about ride height

[rafasosa]

I'm investigating about how the behavior of the car changes with an alteration of the ride height, and so far I have only found that by lowerig the car I can get the gravity center lower. But I also know that it affects the weight transference and many other parameters on the car, and my problem is that i haven't found anything about that.

[rafasosa]

I'm investigating about how the behavior of the car changes with an alteration of the ride height, and so far I have only found that by lowerig the car I can get the gravity center lower. But I also know that it affects the weight transference and many other parameters on the car, and my problem is that i haven't found anything about that.

[Brian Smith]

WOW!

and thats why I dont come here anymore...

[BenB]

Rafael, The lowering of the CG is what affects the weight transfer. I don't know what other parameters it would affect as you mentioned.

[Lukin]

It will also effect roll centre heights (therefore ratio's of elastic to geometric weight transfer), squat/dive % as well as the amount of weight transfer (which will effect mechanical and aero balance).

[A Richards]

Sounds like you should change your investigation to how a suspension system works. Absolutely everything will change!!, Roll centres, CG, Roll stiffness, camber, wheel rates, just to name a few. The rates at which these things change will also change.

Any basic book on vehicle dynamics would certainly cover these in great detail.

[Christopher Catto]

hmm, since it looks like you are a beginner (no offence, nobody is master of everything http://fsae.com/groupee_common/emoticons/icon_wink.gif ) I would go by proving some of these guys that you can work it out.

Like many sensibility or max/min studies I would try working out the MINIMUM: how low the car can go before bottoming out (simply calculate it or move some bits in your cad) with some good guesses of acceleration and cornering loads (pitch and roll). worrying about the maximum is a bit silly.

Then I would look at weight transfer and quantify changes in percentage. you know for example that in F1 when they reduced the track of the cars (dist from centre of each wheel to centre of other wheel) it had an effect on cornering speeds. so if your car is lower in theory it will corner better. BUT just think that you may have to have very stiff springs to avoid it rolling and grounding out somewhere. so stiffer springs equals more wt transfer

there's more but i think that's enough for a week or so (couple of days if you like working)

[Lukin]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">BUT just think that you may have to have very stiff springs to avoid it rolling and grounding out somewhere. so stiffer springs equals more wt transfer
</div></BLOCKQUOTE>

Im assuming you didnt write that one correctly; Stiff spring on one end means more WT on that axle (relative to the soft end), but has no effect on the overall amount of weight transfer.

[The AFX Master]

I'm not a suspension guy, but.. isn't the total weight transfer (in steady state) only function of the CG coordinates, car weight, track and wheelbase?.

Although transient is another history, then, how fast the weight transfer occurs depends on the roll and/or pitch stiffness plus the damping response of the suspension. correct me if i'm wrong.

Cristopher said:
"so stiffer springs equals more wt transfer"
If you're talking about a steady state condition, you need to rewrite that as
"so at a greater WT, you'll need stiffer springs"

if you're talking about transient conditions:
"so stiffer springs equals faster weight transfer"

[Lukin]

That's correct AFX.

Though the "so at a greater WT, you'll need stiffer springs" comment is neither here nor there unless your talking about maintaining roll/pitch values (and rates) for an increased amount of WT.

Don't forget elastic:geometric ratio's in your transient discussions. Raising the RC speed up the way the tyre is loaded and I have found it to have, in many cases, more effect on tyre loading/unloading than damper/spring changes (though it seems to be overlooked a little in these forums as FSAE cars aren't usually RC adjustable).

[PatClarke]

Don't forget that from next year (2008) there is a rule about ground clearance. All cars must have a minimum ground clearance of 1" (25mm)
Pat

[Mike Cook]

I kind of thought that was always the rule....

[mtg]

The 1" ride height is already a rule in the US. At FSAE-West '07, I was a tech inspector and used a highly accurate, MIL-spec broom handle to check for minimum 1" of clearance.

Actually, the broom handle was 1.063" or so, and if the car didn't pass the broom handle test, we would have physically measured the lowest point. Luckily, everybody in my queue passed the broom handle test.

