kart hopping badly in turns.

Robert Padgett · Joined: 07 Oct 2001 Posts: 5 Location: San Franicsco ca.

I've only been racing for less then a year and I've had this problem from the start.
My kart(trackmagic 2000 dragon)wants to lift both wheels on right side in a right hand turn. I've been ruinning tire pressures at 21psi at the rear and 19psi in the front.I've try higher tire pressures and had some changes to the handling of the kart.

This is a problem that i've been after most of the year. I changed the seat hight and got less bite but the kart wants to come around on some turns .

Any help would be welcome.

Bob looking for the answers.

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Scott Kalish · Posted: Mon Oct 22, 2001 5:12 am Post subject: kart hopping badly in turns.

Bob

I had the same problem with my Trackmagic Spitefire. Have you been to the Trackmagic Website? Try using their recomendations. I also went to the Urethane seat struts.

Good Luck

SK

Randy Fergus · Joined: 31 Jul 2001 Posts: 18 Location: Hilliard, Ohio

I'm running the exact same chassis as you and had the same problem when I first started. I'm still not running up front but I'm getting a lot closer than I was. The suggestions on the Trackmagic web site will definitely get you a lot closer too. E-mail me and we'll compare notes.

Randy Fergus · Joined: 31 Jul 2001 Posts: 18 Location: Hilliard, Ohio

Bob, I just realized where you are. Trackmagic's just down the street. Go talk to them (and let me know everything they said)

Paul Kish · Posted: Mon Oct 22, 2001 9:24 am Post subject: kart hopping badly in turns.

Bob,

Here is one possibility. Weight transfers and it has to transfer in a particular direction. With the normal situp position of a sprint kart it may be that you just have a lot of upper body weight. ????

Yes the cg operates the kart but if you just have too much weight up high you can project too much weight above the tire contact patch and not enough at the tire contact patch or below it. If that is the case no matter what you do the kart will tend to work the outside tires toward the outside of the tire. The kart will have a tendency to tip if you move the tire in and very likely hop if there out. You have said that you have adjusted seat height. Well you may have not moved it low enough even though you have adjusted it.

I have not really thought about the following much it just poped into my head. You might try shortening your seat struts to attach them lower on the seat. That might bring where the weight of your body tries to pivot the kart in a turn down lower.

My first guess though, which is probably wrong, is that maby you just have too high a proportion of upper body mass to allow the kart to operate properly. ???????

Steve F · Joined: 05 Sep 2001 Posts: 134

I've had excellent success with my Dragon here at Jacksonville (and elsewhere too). If you're a heavy guy like me (190's) you need to almost drag your seat on the pavement. No lie.

Stay away from the soft compound tires too. YEX's - YGB's are too sticky for that chassis. You'll have much better success with medium grip compounds like the YGCs or MG reds or equivalent. Your tire pressures seem high to me, I think you've got to fix your seating problem before you go way off the deep end with tire pressures.

Dont be afraid to move your seat down or change the tilt in 1/4 inch increments. When you get it right, you will know. For me this kart has been a free pass to the winners circle more often than not.

Good luck.

Steve F

Scott Davis · Posted: Mon Oct 22, 2001 12:24 pm Post subject: kart hopping badly in turns.

Have you weighed the kart out on scales to see what your corner weights are?

Robert Padgett · Joined: 07 Oct 2001 Posts: 5 Location: San Franicsco ca.

To scott Davis menber# 266

HI this is Bob Padgett the guy with the hopping kart.I have set my kart on a scale and I get readings 42% on front and 58% on rear. This should be very close to trackmagic recommended set. I do have the seat a bite high so after reading all the responces from are fellow racer I've set the seat down to about 1" off the ground. I've also taken off upper seat supports to stop some of the side bite. So I've made all they change to my kart and I'm going try them out at track .

Thanks to all of you fellow racer for your suggestion.

Rob Martin · Posted: Mon Oct 22, 2001 8:02 pm Post subject: kart hopping badly in turns.

There are a lot of comments regarding the seat height and possibly driver weight being a factor in your bicycling problem.

I wouldn't go more than a 1/4 inch below the frame rails when mounting your seat. If you do you will just be wearing out the seat.

Driver weight is only part of the effective CG of the kart. Regardless of your overall weight, if you are a tall driver or have a long torso your net effect is to raise the center of gravity.

The solution may not be lowering the seat relative to the frame. The CG of the kart is greatly affected by the incline of the seat. Adjust the distance from the seat back to the rear axle in small increments. As you make this adjustment, additional spacers may be required on the front of the seat.

An inclined seat also reduces the g-forces you may experience (at least it does in jet fighters).

Good luck.

ps. If your butt gets hot your seat may be too low.

Brian Kay · Posted: Tue Oct 23, 2001 5:53 am Post subject: kart hopping badly in turns.

Bob,

Did I read your tire psi correctly??

Hopping is usually the result of being "OVERstuck" in the turn. Try to build more flex into the chassis.

Hopping is when the cornering force cant all be absorbed into the chassis or tires, and the inside leaves the ground. At a certain point, the kart "breaks" grip, and comes crashing back down. Repeat this about 5 times per second!

If you aren't already, try using the urethane struts Trackmagic offers, and reeeally loosen the chassis seat struts. This will help the chassis "wind up" in the center, and absorb some of the force that's causing your hop.

Try coming down a tad on the tire pressures. 9 to 12 psi (cold) is generally considered "normal" for 125's on 5" tires.

Brian K - www.T2racekarts.com

Kathy Barton2 · Joined: 17 Oct 2001 Posts: 35

All of these ideas are good.

In addition, I have had some luck reducing the hop phenomenon with the following strategies:

-- switch from long rear hubs to short

-- if there are pinch bolts that hold the two left rails together, try loosening them

-- if there is a rear torsion bar, remove it

My chassis is not a Track Magic, so your results may vary. Best of luck.

Kathy

Paul Kish · Posted: Wed Oct 31, 2001 2:27 pm Post subject: kart hopping badly in turns.

HEY BOB....

Did you get to try the kart out last weekend? Can't waite to hear if what you said you were going to try helped. Or if not how it changed the handling.

John Wehrheim · Posted: Wed Oct 31, 2001 11:30 pm Post subject: kart hopping badly in turns.

I don't know much about TrackMagic chassis, but I can tell you that the seat incline from the axle should be around 9". Tire pressures are waaaaay to high. Brian is correct, we typically run 10 and 12 cold on YGC's.
You did not mention the axle(soft, med or hard) Nor did you mention the size rims to the tires. This will also have an effect on hopping.