CM category suspension design

[delacf]

Greetings. I want to design a suspension for a vehicle of the category CM (hill climb races) as bango, Jema, Speedcar, Silver car... The weight of the vehicle must always remain above the 550 kg. Tires that I use are the A15 AVON crossply 13 inches in diameter. How I can know the values of scrub, Kingpin, caster, camber which are more convenient. Thank you very much

[Caito]

You could buy or use a trial of a suspension software.

There's susprog3d and mitchell to try out there I think.

CAD programs may be useful too.

[delacf]

Thank you very much

[mep]

Those programmes will not tell you what kind of values you need they just tell you how the values change during car movement.
I think you should have a look into a related book (race car vehicle dynamics is always a good recommendation) or you check out how existing cars look like.
Yea maybe best start is to copy some existing cars.

[747heavy]

as it looks like, your serie uses an spec tire, first and foremost you should try to gather as much data as possible about the tire.
Avon is normally quite open, when it comes to their tire data.
But I did not find a download on their website for your tire.
http://avonracing.com/Downloads.aspx
So maybe it´s worth to call or e-mail them.

This will give you some informations in regards to the camber and toe settings you should run.
It will give you also some ideas about how much load your tires are able to carry and how their grip will change with different vertical loads.
These informations are important to define the load transfer you would like to have in your car.
Keep in mind that hillclimb is a bit specific, compare to road racing, as you race normally only up-hill, this fact you should keep in mind, when you assess your load tranfer.
Do you only race at one track/hill or do you have different tracks/hills?
Try to find informations about the tracks/hills.
What is the inclination, what are the corner radiuses, what are the corner speeds?
Group them, and see if you have a predominat combination.
For example maybe 45% of all corners are 50-65 km/h midcorner speed at an 25% inclination etc.
If you find some things like this, it is maybe worthwhile to consider a optimization for this type of corner.
But before you start to draw a line on paper or in your CAD progam, and design your suspension, you need to know your tires first.
Every thing else could be fruitless, unless you get very lucky.

As mep mentioned, have a look at some of the winning cars in your class.
It will give you a feel, for the ballpark in which you should end up with your design.
But remember, it is only worth to copy something, that you fully understand.
You will need to know/understand why these guys designed their suspension in the way they did.

some examples for useful tire data ( if the data is correct







Good luck

maybe some additional reading on the matter of how to use tire data for your design
http://www.smithees-racetech.com.au/ackerman.html

[marcush.]

before copying an existing design It might be a GOOD idea to look at their tyres directly after a run.or after a whole day of competition.
To be at the finish line area before the cars are guided down the hill is a good idea ..and possibly the drivers are still pumped up willing and able to tell from fresh experience what the tyres do on the run.Maybe you offer to supply tyre temp data to them ...to be allowed to measure...
so from this feedback and what you can gather in terms of layout-a lot of things like Ackerman ,caster ,castertrail,KPI and Antidive geometries you can see a lot in the paddock maybe the technical guys are willing to explain some things on geometries as well(if they know).
Take a good look at the tyres and have a IR pyrometer to hand to see the temps of the good cars (and the temp spreads ).so you will know what works for them.But usually the lower the better with soft "hill" compounds...

[delacf]

Thank you very much everybody. I liked very much your comments =D> .

The first is the data about the tires but I have a problem:

What can be done when the manufacturer says: "compound A15 is very soft therefore the results from test rig can be inconclusive."

The tyres are AVON crossply A15. 7,2-20,00-13'' front and 8,2-22,00-13'' rear

Thanks, I'll do what you said to me

[marcush.]

You will be good advised to look at the tyres the front guys are using .
the really soft compounds are quite delicate and maybe some of the competitors go as far as shaving new tyres -get rid of some tread thickness to avoid graining and tearing of the tread as normally you will not see a lot of wear with the few runs you do over a weekend.
then the next question is how will these supersoft tyres behave after being used one weekend and then stored for the next event ...will it help to keep them stored under special conditions packed into vaccum bags or does nothing help and you just need new ones if you want to be quick..
But of course the first step is to get an idea why some cars are performing better than others .Go out and look at the key points of the track -hairpins ,power down conditions corner exit corner entry.. and then take a look in the paddock and try to figure out what the differences in setup and geometry may contribute to this behaviour.

[747heavy]

Is the Avon A15 like a "controlled" tire in your class/formula?
Meaning that all cars in the class have to use this tire and compound at all times?
Or is it "just" your tire of choice?

very soft compunds are usally quite temperature sensitive, so you may need/want to be careful how hard you "push" your tire in hot/warm conditions.
That usally has an influence in damper and spring choice, among other things.

