Alignment Questions Feed-Back

[rich46]

Hello All,

After some back and forth about alignment I find that I've had PM's and even some phone calls as to my saying that our Spyders have under-steer and that's just part of the beast and something we need to live with and minimize. Some folks almost seem insulted that I would say such a thing.

Almost since there has been a discipline within engineering called Automotive Engineering we have designed vehicles to under-steer as a safety matter. This is because there is nearly no way to make vehicles be totally neutral. Therefore you are left with designing them to either under-steer or over-steer. Under-steer is the choice because it is the safest option. When Grandma come smoking off the freeway and realizes she is going way to fast her first reaction is to lift off the gas and tap the brakes. Letting of the gas and braking is the fix for under-steer.

Both Porsche and GMC (Corvette) tried to design a wee bit of over-steer into their high performance cars because it makes for a faster car in the twisties. GMC gave up that idea years ago. I don't know what the Porsche guys did but in the late '70's I worked for several insurance firms on a car that seemed to have a high roll-over tenancy while going through a stack of crash records of all manufactures and models I was surprised at the number of first time German car owners that had put their shinny new sport-cars into the hedges. Almost all those were new rear engine cars with first time drivers.

So anyway I don't think ill of CanAm for the Spyder having the under-steer tendency. If we want our rides to handle really well on windy roads while ridden quickly. Being aware of this will help when doing your aligning and in how you ride.

Just a little history and a few thoughts


Cheers

 

[PMK]

Rich, while a Spyder will understeer pretty much as default on dry surfaces, I never found the understeer excessive (except the time testing lower tire pressures), unpredictable or unsafe with a decent front alignment setup, AND adequate roll stiffness for the rider weight.

The most alarming concerns I have had experience with on the Spyder, is at times, a somewhat violent twitch as you apex a corner, in such a manner the outside tire goes toe out. As that transition, under cornering, from a correct slight toe in converts to bump steer induced toe out, the entire chassis becomes upset. Once the rider senses the upset chassis and compensates, typically the outside tire then quickly transitions back to toe in, sometimes resulting in a violent turn in towards the inside of the corners apex.

The more swoopy and flowing the road, the less likely that happens. Enter a decreasing radius corner with applicable speed and the snap happens. Exactly the reason I plan to adjust the front roll center, then validate my current toe in settings that work excellent except in those conditions mentioned.

Having tested various toe settings, it became apparent, what certainly was not fun to ride, what was ok, what is good and how each change alters other parameters. I could very easily reduce the snap tendency by running excessive toe in. Downside being, doing that kind of pinches the chassis and scrubs tires. As the front becomes freed up, the Spyder gets very good (except the toe out snap / twitch), rolls without resistance like a skateboard, and is quite fabulous for touring but less fabulous at more sporty riding.

As in the other topic / posts, it is very exciting to know you purchased ROLO laser alignment equipment and BUDS or BUDS2 software to accurately and consistently reset the Spyders sensors to null them. All very cool, and again, all the best doing it.

 

[rich46]

PMK,

Remembering that all a sway-bar really is, is a torsion bar connecting the left and right side of the suspension. What it does is pretty much make one side mirror the other as we turn left to right and back. The stiffer the bar or where on the end of the bar you mount the link dictates how quickly and how completely the mirror effect is.

Because this torsion bar is spring steel I kind of think that the "violent twitch" is a result of energy building up and being stored in the bar as the vehicle is turned into the corner. Then something releases that stored energy and you get the "violent twitch". So what we must ask ourselves is what causes the release of energy ?

When I take my Spyder out into the Dairy farms around my home, where I can really push the limits, where the worst that can happen is that I'll need to wash the cow pies off and repair some bodywork, I have also felt the very twitch you describe. So what am I or the Spyder doing that would cause the VT. Within the "I" part of the mystery there's throttle, brake, body position or/and misconception of what's happening. As to the Spyder, it must be mechanical loss of connection either from failure (breakage) or disconnection, non-engineered release (chassis deformation and return) within the chassis. The same deformation and release would hold true for the suspension. I suspect it could also conceivably be some sort of electronic counter measure within the ECU.

So the "I" part; I know I do not jerk the bars, I do not chop the throttle (that would cause weight transfer), nor do I hit the brakes. I am making the direction transitions as smoothly as I can. We're now left with the Spyder. It has been mentioned that the control arms may not be the best (and could be at fault) I did look at these and I'll admit there was no easy way to do a good Rockwell test because of the wrinkle powder coat but the control arms are beefier than most F2 and F3 race cars and seem to be made of aircraft strut tube (would not be a surprise considering BRP heritage) so I doubt this is where the wind up is. It could be chassis wind-up (I have not, nor do I intend to strip my scooter down to do a proper test) but this usually manifest itself as a more slow issue rather than a quick reaction to loading. This is unless something is broken and because we both feel the VT I would rule that out.

Rather than going any deeper into the possibilities I think what we are feeling is the sudden failure of the mechanical connection between the tires and the road surface. Not really a choice of tires as I think that, that only would dictate when (at what speed (MPH or turn-in)) not what the root cause is.

It is a fun engineering puzzle. My professors and instructors would say check for open windows before replacing the shop heater and I have a few thoughts but I throw it back to you....what is your thinking ?

 

[PMK]

As you begin testing your settings, a simple test is to run different toe settings, including some toe out. Pretty certain you, as I did, will find the toe setting and bump steer will cause the twitch.

Yes the mild steel chassis and suspension components add flex that may contribute, but do not induce the twitch.

Regarding the swaybar, a firmer bar increases roll stiffness, thereby reducing bump steer induced from suspension compression.

Like I mentioned, test a bit and see how your results compare. Our Spyder was horrible, and super sketchy as delivered new. With no other chassis changes, I merely kept testing different toe settings, until the Spyder became very good. Adding the firmer swaybar and aftermarket Fox Shox, plus high performance tires each increased the Spyders cornering ability.

The twitch I shall work out, as I explained will require testing a roll center change and toe in resets. I would love to have 4130 suspension arms and a braced swingarm. Sadly though, it seems unlikely the spindly RT series frame could cope without a lot more flex. No intentions to brace or build a 4130 frame, simply just not a high enough performance machine to warrant that much work.

 

[rich46]

I did find that my dealer's PDI set up well - sucked! As I started going through the settings, the first check I made was the basic ride height - it differed by 20% left to right. I think that if they didn't get that right them OMG, what will I find elsewhere?!

 

[PMK]

I did find that my dealer's PDI set up well - sucked! As I started going through the settings, the first check I made was the basic ride height - it differed by 20% left to right. I think that if they didn't get that right them OMG, what will I find elsewhere?!

FWIW, dealer setup does not accomplish any suspension set up, nor alignments.
Simply, the unit is removed from the crate, packaged items are fastened on, most places add gas, and start the engine. Many times, next, the unit is wheeled into the showroom. Upon purchase, buyer selected options may be installed, including if available, a laser alignment.

As you read through so many topics and posts here, plus on FB, it is obviously apparent, many dealers fail to correctly accomplish a PDI. Most recent years of RT series, the rear shock lower mount is not correctly assembled AND the dealers fail to connect the air ride followup link.

Eventually, you will sort out your machine to your own liking.