00-NUKE
Expert
Re: Testing
I'll look into that. My whole idea is to keep the co$t down. If I can develop something for the height of the steering heims and it works, I'll post it. I would like to factor in the heavy steering issue as well. Mine handles better than it ever has but still has heavy steering. I wish Yamaha would have applied that power steering to the Nytro's. I have a buddy on Yamaha's sales team that says Yamaha has a new lineup they're pushing to have ready by 2013. If that's the case, it might be the end of the Nytro????
Crewchief47 said:
I'll look into that. My whole idea is to keep the co$t down. If I can develop something for the height of the steering heims and it works, I'll post it. I would like to factor in the heavy steering issue as well. Mine handles better than it ever has but still has heavy steering. I wish Yamaha would have applied that power steering to the Nytro's. I have a buddy on Yamaha's sales team that says Yamaha has a new lineup they're pushing to have ready by 2013. If that's the case, it might be the end of the Nytro????
Initially I didn't think that raising the upper a-arm would have any effect on bump steer. Now I'm not so sure. The geometry calculator shows that the more parallel the a-arms are, the less camber change that occurs. You do end up with more scrub, but that maybe a lesser evil than camber change which likely causes the skis to toe out as the suspension compresses.
As far as heavy steering goes. The stock skis are flat across the bottom. I think the Pilot skis are rockered which would both reduce steering effort and bump steer in certain snow conditions. I'm thinking the rockered design is making more of a handling difference on the Nytro than is the duel skags.
I just spent some time inputting the Nytro measurements into the calculator and the 17mm raised upper a-arm mod will keep the spindle extremely close to verticle throughout the stroke until it hits the very end. Once close to bottom out, the spindle goes into negitive camber. I started off with 0 degree camber at full extension as would be present on stock '08 geometry.
As far as heavy steering goes. The stock skis are flat across the bottom. I think the Pilot skis are rockered which would both reduce steering effort and bump steer in certain snow conditions. I'm thinking the rockered design is making more of a handling difference on the Nytro than is the duel skags.
I just spent some time inputting the Nytro measurements into the calculator and the 17mm raised upper a-arm mod will keep the spindle extremely close to verticle throughout the stroke until it hits the very end. Once close to bottom out, the spindle goes into negitive camber. I started off with 0 degree camber at full extension as would be present on stock '08 geometry.
Right like I said..make all the arms on the same plane..for that sled.
You could have actually taken the shocks off completely..to test.
The last time I took time to fix the heavy steering on a Yamaha was the big Enticer ( I think) we just lowered the front bolt hole 1/2 to 3/4 of a bolt lower. We welded an new washer on.
Doing that changed a lot of geometry(not the same as changing strap) and the sled felt ..so new and nimble and faster..
You could have actually taken the shocks off completely..to test.
The last time I took time to fix the heavy steering on a Yamaha was the big Enticer ( I think) we just lowered the front bolt hole 1/2 to 3/4 of a bolt lower. We welded an new washer on.
Doing that changed a lot of geometry(not the same as changing strap) and the sled felt ..so new and nimble and faster..
I left the shocks on so I knew where the limits of extension and compression were. I agree with you, I'm thinking that the a-arms being made to be parallel on the Nytro is an improvement because the camber changes less as the suspension strokes through its travel. Less camber change should reduce the toe out since the spindles are not tipping inward. As they tip inward, they have to rotate outwards since the tie rod cannot compress.
In a perfect front suspension design, parallel a-arms are not ideal for handling since they will never line up with the instant center. This can create issues with roll center causing the sled to lift a ski. But, because the bump steer is so fricking bad on this sled, any improvement to bump steer is a GOOD thing. The old Indy's used parallel radius rods and they handled quite well. Between the shorter travel (6") and probably less bump steer, the Indy's worked great.
I inputed the measurements into the calculator for the 17mm mod on a front end with the 2.5mm ball joint mod. That should be the same as the '09 front end with the 17 mm mod. The spindle stayed pretty much vertical throughout the travel until the end where it went -1.7 degrees camber. It scrubbed 33mm, same as stock, but the spindle stayed more vertical than either stock or 2.5mm mod alone. I'm going to try the 17mm mod this winter.
I've learned quite a bit about a-arm front suspension from this exercise. I think rockered skis will make another improvement. Maybe we can figure out how to get this ill handling b!tch to handle halfway acceptably with out spending $1000-$1500 on a new front end?
In a perfect front suspension design, parallel a-arms are not ideal for handling since they will never line up with the instant center. This can create issues with roll center causing the sled to lift a ski. But, because the bump steer is so fricking bad on this sled, any improvement to bump steer is a GOOD thing. The old Indy's used parallel radius rods and they handled quite well. Between the shorter travel (6") and probably less bump steer, the Indy's worked great.
