Evaluating Chassis "straightness"

gettingstarted

(Andy Kutscher) #1

I’m actively looking for a replacement chassis for myself…actually sulking because I procrastinated on one that I should have bought and my hesitation meant that someone else nabbed a really good deal.

Anyhow, You generally see advertisements of “Straight and no issues”…but short of actually putting it on a table how can someone quickly evaluate if a chassis has been bent and needs work on a table or not? Having raced enough by now I realize that contact is much more common than I figured it to be but what I don’t know is how much contact it takes to tweak a chassis.

One of my friends who raced SKUSA said that sometimes even out of the box new karts weren’t 100% straight and that they would have them straightened at minimum mid season if they even kept a chassis around that long.

So how does the average joe, looking at something advertised as “Straight” actually confirm this?

Thanks,
Andy


(Christopher Ramnauth) #2

Looking at it visually I’m afraid there is no 100% sure way to tell. You can get a fair idea if you walk with your sniper laser aligner though. The V2 model can give you this but if you have access to the much more expensive V4 then that can tell you much more definitively as its designed to do just that…check chassis squareness.

I know most people don’t own the v4 though so I’ll go through a little procedure for getting a rough idea with the more common v2.

Basically you’re gonna do a proper alignment. Check the steering sweep first and foremost and ensure it is even left to right, then find true centre and set the wheel there. Next set both tie rods toe in/out to something easy to see…say one box toe out per side. Recheck the steering sweep. If it remains spot on it’s a good sign the chassis is straight.

Next set both the eccentric pills in the same physical position. Meaning, ensure that the pill on the right is set physically to the same position as the one on the left. Now look at the sniper. If the front end is 100% straight then the camber on either side should be spot on if not very very close.

Lastly you can check the caster with a metal ruler and a magnet. Set the ruler to stand vertically in the middle of the kart all the way to the front on the floor board. Sort of directly under the nasau panel. Next slowly turn the wheel left and right and take note of where the sniper cuts the ruler each side. If the chassis is straight on the front end then it will cut the same spot.

The last thing to look at is the amount of exposed threads on the tie rods adjacent to either rose joint. If the chassis is 100% straight after you’ve done all the above, the amount of threads exposes should be identical (once the tie rods or rose joints are themselves straight).

Once complete you can be fairly certain the front end at least of the kart is pretty straight. Without the v4 the last thing you can do to get a fair idea of the back with respect to the already confirmed front is to set the wheel back in the true centre position and then take a straight bar (must be 100% true) and put it on top the snipers. So the bar must be long enough to go the front width so it sits on top the snipers. Now go to the rear of the kart from a distance. Look at the gap made between the bottom of the bar and the top of your rear axle. This is just a rough eyeball test mind you. The gap should be parralel if the rear is straight with reference to the front.

Hope this helps you out.

Chris.


(TJ Koyen) #3

A quick-and-dirty way to determine if a chassis is roughly straight (or close enough that you won’t be able to tell or that it can be easily bent back), is to put the kart on the ground, give it full steering lock to the left, and look at how much the inside rear wheel comes off the ground. Then do the same with full steering lock to the right, and compare how much it’s unloading the inside rear on both sides. Also, when you set the kart on the ground, place the rear down first so both rear wheels are touching the ground, and then straighten the steering wheel the best you can and slowly lower the front, watching to see if both wheels contact at the same time.

If the inside rear doesn’t immediately pop up at full-lock, that’s not necessarily a worry. Some kart brands are springier than others. But you can go back and lift the inside rear wheel with your hand on either side and kind of get a feel for how unloaded it is.

This is usually a good evaluation if a chassis is close and it’s how we check it when we are in a hurry.


(James McMahon) #4

Some tips here on inspecting a used chassis:

You can also run a piece of string from the kingpin to the axle along each side and diagonally to gauge the dimensions. Of course the latter can be challenging if the seat is in place.

Both sides should be the same length.
On the diagonal measurement the distance to the point where the two strings meet should be the same distance on both strings.

I’ve found the “placing on the ground” method can be unreliable unless you’re very particular about it…

For the “ground test” to give an accurate representation, some conditions to be met:

  • Ground must be VERY even. (Most ground that looks even is far from it)
  • Ensure tire circumferences are equal on both sides. (Getting the circumferences equal might require some tweaking with tire pressures outside of normal racing ranges)
  • Tires should of course be clean and devoid of “clag”.
  • Caster, camber and ride height on both sides on the front should be the same.

(James McMahon) #5

I would not judge by the number of threads on heim/rose joint as this varies greatly with track rod length and steering column offset.


(Andy Kutscher) #6

Let me ask a follow up question here if I could please.

