Winston
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| posted on 30/5/03 at 06:19 PM |
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+1 Chassis
Hi all, first post here! Long-time reader, though (over a year).
I just bought a 1980 Toyota Celica as a donor, and due to several constraints (including engine size, axle width, and diff offset), I need to build
the chassis 1" wider than book specs. I believe that I have a good idea of which members need to be lengthened, but if someone else has done
this I would like to check my work. I am positive about the need for +1", as this has been discussed on the Locost North America list.
Apparently book specs are too small, +2" is a tight fit for the axle (too close for my tastes), but +1" is just right. Thanks in
advance...
-Winston
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theconrodkid
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| posted on 30/5/03 at 06:31 PM |
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welcome to the mad house trywww. mcsorley.net
who cares who wins
pass the pork pies
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Winston
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| posted on 30/5/03 at 06:47 PM |
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Been reading that site for about a year, too, but thanks anyway. Unfortunately, he doesn't have +1 chassis plans up. He offers to draw up custom
ones, but since it's a relatively easy task to go +1" I didn't want to bother him. Like I said, I just want to check my work if
someone's else has already done it  If not, I don't mind blazing that trail... I have an engineering degree so I feel fairly confident
in my work .
-Winston
EDIT: I've also sent emails to some of the other Celica builders listed on McSorley.net. I'm just trying to cover all of my bases. Out of
curiosity, was the '80 Celica sold in the U.K.? If so, was it called the Celica?
[Edited on 30/5/03 by Winston]
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Lars
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| posted on 30/5/03 at 08:10 PM |
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you might be able to just lengthen the cross members, it's only an inch and i'm sure it won't look disproportional
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craig1410
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| posted on 30/5/03 at 08:27 PM |
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Winston,
I'm building a McSorely 7+4 and firstly I would encourage you to build a +4 if you're not going to go for the standard book width. The
reason being that if you're going to have the hassles of being non-standard like me then you might as well go +4 because it's probably the
next most common size and parts like scuttles and rollbars and windscreens are more likely to be available by the time you need them. Also, you will
have much more chance of getting decent seats to fit a +4".
However, if you are set on +1" then my advice would be to build the chassis as you go along by adding 1 inch to all crossmembers as someone else
said and then just make the diagonal and triangulation pieces to suit. If you compare the McSorely +4 plans with the standard book plans then you will
see which tubes are affected by change of width (some obvious, some not so obvious). Someone check my geometry but if you just take the McSorely sizes
for these "different" tubes and subtract the book size then divide the difference by 4 then that should be the size you need to add to the
book chassis tubes for a 1" wider chassis.
Make sense?....Thought not!
Cheers,
Craig.
ps. You've been on the list for a while so will probably know already but research the errors in the book dimensions before starting and note
that the errors are also in the McSorely plans AFAIK. Have fun!
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Winston
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| posted on 30/5/03 at 09:16 PM |
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Thanks for the advice, guys. I am pretty much set on +1 because that's the only way I can use the Celica axle. I don't wish to try and
source a different axle (scrimping everywhere I can), so I'm sticking with +1. Craig, your geometry is mostly correct, except when it comes to
the diagonals. That, and you have to add the number you came up with to the book length to get the new (+1) length. Which basically amounts to +1 on
all of the crossmembers, since the geometry won't let you just add +1 to diagonals. There, that should totally confuse the subject.
-Winston
P.S I'm not buying any parts if I can help it (except for possibly the wheel arches), so if I'm making it then I can just make it 1"
larger.
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Lars
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| posted on 30/5/03 at 09:43 PM |
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you could always build a +2" and use spacers
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craig1410
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| posted on 30/5/03 at 10:49 PM |
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Winston,
I don't think I explained my idea very well because it should cover diagonals and compound angles as well.
I did say "then that should be the size you need to add to the book chassis tubes for a 1" wider chassis. " which should cover your
point about adding the extra length to the book length to get the desired NEW diagonal length.