I inputed the measurements into the calculator for the 17mm mod on a front end with the 2.5mm ball joint mod. That should be the same as the '09 front end with the 17 mm mod. The spindle stayed pretty much vertical throughout the travel until the end where it went -1.7 degrees camber. It scrubbed 33mm, same as stock, but the spindle stayed more vertical than either stock or 2.5mm mod alone. I'm going to try the 17mm mod this winter.
I've learned quite a bit about a-arm front suspension from this exercise. I think rockered skis will make another improvement. Maybe we can figure out how to get this ill handling b!tch to handle halfway acceptably with out spending $1000-$1500 on a new front end?
00-NUKE
Expert
AKrider said:
This mod helped my 2011 XTX out a lot on the studder bumps and rough trails. I wouldn't say it's a 100% fix but worth the $70 in machined bushings by FAR! The Rockered skis are an awesome idea as well. I have C&A Pro XT's right now and they steer HEAVVVVY, although they hold a corner like a fat kid holds a doughnut.
00-NUKE
Expert
Break Down minus the numbers
A little more breakdown for you all without numbers to simplify things as much as possible:
- I've modified the 1st image of my breakdown on the first thread to show you that the mounting point for the steering (tie rod) on the spindle is higher than mounting point of the lower ball joint. Think of the lower ball joint as the "pivot point" of the spindle. As it travels vertically, it pivots between the upper A-arm and the spindle base (the ski).
Stock settings - During vertical travel upward of the spindle, there is a change in toe direction because of camber change. As the upper A-arm pushes the spindle outward to reduce scrub, the tie rod pulls the back of the spindle inward, changing your toe direction outward as the suspension compresses.
17mm mod settings - During vertical travel upward of the spindle the mounting point of the upper A-arm, steering (tie rod) mount, and the pivot point stay fairly consistant with each other reducing shift of the ski toe during suspension compression.
It is true that you will end up with more scrub after the 17mm mod, but in turn you are keeping your steer and camber consistant. Keeping your steer consistant - helps bump steer. Keeping camber consistant - helps in corners by keeping the carbide perpindicular to the ground.
IMO: When dealing with A-arm suspension, one will always have scrub to maintain stability. I'd also just like to add..... Although heavy, Yamaha's "pogo stick" suspension in the late 80's and early 90's was a sweet simple alternative to the trailing arm that polaris invented to maintain consistancy.
AKrider said:
A little more breakdown for you all without numbers to simplify things as much as possible:
- I've modified the 1st image of my breakdown on the first thread to show you that the mounting point for the steering (tie rod) on the spindle is higher than mounting point of the lower ball joint. Think of the lower ball joint as the "pivot point" of the spindle. As it travels vertically, it pivots between the upper A-arm and the spindle base (the ski).
Stock settings - During vertical travel upward of the spindle, there is a change in toe direction because of camber change. As the upper A-arm pushes the spindle outward to reduce scrub, the tie rod pulls the back of the spindle inward, changing your toe direction outward as the suspension compresses.
17mm mod settings - During vertical travel upward of the spindle the mounting point of the upper A-arm, steering (tie rod) mount, and the pivot point stay fairly consistant with each other reducing shift of the ski toe during suspension compression.
It is true that you will end up with more scrub after the 17mm mod, but in turn you are keeping your steer and camber consistant. Keeping your steer consistant - helps bump steer. Keeping camber consistant - helps in corners by keeping the carbide perpindicular to the ground.
IMO: When dealing with A-arm suspension, one will always have scrub to maintain stability. I'd also just like to add..... Although heavy, Yamaha's "pogo stick" suspension in the late 80's and early 90's was a sweet simple alternative to the trailing arm that polaris invented to maintain consistancy.
Attachments
Great photo and explaination to simplify whats happening. I agree, the a-arm front suspension will always have scrub if you've got long travel and the lower a-arm is not parallel with the ground. It appears the new Arctic Cat front end will have a lot of scrub, but they will also have excellent control of their camber as the suspension strokes through its travel.
I'm thinking another thing going on with the '09 geometry is as the suspension compresses and the spindle goes into negitive camber the toe rods are pushing outwards causing the skis to toe in. But, becuase I've got an '08 with the 2.5mm ball joint mod, my toe rods are longer and mounted to the outboard side of the spindle. I found my skis toeing out at full compression. Did you do any testing to see what the toe was doing on your sled?
