BUMP STEER IMPROVEMENT

[BETHEVIPER]

evidently the guy who designed this didn't talk to the guy who designed the 97sx. that guy managed to steel other peoples designs, copy them, make them without any reguard to bump steer and the sled still hangled good.

 

[bulldogbones]

Good point about the ball joints being bent upwards at the spindle I didn't take that into account. I'll recheck mine.

Is the spindle in the picture an '08 or '09? From the current view, it could be either one as the tie rod tabs are different between spindles. My guess is its a right hand side '09 spindle since the RH side is beat up from running into things. Note the position of the tie rod tabs. On an '08 RH spindle they'd be mounted on the outside, RH edge. The '08 uses longer tie rods that pivot on the outside of the ball joints while the '09 tie rods pivot on the inside of the ball joints. Since both front ends exhibit bump steer and darting (the '08 being worse) we know that changing the length alone was not enough to fix the problem.

Out of curiosity and testing, I bolted my tie rod end to the top, on the outside of the tab, and did the same thing on the bottom. Both positions were way too much and visibly toed the skis back and forth.

That is an 08 spindle.

 

[scmurs]

I got curious about the bump steer in my Nytro so I removed the springs from the shocks and reinstalled the shocks. I then checked my ski alignment and it was 1/16" toed out with a strap keeping a light tension on the front of the skis. I then measured toe at full droop and then full compression. The toe changed 13/16". That is a lot of toe out change. The '08 front end toes out as it compresses and when you think about it, it makes sense that the front end darts all over in the bumps because each ski is trying to turn into each bump. From what I've read about bump steer in race cars, they recommend no more than 1/16" of toe change. I measured my toe out change the front of the skag on C&A skis.

AK, can you take a few more measurements throughout the travel of the front end on your '08?

I took some with the new SPG front end on my '10 MTX and noticed that the skis stay aligned in toe, right up until it reaches the upper ( airborne attitude ) range of travel. It's past the limit of what the shocks would hold it to, but starts to toe in at that point.

I took 5 different measurements, equally spaced, throughout 9.25" worth of front end travel.

Thanks, Scott

 

[bulldogbones]

Now i really wanna get home and do my test. Because if all that needs fixing is the tie rod mount, then were in business.

 

[Crewchief47]

Parallel tie rod to control arms is not what you want. You need the tie-rod shaft to point at the instant center the upper and lower control arm s make. And the tie-rod shaft needs to be the same length as the distance between intersection points on the ball joint plane and control arm mount plane, even if it's shifted in or out of the actual intersection points.

http://www.circletrack.com/chassistech/ ... to_03.html

 

[00-NUKE]

Parallel tie rod to control arms is not what you want. You need the tie-rod shaft to point at the instant center the upper and lower control arm s make. And the tie-rod shaft needs to be the same length as the distance between intersection points on the ball joint plane and control arm mount plane, even if it's shifted in or out of the actual intersection points.

http://www.circletrack.com/chassistech/ ... to_03.html

Crewchief,

Thanks for the feedback.

That is a GOOD point........ If we were trying to fix bump steer on a car.

A few BIG things not taken into consideration is that the "ball joint" plane in these circle track breakdowns are not aiming for a completely vertical transition like a snowmobile does. The "Intersection point" in the breakdown sits far lower on a car in proportion to it's mass than it does on a snowmobile. Also A-arms on a snowmobile don't share an intersection point like a circle track car. They actually separate the intersection points in order to maintain vertical travel of the spindle and ski. Some of these charactistics in this breakdown do apply, but the angles don't. IMO: Comapring the geometry of a snowmobile to that of a circle track car will only confuse people. But again thanks for the feedback!

 

[00-NUKE]

Shimming them wont do it imo. But what needs to happen is the hole that the tie rod bolts to need to be brought in so it is on the same plane that the upper and lower ball joints are on. This weekend I am going to experiment with my theory.... pen lazer and a wall should tell me where the tie rod needs to be mounted. Then from there if what I think needs to happen I can fab up a bracket of sorts to relocate the tie rod bolting point. But until I actually test my theory Im not sure. I am going to use this guys idea and see where it starts to have a mind of its own.

http://www.youtube.com/watch?v=ZrPJupRSoCI&NR=1

This video is an awesome example of an extreme case. However, on the Nytro, the Lower A-arm and the Tie Rod are already parallel from each other using the same plane. The only factor that I can see forcing the toe to change during travel is the stock angle of the upper A-arm.

There not though.

Notice the tie rod tab's hole is farther out then the center of the spindle.

My angles between the tie rod and lower A-arm seemed pretty close on my Nytro.

So I understand you right...... If we're talking about the tab in the back of the spindle.....

