dream
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| posted on 10/4/12 at 03:55 PM |
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mirach front suspension picture
does someone have pictures of the front suspension of the mirach ?thanks
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MikeCapon
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| posted on 10/4/12 at 04:23 PM |
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quote:
Originally posted by rdodger
I have always wondered why kit manufacturers use inboard for a much more simple reason.
They all appear to place the shock directly behind the radiator. So what happens as the hot air flowing out of the radiator heats up the oil in the
shocks? Surely the viscosity changes and the damping alters?
I know shock oil is meant to be quite stable but since expensive shocks and small bike shocks have remote reservoirs to prevent this. What happens to
our cheapo Protec or Gaz shocks?
I asked a couple of manufacturers this question at a show last year. I was basically told to bugger off.
A bit off the topic of the thread but the remote reservoirs on a lot of bike shocks and high end car shocks are not there to provide cooling. They are
primarily a gas chamber although some of the heat generated (not a lot as it's only the lower compression forces) is generated in the reservoir
and hence there will be a slight improvement in dissipating heat but only really due to the increased surface area.
The real answer to limiting fade through heat is the use of lighter oils with higher viscosity indices together with well engineered components.
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hughpinder
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| posted on 11/4/12 at 11:58 AM |
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I thought about going inboard with my front suspension, but didn't in the end. Here was my reasoning:
The pros were:
a) Looks nicer.
b) Allows creation of really neat/small and light anti roll bar
c) Easy to set up for rising rate, but you can also do this if the suspension is outboard (not to the same degree though) - just put the upper spring
mount point so it is outboard somewhere between:
1. the arc drawn with its centre on the lower arm chassis mount and the 'drawing' end on the lower arms lower shock absorber mount, and
2: the point where a tangent to the shock absorbers lower mount does not pass through the upper mount point at maximum bump (otherwise the rate will
start to drop)
The cons were:
a) Gain in aerodynamics from putting the shocker/spring inboard offset by the fact they are still in the airflow behind the radiator(less because the
air is slowed by the rad though), and extra introduced by the push rod and lever.
b) Extra cost for bearings and rod ends
c) More parts to fail/maintain
d) Extra metal for shocker mounts inboard
e) Extra strengthening of upper chassis bracket/rocker mount required.
f) Exponential increase of 'wheel rate'and spring poundage if inner arm is shorter than outer
g) You will need double adjustable shocks at least so more £££
h) Shockers are in the hot air flow from the rad, which isn't especially good.
i) little experience in setting them up properly to draw on, seemed like even the 'proper' companies had design problems like rapidly
wearing pivot bearings/problems getting a good ride, chassis rails bending......
Just my thoughts when I did my early design decisions.
I'd still like to do it though, and may do if I build a second car!
Regards
Hugh
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loggyboy
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| posted on 11/4/12 at 12:09 PM |
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You missed the pro of less unsprung weight
Also some of the cons can be easily negated by good design:
Gain in aerodynamics from putting the shocker/spring inboard offset by the fact they are still in the airflow behind the radiator(less because the air
is slowed by the rad though), and extra introduced by the push rod and lever.
I think the engine thats sat right behind the shocks would be alot worse!
Extra cost for bearings and rod ends can be designed out
More parts to fail/maintain
Exponential increase of 'wheel rate'and spring poundage if inner arm is shorter than outer
not with good design
You will need double adjustable shocks at least so more £££
why?
[Edited on 11/4/12 by loggyboy]
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hughpinder
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| posted on 11/4/12 at 12:28 PM |
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Ah yes, I did consider the unsprung weight at the time, but I forgot to mention it. I believe its traditional to consider half the weight of the
shocker/spring as unsprung - I couldn't decide if the unsprung weight actually goes up since the pushrod/rocker and half the shocker/spring
weight are on the 'wrong' side of the spring and still need to be moved by the spring and damper relative to the chassis, to keep the
wheel in contact with the ground.
Mines a midi/rear engine which I forgot to mention, so the engine thing didn't figure in my design I suppose!
I don't see how the extra cost of rod ends and bearing can be designed out, as in one case you need them, and in the other you don't!
The exponential increase in wheel rate etc can only be designed out by having a 1:1 arm ratio, hence my caveat "if inner arm is shorter than
outer ". I couldn't get a packaging setup that allowed better than (inner uter) 1:1.2 in my design, but I could have gone for a setup
with the shockers offset front/back to avoid overlap I suppose.
The double adjustables I suppose is hearsay as I have no sound design reason for saying it - I just spoke to almost anyone I could running inboard
setups at trackdays/hillclimbs/races and it seemed everyone had already changed to them or thought that they needed to!
