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miagi
12-08-2015, 00:07
Hello,
I have a question about the spring travel on the BMW 320 Turbo Group 5 car. I drove it with the HUD and recorded to see if my springs are stiff enough. There I noticed that I have quite a different spring travel on the front, what I found odd as I had a symmetrical suspension setup. Checked it while standing, and there it shows too. Where does that come from, and it is how it should be? How do the wheel loads look on this car? Also the difference seems to increase at speed, with downforce.

Pictures and tests done in TT.

Setup:
214892

Standing1:
214895
Standing 2:
214896

Speed 1:
214893
Speed 2:
214894

miagi
12-08-2015, 00:28
One more thing I noticed on this car, when I roll and brake the front dives quite hard, then it comes back up. But as long as I stay on the brake, the body will not come up to it's natural position. Does that makes sense? I mean it's just a few mm but still kinda suspicious?

I haven't investigated that on any other car, see the video.

---- That video is done with a different suspension setup but also in TT -----


http://youtu.be/6-pjLQKsvus

Jussi Viljami Karjalainen
12-08-2015, 04:20
That is actually something that can happen, there's some tension left into the springs from the braking that doesn't get released until you release the brakes (because the tyres won't rotate when you're on the brakes the suspension can't move freely). We discussed this during development a couple of times as well.

rams1de
12-08-2015, 07:19
There are a few variables to consider in your standing images. Assymetrical tyre pressures, different tyre temps and the great unknown, road surface gradient.

6cm difference on front left looks a lot, that's the corner we get the bogus bump stop indicator - could be related.

miagi
12-08-2015, 07:43
I parked the car in the same spot in different directions to make sure it's not just the track.


It's just 0.6 cm so 6mm. Still a bit weird that ride height is the same and spring travel is different left to right.

Mahjik
12-08-2015, 13:32
I don't have the details, but it could be due to the weight balance of the car. Sometimes the left and right adjustments will be a little different to account for either driver, fuel tank, or engine components (like when using a large turbo with extensive manifold work).

ironik
12-08-2015, 14:04
Sorry to hijack this thread but it doesn't need a new topic on its own IMO. (And maybe it could be related)

I have a weird issue with this car and I'd like to have some insight about it :

After 7-8 laps of Silverstone GP, the rear is getting really unstable on the brakes. So much that it's getting difficult to keep it on track.
Plus, the car is wandering a bit on straight.
The tires temp are ok (in the 80-95c zone), the wear seems ok too (Less than 10%). Almost no brake damage (1-2). No suspension damage and no aero damage.

Eventually, it ends up with a big spin or with a contact. After that, the car is stable again and I can go as fast as before the issue occured.

Any idea / Explanation / Workaround ?

Bealdor
12-08-2015, 14:10
Any idea / Explanation / Workaround ?

What are your brake temps?

Possible reason could be less fuel in the tank and therefore less load on the rear axle.


After that, the car is stable again and I can go as fast as before the issue occured.


That really sounds strange though.

ironik
12-08-2015, 14:28
What are your brake temps?

Possible reason could be less fuel in the tank and therefore less load on the rear axle.

That really sounds strange though.


The brake temps were about 200-250c.
I started with 90L so in 8 laps I should have something like 58L left.

I'm going to try to repro and record it then. :p

EDIT: But I know that Miagi experienced the same behavior. He solved it by changing the tires in pits.

Jussi Viljami Karjalainen
12-08-2015, 15:20
I don't have the details, but it could be due to the weight balance of the car. Sometimes the left and right adjustments will be a little different to account for either driver, fuel tank, or engine components (like when using a large turbo with extensive manifold work).According to the setup the lateral weight bias is locked at 50/50 left/right.

Lagoa
12-08-2015, 15:50
whats ideal brake temp?

Lagoa
12-08-2015, 15:50
I mean how much degrees offcourse ;)

ironik
12-08-2015, 17:09
The brake temps were about 200-250c.
I started with 90L so in 8 laps I should have something like 58L left.

I'm going to try to repro and record it then. :p

EDIT: But I know that Miagi experienced the same behavior. He solved it by changing the tires in pits.

Ok, just tested it again and it happens every time (repro: 100%)
I recorded it but I'm not sure it will be really informative...

Edit: maybe I should do a proper bug report for this?