Home Forums Chassis & Handling Seat stiffness and effect on chassis flex

This topic contains 29 replies, has 8 voices, and was last updated by  jt colegrove 3 weeks, 3 days ago.

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  • #58849

    Dan Brown
    Participant

    I have had a difficult time the last several seasons getting a chassis to work with my body size. At 6’2″ and 220 lbs without gear on, I have trouble getting a kart to lift the inside rear wheel and carry it predictably through a corner. I ran a Tony Kart Racer  30mm in 2014 and  Margay Brava 1.25 Limo in 2015. The Margay handled much better than the TonyKart did for me, I attribute that to the Limo’s extra length allowing me to get the kart to scale out better. I have switched to a super flexible iKart now. As I was setting it up today I realized the one thing that has remained the same through all three karts is my  XXL seat, which I have moved from kart to kart. It’s a super stiff fiberglass Tillet. Would a more flexible seat help the kart respond better and help eliminate the binding I have been experiencing? Any suggestions on a good flexible seat for a bigger guy like myself? Thanks in advance.

     

    #58876

    TJ Koyen
    Participant

    At your size, you should struggling with the OPPOSITE problem; it should be difficult to keep the kart from hopping and lifting too hard.

    What model seat are you using? Stiffer seats don’t allow the kart to flex as easily, so if your seat is too stiff, that might be part of your issue. It’ll be important to not go too soft though, otherwise you’ll run into the opposite problem and the kart will be difficult to keep from bicycling.

    Team Driver - Innovative Performance/Tony Kart // Owner - Oktane Visual Custom Helmet Paint and Graphic Design

    #58913

    Dan Brown
    Participant

    My seat that I used for the last two karts is a Lightning Light Twister in XXL. It is a fiberglass seat, and its pretty stiff. I just bought a Tillett T8  1/4 padded in XXL and installed it in the iKart, which due to the winter weather here in NY I have not driven yet. My last 2 karts, The TonyKart and the Margay Limo, both had similar characteristics when entering a corner. The front tires would push terrible with minor steering input, when the steering was turned more the inside tire would sometimes lift slightly but not carry for very long, always touching down before the apex of the turn. Giving large amounts of steering input to try and get the kart to rotate would cause the front tires to chatter and hop, or if they grabbed sufficiently the rear end snapped violently loose. On a fast, wide open left hand sweeper, I would lose over 1000 rpm when attempting to turn as the rear tires stayed glued to the track and the chassis would bind. Most of the decent driver/tuners I ran with all said to keep moving my seat ahead to get less weight on the rear end, but I couldn’t comfortably move ahead any more , my knees were in my chin already. Front/rear percentage on the Margay was 39% front, 61 % rear with an on track weight of 405 with me in kart and a half tank of fuel. I was running a Yamaha pipe package and YLC tires.

     

    #59080

    Tim Koyen
    Participant

    Dan-

    I would say the tuners were giving you decent advice.  39% on the front is on the light side.  I’d try to get that up a few points.  TJ is right, a guy your size should have the opposite problem.  Your kart should be over flexing.  It’ll be interested to see how the IKart handles someone your size.  You may need to try several different seats to get where you want to be.  In addition to being too far back, perhaps your seat is too high.  You should have it as low as possible, with the bottom somewhere below the frame rails, maybe a couple cm or so.

    I just googled Twister seat and that thing looks super stiff.  It looks like a flat, or oval kart type seat, which isn’t what you’re going to want in a Yamaha sprint kart.  Most oval kart seats don’t really need to flex, as they aren’t really integral in the chassis function.  They’re more a place for the driver to sit and keep his/her weight down low.  The Tillet T8 is going to be a way better application for the Ikart or the Margay, for that matter.  If that doesn’t work for you, contact me and we’ll see if a DeepSeat puts the weight were you need it, yet still keeps you comfortable.

    One big thing, is to make sure the seat isn’t in a bind when you install it.  It should sit neutral in the kart when you tighten up the bolts.  Make sure you bend all the tabs so they are parallel with the seat surface, and fill any gaps with spacers or washers before tightening.  You definitely don’t want the seat to be pulled in any direction when you tightening up bolts.

