[DeTomaso] more on rear tire width beware or be educated.

j g notstock at yahoo.com
Wed Aug 25 19:25:01 EDT 2010


In my experiences over the past ages one needs to be very careful when adding tire width to any vehicle. In vehicles with rear weight bias  the wider tire even if kept on the same track width if added to the rear will almost always significantly increase push on corner exit  as well as  a loss of  front cornering grip in general due to the increased rearward weight transfer with bigger rear tires. If the offset is changed to move the tire outward this effect is amplified.  Unless you are prepared to play with both front and rear widths and with offsets to adjust either front or rear or both;   wider tires cause real bad things even on race cars. . Through many years of running cars in lots of types of series as well as just for show and fun driving a good rule of thumb that appears to get one in the ball park for mid engined high power cars is keep the front tire width including rim to about a 1.33 ratio rear / front  on real, race rubber
 always run a rim that is at least 1/2 wider than the tire contact patch, 1 inch is better. Next is front to rear track numbers . To help eliminate corner push as well as to increase lateral cross weight transfer making the front track 2 inches to 2.5 inches wider than the rear track helps keep the car civil and controls the majority of the push. as well as allows quick but controllable throttle induced steer either way.  Additionaly front and rear toe settings can make an un drivable car into a slot car handeling by looking at a few things. Irs rear suspensions do not transfer the tractional torque directly into the chasis like a live axle. so to help control corner entry as well as straight line acceleration stability some amount of rear toe in is helpful. On short tight tracks I run 1 inch total tow in in the rear with 15 inch wide rims and race rubber . To help corner entry the front is usually set to 1/8 to 1/4 inch toe out. These settings allow
 the vehicle to turn in quicker as well as apply power sooner without push than woud be possible with zero toe in the back and toe in in the front . Tire slip is assumed to be about 6 to 7% in the rear and has shown to be not a bad estimate on mid engined high power vehicles.    sway bars now can be used to tune the amount as well as when the push is exhibited . In real nasty responsive short wheel base cars  I always bring 1/8, 1/4  spacers 
for each wheel to any event to allow a track width change and also to increase front scrub radius on smooth or wet tracks .  the spacers if made correctly with the proper lugs are safe and approved by most sanctioning bodies.  Putting huge rubber all around without considering  scrub radius , change in axle position from zero or trailing  to leading in the front upright can improve or  destroy the vehicles smooth driving characteristics with too much increased steering force, too much steering feed back , too little steering force and radical side loads with negative scrub radius that causes the car to hunt rather than hold a line. Wide tires generally do not like lots of camber to create a maximum lateral force curve , and increased caster or scrub radius  without changing the axle relationship could destroy your ackerman as well as radically effect steering force and breakaway points with the same tire and set up. Lots of caster is usually a sign
 that the suspension bump steer or geometry cannot maintain the appropriate camber curve to match the vehicle body roll or the tire optimum camber through the steering range with side load. Increased caster increases the steering effort , increases the self centering forces and causes decreased camber in one wheel and increased camber in the other in a turn in situation . wider tires if not set to a reasonable scrub radius or not used with a leading axle position in the upright make for a vehicle you have to fight with in every turn , runs great in a straight line but so does a solid axle with king pins. 
 
Too much of any thing will create increased tire wear  or abrupt handeling transitions .
 
 
IMHO
 
john garcia 

--- On Wed, 8/25/10, Curt Hall <cuvee at sbcglobal.net> wrote:


From: Curt Hall <cuvee at sbcglobal.net>
Subject: Re: [DeTomaso] more on rear tire width
To: "Kirby Schrader" <kirby.schrader at gmail.com>, "Garth Rodericks" <garth_rodericks at yahoo.com>
Cc: "DeTomaso Mail List" <detomaso at realbig.com>
Date: Wednesday, August 25, 2010, 5:24 PM


Go to Team 3 Wheels...team3wheels.com   They make a nice looking GT40 type wheel. 15"-17" pretty much any back space you want. I thought about buying these wheels, but with this great economy and being unemployed its just not a good time to spend the $$$$$!  

--- On Wed, 8/25/10, Garth Rodericks <garth_rodericks at yahoo.com> wrote:


From: Garth Rodericks <garth_rodericks at yahoo.com>
Subject: Re: [DeTomaso] more on rear tire width
To: "Kirby Schrader" <kirby.schrader at gmail.com>
Cc: "DeTomaso Mail List" <detomaso at realbig.com>
Date: Wednesday, August 25, 2010, 12:26 PM


Those purists might also say it's not a 'real' GT40. So who the hell cares. 
That's one amazing car you have there.

I've always liked the GT40 BRM wheels too, and think they'd look great on a 
Pantera, but I think the offsets are wrong:
http://www.poca.com/index.php/gallery/?g2_itemId=18911





________________________________
From: Kirby Schrader <kirby.schrader at gmail.com>
To: Garth Rodericks <garth_rodericks at yahoo.com>
Cc: DeTomaso Mail List <detomaso at realbig.com>
Sent: Wed, August 25, 2010 12:07:38 PM
Subject: Re: [DeTomaso] more on rear tire width


I have the 'Halibrands' from Vintage Wheel on my GT40....

http://www.vintagewheelsus.com/

http://web.mac.com/kirbyschrader/

Some purists will say that they are not 'real' GT40 wheels though... they are 
missing the 'wine glass stem' and they are 17" and.... well, you get the idea.
:-)

Personally, I like them purely because I can get decent tires for the street.
When I take it to the track next month, I plan on using the 15" wheels with 
track tires/slicks.

FWIW,
Kirby



On Wed, Aug 25, 2010 at 12:40, Garth Rodericks <garth_rodericks at yahoo.com> 
wrote:

I think those are the same wheels Bob Benson runs on his black #3 Pantera
>http://www.poca.com/index.php/gallery/?g2_itemId=25547
>
>I also like the look of the Halibrands as far as aftermarket wheels go.
>http://www.poca.com/index.php/gallery/?g2_itemId=18914
>http://www.poca.com/index.php/gallery/?g2_itemId=18786&g2_page=7
>
>
>
>--- Original Message ---
>
>Oh.... You mean like these?
>
>http://www.pbase.com/oburg/image/127279124
>
>Orville
>
>-----Original Message-----
>From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com]
>On
>Behalf Of Kirby Schrader
>Sent: Wednesday, August 25, 2010 9:58 AM
>To: wkooiman at earthlink.net
>Cc: DeTomaso Mail List
>Subject: Re: [DeTomaso] more on rear tire width
>
>Kinesis K58
>
>For example...
>
>http://superbuytires.com/Kinesis/K58%20RWD/
>
>
>
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