suspension--tail swings out a bit at first stage of sharp cornering/turning

[soccerballtux]

* Scion tC first gen has approx 60/40 weight distribution FWD
* Koni Yellows on full stiff in front (just dialed that yesterday), bit less than half-stiff in rear
* Eibach Pro-Kit spring set
* tRD rear sway bar (it's pretty thick) on sport setting
* alignment good

I've noticed on heavy braking especially while turning, nose dive and ... unstable handling.
So I set the front suspension to full stiff. Helped a lot with the nose dive. But I miss the cushier ride.
That's not why I'm posting though--

I'm experiencing a bit of, I guess chassis roll. At 70-80mph, I start a turn, car starts the turn, chassis squats a bit with the weight transfer, finally grabs, and then as it grabs the tail swings out a bit. What should I change? Is that a bit of oversteer? I'm leaning towards setting the rear shocks to full stiff as well since this helped so much with the front end's behavior. However, I previously had them at full stiff and dialed them back due to "harshness" on speedbumps. Now, I think I don't care-- I want clean handling.

 

[Ferzerp]

Heavy braking + turning?

Yeah, stop that, that's your problem.

 

[soccerballtux]

Heavy braking + turning?

Yeah, stop that, that's your problem.

re-read, this general case I'm talking about is without braking, I don't usually brake and turn
sometimes necessary with the crazy drivers around here though...so unsafe....

but thank you for reading

 

[monkeydelmagico]

Jesus christ koni yellows on full stiff is a punishing ride. Full stiff on rear sway isn't helping either. Pro Tip: Some suspension travel is a good thing.

Braking and turning at the same time is a more advanced driving technique best left to the pros (trail braking). Is it so severe that the ass trying to pass the front or you have to panic counter-steer before going into the weeds? If so, the setup is definitely off. For a twitchy rear loosen up the rear sway, soften the rear koni's a few more turns, and double check your tire pressure.

 

[tweakmonkey]

Soften the rear sway bar.

 

[Squeetard]

That is called step out. Caused by slack in the rubber rear bushings. Install aftermarket urethane bushings.
http://www.fastscions.com/Scion-tC-Suspension-Bushings.aspx

The new Camaro has this issue and installing an energy urethane kit fixed it for me.

By the way. This kit will really step up the handling too.

Edit: I see that is a trailing arm suspension. Just installing the trailing arm kit will do wonders for you. That is the main cause of step out as that slack will cause your rear tires to actually toe out as you turn.

http://www.fastscions.com/energy-su...r-trailing-arm-bushing-set-scion-tc-2005.aspx

 

[soccerballtux]

That is called step out. Caused by slack in the rubber rear bushings. Install aftermarket urethane bushings.
http://www.fastscions.com/Scion-tC-Suspension-Bushings.aspx

The new Camaro has this issue and installing an energy urethane kit fixed it for me.

By the way. This kit will really step up the handling too.

Edit: I see that is a trailing arm suspension. Just installing the trailing arm kit will do wonders for you. That is the main cause of step out as that slack will cause your rear tires to actually toe out as you turn.

http://www.fastscions.com/energy-su...r-trailing-arm-bushing-set-scion-tc-2005.aspx

genius. that's exactly what it feels like
will look into this. was hoping not to spend more

 

[soccerballtux]

Jesus christ koni yellows on full stiff is a punishing ride. Full stiff on rear sway isn't helping either. Pro Tip: Some suspension travel is a good thing.

Braking and turning at the same time is a more advanced driving technique best left to the pros (trail braking). Is it so severe that the ass trying to pass the front or you have to panic counter-steer before going into the weeds? If so, the setup is definitely off. For a twitchy rear loosen up the rear sway, soften the rear koni's a few more turns, and double check your tire pressure.

you know I've had them for 3 years and they feel softer on stiff than they used to, but they're also softer in the summer, 90s+ down here, I assume oil viscosity changing in the heat

nah just about 5 degrees or bit more or so.

 

[Wuzup101]

Soften the rear sway bar.

While the bushings posted above may certainly help - I too would try to soften the RSB as my first course of action.

 

[thomsbrain]

While the bushings posted above may certainly help - I too would try to soften the RSB as my first course of action.

Same here. Free change, and will make the rear feel more planted.