    KartLift Kart Stands
    DeepSeat Kart Seats
    877-777-8020
    ------------------
    Don't bother PMing me, it doesn't work. Email is best: tim@kartlift.com.

    #59103

    Dan Brown
    Participant

    Tim, thanks for the response. John Martin has called me several times over the last few weeks giving me setup recommendations , he is truly a great guy with fantastic customer service. He feels the iKart will work extremely well for a driver my size due to the huge amount of front end grip built into the iKart chassis. I should be able to move the seat farther back and still carry enough front end weight to help eliminate a push. I installed the new Tillett seat and I agree it does feel more flexible then the Twister. I have heard good things about the DeepSeat as well, so if this doesn’t seem to work as planned I will be in touch with you about buying one. Thanks again. Dan

     

    #72494

    Dan Brown
    Participant

    It has been  a while since I posted on this topic, but I am still having some problems with tuning so I thought I should re-address it. I Removed the Lightning Light seat and put in a Tillett T8 1/4 padded in an xxl size. This was on the last week of March. I drove the Ikart at our local track that weekend, it was only 40 degrees out and the snow had just melted, I was the first kart on the track for the season. The ikart drove okay, much better than the Tony Kart or the Margay did for me. The Tillett seat was too large, I found myself sliding around too much  and as my weight kept shifting in the corners it made the kart very unpredictable. I then proceeded to destroy me shoulder at work and had reconstructive surgery the next week which took me off the track for several months. I purchased a carbon fiber Ribtect XLT seat and installed it. I love the seat, it holds me in place perfectly. But the rear grip on the ikart went away badly. The kart starts to rotate perfectly, it just floats into the corners. But from apex out the rear just washes out, I can’t keep the rear tires planted in the track and get off a corner with any speed. I went from a Swift T1 soft, To a T3 and a T5 in medium and med/hard. I have the med/hard in it now with long hubs, and although it is slightly better it still isnt great. I have changed rear widths in and out, running 54.5 now. I removed caster and went to neutral, have 2 degrees positive camber and zero toe. This front end setting gives me nice even tire wear, a great stable feeling on the track and really lightens the heavy feel of the ikarts steering and removes some of the insane front grip these karts have. I have the front width as narrow as possible with 80mm front hubs installed. I have 62% rear weight, 38% front and side to side scaled almost perfectly at 50%. Running MG yellows and a Leopard Tag, best results are rears at 9lbs starting pressure. I recorded my last few runs in video, the inside rear appears to lift at entrance, then the outside rear tire washes out, the inside tire starts to drop back down, then the outside gains grip again and it happens over and over. In slow motion the rear of the kart appears to chatter up and down or flex almost snake like. 2 of my buddies bought new 2016 ikarts and we raced together yesterday. One has a Tillett, the other has an Ikart brand carbon fiber seat. The tillett equipped kart seemed much more stable, the carbon fiber kart seemed to hop in the corners too but was still better than mine. I love the feel on my body of the ribtect, it allows me to run many more laps without my body hurting as quickly as  it does in other seats, so I really do not want to change it. Any tuning suggestions?

     

    #72515

    Patrick Roth
    Participant

    How many seat struts do you have?  I found that when I ran the Ribtect I either ran only 1 additional strut per side and many times I ran without additional struts.  I even experimented with slight loosening of the mounting bolts (just enough so they turn a little by hand) without any struts.

    I’m not familiar with the ikarts but if I were experiencing the same in my CRG’s than I would lower the rear ride height (axle up) and narrow the rear width… but I would try the seat adjustments first.

    #72519

    Dan Brown
    Participant

    2 struts per side, rear ride height is all the way down. I have experimented with different widths, but have not tried removing seat struts, so I will give it a try.

     

    #72524

    Patrick Roth
    Participant

    Please let us know how it goes when you try removing the seat struts.  I would suggest starting by removing the highest seat strut on each side.  If this gets you headed in the right direction than remove the seat struts completely and see how it goes.  If removing the highest seat struts doesn’t help than put them back on and try removing the lower seat struts.

