Rupunzell
Bernice Loui
There are low cost threaded collar kits known as "LeMons lowering specials" found on eBay for not a lot of $. When these first appeared en-mass on LeMons cars, the Lemons folks went looking to discover they were very much low-$.. They work ok, sort of ok.
What is often not appreciated, traction or mechanical grip capability of the tire does depends on the dynamic roll center, it is where force is effectively applied when cornering. One way of visualizing this, take a broom and put one hand on the top of the broom stick. Put the other hand about center of the broom, then push the broom with that hand and note the amount of force needed to move the sweeper bristles of this broom. Repeat the same with the hand near the sweeper bristles of the broom, it will take more force to move the broom. This is a gross illustration of where the force applied makes a difference in traction-mechanical grip. If the dynamic roll center moves below road or ground level, the force on that tire will tend to cause that tire side wall to roll reducing the tire's ability to produce traction.
The dynamics involved is a LOT more complex than lowering the overall center of gravity, there is suspension geometry, dynamic roll centers that move and LOTs more. Dynamic roll center can be used to tune the mechanical grip of the suspension along with a long list of other various other chassis-suspension-wheel/tire combos that are interactive with no specific absolute for a given chassis-suspension and driver preference-style..
That said and given there are absolute geometric limitations to the suspension parts in the exxe, it makes sense to limit the suspension travel to keep the suspension part curves reasonable. This is partly due to the need for camber control and control of how much the dynamic roll center is allowed to move around. This translates to what is perceived as high spring rates, but they are not that high once cornering roll angles are considered, the spring rates are simply a product of the cornering loads involved and what is needed to keep the suspension curves reasonable.
Typically, the LeMons chassis which is stock begins with setting the ride height with the front lower control arm about level with the road level. Once this is set up, put the chassis on the corner weight set up, level the rest of the chassis and get the weight per corner reasonable and cross weights near 50%. This means same tire pressures all around with typical driver weight in chassis. Beginning static camber about 3 degrees negative rear, 2 degrees negative front. The steering links have been modified to allow bump steer adjustment which should be done once the static ride height is set. Rubber bushings have been replaced with alloy steel, fiber reinforced teflon liner spherical bearings made by Spec-Line (aerospace supplier) Spherical bearings should be staked at the outside of the bearing to pre-load the bearing and lesser quality spherical bearings will not last. If crappy spherical bearing or rod ends are used, they make chassis set up awful as they will not hold a setting and be repeatable. Dampers must have the ability to control the spring rates involved. Memory notes 550lb/in front and 425lb/in rear (?) no stability bars on a 1,700 pound car. Loaded roll angles are about 2 ish degrees. Chassis easily produces 1G on track with DOT 180 tires. Rear spring/damper rates were tweaked a few times to deal with corner exit wheel spin, there is enough torque from that rotary to make this a very real problem.
Then it is up to the drivers to note and FB on tweaks. Tire pressures and tire temps become the other easy tweaks to adjust as needed Tire temps should be taken soon as the car comes into the hot pits as tire temps can change rapidly. Keep those tires happy will keep the driver and most involved happy as those small patches of road contact are the only things keeping it all together.
What works on a smooth track chassis-suspension often does not work or is acceptable for the driver of a road car with very different road and driving needs.
This said, the PBS approach was to gain-preserve as much suspension travel as possible using 200lb/in springs at all four corners. Add stability bars to aid with cornering roll angles. Then there was the moving of the suspension pickups to effectively lower the overall center of gravity and gain a better camber curve? No mention of dynamic roll center, bump steer compensation and more was not discussed of mentioned in the PBS prep book. What remained as a question from that era when Fiat North American decided to do the X1/9 race car project, why did FNA not go to Abarth or Dallara or Giuseppe Puleo to modify or set up the X1/9 for SCCA events?
Bernice
What is often not appreciated, traction or mechanical grip capability of the tire does depends on the dynamic roll center, it is where force is effectively applied when cornering. One way of visualizing this, take a broom and put one hand on the top of the broom stick. Put the other hand about center of the broom, then push the broom with that hand and note the amount of force needed to move the sweeper bristles of this broom. Repeat the same with the hand near the sweeper bristles of the broom, it will take more force to move the broom. This is a gross illustration of where the force applied makes a difference in traction-mechanical grip. If the dynamic roll center moves below road or ground level, the force on that tire will tend to cause that tire side wall to roll reducing the tire's ability to produce traction.
The dynamics involved is a LOT more complex than lowering the overall center of gravity, there is suspension geometry, dynamic roll centers that move and LOTs more. Dynamic roll center can be used to tune the mechanical grip of the suspension along with a long list of other various other chassis-suspension-wheel/tire combos that are interactive with no specific absolute for a given chassis-suspension and driver preference-style..
That said and given there are absolute geometric limitations to the suspension parts in the exxe, it makes sense to limit the suspension travel to keep the suspension part curves reasonable. This is partly due to the need for camber control and control of how much the dynamic roll center is allowed to move around. This translates to what is perceived as high spring rates, but they are not that high once cornering roll angles are considered, the spring rates are simply a product of the cornering loads involved and what is needed to keep the suspension curves reasonable.
Typically, the LeMons chassis which is stock begins with setting the ride height with the front lower control arm about level with the road level. Once this is set up, put the chassis on the corner weight set up, level the rest of the chassis and get the weight per corner reasonable and cross weights near 50%. This means same tire pressures all around with typical driver weight in chassis. Beginning static camber about 3 degrees negative rear, 2 degrees negative front. The steering links have been modified to allow bump steer adjustment which should be done once the static ride height is set. Rubber bushings have been replaced with alloy steel, fiber reinforced teflon liner spherical bearings made by Spec-Line (aerospace supplier) Spherical bearings should be staked at the outside of the bearing to pre-load the bearing and lesser quality spherical bearings will not last. If crappy spherical bearing or rod ends are used, they make chassis set up awful as they will not hold a setting and be repeatable. Dampers must have the ability to control the spring rates involved. Memory notes 550lb/in front and 425lb/in rear (?) no stability bars on a 1,700 pound car. Loaded roll angles are about 2 ish degrees. Chassis easily produces 1G on track with DOT 180 tires. Rear spring/damper rates were tweaked a few times to deal with corner exit wheel spin, there is enough torque from that rotary to make this a very real problem.
Then it is up to the drivers to note and FB on tweaks. Tire pressures and tire temps become the other easy tweaks to adjust as needed Tire temps should be taken soon as the car comes into the hot pits as tire temps can change rapidly. Keep those tires happy will keep the driver and most involved happy as those small patches of road contact are the only things keeping it all together.
What works on a smooth track chassis-suspension often does not work or is acceptable for the driver of a road car with very different road and driving needs.
This said, the PBS approach was to gain-preserve as much suspension travel as possible using 200lb/in springs at all four corners. Add stability bars to aid with cornering roll angles. Then there was the moving of the suspension pickups to effectively lower the overall center of gravity and gain a better camber curve? No mention of dynamic roll center, bump steer compensation and more was not discussed of mentioned in the PBS prep book. What remained as a question from that era when Fiat North American decided to do the X1/9 race car project, why did FNA not go to Abarth or Dallara or Giuseppe Puleo to modify or set up the X1/9 for SCCA events?
Bernice
