nick205
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| posted on 9/1/08 at 01:57 PM |
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unsprung weight - do the wishbones count?
When considering the the unsprung weight of a double wishbone set-up it's obvious you include the upright, hub, wheel, tyre, brakes etc. Should
the weight of the wishbones and shock be considered part of it as well.
i.e. does pushrod inboard suspension improve the unsprung weight of the front end (all other things be equal)?
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NS Dev
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| posted on 9/1/08 at 02:04 PM |
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the spring is the dividing line isn't it????
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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02GF74
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| posted on 9/1/08 at 02:07 PM |
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the weight of the wishbone is distributed from fixed (at bush end) to moving (at upright) so there should be some allowance made for it - but how you
go about calculating it I can only guess.
inboard should be lighter, unless the rocker arms is heavier than the wishbone but the shock is no longer part of the equation.
now let's wait for someone to post the definitive answer.
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nitram38
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| posted on 9/1/08 at 02:08 PM |
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This has probably been asked before, but I thought any item on the suspension is sprung and the rest of the car unsprung?
Any which way, your wishbones do count as so does the pushrods.
There are small gains by moving your shocks inboard. Aero is one and some weight loss on your wheel.
The biggest advantage is the adjustability.
By varying the pushrod length and rocker ratio you can adjust your spring rate and ride height.
The normal locost setup can be hassle if you want to adjust ride height, because you have to wind the springs up or down which can reduce their
effectivness.
A simple pushrod with LH/RH rod ends can be adjusted without altering your spring platforms.
Remember that by adding the pushrod and pivot, that you are adding weight to the car, but I think the benefits outweigh the extra weight.
I prefer inboard so that is what I have used on both my homebuilds. It has been simpler to set up my suspension.
It also helps on my MotaLeira as I have a 2 to 1 ratio on my rockers and air springs that can extend the shock by 3".
The 2 to 1 ratio means that I can change my ride height from 0 to 6" at the flick of a switch!
[Edited on 9/1/2008 by nitram38]
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Puk
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| posted on 9/1/08 at 02:37 PM |
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Another advantage for inboard suspension is that the relatively expensive dampers are protected in a prang. The wishbones on a race car often get
damaged in a shunt, but that can prevent the chassis seeing high impact loads.
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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matt_claydon
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| posted on 9/1/08 at 02:45 PM |
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It's complicated as the wishbones are rotating, not moving linearly like the wheel and hub. However the rotation is relatively small and for the
sake of most purposes you would be fine just counting half the mass of the wishbone as unsprung.
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indykid
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| posted on 9/1/08 at 02:50 PM |
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in an inboard setup, only the rod, top eye and spring mount of the damper move.
in an outboard scenario with normal coilovers, the whole mass of the damper body and oil has to react to the bump unless you run the expensive upside
down versions where the body is attached to the chassis.
the benefits of pushrod are beyond unsprung weight as the pushrod and rocker cancel much of the gain, but it's negligible either way for a road
car.
back to the OP, i'd always assumed you worked on half the wishbone's weight as unsprung.
tom
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liam.mccaffrey
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| posted on 9/1/08 at 02:53 PM |
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i thought that was the rule of thumb, half the weight of the bones and half the weight of the shocks (if they're mounted conventionally)
You would be far off evn if this isn't the correct way to do it
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britishtrident
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| posted on 9/1/08 at 08:16 PM |
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with a conventional set up the normal assumption is
1/2 the weight of the wishbones
1/2 the weight of the springs
2/3 the weight of the dampers (unless theyare upside down Bilstiens in which case 1/3)
Rocker arm system may actually increase the unsprung MASS -- it is the inertia of the suspension that matters no the weight.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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nasty-bob
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| posted on 9/1/08 at 08:48 PM |
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Best way to accurately measure unsprung mass is to remove the springs, support the car on blocks under the chassis and weigh each corner.
I think one main advantage of inboard, pushrod operated suspension has been overlooked. You are able to acheive a 1:1 ratio of the damper travel to
wheel movement rather than about 1:2 for outboard set ups. This means that cheaper dampers can be used as the system will be less sensitive to the
quality of the damper.
In most cases you will not increase the unsprung weight as the damper now becomes effectively upside down, thereby cancelling out weight added with
pushrod.
Cheers,
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procomp
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| posted on 10/1/08 at 07:59 AM |
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Hi Although not a single mention of inboard dampers running hotter due to less air flow. Some times by 20degrees. And if mounted behind the radiator
they really need to be separate reservoir type. Or that you need different valving which is not just off the shelf dampers. Which funnily enough non
of the manufacturers are paying any attention to or supplying with their inboard kits.
Inboard setup's have their advantages but only when done properly and with the right dampers.
Cheers Matt
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britishtrident
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| posted on 10/1/08 at 08:04 AM |
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quote:
Originally posted by procomp
Hi Although not a single mention of inboard dampers running hotter due to less air flow. Some times by 20degrees. And if mounted behind the radiator
they really need to be separate reservoir type. Or that you need different valving which is not just off the shelf dampers. Which funnily enough non
of the manufacturers are paying any attention to or supplying with their inboard kits.
