Help! Rear is always loose

[Mark Shelton]

To the guru's who have the answers: I have not been able to get straight answers on this in over a year. Please help me out.

I have a CTS 80 shifter, and I run YDS tires. My kart is always loose. ALWAYS.
I have read and heard non stop to widen the rear, raise rear tire pressure, and harden the axle. I've also been told to narrow the front to reduce front grip.
The thing is, all of those things make my kart MORE loose. The most rear grip I get is when I am as narrow in the rear as I can get, with like 20 pounds (Hot) in the rear tires, and a soft axle with short hubs, and my set up as soft as I can get it. The more narrow I get the front, the faster it reacts, and makes me more loose in the rear. I'm confused bad. Why am I experiencing the opposite of everyone else? I run a high rear ride height, and 2nd seat struts.

[John Denman]

No wonder.

Narrow the rear to get more rear grip. Widen the front to get more front grip.

Get as much grip as you can to keep it from bicycling or hopping, then balance the front & rear.

I would start by moving the rear wheels in a half inch either side. Do this at the track - run it like it is, then move them in and compare. If that works, go another half inch.

There are a lot of other things like seat position to consider.

[Mark Shelton]

I am as narrow as I can get in the rear. I've even cut the keys in half so I can get more narrow. My rear width is 49".
When I widen the front out, I actually seem to develop a push then, rather than get more front grip.
My seat is set back pretty far. The last time I scaled my kart, I was at about 58% rear weight.
Would raising my seat height help? I weigh about 190, so I have some weight to throw around in there.

[Roger Miller]

DIfferent karts are different, so, what works for some, may not work for others. But, in general, anything you do to soften the kart, makes it looser.
Narrow rear, stiffer axle, longer hubs, add axle collars, seat struts tied to the bearing cassette mounts, higher tire pressure, like 25, all of these might help.

However, you need to start with these questions: How is it on corner entry, how is it mid corner, how is it on corner exit? Also, what do the front tires look like after a session and what do the rear tires look like after a session?

What might seem loose could be a push on corner entry. Many folks get fooled by this. Entering the corner, turning the wheel, and turning more, then the back steps out. It's really a push.

Also, for a shifter, throttle control is important.

Your experience may be different

[david stratton]

me too. i ran a topic a few weeks ago and got contradictory advice........we have a 2001 crg heron plus set at factory settings, with red vegas at 13 psi, rear width was 53 3/4, and the front set at three spacers on the inside.........and it is loose on the exit.........we tried narrowing the front till it pushed ....still loose....med hubs on back, bearings turned out,, widened the front, rear bar both in vertical and out .......still loose.......what gets me is the contradictory advice some say narrow rear is more grip, some say wide is more.......same with the front, i hear narrow till it pushed, and also widen till it pushes........i do notice the out side rear wearing much more than the inside, and still slight coning on the tires...........help

[Rick Blood]

The advise you are getting may be contradictory but is not neccesarily wrong. There is a crossover point on front and rear widths where each case is true. As you start moving in from 55" it may get looser but then it will start getting tighter again after you pass the crossover point.
It may be time to hire a good tuner and put everything in his hands.
or
It may be time to examine your driving style to see if the looseness is drive induced.

[Rob Linders]

I agree with Rick Blood, you may want to hire a tuner. I hired Dodson Engineering and have improved quite a bit. I have worked on many things with them, but my initial problem was I thought I was always loose. However, as Roger Miller stated many people are fooled into thinking they are loose. I really had an initial push, that I couldn't feel, so I turned a bit more and then the rear came around on me. In my first time out with Dodson, he discovered this by reading my tires. It is pretty amazing how 30+ years of experience will quickly diagnose problems you are having.

Having a coach IS the best money I have ever spent in karting!

Have you measured how much your tire temps rise right when you come back into the pits?

Rob

[Chris Sigua]

Mark

Have you called Ray Cunningham at CTS? Ray would be more than helpful and he can give you the info about what the baseline setup is to start with. I have seen him post on this board, so maybe he'll se this.

Chris

[Mark Shelton]

There are some very interesting points in here. I have heard of the "initial push" thing before. I've not been able to tell if that's it or not. I might have to consider a tuner. Who would be a good choice in the Sacramento area? I have talked to Ray Cunigham a few times about this, but honestly have not been able to get that much. He did suggest to try to get as much flex as I could, and suggested I cut my 4th rail out. I did, but I can't tell much difference. The thing that gets me about the "different karts are different" thing, is that physics should be absolute. Weight transfer is what it is, and things like chasis flex, center of gravity, wheel base and track width should make for predictable handleing characteristics.
It seems my problem is on corner exit more than anything. I can't keep the rear behind me for a solid exit. I work hard on throttle roll on, but I'm sliding before I even apply the gas. Maybe that means mid corner is my trouble?
I don't have great notes on tire temps. I started taking them, but without knowing how to use the data for much more than camber setting, and looking for even temps across the tire for indication of pressure settings being good. What would I look for?