[js10coastr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mtg:
The 1" ride height is already a rule in the US. At FSAE-West '07, I was a tech inspector and used a highly accurate, MIL-spec broom handle to check for minimum 1" of clearance.

Actually, the broom handle was 1.063" or so, and if the car didn't pass the broom handle test, we would have physically measured the lowest point. Luckily, everybody in my queue passed the broom handle test. </div></BLOCKQUOTE>

What is this F'ing NASCAR? Mine as well just use "squint calipers".

"...it's a fat eight..."

[kmrobinson]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by js10coastr:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mtg:
The 1" ride height is already a rule in the US. At FSAE-West '07, I was a tech inspector and used a highly accurate, MIL-spec broom handle to check for minimum 1" of clearance.

Actually, the broom handle was 1.063" or so, and if the car didn't pass the broom handle test, we would have physically measured the lowest point. Luckily, everybody in my queue passed the broom handle test. </div></BLOCKQUOTE>

What is this F'ing NASCAR? Mine as well just use "squint calipers".

"...it's a fat eight..." </div></BLOCKQUOTE>

Well, if 0.063" is going to make or break your vehicle, you'd do well in F1 http://fsae.com/groupee_common/emoticons/icon_smile.gif

[PatClarke]

Hi all
There has never been a ground clearance rule in FSAE other than the requirement that the car cannot ground on the track. There was, however, a rule that required 1" bump and 1" droop in suspension travel. That is an entirely different issue.

If you think about it it is quite feasable to have a car with the requisite useable suspension travel, but less than 1" clearance, that will not ground on the track. Many cars have successfully run at less than 1" ride height.

At Detroit, there was an ad hoc decision made by a non technical official to measure clearance with a broomstick, and cars that didn't pass were required to raise the car. I would be interested to hear from any team who were affected by this change.

Several of the professional motorsport judges objected to what they saw as an ad hoc rule change, and the resultant brouhaha saw the Rules Committee introduce a 1" ride height rule at their subsequent meeting.

I have no issues with a ground clearance rule, as long as it can be effectively policed. I do have issue with uninformed rules interpretations being implemented without notice.

I think we will hear more about this.

Cheers
Pat

[Pete Marsh]

Hi Pat,
As I think you have already heard UWA had to lift the car up at FSAE East. We took the car set at around 1/2" under the driver.They wanted to us at have 1" at scrute so we just pumped up the tyres until it passed. But then we were told they would be rechecking during events. We did question the ruling and pointed out there was no rule regarding ground clearence but were told anything on the scrute sheet was a rule and had to be maintained throughout the event.
Our team discussed our options and despite us being in no doubt the car was legal at 1/2" so long as we didn't touch the track we decided to let it go and spend the effort changing and sorting the car. Quite a few teams were affected and none of the really prominant teams looked like they would fight it. It wasn't too flash early on Friday but by the time it mattered it was good enough to win enduro comfortably and score the fastest lap.

I was cut at the time but I'm over it now. As long as they don't change the rule back now the new car is designed to run to it!

As a matter of interest we DID NOT run high enough to pass the 1" with a flat tyre but WERE high enough not to touch the track with a flat. If we had of been excluded for failing the 1" afer enduro becasuse of a flat tyre we would have had plenty to say!

Pete

[Erick Scarpone]

Hey Rafael I see your from Caracas Venezuela, what school are you with, get in contact with Universidad Central de Venezuela Team we have helped before Catolica and IUTEC and some others we have books that will help you and you are more than free to come to take a look at them or if you want you can fotocopy them! go to the web site or contact waldoccs@hotmail.com hes the current president to set a date when you can go there!

Best of luck men and if there anything I can help feel free to e-mail me eass_18@hotmail.com or add me on the msn!

Salu2!

Erick

[The AFX Master]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I'm still looking of ways to get there faster! </div></BLOCKQUOTE>
get rid of 400 pounds

[Robert_USM]

At the UK comp in 07 we got hassle about ground clearance with scrutineers claiming we had to hav 1" clearance. We showed them the rule book to shut them up, but it is now a rule i notice. Under roll having much less than 1" ground clearance can become and issue anyway.

