Date:         Fri, 14 Oct 2011 18:32:51 -0700
Reply-To:     Alistair Bell <albell@SHAW.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@SHAW.CA>
Subject:      Re: tire circumference
Comments: To: mark drillock <mdrillock@COX.NET>
In-Reply-To:  <4E98DE5C.7070905@cox.net>
Content-Type: text/plain; charset=us-ascii

We've been been over a lot of topics before, but it's interesting eh? What is the fudge factor involved in the 1010 calculation?

Must be more than just "simple arithmetic" involved. Maybe they use economic theory :) Or maybe they factor in some sort of slippage.

for instance, Continental's own data* for the Vanco 8, 185/80R14, says diameter is 25.6". This agrees with simple arithmetic. But the revs/mile is stated as 817.

So something is different when they multiply by pi and then divide result into #inches in a mile.

I am not disputing that 1010 gives results closer to the manufacturer's published data in the examples looked at, the question is it accurate for all tires? It seems that "data accuracy" was the point in question.

If one has the tire data from the manufacturer, then none of the calculators are needed.

alistair

*http://www.conti-online.com/generator/www/ca/en/continental/automobile/themes/van_tires/summer/hidden/datasheet_vanco8_en.pdf




On 2011-10-14, at 6:14 PM, mark drillock wrote:

> Yes, we have been over all this before. That simple arithmetic gives one value while the real world tires are something else. That program gives rev/mile results way different than every tire company specification I have checked.
> 
> Some other programs manage to give results that much more closely mirror what the tire companies test results say. I would use one of those other programs if data accuracy is important to you.
> 
> This 1010Tires program gave good numbers for all the sizes of interest to me. By good numbers I mean numbers that fall within the range of specs given by various tire companies for their tires of a given size.
> 
> http://www.1010tires.com/tiresizecalculator.asp
> 
> Mark
> 
> 
> Alistair Bell wrote:
>> funny, when i do it long hand I get 786 (for 80 profile). I must be making the same mistake as the miata calculator is doing.
>> 
>> 
>> let me work it out here:
>> 
>> 185 mm = 7.283"
>> 
>> 80% of that = 5.826"
>> 
>> add that twice to the rim diameter of 14" = 25.652" (overall tire diameter)
>> 
>> circumference is diameter X pi = 80.588"
>> 
>> inches in a mile = 63,360
>> 
>> 63360/80.588 = 786.22
>> 
>> alistair
>> 
>> 
>> 
>> 
>>