Inboard setup's have their advantages but only when done properly and with the right dampers.
Cheers Matt
Yes the bigest single advantage is aerodynamic.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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indykid
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| posted on 10/1/08 at 03:10 PM |
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quote:
Originally posted by procomp
Hi Although not a single mention of inboard dampers running hotter due to less air flow. Some times by 20degrees. And if mounted behind the radiator
they really need to be separate reservoir type. Or that you need different valving which is not just off the shelf dampers. Which funnily enough non
of the manufacturers are paying any attention to or supplying with their inboard kits.
Inboard setup's have their advantages but only when done properly and with the right dampers.
Cheers Matt
why do they need different valving?
is it due to the change in travel?
also, why do they need to be seperate reservoir? is that a heat build up issue? couldn't you run ducting to them to cool the body instead?
it's alright stating neccessary changes, i'm just interested in the reasons
tom
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NS Dev
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| posted on 10/1/08 at 08:50 PM |
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Procomp listed some of the reasons that I really didn't want to get into, hence my very brief initial answer of the springs being the middle
line.
Yes there will be a heat buildup issue behind the rad. ANY change in oil viscosity due to temp change will have an effect on damper rate. Usually a
damper will acheive a steady state temperature and thus a steady rate. Flowing air at 50 to 60 degrees over it will not help this stability at all.
Aerodynamics will be positively affected by inboard dampers, but not by a lot on a 7, where the whole front end is like a brick anyway, you're
just talking different types of brick.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 10/1/08 at 08:53 PM |
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PS dont' even get into damper valving!!
I would bet that 99% on here have no idea what rate their dampers are.
I don't know what mine ar on the road car (locost) but I know that they work ok with my comparatively soft springs and long suspension
travel.
Shorter travel and stiffer springs need better damper specification
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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britishtrident
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| posted on 10/1/08 at 09:09 PM |
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quote:
Originally posted by NS Dev
Procomp listed some of the reasons that I really didn't want to get into, hence my very brief initial answer of the springs being the middle
line.
Yes there will be a heat buildup issue behind the rad. ANY change in oil viscosity due to temp change will have an effect on damper rate. Usually a
damper will acheive a steady state temperature and thus a steady rate. Flowing air at 50 to 60 degrees over it will not help this stability at all.
Aerodynamics will be positively affected by inboard dampers, but not by a lot on a 7, where the whole front end is like a brick anyway, you're
just talking different types of brick.
Years ago the cross channel Hover craft service was introduced, A Rolls Royce techie was taking a Siver Shadow across on the Hovercraft in roughish
weather and noticed how much the car was moving on its suspension during the trip. Worried that this might cause over heating of the dampers he
instigated an investigation, the conclusion was the dampers were working just within the max temperature limit.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 10/1/08 at 09:19 PM |
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For Rocker arm front wishbones assume 50% of the mass of the top wishbone is unsprung.
1/3 of the mass of the damper is unsprung
And 1/2 of the spring.
Anyone for a torsion bar ?
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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NS Dev
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| posted on 10/1/08 at 09:59 PM |
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quote:
Originally posted by britishtrident
quote:
Originally posted by NS Dev
Procomp listed some of the reasons that I really didn't want to get into, hence my very brief initial answer of the springs being the middle
line.
Yes there will be a heat buildup issue behind the rad. ANY change in oil viscosity due to temp change will have an effect on damper rate. Usually a
damper will acheive a steady state temperature and thus a steady rate. Flowing air at 50 to 60 degrees over it will not help this stability at all.
Aerodynamics will be positively affected by inboard dampers, but not by a lot on a 7, where the whole front end is like a brick anyway, you're
just talking different types of brick.
Years ago the cross channel Hover craft service was introduced, A Rolls Royce techie was taking a Siver Shadow across on the Hovercraft in roughish
weather and noticed how much the car was moving on its suspension during the trip. Worried that this might cause over heating of the dampers he
instigated an investigation, the conclusion was the dampers were working just within the max temperature limit.
Yikes!! Just goes to show!!
The rear dampers on my grasser get too hot during a short race, but its amusing to think of them getting hot while parked.
Hope he didn't try the same investigation in a red light district, that really would be "customer service" 
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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procomp
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| posted on 11/1/08 at 02:21 PM |
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Hi Nsdev covered most of it. But to give you a bit more info most of the inboard setups are pushing the limits of what can and can't be achieved
with a single adjustable damper so in most of the applications a double adjustable is a minimum requirement for a start. And if you then add separate
reservoirs ect. Well i will let you work the costs out. But as the works Raw striker in kits found they had to resort to using ohlins to get the setup
to work.
Just because these manufacturers are adding inboard setups for the PR + BS side of things dose not mean that it is automatically going to be better
than the simpler outbord setup. As i said above it can be and is a better setup but only if the whole setup is done properly.
Cheers Matt
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