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If I recall my calculus correctly (a mighty big "if," if you get my drift), and if I also remember my physics correctly (we're now at (if) squared), we can ignore the engineering I may or may not remember correctly and you can wrap your head around it like this:
A 25mm solid bar will have the torsional stiffness of a 25mm hollow bar plus the equivalent bar that would fill the void. If the inside void is 10mm, we just add what the 10mm bar would do to the 25mm hollow bar.
With me so far? I think *I* am ...
Now think of what a 10mm bar adds. Weight, without much stiffness. A 25mm solid bar is marginally stiffer than a hollow one, but if it's a reasonable bar to start with, the extra weight does not proportionally add to stiffness.
If our cars were light, we could quibble over a couple of pounds. They're not.
A reasonable way of thinking about it. If I did the math right, removing the 10mm center of a 34mm rod (Stohlen's example) changes the 2nd polar moment by less than 1%, and I imagine the torsional stiffness is directly related to this.
Of course, this is theoretical, so it doesn't factor in differences in manufacturing a solid rod vs. a hollow rod, which would certainly affect torsional stiffness.
There is another alternative. There is a company called DSC who sells a computer box that uses the existing adjustable damping system but actively re-programs the damping to be much more aggressive resulting in considerably less roll on both axis. Their website does not indicate they have software for the Jag, but perhaps would be willing to develop it if somebody wants it.
From my perspective the Jag OEM dynamic setting is acceptable, but the car could benefit from lowering the suspension. FWIW, the Jag feels exactly the same as Porsche's dynamic system called PASM. Both feel too smooth for a "sporty car". Welcome to the world of modern sports cars.
The mechanical engineer says lizzardo is correct. It would be quite easy to calculate the relative torsional stiffness of the solid vs. hollow bar of the same outer diameter, if we knew the wall thickness. However, increasing the outer diameter is much more effective than increasing the wall thickness (reducing the inner diameter) or going to a solid bar.
I am interested in increasing the front roll stiffness of my XKR-S, but the most effective route might be poly bushings or spherical joint end links, if they would work. I had a set like these with a big rear bar on my old Audi S6.
Lots of great info but let's clarify the effects of the Dynamic Suspension.
In dynamic mode, the piston travel speed within the shock is greatly reduced. This helps greatly in rapid changes of direction. It is NOT going to affect the lateral handling. It will slow down the inevitable body roll.
To reduce overall body roll, all you can do is get a stiffer sway bar
To stiffen the entire chassis response you switch to stiffer springs.
The sway bar WILL not affect the overall ride comfort. I would do that as #1 suspension mod. The springs will certainly make the ride quality worse and dropping 1" or more in clearance is not ideal. Further, the F-Type has ride height sensors linked to the control arm, excessive lowering affects the DSC management especially in the AWD versions.
You can notice dramatic improvements with Dynamic mode in the slalom and figure 8 and of course in evasive maneuvers on the road as well as on track. The downside is that the dampening is reduced and more of the road "disturbances" are passed on to the car chassis and that can upset the stability. This is evident when in very high speed turn over poor tarmac, bridge joints etc.
To reduce overall body roll, all you can do is get a stiffer sway bar
Stiffer springs will reduce the roll with the same sway bars. Lowering the car, even without changing spring rate, would also reduce roll due to lower cg.
Stiffer springs will reduce the roll with the same sway bars. Lowering the car, even without changing spring rate, would also reduce roll due to lower cg.
Changing springs will make the ride comfort worse... I have stiffer progressive springs and lowered .7". The sway bar alone (let me correct that) the sway bar with Poly bushings was by far the biggest improvement. The value of the spring swap (handling vs. ride comfort) was not good. And NO I will not lower the car over 1", I am not into the lowrider stuff..
