Suspension Set up - Ground Clearance

[E35pilot]

Newbee here with a question about setting up the suspension on a 78 Royale RP24.
I was recently at VIR on the Patriot Course and during breaking and compression of the suspension into turn 7, I continually scrapped the underside of the chassis.
Is there a minimum height above the ground the main chassis should be adjusted for?
I guess the follow on question would be is there a difference between what a rule might state as a min height and what height might be optimal?



Lee Grassley
Portsmouth, VA
1978 Royale RP24

[TimH]

Somebody here probably knows the optimum ride height for your car, but a certain amount of grounding is likely to happen once in a while. The important thing is to have a skid plate that protects your flywheel.

[Garey Guzman]

I'll add that front skid blocks are also important, don't want to wear through the rivets and the pan! I've seen this happen.

I was given a rough estimate for ride height for my Swift, with a certain level of rake. Might have been 1.5"? If I raise or lower the front, I need to do the same amount to the rear to maintain rake. Someone told me early on that the front should kiss the ground on your hardest braking point when the car was full of fuel, which seems to work decently on my Swift, as long as the front skid blocks are in place.

[billtebbutt]

Have cut teflon strips from Momma's old cutting boards and used them under noses, chassis tubes and floorpans for years. Works great.
bt

[E35pilot]

I'll add that front skid blocks are also important, don't want to wear through the rivets and the pan! I've seen this happen.

I was given a rough estimate for ride height for my Swift, with a certain level of rake. Might have been 1.5"? If I raise or lower the front, I need to do the same amount to the rear to maintain rake. Someone told me early on that the front should kiss the ground on your hardest braking point when the car was full of fuel, which seems to work decently on my Swift, as long as the front skid blocks are in place.

Gary, this is very helpful. I know some of the rules I’ve read include a rake of no more then 1”, but didn’t really know what the minimum height might be. I can definitely start with this. Thanks.

Lee

[E35pilot]

Have cut teflon strips from Momma's old cutting boards and used them under noses, chassis tubes and floorpans for years. Works great.
bt

Thanks for the Teflon/PTFE suggestion…sounds like a great idea. I do have a few rivets I’ve replaced under the nose and this would definitely help them from being ground off.

Lee

[S Lathrop]

Ground clearance is better understood as ride height. The designer of you car had a ride height number in mind when he designed your car. You can not move a car up or down without understanding the effects it has on the suspension geometry.

As an example, the Zink Z10 was designed with a front ride height of 2.5 inches. I turns out that by running the car at 1.5 inches, the front geometry has excellent characteristics. But running the car say at 2 inches, the geometry is not very good. So the car has to be setup to run the designed ride height or a ride height that works with the geometry of the suspension.

To keep the car out of the ground, I like to use Dynamics bump stops that have enough force to support the car at ground level. But at ride height I have an air gap between the bump stops and the shock body that will allow the car to move down some amount before contacting the bump stops.

Relying on skid blocks to keep the car out of the ground is a good way to induce frame cracks. I have had to repair several cars where pounding the bump stops resulted in frame cracking.

[E35pilot]

Steve, thanks for the advice…this is something I will certainly consider when setting the height. What you explain makes perfect sense. Unfortunately, I have not been successful at locating factory information for setting up the RP24 and have resolved myself to getting as close to something reasonable than just doing a lot of driving/adjustments.


Lee

[S Lathrop]

Steve, thanks for the advice…this is something I will certainly consider when setting the height. What you explain makes perfect sense. Unfortunately, I have not been successful at locating factory information for setting up the RP24 and have resolved myself to getting as close to something reasonable than just doing a lot of driving/adjustments.


Lee

I still use Bill Mitchell's Racing by the Numbers soft ware. I did a quick net search for Mitchell's soft ware. There ae lots of sights that popped up. I would start there and see what is available today.

Part of learning to drive is also being the car engineer if you can not afford to hire one.

[scorp997]

I assume you’ve reached out to RoyaleRacingLLC (Chris Shoemaker) or Alan Cornack in the UK?

I probably don’t need to tell you that ride height is obviously affected by spring rates. Soft springs need more height. I run at pretty smooth tracks, compared to the UK tracks the cars were designed around, and was able to lower my old RP16 to 2”F/2-1/4”R when I upped my springrates to 350/350. Car was balanced, but was near the limit of the frame torsion loads.

[Larry H]

Use the search function for RP24, RP-24, RP 24 in the classified ad section. There you can find previous owners, which you can private message.