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Hello,
I am new to this forum and i was needing some help with some of the suspension designs. I will be using the wilwood Mustang II drop spindles and I have deigned them in cad and imputed the correct dimensions into vsusp. here is the link with the suspension design.

http://tinyurl.com/zxhmpeb

In the front i am planning on running 275/40/17 with a 0.24 inch offset rim with a 1.5 inch wheel spacer and in the back i will be running 315/35/17 with a 1.1 inch offset on the rim and will have a 1 inch wheel spacer.

Could some of you guys run through my measurements and recommend any changes? Also i almost forgot to mention, that the frame in the rear is 46 inches wide, this is why i was thinking of adding in the wheel spacers.

I will be using a wilwood brake kit 140-12275-D for the front which will offset the hub by +.55. I have not incorporated that into the program yet so a bit of help regarding that too would be nice.

Your help will me much appreciated, and thank you in advance!

Any particular reason you are running those wheels/tire sizes? Unless you already have wheels that do not fit why use a spacer? Adding a spacer adds a point of failure to a critical part of the car.

Can you provide an overview of the car. Is it built yet, do you have any parts already? What are you going to be using the car for etc?

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

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Your VSUSP shows a total offset of -0.31 inches in the front. However, your comments above regarding wheel offset and spacer thickness would indicate that it should be -1.26 inches. So instead of 3.3 inches of scrub radius, it's actually 4.2 inches. Add the brake kit, and now you're up to a 4.8 inch scrub radius. I'm definitely curious what the motivation is for especially the front offset/spacer decision.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Hi wrightcomputing,

I already have those wheels and tires unfortunately. Here are the rims that I will be using. http://www.americanmuscle.com/black-sal ... l#shop-by3
You should be able to find the offset at the bottom of the page. My idea of using a spacer was to not play around with the suspension design anymore. After all, Driven5 has brought up a good point about the total offset and that is practically half the rim... The car is a big block chevy 468 CI with a tremec t56 transmission and a for 8.8 irs. I have done a bunch of reinforcements on the chassis and it will be more of a street car than a track car. The frame of this car is built and i have received my spindles and balljoints so now i this is the last step before I start mocking up the front suspension.

Now my next question is, What would the acceptable Instant roll center be? I am trying to keep the front roll center lower than the back and at the same time trying to keep the Roll angle (degrees) ....vs.... Roll center X location (inches) curve with a negative slope since that is the sweet spot for the suspension of most cars. I am not sure if that is true however i have read numerous times that is what it is supposed to look like tho.

Any other ideas on how to perfect it i would be happy to hear. Thank you all.

I don't follow how the front spacers help in this regard. In my opinion they're just making it more difficult to get better numbers.

Your front wheels are also 24mm offset, or .94 inches, not .24 inches. This means that even after you add the brake kit your scrub radius should be improved to 3.22 inches without the spacers.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

I'm not sure the dropped spindles will work for you on the street. For us it's a bit different because we are designing the frame and it's suspension mounting points. Hmmm, maybe your large wheels will make it work for you.

Your model can help here, though with real life parts in hand that should work well for you too. You can also learn about the forces and roll centers etc. with your model. Put in the suspension wishbones and use fixed length bars for the coilovers. Attach the frame to the floor at the axle pins with strong vertical elements. You should be able to observe things like jacking forces.

If you mean transverse location of the roll center when you say "X" migration - it is of no possible import. It is the vertical height of the roll centers that contributes to the geometric roll stiffness of the car ( as opposed to elastic roll stiffness provided by springs and anti-roll bars ). If the height of the roll centers is moving around while the car is moving it's the same thing as adjusting the anti-roll bars while your driving, not a good thing.

Another way to look at this is to consider the line of force which goes from the tire contact patch to the suspension instant center. You want this to only be a few degrees at max.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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Also, in some states spacers are illegal. You can get adapters that retain the existing lug pattern, the crucial difference being the adapters are billet, not cast, and have their own second set of lug studs already pressed in. But getting them thinner than 1.25" is unheard-of. These are not illegal, and are well-proven by Jeep guys, for strength.