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I've been learning tons about suspension in my new project and just wanted to share my experience with Whiteline's B13 Caster kit (KCA303).
The kit consists of replacement lower control arm rearward bushings. The bushings have the control arm pivot offset outboard as far as allowable to increase caster.
Increased caster can improve stability at speed, negative camber gain on bump, and negative camber gain on turn in. My reasoning for doing this is to improve cornering ability without wearing the front tires with ludicrous alignment settings (was running -3.5° camber), since I have retired the Sentra from autocross duty.
Whiteline's bushings appear to be much better quality than Energy Suspensions bushings. The hole is mostly closed at the rear (an opening akin to OEM), the hole is crosshatched to retain lube, the casting finish is much cleaner and the durometer appears (by my handy gefingerpoken gauge) higher.
Bushing install was easy: Drop the front sway bar chassis mounts, unbolt the control arms, swap bushings, reinstall. A slight toe adjustment was required afterwards.
Steering effort is noticeably higher at low speeds (but not killer), and a the self-centering ability of the wheel seems improved (I always found the Sentra vague on self-centering at normal camber settings. Ludicrous settings made the steering feel so much better.).
The steering wheel is a bit more stable on the highway, but that feeling is probably psychosomatic.
Turn-in feels much better. It feels much more refined, not as abrupt as it did before. In some ways I kind of miss that, but the car feels a notch higher in "refinement." I don't know how else to define that. Cornering ability seems slightly better, but tests were conducted at my usual commuting speeds on fresh Cooper winter radials (I'm in Canada, eh!). The feel is significant, and makes me feel more confident in pushing the car.
Ground Control believes in This Article that the importance of increased caster is over-rated, and can cause additional problems by upsetting the corner weights on turns. This may have a fair bit of merrit, however, keep in mind that B13 Caster is somewhere around +2.8° fromt he factory? Most racers are shocked to hear it's so low. Aren't BMW's around 7°? If you've ever driven one, you know how easy they are to drive fast. It's "feel." Whiteline's kit will bring you closer to 4° or more (I'll have numbers after the weekend - alignment on Monday) - not outlandish by GC's examples.
Superpro in Australia also makes those too (with remarkably similar features). Good write-up though - I'm interested in hearing how they are after some serious flogging.
btw - factory caster spec = 1*05' - 2*35' for coupe
Back from the rack today - Monday appt was rescheduled (figures).
Here are the specs for the caster (L/R) Before ---- After:
2.2°/1.6° ---- 3.4°/2.8°
An improvement of:
1.2°/1.2°
I guess that's not bad. I thought it should have been more, but I think I was mesmerized by the camber I ran at the previous alignment: -3.0°/-3.5°
I've been driving the car for about a week now, and I am pleased with the results. The car "feels" so much more refined. Gives me much more confidence.
Sadly, Bjorn, I won't be flogging the car on track any more - I've retired it from competition as the Lotus 7 Clone is next. I'm confident that the bushings will work awesome. Does SuperPro have a website? Thanks for the kind words on my website - I spent a lot of time on the Sentra section, I hoped it could be of use to others.
Bennitto, you don't need a special alignment place. Any regular shop can align the car - Caster is not normally adjustable. Anyone can install the bushings - they are a piece of cake.
I look at those bushings and can't for the life of me figure out how a lateral change in the rear control arm location turns into a for/aft change in the entire control arm. If the strut top is fixed, you have to move the entire control arm forward or backward to change kingpin inclination (i.e. strut angle). What am I missing?
Unless the control arm axis isn't directly for/aft... Do we have swing arm FRONT suspension???
__________________
Bruce in Houston
1990 Acura Legend LS, stock (so far)
1994 Nissan Sentra SE-R (original owner) w/ $tuff, converting to ITA (even more $tuff)
1998 Suzuki Bandit1200S w/ $tuff, W.W.B.O.C. #101
2002 Dodge Dakota tow beast, stock! RIP swwwinger
"see" the right side control arm from the top...
A
=====|| B
||
||
||
||
||
|| C
B is the strut mounting point on the arm
A is the front chassis mounting point of the arm
C is the rear mounting point of the arm where the offset bushing goes.
Now, imagine that point C is moved to the right (otwards) as when the offset bushing is installed.
Point B moves upwards (i.e. to the front) , doesn't it?
Rear drive cars can run crazy caster because they don't have to worry about lifespan of front axels and CV joints. We do. Fairly unknown mod for the Honda boys is to swap their upper control arms left-to-right. Gives them crazy caster in the 4ish degree range. Some models, like the Prelude, get over 5+, and axels snap like twigs.
Several questions:
I though point "A" is fixed in the plane that you guys are saying it will pivot. I can't see how this works.
Are these legal for STS/STX autocross?
How much?
Any decrease in axel lifespan?
Matt<---likes positive caster, but, sadly, even with GC camber/caster plates is caster-challenged....
