re: Tire size: 165 HR 14

[Carscribe@domain.elided]

In a message dated Fri, 22 Feb 2002  3:59:19 PM Eastern Standard Time, Jay Negrin <jmnegrin@domain.elided> writes:

> I always thought that the replacement for 165 was a 185/70.  closer to
> the same overall diameter.  the easier steering is a benefit.  Of
> course, there won't be as much rubber on the road to "stick".
> 
> The other option that has been mentioned, as a replacement of similar
> diameter is a 195/65.  I don't think the difference in steering between
> the sizes is significant, but that's just me.
> 
> The HR on the tire is the speed rating.  SR is for continuous speeds up
> to 113 mph.  HR is for speeds up to 130 mph.  VR is for speeds up to 150
> mph.  I look at the speed rating as, not so much, just for the speed,
> but for the overall strength and quality of construction.  I expect, but
> do not always see, that the higher the speed rating, the higher the
> overall performance of the tire.  YMMV
> 
> Jay Negrin
> ARO So Cal



The actual replacement for a 165 HR 14 is a 165-80-14.

Over the years there have been many different naming and measurement systems used. That's what's causing confusion here. In the older European tire size nomenclature the "HR" referred to the aspect ratio as well as the speed rating. So HR has a one-to-one relationship to the later 80 series aspect ratio naming convention. In fact, it was not uncommon to see just "R" alone, ie; 175R15, for tires that had no speed rating at all.

The older system was sufficient when the only tires offered for these cars were all what would later be called 80 series-- from approximately 1960 through the early '70's. It was then when 70 series tires started becoming common with the introduction of the Michelin XWX, then considered a 'low profile tire." 

With the 165 part remaining the same as it has, and referring to the tread width in millimeters, any 185 tire will be wider by appx. 20mm than a 165, and if it's a 70 series, will be significantly lower in profile than a HR tire. Mind that the "70" is a ratio between tread width and cross section, meaning that the sidewall height varies with tread width-- a 165-70-14 will be have a smaller overall diameter than a 185-70-14, though both are 70 series tires fitting 14 inch wheels. 

A new "vintage" Michelin XAS (from Coker Tires) in 165 HR 14 has an overall diameter of 24.5 inches; a newer 185-70-14 averages around 23.7 inches, and a 195-65-14 at 23.5. A one-inch difference in rolling diameter effectively lowers the car's gearing substantially, resulting in many more revs per mile. Someone else is welcome to do the math to calculate how many for a particular car. Hope this clears it up.
Cheers,
Paul Mitchell

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