Can I lower the front of my Mondial?

cianfichi · Oct 21, 2019

afterburner said: ↑

Hi Vince

Here is what happens when you drop the front 1.5". I drew the geometry and put the findings into my Exel to get some data. Not much changes:
Basic assumption is a CG height of 475mm and gross weight of the Euro QV:

1) with an identical lower wishbone, you loose 9mm of track
2) to keep identical camber, you need to lengthen the upper A-arm by 1/2"
3) same re the track rod, plus accentuated bump steer as a result of heavily inclined rods
4) the roll centre drops from 59mm down to 13mm (I haven't looked at the roll centre movements of either case)
5) the overall CG height is reduced by 17mm
6) at 0.81g lat acceleration (R&T skidpad result), the resulting roll angle remains at 4.3°
7) the sprung weight roll arm increases by 1mm, the front one is reduced by 1mm and rear one increases by 4mm (the mass centroid axis changes)
8) as a result, the total roll stiffness decreases by 1%, - 1% in the front and in the rear it stays identical (lower CG plays here)
9) the decreased front roll stiffness will shift the cars balance from where it is now toward less understeer - not by a significant margin though

Basically the benefits of the lower CG are negated by the longer roll arms and narrower track.
Remains the missing ground clearance issue and bump steer that you might start to feel as you are essentially driving your car with the wheels permanently in a bump position.
Click to expand...

That is really some in-depth analysis, some of it I understand, and some I dont. What sends a flag up is having to lengthen the upper A arm by a half inch. If you don't do this the tires will wear unevenly correct? And not steer properly? All in all it seems like its best to leave well enough alone.
Vince

MvT · Oct 22, 2019

afterburner said: ↑

Hi Vince

Here is what happens when you drop the front 1.5". I drew the geometry and put the findings into my Exel to get some data. Not much changes:
Basic assumption is a CG height of 475mm and gross weight of the Euro QV:

1) with an identical lower wishbone, you loose 9mm of track
2) to keep identical camber, you need to lengthen the upper A-arm by 1/2"
3) same re the track rod, plus accentuated bump steer as a result of heavily inclined rods
4) the roll centre drops from 59mm down to 13mm (I haven't looked at the roll centre movements of either case)
5) the overall CG height is reduced by 17mm
6) at 0.81g lat acceleration (R&T skidpad result), the resulting roll angle remains at 4.3°
7) the sprung weight roll arm increases by 1mm, the front one is reduced by 1mm and rear one increases by 4mm (the mass centroid axis changes)
8) as a result, the total roll stiffness decreases by 1%, - 1% in the front and in the rear it stays identical (lower CG plays here)
9) the decreased front roll stiffness will shift the cars balance from where it is now toward less understeer - not by a significant margin though

Basically the benefits of the lower CG are negated by the longer roll arms and narrower track.
Remains the missing ground clearance issue and bump steer that you might start to feel as you are essentially driving your car with the wheels permanently in a bump position.
Click to expand...

I like your write up and I think you will notice if you race or do track lap times, but do most of us notice when driving our horse in normal conditions?

When I drive to Italy or any other longer destination I am taking quite some stuff with me inclusive a 5kilo garage jack in the front. The luggage compartment was stacked 9luggage, some tools) and last spring a SeaSucker imperial together with a Cybex system on the back seat and 3 persons. It handled perfectly to my surprise. If I would do this with my Alfa 156 I have a totally different ride and even somewhat uncomfortable.

Speed ramps do becomes a problem though..

afterburner · Oct 22, 2019

Yes, you will have a lot of negative camber leading to tire wear, tram-lining, you need to compensate with less toe-in..., aggressive turn in (> tendency to "oversteer"), silly look ;-)

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