Masters [email protected], CHASSIS HANDLING ISSUE

2009 TrackMagic Shifter Prototype, Very Similar to a Praga Tacho Evo, 30/32mm chassis.

The problem I am having IMHO most likely simply a limitation of running such a stiff chassis with a 206 but I will see what your thoughts are on it. The problem I am having and clearly where I am losing time is coming off the corner but not any corner. So, if the corner is followed by a strait of any distance there is absolutely no loss in speed infact in many corners I am coming off faster then every other racer. However, if the corner is followed by a corner in the opposite direction I am losing significant time and dragging down the motor during the transitional time between right and left or left and right. The quick transfer in load seems to be having a major effect on the speed of the kart. So usually only in 1 or 2 spots on the track does this negative effect hit.

So far, I have increased Caster, widened front track, reduced rear track, cut the axle down further, moved weight to the rear (seat change) and each time the kart has gone quicker. The biggest change was for sure moving weight to the rear. I have had tire pressures from 15psi-23psi during different sessions but generally I have found tires around 16-19 depending on temp work the best for my kart on Hoosier 60B

My Theory, The 32mm cross bars are simply not allowing the load to transfer from inside wheel to outside wheel and back quickly enough to keep the motor from dragging down after all there is a reason most people don’t run shifter chassis.

I have tried as well with seat forward widening rear and that definitely made the problem much worse.

Option 1, Go to the extreme and see just how much rear weight etc… it can take

Option 2, Run my 2020 Intrepid Freedom 206 chassis…

Watching this thread.

I have a 2017 TB Kart S55, which I’m finding is/was a 2 stoke chassis (32mm chassis). Didn’t notice until I saw a newer model (2019’ish) S55 chassis, and noticed the design was changed to a more traditional 4 stroke chassis. My chassis handles extremely well, but it can be best described as “twitchy” from time to time. I have zero knowledge on chassis tuning, so I leave it alone for the most part.

We scaled my chassis at Jacksonville and it was sugguested that I add 5 lbs to the front. I have zero weight added to the rear.

Can’t you just load up the rear first, and if it doesn’t work, then go to the Intrepid?

By dragging down the motor, do you mean that coming off the corner it boggs down?

If so, this would mean that you have too much grip in the kart as you have increased front and increased rear grip (narrowing the rear width). Your inside tire is dropping and then not lifting the opposite tire quick enough. You’re scrubbing speed and the 206 will just bog.

You need to have the chassis flex faster and stacking grip is going to overpower the hard compound. I’d try and take out the front bar, remove seat struts (if any), loosen the seat hardware until it just rotates. Also a super soft axle may help and I’m guessing you’re not running the 3rd bearing

Have you tried increasing steering rate or Ackermann to see if you can get it to change directions quicker?

I’m guessing it doesn’t have adjustable wheelbase, but shortening the wheelbase would be another thing that would help it change direction.

Might be worth trying to go negative on the camber too to see if it will help it point into the corner a little quicker.

Yea, I think wheelbase is gonna be a big factor its a long wheelbase at 1040mm not adjustable. Most 206 chassis that seem to be successful are down around 1010-1020. My intrepid is 1035 so its still a pretty long wheelbase.

I have thought about changing Akerman for sure next test day I will give it a go.

I was in a Praga with a 1045 wheelbase before switching to a CKR in Briggs. Here is the full list of changes we did to make it work for the heavy #385 class

  • Max caster and Akerman
  • Nylon front bar but kept the front lower and upper hoops loose. Not 100% tight with rubber washers
  • Kept floor pan loose with rubber washers
  • Switched to a Greyhound silver seat for max flex and kept seath bolts loose enough to spin
  • No seat struts
  • Cut the third bearing race out and super soft axle (non cut)
  • 85mm rear hubs

All of this is to help the chassis flex as quickly as possible. It was a TON of problem solving but doable.

do you actually have independent evidence (stopwatch) that your slower through these sections than your competition?
Is there any throttle manipulation in these areas?

How about kart weight/drivers weight ratios. are they adding weight, are you adding weight?

how slow are the corners, does the clutch come into play?

Have you tried seat stays to force transfer?

Also, I know you said widening the front helped, but I just remembered a specific instance where I noticed one kart had an advantage in a quick change of direction corner complex.

At USAIR in Shawano, turns 7 and 8 is a quick transition from a tight right to a long left carousel, and I specifically remember getting beaten there consistently by Lemke on the Merlin MR29, which had a notably narrower front track width than my Tony Kart I was driving at the time. I’m not sure if the wheelbase was the same, but we noted in that quick change of direction, no matter what we adjusted, we would get pulled 1-2 kart lengths, getting down to the apex of the second corner.

