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      11-26-2019, 06:18 PM   #45
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Quote:
Originally Posted by Daytona_550 View Post
May be my eyes but that tire (left rear) seems planted to me. The daylight seems to just be the sunny area between the front's shadow and the rear tire.

Ha! Zoomed in as close as I could on a bigger screen and I think youíre right. The light/shadow got me. Oops.

The back end definitely feels like it skips over bumps due to what feels like a spring rate/damper mismatch, while the front just sucks it all up, so I guess I saw what I wanted to see.
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      11-26-2019, 06:27 PM   #46
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Originally Posted by Daytona_550 View Post
May be my eyes but that tire (left rear) seems planted to me. The daylight seems to just be the sunny area between the front's shadow and the rear tire.
Agreed.
It is a bumpy corner but your weight transfer has already happened so that back wheel is on the ground.

Glad what I posted agrees with your thoughts too.
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      11-26-2019, 07:36 PM   #47
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      11-26-2019, 07:46 PM   #48
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Quote:
Originally Posted by K-Fab View Post
Agreed.
It is a bumpy corner but your weight transfer has already happened so that back wheel is on the ground.

Glad what I posted agrees with your thoughts too.
I suppose thatís true. We donít get much sun up here so Iím not used to seeing shadows in photos.
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      11-27-2019, 12:46 PM   #49
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Quote:
Originally Posted by K-Fab View Post
Back end is skittish (as mentioned in a post above). It's just slightly stiff with spring rates and it desperately needs more rebound damping. It rebounds quickly enough that it can get the rear loose and make it a handful - or fun, depending on how you look at it. A little rear drift is fun but not as quick.

A bit more damping control on both ends and a slightly softer rear spring will definitely get rid of the jitters over rough stuff.
Quote:
Originally Posted by bentom2 View Post
Ha! Zoomed in as close as I could on a bigger screen and I think you’re right. The light/shadow got me. Oops.

The back end definitely feels like it skips over bumps due to what feels like a spring rate/damper mismatch, while the front just sucks it all up, so I guess I saw what I wanted to see.
Are you guys sure it's not because of too much rebound? When the rebound is too high it'll pull you into the bump stop and keep you there, and then it's the bump stop that's bouncing you up. BMW dampers typically have a good amount of rebound bias.

As an example, at ACNA Sonoma at the beginning of the month a bunch of drivers were talking about how rough the curbing was at T2, and T8. My friend and I found that amusing because our vehicles (435i on Ohlins R&T and 328d on FCM reworked Bilsteins) handled all the curbing very smoothly. On the 435i I turned down his dampening from the Ohlins recommended "track" setting the weekend before to optimize things. This made the car less harsh and upset over bumps like track curbing and let him attack corners with more speed. He said the car felt smoother and more in control. On my own setup my dampers don't have any rebound bias. My instructor even mentioned how comfortable and smooth my ride was over all the curbing.
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      12-06-2019, 11:45 AM   #50
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Quote:
Originally Posted by FaRKle! View Post
Are you guys sure it's not because of too much rebound? When the rebound is too high it'll pull you into the bump stop and keep you there, and then it's the bump stop that's bouncing you up. BMW dampers typically have a good amount of rebound bias.
I guess we need to make sure we're all on the same page as far as description.

Damping (not dampening, that's what you do with a wet cloth) - The control of motion (via the shock).

So when you say rebound is too high (as in motion?) - do you mean that it's too soft so it rebounds too quickly?

Or do you mean it's too stiff (as in the setting is too high) and the rebound is slow?

I feel that there needs to be more rebound damping (slowing the extension of the shock). Presently the rebound is too fast and it's allowing the suspension to extend too quickly so the car feels jumpy. The rebound action needs to be slowed down.

Slowing down the compression damping a tad will also help as right now it feels like the suspension blows through the travel and (as you've stated) lets the car get to the bump stop and then there's no wheel travel left to deal with undulations of the track. That "packs" the suspension up and it can't do anything anymore. Too much damping on compression will also cause "packing" as the shock can't respond quickly enough so it acts like it's on a bump stop.

The car needs better rear damping control - more rebound resistance, a slight increase in compression and I think it needs to get away from progressive rate springs. They get stiffer more quickly and the valving in the shock needs to be able to do the same (shaft speed control). As you get to the limits of extension or compression you start taxing the limits of the damping control with progressive rate springs.

Just for background on my suspicion of what's needed, I have about 25 years of suspension tuning under my belt in the off road world. I'm used to controlling 20+ inches of travel with (generally) three zones of damping in compression and two in rebound along with playing with spring rates, cross over points of the springs and such. Lots of time (43 years) on motocross bikes too.

