peter pyce
Veteran Member
- Joined
- Nov 6, 2001
Continue from above – Ceilidh’s posts from two years ago all the way to the end:
9. Rear Bar with Stock Springs
Reminder -- GT Goals
1) excellent roadholding (good mechanical grip) on a variety of road surfaces
2) forgiveness for unexpected events
3) handling that is consistent under changing road, weather, and load conditions
4) responsiveness to good throttle/brake/steering technique
5) reasonable ride comfort
We come now to a setup that inspires a lot of discussion on the Vortex: stock springs with an aftermarket 25mm or 28mm rear antiroll bar. Some people absolutely love it, calling it an ideal first mod after improved damping; others feel it is a misguided way to improve handling. What must be very confusing to the suspension novices is that some very experienced people come out on opposite sides of this discussion. So let's see why:
The Nice Things About a Rear AntiRoll Bar
If you add a rear antiroll bar to an otherwise stock Golf/Jetta IV, you reduce the amount of roll at low to moderate-high g-forces, and you increase the lateral weight transfer (again at low to moderately high g-forces) at the rear, while decreasing the transfer at the front. All these effects serve to decrease understeer: by reducing the roll, you keep the front tires more upright; and by decreasing the front lateral weight transfer, you increase the overall grip of the front end. Moreover, because the car rolls less (and because the "roll rate" -- the "springiness" of the car in roll -- is increased), it takes less time for the car to take a set, and the transition time is decreased.
Because of all the above, many people will like what a rear bar does to an otherwise stock Golf or Jetta: the car will corner flatter (at least at low- and mid- g-forces), it will turn-in more incisively, it will be quicker in left-right transitions, and in general everything will feel more agile. So for many people, a rear bar with stock springs can be pretty nice.
What's Not Nice About a Rear Bar with Stock Springs
The problem with the rear bar/ stock springs approach is that it doesn't move you towards a GT setup. In contrast to improved damping, which significantly improves #1-4 on the GT list at a modest cost to #5 alone, the rear bar/ stock springs setup will:
1) increase roadholding in some situations, make no difference in others, and actually degrade roadholding in some circumstances.
2) decrease forgiveness
3) degrade handling consistency under different weather/ road conditions
4) retain or slightly improve handling responsiveness
5) somewhat degrade ride comfort.
In short, the rear bar / stock springs approach tends to improve #4 while losing out on #1,2,3, and 5 -- that is, it can be nice for agility, but in other GT respects it's a bit of a step back.
The reasons why can best be seen by considering a stock Golf/Jetta at the cornering limit: at high lateral-g, the stock Golf/Jetta is understeering very heavily (because of the leaned over front tires) -- but it is also cornering on three wheels. This 3-wheel stance arises because even the stock suspension applies a lot of weight transfer across the rear wheels, so as to reduce understeer at low to medium g-forces.
Now consider a rear bar / stock spring car, cornering at the same speed & lateral-g. It too is cornering in a 3-wheel stance. Moreover, the rear outside wheel is carrying the same load as before (the weight of the back of the car), while the front lateral weight transfer is the same as before (because the total weight transfer is determined by the CG, mass, and track width, not by springing). Because the front springs are the same as before, the roll must be the same as before. And if the roll is the same as before, the front tires are leaning over the same as before.
Hence at high lateral-g, the rear bar/ stock spring car is cornering exactly the way the stock car corners, with the same heavy amount of understeer. Moreover, the ultimate roadholding limits are no higher than before, and are indeed perhaps a little less on rough roads: as discussed earlier, by putting on a stiff bar, you've increased the 1-wheel spring rate (which decreases mechanical grip), and you've made it more difficult to set the shocks to cope with both 1-wheel and 2-wheel bumps (which further reduces grip).
Perhaps even worse (as discussed in an earlier post in this thread) you've now exaggerated how the handling changes with g-force: at low to moderate g, you understeer much less than before (because the car corners flatter, and there's more weight transfer at the rear wheels), but at high-g you still understeer a lot (because once you're 3-wheeling, you can't shift any more weight onto the outside rear tire, and the amount of roll is controlled entirely by the stock front suspension). If the understeer at low g-force is reduced enough, you can in some cases (judging by Forum posts) get to a point where the car handles differently on slick roads (where it's tail-happy) than it does on dry roads (where it's forgiving and benign). That's a terrible thing to have happen on a GT car: the last thing you want is a car that corners safely on dry roads, but which turns vicious when the weather is bad.