[John Valerio]

Mark,
try widening the front end. 40"-42". If the kart is loose widening the front end helped with my kart. It adds more jacking effect especially on turn in. Although I run an Invader pro-works everybody in the mother told me to change axels,longer hubs,move my seat and the track promoter of people told me to widen the front. I made the change in less then 2 minutes and picked up almost a second a lap. Seemed a little out of wack but you've got nothing to loose and most of all its easy and cheap.

just my 2cents

[Roger Miller]

Well, first of all, different karts are different because:
different tube diameters
different tube wall thicknesses
different tube configurations including front, side and rear rail placements. All of this adds up to varying response and flex affecting what happens, and what changes result.

That said, if all is well through the corner until exit, then you may need to work on your line and entry speed. Try going in wider, and a touch slower, to get out faster and cleaner. A later apex, just by a foot or so can be the difference.

The primary reason for exit loose is usually throttle, but you say you are working on that already, and, it may even be happening before you get to the throttle.

Consider making the side nerf bars tight as well.

Also, I meant to say, that like was mentioned above, some adjustments, especially track widths, have breakover points where it goes from helping to hurting. Testing testing testing in controlled conditions helps to find and define those. And all of this depends on the day, the amount of rubber on the track, the temperature, the position of the Moon, and, the alignment of Venus and Jupiter.

In other words, chassis tuning is a quest and there are no "golden" answers that work all of the time.

[ December 15, 2001: Message edited by: Roger Miller ]

[pat slattery]

Mark, I think I would start be having the kart scaled out with the driver in it. Most karts have a recommended front and rear percentage and you may simply be to light in the rear. This also can tell you sometimes if something is slightly bent. I would shoot for somewhere around 56-58 percent of your weight to the rear. If you are lighter than that my first move would be to get some weight back there either by moving the seat or if you are using weight to move it to a reward location. Once you find out what the weight bias is then let try something else.
let me know.
pat slattery

[Joe Janowski]

General rule of thumb...when you keep trying things to solve one problem, and nothing works, you're seat is in the wrong position. Have you tried moving the seat yet? It's a pain, but something that needs to be done to achieve correct chassis balance.

Joe Janowski
Fury
GP Chassis/CRS ICC

[Dave Boles]

I solved a my loose problem by moving from an MBA to an Emmick. I fought for about 2 years before the problem was solved

[Patrick Hubbell]

quote:

---

Originally posted by Mark Shelton:
To the guru's who have the answers: I have not been able to get straight answers on this in over a year. Please help me out.

I have a CTS 80 shifter, and I run YDS tires. My kart is always loose. ALWAYS.
I have read and heard non stop to widen the rear, raise rear tire pressure, and harden the axle. I've also been told to narrow the front to reduce front grip.
The thing is, all of those things make my kart MORE loose. The most rear grip I get is when I am as narrow in the rear as I can get, with like 20 pounds (Hot) in the rear tires, and a soft axle with short hubs, and my set up as soft as I can get it. The more narrow I get the front, the faster it reacts, and makes me more loose in the rear. I'm confused bad. Why am I experiencing the opposite of everyone else? I run a high rear ride height, and 2nd seat struts.

---

Mark,
You may have one of two problems or both. Either the seat is in the wrong place(to far forward) or the set-up is all wrong. I also have a 98' CTS 80cc. Let's get the basics down first.

Long hubs(rear) = more grip
Hard axle = more grip
Rear torsion bar = more grip
Widen front track = more grip
Narrow rear track = more grip
Increase caster = more grip
Raise rear ride height = more grip
Raise seat = more grip
4th rail pinch bolt = more grip
Seat struts = could go either way.

First you need a base line. Start with new tires to eliminate that variable. YDS's are realy only good for the first 4 races. After that your waisting your time if you have a handling issue. As long as the frame is in good order you may want to try this:

Start with the front track with 4 - 5 1/4" spacers on the inside, maximum caster, no camber and zero toe to 1/8" toe out. A medium to hard axle in the rear and long hubs. Set the rear track outside to outside at 49". Start with 22 psi cold on all 4 corners. No pinch bolt and no seat stays. Set the seat bottom level with the bottom of the chassis. This should be close. If you feel like you can steer it any where you want to go then decrease the caster.

The problem may not be at the rear of the kart but rather at the front. To much front grip will oversteer the rear.

With the above set-up go out and see how the kart feels. If it is still loose in the rear decrease the caster. If it is still loose try moving the seat back. Also as soon as you exit the track check the tire pressure. You want a 2 psi increase from cold to hot. If you get more than 2 psi decrease the pressure by 2 psi. If you get no increase or less than 2 psi than increase by 2 psi.

You didn't mention which track you are running at. Also, which part of a turn are you experiencing this loose condition. Is it at turn in, mid corner or exit. Which axle do you have.

My CTS came with a A/B stiffness axle usualy used with a sticky tire. I also got a "YBN" axle. That thing is so thick it's unbelievable. I tried it and it made the kart understeer. I put the softer axle back in with long hubs and it's perfect now.

Also, how big are you. Tall ,short etc. If you are still having trouble I'll hook you up with Damon Meek. Factory CTS driver. I call him the professor. He can get you dialed in.

I might be at Dixon in the morning with my CTS. If you make it to the track I drive a Chevy Silverado x-cab (silver) w/white trailer. #21

[ December 15, 2001: Message edited by: Patrick Hubbell ]