All inclusive front suspension thread: spindles, UCAs, settings, etc.

I need to replace my spindles. What started as a seemingly simple phone call to PAD to order parts turned into something that would rival Lewis Carroll's most famous writing.

I have talked to the guys at PAD and researched the Coleman website. I have also read all of the old posts about the equal length vs. offset UCAs, caster, camber, ride height and toe settings...

Here is what I understand (in bullet format, no particular order):

All cars left the factory with equal length UCAs (according to Brandon & John). Once the cars went to the school or the WC prep garage, then all bets are off.

The offset UCA moves the upper ball joint location back 2" versus the equal length arm fitted by PAD.

The Coleman Impala spindle (PN 19975) is 8" tall, 3.75" pin height, 10 degree kingpin inclination angle. The spindle that PAD has Coleman manufacture is identical with the exception of the kingpin inclination angle, which is 7 degrees.

Therefore:

If the ball joints are in the same vertical plane, then the caster should be 7 degrees positive due to the included kingpin inclination of the spindle upright.

All other variables held constant, the offset UCA should increase the caster significantly, as would fitting the Coleman spindle PN 19975.

Other interesting findings:

Coleman also makes a spindle that has the same dimensions as 19975 (PN 19976) that is 3/4" taller. Keeping the ride height the same should increase the camber gain by moving the UCA higher in its arc of travel.

PAD retail price for the spindle uprights is ~ $158, with a 10 - 14 day turnaround. Coleman has the Impala spindles as priced on the website. Depending on whether or not you can verify what you have on your car currently, one will require an alignment and the other shouldn't...

I invite any corrrections to what I have posted. This is all in the vein of getting the word out...

Please add your findings if you have fitted any of these parts, to include what settings you are running.

Also, I ask the forum moderators to move old front suspension posts with quantitative data to this thread for one stop shopping.

FWIW, I still haven't ordered any spindles!

I need to replace my spindles. What started as a seemingly simple phone call to PAD to order parts turned into something that would rival Lewis Carroll's most famous writing.

I have talked to the guys at PAD and researched the Coleman website. I have also read all of the old posts about the equal length vs. offset UCAs, caster, camber, ride height and toe settings...

Here is what I understand (in bullet format, no particular order):

All cars left the factory with equal length UCAs (according to Brandon & John). Once the cars went to the school or the WC prep garage, then all bets are off.

The offset UCA moves the upper ball joint location back 2" versus the equal length arm fitted by PAD.

The Coleman Impala spindle (PN 19975) is 8" tall, 3.75" pin height, 10 degree kingpin inclination angle. The spindle that PAD has Coleman manufacture is identical with the exception of the kingpin inclination angle, which is 7 degrees.

Therefore:

If the ball joints are in the same vertical plane, then the caster should be 7 degrees positive due to the included kingpin inclination of the spindle upright.

All other variables held constant, the offset UCA should increase the caster significantly, as would fitting the Coleman spindle PN 19975.

Other interesting findings:

Coleman also makes a spindle that has the same dimensions as 19975 (PN 19976) that is 3/4" taller. Keeping the ride height the same should increase the camber gain by moving the UCA higher in its arc of travel.

PAD retail price for the spindle uprights is ~ $158, with a 10 - 14 day turnaround. Coleman has the Impala spindles as priced on the website. Depending on whether or not you can verify what you have on your car currently, one will require an alignment and the other shouldn't...

I invite any corrrections to what I have posted. This is all in the vein of getting the word out...

Please add your findings if you have fitted any of these parts, to include what settings you are running.

Also, I ask the forum moderators to move old front suspension posts with quantitative data to this thread for one stop shopping.


Good Info, I need to tackle this sometime soon as well. I am using the original spindles from when I bought the car(they were pretty when when I bought the car in 2008 though)

Good Info, I need to tackle this sometime soon as well. I am using the original spindles from when I bought the car(they were pretty when when I bought the car in 2008 though)

Also, what was the price for the Colemen spindles?

Coleman's website shows $125

http://www.colemanracing.com/DisplayCatalogPageColeman.aspx

Reusing steering arm and caliper bracket should be okay, will probably use new hardware.

I use the unequal upper A-arms and the 19975 Coleman spindles. I like the added caster.
As part of my off season maintenance I magnaflux my spindles each year. The first spindles on the car when I bought it were cracked, and hence I replaced them. The use of slickes significantly increases the loads on the spindles and its recommended that they are replaced at least every other year. Good advice.

Kingpin angle is the angle from vertical toward the center of the car about which the spindle rotates. Using the wrong angle will change the adjustment required for camber, not castor. It also effects the rate and amount camber and castor change with turning, although I'm not sure in which ways. The unequal upper control arms are available from Colman in 1 inch increments, so you can get a 1 inch, 2 inch etc. offset. This may help you maintain the correct wheelbase without unduly extending the trailing arm the required amount to obtain the desired castor. I like the Unequal UCA because it keeps the castor constant with bumps.

Craig

All,

I stand corrected! Upon further research, Craig is correct. The KPI angle is the angle defined by a vertical plane and the plane defined by the two ball joint tapers as viewed from the front of the car.

I was describing the caster angle, but calling it by the wrong term.

All,

I stand corrected! Upon further research, Craig is correct. The KPI angle is the angle defined by a vertical plane and the plane defined by the two ball joint tapers as viewed from the front of the car.

I was describing the caster angle, but calling it by the wrong term.

Not being suspension savvy, I am having difficulty in understanding your initial post in this thread while trying to correct the terminology. Could you correct it and post it again, with any other additional remarks you think will help me get a full understanding of the implications for using the three different spindles and two (three) different upper control arms. I'm a little slow to catch on.

