pushrod actuated double wishbone suspension queries

[tanvi]

hi ,
we r freshers and our college team is making a racecar for the first time and we needed as much help as possible.we r workin on suspension analyser v2.0 for suspension designing and analysis.
here are some doubts to begin with:
1. roll centre

Static rc is at -5.56 (below the ground), we have read that rc should ideally lie on the ground plane as otherwise it gives to the jacking forces. So kindly advise if the above rc height is acceptable .

2.roll centre movement
we have gathered that rc movement should be minimum so we wanted to knw if the following rc movement is permissible.
for four degree roll(-2 to 2) the lateral variation in the roll centre position is -0.97 to 0.96 and the vertical variation is -5.61 to
-5.58.
for four degree dive (-2 to +2) the lateral variation in the rc position is -0.10 to 0.03.
and the vertical variation is -8.63 to-3.12(rc always stays below the ground)

3. these are some other parameters. please tell me if something is out of place
Scrub radius :1.40
KPI:2.83( i knw it should be zero. is this value fine or do i need to work to make it smaller)
static camber:-3
castor:7.32
static toe in: -1.5

4. control arms
we made the LCA such that it is sloping up from inside to outside while the uca is sloping down from inside to outside for reducing lateral rc movement.
bt i have read that the fsae cars usually have horizontal lca and uca is usually slopin up from in to out(towards the wheels).so plz tll me the above arrangement is feasible.

5. Ride height
i hav been looking for formulae to determine the ride height bt hav been unable to find one so far. how do i go ablout finding the right ride height

6. CG position
Since my rc is below the ground, i figured that the cg should also be close to the ground . In my initial stages of suspension design, do i need to knw the cg?

7. since we have been to the competition, we wantd to knw wat is the max dive and roll encountered (so that we can put these values in the suspension analyser v2.0 for dynamic testing )

plz help us out
thank u

[tanvi]

hi ,
we r freshers and our college team is making a racecar for the first time and we needed as much help as possible.we r workin on suspension analyser v2.0 for suspension designing and analysis.
here are some doubts to begin with:
1. roll centre

Static rc is at -5.56 (below the ground), we have read that rc should ideally lie on the ground plane as otherwise it gives to the jacking forces. So kindly advise if the above rc height is acceptable .

2.roll centre movement
we have gathered that rc movement should be minimum so we wanted to knw if the following rc movement is permissible.
for four degree roll(-2 to 2) the lateral variation in the roll centre position is -0.97 to 0.96 and the vertical variation is -5.61 to
-5.58.
for four degree dive (-2 to +2) the lateral variation in the rc position is -0.10 to 0.03.
and the vertical variation is -8.63 to-3.12(rc always stays below the ground)

3. these are some other parameters. please tell me if something is out of place
Scrub radius :1.40
KPI:2.83( i knw it should be zero. is this value fine or do i need to work to make it smaller)
static camber:-3
castor:7.32
static toe in: -1.5

4. control arms
we made the LCA such that it is sloping up from inside to outside while the uca is sloping down from inside to outside for reducing lateral rc movement.
bt i have read that the fsae cars usually have horizontal lca and uca is usually slopin up from in to out(towards the wheels).so plz tll me the above arrangement is feasible.

5. Ride height
i hav been looking for formulae to determine the ride height bt hav been unable to find one so far. how do i go ablout finding the right ride height

6. CG position
Since my rc is below the ground, i figured that the cg should also be close to the ground . In my initial stages of suspension design, do i need to knw the cg?

7. since we have been to the competition, we wantd to knw wat is the max dive and roll encountered (so that we can put these values in the suspension analyser v2.0 for dynamic testing )

plz help us out
thank u

[woodsy96]

Hi Tanqi,

Every team has these questions to start off with.

Most of your answers can be found
-by reading a book such as Race Car Vehicle Dynamics by Milliken and Milliken or Tune to Win by Carrol Smith
-by searching for photos of other cars

These won't tell you if your specific numbers are "acceptable", but the photos will give an indication of what your suspension should look like and the textbooks will explain the how these values affect car handling.

[Yellow Ranger]

In some cultures, they only eat vomit. I never been there, but I read about it... *in a book*.

[tanvi]

hey,
thankx woodsy96 for telling us about the books . we r going through them. meanwhile another question
regarding the placement of the inboard spring for the front suspension. till now i hav com acrss three ways namely lateral.longitudinal and vertical. but hav been unable to decide out of the three, cud u tell us advantages/disadvantages of the above(as i havent been able to find much on the net)?
thankx
tanvi

[Adambomb]

Ahh, the dreaded shock packaging problem. First off, it's fairly simple, just sketch up how they'll sit in the car, and do a free-body-diagram on the rocker. Some setups will cause much larger loading than others.

Beyond that, the setup that fits well on the car and meets your kinematics requirements is always the "best."