    #72532

    Dan Brown
    Participant

    https://www.facebook.com/photo.php?fbid=10153867186554091&set=pcb.1637410956575502&type=3&theater

    I will try it, thank you. I am starting to think that I may have gone too far with stiffening the rear axle, moving the seat back, longer hubs etc. I think I may be overloading the outside rear tire, asking more out of it than it is able to give. I have noticed that I am getting a very short life out of the rears, and that they show some coning on the inside corners.  I tried something today that I am not sure has been tried on an ikart yet. I welded in two pieces of 32mm tubing and added a rear clamp in flat bar off my CRG Kali. On the CRG in the vertical position it binds the chassis up tight, but when I clamped it in the ikart it basically does nothing. No matter if it’s in flat  or vertical it feels basically the same, maybe a touch worse.Here is a pic of me at speed heading into a right hander, it feels perfect here, but apex out it just gives up any and all rear grip.

     

     

    • This reply was modified 2 months ago by  Dan Brown.
    • This reply was modified 2 months ago by  Dan Brown.
    #72538

    FREDDY SANDOVAL
    Participant

    Dan

    I’m not an expert, as I do have my share of struggles with chassis set up and tuning.

    But that lift looks pretty good to me, and that kind of lift is what gives you better engine speed, as you’re not binding the power when the kart is flat like a pancake.

    I would try changing your line, and apply very minimum steering?

    #72545

    Ambrose Buldo
    Participant

    I run an iKart with Rotax at OVRP. I also run the MG Yellow. I am disappointed that I can only get 3 days out of a set of MG Yellows. The RR (Out Side Tire) gets worn down to cords. The other 3 tires are in good shape. When the tire is worn, kart gets massive oversteer. This is the second consecutive set of new yellows where I have destroyed the RR.

    At 205 with a Tillet XL, I run similar setup.
    8.5 PSI cold
    T-5 Axle
    54-5/8 Rear width
    Toe 0.5 mm in
    Caster neutral
    Camber 1 mm positive
    Front width 1.5 spacers
    Seat 25″ from frt tube
    105 MM Med Log AU Hubs
    Bar Tight, rear bumper loose, front bumper tight

    Below is a video of my best lap in slowmo.

    https://www.youtube.com/watch?v=f4Dd3EjcBck

    Any feedback? There is a little corner exit over-steer in left handrs.

    I find the ikart steering to be excessively Heavy, may consider tying your front end setup.

    For comfort issues I plan on switching to a Ribtect or a Deepseat. Intrested in seeing how it works out for you.

    #72581

    Dan Brown
    Participant

    Ambrose, thanks for replying. We have been down to OVRP once this season, as well as Cherry Valley and Avon half a dozen times and even got a practice day in up at St.Lawrence Motorsports Park. I am thinking what we are experiencing is just an unwanted condition built into the ikart. I have spoken with several drivers who have run them on these same tracks, and it is a common response to hear that the steering feels extremely heavy and the rear end is consistently loose.  I removed some of the Ackerman  and caster, as well as going to zero toe and that lightened the steering up a lot, it feels much better but still not exactly to my liking. The T5 rear axle setup with the long hubs and dual struts seems has given me the best results in the rear so far, but I am looking for a lot more rear grip. I watched your video and it looks really familiar! Because of the constant oversteer on exits and you having to countersteer at every corner, it throws the entrance to the next corner off. Instead of concentrating on hitting my marks and trying to set up a pass in a corner, I am just trying to get through the corner with the least amount of lost time. I will readily admit I am not a finesse driver, it isn’t my style. I am more of a bulldozer kinda guy lol! I don’t race dirty and try to avoid contact with other karts always, but I like to get out of the groove and use the whole track to make a pass. I hate having a limited race line that I have to tiptoe on to get around a track. To me, that isn’t racing the competitors, it’s racing the track and that isn’t what I am looking for . The ikart performed the best for me at St.Lawrence, but that is a high speed track with sweeping corners and not nearly as tight and technical as the other 3 tracks. The heavier steering actually felt great, it helped stabilize the kart at the higher speeds while my CRG seemed to dart around more.

