The effect of wheelbase and track on vehicle dynamics

[Hamid Abdollahi]

Hi.
as we all know, the first step to design the suspension system is to determine the ideal wheelbase and track width. with your help, we would like to know the efect of these parameters on vehicle dynamics. we also wish to share information with others on this matter, whether in forum or by E-mail. http://fsae.com/groupee_common/emoticons/icon_smile.gif
hamidabdollahi.up@gmail.com

[Hamid Abdollahi]

Hi.
as we all know, the first step to design the suspension system is to determine the ideal wheelbase and track width. with your help, we would like to know the efect of these parameters on vehicle dynamics. we also wish to share information with others on this matter, whether in forum or by E-mail. http://fsae.com/groupee_common/emoticons/icon_smile.gif
hamidabdollahi.up@gmail.com

[Mbirt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Hamid Abdollahi:
as we all know, the first step to design the suspension system is to determine the ideal wheelbase and track width. </div></BLOCKQUOTE>I do not believe that many would agree with this. The first step in designing your suspension should be to know your tires and what they need to perform their best. You then design your suspension according to the needs of your tires.

For benchmarking other teams, you should go to http://students.sae.org/competitions/formulaseries/ and download the spectator guides available for the 2011 competitions. They're good for basic design parameters like these.

[PatClarke]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">as we all know, </div></BLOCKQUOTE>

Hamid, never ever use this phrase, especially with Design Judges.
The truth is we all know very little (in the bigger scheme of things) http://fsae.com/groupee_common/emoticons/icon_smile.gif

Pat

[Xeilos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">determine the ideal </div></BLOCKQUOTE>

Pat, I am bit surprised you decided to pick on the quote you did. The word 'ideal' is very similar to 'optimize' http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Buckingham]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The first step in designing your suspension should be to know your tires and what they need to perform their best. You then design your suspension according to the needs of your tires. </div></BLOCKQUOTE>

This comment may or may not spark some debate, but you could give me any 'standard' FSAE tire from the last 15 years and I would probably pick the same wheelbase and track width.

IMHO the sensitivity of lap time to those two parameters has very little to do with tire data.

[exFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
The first step in designing your suspension should be to know your tires and what they need to perform their best. </div></BLOCKQUOTE>

Disagree. First step is deciding how you want your vehicle to behave. Manipulation of tire properties, linkages, inertia... are all tools to reach that end.

Perhaps a subtle, but important point. Despite this, few people start at the starting point. Instead, they pick some effectively arbitrary thing to focus in on.

"Well, where should our roll centers be?"

"What should our camber curve look like?"

"Should we use bump steer?"

"What are the best tire properties?"

It's like trying to plan what you're going to make for dinner by starting with whether or not you're going to use table salt, or sea salt.

[Mbirt]

I'm just the engine guy that attended Optimum G once, so I'm out of my element here. Glad to have sparked some debate, though. Back to finding ECU pinouts...

[Pennyman]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Buckingham:
IMHO the sensitivity of lap time to those two parameters has very little to do with tire data. </div></BLOCKQUOTE>

Disagree. (to continue the theme)

I would argue that the tire data is imperative to guiding you to define a trackwidth if your vehicle handling requirements place an emphasis on low yaw inertia. But each to their own. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Mike Cook]

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


Disagree. (to continue the theme)

</div></BLOCKQUOTE>

Disagree.

Track and wheelbase affect your path length and radius very much. That is very independent of the tires. Pick those things, and then pick an appropriate tire to handle the loads expected. It isn't like we have a spec tire.

[Hamid Abdollahi]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
The first step in designing your suspension should be to know your tires and what they need to perform their best. You then design your suspension according to the needs of your tires.
</div></BLOCKQUOTE>
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClerk:Hamid, never ever use this phrase, especially with Design Judges.
The truth is we all know very little (in the bigger scheme of things) Smile
</div></BLOCKQUOTE>
@Mbirt:I have the tire date but I try to determine the track by selection of A-arms lenghth &I dont think that tire data have a considerable effect on selecting the wheelbase &track.what I want to debate on is "The effect of wheelbase and track on vehicle dynamics"
@Ms Clerk:hi pat thank for your advice.I'm a beginner &I wanted to beautify my question but perhaps it was a mistake.

[Rotary Sprocket]

Some simple equations:

Lateral WT = mass(lbm) x radial accel. x CG height / Track width x 32.2 (assuming front are rear are equal)

Longitudinal WT = mass(lbm) x accel. X CG height / Wheelbase x 32.2

Plug in your vehicle weight, CG height and pick an acceleration value and try different values for wheelbase and track. That should give you an idea for how those variables effect vehicle dynamics.