Quote:
Originally Posted by gmx
I've got those docs. Although the motion ratio would be similar, I wouldn't suggest making such assumption. There were good examples in the doc itself that look like they will result in different motion ratios due to packaging and pickup points even though they use the same suspension generational design and concept.
Case in point, I have 0.83 written down for the rear damper motion ratio! Did you measure 0.72? The problem with the internet :P
Btw, why do you square .59 ? Isn't that only squared to find / calculate the wheel rate (after multiplying spring rate)
There is some BMW document technical comparison at the launch of the F82, where they compare to previous gen front M3 geometry. The only difference was slightly more SAI (KPI angle) which will affect camber. Apparently the GTS has the same overall geometry except a larger hole for the bespoke damper. You'll see JDM cars usually have a strut / knuckle fastened with an eccentric bolt allowing adjustment here.
I noticed this over the last 2 seasons. Asked a former pro as he has both GTS (E92 and F82). His first comment, much more neutral balance and can get away with less Fr static camber whereas the E92 had inherent understeer. It was also evident by his tyre wear / usage on the front.
Not to mention F8x cars easily get -4 static camber very easily. The strut tower is huge and simply has more space to place the strut inboard. Those 1M/135i racing above ended up with -5 by using an additional offset sandwich plate. One (or maybe more?) other team simply notched the towers. Important to note, you weren't allowed to change the spring location in those championships effectively banning rear C/O. Moving up a category, you could like this car (revalved, rear C/O clubsports):
https://f80.bimmerpost.com/forums/sh....php?t=1674814
I talked to the suspension builder and he explained they use a slightly lower frequency due to the range of tyres used, and inexperience of the drivers (gentlemen racers).
I might have an opportunity to acquire a set of F80 knuckles, I'd need to get new BBK brackets built for it though.
ShaikhA Happy to see you post here. We spoke before mutually deciding that I preferred local support.
If you're local, I think it's a no-brainer for you guys. |
Not really sure to what end point youre mentioning any of this stuff to. We are talking about 135i's. The data was only presented to show that race cars run fairly neutral spring rates when looking at things at a macro level, for the most part. At the very least, they are not running springs operating at 3hz up front and 2hz on the rear like many 135i's. People also said all of the same things when moving from E36 and E46 M3's to the E92 M3. They needed less camber.
135i is supposed to be:
Springs:
Front 0.960^2 0.9216
Rear 0.563^2 0.316969
Damper:
Front 0.960^2 0.9216
Rear 0.813^2 0.660969
Motion ratio is further reduce by angle but it's a fairly lower % adjustment so most people just ignore the "ARC" component of the formula. You could throw a camber gauge on the rear spring and strut to get an idea of how "vertical" they are.
And yes I was rattling off numbers based on that pic. not a perfect shot it's taken from an angle and measurements are probably skewed by aspect ratio a bit. The numbers being close enough to actual though. Just to show conceptually that where the spring mounts in the control arms changes how effective it is... not to present factual numbers. Whether or not an M4 has a strut ratio of .72, .69, .68 or whatever doesn't really matter and I don't have an M4 GTS to measure.
Pickup points matter for kinematic geometry and dynamic spring rate. Static motion ratio as we are calculating is a simple formula dependent upon the length of the lower camber arm and the attachment points and angle of the spring and strut. It's a simple proportion, really. Seeing as how you are saying the lower control arm is the same the motion ratio would also be the same or very close to it. Part number is not the same for a regular F8x and a M4 GTS, but, neither is the 135i and 1M part numbers. Yet, the spring and strut sit in the same spot. The strut just mounts differently and the arm is aluminum. Motion ratio between a 135i and a 1M should be almost the same. These two cars having different toe arm pickup points does not change the static strut or spring motion ratio calculation.