Bob C
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| posted on 24/3/08 at 05:42 PM |
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Thought you lived in UK BT......... ;^)
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MikeR
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| posted on 25/3/08 at 06:51 PM |
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Just got the sierra diff brackets from short track (excellent quality by the way - very impressed) weighed them and its another 2kg to the sprung
weight.
(they are to the haynes roadster design so it needs a bit more steel welding into the chassis as well.)
I remember that caterham used a 'thin' tube. I also remember they had a problem with diff mounts bending / breaking / going through and
had to revise the design. No idea what the revised design weighs (or if they just welded something thicker around the shock mount).
Bob - your weight, does that include the wheel weight? Mine includes a wheel at 14kg (which is what my steel escort 155x80x13 weighed). If it
doesn't it makes it re-addresses the balance and makes the IRS look far less favourable.
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NS Dev
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| posted on 25/3/08 at 11:16 PM |
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quote:
Originally posted by MikeR
For a long time (2+ years) i've been looking at going de-dion. Well before i make the cuts to my chassis i decided to weigh things to prove to
myself its worth it. A final 'get out clause' if you like.
Can someone see what i've done wrong here cause according to these figures de-dion gives almost no advantage.
Escort axle, with wheels and brakes but not hand brake cable = total weight 75kg (no wonder its a bitch to move around)
Wheels (155x13 80 profile) 14kg
brakes (from sierra but look identical) 9" (thats drum, back plate, mechanism and shoes) 7kg
So weight of axle inc diff = 75 - (wheels X 2 + brakes X2) or .... 33kg
Going through a one wheel bump the 'mass' moved is .... 1 wheel + 1 brakes + guestimate 66% of axle (can't be half as the mass
between the other wheel and the centre must come into play somewhat) = 42.78kg. Or to put it another way "eeek".
Now de-dion.
Axle 11kg (unwelded).
drive shaft (drum brakes) 14kg
brakes (from before) 7kg
wheel (14kg)
so total weight is axle+ drive shaft *2 + brakes *2 + wheels *2 = 81kg
but i'll say unsprung means only 0.66 of the drive shafts or 73.86kg or 1.5kg lighter than the live axle.
Now more importantly one wheel bump which is what i'll encounter most of the time.
live axle, 1 wheel, 1 brakes and 66% of the axle weight = 42.78kg or yowsers, far higher than i expected.
De-dion 1 wheel bump = 1 wheel, 1 brake, 66% of drive shaft and 66% of de-dion beam or ... 39.88kg or 2.9 kg lighter.
(oh for reference the sierra push in shaft diff came to 20kg making the total de-dion package 26kg heavier without taking into account the chassis
mods for the rear axle or diff mounting. i'd guestimate maybe 30kg heavier in total.)
So, the million dollar question - what have i done wrong above? The advantage seems very small. For some reason i was expecting something like half to
two thirds the weight in 1 wheel bump.
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 25/3/08 at 11:31 PM |
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all I can say Mike is are your scales right??
Firstly, 2.3kg of UNSPRUNG weight is definitely not to be sniffed at, BUT...........
How can the brakes be 7 kg, or if they are, then there's a good argument for discs!!!
The sierra rear std caliper is 3.1kg ish and the disc is approx 3 kg (before lightening it) so thats saved nearly a kilo for a kickoff.
then the driveshafts!!!....
14kg for those shoddy articles!!!
Lobro joints, again before lightening, are 1.5 kg each so 3 kg per shaft, and the shaft itself is around 1.6 kg in the case of my GB items, so that
saves nearly 10kg a shaft, ok a bit less with grease and boots included but you get the idea
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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MikeR
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| posted on 26/3/08 at 12:04 AM |
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the scales could be wrong and bathroom scales are supposed to be less accurate at lower weights. At 80kg weights it gives an identical reading to an
electronic set of scales i've got.
(i picked 80kg as i have an easily transportable 80kg mass known as my fat arse).
Drive shafts - yep, i was surprised. But they are physically heavy.
drums - thats back plate, drum + brake shoes and adjusters. That sierra stuff certainly isn't light weight, and compared to the drive shafts it
seems to be about right.
As a 'check' i weighed the diff mounting brackets on kitchen scales and then on the bathroom scales. They did come out about the same
weight.
Think i have decided to go de-dion. I'll just have to upgrade the crossflow engine to cope with the extra 30 or so kg mass the poor car is going
to get to do it. Now i need to bite the bullet and start welding up the axle / modifying the rear end.
(at least if i change my mind again the rear end will cope with either axle!)
