Chassis design

Komet99

Member
I am considering putting one of my karts on the jig table and updating the front end. My question is spindle elevation. Is it supposed to be along the same plane as the rear axle in comparison to the frame rails?

It cant be too much of a secret bc they are all the same other then the amount of adjustability. Maybe this isnt the correct forum. If I make the axle and spindles on the same plane, then put smaller tires on front, this will provide negative rake. Is there a majic number or range?
 

flattop1

Dawg 89
I would put it on the table use a height gauge to find the current height .
Then make any adjustments i deem needed . Besides the rake the cross weight is also considered in the height.
More cross lower rt frt .
 

Komet99

Member
Well the issue I have with that is, last winter I took it to the dude who built it and when I got it back, it wasnt right. So I dont have the original baseline.
 

flattop1

Dawg 89
Need the rest of the story .
So its a custom built chassis?
It handled fine then you wanted something changed and now it handles terrible ?
What was changed ?
What is it that's not right ?
For me theres 3 different planes in the front end .
Height , caster and kpi.
 

Komet99

Member
I suppose you could say its a custom chassis. It measures the same as on old straight rail. The story is, I used it on dirt ovals years ago and did well with it. Then switched it over to an enduro CIK kart. after a few races, I cut the C-bracket off and changed the geometry. Thats when it was really fast. Quit for 12 years and now Im revisiting this thing, but I wanted to update it to adjustable front end. I took it to the guy that built it, and he kinda acted like he didnt want to mess with it. When I got it back, I was unhappy with it, so I'm going to do it myself...AGAIN.

When he put the welded plates on the chassis, he didnt put them on square.

all this why??? Because I like beating people with old stuff!! And I know this thing is fast. It can be fast again.
 

flattop1

Dawg 89
Square , too the rear axle, or chassis rails or each other . Tha seems like it would have minimal effect what with the fact the wheels turn either direction . It could affect camber gain though. Pm Legend im sure he could give good honest advice .
 

flattop1

Dawg 89
Main frame level . With wheel heights set for cross weight , and tire sizes.
Enduro racing level and even seems good.
Front roll center is worth a google search .
Mike McCarty was big on that factor .
 

flattop1

Dawg 89
Thinking on this . The bracket not square to the centerline adds another plane into it . So 4 planes .
 

Komet99

Member
So your saying front spindle should be lower in relation to the main frame rails as compared to the rear axle. because the front tires are 1/2" shorter. That would give the chassis a negative rake.

More thinking...lets say that I installed only a rear axle, hubs and tires. Then installed steering shaft, tie rods, spindles and tires. Then put it on a scale. Would it be a wise assumption that it should "scale" with a slighlty higher rear percentage and a near perfect left/right percentage?

I would think that after the kart was assembled as race ready, it could be easily adjusted to scale to my preferred numbers.
 

paulkish

old fart
I don't think there anything general to relate RF spindle height to the plane of your chassis rails.
Normally because LTO only turn left off the ground the RF will sit lower then the LF and it's called RF preload.
And normally how high or low the RF spindle is can be put where you want it by adjusting washers.

Your into it's a what ever works for you thing.

There are so many variables operating your chassis and the RF corner.
Unless your on something others know about and how to set up for different weights, tracks and engines/speed, your pretty much on your own.
You have two things helping you turn out on the track and they are Stagger and your Front Tires.
What ever turning stagger doesn't get done for you has to be done by the front tires.

Throw your best guess at it, put it on the track and go from there fixing on track problems to get around the turns better.



.... and never mind, just read "road course" above ... :)
 

paulkish

old fart
Road Course all depends on where you put the apex and where and how you kill speed getting to the apex either by braking on the straight. trail braking or lifting on the go pedal.
And then if you need to start accelerating before, at or beyond the apex to maximize straight speed.

You can't accelerate if you don't slow down somewhere.
What's fast is spending the least amount of time slowing down and the most amount of time scuffing off the least amount of speed accelerating.

