ed_crouch
|
| posted on 4/12/03 at 08:18 AM |
|
|
sierra back end into locost - will it go??
I want to build a locost chassis, and have some drawings of an IRS variant. Question is, will the sierra 7 inch diff (lobro type for rear discs), and
the standard unmodified half shafts fit, or is the sierra track too wide as standard?? i.e. will i need to add 4 inches or whatever down the middle of
the chassis to make it fit??
Much appreciated.
Ed.
|
|
|
|
|
JoelP
|
| posted on 4/12/03 at 09:20 AM |
|
|
the rear track is a lot wider. Cant see why you would have to make it bigger, but it may look odd. sierra track is 56 inches IIRC, which is
much wider than most other donors.
|
|
|
ned
|
| posted on 4/12/03 at 09:37 AM |
|
|
As already said IIRC the sierra track is 4 inches wider. Some people have talked about leaving it like that with standard front end, but personally I
think it wouldn't look or handle quite so well.
I'm going to shorten the sierra half shafts on mine, the other option is a wider chassis (eg mcsorleys plans) or wider front wishbones as per mk
indy/luego velocity.
I'd be interested to see the IRS plans you have!
cheers,
Ned.
beware, I've got yellow skin
|
|
|
Ben_Copeland
|
| posted on 4/12/03 at 09:46 AM |
|
|
I'd like to see them too 
Ben
Locost Map on Google Maps
Z20LET Astra Turbo, into a Haynes
Roadster
Enter Your Details Here
http://www.facebook.com/EquinoxProducts for all your bodywork needs!
|
|
|
PeetBee
|
| posted on 4/12/03 at 10:07 AM |
|
|
It's not IRS, but the de dion set up from GTS looks good and I may well be tempted to go for it, at least that would use your sierra bits!
|
|
|
James
|
| posted on 4/12/03 at 10:35 AM |
|
|
Ed,
You can get it to fit and no, you don't need the chassis any wider (just look at the Luego Velocity XT). You need to decide how (or if)
you're gonna get the front track to match- longer wishbones at the front or a wider chassis or getting your rear drive shafts cut down (as in
the original Luego Velocity).
The thing to do is ask whether IRS is really worth the effort. It's not *that* hard to source a Live Axle from a MK2 or a Cortina or a Capri (if
that's your reason for IRS) so unless you're sure that you want IRS I would stick with what's straightforward.
If I'd known when I started what I know now I would have a Live Axle standard chassis and possibly a finished car! The more deviations from the
book the longer the whole project is gonna take you.
HTH,
James
|
|
|
James
|
| posted on 4/12/03 at 10:39 AM |
|
|
quote:
Originally posted by ned
As already said IIRC the sierra track is 4 inches wider. Some people have talked
I'm a bit dubious about the 4". It depends which data books you look in. I'll measure my rear track tonight to be sure! 
James
|
|
|
mackie
|
| posted on 4/12/03 at 11:25 AM |
|
|
Also, don't discount the GTS de Dion kit! Much simpler than IRS (only minor mods to rear of chassis required) and you can used unmodified Sierra
rear end parts. That's what we are doing. We are making a 4inch wider chassis too (to accomodate the wide engine).
|
|
|
stephen_gusterson
|
| posted on 4/12/03 at 11:37 AM |
|
|
my car has 'non book' susp front and rear. the rear is IRS using swinging arms.
I cna without doubt say this has added masses of time to the build, plus its a bu%%er to set up the alignment and stuff.
Many cars on this site handle (apparently) brilliantly with a live beam axle. it will save LOTS of time.
Also, using a wider chassis has another load of knock on problems. You may need unstandard rear arches, front, bonnet, windscreen etc. Making the car
wider is almost as big a hassle as IRS.
If you want a slow, custom build, deviate from book. if you are more interested in driving than building, then follow the book as much as poss.
As far as using the sierra rear, robin hood also do this. (whatever people might think of RH!). If you look at a chassis for a hood 2b, you will see
it swerves up in the rear corners to allow for the sierra 'subframe' fixing. It needs a few changes to a locost chassis to come anywhere
near fitting....
atb
steve
|
|
|
ed_crouch
|
| posted on 4/12/03 at 12:00 PM |
|
|
heres the IRS plans. Not that good, but maybe its possible to scale from them.
Ed.
|
|
|
craig1410
|
| posted on 4/12/03 at 12:54 PM |
|
|
Hi,
Sierra rear track is 57.8 inches according to www.carfolio.com. This is what I have built mine to match. My front track is 56" using book
wishbones on a +4" chassis.
I would agree that IRS is not worth the hassle, especially for a first build but de-dion is definitely worth a look. That's what I am using
along with a +4" McSorely chassis.
I don't feel that the +4" wider chassis has caused a lot of problems and the extra space it gives you in the seating area and engine bay
are well worth having (essential if you want a Rover V8 engine like me...)
