Limited slip diff and vsa

[Dragos]

Disabling the car plus skid marks button on the Si disables the loss of control smarts VSA/stability control and TC as well. Every aid but ABS sadly No econo button

VSA applies brakes on each wheel to control what the car thinks is a loss of control, usually when taking a corner too fast, sliding or braking too harsh too late in a corner or changing direction too abruptly that the car tends to slide a bit.
Traction control cuts gas when it detects wheel loss of grip mostly at the moments you want it not to

 

[Dragos]

Like I said in my earlier post, the Feds require all model year 2012 vehicles sold in the US to have some form of ESC. Just FYI, the actual mandate is in the Federal Motor Vehicle Safety Standard 126, enacted in 2007, which states:

"As part of a comprehensive plan for reducing the serious risk of rollover crashes and the risk of death and serious injury in those crashes, this document establishes a new Federal motor vehicle safety standard (FMVSS) No. 126 to require electronic stability control (ESC) systems on passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 Kg (10,000 pounds) or less. . . . This rule requires installation of ESC in 100 percent of light vehicles by MY 2012 (with exceptions for some vehicles manufactured in stages or by small volume manufacturers)." (Emphasis added)​

​

This is the reason why ALL 2012 MY Hondas have VSA.

That makes sense as a reason though it is mostly due to SUVs, minivans and trucks and other high center of gravity cars. Either way I am very thankful I can turn it off, only if ABS could be turned off as well. Non ABS cars brake much nicer, ABS kicks in too soon, I wish it could allow a tiny bit of grip loss before kicking in. If not fully turned off at least an adjustable loss of grip triggering ABS threshold.

 

[hey_mikey]

I guess I was not clear enough on first post. I am asking about an si. Let me give an example of my question. If I am in a tight turn and accelerate hard the LSD will transfer power to the outside wheel to limit any spin from the inside wheel so the vsa will not kick in? If one accelerates hard in a straight line on a wet surface the LSD will help reduce spin, but will the vsa put on a brake And reduce power. If that is the case would you get the best acceleration with the vsa turned off. I could test but the car is still low mileage. Thanks

To answer the OP's original question, in such a situation (low traction, slippery surface), you might see better acceleration times with VSA active. because of the way the helical-type LSD is designed, it requires both wheels to have traction to create the LSD effect. once one wheel completely loses traction, there is no torque bias created in the diff, and the differential acts no differently from an open (non-limited-slip) diff. In such a case, the reduction in power from VSA might help the tire to regain traction and keep the car accelerating, and keeping the car moving forward. While the reduction in power will no doubt have an effect on acceleration, the loss of traction that occurs from a spinning wheel will also result in slower acceleration times, which is why I say you might accelerate faster with VSA on, depending on how slippery the road really is.

 

[Bulkybear]

No I haven't looked at the new non si models. The ones I have looked at had a button labeled vsa. Thanks for pointing that out though. Now I know. I had no idea my car actually applied brakes to the wheels for cornering. At least we can disable it. I had a jeep that did that. But you could feel it. I can't feel it on my Si.

 

[Dragos]

No I haven't looked at the new non si models. The ones I have looked at had a button labeled vsa. Thanks for pointing that out though. Now I know. I had no idea my car actually applied brakes to the wheels for cornering. At least we can disable it. I had a jeep that did that. But you could feel it. I can't feel it on my Si.

Try drifting or taking a sharp left right turn combo at high speed, it will kill all the fun very noticeably.
On my way to work there is a 30 degree turn right followed by a 100 degree left turn in the road, if I use a fast racing line as soon as I turn for the 100 degree one it actually kicks in, I find it dangerous since the car tries to go slow down and applies brakes I correct towards the turn and it yields a 2 3 left right dance like moves of the car. For some reason VSA instead of turning in the corner tends to go straight, that is in my opinion very dangerous. Without vsa car flies through the two corners with a tiny drift on the second turn.

Basically I do not even try to drive spirited with it on, it makes the drive dangerous and unpredictable.

 

[Dragos]

To answer the OP's original question, in such a situation (low traction, slippery surface), you might see better acceleration times with VSA active. because of the way the helical-type LSD is designed, it requires both wheels to have traction to create the LSD effect. once one wheel completely loses traction, there is no torque bias created in the diff, and the differential acts no differently from an open (non-limited-slip) diff. In such a case, the reduction in power from VSA might help the tire to regain traction and keep the car accelerating, and keeping the car moving forward. While the reduction in power will no doubt have an effect on acceleration, the loss of traction that occurs from a spinning wheel will also result in slower acceleration times, which is why I say you might accelerate faster with VSA on, depending on how slippery the road really is.

