[ebonho]

Originally Posted by DeepakMenon

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.

Agree. Add to that the fact that the bike is leaned over when it hit the sharp vertical edge - at speed.

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

Let me play the Devil's Advocate here.

Bajaj claims that even the Ninja suffers cracked and bent rims.

The Ninja has been around for over 5 years now. The Ninja has always been capable of Duke 390 matching performance.

Agreed its not a mass bike. But there are enough of them out there for a decent sample size denominator. And the advantage is that most would be online on one or the other bike forum.

Now considering the Duke rim costs 3.5K and the Ninja rim costs 10 times that - i.e. 30K, I'm betting if there were near similar numbers (as Bajaj claims) we (the online biker community) would have heard of them by now - no biker (even richie rich with papa's money funding) is going to keep quiet when he shells out half the price of a commuter bike for a damaged rim .....

Have you?

I know I have not.

[DeepakMenon]

Originally Posted by ebonho

Agree. Add to that the fact that the bike is leaned over when it hit the sharp vertical edge - at speed.



Let me play the Devil's Advocate here.

Bajaj claims that even the Ninja suffers cracked and bent rims.

The Ninja has been around for over 5 years now. The Ninja has always been capable of Duke 390 matching performance.

Agreed its not a mass bike. But there are enough of them out there for a decent sample size denominator. And the advantage is that most would be online on one or the other bike forum.

Now considering the Duke rim costs 3.5K and the Ninja rim costs 10 times that - i.e. 30K, I'm betting if there were near similar numbers (as Bajaj claims) we (the online biker community) would have heard of them by now - no biker (even richie rich with papa's money funding) is going to keep quiet when he shells out half the price of a commuter bike for a damaged rim .....

Have you?

I know I have not.

Well let me bring another angle to this

I too have a Ninja 650, in the past I had a RZ350 with Suzuki Rims, RD350, and RX135

Now when I am riding RX I am more carefree as parts cost less, however when I was on the RZ with no insurance for replacement parts I would brake sooner and slower on bad section, I end up being more careful as I do not want to damage. The funny part is one day I ended in a pot hole and dented the front rim and bent and cracked the rear :(


on the Ninja, I am carefree as it is comprehensive however still expensive so the degree of me flying over craters is calmer.

The bullet rim was a recent occurrence as I was flying through ladakh with no care in the world; if I was slower I would have saved the rim

in my mind it is the combination of carefree use, low aspect ratio and speed

cost can be a concern; however unless the material put through scientific stress test it is not gonna be conclusive


The above is no different from car guys with low profile tyres and the risk of bent rims; Mercedes, Audi etc. they too face it

[ebonho]

Originally Posted by DeepakMenon

The bullet rim was a recent occurrence as I was flying through ladakh with no care in the world; if I was slower I would have saved the rim

The Bullet rim is damn strong. In fact any spoked steel rimmed wheel is.

The one time I managed to bend mine, I also ripped out more that half the spokes from their bedding in the hub.

The difference here was that the tyre did not deflate, and wobbling all over, I was still able to ride the bike to safety and transport. In short, in spite of terminal damage, I was not stranded.

in my mind it is the combination of carefree use, low aspect ratio and speed

cost can be a concern

Agreed on cost having a bearing on usage pattern. Am also with you on aspect ratio. In fact my experience has taught me that 9 times out of 10 the damage happens because you instinctive reaction is to tilt the bike away to try to dodge the pothole at the last instant - and land up hitting the edge on the the edge of your rim as a result instead of front on with the meaty / fattest part of your tyre's air cushion. Its an instinctive reaction. Very dificult to control and hit it straight.

But the point of the aftereffect remains the same whether its a 3000 buck rim or a 30,000 buck one.

You are stranded with a broken bike that's not going to be moving anywhere on its own.

[VW2010]

Why not the inverted fork. The Bullet fork is potentially taking the max hit and the amount of travel it does it may first create damage to the mud guard than the rim itself.

The travel is too short and its not meant to handle that huge a change in vertical movement of the bike.