My rule of thumb would be that if you are going for a book build with a ford crossflow or similar engine and live axle etc then just stick with a
standard width chassis. This is the quickest route to completing a build. However, if you want to use the likes of a Pinto or RV8 engine or any other
larger engine which requires a wider tunnel or whos bellhousing impedes on footroom, then seriously consider a +4" wider chassis. Don't go
for +2" or +6" or anything else as +4" is looking like becoming a popular and well supported secondary standard. There are many
suppliers who are providing or currently designing body and suspension parts for +4" wider cars so it should become much easier to complete such
a build in the next few months.
Check out my website for more details at http://www.craig.chamberlain.name
I hope this helps,
Craig.
|
|
|
JoelP
|
| posted on 4/12/03 at 02:40 PM |
|
|
to agree with craig and steve, if i was to start again i'd buy a standard chassis off Ebay, saves 12 months and lots of crap. then use a dedion
rather than IRS, would be so much easier. I would be driving now had i done that, as opposed to just finishing the chassis.
|
|
|
kingr
|
| posted on 4/12/03 at 11:00 PM |
|
|
While I've got no specific examples or even heard about it particularly, I wouldn't choose to buy an amateur built chassis off ebay -
you're buying someone elses welding, someone elses incorrect dimensions and hence someone elses problems. I've no doubt that there are
plenty of perfectly good chassis out there, I'm just saying it wouldn't be my choice.
Just to disagree with most of you, I don't have any problems with the looks of having different track widths front to back, and I also have my
reservations as to whether the handling will be detrimentally affected. If it does, hell, I'll redesign the front end and make the track there
wider, won't take long at all.
Just to chuck another potential problem in, shortening shafts is not the perfect solution - it's unlikely that they'll ever be as strong
as the original items : from the factory, the splines are pressed into them, which can't be done to shortened shafts (it's not so much
that it "can't" be done as that you'll probably never find anywhere with the facilities to) which leaves you two options : cut
them in the middle and weld a sleeve over them or cut them at one end and machine splines into what's left. Welded shafts tend to snap under
power, and machined shafts tend to sheer their splines under power. Obviously this probably isn't an issue if you're using a Xflow 1300,
but almost definitely would be if you're looking at the Chevy or Cossie end of the market.
Now for a bit of positive news : I haven't had any significant problems using IRS (so far, touch wood), and don't think it took an aweful
lot longer than using a live axle. It reduces the unsprung weight (remember that with live axle, the diff and even 50% of the prop count as unsprung),
LSDs are a stupidly easy to find and rear disks, even if unnecesary, can come as standard.
Anyway, the various merits of both sytems have been well discussed, so take a look in the archives for more info.
Kingr
|
|
|
craig1410
|
| posted on 4/12/03 at 11:12 PM |
|
|
Kingr,
I respect your opinion on IRS but many people seem to curse the decision to go for IRS (like James) as it has delayed their build considerably.
Perhaps IRS is fine for someone who has built a car before or already has extensive applicable skills and resources but for someone new to Locosting I
think Live and now de-dion are the way to go.
All IMHO of course...
Cheers,
Craig.
|
|
|
stephen_gusterson
|
| posted on 4/12/03 at 11:27 PM |
|
|
to put it another way....
several times on this site I have said that people with live axles have good handling cars, and that its a hassle going IRS.
never, at any time has
a. a live axle owner said, no way, if i did it again i'd replace my crap axle with an independent system
b. someone with an independent system say how much better it is than a live axle car.
prove me wrong anyone?
atb
steve
[Edited on 4/12/03 by stephen_gusterson]
|
|
|
kingr
|
| posted on 5/12/03 at 12:46 PM |
|
|
Steve,
True, I've no doubt that live axle is comparable to IRS. Which one is better will likely remain a matter of debate for the forseable future. A
lot of the reason to go IRS is nothing to do with handling, but with availability and personal preference. I choose IRS, because I prefer designing,
modifying and building to searching, haggling and delving around in scrappies. Your mileage may vary though.
Kingr
|
|
|
craig1410
|
| posted on 5/12/03 at 12:57 PM |
|
|
Kingr,
That's where I see de-dion coming into its own. No haggling and searching around scrappies for old live axles. Just buy a de-dion kit from the
likes of GTS and use Sierra bits from there on in. A good bit cheaper than building/buying rear wishbones and uprights and with most of the advantages
of IRS (unsprung weight etc) plus better start line traction by all accounts due to less camber change on squat.
It's a personal choice so all opinions are given due respect. In my view the important thing is that we all know the options and the associated
pro's and con's and try to ensure that any newcomers to Locost building are aware of them all and can make an informed choice. Hopefully
we can all agree on that at least...