That said, with Koni shocks (large amounts of variation in damping between individual shocks), where you have been messing with the adjusters (which do not act uniformly from shock to shock, nor act the same in each turning direction, nor act the same without being fully "reset" to full stiff each time you change them), combined with Eibach pro-kit springs (progressive spring rate, meaning your spring rate changes depending on wheel position), you may never be able to have this car handle predictably.

I would ditch the cheap lowering springs, get some decent, linear springs, have the Koni's valved and adjusters set by the shock builder for your chosen spring rate and street application, put them on and don't touch the adjusters.

 

[JCH13]

* Scion tC first gen has approx 60/40 weight distribution FWD
* Koni Yellows on full stiff in front (just dialed that yesterday), bit less than half-stiff in rear
* Eibach Pro-Kit spring set
* tRD rear sway bar (it's pretty thick) on sport setting
* alignment good

I've noticed on heavy braking especially while turning, nose dive and ... unstable handling.
So I set the front suspension to full stiff. Helped a lot with the nose dive. But I miss the cushier ride.
That's not why I'm posting though--

I'm experiencing a bit of, I guess chassis roll. At 70-80mph, I start a turn, car starts the turn, chassis squats a bit with the weight transfer, finally grabs, and then as it grabs the tail swings out a bit. What should I change? Is that a bit of oversteer? I'm leaning towards setting the rear shocks to full stiff as well since this helped so much with the front end's behavior. However, I previously had them at full stiff and dialed them back due to "harshness" on speedbumps. Now, I think I don't care-- I want clean handling.

Konis on 'full stiff' are not helping. Comfort and handling are not different goals - both seek to keep the loading on a given tire even. You won't gain any performance from setting your shocks at 'full stiff', in all likelihood you'll ruin it. Koni adjusters only work in rebound, not compression, so by setting the shocks to 'full stiff' they will compress easily and take a long time to rebound. This causes 'jacking down' where your suspension becomes artificially compressed, and this causes a loss of grip, unpredictable handling, etc. Stop it.

You are experiencing generally shitty handling and oversteer. The oversteer is being caused by the TRD springs and using a stiffer RSB, both of which increase the weight transfer carried by your rear axle. Get a stiffer front bar or soften the rear bar.

That said, with Koni shocks (large amounts of variation in damping between individual shocks), where you have been messing with the adjusters (which do not act uniformly from shock to shock, nor act the same in each turning direction, nor act the same without being fully "reset" to full stiff each time you change them), combined with Eibach pro-kit springs (progressive spring rate, meaning your spring rate changes depending on wheel position), you may never be able to have this car handle predictably.

I would ditch the cheap lowering springs, get some decent, linear springs, have the Koni's valved and adjusters set by the shock builder for your chosen spring rate and street application, put them on and don't touch the adjusters.

^100% agree.

Shocks are designed to work at a specific linear spring rate, when a spring is progressive (i.e. the spring rate changes over travel) the shock doesn't work effectively across the whole suspension travel. This can result in different wheels being over- or under-damped at the same time - not a good situation.

 

[soccerballtux]

Well, I guess I listened to the wrong people when I asked what springs and struts I should get.

I keep forgetting the dial on the Koni's only adjusts rebound.

ok I put everything back to how it was before.

step out is about 40% as bad as it was. More chassis roll though, which I feel is more of a bother than the step out. Aside from the step out, it felt more planted when cornering with sport RSB setting. How do I get the step out even better? What do I need to do if I want to put the RSB on sport and not have the step out? I really prefer it without the chassis roll, if I could just solve the step out.

I can't ship the struts off for rebuild, the fronts were inserts and the rears were trashed and I need to drive. Rear Eibhach springs are linear, only the fronts are progressive. Springs are cheap enough and I'm OK with adjusting the rebound myself--pretty sure I can determine the optimal rebound (for comfort, at least), and I enjoy this learning experience. can anyone recommend different springs?

In what order should I upgrade what else? should I go ahead and get that bushing set?

I think I really want to get the handling tight on this, I expect I'll be keeping the car

thanks

 

[theeedude]

I would fund Roth IRA first.
Back when I had my Maxima and cared about car stuff, after I funded my Roth IRA, I bought an RSB for it, and it woulds step out over rough pavement too. I kind of liked the effect. Then I bought a Mazda3 and realized how a FWD car should handle when the suspension is properly designed from the factory.

 

[JCH13]

Well, I guess I listened to the wrong people when I asked what springs and struts I should get.