[Patrick]

At Michigan 07 the course workers etc were broom stick nazi's. They were checking for the min ground clearance at the endurance grid AND after (if) you completed the enduro. The minimum ground clearance has been in the rule book for some time now IIRC, but it has rarely been enforced like this past year.

-Patrick DeGrosse Jr.
NASA - Jet Propulsion Laboratory

[Patrick]

Okay I went back and took a closer look at the 2007 rules. As PatClarke said it doesn't specifically spell out a minimum ground clearance. But it says you must have "useable wheel travel of at least 2 inches, 1 inch in jounce and 1 inch in rebound, with driver seated" (2007 Rules, 3.2.3 Suspension, pg 20). Now in order to have a "useable" 1 inch of jounce travel at the wheel, you sort of need the rest of the car to be at least 1 inch off the ground (with driver seated) right? This is analogous to a minimum ground clearance in my book.

-Patrick DeGrosse Jr.

[PatClarke]

Patrick,
The point is there has never been a ground clearance rule! There was a suspension travel rule, but that is NOT the same thing and that was the cause of the disagreement.
The Motorsport judges in particular were upset at the implementation of a 'rule' that didn't exist.
The matter is now moot as there is a ground clearance rule in the books from next year.
Pat

Edit,
You posted as I was posting.
I still disagree that a wheel travel rule is the same as a ground clearance rule! I am not splitting hairs here, you have to think about the entire range of vehicle movement.
Over the years there have been many cars that ran lower than 1", had legal wheel travel and never contacted the ground.
There was a rule where you could get DNF'ed for ground contact.
PC

[John Grego]

Lets say you are running 0.5" ride height. You go into the corner hard on the brakes and front of the car drops to just above the ground. Then you hit a cone with one wheel. The wheel could travel up and the chassis still not hit the ground. This would be an example of a useable 1" of travel (in bump) and less than 1" ride height (static).

[Patrick]

John,

Your example is completely incorrect and irrelevant..... I don't hit cones http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Alright enough talk about min. ride height... it's a rule now and that's all that matters.


-Patrick DeGrosse Jr.
NASA - Jet Propulsion Laboratory

[Kirk Feldkamp]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClarke:
There was a rule where you could get DNF'ed for ground contact.
PC </div></BLOCKQUOTE>

Ya, it's been on the books for years, but it has NEVER been inforced. Having spent a good amount of time on track chasing cones at West for the last couple years, it's quite obvious that said rule is wholeheartedly ignored. At least with a minimum ride height rule there is a static measurement that can be taken to confirm compliance with the rules. I'm a-ok with that.

-Kirk

[Steve O]

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

Your example is completely incorrect and irrelevant..... I don't hit cones http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

</div></BLOCKQUOTE>

Good answer (although it is correct even if it is irrelevant)! I must say that worse then hitting cones, is hitting a manhole cover in our test track that we never noticed before... the pavement happens to rise about 1 inch up around the manhole cover and there is a tiny lip on the cover itself. We didn't notice it until somebody put it in the center of the car and smashed up the car and all of the motor mounts pretty good. Needless to say I think I'll feel more comfortable with our 1.25" clearance this year so I'm not concerned about it being a rule. At least they are putting it in the book this year instead of forcing a non rule on people.

Steve

ps. I have pictures of the damage if anyone is interested!

[Grant Mahler]

Pictures of carnage formally requested!

[Infinity]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">or break your vehicle, you'd do well in F1 Smile


Texas A&M FSAE '08 </div></BLOCKQUOTE>
We participated in FSAE West 2007. We had to inflate our tires much more than their capacity to raise its ride height. We had usable Suspension travel of 2 inches but Radiator pipe was hanging loose for which we had to raise the Chassis more than half inch. That really affected us a lot. So guys be careful on that issue, u never know the judges and your luck [http://fsae.com/groupee_common/emoticons/icon_smile.gif].