Quote:
Originally Posted by jhein
That Falken tire looks fantastic but I don't see a size that will work for me.
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You would be required to move to a 17" wheel or larger to run this type of tire. You should be able to run a 9" wide wheel in the back, you'd run a 275/40/17, which is close to a 26" tall tire. If you can only run an 8" wheel, you'd run the 245/45/17 which is the same height.
I put this together quickly on my lunch however. It's a "good enough" plot of the anti-squat line on my car. If you know your total vehicle weights and front and rear weights it's fairly easy to plot.
My car weighs 2000 lbs on the front and 1402 lbs on the rear for a total of 3402 lbs. My car has a measured wheel base of 107". If you take 1402 x 107 you end up with 150014. Divide that by total vehicle weight of 3402 and you get 44.10 which is inches from your front centerline. This give your your center of gravity position behind the front wheels, but does not give you it's height.
The easiest way to do this and how most people do so is to use the height of the cam. There is a formula to arrive at the exact height but it involves taking weight measurements front and rear, the independently lifting the car 10" front and rear and taking measurements again. For most purposes, using cam height is good enough.
You'll see the CG as the top most blue dot on my car door. The lower blue dot is the location of the forward spring eye on the leaf spring. This is your forward link and where all torque is being applied to push your car.
Now you can draw a line from the centerline of the bottom of the tire, up to your CG and see where your forward link is in relation to the anti-squat line. Notice on mine that my forward link is below the AS line. Not by a lot, but definitely below. This would be a percentage of AS below 100%. Lets' call it 97% here.
What this means practically is that my suspension will allow a bit of squat under power. This increases the suspensions ability to deal with uneven pavement, bumps, or even acceleration off corner. However because the suspension is allowing some squat, available power to the wheels is reduced and some traction is lost.
Notice that with a leaf spring, the physical mounting point determines your anti-squat, unlike a link style suspension. What that means is you can play around with your anti-squat by changing the relationship of the mounting point to the AS line. If you lower the front of the car, this will tend to increase AS. If you raise the rear, especially in relation to the front, your AS will increase.
Drag cars will run AS percentages between 120%-150% or so, depending on the type of suspension, tire used etc. It's not an end all be all here, but it gives you an idea of what you're up against with a leaf. All of this also assumes that you aren't overpowering the leaf and causing axle wrap. The wave that forms in the leaf pack when this occurs loads and unloads the tires. In this situation you'll either blow the tires off completely, or induce wheel hop. That's one of the things the cal-trac is aiding in. It's also adding some separation of the suspension, making it act like it's got more AS percentage.
On a performance street car that cares about more than going fast in a straight line, having AS percentages below 100 is pretty typical. This becomes somewhat neutral and provides off corner traction, braking stability and less oversteer.
Might be worth taking 20 minutes and plotting this on your car. Might be eye opening to see where it is.