The spindle tab for the tie rod being off center to the left or right is somewhat irrevalent, due to the fact that your onlly effect will be toe in or toe out which is already adjustable on the tie rods.

If you're talking about the tie rod mounting distance to the rear of the spindle, that is irrevalent as well in the case of bump steer because that distance is only affecting rotational force of the steer applied to the spindle.

Mounting the tie rod up or down on the spindle like AKrider is attempting is the only way to make a difference in bump steer, although IMO the angle for the tie rod on mine seems to be about as good as it can be in the stock position without changing spindles or major work.

 

[AKrider]

I really like this thread!

Scott,
I had a very late night working on my house I'm building but I will post the measurements. I've been curious about your kit since you guys first advertised it here in TY. Like I posted in those threads, it has a lot of similarities to the prototype race front end I got to check out on my buddy's sled in '08.

A TY Yamaha racing history lesson
The Yamaha Race Dept had a number of prototype front ends built, and then tested by their factory racer(s) in Alaska, the USCC circuit as well as in sno-X. I've posted it before, but for the sake of this thread, I'll post it again. The prototype front ends featured forward swept a-arms (like an IQ race sled) that increased the wheel base by around 3". The front shocks were remounted on a modified stock subframe by cutting off and reattaching the upper shock mounting tabs. The new mounts leaned the tops of the shocks back into the chassis just like a Polaris IQ consumer sled. The a-arm mounts were fully equipped with heims so caster and camber could be adjusted. Finally the stock spindle tie rod mounting tabs were cut off and relocated. I believe they were mounted further up on the spindle. I was told the front end worked pretty well and allowed the sled to be ridden more like a Polaris. You could slide it into a corner and both ends kinda broke loose at the same time. The sled was also more stable at high speed. Of course there is a down side and the front end broke while being race tested. Like has been shown on these forums, Yamaha had some trick all aluminum front ends on their sno-x and USCC sleds. Bad thing is the front ends broke during race testing in USCC competition. I don't know how they held up in sno-x? In any case, Yamaha dropped their factory racing effort and isn't doing anything. This is really unfortunate but they are a weird company. So, since they are not going to come up with a fix, it is up to us. If we can fix the Nytro factory front end then we can always buy replacement a-arms and other parts which is huge!

I actually had the opportunity to buy a Nytro with a Yamaha racing prototype front end but declined because replacement parts were not available and would have had to have been custom fabricated. I didn't want to have a sled that I was scared to ride fast since if I wrecked it or hit anything, I'd have a one off type of sled and no replacement parts available. I certainly didn't want a museum piece, even though that would have been pretty cool!

00-Nuke,
You bring up some good points. In automobiles, they prefer the spindle go into negative camber rather than scrub the tire. Anyone who's owned an 80-95 Ford pick-up with the twin traction beam (TTB) front suspension can attest to how bad scrub wears out a tire. In the off road world, it doesn't matter as much and seems to be a necessary evil of long travel. From what I've researched, most quads and sleds use parallel a-arms, at least that is how they appear in pictures.

I've got a couple ideas how to get our tie rods in the right spot. The first is to play around with shimming them on the steering frog or to unbolt them, and mount them upside down (and maybe add some shims) to see what happens. I've not had a chance to do this. I'm also thinking a guy could grind off the upper and lower collars on the outer tie rod ends which would turn them into a sphere. This would allow them to be shimmed up and down within the confines of the mounting tabs on the spindle. Bad thing is you permanently alter your toe rod ends for the experiment. Still, I might try it since my sled has 3500+ miles. Today I borrowed a laser level from work and only got to play with it for about 10 minutes tonight. I clamped it to my spindle watched the laser track widely across a piece of plywood I set about 10' away from the front of my sled. I realized I need to do some math and figure out the correct distance to set the plywood or better yet, use a mirror. Check out this youtube video.
http://www.youtube.com/watch?v=LO07qmJ9zkk&NR=1

What I like about this method is you can easily tell if you are getting close to reducing the bump steer or not. I could not get the race car method to work on my Nytro since the scrub was so bad that it bottomed out my dial indicator and I kept having to move it which ruined all the measurements.

 

[00-NUKE]

I really like this thread!

Scott,
I had a very late night working on my house I'm building but I will post the measurements. I've been curious about your kit since you guys first advertised it here in TY. Like I posted in those threads, it has a lot of similarities to the prototype race front end I got to check out on my buddy's sled in '08.

