Another question from a newbie

[BigNilla]

These are great replies thanks again keep 'em coming

[BlackMagic]

I would think that with the RF out further that would tend to tighten the car up through the corner on or off the throttle just strictly based on front to rear track alignment. Also with it softening the spring rate that would tend to tighten you up getting in the corner off the throttle, but free you up getting in on throttle. Or does it do the opposite because of the increased roll steer and car "rolled up" attitude because of the softer rate in the RF and the increased aero advantage putting more air on the front end allowing it to steer better? Guy don't really comment on a tighter or looser handling car, they just say it steers better. Maybe their car was to tight or loose to begin with and this was an adjustment that unknowingly fixed a setup problem? Racing would be so much easier if there was just one answer for everything, it all makes my head hurt trying to speculate and analyze every scenario when making adjustments. I need more time and money to test!

[Matt49]

To avoid confusion, we should use the correct terminology. Spring rate doesn't change with any of the things we're talking about moving. The term you're looking for is "wheel rate" which is the effective rate felt at the tire contact patch.
That being said, moving the tire/wheel out with a spacer has NO effect on wheel rate. None whatsoever. I know I'm going to get push back on this statement but it is the absolute truth. I can prove it if anybody wants a little homework/science experiment to work on.
There are three variables that affect wheel rate: spring rate, spring angle, and motion ratio.
At the angles we're dealing with, the spring angle has relatively little affect on the wheel rate. The angle is mostly there to keep the rate linear as the lower control arm travels. The motion ratio (how mar the spring/shock is on the LCA from the end of it (the ball joint)) is a HUGE factor in wheel rate.
The other thing that you meed to consider when moving the RF wheel out with a spacer is that you're changing your scrub radius which changes the weight jacking effect of the RF tire with steering input.
Without getting into too much detail, I'll say this: the biggest positive byproduct of moving the RF out with the lower while keeping the upper relatively short is increased camber gain. With the amount of body roll that the cars have today, we need more RF camber gain than what was ever imagined would be necessary 15 years ago.

Here's a handy dandy link to explain that math of the wheel rate thing a little for those interested in such things:
http://eibach.com/america/en/motorsp...sion-worksheet

[Matt49]

Blackmagic,
I think you're pretty close with your assessment of why softer RF helps the car turn. The old school thinking of "heavy spring gets the weight" always told us that a stiffer spring would free up entry but now it seems all backwards. I think it's for 3 reasons:
1) More RF travel = more LR travel = more rear steer
2) Increased from end stability due to aero
3) (last but not least) Lowered dynamic roll center due to increased dynamic bar angles of RF

Just my two cents...

[TLM4t4]

Thanks for the correct terminology Matt, that's what I was referring to about the question asked about the difference in wheel spacer and wide RF option. So if I wanna run say the shorter control arms and a wheel spacer to get the nearly same affect I would have to soften the RF spring rate which will initially enter the corners better by gaining camber, bar angles, and chassis roll which interns the car to steer more positive in corner entry, scotch off the RF tons across center, and help with drive factor and rear steer?

[Matt49]

Thanks for the correct terminology Matt, that's what I was referring to about the question asked about the difference in wheel spacer and wide RF option. So if I wanna run say the shorter control arms and a wheel spacer to get the nearly same affect I would have to soften the RF spring rate which will initially enter the corners better by gaining camber, bar angles, and chassis roll which interns the car to steer more positive in corner entry, scotch off the RF tons across center, and help with drive factor and rear steer?

I agree with pretty much everything except for the part about drive. Usually when we're talking about drive we're talking about a tight on throttle condition. Softer RF decreases dynamic wedge which actually hurts drive. In other words, no silver bullets here. You'll need to work in other areas to get dynamic wedge back in the car on corner exit as you soften the RF. There are many ways to do this and different things work for different people. Unfortunately, we're drifting into subject matter that not many people are going to be willing share info about on here.

[Kwoods25]

matt knows his stuff. Good read

[BlackMagic]

Matt I agree with your posts, and the corrected terminology. I am going to have to give you push back on the wheel rate not changing with a spacer installed. It was always my understanding that to calculate the motion ratio of the RF suspension for this case that you measure from chassis mounting points to center of tire, chassis mounting point to center of spring mount location on lower, and center of tire to center of spring mount. The actual measurements and correct math formula eludes me right now, but maybe you are familiar with it? Wouldn't the motion ratio directly effect the wheel rate? Therefore softening it? Or did you mistype and mean to say that just moving the rf assembly out 1" will not effect wheel rate? In that case if you didn't correct the spring angle change wouldn't that make the wheel rate softer in bump travel? I agree that the spring angle change would be so minimal that there probably wouldn't be any noticeable handling changes, but for arguementive sake I would like to know the correct answers.

[Matt49]

Matt I agree with your posts, and the corrected terminology. I am going to have to give you push back on the wheel rate not changing with a spacer installed. It was always my understanding that to calculate the motion ratio of the RF suspension for this case that you measure from chassis mounting points to center of tire, chassis mounting point to center of spring mount location on lower, and center of tire to center of spring mount. The actual measurements and correct math formula eludes me right now, but maybe you are familiar with it? Wouldn't the motion ratio directly effect the wheel rate? Therefore softening it? Or did you mistype and mean to say that just moving the rf assembly out 1" will not effect wheel rate? In that case if you didn't correct the spring angle change wouldn't that make the wheel rate softer in bump travel? I agree that the spring angle change would be so minimal that there probably wouldn't be any noticeable handling changes, but for arguementive sake I would like to know the correct answers.