I keep forgetting the dial on the Koni's only adjusts rebound.

ok I put everything back to how it was before.

step out is about 40% as bad as it was. More chassis roll though, which I feel is more of a bother than the step out. Aside from the step out, it felt more planted when cornering with sport RSB setting. How do I get the step out even better? What do I need to do if I want to put the RSB on sport and not have the step out? I really prefer it without the chassis roll, if I could just solve the step out.

I can't ship the struts off for rebuild, the fronts were inserts and the rears were trashed and I need to drive. Rear Eibhach springs are linear, only the fronts are progressive. Springs are cheap enough and I'm OK with adjusting the rebound myself--pretty sure I can determine the optimal rebound (for comfort, at least), and I enjoy this learning experience. can anyone recommend different springs?

In what order should I upgrade what else? should I go ahead and get that bushing set?

I think I really want to get the handling tight on this, I expect I'll be keeping the car

thanks

Body roll isn't a bad thing, neither is suspension travel. You'll hate the 'step out' when it because 'dramatic over-steer' in low traction or emergency situations.

Like I said before, if you want to keep your RSB on 'stiff' you should get a FSB as well to reset the balance of your car. This will help control your car's body roll without too much sacrifice in comfort. Your other option is even stiffer springs, which will have a significant negative impact on comfort.

If you can, get Koni FSD shocks for your car. You can try to adjust your sports yourself, in that case I would suggest adjusting them roughly proportionally to their spring rates (i.e. if the front was 100in/lb and the rear was 200in/lb you would adjust the fronts half as far from 'full soft' as the rears). Know that the adjustment values are not well-controlled and two shocks at the same adjustment setting might not behave the same way.

I have no suggestions on springs other than making sure they have a linear rate and aren't too stiff. If you plan on keeping the car for a while you won't want a rough ride. Also consider getting improve bump stops, this can make a huge difference in comfort.

Side note: please stop calling it "step out," what you're seeing is oversteer

 

[jlee]

I think this issue has more to do with the sway bar setup than the springs...I have Konis/ProKit on my MR2 and it doesn't do anything funny like that. I can have throttle induced oversteer, but that's different.

On my car, I like ~1/3 up from full soft. I would try relaxing your rear sway bar setting and drop some stiffness from the struts, then see how it goes.

 

[Squeetard]

That is called step out. Caused by slack in the rubber rear bushings. Install aftermarket urethane bushings.
http://www.fastscions.com/Scion-tC-Suspension-Bushings.aspx

The new Camaro has this issue and installing an energy urethane kit fixed it for me.

By the way. This kit will really step up the handling too.

Edit: I see that is a trailing arm suspension. Just installing the trailing arm kit will do wonders for you. That is the main cause of step out as that slack will cause your rear tires to actually toe out as you turn.

http://www.fastscions.com/energy-su...r-trailing-arm-bushing-set-scion-tc-2005.aspx

This again. The tc has an independent wishbone rear suspension. Step out is inherent with this type of rear geometry and the soft bushings they use to add comfort.

 

[JCH13]

This again. The tc has an independent wishbone rear suspension. Step out is inherent with this type of rear geometry and the soft bushings they use to add comfort.

You have a whole different ball of wax with a RWD car, where the rear suspension has to handle the reaction forces of the drive wheels as well as the suspension.

I'm not saying rear bushings wouldn't work, they might help, but OP has made serious changes to the car's front roll couple and it would be ignorant to think that suspension bushings could change that. Adding in a little bit of rear toe to the alignment would address the issue, if indeed it is a problem.

 

[soccerballtux]

Side note: please stop calling it "step out," what you're seeing is oversteer

the tires aren't breaking loose at all, ???

 

[JCH13]

the tires aren't breaking loose at all, ???

oversteer != drifting

The slip angle of the rear tires is getting higher than the front tires, so the rear axle is moving more to the side than the front axle. This does not mean that the tires are sliding. Tires have to see some slip angle to create grip, as more and more grip is demanded of a tire its slip angle increases. Your RSB is making the rear tires work harder than the fronts (due to moving weight transfer loads from the front to the rear), so the rear tires' slip angles are rising faster than the front tires' slip angles, causing oversteer. At a high enough speed, or sharp enough turn, you would lose traction and start to spin.