Oh, just realised, your disk argument - how much does the mounting bracket weigh for the calliper? (and will they fit in 13" wheels :p)
[Edited on 26/3/08 by MikeR]
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Bob C
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| posted on 26/3/08 at 12:08 PM |
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Hi Mike,
yes wheels and tyres included in the IRS measurement, they were the 14" original mx5 wheels (slightly minilight look -e -like).
My rear & front unsprung weights are identical. I'm using mx5 uprights, wilwood dynalite single calipers & homebrew discs with alloy
bells. The other chap who weighed his might well have been an indy with drums at the rear. Considering the above, a more "standard" rear
setup would probably be +2kg for caliper and maybe another 1kg for the disc.
Bob
PS the www button below gives all the details......
PPS hazy memory has the wheel + tyre at around 14kg too......
[Edited on 26/3/08 by Bob C]
[Edited on 26/3/08 by Bob C]
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Bob C
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| posted on 26/3/08 at 12:21 PM |
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Hopefully this link will work to old thread (plus details of measurement....)
http://www.locostbuilders.co.uk/viewthread.php?tid=33933&page=1
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MikeR
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| posted on 26/3/08 at 01:16 PM |
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If i get the chance i'll re-weigh components tonight. I'll use the kitchen scales (the joy of not living with a woman) and update where
necessary.
(i'm starting to think some of my weights must be wrong for things like the drum brakes / drive shafts etc).
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MikeRJ
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| posted on 26/3/08 at 01:23 PM |
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Something mentioned in that thread that Bob linked to which hasn't been discussed for a while is inboard brakes. This is something that a
de-dion (and IRS) make possible, and should result in a significant USW reduction.
I assume the Sierra driveshafts and CV's are up to the job for this when used on a Locost?
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MikeR
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| posted on 26/3/08 at 06:10 PM |
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i've re-weighed the de-dion using the kitchen scales (ok and the bathroom scales for the de-dion beam, but with me holding it and then without
it and the assumption its more correct at circa 90kg)
beam 5.3kg
cv tube 1.1 (but there are two)
ear 800g (but there are two)
trailing arm mount 550g (but there are two)
panhard rod mount 250g
giving total of 10.45kg (i did say 11kg before)
i'll be in the garage later weighing the brakes etc once the rain stops (assuming the footy hasn't started)
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NS Dev
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| posted on 26/3/08 at 11:28 PM |
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quote:
Originally posted by MikeR
the scales could be wrong and bathroom scales are supposed to be less accurate at lower weights. At 80kg weights it gives an identical reading to an
electronic set of scales i've got.
(i picked 80kg as i have an easily transportable 80kg mass known as my fat arse).
Drive shafts - yep, i was surprised. But they are physically heavy.
drums - thats back plate, drum + brake shoes and adjusters. That sierra stuff certainly isn't light weight, and compared to the drive shafts it
seems to be about right.
As a 'check' i weighed the diff mounting brackets on kitchen scales and then on the bathroom scales. They did come out about the same
weight.
Think i have decided to go de-dion. I'll just have to upgrade the crossflow engine to cope with the extra 30 or so kg mass the poor car is going
to get to do it. Now i need to bite the bullet and start welding up the axle / modifying the rear end.
(at least if i change my mind again the rear end will cope with either axle!)
Oh, just realised, your disk argument - how much does the mounting bracket weigh for the calliper? (and will they fit in 13" wheels :p)
[Edited on 26/3/08 by MikeR]
mount bracket is part of the hub, so no idea as it doesn't come off! (the weight I quoted includes the caliper slider section)
They will fit in "some" 13" wheels........yes that is a downside!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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MikeR
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| posted on 30/3/08 at 10:00 PM |
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got into the garage and weighed a drum brake assembly in bits on the kitchen scales.
(Which i've just realised i've left in the garage with the bit of paper).
Basically, the initial weight of 7kg was close enough.
Only thing i need to re-weigh now is the drive shafts.
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MikeR
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| posted on 4/6/08 at 11:55 AM |
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finally got round to re-weighing the drive shafts. Did it three times. once just on the scales and twice with and without me holding them on the
scales.
Got a consistent set of results. 9kg (5kg lighter than before)
Makes De-dion far more interesting now (and with the option in future of doing lightened shafts from GB or just cut down shafts to fit escort track +
rear disks perhaps)
I believe in one wheel bump de-dion is 9kg better off than an escort axle & 15kg better off in two wheel bump + with the total sprung de-dion
weight (brackets / diff etc) being higher than the escort axle by just under 25kg that will also improve handling (more sprung weight for the unsprung
to move).
Right, just need to get the drive shafts and trailing arm mounts made now 
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