What is a reasonable rake setting on a 355, inconclusive info, wrong data in the manu

It is me and my H&R springs again ;-)

I have just finished changing my spring and am sitting thinking about ride height and rake. After reading an article by Mitch Alsup, I have understood that rake and ride height is very important for the handling and behavior of the 355.

Reading through the technical manual I see that the recommended setting for the 355 is 162-171 in the front and 182-191 at the rear. This gives a diff (or rake?) of 20 mm front to rear. The rear is 20 mm higher than the front.

My car had originally 165 mm in front and 200 mm in the rear and I am pretty sure this was factory settings by the reading of markers on the damper etc. The car is for some reason 10 mm higher than the manual at the rear from the factory. The diff becomes 35 mm (was the higher rear from factory done to give more over steer?)

The new spring has lowered the car to 145 mm in the front and 190 mm at the rear, the diff is now 45 mm! I have seen different recommendations of combinations in ride height but am not sure of where to start.

All measurement was taken at the lower suspension arm bolt as described in the manual.

So to my dilemma; I have read all I can find on this subject at different Ferrari forum but can come to a conclusion. I want to get to a reasonable rake where I can start tuning in for the correct over/under steer without going to extremes. I have driven the car as it is now, no changes made yet to camber and toe in etc. And so far I like the change but I am not sure what will happen as I change camber and toe in back to factory spec. The new diff of 45 mm sounds extreme to me but I can’t really say the car felt that different as I drove it yesterday. Surely it was more nervous but it cornered so much better, steering in to corner felt superb and the gain in steering control gave me confidence in at high speed.

Can some one please help me decide what to do!

 

Nice weather today so I decided to lower the rear by 3 turns (~5 mm), making the rake less extreme and see what happens.

I took the car for a test run on the same roads as the other day. It was not hard to realize that the 5 mm changed the feeling of the car again. The meatier steering was not as noticeable, it did not steer into the corner as precise and I can feel that the rear has more grip pushing the front out of the corner in mid speed accelerations.

At high speed however it did not feel as safe as before, didn’t expect that since I thought that it would be more stable. The overall feeling is that it was better before and I will go back to the original setting and take the car to do a wheel alignment next week. Maybe H&R had an idea with the spring characteristic and the change in rake?
I am still looking for input in this subject. Hasn’t anyone else that tried what I am doing, would really like to have someone to discuss ideas with

 

Today I went to do wheel alignment. We started by checking how much the lowering changed the original setting from the set up we did in June.
This is what we found out:

The initial settings were standard and based on the workshop manual:
Front (L R)
Camber: -0°.46’ -0°,48’
Caster: 7°04’ 6°.6’
Toe: 2.0mm 1.9mm
Rear (L R)
Camber: -2°.04’ -2°.08’
Toe: 2.0mm 2.2mm

After lowering the car these were new settings:
Front
Camber: -1°.27’ -1°,27’
Caster: 7°29’ 7°20’
Toe: 1.1mm 2.0mm
Rear (L R)
Camber: -2°.35’ -2°.48’
Toe: 2.9mm 4.0mm

Camber and toe changed a lot, not very surprising as this was as expected I guess.
The changes we did this time were to correct the toe, front and rear and leave the camber and caster for now. The change in camber in the rear doesn’t seem to be that extreme but in the front it might be a little too much, but I wanted to try this out and decided to stick with it for now.