MaddMatt - I can't see how increasing caster can significantly reduce the life of axles. The change is not substantial enough to even be perceptible to the eye. The front wheel might be slightly more forward than before, or it's my brain thinking it is. I'll have to compare to pictures of the car before. At any rate, the slight change in hub location is nothing compared to even a 1" drop - and CV's are designed to handle increased angularity. Unless of course the axles are so worn that a change causes the balls to run outside their groove..... Should be no worse than what people are already doing with GC plates.
Keep in mind Honda axles are garbage to begin with. Especially jobber axles. I got really good at swapping axles on my old Civic many moons ago. Perhaps the Hondas are having problems with the axles binding? I mean, swapping the upper arms might not have been engineered and tested to the extent that an aftermarket company might go.... Hmmm.... Further testing....
There will be a slight change in steering, probably imperceptible, since now the rack is further away from the hub centerline, which would further reduce ackerman at extreme angles. Will you feel this? Never.
They appear to be legal in Street Touring(Moutons SCCA Rules - STS), as "offset bushings may be used." We don't run STS in Canada, so I haven't studied SCCA/Other rulings.
The set cost me about $85 CDN taxes in ($71 USD).
I can't see there being a decrease in lifespan. I've driven/raced for three years on more than -3° camber, and no axle noise/snappage yet. I put on about 30,000km (18,000miles) a year. Mind you, it's a GA16DE, not an SR20.
These might really help out your car, Matt!
Slartibartfast - This should not affect the scrub radius at all. If you imagine the KPI as viewed from the front, the scrub should stay the same as the ball joint is merely moving towards you (albeit in a slight arc). What it will change is "trail" - that is, how far the center point of the wheel on the ground "trails" behind the KPI intersection of the ground as viewed from the side.
Too much trail can really increase steering effort. But so does increased scrub. Or increased KPI. They're all related. We're trying to make the most out of something that wasn't engineered to do what we want it to do. Which is why now I'm building something else. Might as well start with a better slate, eh?
I've looked, and looked, and looked again. I just don't see it. I can't see how the control arm pivots around point "A" in the diagram. It can't. It's fixed in that axis. Cannot move. How do these things work???
In the top picture, if you move point "C" (rear mounting point) to the right, how in the hell does point "A" (front mounting point) pivot?
Sadly, Bjorn, I won't be flogging the car on track any more - I've retired it from competition as the Lotus 7 Clone is next. I'm confident that the bushings will work awesome. Does SuperPro have a website? Thanks for the kind words on my website - I spent a lot of time on the Sentra section, I hoped it could be of use to others.
their catalog isn't working for me, but I have seen it before and know for a fact they have bushings for all the control arms, steering rack and anti-roll bars for the B13
this is the fourth attempt of mine to try to post , so I'm not gonna press my luck trying to type more right now
I've looked, and looked, and looked again. I just don't see it. I can't see how the control arm pivots around point "A" in the diagram. It can't. It's fixed in that axis. Cannot move. How do these things work???
In the top picture, if you move point "C" (rear mounting point) to the right, how in the hell does point "A" (front mounting point) pivot?
bushing flex/slop - easier to visualize w/ a sph. bearing
Matt, the bushing pushes the REAR of the control arm out. The front is fixed so the control arm must pivot in the front bushing ever so slightly to accomodate the new rear position. It basically toes-in the entire control arm (changes the control arm pivot axis).
After some thought, it appears scrub radius is increased.
1) We have the ball joint area.
2) We have the single bolt pivot area.
3) We have the area where the new castor bushing we'll be installed (w/the 2 bolts).
Now in order for caster to change the control arm needs to move closer to the outside of the car for each respective side and that is why the bushing hole is off centered. The only concern I would have with this method of gaining caster is the awkward bind you put on the single pivot bolt area which might cause premature wear even though it is slight it is a move that isn;t natural. Sorry it sorta hard to type this out with out illustrations.
After some thought, it appears scrub radius is increased.
Lol. Now it's my turn to not be able to visualize this. Can you describe how it increases scrub? I'm thinking that scrub is a constant since the wheel size and KPI are fixed as viewed from the front.
MaddMatt - there is some compliance in the forward bushing and fastener to allow some movement. It's not much movement, mind you.
The only concern I would have with this method of gaining caster is the awkward bind
A valid concern. On the other hand, there is significant bind in the rear suspension, but nobody complains about it. We're also assuming the factory bushing mounts were even in correct alignment to begin with.
Well what i mean is the front control arm simply fits into place in stock form. I can imagine when u add these castor bushing with the off center hole there has to be some munipulation envolved to get the single bolt pivot threw the hole and by that happening a squishing of one side of that bushing will happen while the other side becomes somewhat unloaded. IMO they should have also made a cross angle hole threw the single bolt hole pivot bushing to spread the load evenly.
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, so I'm not gonna press my luck trying to type more right now
Can you describe how it increases scrub? I'm thinking that scrub is a constant since the wheel size and KPI are fixed as viewed from the front.