I'm getting tight

chall · Joined: 25 Aug 2001 Posts: 16

My kart tightens up after about 5 laps and I have trouble keeping 3 tires in the track. It is a little loose the first lap, cold tires. Works well for a lap, then starts to tighten up. I think the tires heat up and are gripping too much (wrong kind of grip). I would hate to loosen it up and give up that much at the beginning but I would like to stop the betting on wether I'm going to roll it. Tires are Dunlop DAM, air is 13 psi. Where do I look to stabilize grip?

thanks
Chris

Jimmy Moore · Joined: 26 Jul 2001 Posts: 664

Simply put a harder compound on the kart like a set of YGC Bridgestones. If you want to play with those DAM tires a while longer then spread your front and rear track width out to the maximum and, pump up the pressure to 17psi. If you're still tight after that then find out who's been pouring glue on the track.

Steve DiVirgilio · Joined: 27 Aug 2001 Posts: 54

You'll need to go as wide as possible in the rear and depending on front end bite (the wider the front the more bite you'll get)bring that in a little at a time. You can also tighten the chassis down, when you get chassis flex, you get grip. This is not the be all end all but it's a start.

ron brolley · Posted: Tue Sep 11, 2001 2:18 pm Post subject: I'm getting tight

I agree get the seat as low as possible and run it at 14 inches from the ground. I wouldnt make a lot of changes one at a time. If that doesnt work try a softer axle and then go to short hubs. I would first try the seat if your butt isnt dragging its not low enough. Also run the same pressures. One change at a time is important or you wont know what corrected the problem.
Ron

David Mayhew · Joined: 31 Jul 2001 Posts: 209

I would first off make sure that all of your weight is as low as you can get it. If your seat doesn't hit the ground at least one time a lap then lower it some more. Maybe want to lean it back a little to lower your upper body down. I would also lower the psi down a couple pounds and that should help that kart come in later in the race and keep it there for a while longer. Other things to try are, Softer axle, softer wheels, shorter hubs, more flexible seat and the list goes on and on. Try those and good luck to ya.

David Mayhew

chall · Joined: 25 Aug 2001 Posts: 16

OK not I am confused. I understand winding and lowering the seat, but soft axle and short hub? Stiffening the rear helps a lot, so doesn't a soft axle soften the rear, and don't long hubs help support the unsupported axle stub. What am I missing here?
Chris

ron brolley · Posted: Sun Sep 16, 2001 5:51 am Post subject: I'm getting tight

If you use a softer axle the axle flexs more in the turns and the tire has less of a footprint on the track. Thus giving less grip. The same is true with shorter hubs if you you have less hub on the axle it flexs more. At all tracks you should use a medium axle as a baseline with the rear width at the maximum your class is allowed. Try medium hubs first on the axle. If you dont have seat stays i would try them as well. soft axle=more flex=less grip the opposite is true for hard and medium axles.

chall · Joined: 25 Aug 2001 Posts: 16

The axle deflection must be greater then the angle of the frame lift in a turn. That would explain the ware on the inside edge of tires. Guess i have been underestimating the vertical vector of the centripetal force. Thanks Ron.
That leaves me with a kart that starts to bounce in the middle of a turn after about 6 laps. I have soft axle, short hubs, hubs out to the snap rings, 15 PSI in the rear. I can still widen the front 1/4" each side to try to get more lift in the rear. I can use wheels with greater offset and or a longer axle (now 40"). I have been warned to watch for blistering if I increase tire pressure much more. Any other suggestions and which of the above would be best to try first. Thanks, Chris

ron brolley · Posted: Mon Sep 17, 2001 5:15 am Post subject: I'm getting tight

Chris if u have a soft axle on it now and short hubs what i would do is narrow the front end a few spacers. If you do that it will break the back end loose because it has less of a pivoting effect. The narrower the front end the less grip at both ends of the kart the wider the front end the more grip and both ends and the wider the axle the less grip. It sounds like your front end to too wide. Also try 10 psi front and 12 psi back. Everytime you come in take and record hot tire pressures your looking for about 2 psi growth all around. This is the fun part of racing making changes and hopefully getting positve results. Does you track have a lot of rubber down on it?

Gary Kozuma2 · Joined: 03 Aug 2001 Posts: 446

Hey Chris,

Getting back to tire pressure, if you're not using nitrogen you should give it a try. It pumps up a lot less when heated so the tire performance is much more consistent.

As far as all that axel stuff, please read Mike Speed's comments on the Tech Hit Squad. I think the general advise is to go as wide as the rules allow, then soften the axel to remove grip. Softening is with a softer axel or shorter hubs.

Good luck and have fun.

Gary K.

Drew Cleaver · Posted: Tue Sep 18, 2001 2:04 pm Post subject: I'm getting tight

So is our budget

chall · Joined: 25 Aug 2001 Posts: 16

What effect can I expect from tightening the nerf bars. I would expect greater front weight transfer due to greater torsional stiffness. More front grip? Thanks for all the help, its been great. Chris

Paul Kish · Posted: Thu Oct 04, 2001 4:01 pm Post subject: I'm getting tight

From what you described the only possibility is that the inside rear is not unloading.

Either the center of gravity on your kart is located where it is not able to do enough work for you to get the inside rear unloaded or your kart cannot mechanically unload the inside rear.

If you want more action and work out of the cg then you need to raise it and/or move it forward.

If you want more action out of the mechanics of your kart then adjust the ackerman to do more for you in the way of weight jacking.

You can also adjust caster, camber and kpi to gain some ability to unload the inside rear but the primary use for caster camber and kpi should be tire presentation to the track. Basicly anytime you adjust the front end it is to time time the caster, camber, kpi and ackerman to give the desired results at a particular turn of the steering wheel or something that is a compromise. Mainly you should setup for the particular turn on the track that if you can get around it well it will produce most gain in passing potential.

Paul Kish · Posted: Thu Oct 04, 2001 4:06 pm Post subject: I'm getting tight

Just another quick thought. You can either adjust the mechanics of the kart to work like you need them to.

Or you can fudge the grip factor of the tires.

I want all the grip out of the tires at any given time that I can possibly have. Once I have that then its a matter of setting the mechanics of the kart to not put that grip in conflict of bind the kart. That makes for a fast kart, fudging the tire grip by moving tires in or out is a last resort.