Rear Suspension and Torsen Diff

[sholzer]

Went to the DC Pro Solo this past weekend and had a blast (even with my sub par driving lol). I did notice though that in some corners, I'd get a bit of wheel spin from the inside wheel. I'm assuming this was the result of a combination of off-camber corner + suspension loading up on the left side taking enough weight off the inside tire to allow it to spin without "engaging" the differential.

It was most noticeable in the right hand corner a little after the 30 second mark (you can hear the car rev-up freely).



What can I do suspension wise to help remedy this in the future? The car has eibach pro-kit springs, koni yellows, whiteline sway bars, and whiteline panhard bar. Rear sway is set to second from full stiff, rear shocks are about halfway to full stiff.

 

[Whiskey11]

Went to the DC Pro Solo this past weekend and had a blast (even with my sub par driving lol). I did notice though that in some corners, I'd get a bit of wheel spin from the inside wheel. I'm assuming this was the result of a combination of off-camber corner + suspension loading up on the left side taking enough weight off the inside tire to allow it to spin without "engaging" the differential.

It was most noticeable in the right hand corner a little after the 30 second mark (you can hear the car rev-up freely).

What can I do suspension wise to help remedy this in the future? The car has eibach pro-kit springs, koni yellows, whiteline sway bars, and whiteline panhard bar. Rear sway is set to second from full stiff, rear shocks are about halfway to full stiff.

Stiffer front springs will keep more weight on the rear axle during braking and cornering. Could also be related to the PHB but unlikely that it is sufficiently unloading the rear tires.

PS: How did you do?

 

[Vorshlag-Fair]

What can I do suspension wise to help remedy this in the future? The car has eibach pro-kit springs, koni yellows, whiteline sway bars, and whiteline panhard bar. Rear sway is set to second from full stiff, rear shocks are about halfway to full stiff.

What tires were you on? What class? I assume it was STX and street tires. The surface of that lot looks like nasty old asphalt, with the friction level of greased snot, heh. It didn't look like wild power oversteer, but I could hear some wheelspin in the videos, sure. Don't know if anything is going to help tremendously, within those tire/class/surface limitations.

The Torsen doesn't like to work if one tire is in the air. Can you get someone to take good digital photos of your car in big transitions, where it seems to be letting go? What you want to see is if the inside rear tire is ever coming off the ground. If so, that's going to cause wheelspin on a Torsen. Could be that stiffer spring rates and less bodyroll could minimize that.

The STX and ESP classes don't allow for easy/common rear geometry fixes (LCA relocation brackets, lower arms, etc), so you are stuck with only unusual/expensive options like a Torque Arm. But until you upgrade shocks and springs, that's probably throwing money at the wrong areas.

 

[sholzer]

Class was ESP and I was on 295/40/18 A6s. I'll try and track down some pics of the car from this past weekend and see if I see anything. But I was thinking spring rate and less roll was the answer, but I wasn't 100% sure. Guess I'll be saving up for some coils while I get more seat time this year lol

 

[sholzer]

Thought I replied to you on my phone Chris, but I didn't do nearly as well as I hoped lol. I couldn't get the left course down to save my life and was about 1 second off pace from the middle of the pack. Right course I was better off, but there was obviously a lot of time left on the table on both sides. I need a lot more seat time and probably a little more prep (wider wheels, better sized tires mostly) to be where I would like to be with the car. I was playing with tire pressures all weekend too and I think I have a good starting point for the next event. After talking with the other ESP drivers, I tried running lower pressures (32F 28R) and the car felt floaty and odd early Saturday (But better as they got hotter and pressures rose). Ended up running 36F and 33R and the car felt much better, but the rear felt a little loose and the tires looked they weren't getting scrubbing all the way to the edge of the tread so I'm going to try and run them at 36F and 31R and chalk them next event and see how it feels and looks.