As for the diagonals, thinking about it more carefully, because the angle formed by the diagonal will be different compared with book then my
proportional extension of the diagonals by 1/4 of that for a +4" chassis is not quite correct but provided that the corresponding
diagonal's angle doesn't change by much then it shouldn't be a significant error margin. If the angle does change significantly
then you might want to rethink it anyway because this will affect the structural design.
An example is called for: Let's assume that you have a 30-40-50 triangle with 30 longitudinal, 40 lateral and 50 diagonal. Now if you added 4
inches to the width you would have a 30-44-? with pythagoras yielding 53.254 for the diagonal. Thus the DIFFERENCE in the diagonal is 3.254 from
'book'. Now I'll bet that the diagonal DIFFERENCE required for a 1 inch wider lateral distance will be almost exactly 1/4 of the
3.254 = 0.8135 thus giving a total diagonal size of 50.8135 Checking this against pythagoras gives sqrt(30x30+41x41)=50.8035 which is only a 0.01 inch
error. Of course we could just use pythagoras for everything but that would require that you knew all the "pure" lateral and longitudinal
dimension components of each diagonal beforehand which is not easy to calculate.
I hope this makes my ramblings clearer... 
Cheers,
Craig.
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craig1410
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| posted on 30/5/03 at 10:57 PM |
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Oh, just one final point.
I have heard it said that a standard "book" chassis with Escort axle doesn't fill the wheel arches very well and that a slightly
wider rear axle would be beneficial to achieve this. Have you considered just leaving the chassis as standard book size and just fitting the
wheelaches to the chassis by spacing them out very slightly as required? We are only talking 1/2 inch each side which I don't think will require
any mods to keep the tyres within the wheelarch but if it does then it will be a simple matter of altering the mounting brackets slightly to push them
out and then filling in the small gap with Isopon P38 or fibreglass matting or whatever if required.
I don't think any changes will be required though to keep the tyres covered and you will have a nice standard chassis with loads of
off-the-shelf and second hand bits available when you get fed up making everything yourself
Anyone with a book chassis care to comment about the wheelarch issue?
HTH,
Craig.
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Simon
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| posted on 30/5/03 at 11:35 PM |
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Winston
First - welcome.
I'd go along with Craig - if you're going to go a little wider, might as well go much wider!!
Though I've never sat in a book chassis, I have sat in my +4 chassis - usually turning the steering wheel and making V8 noises, and if it had a
roof, I think I'd become claustrophobic.
Anyway, if you insist on +1" just add them inch on the cross members - cymtriks may have something to say about it (I hope:-), but I don't
think 1"
will affect the structural integrity of the chassis to any great degree.
ATB
Simon
PS Craig - I've sent you an email!!
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Winston
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| posted on 31/5/03 at 11:48 PM |
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Craig, thanks for the exhaustive explanation  I believe that we are on the same page regarding adding additional width and its effect on diagonals.
Regarding the spacer idea, would that increase backing-plate to backing-plate distance? That's the area of concern with going +2. Supposedly the
stock axle assembly fits, but just barely. I must admit that I'm not too familiar with how spacers work (i.e. onto which portion of the axle
assembly they are fitted), so enlightenment here would be helpful.
Regarding the idea of a book chassis, I have recently spoken with another builder here in the states that ordered a CMC book spec chassis. He's
using the same donor. Apparently, the whole setup fits -- but just barely. The part that is the tightest is the transmission tunnel (due to the offset
pinion of the diff). I don't like tight clearances when it comes to things like this, so I'm not planning on building a book chassis. So
from the sound of it, nobody else has been brave (stupid) enough to build a +1?
Regarding the usability of off-the-shelf parts for a +1 chassis, the only ones that I can think of that would be affected would be the nosecone and a
rollbar. The rollbar might still be usable, actually. The nosecone could be modified.
Anyway, I still think that +1 is the best route to go if my goal is to save money by working with what I have. If it were not, then I would just go +4
and be done with it!
-Winston
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craig1410
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| posted on 1/6/03 at 12:04 AM |
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Winston,
I'm sure Lars will answer in his own words but what I think he is meaning is to build a chassis which is 2" wider and then fitting spacers
between the wheel and hub along with longer wheel studs/bolts. This can be very effective and quite simple but you should be aware that it alters the
loading on the wheel bearing and should not be taken to excess. 1 Inch is about as far as I'd recommend.
