Caster

W

W5R

New member
When someone says "add caster" or "take some caster out", what does that mean actually? Does it mean increase the caster from say, 8 to 9 on the left side and 12 to 13 on the right side both at same time, or to increase one side only? Or does it mean to just increase or decrease the caster split by one number, or more? Its a little confusing to me, mainly because where I race it is basically a "set it and forget it" type of thing, and rarely have I had to change it.

But its indoor time, and I was told I might need to add more caster or take some caster out of it, I'm not sure which way I need to go with this because I don't fully understand what it does, how it works, or how it will affect the handling of the kart, and thats why I am asking. Can someone help me with this a little? I ride a 2011 Impulse, the track is an indoor bullring type track with somewhat wide turns and almost no straitaways, we use 13-14 drivers here. Class is Clone light and medium, and tires are Burris Any 33's. Track is Liberty Ky Indoor, which the layout has changed from last year to a shorter track.
 
adding caster is rolling the top of the spindle towards to rear of the kart, usually just done to the RF to take weight OFF of RF on turn in, adds weight to RF on turn out...improves a push on exit in my experience.
 
So if moving the Rf back is adding caster, would moving the Lf forward be considered same thing? Also, wouldn't moving the Rf back also be decreasing the caster split? I'm just trying to get a general idea of how it works, sort of like stagger or cross works. Caster is the main thing that confuses me, the rest I already know. Just wanting to know like when you would change it and why, or to fix what type of handling problem. Usually I dont have handling problems but if I do, its almost always a push on exit or slightly loose in the center of the turns
 
So if moving the Rf back is adding caster, would moving the Lf forward be considered same thing? Also, wouldn't moving the Rf back also be decreasing the caster split?

Caster is the inclination of the spindle. If you leave the bottom of the spindle in the same place and move the top back toward the driver, you have positive caster. Caster makes a vehicle track and makes the weight transfer, ie - if you are in a LH turn and turn the kart steering wheel to the right, you will jack weight to the LR wheel.
Moving the LF forward would decrease positive caster on the LF and could move you into negative caster on the LF ie - the bottom of the spindle is closer to the driver and the top is further from the driver.
Caster split is the difference between the caster LF vs RF. 8*LF vs 14*RF would be 6* caster split.
A fun exercise is to look at RF tire movement with the kart on the stand as you turn the steering. You will see the spindle/tire move in an arc. And depending on what your caster is the arc is different.
 
To help really over simplify it, adding caster to the LF will help move more weight off of the LR. Depending on the rest of your set up, it will move most of it to the RR and some to the RF. If the kart is really lazy on turn it and not getting to center well, I would think you could add LF caster to cure that problem. To the seat of the pants, it will feel similar to adding a half of a degree of LF positive camber. You're just transferring more weight. #MoCastaGoFasta
 
Think of it this way; looking at the kart from the right side, if the spindle bolt looks like a " \ ", that's positive caster. If it looks like this " / ", that would be negative caster. In a left-hand turn, with positive caster, the LF tire is forced down, and the RF tire is lifted. This will take weight off the LR tire. With a live axle, on pavement especially, if you don't take weight off the LR tire, and you attempted to make a left-hand turn, with no stagger, the kart wouldn't turn well, the kart would push. My feeling is; whenever the kart is pushing, it can only be one of two things, too much rear bite or not enough front bite.

Look it up in Wikipedia, they have some good illustrations and comments on the use of caster and kingpin inclination. Most of the information is automotive related, and does not directly apply to karting. The reason being; most cars have non-locking differentials, not live axles like karts, so they use kingpin inclination and caster to keep the front wheels pointed straight and make it easier to steer. Kingpin inclination keeps the wheels pointed straight and negative caster makes it easier to steer. These things were more important in the years before power steering. The intended use in karts is different than the intended use in cars.

Having never raced dirt karts, I find their use of kingpin inclination and caster very confusing. Let me try to explain why.

For many years, Bug manufacturing, and I, built very successful karts with no kingpin inclination. Obviously, Bug having been more successful than me. But in any case, both the Bug Stinger and my Mayko shark handled quite well without kingpin inclination.

Something that confuses me, ("so what's new", I hear people saying) is the need for so much caster in dirt karts. Positive caster, in a dirt kart, does the exact same thing as it does in a Sprint kart. It takes the weight off the LR tire. Now I could be wrong, but isn't it the whole point of the offset kart to keep the weight on the LR tire? After all, you have stagger, and that means the kart will want to turn left even if you don't turn the steering wheel. With the correct stagger, if you push an axle with two staggered wheels across a parking lot, it can't help but turn. With the proper stagger, I would think you could get that axle to make the turn radius on any track. Of course I understand there's a lot of other dynamics involved in turning a kart around the track, but I'm guessing rear stagger is one of the more important considerations in oval track racing.

Wild ramblings I know.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
Al, that is camber, not caster, when your referring to the angle of the tire/wheel. Like if the top of the RF tire is leaning in towards the frame, that is positive camber, if its leaning out towards the outside, its negative camber. Camber I understand, as well as other percentages and changes, its just caster that has me a little confused because its something I never change or needed to change. Just wondering if I can get the kart to respond better by changing the caster for this particular indoor track, thats why I asked. The problem I have had at this track is a push from center off on exit, the entry feels fine and no problem there, but I am scrubbing speed because of the push on exit, having to trail brake to get thru the turns.

