F40: Some suspension analysis done and questions remaining..

Hi!

In a previous life I was a simulator physics 'developer' (that's a stretch). Nowadays it is a hobby and I'm throwing together a F40 for Automobilista, a very niche, somewhat graphically dated but fine (if I may way so) driving simulator.

The F40 user manual has frontal views of the front and rear suspension. I used CAD to scale it and draw some lines, giving us some specs, with of course plenty of tolerance and doubt:

F40 Suspension, static height versus ~30mm bump travel analysis:
Front:
Wheel / damper motion ratio: 1.65
Camber gain: 0.049 degrees per mm wheel travel
Scrub radius: 52mm
Roll center height static: 106mm
At ~32mm bump travel: 64mm
Bump rubber gap ~22mm at damper giving ~36mm at wheel

Rear:
Wheel / damper motion ratio: 1.47
Camber gain: 0.034 degrees per mm wheel travel
Roll center height static: 99mm
at 30mm bump travel: 52mm
Bump rubber gap ~26mm at damper giving ~38mm at wheel

Questions..
The manual has perfect frontal views, but it is likely that the suspension has some anti dive, lift, squat, making the height of the front and rear mounts a bit different, so that adds a question mark on the validity of the numbers.

The bump rubber gaps are fairly small, and maybe these drawings were made for the manual specifically and aren't quite the same as the real specs. Has anyone ever checked the damper travel you have until you hit the rubbers? Less than 40mm of travel until the bumpstops could be fine but maybe especially at the rear, is it that not a bit too little?

Elsewhere on this forum I found somebody claiming the rear spring rate is 480 and the front 330 pounds per inch. This may very well be true, but what is the source for this and has it been confirmed?

Has a damper dyno chart ever made it out in the public to get some idea of the damper force curves?

I realize info is rare, so I don't expect a flood of replies. At least by posting my findings, a tiny bit of F40 data has been added to the web!

 

Update, fixing a probable error..

Upon inspecting some more pictures, the rear damper is mounted to the upright, not the upper wishbone, which changes the motion ratio significantly, from the 1.47 to about 1.17 which is a huge change, because the wheel rate is a function of the motion ratio ^ 2.

Also, it makes it likely that the spring rate information I found elsewhere on this forum, may have been back to front, i.e. 480lb/in for the front and 330lb/in for the rear, the opposite of what was posted on this site. This makes the wheelrates roughly 31 N/mm front and 42N/mm rear, and somewhat depending on weights and unsprung weights, about a ride frequency of 1.9hz front and 1.8hz rear

Using the original 480 rear and 330 front spring info, ride frequencies are about 1.6 front and 2.2 rear, which seems quite rear biased, and you need significant anti dive on the front suspension to control nose dive. But without any source, who knows if the 480 and 330 are even the right rates, let alone which side of the car they are supposed to be on!

A side effect of this new 1.17 motion ratio on the rear, would also mean the bump rubber gap needs way less wheel travel to be filled. The gap would be smaller at the rear than the front, which feels counter intuitive. I would expect there to be more room in the wheelarches at the rear for some extra bump travel, plus going over bumps mid corner, you probably want the front to hit the rubbers, stiffen the suspension as a result, and 'loose grip' as a result before the rear does..

So it seems maybe the car manual drawings have a generic bump rubber gap drawn that may not reflect the actual installation gap.

 

Seems I can't find the option to edit posts, here is an update instead.

F40 Suspension, static height versus ~30mm bump travel analysis:
I made an oopsie with the motion ratios, I over corrected for the spring installation angle, which is not needed if you simply check the displacement of spring vs tire. The updated values are:

Front:
Wheel / damper motion ratio: 1.51
Camber gain: 0.049 degrees per mm wheel travel
Scrub radius: 52mm
Roll center height static: 106mm
Roll center at ~32mm bump travel: 64mm
Bump rubber gap ~22mm at damper giving ~33mm at wheel

Rear:
Wheel / damper motion ratio: 1.14
Camber gain: 0.034 degrees per mm wheel travel
Roll center height static: 99mm
Roll center at ~30mm bump travel: 52mm
Bump rubber gap ~26mm at damper giving ~30mm at wheel

Alledged spring rate and ride frequency info
- For a 1260kg total car, with 40% front and 60% rear weight (actual full tank EU car data)
- With a front axle unsprung mass of 80kg (just an educated guess)
- With a rear axle unsprung mass of 100kg (just an educated guess)
- Using 480lb/in front and 330lb/in rear springs, assuming data found on the forum is back to front as that makes more sense

The front ride frequency is 2.06 hz
The rear ride frequency is 1.87 hz

Alledged oopsie in the EU gear ratios found on this forum
The USA manual of the car has the ratios and somebody on the forum posted the EU ratios.
The USA ratios from 1st to 5th with 5 decimals are:
10.70769
6.62857
4.74545
3.72346
2.96444

The posted elsewhere on this forum EU ratios are:
10.069
6.262
4.463
3.501
2.787

If we divide USA by EU we find the % difference in each gear:
6.34%
5.85%<<
6.32%
6.35%
6.37%

Notice how 2nd gear is an outlier, all the other gears are about 6.34% different.
I think I may know what is going on. If we assume a typo in the EU ratio where 6.262 was meant to be 6.232 (easy to do on a numpad), 2nd gear also becomes 6.36% different.

I would assume Ferrari has changed the final drive from 11/30 to 10/29 which is a change of 6.33%, and all the actual box ratios are the same.

478HP is enough to match period car reviews
And on a final note, there is a period review at what seems to be Nardo, where they go 0 to 263kmh. They didn't mention the weight of that vehicle. With a total weight of 1290kg, which is about an EU car with 80kg driver and 30kg fuel it seems like, I match the real acceleration in the simulator using an engine with some 15% power losses, 500Nm at 4000RPM and 405hp at 7000RPM. Above this there are a few more losses in the simulator such as rolling resistance, and a few bearing frictions. A 15% drivetrain loss sounds fair enough to me and I don't think EU cars over delivered on power from the factory.

The sim is pretty solid, but of course in the chain of numbers entered, errors always creep in, so it is just a finding with a degree of tolerance on it.
Attached the time vs speed curve of the Nardo test and my simulator.


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