Unsprung Weight
Discussion
Chilliman said:
Thanks ChilliMan,i do know that resource but I was looking for a more simplistic explanation which was more linked to TVR's.take a Griffith or a Chimaera,increase or decrease the weight of the brakes for example.what is the effect on the car in performance and handling terms,tyres and wheels,whats the trade off with light and heavy etcThe crude way that I have heard unsprung weight described the most is to imagine throwing a punch whilst holding a weight. It takes a lot more effort and time to stop your hand and change direction than it would without the weight, which is what your suspension is doing with the wheel. The less weight that there is on the wheel then the easier it is for the suspension to control its movement.
Actual wheel weight (rather than just sprung mass) also has a gyroscopic effect on braking and steering.
Actual wheel weight (rather than just sprung mass) also has a gyroscopic effect on braking and steering.
BarnFind said:
Chilliman said:
Thanks ChilliMan,i do know that resource but I was looking for a more simplistic explanation which was more linked to TVR's.take a Griffith or a Chimaera,increase or decrease the weight of the brakes for example.what is the effect on the car in performance and handling terms,tyres and wheels,whats the trade off with light and heavy etcOK, so... just my own thoughts, but I would say any gains in mechanical grip through reducing unsprung weight would be meaningless if you haven't got the right shocks/springs, tyres, and proper geo set-up. Plus bushes etc being 100%... I seriously doubt you would feel any difference on the road just by reducing unsprung weight, but I'm very happy to be proved wrong... I also can't see how you would measure this in a road going car....
Interesting subject though....
Chilliman said:
.. I seriously doubt you would feel any difference on the road just by reducing unsprung weight, but I'm very happy to be proved wrong... I also can't see how you would measure this in a road going car....
Interesting subject though....
I'm very much on the other side of the fence. Interesting subject though....
Coming from a bike background, unsprung weight is king.
It affects the handling so much it hurts at times to save a few grammes.....
The feel from a lower unsprung weight in ability to change line is immense. On bikes it can make the bike feel alive or it can make it feel wooden.
For me, it's not a case of measuring the difference in unsprung weight, it's feeling it.
It does have its downsides though. Low unstrung weight means a wheel is thrown off course easier from bumps and undulations.
I'm watching this thread to see how others feel.
Edited by A900ss on Sunday 24th November 22:18
Changes in unsprung weight are very obvious. It's also 2-fold.
Increased rotational inertia resists acceleration and deceleration. The wheels have strong gyroscopic behaviours and increasing mass of everything that rotates magnifies this. If you've never studied engineering at all then you may not be aware that gyroscopes have strong and bizarre reactions to being moved or angled - they cause a strong reaction at 90degs to the direction or angle it was turned. On the big piston engined aeroplanes towards the end of WW2 with big heavy propellers - if the pilot raised the tail off the ground too abruptly the aeroplane would swing strongly to the left or right depending on which direction the prop turned. This could be uncontrollable.
Secondly, on a car the suspension can only work at all if the wheels stay on the road. The lighter the wheels, the less momentum and inertia they have. If you hit a ramp in the road, the wheel will try to ski-jump in to the air. Light wheels will be completed dominated by the mass of the car. Heavy wheels can noticeably be felt to have a mind of their own under the suspension. Regardless how well set up the car is, heavy wheels will pretty much always be worse to drive on than light wheels.
Increased rotational inertia resists acceleration and deceleration. The wheels have strong gyroscopic behaviours and increasing mass of everything that rotates magnifies this. If you've never studied engineering at all then you may not be aware that gyroscopes have strong and bizarre reactions to being moved or angled - they cause a strong reaction at 90degs to the direction or angle it was turned. On the big piston engined aeroplanes towards the end of WW2 with big heavy propellers - if the pilot raised the tail off the ground too abruptly the aeroplane would swing strongly to the left or right depending on which direction the prop turned. This could be uncontrollable.
Secondly, on a car the suspension can only work at all if the wheels stay on the road. The lighter the wheels, the less momentum and inertia they have. If you hit a ramp in the road, the wheel will try to ski-jump in to the air. Light wheels will be completed dominated by the mass of the car. Heavy wheels can noticeably be felt to have a mind of their own under the suspension. Regardless how well set up the car is, heavy wheels will pretty much always be worse to drive on than light wheels.
Chilliman said:
I seriously doubt you would feel any difference on the road just by reducing unsprung weight, but I'm very happy to be proved wrong... I also can't see how you would measure this in a road going car....
Just to clarify the statement above, the options for reducing unsprung weight on a Chimeara are somewhat limited, and I would have thought the % reduction in weight (by fitting lighter brakes, wheels etc) wouldn't be such that it would be noticeable 'on the road' (where we all drive sensibly) and any improvements it did make would (might) be difficult to quantify.... Definitely noticeable when it comes to bikes - I've had a few No lessons needed here on gyroscopics, I commute to work in a helicopter
Chilli
Chilliman said:
Chilliman said:
I seriously doubt you would feel any difference on the road just by reducing unsprung weight, but I'm very happy to be proved wrong... I also can't see how you would measure this in a road going car....
