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Re: [Fot] Fwd: Hoosier R6 tire pressures

To: Bill Babcock <billbab@me.com>
Subject: Re: [Fot] Fwd: Hoosier R6 tire pressures
From: Larry Young <cartravel@pobox.com>
Date: Fri, 10 Sep 2010 10:11:56 -0500
Bill,
I've heard you describe this modification before.  I'm not as 
knowledgeable on this subject as you, but I have trouble seeing how this 
helps.  When I did the suspension on my TR3, I did a lot of measurements 
and used the Front Suspension Geometry Pro software to help figure 
things out.  I also found the Puhn book on handling to be useful.  At 
that time most people were shortening their upper A arms to increase 
negative camber, which moves the upper outer pivot inward.  There was 
also the "Irv Corey" modification which moved the upper inner pivot 
inwards.  This is done by mounting a piece of angle iron where the 
fulcrum would normally sit on top of the spring tower.  Then two of the 
ears are cut off the fulcrum so it can be turned on it's side and 
mounted to the angle iron.  I think either Irv or Jack sent me this 
sketch several years ago - 
www.tildentechnologies.com/downloads/Irv_Korey_Mod.jpg.  To get about 
-1.5 camber from stock would require this pivot to be moved about 0.5 
inches. The software indicated that it didn't matter much whether the 
inner or outer pivot were moved laterally this amount.  The software 
indicated you could make major improvements if you moved the fulcrum 
down by shortening the spring tower. This modification increases the 
camber gain which improves the camber when the body rolls in a turn. I 
think Jack told me he had seen this mod on someones car, perhaps Doug 
Karon's Ambro (current owner unknown).  I never implemented this change, 
but I thought it was an interesting idea.

Front Suspension Geometry Pro is not a very user friendly program.  It 
requires you give all the dimensions in an awkward way.  To save others 
from having to go through this, I wrote a report containing my 
measurements.  Since it was written by an engineer, it is not the 
easiest report to read.  Anyone that wants to get into this can download 
the report at - www.tildentechnologies.com/downloads/TRsuspension.PDF.
-Larry

Bill Babcock wrote:
> You can do a couple of very nice things for your handling by moving the
> pivot arm inwards the width of the bolt spacing and drilling just two new
> holes. Unfortunately you then need to lengthen the upper arms about half an
> inch, but you can make them adjustable when you do that. It decreases camber
> gain and allows you to adjust camber at the same time. It might also decrease
> bump steer--I suspect it will on TR4s, though I haven't measured it. The inner
> pivot of the tie rods on TR3s are inside an imaginary line drawn from the
> lower inner suspension pivot and the upper inner suspension pivot. I think
> they are on TR4s too. Moving the upper inner pivot inwards will move the line
> closer to the tie rod pivot.
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