Freestyle Suspension Geometry

Anything Buggy suspension and running gear related
User avatar
Lilspeed
Posts: 288
Joined: Mon Jul 25, 2011 11:54 am
Location: Yeovil

Freestyle Suspension Geometry

Postby Lilspeed » Mon May 02, 2016 10:19 am

OK, had a good catch up with the Muddybuggies Massive at Stoneleigh yesterday, and talk turned to wayward handling and suspension geometry.
Now, I've had my fair share of buttock clenching moments in my own and other people's buggies, and decided when I started my own build that getting it to handle as best it could was one of the main priorities.
So, a bit of background so you don't all (Ok maybe some of you don't :-) )think I'm talking out my arse! I am a qualified Mechanical Engineer and have messed about with Mini's for more than half my life, with my old blue one developing in to a 1293cc fast road/track stormer, giving me lots of experience with geometry and it's effects. As well as my 'experiments' with the buggy I also help out with development of a friend's supercharged mini competing in the DEWS Speed Hillclimb series.
I don't have a garage full of expensive alignment equipment. My 'toolkit' consists of a 60 quid laser tracking kit from eBay, a tape measure, spirit level, and various lengths of metal and wood considered straight enough for the job! I don't feel that full four wheel laser alignment is at all necessary unless your vehicle has fully rose jointed suspension eliminating all the variation in geometry that is inevitable with bushed suspension.

So, in trying to give a Freestyle road manners the first point is - the standard Freestyle geometry. Too much negative camber on the front. The reason for this is the kit was designed for off roading with the huge camber angles allowing chunky tyres to bite into the dirt and make up for the lack of front end weight and grip. On the road, this makes for very aggressive turn in - often making the back end feel loose as a result, slow speed under steer as the lack of body roll fails to increase the tyres small contact patch, and a lack of steering self centring. The answer is obviously to reduce the camber angle with adjustable arms. I first tried sticking with the tried and tested figures I liked on my Minis. 0.75 deg Neg at the front. Measured and adjusted with the car on level ground using my spirit level and some trigonometry.
(Tan0.75 x wheel rim dia) gives you the gap between spirit level and top of the wheel rim when the camber is neg 0.75 deg and the spirit level is vertical. Gap at the bottom for positive camber.
This, running 0.1 deg of toe-in improves matters considerably and I moved on to setting up the back.
A standard Mini front subframe runs positive camber in the order of 0.5 to 1 deg. Totally unsuitable for the rear of a mid engined car unless you like the back end VERY loose. *Snigger*
So, another pair of adjustable arms were set to give 0 deg camber. I then set 0.2 deg of toe-in at the rear to give a bit of stability and started testing. (A straight piece of wood/metal held against each rear wheel, and an equal gap to the same point on the chassis each side aligns the rear wheels with the chassis)
In the time with this set up I found the main issue to be general instability. Changing lanes at 70(ish) required the minutest steering input and the reactions of a fighter pilot. Bumpy roads at speed would make the buggy change direction all by itself no matter how straight the steering was held.
I continued wrestling the buggy around Darkest Somerset for a while and the solution occurred to me while following a Lotus Elise and looking at it's wheel angles.
I had completely overlooked the fact that I was using geometry settings for a front engined car whilst trying to set up a mid engined car.
Next time you have the pleasure of being near a mid/rear engined Porsche or Lotus, take a look down the side of the car from the front or rear and look at the wheel angles. Generally - positive camber at the front to give a slow progressive turn-in without flinging the weight in the back end around, and negative camber at the rear to allow the weight to press the contact patch onto the tarmac as it sits into a corner.
The next nice day I headed to the workshop. This time I tried;

Front - 0.5 deg positive and 0.1 deg toe-out.
Rear - 1.5 deg negative and 0.2 deg toe-in.

And the buggy is now stable to the point of almost being boring! No more twitchy lane changing, one hand on the wheel down the bumpiest roads I can find and much improved self centring. Even if I give it a monstrous Scandinavian flick on a quiet (private) roundabout it just turns nicely into a balanced four wheel drift.
This is the set up that currently remains, but I am considering reducing the rear camber just to loosen up the rear a bit and keep things fun!

Right, if you made it this far, well done you deserve a cup of tea and a biccy.

Hope this is of some help to the people who are looking to improve their buggy's handling.

User avatar
Phaeton
Posts: 4722
Joined: Mon Jan 29, 2007 9:13 pm
Location: Worksop
Contact:

Re: Freestyle Suspension Geometry

Postby Phaeton » Mon May 02, 2016 3:47 pm

WOW I made this far but I don't like tea is coffee & a granola square a suitable alternative?

But very interesting reading from somebody who actually understands what is happening rather than me who changes something & hours for the best.

