Suspension geometry models. Roll center etc...
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 1,102
Likes: 0
From: Montreal QC
Suspension geometry models. Roll center etc...
Hi all!
Now that I've started the 3D model thing: http://forums.corvetteforum.com/zerothread?id=725050 I have also started modelling the rear suspension. At the same time modelling the geometry it's easy to check the rear travel and body roll efect to wheel alignment.
Here is rear travel sheet: rear-travel in PDF. This is fairly simple and straight forward. I still have to check the geometry once again to be sure about the dimensions, but this shows that in normal travel C3 suspension is pretty good.
But this was really horrible to find out: rear-roll in PDF. This is simply shocking! Please, suspension gurus check this out and tell me if the RollCenter is located correctly... Is it really so that CoG/weight doesn't have any impact on rollcenter? CoG/weight affects only to how much the body rolls, but in the rollcenter? This is how I figured it out, am I correct or not?
I have also videos on both travel and roll, but I have to somehow change the format first. Now they are in .AVI format and they are about 100MB each. Pretty much for a small ten second movie with not too many moving parts...
Now that I've started the 3D model thing: http://forums.corvetteforum.com/zerothread?id=725050 I have also started modelling the rear suspension. At the same time modelling the geometry it's easy to check the rear travel and body roll efect to wheel alignment.
Here is rear travel sheet: rear-travel in PDF. This is fairly simple and straight forward. I still have to check the geometry once again to be sure about the dimensions, but this shows that in normal travel C3 suspension is pretty good.
But this was really horrible to find out: rear-roll in PDF. This is simply shocking! Please, suspension gurus check this out and tell me if the RollCenter is located correctly... Is it really so that CoG/weight doesn't have any impact on rollcenter? CoG/weight affects only to how much the body rolls, but in the rollcenter? This is how I figured it out, am I correct or not?
I have also videos on both travel and roll, but I have to somehow change the format first. Now they are in .AVI format and they are about 100MB each. Pretty much for a small ten second movie with not too many moving parts...
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: Suspension geometry models. Roll center etc... (FinnShark)
what are we looking at? I have a hard time figuring out what is exactly what in those pics. I see toe in.out and the rest looks like a schematic presentation of body roll and camber change. So, how on earth can you see camber, roll and toe in the same axis plane?
Can you please explain what is what in those pictures?
It looks like you drew lines from the control arms, they intersect somewhere outside the pic in the IC, then you connected IC to wheel centerline to ground contact point and this, crossing the vehicles centerline gives roll center
Also, it looks as if you placed the instantaneous center for the front on the inside of the car, where it really is on the outside because of the control arm angles
Can you please explain what is what in those pictures?
It looks like you drew lines from the control arms, they intersect somewhere outside the pic in the IC, then you connected IC to wheel centerline to ground contact point and this, crossing the vehicles centerline gives roll center
Also, it looks as if you placed the instantaneous center for the front on the inside of the car, where it really is on the outside because of the control arm angles
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 1,102
Likes: 0
From: Montreal QC
Re: Suspension geometry models. Roll center etc... (Twin_Turbo)
Sorry about the toe in, it should be camber. Just a confusion with the language... Sorry...
This is how it's done, so I suppose that the RC is in correct place. The IC is not visible in this one, but it is in parallel lines to control arms.
For now I have two guestions.
1. Does CoG or weight of the vehicle have any effect to roll center?
2. What happens to RC when suspension is tilted and the RC locations for left and right side are not at the same height in center line of the car? As you can see from the pics other side is 77mm and the other one 127mm when roll is 3deg? is the roll center in the cross section of these lines (not at the centerline of the car) or at the middle of these lines (about 102mm above ground)? Hope that you can understand what I'm trying to explain...
Both figures are for rear suspension and the measurements are from my car. I have to re-check the measures, but it seems that at least in rear the IC is inside the car. You can see that at 100mm (About 4inch) out travel the IC is outside the car. Have you done any calculations if this is correct? Also the RC is not correct in the pic where IC is outside the car.
It looks like you drew lines from the control arms, they intersect somewhere outside the pic in the IC, then you connected IC to wheel centerline to ground contact point and this, crossing the vehicles centerline gives roll center
For now I have two guestions.
1. Does CoG or weight of the vehicle have any effect to roll center?
2. What happens to RC when suspension is tilted and the RC locations for left and right side are not at the same height in center line of the car? As you can see from the pics other side is 77mm and the other one 127mm when roll is 3deg? is the roll center in the cross section of these lines (not at the centerline of the car) or at the middle of these lines (about 102mm above ground)? Hope that you can understand what I'm trying to explain...
Also, it looks as if you placed the instantaneous center for the front on the inside of the car, where it really is on the outside because of the control arm angles
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Re: Suspension geometry models. Roll center etc... (FinnShark)
1. Does CoG or weight of the vehicle have any effect to roll center?
2. What happens to RC when suspension is tilted and the RC locations for left and right side are not at the same height in center line of the car? As you can see from the pics other side is 77mm and the other one 127mm when roll is 3deg? is the roll center in the cross section of these lines (not at the centerline of the car) or at the middle of these lines (about 102mm above ground)? Hope that you can understand what I'm trying to explain...
Pete
[Modified by Pete79L82, 7:14 AM 1/12/2004]
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 1,102
Likes: 0
From: Montreal QC
Re: Suspension geometry models. Roll center etc... (Pete79L82)
The Roll Center is constantly moving during suspension movement. A stationary measurment is only a guideline to suspension design. You must also look at the R/C at full suspension compression and droop, and body roll.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: Suspension geometry models. Roll center etc... (FinnShark)
yes, for your model it is fine putting the rc on the car centerline, we can view our cars as being symmetrical for the model, it would probably be way too involved to do otherwise and we don't need to since we drive on roads so the number of left & right hand turns is about the same. Now if you had a staggered car that runs on an oval, then it's a different story.
