BUMP STEER IMPROVEMENT

[multi sled]

My '05 Vector had more stable handling than the Nytro. How Yamaha managed to f-this thing up as bad as they did is anyones guess. In talking with a friend who had a racing relationship with Yamaha for many years, patents could have been involved that prevented Yamaha from designing the front end properly. They may not have wanted to pay Ski-doo or Polaris or Cat for certain infringments like steering post design or linkage.

The '09 geometry slackened the caster angle from 22 degress to 26 degrees. It also increased the amount of trail in the ski. The reasons I'm convinced bump steer is the culprit for the Nytro's unpredictible handling is #1 the traits match everything you read about in automotive text books and online race car articles and #2, because I've experienced it first hand over and over again through the years. In one race I ran 1" shorter GYTR shocks (off my Vector) on my front end since my stock ones were being revalved. I also ran Sly-Dog race skis with either 6" or 9" shaper bars. i hit a section of wash board at a narrow crossing next to open water on a river at speed. The fricking bars were ripped from my hands as they went wildly from side to side. It put a good scare in me as I thought I was going to get bounced into the open water. I've never been able to trust my Nytro's handling at high speed through the rough.

Here are pics of the conditions where I experience bump steer.

You can ride a Polaris Pro-R through these same conditons and it tracks through them straight and true.

i have had the same experience with my own nytro,in particular instance,we were riding down a ditch trail just cruising,no johnny hot rod or anything.so i was taking in the scenery,and not paying attention and i hit a series of moguls not unlike what you show in the picture,i had simmons skis on at the time and it came down somewhat on one side,and it ripped the handle bars out of my hand and i wound up getting tangled up in a barbed wire fence.i put the zbros frontend on it last year and it made it a way more stable,but as noted before it lowers the frontend and i have had some issues with that.in reference to the polaris ride,you are right,bought my younger son a 2011 600 switch back this spring,after he had about 600 miles on it we traded sleds one afternoon for awhile,i about cried when i climbed back on the nytro,smooth responsive,but that two sroke motor,yuck!!!and a little fyi,bent a lower a arm for no apparent reason.love this topic.

 

[AKrider]

I wasn't impressed with the 600 engine in the Pro-R either. In all honesty it felt gutless as I rode it right after racing my Nytro for 150 miles. I really liked the chassis however! Truly and night and day improvement in handling over my Nytro. I also rode a Sno-Pro 600 after the same race and since that sled used race gas, the power felt similar to my Nytro, it just didn't have as broad of a power band. The Nytro has so many good things going for it (especially the motor) that it is worthy of being modified for better handling.

Could you provide more details into what you don't like about the Zbros front end? I've never ridden one or seen one in person. Is the improvement in stability mean it doesn't high side as much in the corners or does it dart less going though the bumps and at high speed? I'd love to know for certain if they tuned out the bump steer on that kit.

My suspicions are they reduced the bump steer a minor amount by running the a-arms parallel with the ground. They then tried to make up for the lowered ride height by turning down the a-arms at their ends so the spindle was pushed downward. The additional width was to reduce the ski-lifting in the corners.

 

[AKrider]

Something else I was thinking about is the high speed darting and instability. I was doing some testing on the 2.5mm mod late this spring. I've got a 2000' straight away right by my home and my Nytro was not stable at high speed on this straight away, especially when testing in the early morning when the snow was frozen and set up. You'd hit a small bump and the darting became magnified at that speed.

I also thought about when I made a high speed run on an ice road when I first installed my studs and new carbides. I got up to an indicated 98-100 mph and then let off completely. I experienced head shake and the sled felt out of control for a brief second. That scared me! Thinking about these two events now, I believe that because of the bump steer, the sled is unstable at high speeds because you hit any bump or let off and the suspension compresses and it toes out. This combined with the steep caster angle (compared to a Polaris) and it is a disaster. Think back to being a kid and riding a BMX bike down a hill at speed. Remember how twitchy the front end was? That was due to the steep head angle on the BMX bike. Great for tight turns at lower speeds but not for high speeds on hills. The Polaris sleds are a little lazy when turning at low speeds but I think that is a worthwhile trade off for more stable high speed handling.

 

[bulldogbones]

Just came across this vid, while trying to FULLY understand B/S. You will notice six seconds into the vid that the tie rod is farther out then the upper and lower B/J's causing the B/S. Thats the same thing as on the Nytro, the tie rod is about 1/2" farther out.

http://www.youtube.com/watch?v=gKJAukSZRT0

That being said he the mounting point for the tierod was moved in to match the upper and lower B/J's, would that potentially correct the problem?