A TY Yamaha racing history lesson
The Yamaha Race Dept had a number of prototype front ends built, and then tested by their factory racer(s) in Alaska, the USCC circuit as well as in sno-X. I've posted it before, but for the sake of this thread, they featured forward swept a-arms (like an IQ race sled) that increased the wheel base by around 3". The front shocks were remounted on a modified stock subframe by cutting off and reattaching the upper shock mounting tabs. The new mounts leaned the tops of the shocks back into the chassis just like a Polaris IQ consumer sled. The a-arm mounts were fully equipped with heims so caster and camber could be adjusted. Finally the stock spindle tie rod mounting tabs were cut off and relocated. I believe they were mounted further up on the spindle. I was told the front end worked pretty well and allowed the sled to be ridden more like a Polaris. You could slide it into a corner and both ends kinda broke loose at the same time. The sled was also more stable at high speed. Of course there is a down side and the front end broke while being race tested. Like has been shown on these forums, Yamaha had some trick all aluminum front ends on their sno-x and USCC sleds. Bad thing is the front ends broke in USCC. I don't know how they held up in sno-x? In any case, Yamaha dropped their factory racing effort and isn't doing anything. This is really unfortunate but they are a weird company. So, since they are not going to come up with a fix, it is up to us. If we can fix the factory front end then we can always buy replacement a-arms and other parts which is huge!

I actually had the opportunity to buy a Nytro with a Yamaha racing prototype front end but declined because replacement parts were not available and would have had to have been custom fabricated. I didn't want to have a sled that I was scared to ride fast since if I wrecked it or hit anything, I'd have a one off type of sled and no replacement parts available. I certainly didn't want a museum piece, even though that would have been pretty cool!

00-Nuke,
You bring up some good points. In automobiles, they prefer the spindle go into negative camber rather than scrub the tire. Anyone who's owned an 80-95 Ford pick-up with the twin traction beam (TTB) front suspension can attest to how bad scrub wears out a tire. In the off road world, it doesn't matter as much and seems to be a necessary evil of long travel. From what I've researched, most quads and sleds use parallel a-arms, at least that is how they appear in pictures.

I've got a couple ideas how to get our tie rods in the right spot. The first is to play around with shimming them on the steering frog or to unbolt them, and mount them upside down to see what happens. I've not had a chance to do this. I'm also thinking a guy could grind off the collars on the outer tie rod ends. This would allow them to be shimmed up and down within the confines of the mounting tabs on the spindle. Bad thing is you permanently alter your toe rod ends for the experiment. Still, I might try it since my sled has 3500+ miles. Today I borrowed a laser level from work and only got to play with it for about 10 minutes tonight. I clamped it to my spindle watched the laser track across a piece of plywood I set about 10' away from the front of my sled. I realized I need to do some math and figure out the correct distance to set the plywood or better yet, use a mirror. Check out this youtube video.
http://www.youtube.com/watch?v=LO07qmJ9zkk&NR=1

What I like about this method is you can easily tell if you are getting close to reducing the bump steer or not. I could not get the race car method to work on my Nytro since the scrub was so bad that it bottomed out my dial indicator and I kept having to move it which ruined all the measurements.

AKrider,
SWEET video!

The laser level seems to be the way to go. I did my measurements with a home made T square mounted to the floor and a caliper. At this rate I believe we'll have the Nytro riding on rails by snow fall. For a while I thought that I was the only sled junkie dialing in my snowmobile suspension in the month of July. Now I know I'm not the only one.

FYI: The mounting point for the tie rod on my 2011 looks to be a lot more centered than that image of the 2008 spindle.

THANKS TO EVERYONE FOR THE FEEDBACK! PLEASE KEEP IT COMING.

 

[rlcofmn]

Very cool thread guy's!

AK, if you need anymore tie rod ends or help with fab work, hit me up.

 

[bulldogbones]

Shimming them wont do it imo. But what needs to happen is the hole that the tie rod bolts to need to be brought in so it is on the same plane that the upper and lower ball joints are on. This weekend I am going to experiment with my theory.... pen lazer and a wall should tell me where the tie rod needs to be mounted. Then from there if what I think needs to happen I can fab up a bracket of sorts to relocate the tie rod bolting point. But until I actually test my theory Im not sure. I am going to use this guys idea and see where it starts to have a mind of its own.

http://www.youtube.com/watch?v=ZrPJupRSoCI&NR=1

This video is an awesome example of an extreme case. However, on the Nytro, the Lower A-arm and the Tie Rod are already parallel from each other using the same plane. The only factor that I can see forcing the toe to change during travel is the stock angle of the upper A-arm.

There not though.

Notice the tie rod tab's hole is farther out then the center of the spindle.

My angles between the tie rod and lower A-arm seemed pretty close on my Nytro.

So I understand you right...... If we're talking about the tab in the back of the spindle.....

