×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

A roll center based question...

A roll center based question...

A roll center based question...

(OP)
To give an example of the knowledge I am after Ill make a theoretical example and ask what the effects might be.  You have a 4 wheeled vehicle that has a monoshock arrangement front and rear.  The front axle controls the roll rates and roll damping and obviously also has a spring and damper for pitch.  The rear axle has no roll springs or damper only a spring and damper for pitch.  Theoretically this should have similar effects to a three wheeled vehicle, with two front tires controling roll and a single rear which cannot control roll or in this case a 4 wheeled vehicle with evenly loaded rear wheels no matter the lateral load, correct?  Then you throw in the roll centers. Assume the front is where ever, but the rear is above ground.   Will the rear tires now have uneven loading under lateral acceleration?

RE: A roll center based question...

Yes, if the cg is above ground and not at the front axle longitudinally. Draw a free body diagram of the rear axle.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: A roll center based question...

Additionally, if the rear suspension is independent, it will have a jacking-up component during cornering if the roll centre is above ground (think swing-axles i.e. original VW Beetle and original Corvair and many other old cars), but if a regular axle is used, the jacking-up force will generally be much reduced or eliminated depending on the geometry.

RE: A roll center based question...

(OP)
Ah, yes jacking.  So if the roll center at the rear is at ground level always, the front takes all the roll forces, it is a solid axle, and there is zero roll resistance at the rear then the rear tires will be evenly loaded?

RE: A roll center based question...

Yup, and it's going to understeer like nothing you've ever seen.

RE: A roll center based question...

(OP)
Oh yeah!  The 911 aftermarket guys go a similar direction although not nearly as extreme.  Stiff front, soft rear, relatively, sometimes lifts the inner front tire powering out of corners.  I would imagine if the weight bias in the above example were rearward enough and the rear tires were narrow enough, or the fronts wide enough, it might not understeer so badly, but would probably have problems three wheeling out of corners.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources