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-   -   Analysis: KTM Duke 390 Alloy wheel cracking problem (https://www.team-bhp.com/forum/ride-safe/154536-analysis-ktm-duke-390-alloy-wheel-cracking-problem.html)

So all the existing and potential owners of the 390 Duke are haunted by the sheer number of alloy wheel cracking incidents we have come across from various parts of the country. This, in my opinion is the biggest problem and a case for concern for the 390 and the 390 owners. And there are a good number of people who are not taking the plunge just because of this very reason. Going on a ride to a remote destination and stranded with a broken alloy is NOT a good way to enjoy the ride and more and more reported incidents will only take away our confidence on the bike.





I have been reading up from other sources trying to dig into the cause of this abrupt alloy breaking on the 390 in particular. What confused me much were the following facts.

• The design of the 390's alloy is the exact same (atleast to the naked eye) as that of the 200 except the color change and yet I have not heard about any crack on the 200's alloy. So the fact that it has to do with the design change of the alloy can be 'almost' ruled out

• The 390 is only 15kgs heavier than the 200. Most of the components in a mechanical system will be developed with a 'Factor Of Safety'. Which allows the structure to bear almost twice, thrice or more of the normal weight that the structure is supposed to be carrying. So this 15kg weight difference as the cause can be ruled out.

• Tyre / Metzeler - Not a chance as the profile is not less than the MRF Rev-Z

• High speed capability of the 390. Can be ruled out as I have heard about alloy cracks happening at speeds as low as 40kmph or so

• Tyre pressure - Nop. How many of us religiously check the pressure every morning or atleast once in a week? So the point is that other bikes with alloys are also ridden by people who may only go in for a pressure check may be once in a month or so. yet, they don't suffer this alloy crack

Now, the only difference of the 390's alloy itself from the 200 is the color. Now that sounds as silly as it sounds like. But KTM has said that the alloys (and the frame) are powder coated to ensure the durability of the color and prevent peeling off or fading. And there is a chance that this could be a cause for the weak alloy of the 390.

The powder coating process involves application of the electrostatically charged powder on the ground object and then heating it to cure the coating.

Source : http://home.howstuffworks.com/home-i...er-coating.htm

Now, this curing or reheating the cast or forged alloys may lead to premature aging of the alloy which can weaken it. Also note that this procedure is not the same as tempering process of raw steel which will make the steel stronger.

Although forged alloys will be stronger than cast ones (although we have no idea if the alloys on the 390/200 are forged or cast) the alloy 'may' still suffer from the aging process.

It is interesting to notice that some high-end alloy wheel manufacturers like ENKEI voids the warranty on alloys if it is powder coated.

Similar discussion happening elsewhere :

http://www.nsxprime.com/forum/showth...ms-weaken-them

http://www.evoxforums.com/forums/showthread.php?t=15316

Now nowhere I was able to find out any hard evidence supporting this. But I just cant think about anything else as a cause of the infamous alloy breaking incidents on the 390.

Disclaimer: I am not an expert in metallurgy or mechanical engineering. Experts in the field can point out any mistakes in this opinion.

@Mods: Posting as a separate thread as I felt that a discussion narrowed on to this specific topic may help us to get to the root of the problem. However please do merge this thread if the discussion on this seems inappropriate.

Sounds like a likely cause. Definitely more plausible than the official "high-er speed" and "other bikes with alloys also suffer similarly so this is not KTM specific" lines.

Btw, I've heard of 200 rims cracking as well. One of an old timer here itself.

Will be interesting to know how much this impacts the export inventory. Can be catastrophic for KTM considering the laws in the western world won't spare them for a mistake like this.

I am guessing you don't need to even hit a pothole for this problem. Keep hitting the front brakes hard and the front rim might just buckle one day.

Do we have a count of wheel rim failures?

What you are talking about is heat treatment of metal alloys. The type of failures seen so far in photos point to brittleness in the metal.

The powder coat curing is done by air inside the oven heated to the required temperature. For the duration that the rim is inside the oven, only the surface layer and thin sections of the rim will be significantly heated. In my opinion, the temperature that the metal reaches, the duration for which it remains at the temperature and the rate of cooling thereafter (air cooling), will not be sufficient for the metal to become brittle. Many OE wheel suppliers use powder coating as their preferred coating process because of many advantages over liquid paint.

