Springs rate help

[jayz395]

Im dont know how to work out the spring rates that i need. I building a new car for next year. I race short oval stock car, it will weigh in at 625 kg, i dont know where to start or any sums etc. Any help will be VERY much appreciated.
regards jason

 

[hemipanter]

Tricky question. To calculate these things one must know the motion ratio of the suspension, and what type of suspension you plan to build. I don know to much about short oval racing but I guess these cars are built pretty much alike and that the wheelrate to use are very much sorted out among teams. Are these ovals banked?
Regards
Goran Malmberg

 

[jayz395]

no there flat tracks. what info do i need to get?

 

[GregLocock]

I strongly suggest you find out what wheel rates your fellow competitors are running.

Failing that what steady state lateral g do you run?

is it a smooth track?

do you run aero?

do you hop curbs?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jayz395]

i have another f2 that i currently use but are putting the shockers more up right on my new one. i have 250 257 front
185 225 rear
on that car. I thought the more upright they go the softer the springs needed?

there some smooth tracks some not. we dont run areo and dont normally hop curbs.

So do i find out what wheel rates i currently run then try to get them the same or inprove them?

Ive just bourght rollcentre software dont know where the rollcentre needs to be either.

regards

 

[hemipanter]

There is a lot of things to take in to account here so your question has no short answer.

We can not in general "improve" things, it is more a question of balancing the car to suit your specific track condition, provided the wheelrate are in the ballpark.

Yo must also separate the vertical wheelrate from that of the wheelrate in roll to get a picture of the balance of the car.

The roll centre is dependent on the geometry like camber gain, but also the CGH. Not to mention the tires in use.

It seem like a good chassis dynamic book should be on your list.
Kind Regards
Goran Malmberg

 

[jayz395]

For spring rates lets say unsprong weight of the left front of the car is 300pounds. i would need a spring load of 150ibs to hold the car at ride height for 2 inch of suspention travel on a smooth track. but because of motion ratios i divide that in.
so 150/0.76 = 197 the shocker angle are 18 deg so i found you divide 197 / .90 =218.8 ibs (i found a angle correction chart)

is this correct??

 

[hemipanter]

Allright Jason, I have sent you my counter. Check it out and we will see if it is of any help.
Regards
Goran Malmberg