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So I'm looking to upgrade the rear suspension on the Omni. I'm looking for the right spring rates I would need in order to catch the weight and throw it back forward smoothly.
If the rear corners of the Omni were to weigh around 400lbs each, would it be appropriate to run around a 300lb/in spring? I would think that if you were to match the rear corner weight with a matching spring rate, that it would be too stiff for launching.
This is a good topic! I have put a lot of thought into this topic but I have no solid answers yet as I have not had a running car for several years now. Shocks/struts also play a huge role and are just as important.
Might as well put out there that auto and manual cars will have different needs here. My car is auto and is very happy to have 500lb springs in the rear and very soft springs up front.
Agreed on the auto vs. manual needing different rates. I feel the front springs needs to allow enough front end rise/travel during launch to keep the front tires from possibly being jerked off the pavement (wheelie effect) which will cause loss of traction. But then allow the front end to settle back down as quickly as possible. Adjustable rate struts can help accomplish this. Even the number of coils of the springs front and/or rear while keeping the spring rate the same will effect things (stored energy).Quote:
Originally Posted by contraption22
Well, what I mean is that spring rate is defined as how many pounds it will take to compress a spring by one inch. So a 100lb/in rated spring will take 100 pounds to compress the spring one inch.
When a FWD car launches, the rear tires can see a significant increase of load on the rear suspension. At the same time, the front tires will have a decrease of load on the front suspension and on the front tires. So if the rear corners weighed 400 pounds each at static (not moving) and we had 400lb/in springs on them, then they would compress one inch downward. It would take an additional 400 pounds to compress the springs one more inch.
Now the reason I want to ask if 300lb/in rated springs would be appropriate is for the initial launch. I understand that shocks also help, which is why I've ordered some adjustable rear shocks to dial in the dampening. With 300lb/in springs mounted under the corners of a theoretical 400 pound corner weight rear, the springs will be just soft enough to compress under the static weight of the vehicle plus the extra load on launch in order to give way for the shocks to lend a helping hand.
The way I see it is that if you have too heavy of a spring supporting the car, you're not really giving the shocks a chance to work..?
I can agree with your logic but I feel this is something that will have to be setup for each car combo to get the best results. In other words document all spring rates and shock settings, then get the 60' times. Make a change (one at a time) then see how that change effects the 60'.Quote:
Originally Posted by BoostedDrummer
I think it would be awesome and very helpful if someone would post results of how different spring rates and shock/strut settings effect 60' times.
On shock settings, up front I'd think you would want min ride height, minimum rebound dampening and max compression dampening. Kind of the opposite of what you would do in a stock class autocrosser. Jacking up instead of jacking down. When the weight transfer tries to squat the rear, then throws it back up front.. the compression damping will keep the front from squatting back down to where it was, and instead that force will push the tires in to the track. I think this "throwing back" was discussed by a few peeps in a previous thread.
Coilover setups you can get away with buying multiple springs since they are affordable. Try some things out because I would take the guesses with a grain of salt. I would also have the adjustable struts that can handle your spring choices. Double adjustable for the most options to play with.
My theory would be that for the front, you would want enough spring weight to hold the engine and all that a a respectable amount with a little bit of softness to them. For dampening, I'd say they would have to be set toward the upper area of stiffness, maybe the 75% range, mainly due to the "in-between" shifts where the nose would dip down.