Present project - can't wait to start suspension tuning on this.. :


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      12-06-2019, 01:34 PM   #51
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Quote:
Originally Posted by K-Fab View Post
So when you say rebound is too high (as in motion?) - do you mean that it's too soft so it rebounds too quickly?

Or do you mean it's too stiff (as in the setting is too high) and the rebound is slow?
Too high rebound damping forces keeping the damper compressed causing you to stay in the high spring rate bump stops. This can cause the jumpy feeling since the dampers likely aren't tuned for those higher spring rate forces. There isn't much damper travel before the bump stops start to get engaged.

With your off-road rig experience, you're probably very familiar with not having such a high rebound-biased setup too.
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      12-07-2019, 09:32 AM   #52
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Quote:
Originally Posted by FaRKle! View Post
Too high rebound damping forces keeping the damper compressed causing you to stay in the high spring rate bump stops. This can cause the jumpy feeling since the dampers likely aren't tuned for those higher spring rate forces. There isn't much damper travel before the bump stops start to get engaged.
Yes, this is known as packing and part of what I'm trying to get rid of.

Quote:
Originally Posted by FaRKle!
With your off-road rig experience, you're probably very familiar with not having such a high rebound-biased setup too.
The basic principles are the same, I just get to play with the tuning over a lot more range with off road stuff.
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Last edited by K-Fab; 12-17-2019 at 11:25 AM..
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      12-17-2019, 11:42 AM   #53
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About 550 miles worth of track time (17-18 sessions) on this set of Toyo R888Rs.

This past weekend the front end started letting go more often (had one hell of a fun last session this Sunday - guy in a Cayman and I were having a blast and I had no front end grip).

Pulled the wheels off yesterday to put the car back in street mode and was quite surprised at the inner edge of the fronts! - realizing that I have to look a lot more carefully while they're on the car, as I can't see the inside edge very well. I am quite positive that there were no cords showing before I started playing on Sunday, though. They had to be really close to the surface, though.



I'd say that 2.85 degrees of negative camber is a bit much. The right side tire wasn't as worn as the left (pic) but I'm seeing cording there too.

Rears at 1.8 degrees are also showing signs of too much camber.



Gonna drop the fronts to 2.2 and the rear to 1.4 and see what that does to spread the load a bit better across the contact patch.

Interestingly the surface temps were pretty similar across the tire's width - 140 to 150 was the margin. I didn't check the rears.

Not an excuse, a realization, I need to be a bit more up on checking things during the day. Having students definitely cuts into available time but it's something I need to be more on top of with this car.

My old R8 was set up just right so I was able to be lazy about wear checking as it was an equal opportunity tire wearing vehicle. It didn't tend to bias wear at either shoulder, which is what I'm trying to get out of this M2C.

Cage is supposed to be here sometime (was supposed to show last week) and I'll be ordering another set of Toyos (they're the least expensive and work pretty well) to get the car dialed in.

Ah the joys of modifying. One step forward, half a step back.

Did I say how much fun I'm having with this car? What a blast it is!
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      12-17-2019, 12:06 PM   #54
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Quote:
Originally Posted by K-Fab View Post
About 550 miles worth of track time (17-18 sessions) on this set of Toyo R888Rs.

This past weekend the front end started letting go more often (had one hell of a fun last session this Sunday - guy in a Cayman and I were having a blast and I had no front end grip).

Pulled the wheels off yesterday to put the car back in street mode and was quite surprised at the inner edge of the fronts! - realizing that I have to look a lot more carefully while they're on the car, as I can't see the inside edge very well. I am quite positive that there were no cords showing before I started playing on Sunday, though. They had to be really close to the surface, though.



I'd say that 2.85 degrees of negative camber is a bit much. The right side tire wasn't as worn as the left (pic) but I'm seeing cording there too.

Rears at 1.8 degrees are also showing signs of too much camber.



Gonna drop the fronts to 2.2 and the rear to 1.4 and see what that does to spread the load a bit better across the contact patch.

Interestingly the surface temps were pretty similar across the tire's width - 140 to 150 was the margin. I didn't check the rears.

Not an excuse, a realization, I need to be a bit more up on checking things during the day. Having students definitely cuts into available time but it's something I need to be more on top of with this car.

My old R8 was set up just right so I was able to be lazy about wear checking as it was an equal opportunity tire wearing vehicle. It didn't tend to bias wear at either shoulder, which is what I'm trying to get out of this M2C.

Cage is supposed to be here sometime (was supposed to show last week) and I'll be ordering another set of Toyos (they're the least expensive and work pretty well) to get the car dialed in.

