April 25, 2016 at 10:19 am #64953
Went out to Engishtown this weekend to shakedown kart after winter teardown. Was not really racing, so just started at the back for the race to get some laps in. Kart is a Ikart with Rotax Evo on Used Mojo Reds @ 400 lbs (Most other karts where on MG’s). I know the jetting was a bit off killing me exiting slow corners, that was resolved in the feature by moving pin down.
I have a handling question. I had the same issue at the end of last season. I mounted the camera on he sidepod record issue. I am having persistant corner exit oversteer. Between apex and trackout I need to counter steer to correct, scrubbing off a bunch of speed. I am wondering if this is push/kick and I have understeering going in, forcing me to put in more steering angle to make the corner and at apex front end suddenly bites and I have rear comes out forcing me to make correction. A good example is at about the 5:30 Mark.
What do u guys think? Is that what you are seeing on the video? What corrective setup action would you take? I an thinking of adding caster and going a litte wider in front. Thoughts? Any input appreciated.
I have bar tight in front, lose bumper, hard axle, full with read, short hubs, med with front, camber, caster and toe set as per mfg spec. 10 PSI cold, 12 hot.
April 25, 2016 at 10:43 am #64957
Here’s my “any input”… I would not suggest widening the front or adding caster as it would increase the jacking and keep the inside rear from helping with your drive off sooner.
Do others run the Mojo Reds? I’ve never run them myself but it might be worth trying higher pressures (say 14 and/or 16 psi hot). If 12 psi hot is the absolutely place to be with tire pressures (or it doesn’t get better with higher pressures) than I would suggest narrowing the rear and going to a medium or long hub. If this doesn’t help than you might want to try without the front bar in.
Do you have any seat struts mounted?
April 25, 2016 at 12:37 pm #64975Dan BrownParticipant
I have an ikart with an ’09 Leopard at 400 lbs and I am having the exact opposite problem. My inside tire is setting down to quickly and it gets understeer from apex out. I am running MG yellows, as tire pressure built up it got worse, had best results running at 11.5 lbs. I have a T3 soft axle with 65mm hubs, John Martin and Randy Word both suggested a T1 ultrasoft axle. The track was cold and green the last week of March when I drove it last, I had shoulder surgery 2 days later and haven’t been back out. Before I make any changes I want to run it again on a warmer track that has picked up some rubber to see how is acts. It felt as if the outside rear tire was washing out due to the cold green track, and that was causing the inside to drop early. Even with the not perfect handling, I put down some great lap times as the ikart chassis feels like it recovers quicker from a less than perfect corner than any of my other karts ever did.
April 25, 2016 at 11:01 am #64963
Thanks for the feedback.
If you skip forward to the last lap of the race (About the 5:45 mark) you see I have this issue on exist of almost all the left hand corners. Seems to get worse the longer I run. Not sure because that is due to heat or due to fact I am pushing harder.
I am switching over to new MG Yellow for the next event, so did not spend too much time tuning on these old tires, but I don’t buy new tires every weekend, thus need to get this sorted. The MG will have more grip and being new, should also be more conistant.
I am running one strut each side. I don’t recall effect of running with Bar out, but I recall it was undrivable. I am told bar is only removed running in the wet.
April 25, 2016 at 11:38 am #64965Ric mcDadeParticipant
I too have had a similar problem- TAG Leopard- Mg Yellows- finally decided that if I could get inside tire to set down quicker, it would help. Tightened the rear bumper and bar- better. Made axle stiffeners out of PVC, for a quick ck, problem gone. Little stiffer axle now, and like what I feel. I’m not real smart, so listen closer to these other guys!
April 25, 2016 at 12:23 pm #64973
I think it will be telling when you swap over to new yellows. (make note which end the fast drivers are wearing out first, front or rear tires) I would suggest going back to a medium hub with the new tires and tune from there.
If it does continue with new tires than I would suggest doing the things to add rear grip by narrowing the rear, going to longer hubs, lower the rear ride height (axle up), and adding another set of seat struts.
April 25, 2016 at 1:00 pm #64978
Trying to decide if I take steps to add rear grip or take steps to add front grip. I think it may be a cause/effect thing where I am lacking front grip on entry and put allot of input in and past the apex I finially get front grip and the rear washes out and I need to correct. If this is the case, I think I should take steps to add front grip. If I don’t correct quickly I will slide off the track backwards but that correction scrubs off any speed I carried through the corner.
There is an interesting article here about push-kick or push-whip at link below:
April 25, 2016 at 1:12 pm #64980TJ KoyenModerator
I’m not familiar with the track there, but it looks like you are VERY low on entry to some of those corners. It also looks like you aren’t pushing very hard. If I may ask, how far are your times off the leaders?
