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.
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.
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.
I'd like to see them too
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!
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
quote:
Originally posted by ned
As already said IIRC the sierra track is 4 inches wider. Some people have talked
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).
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
heres the IRS plans. Not that good, but maybe its possible to scale from them.
Ed.
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.
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.
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
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.
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]
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
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.
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.
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
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.
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.
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
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
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.
Looks like Darren beat me to it...
Craig,
I think this is the aspect that concerns me most:
quote:
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.
race cars are looking for every little bit of gain.
schumacher gets wieghed before he goes to the bog as the contents of his rectum will be worth 1.2 seconds over a 90 minute race.
We, on the other hand, will be going down the A24 or whatever and having the occasional track day.
I doubt the difference between dedion and IRS are really gonna show up that much
When I did a single seater experience at silverstone, it taught me that you will NEVER get the best out of a car on the road. I was thinking this
having recovered from a spin onto the grass. Do that on the road and they would have been scraping me up.
You can get more performance on a track due to margins allowable for error - ie grass, not a truck in the way.
but, are not racing lcosts live axle....
atb
steve
[Edited on 5/12/03 by stephen_gusterson]
Steve,
I think the racing locost being live axle isn't really an issue. It's like that because it was in the book (which practically are the regs)
and it keeps the cost and ease of build down.
Ned.
quote:
Originally posted by ned
Steve,
and it keeps the cost and ease of build down.
Ned.
I think that's checkmate to Steve
Sorry Ned,
Craig.
Ned,
One thing in response to some of your points. If IRS is so good for a Lotus 7 type car then why are Cateringvan using de-dion?
Not getting at ned at all.
for each his own.
a well made irs will have very good camber control.
however, a poorly done homer attempt might have the opposite effect!
if i was building a std car (did I mention I wasnt ) then id go live axle - simplest way.
atb
steve
quote:
Originally posted by stephen_gusterson
... a well made irs will have very good camber control ... however, a poorly done homer attempt might have the opposite effect!
what a dangerous question to try and answer!
there are many books on this subject, and I am no expert!!!
However, my small knowlege is that many cars apply a little (negative?) camber at the rear to allow for the distortion of the tire in cornering.
Ideally, I suspect that should be a constant - ie the tire should have the same angle thro its entire travel.
when I did my unstd front suspension, i used a program from TOL group (yahoo) that allowed simple modelling. Its not hard to come up with a model that
accurate to less than adegree over an 80mm travel. However, translating that into metal and getting the same results insnt always that accurate.
my front suspension is accurate to approx 0.5 or so degrees over the normal travel.
I wouldnt be suprised for someone to now tell me that in some instances you do need varying camber.......
suspension appears to be a minefield - which is why I would go live axle if I was building a locost and not this frankenstien car
atb
steve
quote:
Originally posted by jcduroc
quote:
Originally posted by stephen_gusterson
... a well made irs will have very good camber control ... however, a poorly done homer attempt might have the opposite effect!
Steve
How "much" is good camber control? (In your opinion, of course)
Joćo
Guys,
Surely on an IRS car you would want to gain negative camber on the outer wheel and gain positive camber on the inside wheel to counteract body roll? I
think this is one area where the complexity of interaction on an IRS system is much greater than on a live or de-dion axle and thus more difficult for
the novice to get anywhere near correct.
Of course the problem with gaining negative camber like this is that it adversely affects the contact patch during straight line acceleration when the
car squats.
I am starting to think that IRS only really makes sense when you add anti squat anti dive geometry and anti-roll bars. Without those I don't
think you can avoid the compromise between cornering performance and straight line traction. Of course de-dion and live have other compromises too but
they have simplicity on their side.
Does that make sense?
Cheers,
Craig.
hello...
Steve - If you want no camber change you can just have parallel equal length wishbones! But you do want camber change - when the car rolls in a
corner the outside wheel effectively goes into bump and the inside wheel into droop. To keep the wheels upright and gripping you want suspension that
gives negative camber in bump and positive in droop - unequal length converging wishbones. Of course if you achieve this then you have undesirable
camber change in squat and dive.
The design of unequal length converging wishbone geometry is simply a compromise between keeping the wheels upright in roll and keeping them upright
in dive and squat. When i was waving tape measures at various sevens in my early stages i noticed that choosing this compromise is a matter of
guesswork and voodoo. And maybe experience. A book locost has a lot of camber change hence good performance in roll and poor performance in
dive/squat. A Dax has near parallel wishbones giving good performace in dive/squat. My geometry lies somewhere between but erring towards better
performance in dive/squat (i'll avoid bad camber change in roll with anti-roll bars stopping me roll so much).
A decent IRS is always potentially better than live or de-deon, but like many have said, not all that much, and drivers like us would probably never
notice (unless we're talking really bumpy roads). I do disagree, however, with some peoples opinions that the inexperienced home builder should
avoid the 'black art' of double wishbone design for fear of creating an ill-handling death trap. If your double wishbone geometry looks a
bit like what other peoples look like then it'll be fine - as i said it's just a compromise.
Enough Bishop's Finger fueled waffle..
Liam
[Edited on 6/12/03 by Liam]
me, id do it like liam, with a very stiff anti roll bar, and closer to even length wishbones.
Quote from Milliken and Milliken - Race Car Vehicle Dynamics published by Society of Automotive Engineers when i bought it it cost me £100 so its a
very in depth technical book.
"The advantages of the de Dion are that the unsprung mass is much lower resulting in better road holding on rough roads (like independent
suspension). It is a beam type axle so the tires (tyres!!) always remain square to the road, thus no camber compromise exists (unlike independent
suspension). This gives it supposed advantages over both the independent and the conventional beam (live) axle."
Obviously good and bad exist in both designs and it also depends what you are using the car for.
Caterham and Lotus used de Dion for the 7 and were very successful with it in racing.
F1 cars use double wishbones (irs) but i do know of at least one F1 aero dynamics guy who fancies using a live axle style rear suspension in order to
gain camber advantagtes and much improved aero dynamics around the rear suspension. His name is Frank Dernie and he is now Chief race engineer for
Williams.
For me the decision to go de Dion was mainly that everyone on here was discussing it and seemed keen, and when i thought about it i realised that it
was the genuine Lotus 7 alternative to the live axle. Not everyone thinks like me i'm sure but i like the Locost because its an affordable Lotus
7. I'm after building and driving a Lotus 7 and this is the closest i can afford to get.
Other people may not feel so nostalgic and simply want to build a kit car and see a 7 as just that, for them authentisity is not such an issue. Due to
the popularity of the MK and Luego, IRS is quite common and accepted now for the Locost.
Kind regards,
Darren
see
I told you I was better saying nothing mr duroc
suspension for amateurs seems far too tech'y for me and that the potential of getting a worse result than IRS is far too great.
atb
steve