Bottom line, a rear bar on stock springs can make the car more agile and "fun" (particularly at low cornering speeds, or in gentle curves).....but it can't raise the ultimate roadholding, it still permits stock levels of understeer at the limit, and if overdone (with a big rear bar at full-stiff setting) it can significantly degrade handling consistency when the weather changes. Oh, and given how sensitive the rear is to stiffening, your ride comfort and rear traction will also deteriorate somewhat on bumpy roads.
Why Everybody is Right
Given all the above, why do so many people advocate adding a rear bar to a stock suspension? Part of it is that a mild bar (stress the word "mild") can be pretty nice -- the wet weather handling won't get too tail-happy, and the increased agility at moderate speeds can feel very welcome. Part of it is that most of us never really drive near the limits anyway, and therefore we're always in the low-to-medium g-force range where a rear bar can reduce the understeer. And part of it is that many people simply don't want a "GT" suspension. In particular, track racers want to get power to the pavement on corner exit (see Daemon42's posts on this subject), while autocrossers crave agility.
(Hmmm. Maybe here's a good time to explain something about autocross: when you have to throw a car around a tight series of cones, you a couple of related challenges. One is to get the car to quickly "rotate" around a cone; i.e., to get the car to rapidly turn-in and begin cornering. The other is to get the car to *stop* rotating at the appropriate time, so that you don't spin once you're actually in the corner. In this situation, having a car that has very little understeer (or that even oversteers) at low g-forces (which is the turn-in phase of a corner), but which gains a lot more rear-traction at high g-forces (when you're actually in the corner, and don't want to spin off), can often be a good thing. Thus a big rear bar and a relatively soft front can work for some autocrossers, depending upon their driving style, and you'll find many autocrossers who are fans of rear bars.)
Bottom line, if you want a little more snap and flatness in your suspension, especially at low to medium g-forces, go ahead and try a rear bar with stock springs. You might find it very pleasant (at the very least, to paraphrase something Peter found with a 28mm bar, increased ride harshness will make it seem like you're cornering faster!). But if your goal is "GT" -- real, effortless roadholding with good ride comfort and predictable forgiveness in all weather conditions -- there are better ways to go.
That's all for this week. See you all! =)
- Ceilidh
9. Rear Bar with Stock Springs
Reminder -- GT Goals
1) excellent roadholding (good mechanical grip) on a variety of road surfaces
2) forgiveness for unexpected events
3) handling that is consistent under changing road, weather, and load conditions
4) responsiveness to good throttle/brake/steering technique
5) reasonable ride comfort
We come now to a setup that inspires a lot of discussion on the Vortex: stock springs with an aftermarket 25mm or 28mm rear antiroll bar. Some people absolutely love it, calling it an ideal first mod after improved damping; others feel it is a misguided way to improve handling. What must be very confusing to the suspension novices is that some very experienced people come out on opposite sides of this discussion. So let's see why:
The Nice Things About a Rear AntiRoll Bar
If you add a rear antiroll bar to an otherwise stock Golf/Jetta IV, you reduce the amount of roll at low to moderate-high g-forces, and you increase the lateral weight transfer (again at low to moderately high g-forces) at the rear, while decreasing the transfer at the front. All these effects serve to decrease understeer: by reducing the roll, you keep the front tires more upright; and by decreasing the front lateral weight transfer, you increase the overall grip of the front end. Moreover, because the car rolls less (and because the "roll rate" -- the "springiness" of the car in roll -- is increased), it takes less time for the car to take a set, and the transition time is decreased.
Because of all the above, many people will like what a rear bar does to an otherwise stock Golf or Jetta: the car will corner flatter (at least at low- and mid- g-forces), it will turn-in more incisively, it will be quicker in left-right transitions, and in general everything will feel more agile. So for many people, a rear bar with stock springs can be pretty nice.
What's Not Nice About a Rear Bar with Stock Springs
The problem with the rear bar/ stock springs approach is that it doesn't move you towards a GT setup. In contrast to improved damping, which significantly improves #1-4 on the GT list at a modest cost to #5 alone, the rear bar/ stock springs setup will:
1) increase roadholding in some situations, make no difference in others, and actually degrade roadholding in some circumstances.
2) decrease forgiveness
3) degrade handling consistency under different weather/ road conditions
4) retain or slightly improve handling responsiveness
5) somewhat degrade ride comfort.
