F1 Mini
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| posted on 28/4/04 at 09:52 AM |
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Caster and Camber gain on bump.
What is the best caster angle for these type of kits. What is it as standard, has there been any prof that another angle is better etc.
Also what is the standard bump Distance on the front and rear suspension (Bump being compression limit of suspension, not the rebound i.e. wheels of
the floor), and what is the camber gain roughly Per Inch bump.
A bit heavy for a first post I know, but am thinking of using your suspension on a project of mine.
Cheers For any help
[Edited on 28/4/04 by F1 Mini]
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Bob C
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| posted on 28/4/04 at 11:16 AM |
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Caster angle - can of worms this, the book says 5.3 degrees but speculation is that it means 5.5degrees BUT the book drawings give 2.8degrees. Cars
built by the book have difficulty achieving sufficient self- centring to pass SVA. Most people increase the offset in the top wishbone or move the
pivots to get 5.5degrees.
Camber - have a good look at the thread below about "suspension book" I think the stock system has a swing axle length of about 80"
but I'm not sure - I'm using different uprights so my data doesn't help.
Cheers
Bob
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pbura
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| posted on 28/4/04 at 01:24 PM |
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I've modeled the Locost suspension, but looking at my stuff this morning, I decided that it lacks rigor (it was done some time ago, when I was
more of a newbie). I had used information on the Cortina uprights that was gained from someone else, was shocked by the big scrub radius that
resulted, so I elongated the wishbones to eliminate it. Later, when I learned that the Cortina uprights do produce a lot of scrub, I increased
the track, having forgotten what I'd done the first time. So it's wrong.
At the time, my goal wasn't to perfectly capture the Locost, but to get some data for experimentation. I'll fix it soon and post the
results.
I don't think the camber results will change too much. I have .77 negative camber produced in the first inch of bump, and 1.22 positive camber
generated on the loaded wheel in 2 degrees of roll.
You can search around, but an old rule of thumb for travel is 1" of bump and 2" of droop being the typical limits, as far as I can
tell.
For my own planning, I'm using 2" of bump and 3" of droop. This would accomodate a combination of 1" bump combined with 2
degrees of roll, which would be a very extreme cornering attitude for a Locost. Check out some pictures of racing Locosts and you'll see that
they don't move much.
WRT camber, try searching on it. There was a big discussion recently about SVA, wishbone design corrections, and various folks' experiences.
One fellow used 9 degrees, and was very pleased as I recall.
HTH,
Pete
[Edited on 28/4/04 by pbura]
Pete
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MikeP
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| posted on 28/4/04 at 04:41 PM |
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quote:
Originally posted by pbura
You can search around, but an old rule of thumb for travel is 1" of bump and 2" of droop being the typical limits, as far as I can
tell.
Pete, do you remember where you got that from? I have the opposite understanding, 2/3rds bump for 1/3 droop. I think I got that out of the Aldan or
Proshocks catalog, for measuring/installing coilovers. Made sense to me - the wheel would move more dramatically in bump than in droop, and
I'd rather have the unweighted wheel lift than the weighted wheel instantaneously hit a very high spring rate mid corner. Not to mention the
bent control arms mentioned in another thread  .
Mike
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pbura
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| posted on 28/4/04 at 05:01 PM |
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Oops, Mike, you are right.
Pardon my faulty memory; I hate to be a propagator of "net wisdom". 
Pete
P.S. Would you happen to have the Locost suspension layout on your website?
[Edited on 28/4/04 by pbura]
Pete
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MikeP
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| posted on 28/4/04 at 05:46 PM |
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LOL, I was worried about me doing the same thing - it kept nagging at me until I went and found my reference on the proshocks site (the aldan site
being down right now). There's a table in the proshocks street catalog shows ride, closed and open lengths, 10.5", 8.7",
11.7" as one example.
Yep, my suspension stuff is at:
http://www.7builder.com/SuspensionGeometry/
I've got a cad drawing of the locost suspension there. Make sure you check the notes, there's that 1/8" discrepency problem in the
book for which I've made some of my own assumptions.
Mike
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NS Dev
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| posted on 28/4/04 at 05:47 PM |
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Caster angle-wise, unless on the track (and probably not even then!) I wouldn't worry about "0.somethings" of a degree as long as it
is equal side to side. I would aim for 5 degrees as a nice figure for this weight of car and layout of geometry. (2.something degrees as the book
wishbones give is definitely inadequate and will give rise to low/no self centring plus reduced feedback at the wheel on a car this light)
Cars of several types that I have built in the past used between 4 and 7 degrees caster, mainly dependent on weight, lighter car = more caster.