Just for clarification negative is top in bottom out & positive is top out bottom in?

Which means I think I need some new front bottom arms to get the wheels to stand up more as currently I'm running quite a bit of negative on standard arms.

Sent from my SM-T330 using Tapatalk
Muddybuggies FMR Member You Know It Makes Sense

User avatar
Lilspeed
Posts: 288
Joined: Mon Jul 25, 2011 11:54 am
Location: Yeovil

Re: Freestyle Suspension Geometry

Postby Lilspeed » Mon May 02, 2016 8:04 pm

Cheers! Was just going to post my settings but thought a bit of an explanation might be useful.

Phaeton wrote:
Just for clarification negative is top in bottom out & positive is top out bottom in?


Yup!

Phaeton wrote:WOW I made this far but I don't like tea is coffee & a granola square a suitable alternative?


Don't see why not Alan, although I might draw the line at anything chocolate topped. You didn't do that well.

:)

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Mon May 02, 2016 9:08 pm

Epic... going to try these :-)

Sent from my SM-N910F using Tapatalk
Image

User avatar
Phaeton
Posts: 4722
Joined: Mon Jan 29, 2007 9:13 pm
Location: Worksop
Contact:

Re: Freestyle Suspension Geometry

Postby Phaeton » Mon May 02, 2016 10:25 pm

What bottom arms are you using, the big adjustable ones normally don't pull in far enough to give positive camber

Sent from my SM-T330 using Tapatalk
Muddybuggies FMR Member You Know It Makes Sense

User avatar
Lilspeed
Posts: 288
Joined: Mon Jul 25, 2011 11:54 am
Location: Yeovil

Re: Freestyle Suspension Geometry

Postby Lilspeed » Mon May 02, 2016 10:58 pm

I'm using these front and back;
http://www.ebay.co.uk/itm/Adjustable-Ca ... SwM0FXILL-

You're quite right Alan, I had to cut a small amount off each end of the threaded parts of the arms to be able to get positive camber.

User avatar
Phaeton
Posts: 4722
Joined: Mon Jan 29, 2007 9:13 pm
Location: Worksop
Contact:

Re: Freestyle Suspension Geometry

Postby Phaeton » Tue May 03, 2016 12:38 pm

Justin, You have now become my least favourite person :D I liked your idea so much that I decided to buy those adjustable arms, then I thought well if I'm stripping the suspension down I might as well replace the steering rack that has been an advisory on the last 2 MOT's, so from a nice post to costing me over £150 is not good for a Yorkshireman, I'm having to lie down for an hour to get over it :D

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Tue May 03, 2016 2:39 pm

yeah I know...

a quick facebook message earlier just cost me £300 and I think I need to spend more....

User avatar
Phaeton
Posts: 4722
Joined: Mon Jan 29, 2007 9:13 pm
Location: Worksop
Contact:

Re: Freestyle Suspension Geometry

Postby Phaeton » Tue May 03, 2016 3:42 pm

Stop showing off

Sent from my SM-G900F using Tapatalk
Muddybuggies FMR Member You Know It Makes Sense

User avatar
Lilspeed
Posts: 288
Joined: Mon Jul 25, 2011 11:54 am
Location: Yeovil

Re: Freestyle Suspension Geometry

Postby Lilspeed » Tue May 03, 2016 6:12 pm

:o :o :o

*Fetches coat* . . . . . . . . . .

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Tue May 03, 2016 6:29 pm

Lol

Sent from my SM-N910F using Tapatalk
Image

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Tue May 03, 2016 6:30 pm

On a side not 500 quid gets you some 4 wheel alignment guages

Sent from my SM-N910F using Tapatalk
Image

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Mon May 09, 2016 1:52 pm

Right So I bought some gauges :D

Pick them up wednesday :D They do 4 wheel alignment and all the camber caster the lot... So I should be able to set the buggy up perfectly... why I did not do this 10 years ago....

User avatar
Phaeton
Posts: 4722
Joined: Mon Jan 29, 2007 9:13 pm
Location: Worksop
Contact:

Re: Freestyle Suspension Geometry

Postby Phaeton » Mon May 09, 2016 3:07 pm

Because for £500 you're going to be pulling the little bit of hair that you have out when you try to use them

User avatar
Danny
Posts: 4226
Joined: Wed Jan 17, 2007 9:23 pm
Location: Middleton On Sea
Contact:

Re: Freestyle Suspension Geometry

Postby Danny » Mon May 09, 2016 6:45 pm

Haha nah I get how they work....

Sent from my SM-N910F using Tapatalk
Image


Return to “Suspension And Running Gear”

Who is online

Users browsing this forum: No registered users and 3 guests