Ah the joys of modifying. One step forward, half a step back.

Did I say how much fun I'm having with this car? What a blast it is!
2.8 is not a lot. I'd have your toe investigated.
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      12-17-2019, 08:46 PM   #55
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Interesting - you're the third person to say check toe.

I based my original settings on what I'd found here on the forum:
2.8 and 1.8 camber and zero toe.

Looks like I need to find another place to do the alignment. I want to double check everything and see what it reads now that I've run it hard for a few miles.
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      01-12-2020, 11:28 AM   #56
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RSR cage and Team-Tech harness installed:





Car goes in tomorrow for Ohlins and rear camber control arms.
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      01-12-2020, 03:19 PM   #57
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Quote:
Originally Posted by K-Fab View Post
RSR cage and Team-Tech harness installed:





Car goes in tomorrow for Ohlins and rear camber control arms.
Horrible idea to run those seats with that harness setup.
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      01-14-2020, 10:09 AM   #58
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Originally Posted by mcvaughan View Post
Horrible idea to run those seats with that harness setup.
Thank you for the compliment.

Same setup I ran in my R8 - yes, they're slightly wide at the shoulders, that's why the sternum strap is there - keeps them nice and snug across my chest.
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      01-14-2020, 10:43 AM   #59
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Originally Posted by K-Fab View Post
Thank you for the compliment.

Same setup I ran in my R8 - yes, they're slightly wide at the shoulders, that's why the sternum strap is there - keeps them nice and snug across my chest.
These seats are not designed for harnesses, period. If you're going this far, why not put in a proper race seat?
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      01-14-2020, 01:12 PM   #60
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Quote:
Originally Posted by K-Fab View Post


That's some pretty horrible tire wear. I've run NT01s, which are essentially the same compound from what I understand, with over 3.2 front camber and have had very even wear. Somethings off, either alignment, suspension settings, or something else.

Regarding those seats with a harness, I wouldn't run that. I don't think it will even pass tech.
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      01-14-2020, 02:58 PM   #61
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Quote:
Originally Posted by K-Fab View Post
Thank you for the compliment.

Same setup I ran in my R8 - yes, they're slightly wide at the shoulders, that's why the sternum strap is there - keeps them nice and snug across my chest.
Hey, itís only unsafe if you crash
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      01-14-2020, 03:41 PM   #62
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Regarding the harness - just getting things set up. Seats will be a future thing. I'm aware of the issues the setup has.

The tires - yeah, horrible issue there. Not sure what was up. Everything checked out (supposedly) but I wonder if the machine we used wasn't quite right. Dunno. Regardless, the car's getting Ohlins installed and there will be a full four wheel alignment done (again), hopefully with better results. I was blown away when I pulled the wheels off and saw that.
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      01-14-2020, 10:42 PM   #63
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That tire wear looks more like a toe issue tbh.
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      01-16-2020, 11:16 AM   #64
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Quote:
Originally Posted by kpaso View Post
That tire wear looks more like a toe issue tbh.
Completely agreed. The good thing is that it's equal so what ever I screwed up I did it correctly and balanced.

Picking the car up to day with new suspension and settings. Time will tell if it's correct.
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      01-16-2020, 04:51 PM   #65
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Quote:
Originally Posted by K-Fab View Post
Completely agreed. The good thing is that it's equal so what ever I screwed up I did it correctly and balanced.

Picking the car up to day with new suspension and settings. Time will tell if it's correct.
Won't you know it's correct by reviewing your alignment spec sheet?
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      01-16-2020, 07:47 PM   #66
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Originally Posted by mcvaughan View Post
Won't you know it's correct by reviewing your alignment spec sheet?
I never got one. I sat there in the car as they did the alignment so I watched the system and said "There" when they got to the correct place.

Just home.

The settings up front were WAAAYY off.

Looks like the company I use had no clue (and I will admit I kind of wondered - I felt like I understood the system better than the guy running it - who was not the regular guy) Camber was at 3.4 and toe was in three degrees. Explains the sever cording.

Aligned on the latest Hawk-Eye system:

Car is now set at 3 degrees camber, zero toe front
1.9 camber, presently mentally blank on toe in - 1 degree or did he say 1.8...
And now that I type this I realize I didn't get a sheet from this guy either (although I trust him - It's very obvious he does know his stuff.)

I have to take the car back so he can replace the upper pivots in the Ground Control plates. They're a one time use (have a crush washer that deforms) and it was overlooked when the new spring perches were installed. Installer is covering the bushings and installation, as he should.

Looking forward to getting on the track and seeing what the new legs are like.



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