 

[AKrider]

Great video, that gives a good example of what I've measured with toe out. Lately I've been comparing the '08 and '09 spindles and the 09's tie rod mounts are on the inside of the spindle while the 08's are on the outside. Yamaha was able to reduce the bump steer in the 09's by shortening the tie rod but they still did not eliminate all the bump steer. From what I've measured, the tie rod angles do not match the lower a-arm angles at any point during the suspension stroke. I believe the tie rod is pointing above the intersection point which will also result in the wheels to toe out during compression. Now what I'm wondering is if it is possible to shim the tie rods so they match the angle of the lower control arm. If it is, than I've really got to wonder why no one in the aftermarket has done this and why Yamaha did not do this from the factory?

If it is possible to shim the tie rods with washers than maybe there is no money in it to the aftermarket because who'd want to pay for some hardware store washers and a sheet of directions? I'm guessing that if someone offered a kit the concept would quickly get stolen and once the directions got out there of how to do it and how many washers would need than everyone would just do it themselves. I don't know, I'm not a business guy, I just want my sled to handle. From going through this exercise and guys bouncing ideas off one another in this forum, I'm now thinking '09 spindles are a worthy upgrade to an '08 provided the bump steer can be shimmed out.

 

[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

 

[BETHEVIPER]

don't forget that when you change the location of the tierod in or out or back further, you are canging your turning circle or "akermann effect"

this is not as important on a sled as a car but if you change it too much, when you corner your going to change your toe.

 

[AKrider]

The pen laser is an excellent idea! I've not had any luck in checking bump steer with a plate and a dial indicator due to the amount of scrub. In the articles where they do it on a race car, the suspension has no where near the stroke or scrub.

I know that moving the flat washers around on the spindle mounts will not correct it. Because there are two ears, the tie rod is "locked in" and can't move up or down enough. I need to strip my plastics to check the inner tie rod mounts. Maybe they can be spaced upwards or mounted upside down to make a difference?

Here is a diagram of what I think is happening with the Nytro.

If the tie rods can be positioned to the correct location, than the front end should work as good as a Polaris, Cat or Doo. I'd then wonder if the '08 or '09 had an advantage is geometry. The '09 steers slower stock but would probably have the advantage in high speed stability with the slacker caster angle.

 

[AKrider]

don't forget that when you change the location of the tierod in or out or back further, you are canging your turning circle or "akermann effect"

this is not as important on a sled as a car but if you change it too much, when you corner your going to change your toe.

You are right. Presently the Nytro toes out a bunch on compression so it probably has ackermann effect. If it did get eliminated or more likely reduced, as part of correcting bump steer, I don't think it would be a big deal.

 

[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.

 

[AKrider]

00-Nuke,
Thanks for starting the best thread I've seen on TY! Can you double check to make 100% certain that your 09's tie rod and lower a-arm are parallel? On my '08 I found my tie rod is not parallel with the lower a-arm. At full compression there is a 6 degree difference and at full drop its a 7 degree difference. My tie rod always measures a different angle than the lower a-arm throughout every inch of the stroke. I'm using a KD No.2968 angle finder. On my '08, the angle difference between my tie rod and lower a-arm is visible just from viewing the sled head on.

 

[00-NUKE]

00-Nuke,
Thanks for starting the best thread I've seen on TY! Can you double check to make 100% certain that your 09's tie rod and lower a-arm are parallel? On my '08 I found my tie rod is not parallel with the lower a-arm. At full compression there is a 6 degree difference and at full drop its a 7 degree difference. My tie rod always measures a different angle than the lower a-arm throughout every inch of the stroke. I'm using a KD No.2968 angle finder. On my '08, the angle difference between my tie rod and lower a-arm is visible just from viewing the sled head on.

Thanks for the kudo's The Nytro's lower A-arm has a bend in it just prior to the ball joint, so are you measuring from point to point or are you following the angle of the A-arm? From point to point they should be pretty close to parallel. Mine is a 2011, not that it should matter. I don't think they changed much between 2009 and 2011. I know that the geometry on the 2008 that I had was all screwed up in the front end. The ball joint mod wih a 3.5 mm change seemed to help quite a bit. I was glad to upgrade, although the 2011's aren't perect either.

 

[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.

 

[AKrider]

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.

 

[sherlock29]

It sure would be nice to have a chat with the Engineering dept. that is behind this design and just plain ask why...... was it a friday afternoon design, patent laws, hicup in design...

Yammy has alot of very smart people that design these... and there is a reason for everyhting! Even if its not the best.