Does bending and straightening a chassis make it weaker and more likely to have issues down the road?

I’m looking at two OTK chassis currently. One is a 2016 that I know was in a crash in 2017 and needed to be straightened. It was then straightened again this year prior to sale just to insure it was straight for the sale. It has been raced for a full season in 2016 and 2017 and then half a season in 2018.

The second is a 2018 with 3 races on it that’s never been crashed. it’s $800 more and comes with less spares / extras but it’s never been crashed and is pretty fresh.

My brother and I are both looking…I’m leaning towards the 2018 for myself but are there reasons to be weary of the 2016 because of the time on it and knowing it’s been straightened on multiple occasions?


(Eric Gunderson) #7

The basic answer about chassis staying true after straightening is “it depends.”

I know. Not the most helpful. But different chassis bend at different rates. Modern tonykart are known to sag a bit in the middle over time.

While $800 is something to chew on, a 1.5-2 season old chassis isn’t necessarily promising, especially if it’s been crashed…

Locally, I’ve had a client that has a Kosmic Mercury. Great guy, solid driver. However, you can just see the front end is bowed. We put it on the table, and it’s way off. No matter what I try, no matter what he tries, we can’t overcome that chassis. It’s just too bent.

From your description, it doesn’t sound like the older chassis is a terrible buy. However, the runtime is what concerns me. Chassis do wear out, eventually they just aren’t quite as fast.


(TJ Koyen) #8

To make your decision harder, I will offer a competing anecdote to Eric’s and just say that I saw a teammate run best lap in the TaG Sr. heat at SuperNats a few years ago (beat a certain Charles Leclerc) on a 2 season old Kosmic. Also Ashley Rogero often ran multiple season-old stuff when she was on OTK and did more than fine.

Obviously, obviously, obviously these are just a couple cases and no in way a representation of all used chassis. But just because something is a couple seasons old doesn’t mean it still can’t be fast and usable.

Karts that have been bent tend to spring back a little bit after running them again, so it’s just good to keep an eye on it. The frame might need to be tweaked back a couple times to ‘set’ it again.

For the average Joe, I would save the $800 and spend that money on other things like spares or axles to tune with. BUT if the peace of mind of having a definitely straight chassis is worth $800 to you, that’s your call.


(Andy Kutscher) #9

Went with the 2018 with only 3 race weekends on it. Was spotless in person, had frame protectors on it and very little wear on the underside of the chassis.

What I didn’t get was paperwork / setup guide for the kart. I keep reading all the time that you don’t need to stray much from the standard setup on the OTK karts but I’m now searching for what that standard setup is. If there’s an online setup guide that I’m just not finding a link to that would be great. Seat fitting will be first but I’m pretty sure the seat charts are floating around here somewhere and pretty easy to find.


(TJ Koyen) #10

• 1390mm rear track width
• Medium rear hubs
• N axle
• 1 big spacer inside front hubs
• Front blade bar in flat position
• 3rd axle bearing loose
• Neutral caster/camber
• 1 chrome seat strut on each side
• Front/rear ride height in middle position

I can’t find my seat chart right now but I posted it here a couple times in the past.

Plop an engine on and go out and have fun!


(Alan Domme) #11


This may be useful if you haven’t found it already.


(Noah Koenig) #12

Interesting article… I have never seen this one. I wonder how old it is as it suggests that the N axle is better in high grip conditions than the H axle which is better in my opinion. These seat numbers are close enough.
62.0-62.5 and 200mm from the axle and level with the bottom of the rail should do it.


(Andy Kutscher) #13

Great stuff. I did find that after a little searching.

They are very specific on driver height when it comes to placement front to back but when talking about height of the seat it’s a little more general. At 5’9” I don’t consider myself tall but I’m guessing this is still aimed at younger drivers too.

So at 5’9” mount it level with the bottom of the rail or different?

I’m also assuming I’m considerably heavier than most drivers (intent to be 200 by the time I run this next season). Will that throw bias to the rear and I need to be prepared to move it some forward to get back to 47/53?


(TJ Koyen) #14

I’m 5’7" and I run it even with the bottom of the rails. I would start 5-10mm below the rails at your height and weight.

At your weight it’s tough to predict what the distribution will come out to. You might need to move the seat a bit to get the weight in the right spot, but we’ve got guys at 190 running with the seat right where the chart recommends with no issues.

47/53 is too high on front-rear bias. We aim for 42-ish on the front, but the seat chart is designed to keep you in the right range so the bias is correct as well. Put it where it recommends first, and then when you get a chance to scale it, you can adjust from there if you feel there’s a handling issue coming from it.


(Andy Kutscher) #15

Can’t thank you guys enough for the help. I hope to be able to repay the favor one day