Cheers,
Craig.
|
|
|
craig1410
|
| posted on 5/12/03 at 12:59 PM |
|
|
Before anyone says it, yes IRS wishbones could be set up to resist squat and thus improve start line traction but not many of us will be capable of
calculating the CoG accurately enough to set this up correctly.
Cheers,
Craig.
|
|
|
kingr
|
| posted on 5/12/03 at 01:02 PM |
|
|
Craig,
Yes, I'm becoming more of a fan of DeDion by the day, it gets rid of some of the biggest problems with live axles both in terms of handling and
practicallity/availability. One of the bigger problems with DD is building the tube - there's no scope for correction once it's welded up,
but with GTS making them now, that solves that problem.
Kingr
|
|
|
craig1410
|
| posted on 5/12/03 at 01:12 PM |
|
|
Kingr,
Yes you are correct about the tube thing, it is crucial for accuracy and difficult to achieve in practice. I think I have managed it with my home
built De-dion setup though and that was a relief to say the least. I have even managed to achieve a very small amount of toe-in and negative static
camber which was my aim.
It should be possible for someone to devise a method of making de-dion adjustable by perhaps some sort of "cam" arrangement to cause
deflection in either castor or camber as required. This would make the whole thing much easier to set up and remove the need for the very high levels
of accuracy during assembly. If that problem was solved then it would be almost ideal for Locost use and would perhaps even displace IRS as the
panacea we all seek. In the meantime if a de-dion axle is built on a good jig then it should be fine for the vast majority of us. Only true
enthusiasts and motor sport participants would really need the adjustable axle IMO.
Cheers,
Craig.
|
|
|
ned
|
| posted on 5/12/03 at 01:14 PM |
|
|
I personally feel that pure IRS is the best layout, when setup correctly; I appreciate this is the hard bit for most of us amateur builders.
I agree that dedion is a good alternative to irs as already mentioned you can use easily available donor parts and a well priced pre-fabbed de-dion
tube, c/o darren@gts. it makes a quite simple, quicker to assemble and less complicated back end.
My only concern re: handling with dedion over IRS is that you don't get the independent camber change on either side with dedion as this is
governed purely by the stiffness of the dedion tube (assuming i undersatdnt he setup correctly)
Ned.
beware, I've got yellow skin
|
|
|
dozracing
|
| posted on 5/12/03 at 01:20 PM |
|
|
The reason we chose to do a De Dion setup was that its easy to fit, its much lighter than IRS and much more genuine for a 7 as both Lotus and Caterham
did it for the original cars.
We have chosen not to widen the chassis or lengthen it because you end up with a big monster car, from one thats supposed to be a little light weight
2 seater sports car. e can do longer chassis' if required, but, we had some really tall guys fit nicely in it at the Exeter show so i'm
sometime dubious as to whether you really need another 4". We have chosen to widen the fron track to match the rear to keep the car in
porportion and it handles better this way.
If you didn't already know the plans for the chassis mods are on the website www.gtstuning.co.uk and look under the De Dion Axle section.
Kind regards,
Darren
|
PLEASE NOTE: This user is a trader who has not signed up for the LocostBuilders registration scheme. If this post is advertising a commercial product or service, please report it by clicking here.
|
dozracing
|
| posted on 5/12/03 at 01:24 PM |
|
|
Hi Ned,
The De Dion is better for camber control over the IRS because you maintain the camber and therefore the contact patch with the road. IRS gains camber
with bump thus effecting the contact patch.
I'll dig out the section on the De Dion from the bible of race car handling later (Race Car Vehicle Dynamics) and quote the benefits that
Milliken and Milliken identify.
Kind regards,
Darren
|
PLEASE NOTE: This user is a trader who has not signed up for the LocostBuilders registration scheme. If this post is advertising a commercial product or service, please report it by clicking here.
|
craig1410
|
| posted on 5/12/03 at 01:26 PM |
|
|
Ned,
Why do you need camber change when your wheels are perpendicular to the ground at all times thus maximising grip?
I know that tyre deformation might require some static camber to be dialed in to begin with but with good low profile tryres this should be minimal.
The main reason for static negative camber (AFAIK) is to counteract body roll. With de-dion body roll doesn't affect the axle position in the
same way and it stays parallel to the road.
The only problem with de-dion is when you hit lots of bumps with your inside wheel mid corner as this will change the camber of the outside wheel
which has most of the load.
In summary I think that IRS would only be better than de-dion going around bumpy corners but even then the length of the axle would ensure that camber
changes would be very small even with (say) 2" high bumps. 2 degrees in fact by my calculation (Inv Tan 2/57.8"
However, with the improved start line traction of de-dion over IRS, you wouldn't make it to the corner first anyway 
Cheers,
Craig.
|
|
|
craig1410
|
| posted on 5/12/03 at 01:28 PM |
|
|
Looks like Darren beat me to it...
|
|
|
