[Fot] Curious Tire size conversion

[dustin nicholson]

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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