Wheel travel

[Benz]

I need an advice here. In the rules, it is written that the suspension must allow 1" of rebound and 1" of jounce with driver seated.

To me it sound that when the driver is seated, the the car drop by 1". If so, well the coils must be really soft...can someone help me on this, I'm as bad a newbe can be!

Benz

[Benz]

I need an advice here. In the rules, it is written that the suspension must allow 1" of rebound and 1" of jounce with driver seated.

To me it sound that when the driver is seated, the the car drop by 1". If so, well the coils must be really soft...can someone help me on this, I'm as bad a newbe can be!

Benz

[GTmule]

So like, when the driver is ALREADY in the car, you should have no less than two inches of avaliable suspsnsion travel......1 inch of which should be up, and one in down.

[Matt Gignac]

What this means is once the driver is seated, you need to still have one inch of wheel travel in each direction. So let's say the driver getting in lowers the ride height by 1/4", this means you need at the very least 1.25" of rebound and .75" of jounce travel.

Matt Gignac
McGill Racing Team

[awhittle]

I like 4" total travel The first inch is taken up with just the sprung weight of the car including the driver. The other 3 " accounts for the next inch being taken up when at full cornering and the car just happens to hit a large bump on that loaded side of the car. Do not saaume that if the car has 1.5" of ground clearance at the front you only 1.5" inches of additional compression travel. You always want to ground the chassis before you ever bottom the suspension.

Hope this helps

AW

[mtg]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by awhittle:
You always want to ground the chassis before you ever bottom the suspension.

AW </div></BLOCKQUOTE>

I wouldn't say you always want the chassis to ground first. Sometimes it's good, sometimes not.

If you have a carbon tub for example, you probably wouldn't want to do 400 hours of repair after everytime you take it to Forbe's Field.

[Erich Ohlde]

I agree with mtg. We have the suspension setup to bottom about 1/16 before we grind carbon http://fsae.com/groupee_common/emoticons/icon_frown.gif. and we also run a 15 layer kevlar skidplate.

It also sucks to break a pullrod rod end and grind to a halt from 60 mph, the tub didn't appreciate that one.

[awhittle]

I never said that you want to hit the chassis on the ground very often. There has to be some sort of material that is designed to protect the main chassis for the ocational hit. This is huge with the 1/4" 5/16" rod ends that are that the FSAE care use for suspension. Springs are used to keep the chassis off the ground.

AW

[Kevin Hayward]

The rule is a funny one. The suspension must allow 1 inch of travel in either direction. But does allow mean that it will actually happen during a run?

Some cars are sprung so stiffly that it will never happen.

Some cars effectively run systems to limit droop.

Some cars have less than an inch ground clearance.

These cars do not get penalised. Nor do I think they should. The idea behind the rule is to make sure that each car has a suspension system - at least that is what Carroll Smith once told me. Once the system is on the car it should be the teams priority as to how to use it.

By the way UWA runs a skidplate at the bottom of the composite tub. Except we always called it a bashplate. Very fitting if you have a look at the bottom of it after testing etc.

Kev

[kwancho]

Yeah, that's a good question. For those teams with potentiometers on their dampers, how much travel do you actually end up using?

edit: I actually tried to BS my way through a graphical model of what I expected suspension travel in an F1 car to look like through a corner (with things like downforce and weight transfer factored in). I don't think I got it anywhere near right, but I'd be interested to see a graph of an FSAE car's.

[mtg]

Erich,

That's funny- my comment of bashing tubs at Forbe's Field came from when I drove your 2003 KU car there and felt the tub bashing the pavement in every corner.

I wasn't even on the team and it made me cringe.

[Frank]

looking at numbers:
220kg car
70kg driver
11 kg unsprung per corner
1000 lbs/" tyre vertical spring constant
50:50 longitudinal weight distribution
no droop limitting / preload (as it shold be IMO)

1" bounce / jounce rule
driver seated is static position, and 1" either way is available

would mean unsprung naural frequencies around 3.1 Hz

we were running about 2.9 front, 3.9 rear (which is very tight, Werribee is smooth) and nobody raised an eyelid. we've run frequencies this high for 3 years

i've seen fsae cars hit the ground quite a few times and not get kicked off the enduro...