Changing springs will make the ride comfort worse... I have stiffer progressive springs and lowered .7". The sway bar alone (let me correct that) the sway bar with Poly bushings was by far the biggest improvement. The value of the spring swap (handling vs. ride comfort) was not good. And NO I will not lower the car over 1", I am not into the lowrider stuff..
Comfort and style are separate issues. Stiffer springs *will* reduce body roll and so will lowering the car. Both of those do come with side effects. Too much anti-roll bar has side effects too. It compromises the ability to absorb road irregularities that affect a single wheel (side) at a time. If all your roads are smooth, this may not be a problem for you.
Stiffer springs will too affect the comfort while a single wheel overcomes an irregularity... it will CERTAINLY affect the comfort when both wheels on the same axle overcome an irregularity as well... while a sway bar WILL not affect ride comfort when both wheels on the same axle go over the same irregularity... Lowering springs also reduce travel, that too, depending on the use, is NOT a positive. I am sorry but Style isn't my concern when it comes to handling
Comfort and style are separate issues. Stiffer springs *will* reduce body roll and so will lowering the car. Both of those do come with side effects. Too much anti-roll bar has side effects too. It compromises the ability to absorb road irregularities that affect a single wheel (side) at a time. If all your roads are smooth, this may not be a problem for you.
I never said that the springs will NOT reduce roll, of they they will but marginally compared to a stiffer say bar. The "VALUE" means cost benefit. The reduction in ride comfort isn't worth the modest improvement
I only mention style because you said you weren't into the "lowrider stuff."
Otherwise, I don't think we're disagreeing. The factory setup is a compromise, and so is any modification made to it. Many of my usual roads have irregularities that are not even side to side, and too much anti-roll bar in those conditions can upset the chassis (and the occupants).
I never said that the springs will NOT reduce roll, of they they will but marginally compared to a stiffer say bar. The "VALUE" means cost benefit. The reduction in ride comfort isn't worth the modest improvement
You said that a stiffer anti-roll bar was the only way to reduce body roll:
Originally Posted by FType17
To reduce overall body roll, all you can do is get a stiffer sway bar
Again, we're in agreement on all but fine details and personal preference, and the types of road irregularities we need to cope with.
I would love a mod to allow for the temporary raising of the front end. I have been tinkering with ideal involving small airbags. Has anybody considered this?
Many years ago, when I was involved in rally racing, we used hard rubber spacers in the springs, that would also help with body roll without lowering the car. I will need to google it and see if I can find them. (20 years ago technology)
Unless you're coming from a luxo land yacht, ride comfort will not be an issue with a substantially lowered F-Type. Mine is still a plushy pillow compared the MINI, yet almost (yes, I said almost) handles as well as the MINI.
Unless you're coming from a luxo land yacht, ride comfort will not be an issue with a substantially lowered F-Type. Mine is still a plushy pillow compared the MINI, yet almost (yes, I said almost) handles as well as the MINI.
I lowered it a tad and I dislike the results in ride comfort. The concept of progressive springs is to have variable rates, so that the stiffest part comes in at an advanced point in travel. What seems to have happened is that the plushy rate part gives in right away allowing for the lowering aspect and then it's almost immediately stiff. Again, this is subjective but even the McLaren has better ride quality.
I lowered it a tad and I dislike the results in ride comfort. The concept of progressive springs is to have variable rates, so that the stiffest part comes in at an advanced point in travel. What seems to have happened is that the plushy rate part gives in right away allowing for the lowering aspect and then it's almost immediately stiff. Again, this is subjective but even the McLaren has better ride quality.
Which is 100% relative to the springs you bought to lower it. Maybe a different company has better results.
I lowered it a tad and I dislike the results in ride comfort. The concept of progressive springs is to have variable rates, so that the stiffest part comes in at an advanced point in travel. What seems to have happened is that the plushy rate part gives in right away allowing for the lowering aspect and then it's almost immediately stiff. Again, this is subjective but even the McLaren has better ride quality.
12-05-2017, 10:13 AM