I think what you are worried about is the live axle not being wide enough to span across tubes RU1 and RU2 and not being wide enough to mount the
trailing arms properly. If so then once again I'd recommend using a book size chassis and just weld the axle mounting brackets in the
appropriate position to line up with tubes M1 and M2 to which the chassis end of the trailing arms bolt on. As I said, the book chassis with standard
book wheelarches does not fill the arches and the extra width of the donor axle should help to fill them better whilst still staying SVA compliant.
Try to go and visit someone with a book locost and do some measuring. Fit your wheels and tyres to your axle and measure outside size and compare with
the book standard car. I'm sure some of the guys on the forum will be able to give you wheelarch sizes so you can judge if it will fit.
Cheers,
Craig.
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Lars
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| posted on 1/6/03 at 10:55 AM |
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well craig that's how i would have explained it and i would also say build a book width chassis and have those rear arches fully filled, looks
much better.
craig i would have thoght that the effect of have spacers would not be that great on the wheel bearing in a light car like were building especially on
the rear.
Just wondering cause i'm thinking about some 1" spacers
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Winston
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| posted on 1/6/03 at 12:59 PM |
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If filling the wheel well is the only concern, +1 would do a better job than +2. Though not as good as a book chassis, as Lars and Craig point out.
We'll see what I decide. I still have a little while to think about it, as chassis construction won't begin for several weeks.
I know that the tranny tunnel has to be widened for the W50, I just don't know by how much yet. Footspace is already at a premium in the car, so
I really would like to go wider than book spec -- even if I gain only 1/2 inch foot space. Of course, I could go with an offset tunnel but I fear that
would open up all sorts of problems related to asymmetry. Any comments here? Avoiding asymmetry during a regular build will be hard enough. I'm
afraid that if I plan for asymmetry then that will make the build that much more difficult.
Again, thanks for the advice guys.
-Winston
P.S. There is a fellow with a book chassis and my same donor in the next state that I may get to visit. We just started speaking recently, so
we're not quite chummy yet
[Edited on 1/6/03 by Winston]
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craig1410
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| posted on 1/6/03 at 06:50 PM |
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Lars,
Yes 1 inch spacers should be okay generally provided they are on the back axle and therefore don't have any great effect on geometry (There is
no real geometry on most live axles).
I'd be a little more concerned about putting them on the front though because it will affect scrub radius. This will have the effect of making
the steering "kick back" when you go over uneven ground and under braking can make the steering feel twitchy. You can reduce this by using
a wheel/tyre combination with larger radius but you'd need to do some sums to get the right effect. Yes the bearings should be fine given that
the donor car will have been two of more times heavier than the Locost.
Thinking about the increased tyre radius idea, it's probably not practical because I think you would need about 5.8 inch greater radius (11.6
inch greater diameter) to make 1 inch difference to the scrub radius. It'd be like a monster truck!
The better solution would be to make wider wishbones on the front and leave the spacers off.
HTH,
Craig.
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elewayne
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| posted on 3/6/03 at 12:21 AM |
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Wider
As I under stand one of your posts you have a width problem with the transmission too. Thats why I had to make mine wider as well and could only go +2
for my supra axel. But seem to be over thinking this whole thing. Your first step is to get a 4x8 sheet of MDF and do a fullscale layout to the frame
bottom rails.
Just make the drawing 43" instead of 42" and center everything up on that. then just measure all the tubes with a tape measure and forget
about calculations and angles. Just measrue them or lay the tubing on top of the layout and hand mark it. You can even space the front upper rails to
keep the nose cone standard. Ask Jim Mcsorley how. This is very easy if you don't over think it.
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elewayne
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| posted on 3/6/03 at 12:23 AM |
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Wider
As I under stand one of your posts you have a width problem with the transmission too. Thats why I had to make mine wider as well and could only go +2
for my supra axel. But you seem to be over thinking this whole thing. Your first step is to get a 4x8 sheet of MDF and do a fullscale layout to the
frame bottom rails.
