suspension geometry draft

[josh2417]

Guys we are a rookie team. Doing FSAE for the first time. Would like to know if this suspension geometry is OK?
any suggestions and advice is more than welcome
Weight is 450kg with driver
Caster is 7 deg
Camber is 2 deg negative
Scrub is 29 mm
king pin is 2 degree
The suspension analyse data is shown in the pics
http://img841.imageshack.us/img841/5687/sup3j.jpg
http://img217.imageshack.us/img217/1051/sup1p.jpg
http://img192.imageshack.us/img192/3825/sup2n.jpg

[josh2417]

Guys we are a rookie team. Doing FSAE for the first time. Would like to know if this suspension geometry is OK?
any suggestions and advice is more than welcome
Weight is 450kg with driver
Caster is 7 deg
Camber is 2 deg negative
Scrub is 29 mm
king pin is 2 degree
The suspension analyse data is shown in the pics
http://img841.imageshack.us/img841/5687/sup3j.jpg
http://img217.imageshack.us/img217/1051/sup1p.jpg
http://img192.imageshack.us/img192/3825/sup2n.jpg

[Luniz]

How do you justify the positive camber? Your camber gain is -1.27deg through the suspension travel, so it would still be positive in full bump and even more so in roll. And why is your car so heavy?

[josh2417]

Luniz
Thanks mate for your advice. Guess i got the camber wrong, but shouldn the KPI be equal to the Camber???
With respect to the weight, this car is actually for the Indian FSAE event called the SAE Supra. The teams are required to use a Suzuki engine being used in a car. 800cc. You arent allowed to do any modification to the engine. And the engine weighs an enormous 120 kg!!!!!

Forgot to mention the Wheel track =50 inches
wheelbase=63 inches
roll center height is approx 3 inches
ride height is 4 inches
cheers

[Dash]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
but shouldn the KPI be equal to the Camber???

cheers </div></BLOCKQUOTE>

No. I would say that it might sometimes be the same depending on what you are doing. I would suggest you try reading some books on suspension design. Also, feeling nice today so here is my tip. Shoot for keeping the tire between 1 and 3 degrees negative camber. I have no idea what tires you are running, but I'm sure that it wouldn't be worse than running positive camber.

[josh2417]

Dash
Thanks for your tip mate.Ya sure will read through RCVD again. We are running Apollo Accelere 155/70R13 because slicks are not allowed. And the width is limited to 155 mm max by the organisers.

[josh2417]

And the tire manufacturer is not giving out the tire data, so we skipped the tire data reading part!!!!

[manifold]

mrf provides you guys slick, dont say you don't get

[josh2417]

manifold,
mrf does have slicks but as per the rules of the Supra SAE, the tread width is limited to 155 or 165. But the mrf slicks are 205mm when i checked their products.

[Adambomb]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
And the tire manufacturer is not giving out the tire data, so we skipped the tire data reading part!!!! </div></BLOCKQUOTE>

Just because you don't have tire data doesn't mean you can skip out on reading about tires! There are many many things about the behavior of tires in general that should be the primary influence in your suspension design. Like for example not running positive camber. Positive camber is a terrible, terrible thing, why would anyone want to do that???

As for slick sizes (or any tire sizes in general), always remember that the number on the side won't always match the measured dimensions of the tires. For example, if you take two tires with the same numbers on the sidewall, one being an el-cheapo mega-budget all season tire, and the other one being, say a Cooper Cobra GT, the Cooper will be noticeable larger. The Cooper Cobras on my Firebird are factory original size on the original rims, but are wide enough they rub the inner fenders a bit.

IMCA Hobby Stock racers, who have simlar tire size restrictions, use this to their advantage, and to better get their car to "go fast, turn left" will intentionally run different model tires, which are quite different in size but all say 205/70R15 on the sidewall on different corners.

I'm not familiar with those tires, but I could imagine something labeled as a 155/70R13 measuring as wide as 205 mm.

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:

Weight is 450kg with driver
</div></BLOCKQUOTE>

Are you building your frame out of lead? You'd have to try (or not try) pretty damn hard to build a car that heavy. Just sayin. The average FSAE/FS car probably comes in at no more than 320kg or so with driver. So if you want be at all competitive you should shoot for around there.

[Adambomb]

This is why their car is so heavy, it's for the SAE Supra event in India.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
Luniz
Thanks mate for your advice. Guess i got the camber wrong, but shouldn the KPI be equal to the Camber???
With respect to the weight, this car is actually for the Indian FSAE event called the SAE Supra. The teams are required to use a Suzuki engine being used in a car. 800cc. You arent allowed to do any modification to the engine. And the engine weighs an enormous 120 kg!!!!!

Forgot to mention the Wheel track =50 inches
wheelbase=63 inches
roll center height is approx 3 inches
ride height is 4 inches
cheers </div></BLOCKQUOTE>

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Adambomb:
This is why their car is so heavy, it's for the SAE Supra event in India.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by josh2417:
Luniz
Thanks mate for your advice. Guess i got the camber wrong, but shouldn the KPI be equal to the Camber???
With respect to the weight, this car is actually for the Indian FSAE event called the SAE Supra. The teams are required to use a Suzuki engine being used in a car. 800cc. You arent allowed to do any modification to the engine. And the engine weighs an enormous 120 kg!!!!!

