How long does a chassis last? And how to know when to replace it?


(Steve Wright) #1

I have a Merlin MR29 chassis that was fast and responsive till the middle of July 2017, then it started slowing down?

How do you know when to give up on a chassis and move on to a new one? What’s the theory on stress cracking of the tubing and welds and/ flexing of the chassis?

Do chassis get flexed out? Is there a way to de-stress the chassis? What about other components? Spindles? Axles? Wheels? What do the best drivers do?

I think many people have heard stories of companies using a chassis for a single race and throwing it away. Anyone got real experience with this? I have read articles about motorcycle teams de-stressing their chassis through different techniques, but these were aluminum frames used in motorcycle road racing, anyone got info on what you could do with a kart chassis?


(TJ Koyen) #2

I have no issue running a chassis for 1-2 seasons. But if possible, I try to re-frame every year so that I’m on at least a new frame at the beginning of the year.

I know drivers who have won really big races on karts that were over 2 years old.


(Aaron Hachmeister) #3

Bad example, but my Kosmic frame is a 2012, we’re retiring it this year. It ran the full season for us, which is all we were looking from it.

In general, I’d say at the club, most frames under 5 years old will do. Regionally, you’d probably want a two year old frame or newer. And nationally, well, anything goes. There’s an OTK driver that worked with me for part of the season who gets a new frame every 3 race weekends, others go like TJ with a new frame every year.


(James McMahon) #4

I think the first thing to consider is how we measure the time… Some folks cover more laps in a weekend than others in a season. Some drivers and tracks are brutal on frames.

What have you checked so far? Have you had it re-scaled and or put on a flat table?
Checked all the mechanical components, seat struts etc etc.
Are there other variables, tires for example.
Have you been able to review and compare data pre and post July?

Well they can definitely crack, but they are usually very easy to see once they do.

There’s some debate on this, given that we don’t even measure spring rate, damping or anything else when they are new.

They can deform of course. Left rail sag is definitely a real thing

They drive whatever they have. Sometimes its new, sometimes it’s two seasons (16 or more tough races) old. Yes some teams and drivers get rid of chassis after one race, but that doesn’t make it necessary. It’s more of a business thing than anything else. Generally those chassis are being leased so the next person is expecting a new chassis. It’s easier to just move the old one on rather than hang onto the inventory…

Of course that perpetuates the perception that “the top guys always throw out chassis after a race”, but when you ask around, it’s not true.

I’ve heard about de-stressing after the chassis has been welded, but not much about after some racing.

In short, before you pony up money for a new (or newer) chassis, get the one you have on a flat table first and check things over. Make sure kingpins arent bent, axle in sideways (it happens) etc etc.


(Aaron Hachmeister) #5

I’ll second James on the putting it on a table first. Frames get bent, it happens a lot. Take the engine off, clean the chassis, and inspect it for cracks. Then you can take it to Franklin and have Jamie check it on a table. He does a good job with that and will make sure everything is square (or hunkydory as James says).

I threw mine on a table probably 4 times this year, just to be safe. I think it’s a good habit to get into to make sure you don’t have any extra surprises while at the track.


(Steve Wright) #6

This chassis has been on the table three times this year. Once in February before the season started, and twice at the Route 66 round at Autobahn. It was really good before Autobahn! Then if fell off, I’m going to strip the chassis and look for problems.

Whats the thought on other components? Anything else to worry about? Spindles? Wheels? Axles? I check the axles for run out, does anyone worry about changing spring rates after hard use?


(Eric Gunderson) #7

One area to check for sure is stressed items beyond just the tubing or traditional frame area.

While not super common, a lot of chassis will break or fatigue around weld areas. In particular, areas associated with the seat are the first to go–seat mounting brackets, either front or rear. Once these have fractured, it’s hard to get the chassis performing at it’s best again, although with a good welding job it can be close for a while. Another area to examine closely is the axle assembly hangers. Of course, the bearings themselves wear out, but I have seen the actual welded-on mounting points/structure for mounting bearings to the frame fatigue and fail. Again, not super common, but it can happen with time.

While I haven’t witnessed it in person (just not enough chassis I have thrown on the table), I have heard stories of frames ‘sagging’ over time in the waist area. Mind you, these stories were mostly from dealers, so hard to say for sure. But, with the movement to softer frames in recent years, it wouldn’t surprise me much.

