Near stock setup need advice

[hai1206vn]

A bit of background first....

I'm planning a new suspension setup for next year while winter does its job in the meantime. My s14 will stay a street car with good manner for weekend autocrossing with summer street tires, no track duty. I'm still learning and don't want to blow money on anything crazy that I can't appreciate.

I had Stance GR+ but never liked them. Even with slightly softer rates 7kg/5kg, within 3 months they managed to destroy my brand new rear wheel bearing from just daily driving (upstate NY FTL!!). Damping is quite horrible. I'm hoping the digressive valving of Konis will help.

I'm under the impression that stiffer rates up front like almost everybody runs are beneficial if the car has been lowered to the point that the ugly front camber curve doesn't allow any significant travel. If the stock design allows for example 2" before the strut-LCA angle becomes 90* or more, then lowering by 3-4" won't do any good. So, to counter worsened body roll with 3-4" drop, the solution is using tons of static camber and crazy 600-700lb/in springs. Not my cup of tea.

Questions:

1) My car will only be lowered 1" at most from stock to maintain designed geometry - I'm not spending on correction control arms. I guess that minimal drop will allow me to run softer springs with enough droop. How does 300/300 lb/in sound? Stock springs aren't staggered and car already understeer so why should I? My height drop should keep the LCA from going into the positive camber range, and make use of the slight negative camber gain.

2) I can't seem to find the correct rear motion ratio on 240s. Seems to be about .7, and my rough measurement also gives about that range (measuring RLCA inner pivot to strut mounting point and ball joint). Some people on the other hand have said that rear motion ratio is nowhere near .7, but did not say what number they had.

[jmauld]

Questions:

1) My car will only be lowered 1" at most from stock to maintain designed geometry - I'm not spending on correction control arms. I guess that minimal drop will allow me to run softer springs with enough droop. How does 300/300 lb/in sound? Stock springs aren't staggered and car already understeer so why should I? My height drop should keep the LCA from going into the positive camber range, and make use of the slight negative camber gain.

Just to clear up what I think you are referring to. The understeer with the stock setup isn't because of the matching spring rates. It understeers because of the amount of roll in the front of the car. The positive camber comes from the car leaning, not just from the control arm pointing up.

You could increase your front spring rates, leave the rear springs alone and still reduce understeer, just because you would be making the front wheels stay more consistently level to the ground.

With all that said, 300/300 would probably work fine.

2) I can't seem to find the correct rear motion ratio on 240s. Seems to be about .7, and my rough measurement also gives about that range (measuring RLCA inner pivot to strut mounting point and ball joint). Some people on the other hand have said that rear motion ratio is nowhere near .7, but did not say what number they had.

The rear strut moves 1" every time the rear wheel moves 1". So, the only thing having an effect on the rear motion ratio is the angle of the strut. I think it's fairly close to 1. At least, that's how I've always understood it.

[hai1206vn]

The understeer with the stock setup isn't because of the matching spring rates. It understeers because of the amount of roll in the front of the car. The positive camber comes from the car leaning, not just from the control arm pointing up.

I see. Another reason may be riding the bumpstop as stock front travel is toooo short for given amount of compression???

The rear strut moves 1" every time the rear wheel moves 1". So, the only thing having an effect on the rear motion ratio is the angle of the strut. I think it's fairly close to 1. At least, that's how I've always understood it.

That makes perfect sense, given that the rear strut is slanted front to back.

I have another question while trying to guess the amount of spring compression. Say i have 700lb of sprung weight in the left front corner, and 600lb in left rear corner. In a 1g left turn, can i say that these corners will have to handle 1400lb and 1200lb respectively (assuming front-rear roll bias is equal)? I doubt this is right, as that would mean no load on the other side of the car.

[jmauld]

I have another question while trying to guess the amount of spring compression. Say i have 700lb of sprung weight in the left front corner, and 600lb in left rear corner. In a 1g left turn, can i say that these corners will have to handle 1400lb and 1200lb respectively (assuming front-rear roll bias is equal)? I doubt this is right, as that would mean no load on the other side of the car.

I think you can use that as a worse case scenario for a street car. (no downforce mods).*

The most you can do is lift one corner off of the ground, and even then that weight will be split between the opposite corners. You will still need room for bumps though.

*Someone else, please confirm/deny this.

[RBbugBITme]

You would most likely be closer to 1200/1200 outside front/rear but yeah thats a reasonable ballpark.

[hai1206vn]

Thanks.

I'm going to measure how far up the front LCA can travel before going into positive camber. If anyone has a number that'll be great for me to double check

[hai1206vn]

Ok got some rough measurement done. Picture shows FLCA at stock height. Distance from LCA pivot to ball joint is about 13.5". The tape measure indicates where the LCA makes 90 degrees with the strut axis. The distance between two ball joint positions is 2-2.5", which means in stock form, the strut compresses 2-2.5" before camber starts going positive.

Now can someone explain how a 240 lowered by 3-4" for zero fender gap deals with roll? On such a car, any moment you turn you lose camber. Ridiculous static camber, super high spring rates and fat sway bar seem to be the menu. How much does the benefit of lower CG justify those measures?

[Epstein]

Errr, doesn't the strut axis run through the ball joint?

[RBbugBITme]

Errr, doesn't the strut axis run through the ball joint?

Doesn't have to. Kingpin is just from the upper mount to the ball joint.

[jmauld]

Now can someone explain how a 240 lowered by 3-4" for zero fender gap deals with roll? On such a car, any moment you turn you lose camber. Ridiculous static camber, super high spring rates and fat sway bar seem to be the menu. How much does the benefit of lower CG justify those measures?

That's pretty much the recipe for any strut based car. That's also why a double wishbone suspension is superior in most cases. Especially for street based vehicles where you would prefer to have a softer suspension.

You'll find that if you want to keep the car from going into positive camber in a turn, you will need a static camber setting somewhere between 2.5-3 neg. camber and spring rates starting at 450lbs.

Of course, don't forget that you don't need to be perfect. A stock setup is going to roll so much that you will get +5 degrees* of pos. camber. While a setup with 300lb springs, lowered an inch may only roll over to +2 degrees of pos. camber. While not perfect, that is better than stock.

*Numbers are made up and likely exaggerated for illustrative purposes only.

[Epstein]

Doesn't have to. Kingpin is just from the upper mount to the ball joint.

You got what I meant. What I'm trying to point out is, isn't the critical 90* point based on the LCA and Kingpin lines? The dotted lines in the drawing above are either incorrect or misleading.

[RBbugBITme]

I don't believe you need a 90* angle there. Why do you think that is?

[hai1206vn]

Hmm all places i looked at only mention the strut axis - LCA angle, no kingpin

[Epstein]

What about a steering axis? Same thing as Kingpin, I think.

[RBbugBITme]

Lets clear up confusion here...

Kingpin is from the upper strut mount to the ball joint. This is also called the steering axis.

This does not have to be on the same axis as the strut axis or parallel to it or coincident.

Neither of these axes need to make a 90* angle with the lower control arm.