Tire report Sumitomo

I have two pairs of different size Sumitomo tires:

T4 175/65TR14 (worn) - 919 rpm/mile (specs)
T4 175/70TR14 (new) - 886 rpm/mile (specs)

During my Hybridfest trip, I would find sections of highway with mile markers and measure the differences between indicated and mile marker distances:

175/65TR14 (front) - 1.3% low indicated miles
175/70TR14 (front) - 5.8% low indicated miles

4.5% difference of worn 175/65TR14 vs new 175/70TR14
3.6% difference of specs 175/65TR14 vs 175/70TR14
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0.9% difference due to wear from new vs old tires

With the larger diameter tires on the front, there was more and welcome bumper clearance. Bumps and dips that in the past would scrape the air dam were no longer a problem. Also, the steering seemed more stable perhaps due to the larger angular momentum. However, my indicated 70 mph was actually 74 mph and the indicated 49.2 MPG was closer to 52.1 MPG.

With the smaller diameter tires on the front, the steering seemed a little less stable, more wander. The indicated 70 mph was closer to 71 mph. Unfortunately, I didn't make a record of the MPG (I was pretty tired) but remember it being in the low 50s. Given I have the same four tires, the actual MPG should not change from swapping the front and rear tires.

I like the handling and extra ground clearance of the larger diameter tires. They are a little noisy on the yankee concrete highways but rolling up the windows mutes it out.

I will be ordering another pair of 175/70TR14s so the headlights will be level, increased ground clearance (0.5 cm) and improved stability. The same size tread width means there is no risk of interference with the wheel wells. When I swapped the front and back tires, the larger tires "looked good" as if they were made for the car ... their outer diameter seemed to fit the curve of the wheel well better than the smaller tires.

Bob Wilson

 

The 185 width also means more cross-section drag and probably more rubber flex. As winter snow tires, they'd be great. But for touring tires, I'd go with a narrower tire.

Bob Wilson