Forgot to mention the Wheel track =50 inches
wheelbase=63 inches
roll center height is approx 3 inches
ride height is 4 inches
cheers </div></BLOCKQUOTE> </div></BLOCKQUOTE>

Must have overlooked that. lol
Thanks

[josh2417]

adambomb

my bad. ans ya surely will try looking for such tires, but looks to me like its a gamble, because if the organizers during scrutiny find it out then we might well be on our way out.

robbyobby

lol. We aint building it out of lead. Its just that the engine, gearbox and differential is sponsored by Suzuki and comes sealed. You cant do any modification except a free flow header and possibly fit in a K&n with ss piping.And it weighs 120kg while putting out a mere 37BHP. This year we are trying to make it as light as possible, we are looking somewhere around 320kg without the driver.

[Aditya RS]

http://www.spideralfaromeo.it/images/1950Fagioli58.jpg
http://www.imcdb.org/i046213.jpg

These are pics of the 1950 Alfa Romeo 158 'Alfetta'

Quote from Wiki<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> ...is one of the most successful racing cars ever produced. The 158 and its derivative, the 159, took 47 wins from 54 Grands Prix entered. </div></BLOCKQUOTE>

Just out of curiosity, what part of the geometry in these cars influenced them to have positive camber?
I have noticed this in many other old open wheel cars too.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Adambomb:
... Positive camber is a terrible, terrible thing, why would anyone want to do that???
</div></BLOCKQUOTE>
Adambomb and Aditya,

Just my opinion...

In the really olden days the carts had positive camber to keep the wheels on the axles. That is, the axle sloped down at the outer end, so the wheel kept riding up towards the inner shoulder.

Around the time of the Alfa they had wire-spoked wheels with wide hubs surrounding the bearings. No room for a king-pin in there so it had to be offset towards the car centreline. And since there was no power steering (other than massive diameter steering wheel) it made sense to minimise "scrub radius" by having approximately equal king-pin inclination and positive camber.

Furthermore http://fsae.com/groupee_common/emoticons/icon_smile.gif, the tall narrow tyres were not too adversely affected by bad camber. And most of the racing was town-to-town along relatively straight country roads, with only the occasional manic four-wheel-drift at the town square, then on to the next town. Which was down a dirt track... So cornering power was not a major concern.

Oh, yes, and perhaps most importantly. Positive camber was very much the fashion at the time! It was often exaggerated in the dramatic race posters, like a manly torso, or a V for Victory! SEXY!!!http://fsae.com/groupee_common/emoticons/icon_smile.gif

(Edit: By comparison, negative camber looks like a fat-arsed slob with narrow shoulders!)
(Or a broken axle...)

Z

[JT A.]

Wow, so positive camber was like the "hella flush" fad of the 50s http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[DougMilliken]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">In the really olden days the carts had positive camber to keep the wheels on the axles. </div></BLOCKQUOTE>
Another version, as heard from a very serious collector of horse drawn vehicles--positive camber was used to throw mud (and horseshit!) away from the vehicle and occupants. With coned wheels, the combination of +camber and coning set the lower (compression) spokes vertical for load carrying.
As an aside, a high end sporting carriage is a marvel of lightweight design, just like a good racecar.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Furthermore http://fsae.com/groupee_common/emoticons/icon_smile.gif, the tall narrow tyres were not too adversely affected by bad camber.
</div></BLOCKQUOTE>
From a different source--the T35 Bugatti (even more successful than the Alfa noted earlier) had an aft CG. Bugatti may not have known why, but positive front camber reduced front cornering ability enough to keep the car from being completely tail happy. The T35 Bugatti is known for well balanced handling.
It's fun to speculate about engineering history!

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DougMilliken:
It's fun to speculate about engineering history! </div></BLOCKQUOTE>
Doug, to further speculate, I reckon as carts grew up and got bigger (a natural process), the designers might have wanted to keep the ground level track the same, so as to better follow the existing wheel ruts. The requirement to provide more room for a wider payload would then have led to positive camber and coned wheels. "Yes, more room AND it throws the shit away!"

And with hundreds of years of such an established fashion trend, always to a wider V, who would have dared suggest "leaning the wheels in"!!! http://fsae.com/groupee_common/emoticons/icon_eek.gif

Z

[DougMilliken]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">...And with hundreds of years of such an established fashion trend, always to a wider V, who would have dared suggest "leaning the wheels in"!!! </div></BLOCKQUOTE>
Are you fishing for links to my father?? Getting further and further off topic, but if so, here you go--
http://www.latphoto.co.uk/tags...width=550&height=464 (http://www.latphoto.co.uk/tags/search/photos/882818?width=550&height=464)
He was looking for more grip in the late 1950's, before wide tires were invented. Influences include the Kieft rear suspension,
http://www.500race.org/Marques/Kieft.htm
and tire test data at high camber angles. Many details in his book (shameless plug),
http://www.bentleypublishers.com/milliken
And a teaser,
http://www.multimatic.com/news/release.php?release=43

[wil oberlies]

Going further off topic....anyone here who has yet to read "Equations of Motion" must do so. An incredible book by a man who has made huge contributions to engineering. It should be read by everyone who aspires to be a great engineer and/or has an interest in reading about an extraordinary life.

[js10coastr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by wil oberlies:
Going further off topic....anyone here who has yet to read "Equations of Motion" must do so. An incredible book by a man who has made huge contributions to engineering. It should be read by everyone who aspires to be a great engineer and/or has an interest in reading about an extraordinary life. </div></BLOCKQUOTE>

...or if one plans to build a camber car.