    The reason I thought maybe I am overloading the outside rear tire is partly the same as you said, I destroy that tire long before the other 3.  Also I ran at Cherry Valley about a month ago and during the first heat the kart was driving the best it ever had. I had on a brand news set of MG Yellows and was running real good lap times, within a few tenths of the leaders which is great for me. I kept getting slower every lap, and the kart seemed to get sluggish on acceleration. When I pulled in the pits I realized I had slid the rear axle 1 1/2″ to the left. The kart turned fantastic to the right with the extra width on the left side. I installed axle collars to help prevent it , and the first time back on the track was last weekend, running the same MG’s. After about 30 laps the right rear was junk again, and the oversteer got worse every lap. The pic I posted was taken on the day the axle slid, that pic is in the start of the right hander where the kart actually handles really good.

    #72590

    Ambrose Buldo
    Participant

    Axle Slippage has been problematic with this Kart. I too, quickly resolved it with addition on Axle collers.

    Kart is very quick on New Tires and I guess that is to be expected not sure if wearing outside right tire down to cords in 3 days is abnormal (CCW Rotation on track). I think the only way outside rear tire can be wearing excessively is if it sliding out while loaded in right hand turns. I think the biggest culprit is the double apex box turn just before the Start/Finish line. The outside tire is on the concrete thru the whole turn and that is probably pretty abrasive. If I run allot of laps on new tires, the rear grip reduces dramaticially by the end of the day.

    It starts out with oversteer requiring correction post apex. When all the tires eventually go off, Kart goes into “Push/Kick” mode, requiring massive correction at exit of every corner.

    I will be at OVRP on Friday, I will replace the rear tires and get a baseline time, hopefully close to my best. If I do that, I will take some of the same steps on front end that you did to lighten steering. First change I’ll make is going narrower. Then taking out toe.

    #72592

    Dan Brown
    Participant

    I removed the front crossbar and it helped dramatically. That bar is solid aluminum, not tubing like the rest of the chassis. I have never seen that before. Gary Peterson gave me the front end setup ideas, he has raced an ikart in Gearup for a couple years , until he switched to Kosmic for this season.  My seat is a Ribtect XLT , I started at 26″ back and flush with bottom of frame rails. Have since moved it back to the rear holes on the mounts, and have gone up with it. Next step is to move it down, but I am afraid it will rub on the tracks bad as the waist of these frames flex a lot. Steve Gressell bought a 2016 ikart, just told me he removed all the caster , ran zero toe and it pushed bad. He then added caster one turn of the grub screws at a time until the push went away and it rotates and bites great. He did say that he had a Tillet seat and it drove the best it ever did. The seat cracked so he just switched it to the ikart carbon fiber and it lost rear grip and started the hopping in the corners, so he now needs to find a new sweet spot to run it at.

    #72593

    Dan Brown
    Participant

    Maybe I will drive down to OVRP on Friday and test with you, maybe two heads together can hit on a great setup.

     

    #72619

    FREDDY SANDOVAL
    Participant

    Depending on the track, and how aggressive it is on tires, and if it’s mostly left hander, your right side tires are gonna wear out faster.

    We have the same issue at our local club track, we call it the cheese shreader

    You may wanna try swapping your tires around every heat race, that way they all wear out evenly.

    That MG Yellow tire could be difficult to tune for, we ran the same tire at Cal State championship and we sucked big time. Some of the fastest guys were able to figure it out, and for the rest of us the kart just fell off as they got hotter, not to mention we were running a lower HP engine package, and it did not like it at all ( it became a tank )

    After we finished the main event, the tires were so sticky that when we picked up the kart off the ground it got glued down on the floor.

    P.S. You may wanna run higher PSI and see how it likes it

    Depending on air density and track conditions I used to have the same issue, and was running real low psi, I was told to try 15 or 16 and I thought the guy was crazy, but I tried it anyway, and my kart really liked it, I gess some karts like higher psi? Anyhow, just my 2 cents. Hope this helps.

