RR98ITR

There's a thread asking about caster ( https://honda-tech.com/forums/road-racing-autocross-time-attack-19/caster-effects-worth-going-after-more-2638505/ ) in which some members mention the effects of swapping UCA's left for right to gain caster on bump steer. Here are the before and after values, where the ride height is approx 4.5 inches to the jackpad on a 23 inch tire and the toe is measured on a 14.5 inch spread (that's the width of my toe plate) on a single side:

Stock UCA (low caster): by 1.5 inches bump 0.101 inches toe in, and by 1.5 inches droop 0.058 toe out. The outer tie rod end should be raised.

Reversed UCA (high caster): by 1.5 inches bump 0.140 inches toe in, and by 1.5 inches droop 0.109 inches toe out. The outer tie rod end should be raised more.

There is less than 1/16 inch difference in available bump travel between the two configurations. A Skunk camber adjustable UCA in the reversed high caster position will cost you approx 3/8 inch of travel.

Nobody currently makes an aftermarket UCA that gives you meaningful amounts of caster, sufficient range of easily adjustable negative camber, and clears the knee of the knuckle and the spring, while at the same time not costing any travel. BTW - with a stock UCA bottomed against the tower, there's very little steering angle to be had before the tire hits the inner fender structure, so you can only go so low anyway practically speaking.

Scott, who doesn't like bump steer, roll steer, passive steer, power steer, brake/yaw steer, understeer, or any other kind of steer except for Scott steer...

Egezzy

iTrader: (2)

slammed_93_hatch

3/8 of an inch loss in travel I can deal with.

"low caster"
There is a change/swing of .159 inches of toe in 3 inches. This is between 1/6 and 1/7 of an inch


"high caster"
this gives you .249 inches of toe change in 3inchs of travel. Almost a 1/4 inch switch.


So you gain, in bumpsteer, .09inchs. Close to 1/10th of an inch.



Thanks for this info Scott, really appreciate it. It gives me something to base my adjustments off of.

TunerN00b

Thank you much Scott. Real measurements are always helpful.

These are what I've been using for caster adjustment.

SPC brand.
Only a +-1.5* caster range. At least the camber adjustment range is (listed as) +-4* (more like +4* to -3* in actuality).

BRN12345

I have those SPC UCA's and they cost me 2 races. The big nut on top has come loose on both occasions. I ended up tack welding it. Needless to say, i have since tried another brand with no caster adjustment and felt no difference in handling.

Austin

120 ft/lbs is your friend. Mine slipped when they weren't torqued correctly. 18 races without a problem.

TunerN00b

Agreed. Mine have never slipped, and my camber hasn't been adjusted in 2 years of street driving, 20 autocrosses, and a track day.

My alignment tech sure looked at me funny when I told him the torque spec for them, but he did it anyway with the largest torque wrench I have ever seen.

RR98ITR

Just wanted to add some measurement of the rear end to this thread.

Roughly measured at a typical race car ride height on 23 inch diameter tires etc, with adjustable toe links:

"Medium Length Links" give single side toe in of 0.033 inches at approx 1.5 inches bump, and 0.012 toe out at approx 1.0 inches droop, measured on 12 inch spread.

"Maximum Length Links" give single side toe in of 0.024 inches at approx 1.5 inches bump.

Brian at PCI has pissed me off (j/k) by producing a new version of his excellent spherical RTA bushing with an offset bearing to help reduce the rear bump steer (I've got the original version and a spare set). The propaganda suggests that the new ones correct/zero the bump steer if I recall correctly - not sure about that, reduce yes, but zero?

Scott, who finds the imperfections of the DC2 chassis require microscopes and micrometers to detect...

Lo-Buck EF

i actually had to think about that rear suspension info for a bit before it made sense. good bit of info right there.

TunerN00b

Anyone else find it odd to have the rear of a production car toe out under droop? I mean, last thing I want is my back tires pointing out when I'm in the middle of a severe braking maneuver and have the entire rear end in droop...

Then again, the car probably only has 10% (or less) of the weight on the rear under those conditions, so maybe it doesn't matter as much as I think it could.

RR98ITR

The typical race car ride height is lower than stock, putting it farther into the bump side of the curve. So it's not odd that such a car toes out in droop - it's just backing out of the bump toe in. If you went far enough into droop it'd start to toe in again. That wont happen with race rates of course.

Scott, who really doesn't want the outside rear turning into the turn...

TunerN00b

Makes sense.

100% agreement there. Though, I certainly wouldn't mind the outside rear turning away from the turn a little.

RR98ITR

Just wanted to note my correction to the rear bump steer data. It's less than I originally stated, and in fact it's enough less that I find my desire to do something about it decreased accordingly. As usual, Honda left very little room for improvement. A very practical and economical approach to minimizing the effects would be to run the car a little high in the back to get close(r) to the zero point and the slowest parts of the curve. Of course that may set off your cg height alarm bells. I'm sorry, I can't help you with the bells ringing in your head. I've got my hands full with the bells ringing in my own.

Scott, who apologizes for the error...I've made a couple too many lately...

JuanTushag