Should I run more caster? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 7 Old 07-07-2016, 08:47 PM Thread Starter
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Should I run more caster?

After pulling the K-member and camber plates during an engine bay repaint on my Fox body LTD (pretend it's a Mustang, everything's the same), I got a front end alignment done. Based on research online (much of which came from MFE's posts here) I asked for these specs, as it's a weekend car that's set up to handle and I like to take it out on mountain roads and occasionally autocross:

  • 4* caster
  • -1.5* camber
  • 0 toe

Front end parts:

  • MM K-member
  • MM Fox length control arms, 0 offset
  • '96+ spindles
  • MM coilovers on Bilsteins
  • MM C/C plates
  • Cobra rack with MM solid bushings and bumpsteer kit

Anyway, this is an old school alignment shop with a pit, and the tech was a crusty old dude who clearly knew Fox bodies and MM parts. There was even a Fox Mercury Capri sitting in the parking lot that was chock full of MM parts which he told me he had worked on, so this wasn't like driving onto a Hunter rack at Sears.

When I gave him the specs I wanted, he seemed to balk at the caster. At first he thought the caster was too much and said it would cause the front end to understeer. Once he was actually working on the car, he said the caster was already over 5 degrees, so he had to move the struts forward to get down to 4. I thought that was odd, but sure enough the camber plates tell the story.

I drove the car home and it seems fine, but now I have to wonder if I should run more caster. The struts tops seem to be squarely in the middle of the hole on the strut towers, so there it seems like there is more adjustment left. Is there any reason why I shouldn't run more caster? I've read that too much caster can create bump steer, but I'm certainly no expert.






85 Ford LTD LX - One of 3260 LXs, Cobra SEFI conversion, AFR 165s, T5, Cobra brakes, buncha other stuff
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post #2 of 7 Old 07-07-2016, 10:19 PM
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FWIW, I run about 6* on both of my foxes. One is a street-legal track car; one is a highly-modified daily driver. The geometry in these cars likes as much caster as you can give it.

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post #3 of 7 Old 07-08-2016, 10:50 AM
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Caster is a good thing-- add more.
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post #4 of 7 Old 07-08-2016, 01:34 PM
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[QUOTE=LTDScott;17308698]After pulling the K-member and camber plates during an engine bay repaint on my Fox body LTD (pretend it's a Mustang, everything's the same), I got a front end alignment done. Based on research online (much of which came from MFE's posts here) I asked for these specs, as it's a weekend car that's set up to handle and I like to take it out on mountain roads and occasionally autocross:

  • 4* caster
  • -1.5* camber
  • 0 toe

Front end parts:

  • MM K-member
  • MM Fox length control arms, 0 offset
  • '96+ spindles
  • MM coilovers on Bilsteins
  • MM C/C plates
  • Cobra rack with MM solid bushings and bumpsteer kit

Anyway, this is an old school alignment shop with a pit, and the tech was a crusty old dude who clearly knew Fox bodies and MM parts. There was even a Fox Mercury Capri sitting in the parking lot that was chock full of MM parts which he told me he had worked on, so this wasn't like driving onto a Hunter rack at Sears.

When I gave him the specs I wanted, he seemed to balk at the caster. At first he thought the caster was too much and said it would cause the front end to understeer. Once he was actually working on the car, he said the caster was already over 5 degrees, so he had to move the struts forward to get down to 4. I thought that was odd, but sure enough the camber plates tell the story.

I drove the car home and it seems fine, but now I have to wonder if I should run more caster. The struts tops seem to be squarely in the middle of the hole on the strut towers, so there it seems like there is more adjustment left. Is there any reason why I shouldn't run more caster? I've read that too much caster can create bump steer, but I'm certainly no expert.

Too much over 5* can cause bs but you can adjust yours if necessary. Generally max caster is a good thing.
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post #5 of 7 Old 07-08-2016, 03:31 PM Thread Starter
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Hmm. At this point I'm thinking I should just push back the C/C plates myself for more caster and adjust as necessary if the car pulls to one side, but that somewhat defeats the purpose of taking it to an alignment shop :\

85 Ford LTD LX - One of 3260 LXs, Cobra SEFI conversion, AFR 165s, T5, Cobra brakes, buncha other stuff
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post #6 of 7 Old 07-08-2016, 11:07 PM
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For every degree of positive caster added to the alignment, you need to add 0.068" to the bumpsteer stack height to keep the bumpsteer curve more or less the same.

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post #7 of 7 Old 08-09-2016, 10:53 PM
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Shop guy mispoke, more caster = more oversteer. He may have known what he was talking about, but used the wrong word, or he may just not know.

When caster is increased 2 things happen while turning (among 2-3 other things I won't mention). 1.) The inside front tire gets pressed harder into the pavement, 2.) The camber gets increasingly positive.

The first thing makes the front inside tire do more turning work than it otherwise would by adding weight to that corner while turning. It also lifts weight off the inside rear tire, both aid in turning. The 2nd thing increases the contact patch of the front inside tire by "undoing" some of the negative static camber.

5 degrees is not too much on a fox if you can get it.

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