Bob C
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| posted on 5/11/05 at 01:24 PM |
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Unsprung weight - IRS/other?
I'm trying to establish some hard data here. So I've measured my unsprung weight with some bathroom scales. There's some
'hysteresis' due to stiction (about 6kg) so the figure I give is an average of the weight moving up and down. The photo shows my test
setup.
Unsprung weight -
front without cycle wings is 25kg
rear is 31kg
I have tried to get this as low as is practical using lightweight calipers (£55 a corner) and aluminium disc bells.
I'd like to compare with live axle and dedion setups if anyone can be bothered getting the bathroom scales out and winding back the spring seats!
I hope someone can post the data for these systems.
We get so many posts blithely saying this system is better than that for this or that reason: let's get some hard data!
PS the wheel & tyre is 12.7kg
cheers
Bob C
PS The uprights are mx5 - I note this puts a lot of the gubbins at the front inside the rim which should be handy come sva time!
[Edited on 6/11/05 by Bob C]
 
Rescued attachment Dsc00371.jpg
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kb58
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| posted on 5/11/05 at 02:19 PM |
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That's a good idea but it won't do you any good I'm afraid. If someone else provides you data, it'll be with their tires,
their wheels, brakes, shocks, etc. My point is they'll produce a number which doesn't mean anything, really, compared to your setup.
I think it would be more helpful to use your own weights, and perhaps the weight of a bare de Dion axle, to calculate what the different types of
suspension would be using the same components. Othewires it's impossible to draw meaningful conclusions from different parts weighing different
amounts.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Bob C
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| posted on 5/11/05 at 03:30 PM |
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that's actually why I think it's of interest - these are REAL figures! I'd be interested to compare 17" wheels, MK IRS, capri
axle, GTS dedion - all the combos - see what works, what's important (& basically how well my system has worked!)
I have a feeling that a live axle would be around double my figure and a dedion say ~12kg less than live axle, but it would be nice to see real data.
Anybody?
cheers
Bob
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kb58
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| posted on 5/11/05 at 05:34 PM |
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What if someone posts their unsprung weight on their de Dion car is 30kg at the rear. Does that make their de Dion car a "better" design
then yours? No, because you don't know the differences in the components. Maybe they're using 13" magnesium wheels with racing
slicks.
While I understand where you're going with this, I don't think the numbers will do any good. Besides, how well someone thinks a car
handles is all opinion anyway. There's lots of people here who say a live axle 7 works as well as as an IRS car. Thing is, their opinion of
"what works" will be different then yours. Even if their unsprung weight is more then yours, they're still going to be just as
happy with their car, and that's fine. The numbers don't conclusively mean anything since, as said, it's all opinion, in spite of
what everything weighs.
For me personally, I know IRS will have the lowest unsprung weight, so that's why I went with it. I didn't need to know that it's X
kg less then Y design, but that's just me.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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JoelP
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| posted on 5/11/05 at 05:57 PM |
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well id bear with bob, if people post details along weights it will be a little more meaningful, and we could then extrapolate where the differences
come from 
unfortunately i have no figures myself, but its still a good idea.
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britishtrident
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| posted on 5/11/05 at 07:28 PM |
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Pretty sure a light De dion can be brought in within 1or 2 kg per wheel of the average Sierra based double wishnone irs.
The de Dion axle tube can be made of thinwall tube just like the Escort english case which weighs next to nothing.
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907
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| posted on 5/11/05 at 08:21 PM |
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O.K. I'm game. (Just for fun)
How do I do it?
Support chassis on blocks.
Disconnect top of shock. (The weight of shock would be included).
Scales under wheel.
Weigh wheel & tyre and deduct from above.
???????????
Paul G
(beefy Sierra IRS, 1600 drums)
p.s. Any chance of shrinking the pic Bob.
This threads a pain to read.
