Now that I have a chassis that responds to changes (Praga Dragon Evo 30mm), I spent some time yesterday playing with settings to figure out what differences they made. Started out neutral, added some caster, and the kart started working, but it always felt like I wasn’t able to slow my hands down enough to be stable. End of the day I pulled the front bar. Suddenly all of my oversteer went away, and I got a lot less busy driving. The track was fairly green, covered in goose droppings, and the air temps were below 60°F. I planned ahead for some review videos so I got a before and after which I feel shows what I was experiencing.
Do you think that the front torsion bar was causing oversteer at first because it was too stiff in the front during turn-in?
That’s exactly what I’m thinking. The first couple sessions on these tires (LeCont Whites) I definitely wasn’t jacking at all, and the caster helped with that.
The busyness has been there the whole time, on two tracks and two different tires. I was able to run Evinco Reds two weeks ago before I put the LeConts on at the same track neutral caster but the kart felt the same as far as I guess turning in too quick and constantly having to catch it.
At the end of the day, the kart felt like it was easy to drive and keep a good flow, and the overheating all 4 tires showed went away.
The Evincos I was on the time prior also never showed any signs of overheating even after they suddenly fell off time wise.
It’s good that you were able to get out and test these things. Did you notice any difference in lap time? Sometimes what may feel better or easier might in fact be slower on the stop watch. It was tough to get a good view of what was happening due to the camera angle you used.
Lap time wise I was only a couple tenths off of my fastest time of the day, but I was also a lot more consistent as it felt easier to keep that pace.
I put three cameras on the kart: one on the radiator facing forward, the view at the spindle (I was thinking that watching my hands would be the most important feedback for me) and I put one on the radiator facing down at the tire to confirm what I was feeling was happening.
I suppose I should also point out that I pulled the bar near the end of my day and I was starting to get quite tired around that point, so my times going back up said a lot to me in how much easier the kart was to drive.
Hey guys, I am trying to make sense of the OTK torsion bar range on paper.
The marketing material is vague but the general talk in this thread and elsewhere is that the range of bars are something like this, from softest to stiffest when bending vertically:
- flat bar placed flat (1mm wall thickness)
- round bar 1 (chrome bar 30x1mm)
- round bar 2 (silver bar 30x1.5mm)
- flat bar 45 degrees
- round bar 3 (gold bar 30x2mm)
- flat bar straight up.
The above would suit me as I want to try the gold bar – but without buying one, and if the flat bar vertically is similar than that saves a few bucks.
BUT I don’t understand how this order is possible, assuming the materials for all 4 bars is the same and only the shape and wall thickness varies, wouldn’t the range be more like this (similar to Andy K’s view):
- flat bar placed flat (1mm wall thickness)
- flat bar 45 degrees
- flat bar straight up
- round bar 1 (chrome bar 30x1mm)
- round bar 2 (silver bar 30x1.5mm)
- round bar 3 (gold bar 30x2mm)
For the engineers out there, the logic behind this ranking is based on the cross-section area moment of inertia.
I didn’t mean to go full nerd and of course I would try it on track myself if I had both options, but after checking the numbers, the gold bar works out to be quite a lot stiffer than the upright flat bar (about 3x).
I must be missing something eg are the round bars made from different materials?
The rigidity of the flat bar being…flat has more effect on stiffness vs the fact that it’s only 1mm wall thickness. I too was skeptical but ended up buying all the bars and spending one day testing everything out at my local track and this order is correct as increasing stiffness goes.
- flat bar placed flat (1mm wall thickness)
- round bar 1 (chrome bar 30x1mm)
- round bar 2 (silver bar 30x1.5mm)
- flat bar 45 degrees
- round bar 3 (gold bar 30x2mm)
- flat bar straight up.
It’s almost alarming how much of a change the bars really make on the way the kart drives. I tuned almost exclusively with front bar last year vs anything else. What’s also funny is that I settled on the silver bar as being my default for most tight tracks and thought it was best all around but when we went back to fast flowing tracks I realized it was too much and went back to chrome as my favorite. That said chrome vs. flat bar flat isn’t THAT much different and silver vs. flat @ 45 degrees is also pretty close so you could just play around with angles on the flat bar and simulate all the different round bar situations. The draw back is it’s hard to know if you’re at the exact same angle as you were last time on that bar. Round bars are no brainers and no fear of deviation from last time you set the “angle” of the flat bar.
I never found a situation where I liked the gold and or the flat bar straight up…way too stiff for my '21 chassis, it was a very popular bar at GoPro for guys on older OTK karts and I personally ran it there on my '18 and liked it.