Trail Braking and Not Lifting are two different things.
 

Komet99

Member
My secret to enduro racing is fast and free. If the kart scrubs too much in the corner due to too much chassis load, its going to slow down naturally more than it needs to. Most focus lots of energy on horsepower, exhaust tuning, carb pop-off. My focus is chassis set-up and how fast I can make it turn.

SO speaking of that, in the above referenced kart, after I had "re-invented" the front geometry, I took a gamble on 6* castor and 6* KPI. I got super lucky and the thing would roll through a corner, handle excellent, and be fast while doing it. Then I put front brakes. I was under the assumption that rolling into a corner while not on the gas was slow. So I built my kart around gas or brake, no engine braking. Drive it so far in a corner, lift, cram the brakes, get back on gas asap and burn off. Then I started winning!!

SO now 12 years later I want to put adjustable front end, had a dude "work" on it, now I have to rebuild it right. SO curious as to where my spindle centerlines should be.
 

paulkish

old fart
Reading you post above suggests to me your pretty much running everywhere with as much of the tire as possible flat to the track.

If my thinking is with you then read on if not then don't read on because it will instantly become meaningless junk. ... :)


You can't change your spindle height location because it is determined by your front tire radius.
Your change is to how the chassis rakes down towards the front.
What your after is enough grip up front to get the chassis to work unloading your inside rear tire as needed to be free in the turns.
IMHO put the nose/front of the kart down in the front as low as you can go without scraping on the track..
Then hang your front tires as far out on the spindles as you can put them which drop the nose down the most when you turn.
And because you'll be maximizing dropping the nose down you may end up raising the front up some to keep it from scraping on the track when turning.
Also maybe throw a degree more KPI to it.

edit: Please feel free to pick apart what I offered.
edit again: the extra degree of KPI is to lift the inside of the tire up a bit to keep it more flat in the turns because of moving the tire out on the spindle.

Have you ever heard of John Learmonth in Australia?
Just curious since you said you raced long ago, about if you ever raced with or know Ted Swontek?
You probably know Michael Davis?
 
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Komet99

Member
You can't change your spindle height location because it is determined by your front tire radius. This will determine rake angle
Your change is to how the chassis rakes down towards the front. How much rake do I want?? I think this is my ultimate question. If someone can provide me with a quality answer, I can do the fabrication.
What your after is enough grip up front to get the chassis to work unloading your inside rear tire as needed to be free in the turns. Yes unload a bit. Not the typical European CIK kart. More like an oval kart. There is some loading but not enough to load so much that it dramatically slows the kart down due to the amount of scrubbing.
IMHO put the nose/front of the kart down in the front as low as you can go without scraping on the track..
Then hang your front tires as far out on the spindles as you can put them which drop the nose down the most when you turn.
And because you'll be maximizing dropping the nose down you may end up raising the front up some to keep it from scraping on the track when turning.
Also maybe throw a degree more KPI to it. I plan on using 0* KPI since Im using the adjustable heim front end. The spindles are already built to zero degrees. I may soon have the only CIK sprint kart in the nation!! And no one will know why its fast, even though they can see it!!

edit: Please feel free to pick apart what I offered. picked!!
edit again: the extra degree of KPI is to lift the inside of the tire up a bit to keep it more flat in the turns because of moving the tire out on the spindle. For whatever reason, my kart likes to be narrow. I know its a sprint kart, but it still likes to be narrow. Ive ran it with an open before and put a bigger rear tire set and widened it out. It just didnt like it, so I narrowed it back to 42" CC rear

Have you ever heard of John Learmonth in Australia? No
Just curious since you said you raced long ago, about if you ever raced with or know Ted Swontek? No
You probably know Michael Davis? No
 

paulkish

old fart
My comments on an additional degree of kpi front end angle and moving front tires out were based on your stated 6&6 kpi and castor.
Though not the same the effect of going to 0 kpi is similar in concept to what I am/was thinking..
 
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