[Edited on 5/11/05 by 907]
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Paul (Notts)
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| posted on 5/11/05 at 09:54 PM |
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If you can wait till next friday I will try it with my Viento --
Front - 17 inch wheels with 4 pot callipers
rear - sierra callipers
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Bob C
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| posted on 6/11/05 at 01:24 AM |
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Should be easy to do as long as you haven't got an anti roll bar. Metalastic bushes could also affect results 'cos of their
"springiness"
Disconnecting the shock top will give a slightly high result (by 1 or 1/2 kg or so) whereas taking the spring off as on my picture above will give
slightly low. My back result had the spring on but the adjustable seat wound right down. You should be able to do it with the scales under the wheel
on the deck and the chassis weight supported by a trolley jack. Use the jack to do the weight "on the way up" and "on the way
down" & quote the average to get a decent figure: I also had to "slap" the chassis a bit (apply a series of gentle shocks with
my hand) to get down to the 6kg hysteresis I mentioned above. This was then very repeatable & I'm confident in the quoted figures.
Sorry about the big pic:- I just tried to edit it & got no joy.
Bonfire night turned out OK in spite of the forecasts!
Bob
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dnmalc
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| posted on 6/11/05 at 05:49 AM |
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In the analysis of spring mass system the rule of thumb is that you should consider 1/3 of the spring mass to be lumped with the mass.
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WIMMERA
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| posted on 6/11/05 at 06:15 AM |
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How about including the allup weight as well Bob, then we can do the sprung / unsprung ratio
Wimmera
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907
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| posted on 6/11/05 at 05:43 PM |
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O.K. I've weighed up the situation, probably going to regret this. 
Wheel & tyre, (wolfrace & toyo) 195 50 15
13.5 kgs
Stainless W/B's, D/shaft, Upright, Spax shock, 1600 Sierra drum brakes, Hydraulics etc.
17 kgs
So total unsprung weight = 30.5 kgs
The top bolt only was removed from the coilover which left it still fixed to the upright.
The poly bushes have been reamed so the suspension travel is free.
Off side (longer d/shaft)
The scales are only standard bathroom jobbies,
but the wife did try out 27 sets in the shop before she settled on these ones. 
O.K. ..... Shoot me down.
Paul G
p.s. Don't know if it matters but my car is a +4, so the d/shafts are standard Sierra length.
[Edited on 6/11/05 by 907]
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cymtriks
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| posted on 6/11/05 at 06:59 PM |
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Your rear USW is 31Kg
Caterham reckoned that moving to independent suspension on the latest CSR saved 6Kg, assuming this is the total figure that's 3Kg per side.
Another way to estimate it is that you will still have most of your USW in Deon form. The hub will be different but will still be there for example.
Toting up the tubes in the A arms lets assume that you have 26 inches of tube in the top arm and 34 in the lower arm. Total of 60 inches. For a Deon
tube you will need a minimum of a top longitudinal tube, say 12 inches, and a lower angled tube, say 24 inches, that's a total of 36 inches.
That makes a USW difference equivalent to 12 inches of 14g 1 inch tube. The Deon tube hasn't been considered yet so assuming 2.5 inch 14g and 40
inches long that's equivalent to 50 inches of 14g 1 inch tube per side in USW. The overall difference is the weight of 38 inches of 14g 1 inch
tube, or 1.2Kg.
A very good resource for this sort of question is at fluke motorsports site:-
http://www.fluke-motorsport.co.uk/weight/index.html
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Bob C
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| posted on 6/11/05 at 09:11 PM |
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That's great:- 2 very different IRS coming in within a whisker of each other at 30/31kg.
I hope we get some real measurements, but I just did a search for truck axle weights & the common ones seem to be just under 50kg inc brakes. This
would end up as 25 + 15 (wheel, links, spr/damper) = 40kgs, not as bad as I'd imagined.
Dedion should save half a diff's worth of weight plus an unsprung CV joint... urgh let's hope someone weighs one.....
Bob
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WIMMERA
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| posted on 7/11/05 at 05:22 AM |
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A Escort axle goes 52kg plus 25kg for wheels/ tyres plus half the prop, coilovers, panhard and trailing arms must take it to around 80kg probably
more, thats 40 odd per side.
I know of two De Dion cars here with inboard brakes but don't have details also a couple of IRS cars under construction with inboard brakes, one
of which I am familiar with, it weighs in at 12kg without wheels (top bolt out of coilover) and 11.5kg at the front, again no wheels or cycle guards
so assuming 13kg for wheels/tyres about 25kg per corner.
Wimmera
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