I think it depends as you mentioned on the surface. On ice TC may help a bit since there really is no grip. On snow though I find that TC off and intentionally skidding and going up the gears while the wheels skid gets the car moving very effectively. It is an exercise very harsh on the clutch since it involves slipping the clutch a lot so not something to do on a regular basis but it is something that can propel you really fast in deep snow, gravel or stickier mud. The higher gear ratios will work better on less traction. Basically a quick 1 2 even if skidding to get to third will do a great launch.
LSD will always keep both wheels pushing so even if one skids one will push at the grip limit. One can try going in third or second right away but that is even harder on the clutch and transmission.
I did all this on one of my previous cars and the clutch started slipping after the winter, had some good fun but unless you can change the clutch for a good price or do it yourself not advisable to do on a regular basis unless in a need to get out of the way fast.

 

[hey_mikey]

I think it depends as you mentioned on the surface. On ice TC may help a bit since there really is no grip. On snow though I find that TC off and intentionally skidding and going up the gears while the wheels skid gets the car moving very effectively. It is an exercise very harsh on the clutch since it involves slipping the clutch a lot so not something to do on a regular basis but it is something that can propel you really fast in deep snow, gravel or stickier mud. The higher gear ratios will work better on less traction. Basically a quick 1 2 even if skidding to get to third will do a great launch.
LSD will always keep both wheels pushing so even if one skids one will push at the grip limit. One can try going in third or second right away but that is even harder on the clutch and transmission.
I did all this on one of my previous cars and the clutch started slipping after the winter, had some good fun but unless you can change the clutch for a good price or do it yourself not advisable to do on a regular basis unless in a need to get out of the way fast.

The Si's LSD, because it's the helical type, will apply torque to both wheels as long as BOTH wheels have some measurable traction. if you lift one wheel off the ground (like in a really hard corner), you can actually make the LSD act like an open diff. you can try this by lifting one front wheel up off the ground and trying to turn it. with a clutch type lsd, it will be hard or impossible to turn. with a helical type lsd, it'll turn easily because of the lack of torque differential.

basically it works because of the way the gears in the diff are cut. when the angled teeth between the two half-shafts are forced to turn at different speeds (such as in a corner), they apply an axial force to the pinion gear that forces it towards the differential housing. this increases friction, causing it to bind and creating the LSD effect. when one wheel is free to turn however, only one axle is applying any force to the pinion gear, and without the other side applying a similar force, it's free to turn and the wheel is allowed to spin.

 

[Dragos]

The Si's LSD, because it's the helical type, will apply torque to both wheels as long as BOTH wheels have some measurable traction. if you lift one wheel off the ground (like in a really hard corner), you can actually make the LSD act like an open diff. you can try this by lifting one front wheel up off the ground and trying to turn it. with a clutch type lsd, it will be hard or impossible to turn. with a helical type lsd, it'll turn easily because of the lack of torque differential.

basically it works because of the way the gears in the diff are cut. when the angled teeth between the two half-shafts are forced to turn at different speeds (such as in a corner), they apply an axial force to the pinion gear that forces it towards the differential housing. this increases friction, causing it to bind and creating the LSD effect. when one wheel is free to turn however, only one axle is applying any force to the pinion gear, and without the other side applying a similar force, it's free to turn and the wheel is allowed to spin.

That explains why sometimes while accelerating hard in second I feel a tiny bit of torque steer towards right. Happens after I get off a hard turn so the left front wheel may have very little pressure on it. Only happens for very hard acceleration for a small half second, feel the wheel pull and then it stops pulling.

Thanks for the explanation, I always thought LSD will always keep a minimum amount of torque to a wheel no matter what.

 

[hey_mikey]

That explains why sometimes while accelerating hard in second I feel a tiny bit of torque steer towards right. Happens after I get off a hard turn so the left front wheel may have very little pressure on it. Only happens for very hard acceleration for a small half second, feel the wheel pull and then it stops pulling.

Thanks for the explanation, I always thought LSD will always keep a minimum amount of torque to a wheel no matter what.

No problem. For a FWD car like the Si, the helical type is probably the best type of LSD you can get. It still puts power down effectively in almost all situations the Si will find itself in (unless you're rallying the car). No clutches to wear out mean less maintenance and greater reliability, and it's totally transparent in normal cornering and tight parking maneuvers.

 

[mlhil]

When I was young I really liked to go fast with old fashioned rear wheel drive cars,
and I have enjoyed my Miata, but have not slid the rear around at all in a long time so I can be happy with the fwd si. It sounds like vsa off is the way to go on nice dry roads at a quick buT reasonable pace. Thanks for all the input.

 

[Dragos]

When I was young I really liked to go fast with old fashioned rear wheel drive cars,
and I have enjoyed my Miata, but have not slid the rear around at all in a long time so I can be happy with the fwd si. It sounds like vsa off is the way to go on nice dry roads at a quick buT reasonable pace. Thanks for all the input.

Winter or dry is the same except the speed of grip loss is different. Slippery ice and snow let you experience racing conditions except at sometimes very low speeds And Miata is one amazing car