Just make the drawing 43" wide instead of 42" and center everything up on that. then just measure all the tubes with a tape measure and
forget about calculations and angles. Just measrue them or lay the tubing on top of the layout and hand mark it. You can even space the front upper
rails to keep the nose cone standard. Ask Jim Mcsorley how. This is very easy if you don't over think it. A little cad drawing never hurt
either.
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Winston
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| posted on 3/6/03 at 12:33 AM |
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Wayne,
It seems to me that everybody else is overthinking it for me I've just wanted to add 1" width all along and be done with it. I know the
trick to maintain the capability of using an off-the-shelf nose cone, and I may use it. The problem is that it takes away from the small amount of
clearance you gain by going to a wider chassis. George Cushing's drawings indicate that the 20R engine could really benefit from having an extra
inch of space. Or more accurately, my sanity would benefit from having that extra inch when it comes time to fit the engine.
The thing is, at this point thinking is all I can do because I need to wait until I move before I can even begin the chassis build. We close on the
house in two weeks...
Anyway, thanks for the tips regarding the disregard of calculations and whatnot. I'm an engineer, though, so calculations are what I feel most
comfortable doing I can, however, appreciate the approach you suggest.
-Winston
[Edited on 6/3/2003 by Winston]
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elewayne
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| posted on 3/6/03 at 02:55 AM |
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Winston, I'm in the Heights, drop by the house sometime and we'll talk. I build furniture there at home also so I'm here most of the
time. 713-869-6523
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Winston
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| posted on 3/6/03 at 03:54 AM |
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Will do! I'm only a few miles north of you (until we move, that is), up at 610 and I45! I'll give you a call tomorrow evening.
-Winston
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jbmcsorley
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| posted on 16/6/03 at 08:04 PM |
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great thread!
This is a great thread that addresses lots of concerns when customizing the chassis. I didn't catch mention of wanting more width for the
driver however, which in the US is the most common reason.
Anyway... here's my take on it it, FWIW...
One way to figure a custom chassis width is by measuring between the tires on a fully shod axle. Subtract 4" and you're on to the next
step... nosecone selection. Ah, but wait. Maybe you want something a little wider to fit your derriere, or a little less to fit the book? Wheel
spacers will give you more, wheels with a different offset can give you less. Bolt together you're favorite combination (in your mind's
eye if need be) and measure between the rubber.
Ok, back to the nosecone. You can fit whatever nosecone you like if you know the width across the back in advance... this provides a constraint that
the upper tubes may pivot about... the book's upper rails are exactly 10 degrees...and +4" width in the back pushes this angle to roughly
13 degrees... hardly noticible and easily counteracted by making the front end longer, if you so choose.
Right... back to fitting the nosecone. When designing a chassis there is the little known trick of laying out the upper rails on your MDF first... to
best fit the measure across the back of the nosecone and whatever the dashboard width is projected from the rear. The bottom rails are projected
downward based on the angles that you determined when laying out the toprails... "pretty sneak sis". Had Ron Champion suggested that you
layout the top rails first, then layout the bottom rails second, then join the two with the H tubes, then this trick would be somewhat obvious.
Ok... making a long story short... in about the same time that it took me to write this message I can jump into my CAD software, stretch the book
chassis by 1", retain a book size nosecone, and print the overall dimensional view. The individual part drawings take a little longer, but I
can send you the overall and we can go from there. Oh, and I have since revised the front end to eliminate compound angles... sweet.
I don't mind customizing the chassis to fit specific needs... I hold onto each permutation so that I can sell copies of the drawings on eBay
sometime in the future... or maybe write a book.
BTW, on my build the rear end is 45" and the dashboard is actually 48"... the door sill narrows as it approaches the rear. Subtle, but
tricky. Oh, and my engine sits a full 1" to the right to line up with my offset differential (1st gen. RX7). That should balance the weight
distribution when riding one-up (my preferred driving configuration).
Cheers,
-Jim M.
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