Thread Starter
Burning Brakes
Joined: Mar 2002
Posts: 1,102
Likes: 0
From: Montreal QC
Re: Suspension geometry models. Roll center etc... (Twin_Turbo)
Thanks TT and also everybody else! I'm just a novice in these suspension things and I might be asking more stupid guestions in the future trying to find out small details or even bigger things how the whole system works... This is a good start for now! :cheers:
Le Mans Master
Joined: Dec 2000
Posts: 9,752
Likes: 0
From: Chattanooga TN
St. Jude Donor '08-'09
Re: Suspension geometry models. Roll center etc... (FinnShark)
Thanks TT and also everybody else! I'm just a novice in these suspension things and I might be asking more stupid guestions in the future trying to find out small details or even bigger things how the whole system works... This is a good start for now! :cheers:
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Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: Suspension geometry models. Roll center etc... (e3pres)
shhht.. I've been looking for those books on ebay (drive to win, engineer to win and tuneto win) and boy they get expensive fast. I think they're cheaper off amazon.
The race car vehicle dynamics by will & doug milliken is an awesome book but it's about 100$ and it's THICK (almost 1000 pages). I want to buy that book too sometime in the future.
The race car vehicle dynamics by will & doug milliken is an awesome book but it's about 100$ and it's THICK (almost 1000 pages). I want to buy that book too sometime in the future.
Drifting
Joined: Oct 2003
Posts: 1,426
Likes: 1
From: VetteMOD
St. Jude Donor '05-'07
Re: Suspension geometry models. Roll center etc... (Twin_Turbo)
For good information about the rear suspension of a C3, go to the US patent and trademark site (uspto.gov) and look up number 5,046,753. This is the patent for the 6 link modification but it discusses in detail the dynamics of the stock suspension. And it's free!
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
Re: Suspension geometry models. Roll center etc... (71roadster)
Hello.. damn its been a while I posted here. Just got out of the army...didn't take long.... I didn't get to work much on my vette but at least I installed my 5-link suspension. For those that missed it before, here's a link to pictures I took a while back...
http://photos.yahoo.com/bc/lohkay/lst?.dir=/Corvette
and here's some pics and dimesions I took for the corvettefaq...
http://www.corvettefaq.com/c3/5link/index.html
Now that both sides are installed with the spring (only missing the brake hoses) I'll take some more pics when I get the chance. I should test drive it this summer.
http://photos.yahoo.com/bc/lohkay/lst?.dir=/Corvette
and here's some pics and dimesions I took for the corvettefaq...
http://www.corvettefaq.com/c3/5link/index.html
Now that both sides are installed with the spring (only missing the brake hoses) I'll take some more pics when I get the chance. I should test drive it this summer.
Le Mans Master
Joined: Dec 2000
Posts: 9,752
Likes: 0
From: Chattanooga TN
St. Jude Donor '08-'09
Re: Suspension geometry models. Roll center etc... (Twin_Turbo)
shhht.. I've been looking for those books on ebay (drive to win, engineer to win and tuneto win) and boy they get expensive fast. I think they're cheaper off amazon.
The race car vehicle dynamics by will & doug milliken is an awesome book but it's about 100$ and it's THICK (almost 1000 pages). I want to buy that book too sometime in the future.
The race car vehicle dynamics by will & doug milliken is an awesome book but it's about 100$ and it's THICK (almost 1000 pages). I want to buy that book too sometime in the future.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Re: Suspension geometry models. Roll center etc... (Lohkay)
Welcome back Lohkay. I was just looking at a blowup of your 5 link rearend and it would bother me to send all my power with sticky tires through 4 hiem joints. Also I don't see a spring? What are you doing for suspension? Have to driven it yet?
Race Director
Joined: Dec 1999
Posts: 16,945
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Re: Suspension geometry models. Roll center etc... (norvalwilhelm)
I may have some info on the guldstrand setup in the near future. From what I heard the system uses 8 similar length rods w/ heim ends, all 12" (not verified)
The system uses a special center camber bracket, I have the measurements on that thing somewhere, will have to look. As for the hubs, they use cast aluminium sections over the hubs that connect to all the bars, it's clearly visible in the pics on their site.
The system uses a special center camber bracket, I have the measurements on that thing somewhere, will have to look. As for the hubs, they use cast aluminium sections over the hubs that connect to all the bars, it's clearly visible in the pics on their site.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Re: Suspension geometry models. Roll center etc... (Lohkay)
Lohkay I took this picture from your site. I would be worried about pushing any horsepower through those 2 forward rods.
Double click to enlarge
Double click to enlarge
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
Re: Suspension geometry models. Roll center etc... (norvalwilhelm)
are they steel (the rods)??
I wouldn't be too worried if quality heim ends were used, it's not like the C4 dogbones are exceptionally strong either. They are forged aluminium.
I wouldn't be too worried if quality heim ends were used, it's not like the C4 dogbones are exceptionally strong either. They are forged aluminium.
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
Re: Suspension geometry models. Roll center etc... (norvalwilhelm)
hey! Those pics are old... was only one side installed with no spring attached. Now I have both sides done with the spring on and will be taking pictures as soon as I get the time. As for your worries about the heim joints, both gulstrand and greenwood use the same concept...actually my concept is pretty close to the greenwood one. As for the material used, the tubes are 1" with 1/4" sidewall which is pretty strong but might not be enough... the heim joints are not the best on the market but close and each of them is rated at 22,000lbs of static radial load. Now I know that in a suspension you're far from static load but still thats a lot of load capacity. Anyway, this is not final... I want to try it out and see how it behaves and where it might fail and I'll build a new suspension at that point, I already have a few ideas.