In short, the rear bar / stock springs approach tends to improve #4 while losing out on #1,2,3, and 5 -- that is, it can be nice for agility, but in other GT respects it's a bit of a step back.
The reasons why can best be seen by considering a stock Golf/Jetta at the cornering limit: at high lateral-g, the stock Golf/Jetta is understeering very heavily (because of the leaned over front tires) -- but it is also cornering on three wheels. This 3-wheel stance arises because even the stock suspension applies a lot of weight transfer across the rear wheels, so as to reduce understeer at low to medium g-forces.
Now consider a rear bar / stock spring car, cornering at the same speed & lateral-g. It too is cornering in a 3-wheel stance. Moreover, the rear outside wheel is carrying the same load as before (the weight of the back of the car), while the front lateral weight transfer is the same as before (because the total weight transfer is determined by the CG, mass, and track width, not by springing). Because the front springs are the same as before, the roll must be the same as before. And if the roll is the same as before, the front tires are leaning over the same as before.
Hence at high lateral-g, the rear bar/ stock spring car is cornering exactly the way the stock car corners, with the same heavy amount of understeer. Moreover, the ultimate roadholding limits are no higher than before, and are indeed perhaps a little less on rough roads: as discussed earlier, by putting on a stiff bar, you've increased the 1-wheel spring rate (which decreases mechanical grip), and you've made it more difficult to set the shocks to cope with both 1-wheel and 2-wheel bumps (which further reduces grip).
Perhaps even worse (as discussed in an earlier post in this thread) you've now exaggerated how the handling changes with g-force: at low to moderate g, you understeer much less than before (because the car corners flatter, and there's more weight transfer at the rear wheels), but at high-g you still understeer a lot (because once you're 3-wheeling, you can't shift any more weight onto the outside rear tire, and the amount of roll is controlled entirely by the stock front suspension). If the understeer at low g-force is reduced enough, you can in some cases (judging by Forum posts) get to a point where the car handles differently on slick roads (where it's tail-happy) than it does on dry roads (where it's forgiving and benign). That's a terrible thing to have happen on a GT car: the last thing you want is a car that corners safely on dry roads, but which turns vicious when the weather is bad.
Bottom line, a rear bar on stock springs can make the car more agile and "fun" (particularly at low cornering speeds, or in gentle curves).....but it can't raise the ultimate roadholding, it still permits stock levels of understeer at the limit, and if overdone (with a big rear bar at full-stiff setting) it can significantly degrade handling consistency when the weather changes. Oh, and given how sensitive the rear is to stiffening, your ride comfort and rear traction will also deteriorate somewhat on bumpy roads.
Why Everybody is Right
Given all the above, why do so many people advocate adding a rear bar to a stock suspension? Part of it is that a mild bar (stress the word "mild") can be pretty nice -- the wet weather handling won't get too tail-happy, and the increased agility at moderate speeds can feel very welcome. Part of it is that most of us never really drive near the limits anyway, and therefore we're always in the low-to-medium g-force range where a rear bar can reduce the understeer. And part of it is that many people simply don't want a "GT" suspension. In particular, track racers want to get power to the pavement on corner exit (see Daemon42's posts on this subject), while autocrossers crave agility.
(Hmmm. Maybe here's a good time to explain something about autocross: when you have to throw a car around a tight series of cones, you a couple of related challenges. One is to get the car to quickly "rotate" around a cone; i.e., to get the car to rapidly turn-in and begin cornering. The other is to get the car to *stop* rotating at the appropriate time, so that you don't spin once you're actually in the corner. In this situation, having a car that has very little understeer (or that even oversteers) at low g-forces (which is the turn-in phase of a corner), but which gains a lot more rear-traction at high g-forces (when you're actually in the corner, and don't want to spin off), can often be a good thing. Thus a big rear bar and a relatively soft front can work for some autocrossers, depending upon their driving style, and you'll find many autocrossers who are fans of rear bars.)
Bottom line, if you want a little more snap and flatness in your suspension, especially at low to medium g-forces, go ahead and try a rear bar with stock springs. You might find it very pleasant (at the very least, to paraphrase something Peter found with a 28mm bar, increased ride harshness will make it seem like you're cornering faster!). But if your goal is "GT" -- real, effortless roadholding with good ride comfort and predictable forgiveness in all weather conditions -- there are better ways to go.
That's all for this week. See you all! =)
- Ceilidh