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Unread 03-05-2013, 09:30 AM   #16
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JeeperDon's Avatar
1993 YJ Wrangler 
Join Date: Jan 2005
Location: Albuquerque, NM
Posts: 7,089
On another thread recently they were talking about caster angle and shackles. I did some more research and math after that. I found that less caster is needed with larger tires, since the tire/road contact point is further ahead of the knuckle swivel. The OEM spec for my YJ is 6.3 (+/-1), which turns out to be about 5 needed for a 35" tire (compared to a stock 29" tire).

Doing the caster math as it applies to shackles, changing the shackle length by 3/4" changes the caster angle by 1. So, lengthening a shackle from the stock 4" means lowering the caster, which means for twitchier on-road handling and poorer on-road return-to-center (Jeep seems to have a mind of it's own). My present shackles are 5.75" long, and my caster is about 3.5 (had it measured by a shop), and the Jeep indeed has a mind of it's own on-road.

Actually, today's garage project is to fab up a new pair of front shackles that are maybe 4.5" long to get my caster much closer to the 5 I figure is good. I think it's worth a couple hours of shop time and 2' of steel to experiment.

'93 YJ, '02 GM 4.3V6, SOA, dual ARB's, 8.8+D30(WarnHubs), 4.88s, 35" BFG KM2s, AX15, NP231+4:1+SYE+2LO, York OBA, Warn M8000.
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Unread 03-05-2013, 10:11 AM   #17
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1991 YJ Wrangler 
Join Date: May 2011
Location: Tulsa, OK
Posts: 1,247
4.5"lg with 3/8" bolt holes?
I guess Im asking what size dia. are the bolts?
wondering of how much meat will be needed around the edges
Used to have a good sig but Mod threated to ban me...

[I]Errrrrrr[/I], Will complain else where - &y
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Unread 03-05-2013, 10:32 AM   #18
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1991 YJ Wrangler 
Join Date: Dec 2012
Location: Marietta, GA
Posts: 548
Most heavy duty aftermarket are 3/8" x 2" steel with 1/2" bolt holes and a 1" end radius.
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