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First outing on the stock setup certainly revealed some less than desirable traits:
1/ alot of Bump steer mid turn resulting in a lot of wiggling of the bars or sawing the wood like action......
2/ tendancy for a bit of head shake under brakes and at best only average turn in
adding a steering damper (one of my YFZ 450 setups from NOSS Machine, with a quick mill out of the steering stem mounting) tamed down the wiggling bars in the turns. This provided a fix but doesn't address the cause of the problems
A bit of a general check out of the geometry indicated practically zero camber at typical ride height, that is the the top of the wheel is in line with the bottom, whats really needed in the top of the wheel to lean inwards, this significantly helps turn in.
Camber is the angle of the wheel relative to vertical as viewed from the front of the quad. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the chassis, it has positive camber. The cornering force that a tire can develop is highly dependent on its angle relative to the track surface. The chassis reacts to centrifugual forces in a turn by tending to roll outwards over the outer front wheel, as the chassis rolls laterally outwards from the turn direction an initial negative wheel setting reduces and the outer tire is planted hard on the track genertaing maximum traction enhancing turn in. With nearly vertical or zero camber as the chassis rolls out in the turn the outer tires contact patch is reduced as the tire tries to fold under resulting in understeer ........ all bad stuff......
We dialed in around 3 degrees negative at typical ride height with the rider siting on the quad, this needed 3 by 360 degree turns of the rod ends, both front and back into the top a arm. Viola mega better turn in.
Toe in: stock there was nearly 1" of toe in at ride height, no wonders it's fighting it's self. The stock bump steer or toe in change during the wheel vertical travel isn't flash on this quad, don't compound it with excessive toe in. Compress the suspension until the A arms are horizontal and reset the toe at this positon to 1/8" or 3mm. The steering will lighten up and this setting may not be to everyones liking. The toe setting on a particular quad becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted as the toe approaches neutral, in general avoid toe-out at the compressed ride height (under brakes position) this creates a darty nervousness that can be a real hand full.......
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.
Nervousness under brakes can also be due to a very flat castor angle between the top and bottom a arm ball joints at the stub axle. As the rear of the chassis lifts under brakes , and the nose dives, castor angle is reduced. Positive caster is used to enhance straight-line stability. However the more postive castor the slower the steering action.
Turning the top rear Heim one full turn further into the A arm adds castor, this is what I'm trying now. Not sure if this will be an improvement or not
the good thing is that the KTM top arms are fully adjustable allowing plenty of fiddle factor to get it "just right"......
You need to reset the toe every time you alter the top a arm heim joint settings.
I use a large carpenters square to measure the camber on the rim lips top to bottom, caster is alot trickier to measure. Make records of the adjustments (turns in / out of the heims) and make only one change at a time and see if you like the revised setting or not.
Your lap times will drop with increased camber and reduced toe in combined with a steering damper to control chassis induced bump steer and the light steering action on this quad.
Pictures to follow
1/ alot of Bump steer mid turn resulting in a lot of wiggling of the bars or sawing the wood like action......
2/ tendancy for a bit of head shake under brakes and at best only average turn in
adding a steering damper (one of my YFZ 450 setups from NOSS Machine, with a quick mill out of the steering stem mounting) tamed down the wiggling bars in the turns. This provided a fix but doesn't address the cause of the problems
A bit of a general check out of the geometry indicated practically zero camber at typical ride height, that is the the top of the wheel is in line with the bottom, whats really needed in the top of the wheel to lean inwards, this significantly helps turn in.
Camber is the angle of the wheel relative to vertical as viewed from the front of the quad. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the chassis, it has positive camber. The cornering force that a tire can develop is highly dependent on its angle relative to the track surface. The chassis reacts to centrifugual forces in a turn by tending to roll outwards over the outer front wheel, as the chassis rolls laterally outwards from the turn direction an initial negative wheel setting reduces and the outer tire is planted hard on the track genertaing maximum traction enhancing turn in. With nearly vertical or zero camber as the chassis rolls out in the turn the outer tires contact patch is reduced as the tire tries to fold under resulting in understeer ........ all bad stuff......
We dialed in around 3 degrees negative at typical ride height with the rider siting on the quad, this needed 3 by 360 degree turns of the rod ends, both front and back into the top a arm. Viola mega better turn in.
Toe in: stock there was nearly 1" of toe in at ride height, no wonders it's fighting it's self. The stock bump steer or toe in change during the wheel vertical travel isn't flash on this quad, don't compound it with excessive toe in. Compress the suspension until the A arms are horizontal and reset the toe at this positon to 1/8" or 3mm. The steering will lighten up and this setting may not be to everyones liking. The toe setting on a particular quad becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted as the toe approaches neutral, in general avoid toe-out at the compressed ride height (under brakes position) this creates a darty nervousness that can be a real hand full.......
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.
Nervousness under brakes can also be due to a very flat castor angle between the top and bottom a arm ball joints at the stub axle. As the rear of the chassis lifts under brakes , and the nose dives, castor angle is reduced. Positive caster is used to enhance straight-line stability. However the more postive castor the slower the steering action.
Turning the top rear Heim one full turn further into the A arm adds castor, this is what I'm trying now. Not sure if this will be an improvement or not
the good thing is that the KTM top arms are fully adjustable allowing plenty of fiddle factor to get it "just right"......
You need to reset the toe every time you alter the top a arm heim joint settings.
I use a large carpenters square to measure the camber on the rim lips top to bottom, caster is alot trickier to measure. Make records of the adjustments (turns in / out of the heims) and make only one change at a time and see if you like the revised setting or not.
Your lap times will drop with increased camber and reduced toe in combined with a steering damper to control chassis induced bump steer and the light steering action on this quad.
Pictures to follow
