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Front Roll Centre

Shocks, Springs, Brakes, Frame, Body Work, etc

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Crew Chief
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Front Roll Centre

Post by Crew Chief » Wed Mar 04, 2020 7:31 am

Hello,

Does anybody here know of, or have a good front roll centre height and distance left, for an IMCA style ICAR rule, asphalt modified, racing on a 1/4 mile semi banked race track? The front clip is an early 70's Impala, non-metric. I have changed to the #2 chev spindles.

I changed the spindles on my modified and I am trying to get a good roll centre number. Just thought I would throw this out there to see what some ideas might be to shoot for.

Thanks for your time,

pdq67
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Re: Front Roll Centre

Post by pdq67 » Wed Mar 04, 2020 11:09 am

It is time consuming but this is how I looked at my 1st Gen. Camaro's front roll center changes.

Put the vehicle on a LEVEL piece of smooth concrete.

Then measure all suspension points from the concrete surface up.

Then get a large piece of paper and lay everything out in full scale.

Then start making the needed lines on the paper that will show your roll center height.

I used the old book, "Chassis Engineering", by Herb Adams.

A great book by me and I bet that the illustration that was used was from a 1st Gen. car but can't prove it.

pdq67

PS., Inner A-arm height points closer together than the ball-joint points cause the lines leading to the front roll center to center at the center of the car. Under the tires lines to the car's centerline here...........

Inner A-arm points farther apart than the ball-joint points will see that the lines come from way outside of the car and then back in.

You will see what I mean.

dannobee
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Re: Front Roll Centre

Post by dannobee » Wed Mar 04, 2020 11:18 am

Start with a 2.5" roll center, straight up. Rough track or not so smooth driver = higher roll center. More banking = lower front roll center and/or more offset to the RIGHT. Aluminum heads = lower front roll center. Longer swing arm lengths give more predictable handling, especially on longer green flag runs.

Carefully measure all of the heights then transfer them full size onto the shop floor, snapping chalk lines. If adjustable ball joints are legal, plot out any differences using the shims/spacers that come with them so that you can quickly change the front roll center at the track. Take copious notes.

pdq67
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Re: Front Roll Centre

Post by pdq67 » Sat Mar 07, 2020 3:37 pm

How are you coming along?

Learning anything?

pdq67

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