Home Forums Chassis & Handling Getting the inside rear tire to lift

This topic contains 13 replies, has 5 voices, and was last updated by  TJ Koyen 3 years, 3 months ago.

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  • #47852

    Samir Shah
    Participant

    I am trying to figure out how to get my kid’s kart (old Brazilian Birel R31) to lift it’s inside rear wheel. Tried all kinds of changes, some made him faster, others slower, but I still cannot get the inside rear to left, while the inside front does lift quite often when he is pushing it. Very often, he will have the front tires pointed outwards while going through a turn too, suggesting too early an entry, or a pushing kart.

    But, the bottom line is that the inside rear will not lift (much).

    My latest change has been to remove the rear torsion bar, as well as the rear bumper bar, and to loosen the rear bumper itself. Turn in got better, but still no lifted rear wheel.

    Considering installing the front torsion bar next.

    Would appreciate any guidelines. Thanks, Samir.

     

  • #47857

    Patrick Roth
    Participant

    What do you mean tires “pounted outwards”? I interpret this as I’m going through a left hand corner and I have to turn the wheel to the right. I can only think of this happening when the rear is sliding and I’m countersteering (not a pushing condition). As long as it’s not driver induced, having the rear sliding too much leads me to reduce or slow the rate of lift.

    For the sake of answering how to increase lift you can increase the front width and increase caster. A front torsion bar should help as well but wouldn’t be my first choice.

    Are you expecting to see daylight between the tire and the surface?

  • #47861

    Samir Shah
    Participant

    Hi Patrick. You are correct, I meant he was driving it hard and countersteering. I think the rear is sliding instead of gripping and lifting the other wheel.

    We did have the front wider, and narrowed it, while increasing the rear by 10mm, and he likes it better wih the front narrowed.  We tried increasing castor (to max), but he only got slower – did not like it, prefers neutral caster.

    The other kids literally get their topkarts’ inside wheel to life 4-6 inches off the ground (they have 50mm axles, I have a 40mm).

    Should I see daylight?

    I was going to try:

    – widen front by 5mm each side

    – add front torsion bar

    – try caster at 7.5pm/4.5pm (instead pf 6pm when facing front).

    Would bigger rear hubs help by effectively stiffening the axle?

    Thanks.

  • #47864

    TJ Koyen
    Moderator

    Samir,

    Everything you’ve listed will increase lift, so you’re on the right path of thinking.

    The goal of course is to get enough lift to unload the kart and keep it from binding, but not too much that you start overloading the outside tire and the kart starts sliding or hopping.

    The stopwatch is the ultimate test to see if your changes are working.

    If the kart isn’t lifting but your driver is managing to get it to slide, it might be his driving more than setup. I’m guessing he likes the front narrower because it causes the kart to slide less. If he slows his hands down a bit, he might like the front wider. It might take a slightly different driving style to adapt to a lot of these changes.

    I would try your changes you’ve listed, and also try narrowing the rear track width. If you can’t get the kart to lift with all those changes, your chassis might be tired and may have lost it’s “spring” or your seat placement is incorrect.

    Driver/Coach/Wrench : Innovative Performance/Exprit
    Owner : Oktane Visual - www.oktanevisual.com
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  • #47868

    Samir Shah
    Participant

    Thanks TJ.

    What about going from 17mm to 25mm stub axles. That should increase front grip too. Will it help with rotation?

    Seat placement – I installed it so he can see properly and reach the pedals, with no other science involved. We scaled it at 43/57. I also welded tabs all over the place so I can put weights anywhere to get it corner balanced. As it turns out, he only needs about 10 lbs of weights, so only have 1 7 lb weight on the back of the seat, and use the fuel for the rest.

    Any docs out there on how to install the seat?

    Thanks, Samir.

     

  • #47876

    TJ Koyen
    Moderator

    The 25mm front spindles will give a little more positive front feel, but it isn’t a big change.

    Seat placement is different from manufacturer to manufacturer. Most have a seat placement chart of some kind. It’s based on your driver’s size and aims for somewhere from 41-44% front end weight bias usually, so if you’re in that range, you’re probably good.

    Driver/Coach/Wrench : Innovative Performance/Exprit
    Owner : Oktane Visual - www.oktanevisual.com
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  • #48157

    Troy Berry
    Participant

    One way to see how much lift you will get is to have your driver turn the wheels all the way to one side while sitting in the kart on level ground.  Now grab the inside rear wheel with your hand and give it a lift. Turn the wheel the opposite direction and check the other side to see if it lifts evenly. You can feel how much pressure it takes to lift the wheel. Now go to the outside tire and try to lift it. You can’t. This will give you a basic understanding of how much the front adjustments will influence the inside rear wheel  lift during jacking.

    "The Art is in the details"
    BirelArt AM29 LO206
    Intrepid Cruiser KA 100

  • #48164

    Samir Shah
    Participant

    Thanks. That’s a great tip. Samir.

  • #48832

    Samir Shah
    Participant

    So, we switched from a Birel R31, which is a stiff chassis, to an iKart, which is very soft (28mm) and can twist a lot. He is still sawing and over steering in the turns. I’ve come to the conclusion that the problem is in his driving style, and he needs to slow down entry into turns, turn the wheel less, and get a LOT smoother.  Rather than adapt the chassis to his style (he is faster with a stiffer rear, but this likely means an overall slower kart), I am going to work on getting him to change his driving style to get faster with a faster/softer kart.

     

    Samir

  • #48865

    TJ Koyen
    Moderator

    You’re right, the iKart flexes a ton and you’ll need him to slow his hands and feet down with it. I’m sure he’s used to tossing around that old Birel.

    Here’s a pretty gnarly photo of me behind Mike Giessen in his iKart a couple years ago. They lift like crazy.

    Driver/Coach/Wrench : Innovative Performance/Exprit
    Owner : Oktane Visual - www.oktanevisual.com
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  • #48950

    Greg Wright
    Participant

    Hey TJ, I have a pretty decent handle on making a chassis work, basicly it’s about unloading the inside rear and how long or short of a time that  it stays unloaded.

    However after looking at the picture of Giessen you posted and Samir’s description of inside rears lifting 6″ I have to wonder if there is any advantage to the radical lift that we are hearing (and seeing) in this discussion.

    Greg Wright
    Rapid Racing Inc.
    Vintage B-Stock Pilot
    "When in doubt Gas it, It won't help but it ends the suspense."

  • #48955

    TJ Koyen
    Moderator

    Greg,

    In my experience, an inch or two of lift is ideal for most corners, but it depends on how tight the corner is, what tires, what weight, etc. With the huge lift, for me it has always really thrown the kart to the outside and overloaded the outside tires. Lots of factors to affect it though. Driving style obviously plays a huge role in it as well.

    Personally, if the kart is able to take all that lift and not start hopping or sliding, then it doesn’t matter how high off the ground the inside rear is, as long as it’s up.

    Driver/Coach/Wrench : Innovative Performance/Exprit
    Owner : Oktane Visual - www.oktanevisual.com
    www.facebook.com/oktanevisual
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  • #49457

    Samir Shah
    Participant

    Question about mounting weights on the seat for a Junior driver – should I mount the weights high on the back of the seat for increased jacking effect from leaning? Or low on the back or under the seat to keep the CG low and plant the kart? (The seat is already a little higher than an adult seat, to allow for visibility above the nose fairing.)
    Thanks, Samir

  • #49463

    TJ Koyen
    Moderator

    Start mounting at the top of the seat and work your way down.

    Mount them low and you’ll struggle to get the kart to lift.

    Driver/Coach/Wrench : Innovative Performance/Exprit
    Owner : Oktane Visual - www.oktanevisual.com
    www.facebook.com/oktanevisual
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