The spindle tab for the tie rod being off center to the left or right is somewhat irrevalent, due to the fact that your onlly effect will be toe in or toe out which is already adjustable on the tie rods.

If you're talking about the tie rod mounting distance to the rear of the spindle, that is irrevalent as well in the case of bump steer because that distance is only affecting rotational force of the steer applied to the spindle.

Mounting the tie rod up or down on the spindle like AKrider is attempting is the only way to make a difference in bump steer, although IMO the angle for the tie rod on mine seems to be about as good as it can be in the stock position without changing spindles or major work.

Correct and incorrect all in the same sentence. Correct in the fact when the suspension is not in motion you can adjust toe in or toe out with the tie rod.

But when the suspension is in motion you will get two different arcs of motion.

Sorry for the use of MS Paint. But thats all I had on this computer. You will notice two different arcs being shown red and green. If you, while at suspension rest have your ski set to dead straight to the sled. You will experience ski movement due to the suspension motion. But if you brought your ball joint mounting point in just a litle and got it into the same arc as the suspension then the tie rod ( that affects ski steer ) would track with the suspension.


Im not saying im right, but thats my story and im going to stick with it until I test it and it proves me wrong

 

[AKrider]

I played around with the laser level tonight and photographed bump steer curves it plotted.

Here is my set up. I reinstalled the shock before I did the tests since I wanted to know the exact travel limits.

I shot three different configurations of the tie rod mounting. You can see how you can alter the positions of the stock washers.

I used a piece of plywood I had lying around, leaned it against a saw horse 43.75" from the end of the laser level. The laser level was 11.5" ahead of the spindle bolt hole which is somewhat similar to where the front of the skag would be. The laser is pointing at the top of the stroke.

Here is the curve with the tie rod raised up with two washers underneath. I also measured the toe out distance. Maybe someone can tell me what the correction would be since the plot was taken 43.75" from the end of the laser level? I suspect the toe out angle grew to an extent since it the plot was almost 4' away from the end of the laser level.

Here is the stock tie rod configuration plot curve. My sled has the 2mm upper ball joint mod.

Here is the plot curve with the tie rod in the lower position with the two stock washers placed on top. I was shocked to see how much difference one washer made to the toe.

The skis really toe out at the initial few inches of the travel. Once the suspension hits mid travel it really seems to stroke nicely without toeing out. I'd like to experiment a bit more with either different (thinner) tie rod ends or grinding down one of my stock pieces.

Rlcofmn, do you carry lower profile tie rod ends that would thread into the stock tie rods?

I know the photos of the plot curves are not as clear as I'd like but this is a start and gives us an idea to what the sled is doing. One can see how lowering the front of the sled and running lots of sag helps reduce bump steer and the resulting darting since the front end doesn't toe out much in the upper portion of travel. This also shows why the Nytro is a miserable handling bastard in the stutter bumps since if you are not running a ton of sag (typical stiff set up for big bumps) the a-arms are being worked in the lower portion of the travel and the skis are toeing out as the a-arms compress than toeing in as the a-arms rebound out. It is no wonder why the Nytro doesn't handle for sh!t. The big question will be, can we shim the tie rod ends enough to to plot a nice straight line on the plot curve? If we can, then in theory, the bump steer is tuned out and the Nytro will handle as good as the other brands of sleds.

 

[rlcofmn]

I can pull the ball joints out of my Nytro chassis and machine them down for you to try shimming them. If I do ever do anything with that chassis I will replace them with anything but Yamaha POS tie rod ends.

I have a theory on the bump steer but I have not taken the time to read this thread or really sit down and think about it. So I'm not going to make any UN educated guesses when you guy's are doing a lot better job than that.

 

[RJH]

Nice effort..

You need to place the board at about the end of the ski distance.

Another post above..ya I did that with my older style..moved the steeing rod to the under side of its stock position..bump steer..fixed.

As far as the racing..hmmm..the guy that drove the Yamaha finished in position X in the USA. The next year he drove another brand..tell me where he finished with that sled against the same competition.

 

[scmurs]

You need to place the board at about the end of the ski distance.

The reason for projecting the laser out farther is to amplify the bump steer measurements. It will make it easier to read ( measure ) on the cardboard or plywood and then you can divide the measurements off of that to determine the actual amount of bump steer at the ski tips.

I've pm'ed or talked to 00-Nuke and AKrider about a "universal" way to compare notes. Aint the internet great?

As far as the racing..hmmm..the guy that drove the Yamaha finished in position X in the USA. The next year he drove another brand..tell me where he finished with that sled against the same competition.

I have no clue, please enlighten me. Is it pertinent to the front end on the Nytro?

Scott