The physics of tire size

[thedoctor]

I have an 83 dl daily driver. Looking for recommendations on new tires. Stock size: 155SR13. Knowing that stock is not always best... what size tire is best for economy vs performance? I'm looking for the physics answer. For example, will a larger tire give me better economy on the highway, but ruin my clutch in stop and go driving? Please help me think this through. And please share thoughts about best brands for durability, etc. Thanks

[NoahDL88]

Lighter is better, so theoretically smaller is better, alloy wheels will be lighter, but if you hit a rock or curb they're done, steel wheels are much more forgiving. lowering the rpms will help to some extent, if you have a bigger tire, but if you're lugging the motor and have to down shift the benifit is gone. a smaller side wall will help in cornering, as will a wider tire, but go too wide and the friction goes up, MPG goes down. As far as brands go, go to a shop you trust and ask their opinion, and shop around, a lot of places will have goodyears for the same price as the Les Shwab no-names, you just gotta look around.

 

the only bigger wheel available is the Peugeot(sp) do a search

[MilesFox]

175/70 or 185/70

 

either of these are what i see stock on soobs all the time, generally 175's on fwd and 185 on 4wd. i would go with the 185 for a lot of highway driving

[NorthWet]

Narrow, high pressure tires will give you the best highway fuel economy. Weight for steady state is irrelevant, and only slightly so for stop and go traffic (largely made irrelevant by vehicle's much greater weight). PMI effects are negligible under normal driving conditions.

 

The following is based on "apples vs. apples" (same tire model, different sizes):

 

Miles' recommendation of 175/70r13 or 185/70r13 would give you approximately the same height/circumference as your 155s but much wider tread. The wider tread might decrease fuel mileage somewhat but will vastly improve cornering stability (while somewhat decreasing straightline stability).

 

I personally would compromise on a good quality 175/70 or 185/70 tire. You are unlikely to notice any significant downside (other than cost), and will increase the cornering/object-avoidance/stopping abilities of your car.

[thedoctor]

Thanks one and all. Very helpful.

[MilesFox]

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