Caster question

[Blaner]

Hey all! finally gotten around to getting my front end put together and since the new bits are fully adjustable, im needing to know specs with regards to caster. Bearing in mind i am running YFZ450 Full Flight +2 standard travel arms with 450 geometry.

The caster was the only aspect of my 450 swap I was never happy with, I had too much bump steer although lightning turn in response and agility, im looking for more straight line stability at the expense of response. but obviously not too much!

I have read that anywhere between 4 and 8 degrees, does anyone have a recommendation based on experience?

 

[Blaaster]

On a stock Blaster the caster is 9 deg.

But wether that would work with your setup I cannot comment.

 

[Rich]

Following things by the book for stability on my asr it says a caster of positive 4.5-6.5.The more positive caster the more stable at speed.Also setting the toe in with rear front wheel measurment 1/4 of an inch more distance than the front measurment between front tires.I just eye ball the camber by turning my tires back and forth and press down on suspension to get an ideal on what angle is giving the most traction.

 

[Blaaster]

If I may ask, just how do you get steering geometry the same on both sides by just eyeballing?

Sureley you must use some type of measuring device.

 

[YZ Otis]

Good subject, glad to see caster brought up ...
I don't believe caster has much to do with bump steer ... I think as you tip the top of the spindle yoke back the wheels will want to self center ... this will also increase the force necessary to turn as you are lifting the front of the bike with the inside tire as you turn. We used a buncha caster on our karts so you could use the right front tire to jack weight on the left rear.
I'm making my arms adjustable too, but it would be good so have a sound starting point.
Hopefully someone with actual knowledge will chime in and explained it simply to us.
Would be nice to have the caster deg. settings on several quads for a reference.

 

[Blaner]

ive read up for dune riding 3-5*, recreational riding 5-7*, MX 5-7*, trail 5-7*, desert racing 6-8*

So maybe i must gun for somewhere around 7* as Im happy to put power into turning but need stability at speed. perhaps il go for it and let you guys know how it turns out.

I havent got an angle finder goodle but ive found a way of using some trigonometry to work out the angles based on the distance between the upper and lower ball joints and the distance the tope ball joint lies behind the bottom one on a vertical axis.

Il keep ya posted but please do comment here, the more input the better!!

 

[Blaner]

9* for a stock blaster is alot, but then again they are actually rather heavy bikes in terms of steering.

 

[YZ Otis]

ive read up for dune riding 3-5*, recreational riding 5-7*, MX 5-7*, trail 5-7*, desert racing 6-8*

Thanks for the numbers ... i'm in the ballpark and can adjust either way, although 9 is out of my reach .. I feel better

 

[Rich]

If I may ask, just how do you get steering geometry the same on both sides by just eyeballing?

Sureley you must use some type of measuring device.

Eye balled Just the camber then I check measurement to make sure there equal.

 

[Rich]

May I ask what is your toe set to.I know toe will dramaticly affect strait line stability with toe in keeping it from darting to one side or the other.

 

[YZ Otis]

Since the back suspension plays a big part in how the bike sits I have assumed the caster angle is measured from perpendicular to the ground or surface the bike sits on. I've always figured this angle needed to be measured with the rider on the bike. Is there some line through the bike frame that this angle is measured from?
Sorry ... my drinkin thinkin is gettin confused and wonderin if my thinkin has been confused all along ...

 

[Blaaster]

The lower the back end the more negative caster is introduced.

I believe the bike should be laden when the caster is adjusted.

Is the caster not adjusted from the vertical line through the centre of the spindles. Thats the way I have been taught.

I could be wrong,as I am not a mathmatical genius.

 

[Blaner]

im not convinced that caster changes through suspension travel, It should remain constant throught compression and extension of the front and back end,

think about it, the spindles house the ball joints, and the a-arms and mounted to the frame and the heim joints (in my case) are locked with a lock nut. so if I compress, the two ball joints move down together in relation to each other because they are fixed to the spindle. They move in the same arc, therefore they should maintain the set angle throughout movement??

 

[YZ Otis]

Caster won't change in relation to the frame through suspension travel if the arm pivots are parallel ... you might be able to say caster changes in relation to the ground if the front suspension compresses and the rear extends or vise versa ... the line through the ball joints should be the spindle rotation axis. I thought the angle between that line and a line perpendicular to the ground was the caster angle but that angle will vary quite a bit depending on the height of the rear of the bike. Since a heavy rider would have a different caster angle than a light rider I began to wonder if manufacturers used a reference line, like the bottom rails of the frame or something . Prolly not a big deal, just wonderin

 

[Blaner]

yes ok, ive figured out that having the rear and front tires on is NB, this effects the angle of the line through the spindle relative to vertical, however i dont think suspension travel effects it much, if I measure between the floor and the base of my spindle with the bike standing, then compress the front and measure the same place, the reading is the same because the tires is the governing factor, if you include the suspension travel then things like spring preload, spring sag and rider sag all mess with the values and leave you with way to many variables.

Interesting point, il have to think a bit more, il be away for a week then will get cracking again on setting it up properly....

mmm I smell a write up on the way....

 

[slickerthanyou]

I get the toe adjustment, but not sure how to correct caster camber on stock arms, I don't think you can, can you?

I mean when you adjust the toe with tie rods, it changes the others a little but i'd like to know if there is a way to adjust it.

Gotta hand it to ya blaner brutha, you have some great topics of interest!

 

[Blaner]

haha hey slick, nice of you to join to convo on stock arms you cannot adjust camber or caster and yes you can only adjust toe, the camber and caster are set by the way the arms bolt onto the frame, again stressing the importance of frame mounts,

Doing a bit of measuring with a clinometer and i discovered that the reason for my caster problem on my 450 setup was that my top a-arm mounts had a difference between left and right of 3* not bad considering all the clamping and welding and heat expansion that went on but still, 3* was all it needed to mess it around at speed, I dont know what my caster actually was but the difference was as mentioned.

Now that I have adjustable arms, i can fine tune it all and work out those welding imperfections. looking forward to see how it will feel once i figure and set this all up!

 

[slickerthanyou]

That's what I thought! Thanks for the reply! you have more green than you had!

 

[Rich]

Do you have any pics of your modification.I would really like to see what you have going on.With the plus 2 for a 450 how much more are you gaining all around as far as the blasters oem width.

 

[Teflon]

Do you have any pics of your modification.I would really like to see what you have going on.With the plus 2 for a 450 how much more are you gaining all around as far as the blasters oem width.

Check it out here:
http://www.blasterforum.com/suspens...-450-complete-front-suspension-blaster-36120/

I'm sure Blaner will post more pics once he's made some progress with the new install!I:I