The new setting I am using now is:
Front
Camber: -1°.3’ -1°,3’
Caster: 7°29’ 7°20’
Toe: 2.1mm 2.0mm
Rear (L R)
Camber: -2°.35’ -2°.42’
Toe: 2.1mm 2.0mm

Took the car for a long drive today, great weather and a lot warmer than you normally expect in Sweden this time of the year
Started with my favorite twisty road and can once again establish that in low and mid speed corners the car feels absolutely great. The grip is so MUCH better than before the lowering and I can now feel when the rear moves into a slight over steer. Going through really tight corners like driving fast through a roundabout the grip just makes me laugh

The second part was going back home via the highway and it is easy to feel that the change in toe made the car more on the edge. It is more nervous, not so much that it needs to be checked on all the time, but if I turn the wheel it will react directly. So as long as I don’t move the wheel it is fine ;-) Once again I found it hard to really test mid to high speed corners, there is usually too much traffic and I might have to wait until spring when I can get to the track to really test this. The overall feeling is that I am improving but there is probably more to do. One thing I am not sure of is how the new camber setting will wear the tires.

Feel free to comment on these setting and thoughts as I am in the need of all the input I can get.
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Found this info given by Mich Alsup in 2004:

http://www.ferrarichat.com/forum/showthread.php?t=4948&highlight=355+camber

"Front:
Camber: -0.5 to -0.75
Caster: +7
Toe: 2mm IN
Ride Height: 163 mm

Rear
Camber: -2.0
Toe: 2mm IN
Ride Height: 187mm"

Probably should back off a little on the camber, at least in the front...

 

Hi Rob
Thanks for commenting, really appreciate it!

I went down to the garage and measured the height behind front wheel and in front of rear wheel as you describe. The height is 117 mm in front and 135 in the rear, so in your world the rake is 18 mm. Does this tell you anything, would you say this is an extreme setting? I can’t go any lower in front since this is the very limit of my driveway ;-)

When you say:
“Also be warry of toe settings in the rear. I've run as much as 45' (minutes) total toe-in for the rear to aid stability.”
Are my 4.0mm of total toe-in too much, will this ware my tires excessively. How does my total toe in 4.0mm compare to your 45’?

“Front toe setting is totally personal preference, a little toe-out for turn-in perhaps. I'd stick close to zero front to 15' toe-in total.”
For now I think I will stay with toe-in. How does the total toe in of 4.0 mm compare to your 0-(total 15’)?

When you give values for toe-in you use minutes, my numbers are in mm. Is there a way to convert this? I guess I could go back to Tomas in the workshop and ask him to change the units in the machine, but if there is a way to convert, that would be a lot easier ;-)

So what you are saying is that if I keep the camber settings, a reasonable setting for front and rear toe-in would then be 0-15’ total toe-in in front and up to 45’ total toe-in in rear based on how much rear stability I need. Any chance you could give me that in mm… ;-)

Regards
Johan Lundberg

 

Thanks Rob great info!

Had to think for a second there, but finally got it
Sine (45 arc_minutes) (482.6mm) = 6.3mm is the same as: Sine (45/60) (482.6mm) = 6.3mm

While surfing another Swedish racing forum I came across this reference table, thought it might be useful in thread.
Since this table does not have the 19", extrapolating between 6.0 and 6.55 seems close enough I now understand why it is easier to use degrees rather than mm!
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Got a chance to corner weight the car at this year’s first track day. I was very pleased with the new springs and the setup but wasn’t sure about the corner weight. This is the setting for the car without (and with) me in it.

Total weight 1436 (1512) Kg

LF 302 (331) Kg RF 310 (329) Kg
LR 417 (445) Kg RR 407 (414) Kg

Weight front 43%
Weight rear 57%

It looks like the front is close to spot on, only 2 Kg with me in the car. The rear has a diff of 29 Kg with more weight on the left wheel with me in the car. It looks as if the car is more balanced with two persons in it as the weigh diff is only 10 Kg empty.

I guess that these figures are pretty good but I would love if someone could comment on them as this is my first attempt to tune a car.

Questions so far
Is the 30 Kg diff at the rear something I should try to correct?
Any comments on the front/rear distribution?

 

Thanks for the info, i will try that half tur on the left rear and see whar happens

 

First picture from yesterdays trackday
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Öhlin will be releasing a new series of TTX damper in january. TTX 36 inline. The earlier damper had a fixed canister and could not be fitted to the F355 but this one looks promising!
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