All in all though, I had a blast and learned a lot. I'm still learning that these A6's have a lot more lateral grip than I am used to having and I frequently caught myself turning in too early, not expecting the car to turn so quickly, or just plain driving too slow. Coming into my Sunday runs I told myself that I need to be more aggressive as I hadn't hit any cones up to that point and managed to pick up a good chunk of time on both sides (.2 seconds on left, .4 on right) even though I kind of through my last left side run away (way too aggresive on first turn and picked up two cones.

We have one of the best sites for our region coming up for a two day event and I'm really excited to get back out there and try and get faster after getting my ass kicked lol

 

[sholzer]

Here are the two views from my left side runs




I tried to keep everything tight, tidy, and really smooth on this side and it just ended up being slow haha

 

[Vorshlag-Fair]

Class was ESP and I was on 295/40/18 A6s. I'll try and track down some pics of the car from this past weekend and see if I see anything. But I was thinking spring rate and less roll was the answer, but I wasn't 100% sure. Guess I'll be saving up for some coils while I get more seat time this year lol

ohhh.... my bad. The pic in your sig is a little out of date, I guess. That's a decent sized tire for ESP, of course, but even a bone stock 5.0 makes 380whp - which is a lot for two of those on the drive axle when used in a low speed parking lot event. As I've said many times before, you can never have TOO much tire on these cars, especially when you start adding more power...

This picture above was during a (failed) experiment back in 2012, when we were still running ESP. Front was the same 18x11"/315mm A6 but the rear had the 18x12" wheel and 345/35/18 Hoosier A6. Brand new, for this event. Sealed asphalt lot, and that power oversteer condition was in a medium speed 2nd gear corner, with 430 whp (2 bolt-ons + a tune). Granted, this was before we did the Watts, the Torsen T-2R, and later the LCAs and relocation brackets after we left ESP, but it was still rear traction limited in autocross events. With a 13.2" wide tread width Hoosier A6.

We went back to a 315mm tire because of tire rub issues on the rear, with the 345mm tire. But on a serious ESP effort with one of these S197 cars, I definitely would build the car around this rear tire. Cut the fenders, flare for clearance, etc. And I'd run an almost matching 335mm front. We didn't get that far before we left ESP class, but that's the magic set-up. Every time we've added tire width to this car it 1) got faster and 2) easier to drive.

Not everyone is willing to cut up a new or nearly new $30-45K 2011-2014 Mustang GT/Boss302, so in that case go with the widest that can fit under the stock fenders (315mm) and make the mods necessary to fit that. The 295/40/18 was on close-out for almost 1/3rd the normal cost, so that was a no-brainer. But don't expect it to make the grip of the 315... or the 335... or the 345mm A6.

As for suspension mods... sure, with even the 295 A6 you're probably overtaxing the shocks and lowering springs you have. We had 450#/in front and 175 #/in rear springs on Moton Motorsport 2-way coilovers at the 2012 Nats (above and below) and look at how much bodyroll and brake dive we still had. I've gone to 600#/in fronts and 250 #/in rears (which works great on track) but still have a lot of bodyroll in autocross events. With huge swaybars at nearly full stiff, too.

Autocross S197 Mustangs in ESP really need... ludicrous tires, and ridiculous spring rates.

 

[phoenix335]

Nice to meet you Steve. I was running similar pressures (36F and 34 R). I think the narrower wheel may have required a little higher pressure. The other cars and drivers were better (some better prepared cars and some just plain and simple better drivers). The one guy was a pro road course driver...

I thought my co-driver would do better and was surprised that he was only a little ahead of me. I think on a "real" autocross course we would have done better against the competition. Hope you can make it up for a regular DC event.

 

[Justin_H]

That lot used to have pretty good grip, but it's been years since I've run there, and about 6 years since I ran there in something smaller than a 315 A6.

