Date:         Sat, 15 Oct 2011 18:25:41 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: tire circumference
Comments: To: Alistair Bell <albell@SHAW.CA>
In-Reply-To:  <A55717BD-FE23-4D50-9616-1DAEE4CB323E@shaw.ca>
Content-Type: text/plain; charset="US-ASCII"

The KPH speedo is 1,000 revolutions per kilometer, not per mile. The 805 was
introduce to further make the speedo read faster than reality. It also
through off the odometer. With 4% error you really only traveled 96,000
miles when you thought you reached 100,000.

Dennis


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Alistair Bell
Sent: Saturday, October 15, 2011 10:50 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: tire circumference

one question I have had for a while is why do vanagon speedometers have a
range of revs/mile numbers on them? I have 2 old ones in my parts bins
(mph), one has 820 and one has 805.

And of course, syncros are different. MY '86 with a purely kph speedo, has
1000 on it. I guess I should look for go kart tires :)

alistair









On 2011-10-15, at 7:29 AM, mark drillock wrote:

> The Miata.net tool directly calculates revs per mile but does it
> inaccurately. Other tools do it and get results that match the real
> world. Why the tool always gives bad data matters little. There are much
> better tools that cost the same.
>
> Mark
>
>
>
> Mike S wrote:
>
>>
>> It is simply being misused. The Miata site calculator is intended to
>> compare different tire sizes, not give correct absolute results, and is
>> pretty accurate for that.
>>
>> Tire size can't be used to directly calculate revs per mile - as soon
>> as you put a load on a tire, it flattens on the bottom. That reduces
>> the rolling radius, and it will do more revs per mile. That's why the
>> calculation underestimates.
>>