Why does a chassis wear out?

[Rodney Ebersole]

Ok, I am seeing a little light, Please excuse my rate quote.

[Larry Hayashigawa]

The spring rate of a chassis can be measured in many ways. A simplistic approach to measuring spring rate is to clamp the front axle of the chassis and one rear wheel of the kart to a bolted down table, with the other rear wheel hanging of the table. If a 100 lbs weight were suspended on the free rear wheel, the chassis would deflect, let's say in this case 1 inch. The rate would then be 100 lbs/inch. A stiffer chassis would have a higher rate because it would take a greater weight to deflect the chassis the same 1 inch. The factors that determine rate are geometry and material characteristics. Geometry is tubing size, chassis configuration, axles, tires, anything that can be measured by a ruler or by a pair of micrometers. The other major factor that could change the spring rate of a chassis is the Modulus of Elasticity, which for all steels is the the same (30E6 bs/inch-inch)and remains constant regardless of how it is heated, stressed or aged. Therefore, the spring rate of the chassis or the stiffness of a chassis does not change unless the geometry of the chassis changes. How can the geometry of the chassis change? A cracked weld or poor weld repair could change the geometry of the chassis and therefore the stiffness but stress and aging alone cannot directly affect the stiffness or the springiness of a chassis.

[Todd Bellew]

Interesting thread, seen it take a few forms. This theme seems to be welding.

However, someone asked for concrete proof that old chasis aren't as good as new ones. Simply look at the people who produce the chassis. At the world level, they use chassis for one race, after they drove three or four to find one they like. So I agree they may fall off very little, however factory drivers feel new is better than old(Since they like their jobs and wanna race F1 I believe em). I'm convinced this is why Italians put notoriously bad brakes on karts. They are good for a few races then go to junk (save Brembo). So why put expensive brakes on a kart your going to get rid of.

Also, someone made a very good point about weight. Even in Europe the heaviest weight is 363 (FC) pounds which is still 20lbs lighter then we are. Plus , most karts are actually designed for Formula A at 308 lbs!! (karts handle great! at 308 trust me) This is one of the problems I've always felt we had from running Euro equipment with American rules. Since the chassis is the shock and SPRINGS those rates are important to the unsprung mass of the kart. Basically, we have the wrong springs on for what we do here. Also I think this overloads the chassis and wears it quicker.

I always felt this is what should give companies like TRAckmagic an advantage here. Their karts are made for our weight, tires, tracks and engines.

Thank You,
Todd Bellew

[Rick Blood]

Todd,
The factory drivers in Europe get a different chassis than the general public gets. They are hand built and are more flexy than the off the shelf karts you find in your local kart shop with a few exceptions of course.
I just had a chance to closely compare one of these hand built frames with a showroom piece and there are several differences.
Generally the roller chassis comes in as overly stiff and gets better with use. As an example, S1 Shayne Shipley says his year old MBA gets better every race and our almost 2 year old MBA is the best it has ever been.

[Todd Bellew]

Rick,

I'm not sure I understand if having special chassis makes a difference on wear. They all still wear.

The starting stiff and needing "broken" is a new one to me for kart chassis. That expected change in the properties of the metal sounds like a tricky thing to predict. Plus, the shear idea of being stiff to begin with then coming in after use supports the idea that chassis DO wear.
Which was the question and the reason I used the world championship drivers as an example.


And as anything else, there is a window when its the best, just like your tires, after that new is faster.

BUt, we still haven't got much SCIENCE here explaining whats happening. I want to hear some carbon and interstitial molecules and alloys and heat treating explanation. BUt, just because we don't know why doesn't mean we can't observe the behaviour and know it exists.


Thank You,
Todd Bellew

[John Learmonth]

Think about this; is it in the interests of chassis manufacturers to discourage the widely held belief that the actual chassis do wear out, and wear out rather quickly? You wouldn't hear a factory actually saying their chassis need replacement every season (or sooner), but as long as the thought is out there they'll sell more chassis each year

Sure, the factory teams change chassis every time they change their socks, but is this because the chassis are worn out, or because there's a ready market for 'factory tuned' or 'factory team' chassis??? This way they can have a constant supply of new chassis (and chassis components) for very little cost.

At the very highest levels it may be that chassis are discarded frequently because the factory chassis are largely prototypes that are built, tested, raced, and then chucked in favour of the next developmental chassis??

I've known people who buy a new chassis each year, convinced the old one is no good, but usually they don't actually go any faster in the new chassis. If they don't go any faster, they can often justify the expense with some not easily measured percieved advantage such as 'it feels better to drive than the old one'.

[Chad Stapleton]

What most of you are discribing is better termed "Ageing" rather than wear.
Many alloy steels harden with age - some are deliberately intended to do this - . This effect can be accelerated by heat cycles, but eventually a "stable" condition will be reached.
Also "stress hardening" or "work hardening" occures in most steels when stressed beyond certain limits. Hence, the more a chassie is used the stiffer it is likely to become.
With either of these effects the chassie will become stiffer as it "Ages" from new.

[Larry Hayashigawa]

Age hardening only increases the strength of the material not the modulus of elasticity. It is the modulus of elasticity that determines the springiness of a material and not the hardness.