To reduce the inside wheelspin you'll either need to go to a diff that locks better with light loads or reduce the weight transfer off the inside rear tire. There are several options, but all of them affect the handling to some extent- you just have to find the combination you're happiest with. I'd start with softening the rear bar and shocks and stiffening the front. But you might hate how that drives more than the wheelspin. Stiffer front springs will help also.

 

[sholzer]

Nice to meet you Steve. I was running similar pressures (36F and 34 R). I think the narrower wheel may have required a little higher pressure. The other cars and drivers were better (some better prepared cars and some just plain and simple better drivers). The one guy was a pro road course driver...

I thought my co-driver would do better and was surprised that he was only a little ahead of me. I think on a "real" autocross course we would have done better against the competition. Hope you can make it up for a regular DC event.

Nice to meet you too! I'll definitely try and get up there because like I said, the ESP competition in my region isn't there.. unless Karen decides to come to her home region's events lol

That lot used to have pretty good grip, but it's been years since I've run there, and about 6 years since I ran there in something smaller than a 315 A6.

To reduce the inside wheelspin you'll either need to go to a diff that locks better with light loads or reduce the weight transfer off the inside rear tire. There are several options, but all of them affect the handling to some extent- you just have to find the combination you're happiest with. I'd start with softening the rear bar and shocks and stiffening the front. But you might hate how that drives more than the wheelspin. Stiffer front springs will help also.

The right side of the lot has decent grip for asphalt, left side however, was just resealed and some spots it has decent grip and other spots it has no grip, so that was another challenge. I'll try dialing in the shocks more and see if it helps at all as I have no way on stiffening the fronts anymore other than swapping out to new springs/a coilover setup.

Thanks for all the input!

Pic from the weekend just because

 

[Sam Strano]

Well, you know there was someone actually there (and who drove the course) who might be able to help..... I also setup the Mustang that was 2nd.

You always, ALWAYS start with a better limited slip *ALWAYS* with these cars. Yes, you can make the front stiffer, but that will only help so much because the diff is weak. Also a Watts link (without the argument about which one, etc). helps because it doesn't unload the right rear as much when you are turning.

 

[sholzer]

Well, you know there was someone actually there (and who drove the course) who might be able to help..... I also setup the Mustang that was 2nd.

You always, ALWAYS start with a better limited slip *ALWAYS* with these cars. Yes, you can make the front stiffer, but that will only help so much because the diff is weak. Also a Watts link (without the argument about which one, etc). helps because it doesn't unload the right rear as much when you are turning.

I'll be sure to say hi next time and ask for any help/advice on setting the car!

Watts link is definitely on the list as well as a T2R, but I don't see myself getting those until this winter at the earliest and even that will be a stretch.

The car is setup "decently" now that I think the goal for me right now is getting more seat time to really find the limits before I start changing even more things. Closest car to mine as far as prep goes was the blue 2013 and I was about on par with them on the right, but behind by a second on the left, so I definitely know I have some improving and learning to do.

 

[sholzer]

Had a lot better results this weekend after upping the damping on the front struts. Car would still benefit from proper spring rates, watts link, and a better diff though.

Here is a vid from my quickest run today, definitely not as much wheel spin as before

 

[JesseW.]

are you still on the stock clutch diff? it takes about 8 events to wear one out then its a wild ride. it's probably just sending all the power through one tire which will easily spin an A6 instead of lifting the tire up..... the torsen or the true-trac will really help it out.

 

[sholzer]

My car is a track pack car which came with a Torsen T2 with a 2.7 TBR. Putting the damping on the front struts to full stiff helped a ton to keep the rear tires planted, but I know its just a band-aid/compromise until I get some coils with proper spring rates, better dampers, watts link and a better diff.

Also reading more on how the torsens behave, I highly doubt I was lifting it enough to spin the inside wheel as if it was open, but it was spinning while the diff was trying to divert power to the outside wheel. I think with the way I was reading and interpreting it, with the lower TBR, there is a higher allowable difference in the RPM of the wheels, which is what I could feel and hear.