Just to clarify the statement above, the options for reducing unsprung weight on a Chimeara are somewhat limited, and I would have thought the % reduction in weight (by fitting lighter brakes, wheels etc) wouldn't be such that it would be noticeable 'on the road' (where we all drive sensibly) and any improvements it did make would (might) be difficult to quantify.... Definitely noticeable when it comes to bikes - I've had a few No lessons needed here on gyroscopics, I commute to work in a helicopter
Chilli
Chilliman said:
Just to clarify the statement above, the options for reducing unsprung weight on a Chimeara are somewhat limited
But the options for adding to it are numerous and quite a few seem to be hellbent on exploring every option before asking themselves whether they need to effectively bolt a pair of anvils to their front hubs and what the possible ramifications of doing so are... Chilliman said:
Chilliman said:
I seriously doubt you would feel any difference on the road just by reducing unsprung weight, but I'm very happy to be proved wrong... I also can't see how you would measure this in a road going car....
Just to clarify the statement above, the options for reducing unsprung weight on a Chimeara are somewhat limited, and I would have thought the % reduction in weight (by fitting lighter brakes, wheels etc) wouldn't be such that it would be noticeable 'on the road' (where we all drive sensibly) and any improvements it did make would (might) be difficult to quantify.... Definitely noticeable when it comes to bikes - I've had a few No lessons needed here on gyroscopics, I commute to work in a helicopter
Chilli
MikeE said:
I have nothing to back this up but, I would have thought a 10% reduction in unsprung weight would be even more noticeable on the road given we're talking mechanical grip in a scenario where the suspension is having to accommodate a lot of shocks due to the changing road surface (bumps to us)?
Indeed - given that this rather than braking is the main Achilles' Heel of our cars as they came, this is an area to be taken seriously IMO. Also, rotating weight will affect acceleration and braking performance by a multitude of its actual weight in comparison to overall weight (also depending on which gear you're in). The old Pumaracing site had a table about the effects of rotating weight with some pretty dramatic numbers (and the maths to back it up, at least I think so as I outright suck at maths 
).I completely agree with you guys on the technical side , I'd just be a bit miffed to spend large amounts of money on reducing unsprung weight on the Chim and not feel noticeable benefits to every day driving....
If I was going racing then anything that improved lap times (that I could afford) would be on the shopping list
Chilli
, I'd just be a bit miffed to spend large amounts of money on reducing unsprung weight on the Chim and not feel noticeable benefits to every day driving.... If I was going racing then anything that improved lap times (that I could afford) would be on the shopping list
Chilli
Chilliman said:
I completely agree with you guys on the technical side , I'd just be a bit miffed to spend large amounts of money on reducing unsprung weight on the Chim and not feel noticeable benefits to every day driving....
If I was going racing then anything that improved lap times (that I could afford) would be on the shopping list
Chilli
Going with the general less is better, it's best to reduce the unsprung weight where possible. There's a reason alloys are not cast-irons!, I'd just be a bit miffed to spend large amounts of money on reducing unsprung weight on the Chim and not feel noticeable benefits to every day driving.... If I was going racing then anything that improved lap times (that I could afford) would be on the shopping list
Chilli
That said, the law of diminishing returns can set in quite quickly. The total weight of a 'corner' including: tyre, wheel, brake calipers, brake disc, upright and (simplistically) half the weight of the wish arms and spring/damper can be pretty high. Saving a small percentage of this weight using an expensive goody is not going to make a big difference.
Unless it really is the difference between winning and losing (who remembers 2nd place) then I'd not try too hard. I'd happily take a modest increase in weight for better brakes if I needed them.
Hopefully someone who's upgraded a Cerb from those awful Spiders to SP12s will chime in with a direct comparison.
I'd generally agree that it's on the road where you feel the benefit, as opposed to measure it. Ride quality improves as does grip and handling on uneven roads.
Keep in mind that the wheels and brakes have extra moment arm on the springs because the spring tries to control the wishbones roughly half way between their hinge points at the chassis and the wheels, so the "effects" of unsprung mass at the wheel and brake end will be roughly double what you imagine they would be by simply summing up everything under the springs.
I'd generally agree that it's on the road where you feel the benefit, as opposed to measure it. Ride quality improves as does grip and handling on uneven roads.
Keep in mind that the wheels and brakes have extra moment arm on the springs because the spring tries to control the wishbones roughly half way between their hinge points at the chassis and the wheels, so the "effects" of unsprung mass at the wheel and brake end will be roughly double what you imagine they would be by simply summing up everything under the springs.
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