Unsprung weight
Unsprung weight Can someone please help me understand the effects of unsprung weight?
Here's the situation: I just had a new Moser 12-bolt installed, along with a trans-mounted adjustable torque arm. Presumably, the new rearend is heavier than stock. While out driving around this weekend, I've noticed the car handles differently than before, as I expected. Previously, when I hit a bump, I would feel it once, then the shock would stop the spring oscillation. Now, the bumps are more jarring, and I feel them two-three times before the car levels back out.
I'd like to know not only which way to adjust my Koni SA's (softer or firmer), but also WHY.
Thanks,
-Mike
Here's the situation: I just had a new Moser 12-bolt installed, along with a trans-mounted adjustable torque arm. Presumably, the new rearend is heavier than stock. While out driving around this weekend, I've noticed the car handles differently than before, as I expected. Previously, when I hit a bump, I would feel it once, then the shock would stop the spring oscillation. Now, the bumps are more jarring, and I feel them two-three times before the car levels back out.
I'd like to know not only which way to adjust my Koni SA's (softer or firmer), but also WHY.
Thanks,
-Mike
Unsprung weight is bad. The difference between track shoes and combat boots to a person. Compression damping is what controls unsprung weight (but cannot lessen it). Rebound controls sprung mass and springs, which hasn't changed. You'll just have to play with settings a bit to see if you can get it dialed in and remember you just installed something not in the design parameters of the damper. You might have to consider changing to rear DA's to get some compression damping help because of the mass of the axle (and do you have 315's too?).
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Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
Yes, I am running 315/35/17's in the back, Sam. Obviously, that's a LOT of unpsrung weight (not to mention rotational mass). I imagine going to lighter 17x9.5 rims would help a lot in the back, and it's not something I'm totally against. While I like the LOOKS of 17x11 rims, it isn't the most practical thing in the world.
Out of curiosity, what do a pair of rear DA's run these days, Sam?
-Mike
Out of curiosity, what do a pair of rear DA's run these days, Sam?
-Mike
DA's are about $300 each..... While 9.5's would help, how much depends on the mass of those wheels and tires (at least that's a more normal stock like size). I have 11's that weigh the same as OE 17x9's, and others that are 8 pounds each heavier, that's HUGE in terms of unsprung weight. You need to do whatever you can to get it back down to a more normal range. Hollow rear bar would save you about 5 or 6. Just so much mass working now.
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Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
www.stranoparts.com --814-849-3450
Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
I firmed up the rear shocks by half a turn and that seems to have helped quite a bit. It's far less "bouncy" now than it was, but I need to drive it more to see if that's a placebo or an actual change. I'm also going to firm the fronts up from five sweeps to four sweeps away from full firm, since it feels like the back is "throwing" the nose down a bit now.
Nice to know I have these options, though.
-Mike
Nice to know I have these options, though.
-Mike
Hmmmmm...if you know how much unsprung weight you added (by doing before and after measurements), would it be possible to have a Bilstein shock revalved to compensate? Or is there not enough room to compensate with that particular application?
I only ask because I have a 12-bolt pending installation, but I'd like my car to handle at least like it does now...
I only ask because I have a 12-bolt pending installation, but I'd like my car to handle at least like it does now...
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Originally Posted by JasonWW
As you increase rebound in the rear it slows down the nosedive effect under braking.
Is that what your seeing?
Is that what your seeing?
-Mike
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Originally Posted by chupr0kabra
What I'm seeing is more along the lines of the front dampers being too soft, so it feels like the nose wants to stay down, rather than come back up.
https://ls1tech.com/forums/showpost....03&postcount=9
Well, I tried a sweep softer and the symptoms were worse. I'm probably just not describing it well. I swept them all the way to full firm, then backed off four full sweeps. Car handles MUCH better now. Totally quieted down the bouncing.
Once again, the Koni SA's are $850 well spent.
-Mike
Once again, the Koni SA's are $850 well spent.
-Mike
Originally Posted by MeentSS02
I take it you did this on the rears?
I still need to pound on the inner fenders in the back some more. These huge tires are rubbing again.
Maybe I should just bite the bullet and save up for a set of four 17x9.5 Fikse FM5's.
-Mike
Originally Posted by chupr0kabra
I still need to pound on the inner fenders in the back some more. These huge tires are rubbing again.
Do you have a rod ended PHR already? If not, it can really help with the rubbing.
Originally Posted by JasonWW
I'm glad everything worked out.
Do you have a rod ended PHR already? If not, it can really help with the rubbing.
Do you have a rod ended PHR already? If not, it can really help with the rubbing.
-Mike
Originally Posted by chupr0kabra
Yeah, I do. I measured everything over and over again and it's centered. These GSD3's are just really wide. When the axle gets skewed is when it rubs.
-Mike
-Mike
You'll definetly need the BFH. If the rubbing is bad on both sides and you've rolled your fender lips you can add a thin spacer behind one rim and then compensate by readjusting the PHR. The end result is that it will push both tires out a tiny bit. This may help with the rubbing, but it may now catch on the fender lip so make sure they are out of the way and you don't cut your tire.
What offset are your rims?
Also, a bit more air pressure can reduce the tire from flexing left and right as much. What pressure are you running?
I actually measured in a couple places. The overall axle length and the distance between the frame rails. At one point, I had 8 plum bobs hanging off the car in various places. Looked like some sort of redneck bead curtain.
I used to do it by driving through a puddle and measuring the difference between the tread patterns, but now I'm running staggered wheels, so that's harder to do.
I've already hammered some, but I apparently need to do more. I'll pull the tires again and see where the new marks are.
Rims are 50mm offset, running 38psi, iirc.
-Mike
I used to do it by driving through a puddle and measuring the difference between the tread patterns, but now I'm running staggered wheels, so that's harder to do.
I've already hammered some, but I apparently need to do more. I'll pull the tires again and see where the new marks are.
Rims are 50mm offset, running 38psi, iirc.
-Mike
You'll need some spacer with 50mm offset. I run about 10mm on my wheels that are not build to the offset I need. And 38 PSI? Whew, that's HIGH!!!! Why so much? The load per square inch is less than it is with stock tires, you only need to be @ 30 or so. You'll be shocked (no pun intended) about how much that helps.
__________________
www.stranoparts.com --814-849-3450
Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
www.stranoparts.com --814-849-3450
Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
yeah, thesae cars like less preaaure in the rear. try 27-30psi in the rear with 315's. I ran about 27-28psi to keep the contact patch flat. At 38 you will wear out the center of the tread.
With that offset you may need to try one thin spacer on one wheel and then recenter to compensate like I mentioned above.
With that offset you may need to try one thin spacer on one wheel and then recenter to compensate like I mentioned above.
I think running 38 PSI in the rear is accounting for the good amount of the "jarring" and new rear end. Adding weight and that high of rear tire pressure its going to ride bad IMHO.
good luck on getting it tuned in.
good luck on getting it tuned in.