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One way this could be accomplished with some amount of repeatability would be to use one of those digital angle finders that you could zero off the flat part of the chassis and use it as a reference to set a specific angle.
In my last race where the track was very grippy i tried to put the bar at all in my tony and tve steering felt more precise und the rear was sliding less than with the bar. It first felt quite easy to steer but at the end of the race my arms felt much heavier. The second race i put the flat bar horizontally in to see the direct comparison. Well i felt that the kart was sliding bit more and it felt like the steering is also bit easier, especially at the end i felt less exhausted tjan without the bar. But the time was bit slower but it could be because of the tires.
I was using the mojo d5 and they are quite inique i think. Its pretty easy to slide them compared to the other tyres i drve
I know OTK don’t use them but does anybody know where a nylon bar would sit in the above rigidity list?
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One of these years I’ll make my fortune selling a six-pack of torsion bars made from different kinds of wood.
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Variable torsion bar anyone?
Softest. (20 char……….)
Hi Andy,
So just trying to put all this together. Correct me if I am wrong, but you are saying you can achieve similar results to the 3 round bars with the flat bar at different angles, yes? Secondly, you found that on tight/twisty tracks flat bar at 45 degrees yielded the most favorable results and the flat bar horizontal on flowing/open tracks yielded more favorable results? Lastly, giving the change in OTK chassis from '18 to '21 you did not find a situation where the flat bar vertical had any improvement at GoPro. For those who have not raced GoPro, would you consider it a Tight track or a Flowiing track? As for your progression, it would seem that the stiffer you make the front end with the torsion bar, the better the kart handles tighter/twisty tracks. Fundamentally this leads me to believe that by taking the flex out of the front of the chassis you are essentially relying on the mechanical lift of the inside rear from the steering geometry as compared to the horizontal load created by G forces to lift and hold the inside rear up when you allow more flex in the front end. Would you say this is true? On a follow up thought, how would you suggest changing front torsion bar as track conditions change? For example, would you want a stiff bar for a green track and soft bar for a gripped up track?
Pretty much spot-on, but I would stay away from hard and fast rules about these things. You cannot just look at a track and say “it’s tight, we have to run this bar” or “it’s flowing we have to run this bar”. You always have to tune the kart on the fly for the current situation. For example in my torsion bar test a couple years ago, I found the vertical bar to be far too stiff even at a twisty track like Dousman. It still was better with the bar flat.
Stiffer bar = faster lift, faster set down. You’re stiffening the whole spring of the chassis.
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I completely agree that there is no one silver bullet setup, however this could be a starting point. Every track is different and every track will change from day to day or even session to session. I just wanted a general consensus about direction of changes to make for desired effects. Like so many things in the sport, one could spend a lifetime figuring out what to change and when.
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Hey Andy,
That sounds good for me and for anybody else trying to decide whether to drop cash on the round bars & clamps or instead on other things like after race drinks. And simply use the basic flat bar “variable bar” in different positions, with a few angled positions marked out on the clamps.
I think this is a bit like the axle conversation - we know they make a difference, but how can something with the same dimensions, made from materials with nearly identical mech properties, can be so different?
This is why I ask the question:
- The 30x15mm flat chrome bar has a moment of inertia of 5900mm4 in the vertical direction.
- The 30mm round chrome bar has a moment of inertia of 9600mm4. Which suggests it’s quite a lot stiffer than the flat bar vertically.
Both have a 1mm wall, and both look like they are made from the same material. What’s going on here? When put on a chart you can see a nice even spread between the bars, but in a different sequence.
Yes - at the end of the day the theory doesn’t matter if you can get the handling results you are looking for. It’s just a bit strange looking on paper.
Trust me, trying to analyze it on paper confused the heck out of me too which is honestly the reason I only run the flat bar when I run it flat, the rest of the time the round bars just make knowing what the adjustment is and the result of the adjustment easier for me than moving the bar and not really knowing where it falls in relation to the round bars.
For us, it’s more about how the kart drives off the corners than it is corner entry. Might be due to our driving style or track specific or??? but like TJ said, the stiffer the bar the sooner the rear springs back down and it almost binds the kart on exit which most would love to avoid but seems to suit our situation when we need it for traction off the corner. We’ve played with caster vs. bars and it’s somewhat the same theory but the off-corner feel is different to me.
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Exactly. The bar changes the whole “spring rate” of the chassis. The caster doesn’t change the “spring rate” of the frame but changes how far the “spring” is pulled, if that comparison makes sense.
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