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Date:         Thu, 11 Jun 1998 14:05:12 -0400
Reply-To:     Michael Sullivan <sullivan@OPENMARKET.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Michael Sullivan <sullivan@OPENMARKET.COM>
Subject:      Re: tire size vs. rpm.  the real answer
Comments: To: Vanagon@VANAGON.COM
Content-Type: text/enriched; charset="us-ascii"

Dear Michael,

You are almost correct -- remember that Vanagons all report speeds that are approximately 10% higher than actual. (this was an 80s thing to do)

Thus, with STOCK TIRES when your speedo says 60mph you are probably only going around 55mph. With 27" tires the speedo and actual speeds nearly match: 60mph is just about 60mph. With 29" tires you'll be about 10% off as well -- in the other direction. Thus, your speedo will read 60mph but you'll actually be going about 65mph!! (With this setup be sure to watch out for speeding tickets)

Cheers,

MJS

At 03:06 AM 6/11/98 EDT, Michael Modl wrote:

>If I do

> put on larger tires - say 2" larger in diameter - then at 2000 rpm the larger

> circumference will be covering more ground than the smaller tires in a time

>period.

> Since it covers more distance than the smaller tire in the same unit of time,

>the car

> is going faster. How much will the speedometer be off? The TireRack web

>site has

> some good info on this.

>

> NEW TIRE DIAMETER/OLD TIRE DIAMETER x MPH at a certain RPM = ACTUAL MPH at

>that RPM

>

> In my case:

> 30/28 x 50 = 53.6 So when my speedo indicates 50 I'll really be

>doing 53.6

> so I'll back off a little at higher speeds.

>

> Gary

> 80 Westy, 88GL

>

> >>

>Hi Gary, you can also figure out your real speed by timing how long it takes

>you to travel one mile, on the freeway, between mile markers. Maintain a

>perfect speed, like 70 MHP, time your car to travel that mile, time a few mile

>markers because they all aren't exactly one mile appart, take an average, lets

>say it took 51.5 seconds to travel one mile. Take 3600 seconds and divide it

>by 51.5, there's your speed, 69.9 MPH....... (You'll never see 30 seconds to

>travel one mile, unless it's falling over a cliff.)

> bye, Michael Modl. 87 syncro.

>

>

<bold>Michael J. Sullivan

</bold><italic>Director of Catalog Design

Open Market, Inc.

</italic>

'87 GL Syncro Westfalia

********************************************

work: http://www.openmarket.com

vanagon: http://www.hsdesign.com/vanagon

scan tips: http://www.hsdesign.com/scanning

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