find the 155/80R13 easier to find and have more options available.

Define not pleasant. Repeated replacement of destroyed tires and/or rims. Harshness, noise and vibration?

There is more to tires than their aspect ratio. You have CapriRacer's attention and that's good.

Consider the counterexample. A tall narrow tire will bridge potholes and dodge them better.

You're limited by gearing to ± OEM rolling diameter. Tread compound and the number of radial plys might make the difference.

You're on the right track for coping with poor roads and their potholes:

---the bigger the diameter, the better a wheel can span the gap in potholes

---the smaller the metal wheel for any given overall metal-wheel-and-tire-combo diameter, the more air-and-rubber "cushioning" effect a tire can provide for the combo.

And about the speedometer: IMHO the best solution is the ScanGauge. It is easy to change the gauge's calibrations to the exact speed of the car regardless of its wheel diameter, and it'd think it's a lot cheaper and more convenient than trying to get the car's computer reprogrammed.

I no longer look at my Mazda's speedometer and depend entirely on my ScanGauge. Not only is it more accurate especially since I've got larger-than-OEM wheels and I've adjusted it to them, it's more precise because it's digital and I can read it a lot better than the factory analog speedometer.

Besides, the ScanGauge has allowed me to achieve consistently better fuel economy by showing me how to hone my operating skills relative to speed, hills, wind, and etc.