Avon should still be able to give you some guidance as far as camber and toe (slipangle) settings go. This is more based on the construction of the tire, then on his compound. But I can see, that they may struggle to complete a test cycle with a very soft compound without overheating the tire in the process.
Avon should also be able, to tell you the "target" temperature range, for which this tire/compound is designed, otherwise it´s a bit hard to design a car/suspension to make the tire work well.

[mep]

Tyre related values like camber, caster... should be made adjustable anyways so I don't see a reason to think about them to much in an early design state.
Care more about the parameters that are hard or impossible to change once build in the car.

Start with a basic design concept how the car should look like:

-car weight you are targeting for
-will you get any downforce devices?
-what engine will you use, (check the values power, weight and fuel consumption, also check the revs and torque just to see if the engine has good driveability)
This will give you a power to weight value.


Depending on the rules you can basically go 2 roads then (not valid with the F1 rules):
- have a heavy car with stronger engine
- have a light car with weaker engine

- next thing to care about is centre of gravity location lengthwise and height
- car length
- car width
- engine, driver fuel tank... position

- also decide how your chassis should be build, steel-tube-frame, composite chassis or something else.

Then concentrate on your suspension.
- rollcentre position
- instant centre position
- anti dive/squat
- a couple of other things too

Until this point you have not designed a single part in detail you just do a basic layout.

Thats something like a very rough guideline how to start. Some of the parameters go hand in hand and have to be decided on the same time. Building a performance car is a difficult task so you have to reduce it to simple decisions and go step by step. Don't waste to much time caring about things you can adjust and test later when you have build the car.

[marcush.]

of course the question was suspensiondesign but mep is right in his view of keeping things adjustable as much as possible.
even things like antidive can be kept adjustable .
but some figures like kpi/offset (scrub radius), caster trail and Swingarm length
are things to consider early on just because you will have a big hassle to correct those once you are into the project.

[747heavy]

Tyre related values like camber, caster... should be made adjustable anyways so I don't see a reason to think about them to much in an early design state.

Camber gain in roll / steering comes to mind.

as we have just seen in F1, CoG position is very much tire dependend.

rollcentre/axis position has direct influence on your load transfere, what do you aim for, if you don´t know your tire?

I haven´t seen any successful race car which was not designed with his tires in mind first.

I agree, that you can (and should in the beginning) make things adjustable, on the other hand, it means these things are usally less stiff and heavier then they need to be, if you know which values you want/need.

Seems to be an interesting category, just did a quick check.
1000ccm motor bike engine with 150-170hp

Looks like the Bango cars run very little camber, at least on the few photos on there website.
Weight seems to be important in that class, and they look a bit at aerodynamics as well.
I would consider a pedal shift system for these cars, if permitted by the rules, should not be too difficult with an motor bike style sequential gearbox.

[Jersey Tom]

Alternatively, if you don't feel 100% comfortable with tire / vehicle dynamics and simulation... build something reliable with some adjustment, get out and start testing.

[marcush.]

Alternatively, if you don't feel 100% comfortable with tire / vehicle dynamics and simulation... build something reliable with some adjustment, get out and start testing.

the more you know...
I´m pretty sure the iterative way will be a good choice for a non worksteam and good fun as well as you improve the car.
I´d think a sound not flexi car that is not overweight will be a good starting point.First of all you need reliabilty .

Virgin lotus and dallara build cars 7% off the pace with all their possibilities..so to think you can come and show up with a world beater in your forst attempt will only be possible if the established cars are total crap.

[delacf]

Is the Avon A15 like a "controlled" tire in your class/formula?
Meaning that all cars in the class have to use this tire and compound at all times?
Or is it "just" your tire of choice?

Yes, all cars fit the same tires.

Looks like the Bango cars run very little camber, at least on the few photos on there website.

I agree. In any photo can be seen Camber.

I would consider a pedal shift system for these cars, if permitted by the rules, should not be too difficult with an motor bike style sequential gearbox.

Yes, mounted sequential gearbox.

Seems to be an interesting category, just did a quick check.
1000ccm motor bike engine with 150-170hp

Hill Climb Tamaimo (Canary Islands, Spain)

average gradient of 6.5%
total length of approximately 5550 km

2008 (Impreza WRC 3:09.034, Bango 2:59.289)
2009 (Ferrari 360 3:13.119, Bango 2:58.909)

Hill Climb Arucas (Canary Islands, Spain)
[youtube]http://www.youtube.com/watch?v=xQNvyrMUpEs[/youtube]