Miatav8,MstrASE,A&P,F wrote:
Nice build Josh!
Should I assume “toe in” on the chart is actual just toe with negative representing a toe-in condition or is it toe out in the front and toe in for the rear?
Have you also checked for bumpsteer in the rear as well? Rear bump steer that creates toe out is very unsettling. Consider the static toe condition does not account for the dynamic change due to compliance and the rear tires moving forward in the chassis under load and the fronts moving to the rear. A little tension on a ratchet strap can provide an indication of what actual toe will be when driving.
It appears to me that you may not be using the full tire width considering 1.1neg static and what appears to be a VSA of around 35 inches. With such an aggressive camber gain, zero static may provide more cornering ability if you can get enough heat into the tires to share with a larger area. When cornering, the outside tire will have more leverage and heat further outboard in the tire.
Does the IRS have a similar gain/VSA?
Keep your old springs in case you want a smoother ride with better traction over rough back roads, to add a front bar later and keep the springs on the seats in droop. Stiffer springs cause the chassis to move more than softer springs, so recovery from a pot hole as one example is not as quick and can cause a momentary loss of traction/skipping.
Hello! Thanks for reading.
I list everything as "Toe-In" with Toe-Out being negative Toe-In. So -2mm front is Toe-Out at the front, 2mm at the rear is Toe-In at the rear.
The rear end uses a flat lower wishbone with two joints, so there is no rear bump steer. The wishbone and toe adjustments are entirely inline. I agree with you, bump-steer on the rear would be terrifying!
VSA? Virtual Swing Arm? Yeah they are very short and I am not a big fan of it, but that was the geometry my Dad came up with back in the day when we were designing the car. There is a lot of camber gain/loss. Its great in roll but not great in every other condition. I plan on changing it on the front in the future.
I get what you mean about the static camber and I should be able to run less than other cars because of this geometry, however some amount of negative camber is still required as lateral load is applied, its not just there to account for loss of camber in suspension geometry. I did tyre modelling many moons ago in F1 and the more lateral load you apply to a tyre the higher the negative camber it requires for peak grip. The tyre essentially leans onto its outside shoulder. (inside should for the inside tyre). So zero camber wouldn't necessarily be better, but I have to admit, ~1.0deg is just a shot in the dark at the moment.
The IRS is very similar to the front, just without the added headache of steering the wheels.
Hrm. I don't entirely agree about the springs. Stiffer springs mean less chassis movement for a given change in load. Pot-hole performance is worse because the car loads and unloads more as the wheel follows the shape of the pavement. Recovery time is dictated by the spring and damper combo. I still have the same droop travel and I run helper springs to keep the springs on the seats, but I do agree that the softer springs would give a better ride, but I prefer the balance of this setup.
I don't even run a windscreen at the moment so comforts not really a consideration for the time being! I also prefer to run without anti-roll bars, as I like the simplicity of setup. Its one/two less variables to consider when setting up the car.