 

[soccerballtux]

oversteer != drifting

The slip angle of the rear tires is getting higher than the front tires, so the rear axle is moving more to the side than the front axle. This does not mean that the tires are sliding. Tires have to see some slip angle to create grip, as more and more grip is demanded of a tire its slip angle increases. Your RSB is making the rear tires work harder than the fronts (due to moving weight transfer loads from the front to the rear), so the rear tires' slip angles are rising faster than the front tires' slip angles, causing oversteer. At a high enough speed, or sharp enough turn, you would lose traction and start to spin.

didn't think about the load transfer to rear, makes sense now how FSB to balance that. will consider

 

[Squeetard]

Side note: please stop calling it "step out," what you're seeing is oversteer

Wrong. This is a rear wheel drive independent suspension. As the OP described it. It is the EXACT issue that is inherent in every modern factory IRS.

About 1/4 of the way into the turn the back end seems to wiggle, am I right OP?

I have experienced and dealt with this same issue.

You can tweak your suspension all you want but it will never go away until you stiffen up the movement in the rear geometry.

OP if the Scion has an entire rear cradle assembly that is bolted to the body with bushings, you'll want to get urethane cradle bushings as well.

 

[JCH13]

Wrong. This is a rear wheel drive independent suspension. As the OP described it. It is the EXACT issue that is inherent in every modern factory IRS.

About 1/4 of the way into the turn the back end seems to wiggle, am I right OP?

I have experienced and dealt with this same issue.

You can tweak your suspension all you want but it will never go away until you stiffen up the movement in the rear geometry.

OP if the Scion has an entire rear cradle assembly that is bolted to the body with bushings, you'll want to get urethane cradle bushings as well.

"Step out" isn't a thing when talking about suspension and vehicle dynamics. It's slang at best, it doesn't describe any particular phenomena, and is an imprecise and sloppy way to describe a vehicle's response.

And the Scion tC is FWD, not RWD.

 

[jlee]

Wrong. This is a rear wheel drive independent suspension. As the OP described it. It is the EXACT issue that is inherent in every modern factory IRS.

About 1/4 of the way into the turn the back end seems to wiggle, am I right OP?

I have experienced and dealt with this same issue.

You can tweak your suspension all you want but it will never go away until you stiffen up the movement in the rear geometry.

OP if the Scion has an entire rear cradle assembly that is bolted to the body with bushings, you'll want to get urethane cradle bushings as well.

u sure bro?


Because this isn't an FR-S.

 

[_Rick_]

I'm still not sure how this isn't just normal lift-off oversteer, especially that first moment, as the tire load changes and the outside tire leans out
I don't even have to use the brakes into a corner to get the rear to start shimmying, when the weight transfers to the front under (engine)braking, and the rear gets light.
Cure it with a dab of throttle, until you have more understeer than oversteer, and you balance the car out, at least in the neutral part of the turn. Uner load, you can then steer with the throttle, but with the inverse affect to a rear-driven car: more throttle makes the nose go wide, less throttle makes the tail go wide.

If you trail-brake, you have to adjust the line you take, to account for the rear end going wide, and the front end being more "positive".

Stiffening rebound isn't going to help much, but you may want to adjust your rear camber to the strength of the rear connecting geometry, so you get a better contact patch under the L-R weight transfer induced lean. Also make sure tire pressure isn't too high or too low.

Be careful while tuning not to get too much grip out of the rear, as you want to be able to get it to move around, and you want to make sure that it lets go slowly, and not abruptly. The more you set it up for ultimate grip, the more likely you are to suddenly get into a situation where effective loss of traction happens more abruptly, giving you less chance to correct. That's desirable on a race car, but on the road, it's nice to get that friendly warning, that (dry) grip is going away.

Ideally you should probably take a video of the phenomenon, so we can determine what the rear wheels/chassis are actually doing, and get some "telemetry".
But for now, everything you describe sounds completely....normal. But I don't know how much load you're actually putting into the suspension / tires.

Remember, some oversteer in the setup is often better than understeer being the limiting factor, since at least you can still vaguely control the car with throttle and wheel, while understeering means you have to back off the throttle/straighten, to get the wheel back into a useful state. You also go straight on, which is usually less desirable than being "nose-positive", since you just tried to steer the thing.

Note: I have no idea what I'm talking about, but I'm used to my rear stepping out on my FWD car, under certain situations.

 

[Squeetard]

It's slang at best

Yes it is.

it doesn't describe any particular phenomena

It surely does.

I had the exact same issue as the OP, when I went searching for help I found it under the slang "step out" and the proposed solution cured it for me.