    #72651

    Ambrose Buldo
    Participant

    Dan –

    Re-aligned the Kart & loaded up last night. Went back to dealer recommended front end set-up (Below) as that proved fast on fresh tires. not too different then what I had. Settled on:
    – Toe 0
    – Neg Camber 2 Deg
    – Caster – Neutral (5mm Hex)
    – 1.5 Spacers Front width
    – 3 washers (Bottom) Frt Ride Height

    Hope you can make it tomorrow. Weather is supposed to be great. I would really like to see how I fit in your Ribtect XLT Seat, as I am considering the NON T Version for installation during the winter. Just love the feel, fit, shape, comfort and durability of those seats. Had one on my Intrepid.

    My trailer is near pit out, White 16 footer with a #27 on the side. Will be ready to hit the track as soon as I can get someone to mount those new rear tires. I will be there by 10AM.

    Regards,
    Ambrose

    #72652

    Craig Drabik
    Participant

    Gary’s going to be a good resource on getting the iKart to handle.  I’d take a day to just test, and lay out a program to follow – don’t just run laps and throw things at the kart.  Start by going back to the factory setup front and rear (or ask Gary if he has a go-to setup for that kart) – make sure you check and reset caster, camber, and toe.  If you’ve got a variety of axles and hubs, go with medium axle and medium length hubs.  I’d start with the front end almost all the way out – use only a 5mm spacer on each end and set the back end nearly all the way out – 54.5″.   Take the bolts out of the 3rd bearing.

    If you can get on the scale, check to see if you’re in the ballpark front to rear.  You could adjust rear and front ride height to try to get closer.  My opinion is that if you need to change ride height to get good weight distribution you should ultimately move the seat so you can get back to stock settings on ride height, but it should work for testing purposes.

    Try to feel out your entry and exit – if it pushes, does it push all the way through the corner or just entry or exit?  It’ll help to have someone watching or following you to see if you’re getting enough or too much inside-rear lift.  If you’re doing this at Avon, I’d have them watch the left-hander before the Monza and the right-hander after it.  If you’re getting too much lift, try bolting down the third bearing and putting in the longer hubs – if it gets better you might want a harder axle.  Reverse condition and you might want a softer axle.

    Once you think you’re in the neighborhood, then go to the front end.  Heavy steering sounds to me like caster or Ackerman, but I’d go more by front end feel than heavy steering.  Get it to handle decently then you can try lightening up the steering.  Remember that pretty much anything you change in front is going to affect the back, so keep watching to make sure that you don’t re-introduce problems at the back (not enough or too much lift).  When you’re happy with front end feel, go back to the rear axle and fine tune with track width and/or hubs and 3rd bearing.

    Unless your tires are dead, you should be able to get through turn 1 at Avon flat with a good exit from the hairpin.

    For your size on the MG Yellows (guessing you come in around 415 on the scales?) I think 8.5 is too low for tire pressures.  If you’re doing 5-6 lap test runs at Avon I’d try 10-12 psi.  Check your times to see if you continue to get faster to the end of the run (pressure too low) or drop off before the end (too high).  We run these tires in the Gearup series and I usually practice on the tires I raced at the previous round.  They’ll have four sessions (about 35 laps) on them when I start practice.  They get to be pretty dead by the end of practice, and I’ll put 6-8 more sessions on them (30-60 laps).  You should get 3 club weekends out of them – but not much more.

     

    Good luck!

