[Fot] Curious Tire size conversion

[Brad Eells]

Here is a modern add for a vintage set of Sports Car Specials that
describes some of the dimensions.

https://vintagewheelsus.com/index.php?main_page=product_info&products_id=357



*Brad Eells*
*Chino CA*
*#72 FP 1969 Triumph Spitfire Mk3*
*#35 DP 1962 Triumph TR4*
*1965 Triumph TR4A IRS...for the road!*




On Thu, Jun 27, 2019 at 2:29 PM dustin nicholson via Fot <fot at autox.team.net>
wrote:

> To determine the size of the old tire in modern designation format measure
> the tread width in millimeters, I’m guessing 5.5 inches times 25.4 = 140,
> that’s your first number.
>
> I’m guessing 9.20 is the dimension in inches of the top side wall + The
> bottom side wall. When added to the 15 inch wheel diameter it would give
> you a tire diameter of 24.20 inches. This is just a guess of what they mean
> by 9.20.
>
> Next, Measure the side wall height in millimeters, I’m guessing 9.20
> inches/2 x 25.4 = 117mm. Divide 117 sidewall height by the 140 tread width
> gives you a height to width ratio of 1.20 which is your second number...
> but they don’t show the decimal so it reads as 120.
>
> So the old 5.50-9.20-15 = a new 140-120-15 (if my guess of what 9.20 means
> is correct, if not, just measure the sidewall as my 120 number would be
> wrong).
>
> It appears that the old tire is 1.7 inches narrower than your new
> 185-65-15 and there is only 1/10 of an inch difference in the tire height.
>
> Dustin
>
> Sent from my iPhone
>
> On Jun 27, 2019, at 1:19 PM, Redmond via Fot <fot at autox.team.net> wrote:
>
> I should've been a little bit more clear than mud.
>
> I'm just curious as to what the size tire he was running back in the
> 1960's. Can anyone translate the 5.50-9.20-15 into today's sizing.
>
> FYI - I'm going with the 185-65-15
>
> Todd
>
>
>
> On June 27, 2019 at 11:08 AM Redmond via Fot <fot at autox.team.net> wrote:
>
> Friends,
>
>
> Curious question:
>
> I have 1 Goodyear Blue Streak tire from when my dad raced my TR3.
>
> Size says 5.50-9.20-15
>
> What size would this be in today's sizing?
>
> Thanks
>
> Todd
>
>
>
>
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