So it might be worth a punt to go even narrower on the front. Should scrub less and it should speed up the steering action, even if you do ultimately get less overall jacking.

I wonder when people just totally ignore you. Why would someone not answer specific questions?

Sorry man, I got a full time job + race team + karting and 3 children shit gets crazy around here (My wife is a saint)

I don’t have access to his GPS data but I drove atleast 10 laps behind him and in this sector I would lose 3 karts and could make it up between the draft and being quicker in a few other corners for awhile. I would enter on his bumper, be on his bumper on the exit of the first corner and in transition fall back significantly.

So, do I have a stopwatch? No. do I know exactly where I am losing time… Absolutely.

So, on entry of the first corner to exit is a brake/pick up throttle zone.On the exit of the first corner(right) through the left hander and through the trash/bustop its flat out on the throttle no throttle manipulation and you are above clutch lockup speed the entire time.

I crossed the scale at 392 (no weight) He came across 391.5 with 15/20lbs of lead on the rear of the seat. I am not sure entirely where his weight is located or how much but from photos that looks to be close to accurate. I pretty much just pay attention to what I am doing and what works for me.

Also, I am geared a 1/2 tooth more then he was during the race which in this section should have been a small advantage. He was 3.88 or 3.81 on Ratio and I was 3.89 in the Final, I was 3.95 in Pre-Final

This is Matt’s video from the same day but at 2:16 Matt’s cart is placed exactly where I start to lose time through 2:22 his position. (Note Matt ad a bad exit on 3) You can see me go through at 6:05 or so but Matt is pretty far back at that point. You can probably figure out from watching video I don’t have the best motor but I am working on that…

Nice video, I watched the whole thing. Looks to me like you’re down on power everywhere. Frustrating I know. Gearing is not going to help. Sorry. I’m including a gearing chart just for reference. 3.81 – 3.88 is one tooth on the axle.

What fuel? What oil & how much? What are the rules regarding jetting, plug heat range and fuel.

You know there are good motors and bad motors, and when you can’t do anything to the engine, you’re kind of stuck unless you can afford a new engine, or 2 or 3 or 4.

Spec Fuel, 90oct Sunoco non-ethanol tested on Meter +/- 5 with Subject to Water or 3 part test if tech decides as well as ability to test for 4:1 at club and can be subject to further lab testing at tech Discression.

Oil is a little more open because of the Briggs rule-set, Subject to Burn Test/Sniffer but really no further lab testing because its non-spec. (I think it should be a spec oil myself) I run Redline or Comet 13-14oz depending on track layout

Jetting on a 206 is non-adjustable but in reality spec is .0365 (Must go) .039 (No go) So you end up with about 3 Jet sizes Less then 37/37-38/less then 39. I change jets depending on the air but I was running a 37 on this particular day. There are also many other such adjustments in the Carb.

In the end, you hit the nail on the head, in the sealed 206 if you have the motor tuned in and everything optimized you still end up with motors that are simply stronger then the normal which is really the case here. Matt has a great motor, Mine ATM are mid-pack motors (I have 3) but I know where a lot of the problems are at with the motors so I am going to have to fix those issues. Unfortunately Briggs is on eternal back order with parts/motors right now so I cannot fix the issues I have without at least tearing down 2 motors and building 1 good motor. My problem on 1 motor is absolutely the intake valve which seems to have the production tolerance worse then any Chinese predator motor I have ever seen. I bet its down [email protected] on the flowbench its that bad. I suspect similar poor production tolerances on the other 2 engines but the exact issue for each motor has not been identified.

In the end, most people have been running 206 for many years. This is my first full year in 206 having about 8 races under my belt so I will get my motors sorted and the chassis sorted.

).036 – .037 = over 5% difference in area (flow). A .011 – .060 pin set can be purchased on eBay for chep. Give you a little better pictture of what your putting in the car.

Air density is important when it comes to tuning. 1% change in air density calls for a 1% change in fuel flow. Longacre sells air density gauges.

On the intake valve, what tolerance are you referring to? The valve head size?

The Tolerance in production on my valve is in reference to bad lip prior to the 45, basically this is done when the electric upsetting/forging process happens. I have not looked into detail on how exactly it was formed but some point in the forging process the valve wasn’t very uniform.

Basically, the valve head has a giant ski ramp prior to the 45 cut making airflow around the valve practically impossible.