Setup question - Moving LR tire

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puttinginwork

New member
Hey guys,

Used to be a member here but it seems like the forum has had some trouble since I last visited.

Anyways, because of the desolent nature of the asphalt forum, I'll ask this question here:

Me and a bunch friends run in a cleaned out chicken barn for a couple weeks in the winter. Concrete floor, a little bit of syrup is put down but otherwise really slick. Karts are a mishmash of old road course coyote's and some offset dirt Karts. Mine is an old Coyote. We run HF clones.

Was struggling a bit to get down the power at the beginning of the night. Kart was a tad loose through both entire turns. Decided to try something a little different and pull the LR out. Couple people told me it would loosen it even more, and I know from researching previously that the set-up guides say the same thing.

Alternatively, the kart stuck to the ground for the rest of the night and I ended up winning the last race.

I hypothesize the wider base stabilized the rear and gave me more left side bite.

Just looking to make some sense of it all. Any opinions?

Here's the race if you want to kill some time:
[video=youtube;X_-_Gj7EtK4]http://www.youtube.com/watch?v=X_-_Gj7EtK4[/video]
 
I think it can go ether way, Takeing it out puts more on the RR, it's more of a timeing castor/cross thing.
Donn
 
When you tuck the left rear in, it's going to make it looser. Think about a late model going through the corner with the left rear rolled up under the car, up on the bars, with the right front digging. That's essentially what you have going on when the left rear is pulled in. When you widened it, it made it tighter, think putting a harder LR spring in a race car, allows for less travel and keeps the car planted in a straight line instead of planting it turning left. Either way, you made the right adjustment by pulling it out.
 
Thanks for the replies.

It sounds like at least in Karts, there is no exact science on what each adjustment does. Little changes alter multiple things. While moving the left rear out would put more right side weight on the kart, at the same time you are widening the rear to hopefully have a more stable kart.
 
That really did look like you guys were having a blast...I have found that sometimes you can have a kart that is not turning in well on a slick track that we do what we have to to get her turned..Stabbing the brake...Hard left while shifting our weight...etc.Once we do this and get back to the gas the kart never really gets all the way back under the driver making him think he is loose.Your change just may have loosened the rear of the kart to the point that she turned in and stayed turned so you just needed a slight flick of the wheel and all was good.It is really easy to overcompensate for what we know is coming without even realizing we are doing it.Nice run though...It was real fun watching
 
Loving the feedback.

Rockland: I can really relate to what you said. That might exactly describe the issue in fact. I remember it slid into the corners beautifully after the adjustment

RI: Thanks. We started up a league at my house last year and asked for volunteers and whatnot. One guy got in contact with me, bought, and brought that out. It adds a nice effect.
 
Ditto what everyone else said about it going either way and just depending...

I think which will work depends on which rear tire is causing your on track problem. For instance are you getting loose because of not having enough grip over all from both rear tires, or is it because your not getting enough grip out of the RR tire, or is it because your not getting enough grip out of your LR tire, or is it because your over working your RR tire, or is it because your over working your LR tire ? In any situation you put your best guess out on the track and then it's seeing on track problems and identifying the root cause or combination of causes of the on track problem. There are different ways of identifying the problem. Off track viewers can look for hints to problems, the scales and tire conditions can hint at on track problems and the driver can sense on track problems. As a driver you probably can feel the difference between the whole back end being loose or if maybe the left or right rear seems to be giving up causing you a problem. Also if you do something to fix a problem and it doesn't or creates another problem, can be used to identify the real problem.

thanks for reading and it's all just a guess

just some more thought to help you find out what is causing the problem

Always remember the RR tire is being pushed on and the LR tire is being pulled.
 
There's a simpler way of thinking about why wheelbase adjustments affect chassis in apparently opposite ways on pavement vs. dirt. It has to do with the way tires grip each surface.

Pavement is hard - tires cannot dig into it, and it forces tires to distort if you load them too violently.
Dirt is softer - you can get the edge of the tire (transition from tread to sidewall) to dig in.
We strive to use the most tire surface area that we can, to produce grip. Along with this, the less tire contact we have with the track, the easier it is to overload what contact we do have and cause the tire to slide.

When the tires are mounted close to the frame, the wheelbase is smaller and the kart can transfer weight quicker to the outside tires. In effect, the kart "tips over".
Moving the tires away from the frame creates a longer path for weight to transfer from left to right. That takes more time, so the right side tires are not loaded as suddenly.

On dirt we can move the tires in to take advantage of gaining traction by digging the edges in. But if we try that on pavement the tires can’t dig in, so they distort – you lose tread contact as the inside edges lift and / or the center cups. On pavement with the tires moved out we distort the tread less by easing weight transfer, keeping more tread on the track.

This is a coarse adjustment - a little can make a big difference.
 
Could it be that there was rubber gettin on the track at the end of the day seems to me wider is almost always loser lol!
 
He simply changed the timing events at the LR. By changing the fulcrum point or fulcrum lever angle if you will, he made the weight that did transfer take a different path. By moving the LR out he moved it farther away from the center of gravity, thus making it take longer to traverse around the LR/RR roll axis. In simpler terms he jus made the LR hold the weight a little longer and it help tighten up the rear of the kart. Why? Because with the LR out it took longer to unload it from entry to apex while at the same time helping reload it quick as well. Overall, he kept more weight across the rear of the kart as a whole. Of course that's just my opinion.
 
its not unloading the left rear. if you watch the front tires the more he turns left the more the kart pushes.
 
Had a kart, at Fruitland Park in Florida,, dirt track..had a modified on it . wouldnt go around the race track, super lose in the turn would go in but wouldnt come off...so moved the left rear out about a half inch, was perfect after that...same night,, had a friends kart doing the same thing...moved left rear out was perfect....mine was a 06 Shadow,,his a 07 Prowler.. moving LR out corrected both karts,, undriveable before that. Seems the wrong adjustments ..are sometimes the right adjustments
 
IMHO there's a lateral slip ratio, just like a forward slip ratio. If your using your tire to much holding you in, it will slip latterly. If it then immediately grabs again after slipping, you probably will be thinking it's hopping. Hopping does not have to be so drastic you notice it, as a big hop and then gripping again. It can occur so fast the tire slides. But move the tire out a little and you move it away from easily going beyond the lateral limit of grip or lateral slip ratio. The end result is instead of operating it at the limit, then beyond and then at the limit again, you are able to maintain it gripping slightly below the limit of grip. maybe?
 
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