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#Post#: 12485--------------------------------------------------
Big caster angles
By: Ade Colmar Date: January 24, 2025, 9:07 am
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I'm looking for a bit of advice on caster angles, please.
Go-karts often employ a large caster angle to force the inside
front wheel to lift and the outside front wheel to drop when
cornering. This allows the inside rear wheel to more easily
loose traction so the kart will turn (when using a solid rear
axle). The kart is effectively turned into a three wheeler
while turning! The castor angles used appear to be around 20 to
25 degrees.
I made this basic jig this morning (see photo) to try a few
things out. This confirmed that a fairly radical caster angle
and stub axle length are needed to get significant lift and drop
of the front corners. (I'll be using a large steering wheel and
rack and pinion steering, so that will help with the extra
steering force required.)
Does this approach work on a cyclekart?
#Post#: 12488--------------------------------------------------
Re: Big castor angles
By: jim Date: January 25, 2025, 1:28 am
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Hi Ade, This system with large castor angles works on go karts
because the drivers weight is far enough forward to put the
pressure on the front wheels and lift the rear. Cyclekarts
generally have very little weight on the front axle and even
under braking and turning into a corner may not be enough to
lift the rear. It would be interesting if someone did it as an
experiment though to see what happens. It's possible it will
just be wobbly and a bit unstable on cornering leading to
rolling over. More castor is less turning of the wheel and more
leaning over. The large diameter wheels could be leaning quite a
bit I guess.
#Post#: 12489--------------------------------------------------
Re: Big castor angles
By: Ade Colmar Date: January 25, 2025, 3:02 am
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Thanks Jim. My Riley inspiration car has large castor angles
(see photos below) and that was what started me thinking. My
weight will be further forward than typical and I also have the
engine ahead of the rear axle to help. So I should have weight
transfer onto the front outer axle when cornering. Unlike a
kart, we also have front suspension, which will compress on the
outer wheel in a corner and that will also lift the inner rear
wheel. Im tempted to give this a go, I just don't know how far
to go with the angles!
#Post#: 12493--------------------------------------------------
Re: Big castor angles
By: RhysN Date: January 25, 2025, 9:07 am
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If it's any help at all when I built the ERA (as seen on video)
I put 12 degrees of castor following a similar line of thought.
It would run in excess of a mile on sand hands off the steering,
tracking straight and true. To turn a corner was almost painful
in the wrists, so much so that I needed to change. I went back,
by experiment to 6 degrees, which gave the acceptable stability,
but would tuck into corners much more easily. Those are my
starting numbers now.
Perhaps the extra length of wheelbase of a CK compared to racing
kart as well as wheel size?
#Post#: 12494--------------------------------------------------
Re: Big castor angles
By: jon.pearce Date: January 25, 2025, 10:13 am
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CASTER angles....
to add a bit to the mix here, if you are building a FN or GN
Type front end, then the Caster angle changes on suspension bump
and returns back to the preset angle on flat, even ground
running.
I have run my CK a few times now and settled on 10 degrees
Caster unsprung, which decreases by about 1 degree with me sat
in the car.
When I get my GoPro fixed on, it will be interesting to point it
at the kingpin and see how much angular rotation there is !!!
After 30 years of Karting, I can say that there is NO real
comparisons to make with regard to Caster angles in Karts and
Cyclekarts.
Have fun experimenting ...its the only way.
#Post#: 12495--------------------------------------------------
Re: Big castor angles
By: StefanN Date: January 26, 2025, 12:51 am
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Hi Jon
You get the same change of caster effect on semi-elliptic
springs. I’m pretty sure the effect reverses if the shackles
are at the front.
HTML https://youtu.be/n6wii1lW0AY
#Post#: 12496--------------------------------------------------
Re: Big castor angles
By: jon.pearce Date: January 26, 2025, 2:06 am
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Thanks Stefan,
I believe you are right !
Its worth making the point clear that Caster is a "movable
feast" and the angles change during motion! lol
#Post#: 12515--------------------------------------------------
Re: Big caster angles
By: Ade Colmar Date: January 28, 2025, 4:56 am
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It certainly does seem that way! In fact, the more I look into
the front suspension arrangement on my inspiration car (1936
Riley IFS) the more complex it appears to be! Both the camber
and caster increases as the suspension compresses. Also the
heavy rearward suspension arm that stabilises the lower control
arm and takes the braking forces appears to limit the turning
angle of the front wheels. This might not matter too much on a
full size race car but, from the videos I've seen, cyclekarts
drivers seem to need plenty of opposite lock to catch big slides
and prevent spins! :)
#Post#: 12517--------------------------------------------------
Re: Big caster angles
By: TomFDS Date: January 28, 2025, 10:36 am
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Camber gain in compression occurs in pretty much all suspension
systems, as the wheel eventually moves in an arc due to the
travel limits of the pivot points.
Looking at your prototype design I would say you can include the
track control arm without limiting wheel travel, it would still
look right thinned a little bit, due to the relative wheel size
of the CK. Very few people are building a scale model of their
prototype, we want a working vehicle as close as we can get! I
would follow the advice of experienced builders and go for
something that is easy to construct, safe and handles well
enough vs total prototype fidelity. You can always improve a
visual look over time but it’s harder to fix a structural
handling issue!
#Post#: 12522--------------------------------------------------
Re: Big caster angles
By: Ade Colmar Date: January 30, 2025, 3:59 am
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Sound advice, thanks. :) I think a plan is now emerging!
There are no braking forces on the front suspension of a
cyclekart, so the rear control arm can indeed be thinned down a
bit. Also, I will add more mounting points on the chassis for
the top and bottom control arms to allow coarse adjustment of
caster angle. That way I can keep my options open and see how
things work out once my cyclekart is up and running.
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