Quote:
Originally Posted by gmx
Not surprised with these spring selection. Stripped weight would be as low as the E9x. The swivel bearing (aka knuckle) is practically the same sans some kingpin inclination improvement. Car is structurally stiffer and looks like new rules allowed some more aero performance. Not sure of tyre advancements either.
F82 rear C/O
ARB 26.5mm with triple adjustment
080-005 Helper
170-60-150
170-60-170
170-60-190
Despite rear C/O, I noticed (via realoem, and that is not 100% always correct) the lower camber arm is still the OEM part. Maybe homologation rule, no idea. Motorsport24/Schirmer are known to build their own lower link with their rear C/O.
However, the rear end is completely rose jointed, no rubber anywhere as you would expect. The rear F8x trailing arm (wishbone by internal references) stands out as do the axial mount on the toe arm, trailing arm (wishbone) which are standard on the road-going version as well.
Also no idea what the rear damper motion ratio is of the F8x.
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F series uses the same rear HA-5 multi-link rear-end as the E8x/E9x series cars. G series does as well. Obviously they made small improvements, but, these chassis will all share similar motion ratios unlike E36 and E46 generations which had different designs. You can read about some of the changes in the BMW academy suspension docs floating around the net.
The two cars you're referencing use a true rear coilover. They can do this on race cars because the upper strut mount is tied into the roll cage and reinforced. The rear springs motion ratio is the same as the strut which is going to be around .72.
This is an F8x converted to a true rear coilover. You can see where the spring USED to sit (much more in-board). My oversimplified calculation of motion ratio for an F8x with stock location springs is .59^2 = .35.
https://i.ibb.co/Gsf0BNx/ohlins-f8x-4-1.jpg
The F-series front spindles do have slightly different geometry. I know Hydra Performance could give you more details as he just swapped M4 GTS front spindles into his 135i. He said they produced more camber than E92 M3 spindles. I think the Front control arm is longer which is part of it too? Not really sure but those little nuances of these different cars doesn't matter much within the context of this thread. Point was that for the most part I see relatively neutral balanced springs on most of the actual race cars I can pull up data on... more balanced than many typical setups anyway.