The reason I ask is because it doesn’t look like push-kick that you are experiencing. It looks like you aren’t on the limit that the kart requires to work and flex properly.
Also, it’s basically impossible to try and tune a kart on old worn out tires. It isn’t going to react the way it’s supposed to on old rubber.
First thing I would do if you want to attempt to fix the oversteer, is to narrow the rear by 5mm each side and see if you can get the outside rear tire to dig harder. But my gut feeling is once you switch to a fresher set of MG Yellows, it will completely change the kart. My advice would be to leave it at a standard neutral setup and put the new tires on and see what it does first and go from there. Depending on temperature, probably aim for 9-11 on tire pressure at 405 pounds on Yellows.
Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
April 25, 2016 at 1:21 pm #64981
The thing that sticks out to me is your hands are extremely smooth during your turn-in and I don’t see you trying to “jerk” the steering to get the kart to turn in more.
This combined with the things that stand out to me (short rear hubs, only one strut per side, loose rear bumper, and max rear width) as reducing rear grip, are what prompted my responses.
Cheers and please let us know what you end up finding out! :)
April 25, 2016 at 3:29 pm #64983
TJ, you are very obserative. This the first time I have driven this track in years so you are spot on about not pushing it very hard. I was about a 1.5 sec off pace. Some of that was probably the tires some due some due to some conserativism this weekend.
I would write it off to lack of track knowledge and driving issues (Stop watch does not lie) but I have exactly the same issue at my home track (OVRP) and at that track my times are competitive. The corner exit oversteer is actually a little more pronounced there.
I think you are spot on with tuning with the old tires, expecially being a different compound. So, next weekend (New track to me as well) I will run 1st session on these old tires with same setup to replicate issue (I am sure I will). I will then switch over to the new tires, with no changes and use that as the baseline and adjust kart to what she is doing on the new tires.
If I experience the same issue, I will take your guidance and attempt to fix the oversteer via:
– Narrowing the rear by 5mm each side and see if I can get the outside rear tire to dig harder. I will keep the factory neutral front end setup intact.
Is 9-11 the hot target or cold starting point on MH Yellow?
When you say VERY low on entry, I think you are suggesting I am turning in too early. I’ll pay attention to that this weekend. That should be evidenced by tracking out too early. So sounds like I should be turning in later, being more aggressive on turn in, leaning more on the front tires at corner entry.
Thanks everyone for input… I find the video helps with processing changes.
April 26, 2016 at 9:29 am #65019TJ KoyenModerator
Yes, it looked like you were early apexing a lot of the corners and swinging out way wide on exit, especially compared to some of the karts around you.
All sounds good to me. The 9-11 psi I referenced was cold starting pressure. Report back and let us know what you learn.
Driver/Coach/Wrench : Innovative Performance/Exprit
Owner : Oktane Visual - www.oktanevisual.com
May 1, 2016 at 9:11 am #65256John WilliamsParticipant
Something to consider:
This track has a number of corners that are heavily painted near the apex. The kart actually seems to understeer off corners that are not painted. Most of the oversteer occurs coming off the painted corners. As the heat goes on, it appears that you are consciously (or unconsciously!) adjusting to those corners by slowing through many of the painted sections and “straightening them out”. I agree that the new tires may help considerably and moving the rears in slightly should help with the oversteer but I’d be curious to know how much oversteer remains on an unpainted apex with newer tires. Also, I wouldn’t waste much time trying to dial in handling until you change the tires. Agree that narrowing the rear would be my first change if oversteer remains. Best of luck.
May 6, 2016 at 12:57 am #65482Dale CheesemanParticipant
What stands out to me is that you are having to put a lot of steering into the right hand corners but the kart is so aggressive on the left hand corners that you are counter steering most of the time. This would likely be due to a cross weight issue or an issue in the steering alignment. The most common cause would be that the steering shaft is bent or was not centered properly when the toe was adjusted. If the steering shaft is slightly off to one side when you “Square up” the toe it will cause the steering to be lazy one way and aggressive the other. It only takes a small offset to have a big affect on the cornering. Other issues that can cause this are having different tire pressure on different corners or having a worn out tire compared to other tires. The circumference of the worn tire would be less and would change the weighting of that corner.
May 7, 2016 at 11:42 pm #65529
Thanks for the feedback… I had a few spare hours so I hit the Track this Morning (OVRP). It was an unplanned last minute thing, so I did not put new tires on, did not make a single change. On damp/cold track, ran competitively. The Corner Exit Oversteer was much less pronounced but you still see it.
Was just running some fun laps. Later in the day got much faster. Was playing with Camera Positions and the AIM Mychron 5. Love the big numbers and the predictive lap timing on the M5.
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