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HybridZ

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I think you're suggesting shortening your rear LCAs (and half-shafts, or CV axles) in order to achieve a shorter effective rear axle length, allowing you to run wider rear wheels & rubber without changing the exterior sheetmetal.  True?

 

If so, I think there are better ways to achieve your goals.  Solid narrowed rear end comes to mind, especially if you're making big power and planning to drag race the car.

 

Give us some more info on what you're planning to do with the car, and folks can probably help more and steer you in the right direction.  Your initial post doesn't really provide much info, and just has people guessing at what you're ultimately trying to do with the car.

 

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I'm running a knuckle off a different vehicle so get to attach the strut to the top of it any way I want. I also plan on using a camber plate to slide the strut further inboard towards the diff, I have coilovers on the car so the diameter of the strut assembly is smaller. My main concern is the force being applied to the strut tower. It will place more force in the vertical plane, not sure if that matters though.

Edited by zboi
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On 6/4/2020 at 5:54 PM, zboi said:

I'm running a knuckle off a different vehicle so get to attach the strut to the top of it any way I want

 

Makes sense now, I was trying to imagine how this would work with the factory rear uprights! Watch your roll center as 260DET said, you can easily get into trouble and the car will behave terribly.

 

Since you're already welding in camber plates, good enough time to add some reinforcement up there, although I think if you try and get too vertical, you'll start hitting your springs on the inside of the shock towers. 

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What are you using the car for (street, drag strip, track days,...)?

What size tire are you trying to fit? 

 

If you choose the right wheel diameter and backspace, contact of the strut tube is not the limiting factor.  On the rear, if you have coil-overs, you can run at least 5" of back space with a 15" diameter wheel.  I run 15 x 10 wheels with 5.25" back space.  With Hoosier 275/35-15 tires I have about 1/2" clearance at the strut tube.   As you increase the wheel diameter to 17 or 18", you can increase the backspace of the wheel.  The inner wheel tub is the limiting factor for modern (17", 18") diameter wheels. 

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Car is street and track days use. I'm running 17x9.5 -20mm offset rear wheels, 275/40 tire. I was getting contact on the wheel lip at about an inch of before hitting the inner wheel tub. I don't want fender flares, and to get them to tuck with this size I need to get them right next to the inner wheel tub. I have stock rear struts with coil over sleeves on them, so 3" diameter springs and 10" long. Right now the springs end right at the bottom of that pocket the strut goes in, which is also right where the wheel lip is about. Maybe a shorter spring would also help.

What length coilover springs do people run?

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Where are you getting contact?   Tire to fender lip or tire to strut?  With 17" wheels and coil-overs, you should be able to run more than -20mm offset.  That equates to 4.46" backspace


I run 8" springs, but my rear spring rate is 400 lb/in (probably not street friendly).  With 15" wheels, I could run 5.5 inch backspace. With 17"wheels, you could get away with 5.75" backspace.

 

Its always better to have more backspace than you can use because you can compensate with spacers.  If you don't have enough backspace then there is no way to adjust besides getting different wheels.  I use 5.25 backspace on all four corners, but only use spacers (1/4") on the front.

Edited by 74_5.0L_Z
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