Thanks,
Mike

Mike,
Will do ASAP. I'm posting from my phone at the moment (not while driving!)...

Suspension adjustments are just like high school math word problems....it helps to draw a picture.

Thanks, I think I've gotten confused with the terminology. Mine has the offset UCA and original spindles. I think I'm close to needing to replace the spindles or at least running them through a good testing. If I need to replace, I want to pick the best alternative for good geometry.

Mike

I'm with Mike!

Mike you should have your spindles magnafluxed every year.

If you magnaflux every year and find no cracks, how many years would you run a set of spindles before replacing them?

If you magnaflux every year and find no cracks, how many years would you run a set of spindles before replacing them?

Jerry, I pondered this same question. By the time I pulled them out of the car and paid to get them magnafluxed by a professional shop (who would thoroughly inspect them) I was halfway to paying for a new set........(if you value your own labour) Decided that required replacement cycle really depends on driving style, how often you run, DOT's V slicks fitted, type of circuit you run on, whether you attack ripple strips etc etc.

In the end I decided that I would replace the spindles after every 3 - 4 full race seasons on my car. I only do 10 - 15 hours a year max, run DOT's and my local track is not hard on suspension components or tyres (e.g. we can get up to 12 - 15 hours out of a set of some DOT's if set up is spot on).

Not sure if this helps you or not but I think each individuals variables must be factored into this decision. By way of example, if I was running 40 - 50 hours a year on slicks and driving really aggressively on ripple strips I would probably replace every 1 - 2 years max. A lot cheaper to replace them Vs one breaking and wrecking the car or worse, ending up doing some "sheet time".

Kel.

Well said Kel

Kel;
Thanks for the response. I run the car for about 10 - 12 hours per year with slicks. I don't run over rumbles religiously, although I do aim for them at apexs. :-) I think that your advise is a good guide. I'm going to pull the spindles off the car and have them magnafluxed at my race shop this year to see if they have developed cracks. That will give me a good bench mark to see if they go three years and 30 to 40 hours total.

If you magnaflux every year and find no cracks, how many years would you run a set of spindles before replacing them?

At the risk of being negative.... I'd say that magnafluxing the spindles is worthless. The only potential benefit would be if you happend to "get lucky" and time it just right with a small crack. Given the very high forces, I'd speculate this condition only exists for a few laps at most... but hard to prove.

If you are going to take them apart just replace them as a failure can be deadly and may total the car. We've broken 2 at speed and now replace them every year on the slick car and every 2 yrs on DOT car. Also after any collision or direct blow to the front wheel assy.

We replace essentially every wear and moving component (all joints, eyes, suspension parts, studs etc ) on a 2 yr cycle. That is racing SCCA about 10 weekends and 2-4 test days/year.

Kevin
GTS, GTRA
997 Porsche Cup Car

Digging this one up... so if you were to swap to the standard 19975 spindle with 10 degrees of spindle "inclenation" do you have to change the steering arm as well? You'd have to move the UCA inward toward the center of the chassis more to achieve the same amount of negative camber correct?

I'm not into drifting, but this article (6 pages) does a pretty good job explaining the interrelationship of caster, kingpin inclination, and scrub radius.

http://www.motoiq.com/magazine_articles/articletype/articleview/articleid/1982/the-ultimate-handling-guide-part-8-understanding-your-caster-king-pin-inclination-and-scrub.aspx

I wouldnt mess with the king pin inclination unless you have a specific need to. KPI should be a constant on a base-lined car. I would only recommend changing the angle if you are trying to correct a poor scrub radius.

FYI- Scrub angle/radius explained- Find the dead center of your front tire on the rims you run. Notice where it contacts the ground. Now looking from the front of the car, notice the imaginary line through the upper and lower ball joints. Now compare that line to the dead center of the tire. If the two lines intersect below the contact surface (ground) you have positive scrub angle. Above- negative scrub angle. At the same point, it is neutral.
http://i209.photobucket.com/albums/bb222/roval41/sai-scrub_zps0609b2c8.gif

Why is scrub angle important? Steering effort. Neutral or negative lessens steering effort and can make the car feel like it darts around. Conversely, too much positive angle causes too much scrub, or almost a braking effect when you turn the wheel. This can cause the car to feel like it's "hooking" the inside wheel. The only way to change scrub angle is with rim width and off-set, or changing the KPI. I personally think that 9-10 degrees is about optimum.


Caster is a good thing. It stabliizes the car at speed. Too much caster is not as it causes the wheel to basically "flop" and reduces your contact patch when turning. Therefore: too much caster causes a push that gets worse the more you turn the wheel. I would not recommend more than 5.5 to 6 degrees. IMHO. Also in my opinion, the upper a-arms are long enough to not really need an offest to achieve that much caster. Again, just my opinion. Off-sets are more about driver feel and desire. If you look at the mounting bar that runs through the a-arm, if it is not at an angle as compared to center axis of the car, with the caster settings you want, you're fine. If it is at an extreme angle, you can get in a situation where you are putting the ball joints in too much of a bind. I was messing with mine (as evident in the previous posts) and noticed that because the upper arm is as long as it is, I had to make minimal adjustments to get to 5 degrees (where I prefer it) and nothing was at odd angles. So- IMHO- Offsets are not required.

Sorry about getting so "wordy"

Good info. Question... adding negative camber increases the KPI by default as it lays the spindle further inward at the top right? KPI is measured relative to a vertical line and not the hub face right?

Good info. Question... adding negative camber increases the KPI by default as it lays the spindle further inward at the top right? KPI is measured relative to a vertical line and not the hub face right?

yes, in real-world measurements. However, Coleman and other manufacturers base KPI on it's relationship to the spindle itself

That's what I thought. Thanks for confirming.