Also, you said in a left hand turn the rf tire is lifted, which would not be the case. If the rf tire was lifted in the turn, you would push. Not sure about sprint or asphalt but on dirt, we want the rf tire planted in the turns, from entry to center apex, then from center off we want the weight to transfer from the Rf back to the Lr to get that drive off the corner. At least this is how I have always understood it.
 
Weddle Racing said:
Al, that is camber, not caster, when your referring to the angle of the tire/wheel.
Click to expand...

Al is refering to caster.

Didn't speak of the tire/wheel at all.

Refers to the angle of the RF spindle when viewed from the right side of the kart.



alvin l nunley said:
Think of it this way; looking at the kart from the right side, if the spindle bolt looks like a " \ ", that's positive caster. If it looks like this " / ", that would be negative caster. (Al Nunley)
Click to expand...


I would also say Al's advice on stagger is probably the right area to look also.

PS... Hush Bryan!
 
alvin l nunley said:
Something that confuses me, ("so what's new", I hear people saying) is the need for so much caster in dirt karts. Positive caster, in a dirt kart, does the exact same thing as it does in a Sprint kart. (Al Nunley)
Click to expand...

Al,

Dirt karts use a lot of caster with totally different spindles. I'm not sure what the spindles looked like in the karts you are refering to, but in current sprint style karts the biggest difference would be scrub radius which the more you have causes more of the weight jacking- if I understand it correctly. In dirt, we mainly use it for the camber gain. While it will weight jack on the scales if you crank the steering wheel, true steering input during a race is so minimal if your handling correctly that what little weight jacking that's happening is nothing compared to the weight gained from G-loading.

Zach,

Sorry for taking the thread in another direction with this post.
 
Weddle Racing said:
.Also, you said in a left hand turn the rf tire is lifted, which would not be the case. If the rf tire was lifted in the turn, you would push. Not sure about sprint or asphalt but on dirt, we want the rf tire planted in the turns, from entry to center apex, then from center off we want the weight to transfer from the Rf back to the Lr to get that drive off the corner. At least this is how I have always understood it.
Click to expand...

Caster is directly related to camber gain. This is the rise Al is referring to. With steer input the RF will move in an arc up and away from the COG. If you have scales it would be wise to get on them and check what happens to things when the wheel is given input. You may put -3* of camber on the RF but how much does it change when the wheel is turned. Hmmmmmm......................

So much to learn. :)

Kevin,

You made me do this. LOL
 
Here's a spread sheet for you to do Al.

There's caster, camber, kpi and camber gain.

How about a spread sheet where you input your current caster, camber kpi, tire width and tire radius; and it gives you both the amount of camber gain and vertical lifting of the RF(or LF), from zero to say... 30* of turning. It would put a number to, the amount of unloading of a rear tire. With the spread sheet, racers would know how to set front end angles, to get more camber and keep the same amount of unloading. Or just get more or less action on the inside rear without changing camber. You could also then know what to set to change the rate of unloading or loading, without effecting camber, which really sets the amount of grip at the RF, per degree of turning.
 
paulkish said:
Here's a spread sheet for you to do Al.

There's caster, camber, kpi and camber gain.

How about a spread sheet where you input your current caster, camber kpi, tire width and tire radius; and it gives you both the amount of camber gain and vertical lifting of the RF(or LF), from zero to say... 30* of turning. It would put a number to, the amount of unloading of a rear tire. With the spread sheet, racers would know how to set front end angles, to get more camber and keep the same amount of unloading. Or just get more or less action on the inside rear without changing camber. You could also then know what to set to change the rate of unloading or loading, without effecting camber, which really sets the amount of grip at the RF, per degree of turning.
Click to expand...

Would also have to include chassis rake and tilt, which would change with stagger and cross adjustments, just saying...

Oh no, did I just mention stagger in a Kish post- sorry guys..... ;)
 
Weddle Racing said:
Al, that is camber, not caster, when your referring to the angle of the tire/wheel.
Click to expand...
Doesn't anybody read these posts anymore. If you're not going to read them, don't comment on them. It makes you looked foolish.

Nowhere in my post did I refer to the angle of the tire/wheel! Damn.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
You guys are right, I was looking at what Al said wrong. For some reason the / and \ part of his post caught my attention and I assumed he meant camber instead of caster, my mistake there ill admit. Moody, no problem at all with what you said, the whole point of this thread was to learn something from it, each post has been helpful guys
 
alvin l nunley said:
Doesn't anybody read these posts anymore. If you're not going to read them, don't comment on them. It makes you looked foolish.

Nowhere in my post did I refer to the angle of the tire/wheel! Damn.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
Click to expand...

Al, I can hardly understand half the stuff you say most of the time no matter what the topic is lol. Same goes for Paulkish, thats not a bad thing but your posts go into alot of complicated details sometimes and just loses me, and ill admit I do tend to skip thru some of it. No harm intended, dont get yourself all fired up lol. Trying to keep this positive and on topic.
 
Weddle Racing said:
No harm intended, dont get yourself all fired up lol. Trying to keep this positive and on topic.
Click to expand...
But harm was done, even if done, supposedly, unintentionally. "Fired up", that's an assumption on your part.

And then, by implication, you insult me even farther by implying that I wasn't, "positive and on topic". In fact, your quote was the negative one, and off-topic to boot.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory. (Al Nunley)
 
Wow....30* of steering input. You don't need a spreadsheet for that. The answer will always be the same no matter the numbers you plug in........YOUR SCREWED!!!!

Kevin you know darn good and well the spacer goes under the COG. Stop trying to confuse Paul.

Damage? Someone call the feelings police, sensitivity crime in progress.

When do we get to reverse caster and 2" of front stagger?
 
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