The formula can be found here:
http://eibach.com/america/en/motorsp...sion-worksheet

The measurement for motion ratio is from the lower ball joint to the inner pickup of the LCA divided by the lower shock/spring mount to the inner pickup of the LCA.
The spindle has no leverage on the lower control arm spring mount because it is attached to the upper control arm. So moving the wheel out on the spindle doesn't affect wheel rate. The spindle feels what the ball joint feels. No more, no less.
To demonstrate this, put the softest spring you can find on your RF. See how far you can compress the RF by lifting the spindle by the snout without a wheel on it. Then find the longest piece of 3" pipe you can find that will fit over the spindle snout or a bar that will fit inside of it. Even if it is 20 feet long you won't be able to compress the spring any further by lifting at the end of the bar. You aren't gaining any leverage because the spindle can only provide as much force on the LCA as what is available at the ball joint.

[Matt49]

So by moving the wheel placement out further you won't be collapsing the spring easier?

By moving the ball joint out, yes. By just moving the wheel out, no.
Here's another way of thinking about it:
The ball joint has a mechanical advantage on the spring because it is further away from the pivot point. Hence the motion ratio due to the mechanical advantage. I have to move the ball joint further to get the spring to compress a given amount but I don't have to use as much force to do it because of the leverage/mechanical advantage. Same concept as a cheater bar.
But the spindle offers no mechanical advantage over the lower ball joint because it is also fixed to the upper ball joint. To move the ball joint two inches I still need to move the spindle snout two inches and provide the same amount of force to do so. The spindle is anchored to the lower AND upper control arms so you can't think of it as an extension of the lower control arm.
Beam suspension (like the rear end) is different but for a double wishbone suspension, the mechanical advantage (and hence the motion ratio) ends at the outer ball joint of the control arm to which the spring is attached.

[Matt49]

Earlier where I said, "The measurement for motion ratio is from the lower ball joint to the inner pickup of the LCA divided by the lower shock/spring mount to the inner pickup of the LCA." That is backwards.
It is the distance from shock mount to inside of LCA divided by the distance from ball joint to inside of LCA.

[TLM4t4]

I've always noticed more of a difference on exit by adding the spacer than entry. Everyone told me it only tightens entry but from sitting in the seat I've felt more of a difference on exit. Now with that being said I'm confused as crap! What is it changing besides tracking, is it gaining leverage from LR?

[Matt49]

I've always noticed more of a difference on exit by adding the spacer than entry. Everyone told me it only tightens entry but from sitting in the seat I've felt more of a difference on exit. Now with that being said I'm confused as crap! What is it changing besides tracking, is it gaining leverage from LR?

Scrub radius. Moving the wheel out further from the spindle increases scrub radius.
Assuming you have some caster in the RF (which you should), more scrub radius increases the weight jacking effect of the the RF wheel. When you steer to the right, the RF tire is being pushed down into the ground which loads the LR which tightens on throttle handling coming off the corners.
If you really want to see caster and scrub radius at work, find somebody that races go karts. With the wheel turned hard to the right, the LF and RR weight virtually nothing.

[drtrkr244]

I've always noticed more of a difference on exit by adding the spacer than entry. Everyone told me it only tightens entry but from sitting in the seat I've felt more of a difference on exit. Now with that being said I'm confused as crap! What is it changing besides tracking, is it gaining leverage from LR?

My drivers have told me the same thing. After entering the new measurements on my front end software, adding the spacer has moved the roll center slightly higher and to the right, which would stiffen up the rf suspension somewhat. Just like Matt said, also, when back steering to the right, you are loading the lr more. This is why setting the caster is so important on these cars, plus you can use it to fine tune your setups. Just remember steering to the left, loads the lf and rr more also.

[TLM4t4]

May I ask drtrkr244, what software are you using? I know by adding the spacer to my car I either drop spring rate on RF, or open lock out nut up on my stack if not it would not get the amount of travel I want. Thanks for simplifying it Matt49!

[drtrkr244]

Bob Bolles. That makes good sense to soften spring some.

[jrkracing54]

Has anyone ever put a 1" spacer on the right front as well as one on the left rear for extreme slick conditions? Seems like it might be a huge adjustment but both have positive effects. John 1*

[BigNilla]

I want to thank each of you for your responses and additional questionsreally gives me stuff to think about

[MasterSbilt_Racer]

Has anyone ever put a 1" spacer on the right front as well as one on the left rear for extreme slick conditions? Seems like it might be a huge adjustment but both have positive effects. John 1*

I have put 2" at both locations in the leaf spring days. I have seen plenty of cars with 1" at both locations in the past couple of years. They may be there all the time and not an adjustment though.

[hucktyson]

Every newer rocket car I see always has a 1" spacer on the LR. Why don't they just run an inch longer axel tube ?