HOW TO: Suspension Design

[greenpower dude reloaded]

Ok, as a lot of you will probably have geussed. I am not the person to tell you how suspension should be designed but I think we have such an incredible knowledge base amongst the people that visit this forum, I would be really interested to hear peoples views.

So to get the ball rolling what needs to be considered and what needs to be known before you can begin?

Ok... GO!

[flynfrog]

the type of car and the rule book for starters. What is the end goal for the car?n What type of tires? What type of surfaces.

[greenpower dude reloaded]

Rule book is out of the window. for now this is a hypothetical design, I'm not sure about Tyres, maybe my first how to should have been tyres.

Target speed is about 140/150mph with a 0-60 sub 4 secs vehicle weight 400kg approx 60/40 weight distribution fore and aft any good?

[Jersey Tom]

Picking fore/aft weight distribution comes later down the road.

Step 1 - Determine what kind of track you're going to be at.
Step 2 - Acquire tire data, if possible.

[flynfrog]

Rule book is out of the window. for now this is a hypothetical design, I'm not sure about Tyres, maybe my first how to should have been tyres.

Target speed is about 140/150mph with a 0-60 sub 4 secs vehicle weight 400kg approx 60/40 weight distribution fore and aft any good?

so are you building a drag car a land speed car. Will this car have to turn at speed?

[flynfrog]

http://www.carrollsmith.com/books/

buy all of these

really

[greenpower dude reloaded]

Ok Great well how about this then... http://www.rockingham.co.uk/about/circuits.asp supersport circuit

Not vastly detailed I know but it's something basically we are looking at twisty, relatively short tracks.

I have no idea on what sort of tyre to use? I've only ever used bicycle wheels and it's a totally different science!

I know this is all incredibly vague but I really don't know what needs to be considered and this is the best way for me to learn, I really don't get on with books. [edit] i will try tho flyn

[flynfrog]

Ok Great well how about this then... http://www.rockingham.co.uk/about/circuits.asp supersport circuit

Not vastly detailed I know but it's something basically we are looking at twisty, relatively short tracks.

I have no idea on what sort of tyre to use? I've only ever used bicycle wheels and it's a totally different science!

I know this is all incredibly vague but I really don't know what needs to be considered and this is the best way for me to learn, I really don't get on with books. [edit] i will try tho flyn

he way those books are written is great for gear heads to read. Pick up tune to win first. What type of car are you building here. Electric high performance? What kind of power and weight are you looking at.

[Jersey Tom]

Doing things "the right way," tires will drive most of your suspension design and car setup.

Unfortunately, getting good reliable tire data is difficult at best and impossible at worst. At a minimum, if you know what class you'll be racing in... you can ask some tire suppliers for recommendations on size / construction / compound and design a suspension that will "generally" be good.

Front / rear weight split will probably be driven off of how forward traction limited you think you'll be.

[mx_tifoso]

...

Front / rear weight split will probably be driven off of how forward traction limited you think you'll be.

Can you please expand on this?

[Jersey Tom]

...

Front / rear weight split will probably be driven off of how forward traction limited you think you'll be.

Can you please expand on this?

FSAE car as example, on same (or damn closed to) size tires front and rear.

If I want absolutely max cornering potential (skidpad), I'll want a 50/50 weight distribution.

If I want absolutely max power-down potential (acceleration), I'll want as high a rear weight bias as possible.

Anything else is various shades of in between.

[Ted68]

Old but gold...

Len Terry's "Race car design and development." At any used online book source.

Also Carroll and Steve Smith's books are here...
http://www.cscracing.com/ssmithbooks.html

[marcush.]

I´m not sure if those books are really helpful with suspension layout.

I think first of all your general aims and hard points of the vehicle layout will determine the suspension layout.

so as a first you have to consider the target mass of the car and just were the big masses will be in the vehicle.
JT made it very clear what to look for in terms of weight distribution for different applications ,so compromise starts really ,well at the start.
Of course ,one could start by placing the batteries on a sled and move this ballast for acceleration ,hello DTM of the hightech years...but I think you are not going to
go this far...
with Double a-Arm suspension you will need a lot of internal structure to accomodate
the pickup points ..so packaging might be awkward.there is a reason ,not only cost ,for having dead axles and mcpherson struts...and as we can see from several fine race cars these systems can work just as fine...
so available space /packaging will be a big deciding factor ,I assume ease of manufacturing would also be something to consider as there are enough parts in this sort of car which cost a lot of money..

[greenpower dude reloaded]

annoyingly, my competitive streak is telling me that I should say exactly what my plans are competition wise but I can tell you my aims.

Ideally, I'd like to make this thing 4WD, so there is a factor to consider, I think the weight balance should be pretty close to 50/50 but this could be changed to suit.

The competition it's designed for has no restriction on Tyres but something sensible is what we are after. Accelleration is incredibly important for the circuits it's intended to run at although none have been announced the Rockingham Layout I mentioned is highly likely.

This vehicle won't be your standard sort of electric car either so I think wishbone style suspension would be ideal from a packaging POV. Be it that or rocker arm (which I love the thought of)

[RacingManiac]

I´m not sure if those books are really helpful with suspension layout.

I think first of all your general aims and hard points of the vehicle layout will determine the suspension layout.

so as a first you have to consider the target mass of the car and just were the big masses will be in the vehicle.
JT made it very clear what to look for in terms of weight distribution for different applications ,so compromise starts really ,well at the start.
Of course ,one could start by placing the batteries on a sled and move this ballast for acceleration ,hello DTM of the hightech years...but I think you are not going to
go this far...
with Double a-Arm suspension you will need a lot of internal structure to accomodate
the pickup points ..so packaging might be awkward.there is a reason ,not only cost ,for having dead axles and mcpherson struts...and as we can see from several fine race cars these systems can work just as fine...
so available space /packaging will be a big deciding factor ,I assume ease of manufacturing would also be something to consider as there are enough parts in this sort of car which cost a lot of money..

IMO thats backward. As JT mentioned, you want to figure out what tire you are using and use that as a start. Tire size drives wheel size, which can determine outboard pickup extremities. If you have tire data, you can put the kinematic into the window which the tire works, use that to drive your camber curve and steering geometry, and that should spit out what you need in terms of hard point location, and make a chassis that connects the dot, compromise packaging where needed. Given relative freedom you should be able to make a chassis that works for your desired suspension. Not the other way around I think. Now if you use a ton of aero though, that might put other things ahead of pure tire/kinematic consideration, which should just mean that you are shrinking where the hard points can go.