We may have a case where the skis are both toeing in and out through the suspension stroke which makes it imposible to set the sled up for it to handle consistantly. I'll throw another variable into it and that is the length of the skis. The longer the skis are, the worse the toe in and out will be since the tips of the skis are further away from the spindles.
Funny about the TSS, nothing to mess with there and my old '90 Phazer II is more stable and predictible than my Nytro.
I'm thinking another thing going on with the '09 geometry is as the suspension compresses and the spindle goes into negitive camber the toe rods are pushing outwards causing the skis to toe in. But, becuase I've got an '08 with the 2.5mm ball joint mod, my toe rods are longer and mounted to the outboard side of the spindle. I found my skis toeing out at full compression. Did you do any testing to see what the toe was doing on your sled?
We may have a case where the skis are both toeing in and out through the suspension stroke which makes it imposible to set the sled up for it to handle consistantly. I'll throw another variable into it and that is the length of the skis. The longer the skis are, the worse the toe in and out will be since the tips of the skis are further away from the spindles.
Funny about the TSS, nothing to mess with there and my old '90 Phazer II is more stable and predictible than my Nytro.
Here is another idea to get the Nytro to handle.... Rev spindles.
http://www.ty4stroke.com/viewtopic.php? ... ac7064c49b
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http://www.ty4stroke.com/viewtopic.php? ... ac7064c49b
Here is a link to the 2.5 mm ball joint mod. Between this thread and that one, we've got a lot of info about the Nytro front end.
http://www.ty4stroke.com/viewtopic.php?t=54683&start=75
I was thinking about the Hygear set up and the Zbros front end and both of those seem to want to get the lower a-arm parallel with the ground. You could then set the toe and the sled should track pretty dang well on the groomed, smooth trails. The downside will be that you've lost travel and once you get into the big bumps you'll bottom. This will slow you down so you may not experience bump steer since you are not going fast enough for it to be a problem.
http://www.ty4stroke.com/viewtopic.php?t=54683&start=75
I was thinking about the Hygear set up and the Zbros front end and both of those seem to want to get the lower a-arm parallel with the ground. You could then set the toe and the sled should track pretty dang well on the groomed, smooth trails. The downside will be that you've lost travel and once you get into the big bumps you'll bottom. This will slow you down so you may not experience bump steer since you are not going fast enough for it to be a problem.
Crewchief47
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- 2008 Nytro MTX 45th
The old pro actions had inches of bump steer. The issues involved with this sled come from puting everything ever closer to the front end that has bump steer.
if you want more caster, just cut and reweld either the front lower arm or the back uppper arm, remember when adding caster, your carbide pressure will change.
It is sad that with todays computers, yamaha comes up with a front end that still has bump steer and not enough caster after making the apex that front end works great other than for yamaha's disease of using too many parts to make something work.
if you want more caster, just cut and reweld either the front lower arm or the back uppper arm, remember when adding caster, your carbide pressure will change.
It is sad that with todays computers, yamaha comes up with a front end that still has bump steer and not enough caster after making the apex that front end works great other than for yamaha's disease of using too many parts to make something work.
00-NUKE
Expert
BETHEVIPER said:
I think you're confusing Bump Steer with Darting. Caster a big contributer to darting. You can fix this by spinning your rubber spindle stopper around 180 degrees or by adding shims to the heel of the stopper.
00-NUKE said:
Not confused at all. Changing caster will effect the darting by moving the steering axis intersect for and aft of the carbide. Caster also changes darting by adding or removing pressure on the back of the ski through the rubber. Bump steer's ill effects on a sled are increased when you increase bite of ski(larger carbide, deeper keel, longer keel, more front carbide pressure, more weight on front of sled, more back to front transfer)
This sled has some bump steer, lots of weight up front, lots of engine braking to throw even more weight up front. Most everyone tries to correct this front end by adding better carbides or more agressive ski, this causes even more bump steer related issues since now the ski that is pulling the sled around has even more bite.
on the older sleds, it was very important to line the sled up with a person sitting on the sled and even push down a bit on the front end to simulate the sled slowing down or hitting a bump (longer explanation). I would guess with this sled, it is just as important even though it has less bump steer than the pro action it transfers more weight decellerating and the rider is more on the front.
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.
My Nytro becomes an ill handling b!tch in stutter bumps like this.
You can ride a Polaris Pro-R through these same conditons and it tracks through them straight and true. My Nytro jinks side to side causing me to slow down. It simply is not predictable at higher speeds in big or small whoops.
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.
My Nytro becomes an ill handling b!tch in stutter bumps like this.
You can ride a Polaris Pro-R through these same conditons and it tracks through them straight and true. My Nytro jinks side to side causing me to slow down. It simply is not predictable at higher speeds in big or small whoops.