IMO the "car should not touch the ground" rule is inforced pretty stringently. I think it should be enforced, to avoid bodywork being scattered, and to discourage sliding skirt aero

[Erich Ohlde]

Was that the year when UMR broke a halfshaft at nats'? The chassis must have been scraping cause of Clancy's cream cheese doughnuts http://fsae.com/groupee_common/emoticons/icon_wink.gif. You should see that tub now! the floor plate deflects about 1/8 inch if you step on it and the front suspension had 1/4 inch aluminum plates tying all the mounting points together to keep the mounts from breaking through the chassis. That chassis has since been retired and poses as a "what not to do" poster child in the corner of our shop. although the new tub for it is pretty sturdy but the car doesn't drive anymore... oh well. And don't even get me started on the carbon fiber rear housing, that was even worse!

[mtg]

Let's not talk about the days of breaking halfshafts. That sucked. And yes, that was the year they broke at Nationals. Instead of practicing technique and race lines, I was trying to rig up a halfshaft from some spare crap we had in the trailer, a mig welder, a small torch, and some sandpaper. Drivetrain McGyver style.

There were Clancy's cheese donuts involved.....they were also involved in 2004 when Mike Murray had to drive back to Rolla one night for an engine swap between runs.....hmmm.

As far as the wheel travel goes, you can always add helper springs to give the suspension some "dummy travel" to meet the rules.

[markocosic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mtg:
As far as the wheel travel goes, you can always add helper springs to give the suspension some "dummy travel" to meet the rules. </div></BLOCKQUOTE>

Dummy travel might meet "the letter of the rule" but would you not get pulled up on "the spirit of the rule" for not making a serious enough attempt at it?

[Denny Trimble]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mtg:
Let's not talk about the days of breaking halfshafts. That sucked. And yes, that was the year they broke at Nationals. Instead of practicing technique and race lines, I was trying to rig up a halfshaft from some spare crap we had in the trailer, a mig welder, a small torch, and some sandpaper. Drivetrain McGyver style.
</div></BLOCKQUOTE>

Hehe... I remember you asking me about proper stress relieving technique with a freshly welded halfshaft in one hand, and a propane torch in the other http://fsae.com/groupee_common/emoticons/icon_smile.gif

About an hour later, I remember seeing your car do the one-tire-fire off the line in front of me. D'oh!

Aren't racecars fun!?

[mtg]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Denny Trimble:
Hehe... I remember you asking me about proper stress relieving technique with a freshly welded halfshaft in one hand, and a propane torch in the other http://fsae.com/groupee_common/emoticons/icon_smile.gif

About an hour later, I remember seeing your car do the one-tire-fire off the line in front of me. D'oh!

Aren't racecars fun!? </div></BLOCKQUOTE>

Apparently you didn't give good advice! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Charlie]

I heard Carroll say the same thing: the suspension travel rule is so that you have to have suspension. There's no rule saying how much dynamic travel you should have and there's no need. They just don't want go-karts. Of course you can make a ridiculously stiff suspension but you have limitations and added weight of suspension so why not use it.

I agree that you don't want your suspension to bottom before the frame. That puts ridiculous loads into everything and it's very hard to calculate. Of course you don't WANT to bottom the chassis but it should happen before the shocks do. That's why real racecars have something disposable on the bottom. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Look at any Auburn video from 03-04, the car is very softly sprung and moves a lot, especially in pitch. We had some frame bottoming sometimes, and had delrin blocks for FSAE-A for that reason. We barely used them though.

[Buckingham]

I also think they weren't as worried about the rule because Pontiac a.k.a. "the battlefield" was so bumpy that an uber-stiff suspension would actually slow you down.

[Psychosis]

hi guys,
im working on this at the moment as well, im not exactly experienced in suspension design (our suspension guy left).

for those of you who run elevated chassis rails at the front, do you run more than 1" of bump, and if so, how much more? i was thinking, it wouldnt be detrimental to run 2" bump up front would it? less to worry about bottoming the suspension, but needs different spring rates, any thoughts?
cheers