The area that you are primarily concerned with (and rightly so) is the spring performance of the chassis. From what I’ve seen (others seem to be confirming it), different chassis with different amounts of uses will fade at different times. Regardless of when it happens or how quickly, the consensus does seem to be that it is a very real issue, and actually does indeed happen.


(Steve Pribyl) #8

We have a 2005 american chassis that started to break last season, welded it a couple of times, this year it cracked some more and welded it some more. The last race the front porch show some cracks. This chassis has carried 3 drivers to many championships, I think it’s time for it to rest easy.


(James McMahon) #9

(Don Westlie) #10

@spwright83 I’m assuming we can rule tires out since you race 66 and put fresh rubber on. We had a problem previously where I couldn’t make out what was causing an issue. Turned out we had a slightly bent spindle and was throwing handling out of wack.

Our chassis just got through it’s second season and we are going to retire it. Found 2 cracks on the Ionic at New Castle. One where the motor mount is welded to frame rail and another oddly, along the bend in the cassette hanger. Had never seen that. I’m thinking they are related due to the different stresses. First motor then hanger. Welded it up and ran really good. Son qualified 8 of 35.

If you can find the problem and its a crack, it doesn’t always mean she’s done. Doesn’t mean you should keep her either :wink: Sometimes spending the coin on a bare chassis, knowing you are good is worth it.

Clean it up, look it over really well and see what you can find.


(Davin Roberts Sturdivant) #11

Actually, I’ve heard that some chassis also sag a bit in a the middle, like the softer chassis like the OTK. Like you though, I’ve heard that from dealers.


(James McMahon) #12

I’ve seen this sag in a lot of different brands. Sometimes it’s right behind the center crossbar (between seat and tank), or you’ll have the left rail sag, especially on single left rail karts. Of course, it could be from miles, heavy kerbage or massive air time…


(TJ Koyen) #13

I’ve heard engineering and metallurgist type people say that kart frames don’t sag after use.

However, I’ve seen karts that literally almost drag on the ground in the waist after a few seasons.


(Eric Gunderson) #14

Yeah, this topic is somewhat controversial. But from what I have seen on the table (as well as have been told), some chassis can sag. Although I’ve heard the sentiment that it is less about the center of the chassis ‘sagging,’ and more about the spindle yolks and rear bearing casettes ‘raising up’ relative to the rest of the chassis. To me, this makes a little more sense, as in most crashes if the front end/waist gets bent it is usually an upward bend, rather than downward…


(James McMahon) #15

That makes sense too with how much load there is on the C tabs. Heavy kerbage and other track excursions could cause that I would imagine. Just like taking a hammer to them.

Found this article (and video) today about “freshening” a chassis…


(Aaron Hachmeister) #16

One other thing that I think factors into chassis life is how big the driver is. Frames wear and crack a little but faster with more lead on the seat, as that weight doesn’t move around like a driver would. That’s something to think about as once a frame starts cracking that’s usually a bad sign.


(Eric Gunderson) #17

It’s not just a little. It’s a LOT. Look at any chassis used by a lighter Junior driver or Masters driver, and those chassis pretty quickly begin to show signs of wear and tear. Tons of weight on the seat or a really tall driver is hard on a chassis, regardless of design, make, or class.


(James McMahon) #18

Surely that’s just hard on the seat at the points that the ballast is mounted, rather than the chassis and/or seat brackets. The chassis is (more or less) going to have the same load from everything but the driver’s legs to meet whatever the minimum weight is?


(Eric Gunderson) #19

From what we’ve seen (at least locally), the chassis with small drivers in say Rotax Jr. have had a higher frequency of seat tabs breaking than their older counterparts. Same is true for the really tall Junior drivers. You can watch the karts through the corners, and it just looks…ugly.


(Aaron Hachmeister) #20

Well I fill both of those requirements, so I wouldn’t be surprised if I start going through frames quicker than usual.

@KartingIsLife the thing about mounting weights is that the driver moves around, even if it’s a little bit. A way we looked at it that a support arm will wear quicker if 100lbs are constantly on it as opposed to varying forces up to 100lbs. I’ll try to pay attention to wear with other drivers, mostly heavier than me, on the same chassis as me for the next couple years to see the differences.