Poly bush stiffness measurements?
Discussion
Hi, my Vixen body is away to be painted and the engine waiting for boring and grinding. So, thinking about Griffith.
I love the Griffith, still pretty quick in a straight line, sounds amazing. But, downside is the the body moves a great deal under power on / power on when entering corners. Somewhat inevitable with separate chassis plus relatively flexible high wall tyres.
But, thought came to mind that the wheels must be moving, flexing on the suspension. Bushes, etc allowing some flex. It is running original rubber bushes.
Obviously the bushes allow rotation but try to stop movements in other planes. So, if you consider the effect of braking it tries to push the wheel backwards in the arches, this is reacted by the suspension and associated bushes, in combination with chassis stiffness (which should be much stiffer than the suspension in that plane). Ditto acceleration try’s to pull the rear wheels forwards.
Question. Has anyone ever measured the suspension stiffness in the horizontal plane? With standard and poly bushes? I have never seen any posts.
Poly bushes are convenient, I have used them. But I suspect they are not as good as the opinions when actual measurements are taken. The 'ride stiffness' people talk about is due to the rotational characteristics not horizontal stiffness. They actually move relative to the tubes, causing a type of 'dry friction' (technical term, not me making it up!). Whereas rubber bushes don’t slip they just flex. This would cause the driving experience to be very different (jerky) even if the horizontal stiffness were not improved. Poor design in principle.
So, I think I will try this to do the measurements, if no one has ever done it.? Will settle some arguments!
Best
Nic
I love the Griffith, still pretty quick in a straight line, sounds amazing. But, downside is the the body moves a great deal under power on / power on when entering corners. Somewhat inevitable with separate chassis plus relatively flexible high wall tyres.
But, thought came to mind that the wheels must be moving, flexing on the suspension. Bushes, etc allowing some flex. It is running original rubber bushes.
Obviously the bushes allow rotation but try to stop movements in other planes. So, if you consider the effect of braking it tries to push the wheel backwards in the arches, this is reacted by the suspension and associated bushes, in combination with chassis stiffness (which should be much stiffer than the suspension in that plane). Ditto acceleration try’s to pull the rear wheels forwards.
Question. Has anyone ever measured the suspension stiffness in the horizontal plane? With standard and poly bushes? I have never seen any posts.
Poly bushes are convenient, I have used them. But I suspect they are not as good as the opinions when actual measurements are taken. The 'ride stiffness' people talk about is due to the rotational characteristics not horizontal stiffness. They actually move relative to the tubes, causing a type of 'dry friction' (technical term, not me making it up!). Whereas rubber bushes don’t slip they just flex. This would cause the driving experience to be very different (jerky) even if the horizontal stiffness were not improved. Poor design in principle.
So, I think I will try this to do the measurements, if no one has ever done it.? Will settle some arguments!
Best
Nic
I love poly bushes in the Z3 cars I've owned, felt way better then OEM busjes, but... there are also motorsport rubber bushes for some brands, those I guess are all round better then OEM and , maybe also then poly.
no idea you can get Motorsport bushes for TVR though.
also, my experience with Poly bushes from Strongflex are cheaper and better then those purple examples from Powerflex, those crumble easily in some occasions.
no idea you can get Motorsport bushes for TVR though.
also, my experience with Poly bushes from Strongflex are cheaper and better then those purple examples from Powerflex, those crumble easily in some occasions.
Hi Astonman. Possibly. It is all standard, bilsteins, etc. But, I wonder if the change from power on to power off would cause much load change in the vertical plane? Maybe the back would rise, counter to a bit of power on squat?
The overall point being that change of wheel load shouldn’t change the direction the wheel is pointing, which is what it feels like, a small shift in the place it wants to sit on the road. If you make the springs stiffer you get less wheel movement so any effects (such as bump steer) are indeed reduced.
I will take a close look. You can also get 300kg force meters quite cheaply, so could apply a controlled horizontal force and measure movement.
Best
Nic
The overall point being that change of wheel load shouldn’t change the direction the wheel is pointing, which is what it feels like, a small shift in the place it wants to sit on the road. If you make the springs stiffer you get less wheel movement so any effects (such as bump steer) are indeed reduced.
I will take a close look. You can also get 300kg force meters quite cheaply, so could apply a controlled horizontal force and measure movement.
Best
Nic
Squat and dive have been virtually eliminated,by changing from 200 lbs front and 157 rear springs ( standard on the T350T), to 500 lbs front and 450 lbs rear.The whole car is much more instant and positive. The Sagaris spec is 450f and 400 rear, but with more vertical spring/ damper units, so probably a similar set up to me in practice.
As long as your Bilsteins are in good order,then changing spring rates is easy and pretty cheap.
As long as your Bilsteins are in good order,then changing spring rates is easy and pretty cheap.
It's certainly bumpy on our poor road surfaces.
But,not as jiggly as it was with the original Harvey Bailey dampers,which had " sticktion", initially in their movement,followed by allowing wallow ( little damping effect) once they started moving, generally the worst of both worlds.
Using 400 lbs front and 350 rear, produced a more supple but well damped rear end ( with basic Nitrons replacing the HBs). The front was pretty firm ,but still significant dive under braking.So, I went up to 500/450.
But,not as jiggly as it was with the original Harvey Bailey dampers,which had " sticktion", initially in their movement,followed by allowing wallow ( little damping effect) once they started moving, generally the worst of both worlds.
Using 400 lbs front and 350 rear, produced a more supple but well damped rear end ( with basic Nitrons replacing the HBs). The front was pretty firm ,but still significant dive under braking.So, I went up to 500/450.
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