However what could be a major factor in the failures could be the LACK of heat treatment of the wheels. The wheels are die-cast items and they are normally heat-treated to improve strength and toughness. There are standards that all wheels must meet and only a scientific test will be able to tell us how good the Duke 390 wheels are.

Valid point. From what I know, the temperatures to which powder coating are subjected to is quite small in relation to the temperature to which the metals/alloys are subjected while heat treatment or casting. But what If the proper heat treatment is lacking here (as you mentioned) while manufacturing and then isn't there is a chance that the curing temperature while powder coating weakened the structure further.

Actually, I haven't heard of any similar cracking problems for the export 390s. Not sure if it will be be due to better roads they have.

Waiting for the guys who have replaced their tires to other brands from Metzelers, for any sign of cracks will be a good idea.

Since these tires a soft compound, (I am not sure if that leads to a soft sidewall as well), will contribute in a huge amount to alloys cracking.

Imagine a car with low profile tires hitting a pot hole and many before that, eventually it will crack. Heck, a stock tire with steel rims get bend if a pothole is hit at good speed.

My guess is that , the tires are mainly meant for track, but the MRF's on the 200's are more suitable for Indian roads, also the reason there is no report from export bikes .

My guess will be thrown out of the window if there is a report of a cracked alloy on a bike that is been ridden on good roads always .

The rubber conpound of a radial tyre in my knowledge does little in way of contributing to it structural integrity. That is mainly a function of its internal skeleton or carcass. Especially in radial tyres.

The profile of both the MRF as well as the Metzeler is a likely contributor. Have said this many times before - both here as well as to the higher ups at KTM. There is just no air cushion when the bike is leaned over and hits something at the side rather than when its upright and hits the same thing dead center.

There have been cases of wheels cracking on 200s shod with MRFs. And many cases of wheels bending on 200s - if not outright cracking.

AFAIK the export bikes all come with Metzelers.

It's possible in theory but unlikely.

The simple fact of the matter is that wheels for vehicles used in Indian conditions must be stronger and tougher than wheels meant for use in Europe. For more strength, more material is required which leads to higher weight. So KTM should have just accepted the fact that there is no alternative and equipped the Indian 390 with stronger and heavier wheels.

Here's an interesting fact I found out recently. The KTM wheels are heavier than the NS wheels.

How many NS wheels cracking/breaking have we heard about?

Sidewall height for NS vs Dukes is 91 vs 90 mm for the rear and 80 vs 77 mm for the front .....

That's true.
What I actually meant was what if the sidewall is weak as well.,to add to it, it is low profile.


Thanks for that information.


Yes, which was why I was wondering if there any reports from there about the same issue which leads me to think it is a combo of Indian road conditions and the low profile tires, also waiting to hear about a crack on the 390's shod with the Vertigo's.

If it's not the amount of material that is the problem then it leaves the quality of the metal and the manufacturing process that might be the problem. Bajaj is the only one who has the answer to this.

Doc,
The export 200s wear MRFs.

http://www.visordown.com/road-tests-...iew/21130.html

It is disappointing to hear that rim cracking issue is happening in 200 also :( I thought 200 was safe from that.

--Anoop

The rims are sourced from China I've heard , they are all cast items. The 200's rims are powder coated too (black).

Are there any people on this forum who have cracked rims ? That rim in the first pic seems very much like a crash victim...not a case of hitting a pothole and disintegrating me thinks.

I have put my 200 through some rough stuff (including jumping off speed humps) and I see no such symptoms.

+1 - I have put some pressure on the rims (around 2Ft Jump downs and scaling boulders and few more stuff like that) but fortunately, nothing happened till now. I was (falsely) confident on the fact that there was no reported rim cracks on D200, but now seems like I should be much more careful.

--Anoop

I do not think it has anything to do with the material or process and more to do with the use

Our roads are pretty bad, and a Duke 390 is pushed hard through it and any light alloy design with suffer

I have personally cracked a Suzuki 4.5 rear rim
Bent a front rim on a import Yamaha
Bent bullet 500 rim

all the above happened at varied speeds and proper air pressure, the common factor was that whatever I hit was a sharp edged pothole, something like this ]_[; if you know what I mean. deep pot holes of say a gradient shape never posed a problem.

Its the force and the fact that I did not stand up to reduce the impact.


Coming back to Duke 390; it is a hooligan bike and first time we have got something like this and we are pushing it and cracked, bent rims are some price to pay

if you do not want to pay that price, do either of the following
- ride slow and sane
- choose a heavier rim
- increase your aspect ratio

my two cents