Regards
Hugh
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Twin40
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| posted on 11/4/12 at 12:51 PM |
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quote:
The double adjustables I suppose is hearsay as I have no sound design reason for saying it - I just spoke to almost anyone I could running inboard
setups at trackdays/hillclimbs/races and it seemed everyone had already changed to them or thought that they needed to!
Regards
Hugh
This intrigues me as i understand the principle behind single bump/rebound adjustable shocks, and the benefit of "2-way" shocks ( i ran
them on my tintop) - but i can't understand how running inboard suspension effects the performance of the single bump/rebound adjustment shock?
and require a double adjustable to provide a better set-up?
Does the rocker ratio have a significant effect? Do you need to compensate for a difference in compression? (i'm building an Indy R for racing
so this is a particular concern!)
[Edited on 11/4/12 by Twin40]
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hughpinder
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| posted on 11/4/12 at 01:20 PM |
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twin40, As I said, I didn't have a sound logical reason to see a requirement for the 2 way adjustables - it may just be a symptom of things not
really working and people thinking more adjustment=better! It was about 4 - 5 years ago too, so not as many inboard set ups were around in actual use.
I believe its very difficult to set up 2 way adjustables optimally.
The effect of the lever ratio is quite significant. If you have a certain weight on the front wheel, you need a certain spring poundage to resist that
weight. The shorter the inner arm is relative to the outer, the higher the spring rating will be to resist that weight (think of it as equivalent to
moving the shocker mounting point on the lower wishbone closer to the chassis by that ratio o an outboard setup). The 'wheel frequency'
goes up in inverse proportion to the square root (e.g shorter = higher frequency) of the lever length and the spring rating, so if you have a lever
ratio of 2:1 your spring will have to be twice the pounds rating and the wheel frequency will go up by a factor of 8! (this is all from memory so it
may be worth checking in a suspension book like staniforth or similar). I'm not an expert - these are just my conclusions from my own design.
From memory a wheel frequency of 60-80 was normal road car, 120 about the comfort limit , with full on race cars 200 up to about 400. I'm sure
someone with more practical design experience will correct me soon enough!
Regards
Hugh
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phelpsa
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| posted on 11/4/12 at 06:39 PM |
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quote:
Originally posted by hughpinder
twin40, As I said, I didn't have a sound logical reason to see a requirement for the 2 way adjustables - it may just be a symptom of things not
really working and people thinking more adjustment=better! It was about 4 - 5 years ago too, so not as many inboard set ups were around in actual use.
I believe its very difficult to set up 2 way adjustables optimally.
The effect of the lever ratio is quite significant. If you have a certain weight on the front wheel, you need a certain spring poundage to resist that
weight. The shorter the inner arm is relative to the outer, the higher the spring rating will be to resist that weight (think of it as equivalent to
moving the shocker mounting point on the lower wishbone closer to the chassis by that ratio o an outboard setup). The 'wheel frequency'
goes up in inverse proportion to the square root (e.g shorter = higher frequency) of the lever length and the spring rating, so if you have a lever
ratio of 2:1 your spring will have to be twice the pounds rating and the wheel frequency will go up by a factor of 8! (this is all from memory so it
may be worth checking in a suspension book like staniforth or similar). I'm not an expert - these are just my conclusions from my own design.
From memory a wheel frequency of 60-80 was normal road car, 120 about the comfort limit , with full on race cars 200 up to about 400. I'm sure
someone with more practical design experience will correct me soon enough!
Regards
Hugh
You're making that sound a lot more complicated than it need be  Everything you have mentioned is as valid for outboard as it is for
inboard.
What units are those wheel frequencies in? Certainly not Hz!
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hughpinder
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| posted on 12/4/12 at 08:16 AM |
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phelpsa
Sorry if I've made it sound more complex - I was hoping for the opposite.
It's true that the rising spring rate and higher wheel frequency also occur on an outboard set up - but only if you move the shock absorber
mounting point closer to the chassis pivot point, and this is unlikley to be chosen, as almost all designs anyone is likely to copy have the mounting
points as far outboard as possible, and also this is where the tubes join and it makes the easiest to fabricate arm design - I dont think Ive ever
seen one with the mount half way along the arm, but I'm sure people will immediately provide plenty of pictures! On the other hand, a lot of
people don't think about a 20% difference in pivot lengths as particulaly significant, but it needs at 20% stronger spring and a 70% higher
wheel frequency! (This is not quite accurate - as you move the pivot point inboard the spring becomes less inclined to the vertical, and this reduces
the spring strength a bit).
Sorry - I've had to look up my original notes/calculation to find the frequency units - it was cycles per minute! I'm not sure why - Hz
seems a much more natural frequency to use for me (I think the calculations came originally from the Staniforth book).
Regards
Hugh
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