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pbura
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| posted on 28/4/04 at 06:06 PM |
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quote:
Originally posted by MikeP
Yep, my suspension stuff is at:
http://www.7builder.com/SuspensionGeometry/
I've got a cad drawing of the locost suspension there. Make sure you check the notes, there's that 1/8" discrepency problem in the
book for which I've made some of my own assumptions.
Thanks, I knew I'd seen it before
Sometime soon I'll hash out the differences and post the Wishbone stuff for folks to see.
Pete
Pete
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F1 Mini
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| posted on 28/4/04 at 10:06 PM |
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This sounds like the right forum for any info I need on my Mini Project. I'm building a full T45 Tube chassis with IRS and IFS, so that's
why I'm here ! Picture of car on my flat datumn table.
 
Rescued attachment DSCF0032.JPG
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F1 Mini
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| posted on 28/4/04 at 10:34 PM |
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pbura HELP that suspen program, I have down loaded it, and can get it started but nothing seems to happen once i've put the values in. HELP
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pbura
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| posted on 28/4/04 at 11:24 PM |
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quote:
Originally posted by F1 Mini
pbura HELP that suspen program, I have down loaded it, and can get it started but nothing seems to happen once i've put the values in. HELP
It's an old DOS program, not very user-friendly Instructions are on the website, and they are esssential.
After you enter your values, it takes you out to the main screen. From there you can do either graphic modeling (cheesy, I never use it) or text
modeling. Use your up and down arrow buttons for bump and droop, and the left/right buttons for roll. You can reset by typing 'S' or
exit with the space bar.
From the main screen, if you select 'O', it will save your data and modeling values in a text file like the ones I've posted (except
for the sub-headings, which I added).
Hope this helps!
Pete
P.S. Do a search for user kb58 and look at his website
[Edited on 28/4/04 by pbura]
Pete
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crbrlfrost
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| posted on 28/4/04 at 11:52 PM |
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It might also be of some consideration that your castor angle should reflect the built in kingpin angle of your upright. The kingpin angle will tend
to move the outside wheel toward positive camber as it turns (the greater the angle, the greater positive camber gain), while castor has the opposite
effect. On such a light vehicle, relatively large castor angles (7-11deg) shouldn't be to terribly inconveniant in terms of steering effort, but
its personal preference. Personally I'm going for 7 as I'm working with low kingpin and I like a relatively light touch on the wheel.
Don't know if this helped or not, but its something to think about. Cheers.
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F1 Mini
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| posted on 29/4/04 at 12:13 PM |
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The kingpin angle is normaly set by the chioce of Front upright you use, the choices from the scrap yard being Cortina and Sierra, if you don't
want to Buy expensive Westfield/Caterham options.
Is there any other worth a Mention ?
So what you useing as in Kingpin angle and Uprights ?
[Edited on 29/4/04 by F1 Mini]
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ned
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| posted on 29/4/04 at 12:43 PM |
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From my understanding most people use the donor (upright) car's offset wheels which to me solves the problem. surely it's only if you
start messing with the offset/backspace or ad a spacer behind the wheel that the kpi will go out?
Ned.
beware, I've got yellow skin
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crbrlfrost
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| posted on 29/4/04 at 04:38 PM |
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Yes, the kingpin is set by the choice of upright. What I was trying to say is adverse effects due to kingpin can be somewhat compensated for using the
castor angle. I'm in the US and found some s10 uprights dirt cheap (although I don't highly recommend them after working the geometry). A
high degree of castor isn't a major issue on these light weight cars with stock ratio racks, so it can be used to offset the positive camber
gain indicative of kingpin angles when turning. Anyone have any ACAD or Catia drawings of the cortina or sierra upright? Have a good one guys.
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F1 Mini
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| posted on 29/4/04 at 05:55 PM |
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quote:
Originally posted by ned
From my understanding most people use the donor (upright) car's offset wheels which to me solves the problem. surely it's only if you
start messing with the offset/backspace or ad a spacer behind the wheel that the kpi will go out?
Ned.
Hi Ned, I think your getting confused between Kingpin Angle, and scrub radius. They are closly linked but I haven't got to the wheels yet.
Saying that I can get a 7x15" wheel with 2" of Positive offset, so that should help the scrub radius.
[Edited on 29/4/04 by F1 Mini]
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