    #72653

    Dan Brown
    Participant

    Craig, thanks for the response. The ikart tunes so differently from all our other karts. Both of our Margays and my CRG are tight at Avon, the ikart is crazy loose. I am around 4 seconds off the pace, it is so loose. I am using Gary’s front end setup now, and it feels great on corner entrance but the apex off loose condition is always there. Front ride height on this kart is almost unadjustable, because if I drop the front end down from all the way up even 1 spacer the nose hits the track, at Avon it hits in the hairpin. In April I rented the track for a day to practice for the AKRA event, and I destroyed a brand new Buru nose when it hit the track in the hairpin after dropping the front end down 2 spacers. If I increase rear tire pressure to anything above 11 lbs hot, it is undriveable it is so loose. I usually start at 9 right, 9.5 left and then check after they are at temp and adjust. On Vega Blues I  start at 8.5 on the right. Gary and John Martin both agreed that the ikart loves rear weight, and running rear percentages around 65% seems to work the best. The chassis has an insane amount of front end grip, just point it wherever you want the front end will go there with no complaints. When I get the rear end to stick and follow along with the front I am going to love this kart. Gary was able to get his dialed in and was extremely fast, and I watched Sage Karam put on a show in one, he was untouchable he was so smooth. As far as lift at Avon, I get a great lift on entrance, but when the rear tire washes out the inside tire drops quickly. When that happens the result is usually a push/kick. I think it would be extremely hard to get the kart so tight that the front end pushed much at all. The front grip exceeds the rear grip so the usual result is the rear snapping loose. I may move the seat back  one more time, trying to get it around 65% like John recommended.

    #72654

    Dan Brown
    Participant

    Ambrose, not positive yet I am going to make it, I will let you know tonight. If I do come I have a tire machine in my trailer and a compressor so mounting new tires is no problem. It is about 3 1/2 hours from here so I will have to leave pretty early and make arrangements for my kids to get on the bus.

    #72655

    Ambrose Buldo
    Participant

    Craig – Your feedback on the MG Yellow Tire Life expantancey is appreciated. If wearing one of tires in 3 lapping days is typicially, that’s OK. For practice, I may just rotate them side to side to try to help the budget a bit. I run these tires verses the more common MOJO’s specificially for the occasionial F-Seris/GearUp Race.

    As per the video I posted above, in my view on fresh tires the ikart handles pretty well.

    Just to show the difference, see video below, same setup, different track (Englishtown NJ), but worn tires. You can see what I believe is “Push/Kick” requiring a corner exit correction at every corner. These tires were a 1/2 season old so fully understandable that kart would not handle well. It is painful to watch, it is a night and day difference between this and video I posted above.

    https://www.youtube.com/watch?v=bF-pGLDcEnw

    Just like Dan made the switch, I too would like to move to RibTect of Deepseat in the off-season.

    • This reply was modified 1 month, 4 weeks ago by  Ambrose Buldo.
    #72661

    Dan Brown
    Participant

    Ambrose, I am not going to be able to make it tomorrow. I will p.m. you my cell phone # so we can plan another day hopefully in the next week or two.

     

    #72674

    Craig Drabik
    Participant

    Ambrose, just for grins on a practice day, I’d throw a softer axle in if you have one and see what happens.  If you’re over-gripped in the back you’ll overcompensate by turning in too much or too hard, causing the back to kick out when the fronts do eventually bite.  It’s hard to tell from your camera mounting position if that’s the case in the E-town video.  That place is bumpy as hell all the way around, and that can unsettle a stiff kart as well.  Try taking caster out and see what happens.  If you’re running Rotax on Mojos those are going to have a lot less grip than the yellows.  Either way, any tire with a half season of tag on them are going to be shot and not much good for figuring out your handling issues.

    Dan – I’d recommend higher front ride height and lower rear.  Move spacers under the spindle in front, and raise the axle relative to the chassis in the back.  That’ll shift the weight balance rearward and let you test whether or not you have too much front weight.  The MGs can be a little sensitive to tire pressure but I stand by 10psi as a starting point for your weight.  They won’t suck at 10psi and should handle consistently enough for you to try to sort out your chassis.  Same advise as for Ambrose – if you’ve gone a long way towards adding rear grip with a hard axle and narrow rear track then you may be overgripped in back and overcompensating at the front, which will cause oversteer when the front tires bite.

    On practice days don’t be afraid to throw big changes at the kart – just make them one at a time, check your fastest lap but also consistency of laps, and write down your feedback.

    • This reply was modified 1 month, 4 weeks ago by  Craig Drabik.
    #72676

    Dan Brown
    Participant

    Thanks again Craig, I really appreciate the advice.

     

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