Secondly many probably have learnt a technique naturally to avoid adding more pressure to the front end by doing things including taking hands of the bars, standing up and letting the bike be rode as a cross country etc. If the rim is between a rock and a hard place in which case when hitting a pot hole the wheel is at the rim of the pot hole, suspension full loaded (or completely down) and then the momentum carrying not just the weight of the engine, but the overall bike and the body as well creating the hard or the rock place. The only way that pressure is getting released is by making use of the light weight alloy. This is my personal take and it may and must be scientifically stupid but i tend to believe many are not having those broken rims mainly because they are naturally some how avoiding putting their rim between the rock and the hard place. This could mean they are just braking before and letting go the brake as the enter the pot hole for the suspension to have that enough travel or they are getting up at the right time to shift momentum and weight distribution to cushion the landing or they are naturally adept at hitting the pot hole at right angles that the tyres are taking the punishment.

In my bullet just before i flew to US, i was riding at around 40, a hyundai hit me from behind and i went and rammed at the same speed on a standing swift. I did a rear wheelie in such a way it was so dramatic and right in front of me when the bike toppled and landed just to my sides. I hardly had a scratch. My new helmet hardly had a scratch. I am absolutely sure my pillion was someone divine.

Damage done - Bent fork, bent handle bar, bent mud guard, bent levers etc. Broken bumper for the swift which i paid and fixed because it was my fault.

Took me ten minutes to shake the shivering (yeah i was), get a life lesson from the cop nearby, a big stone and my spark plug removal tool rod to fix the bike to ride another 30 kms straight to the work shop.

Long story short, i believe the way the bike bit, the design of those bumpers(Read here the lack of stupid bull bars that someone install even at the rear), the travel of the suspension actually had zero impact on the wheel or the Rim.

Mine is a steel spoke wheel and i aint changing it any time soon.

And i think the suspension in KTM390 is not designed for our indian roads but more so for smoother winding roads where the action is minimal but optimum and the right amount.

[ebonho]

VW, the stroke of the front telescoping suspension (travel) of the old Bullets (ours) is 155 mm while that of the Dukes is 150 mm.

The new Bullets ("modern") for some reason have much reduced front suspension travel of only 130 mm. Wonder why?

[DeepakMenon]

Originally Posted by ebonho

VW, the stroke of the front telescoping suspension (travel) of the old Bullets (ours) is 155 mm while that of the Dukes is 150 mm.

The new Bullets ("modern") for some reason have much reduced front suspension travel of only 130 mm. Wonder why?

More or less travel does not mean good or bad, Compression, Rebound rate along with Preload is the key

[ebonho]

Originally Posted by DeepakMenon

More or less travel does not mean good or bad, Compression, Rebound rate along with Preload is the key

If you're saying (or indicating) the KTM front forks are too much on the softer side, I'd agree. The 390s are better than the 200s on that score though.

That said, the degree of travel does indicate the extent of "give" before full stop and then something else taking up the force. Namely in the scenario of the current discussion, the rim. A stiffer fork could compensate for lesser travel. But such is not the case on the Dukes. Much the opposite. Even though there is not a lot of weight of the bike to start with to take up the initial suspension sag. Its a purely road tuned suspension. Which gets swamped beyond its design envelope in certain instantaneous situations - like hitting the steep edged pothole at speed and leaned over. The rest of the shock absorbing is then done by the rim. Which unlike pressed steel does not bend beyond a point. It breaks.

[B O V]

Interesting issue.I'm curious.

I feel(from my limited knowledge in mechanical design)that it could be a simple manufacturing defect.

From the spec sheets on the net the difference in weight and wheelbase between the motorycles is 5kg's.Now the Factor of safety of these rims would definitely compensate for the increase in weight.

Fatigue could be a reason.I mean,if over extended periods these rims(read motorcycles) were subjected to different conditions that could add to the fatigue there could be a breaking point at which failure occurs.

I don't think that the difference in tyre's between these 2 motorcycles would be a contributing factor to this cause.

If we could get some details on the motorcycles that this happened to,such as

*Kind of terrain/conditions in which the bike was ridden for a period(say 6 months) before the cracking happened.

*The weight of the rider.

*If there is a regular pillion rider.

I suppose if we could get such info maybe we could narrow down the possible problem.

I wonder who KTM outsources the manufacture of these rims to.

[abhishek46]

I am no expert, but my 2 cents here,
I feel that the low profile tyres have a role to play here. Because the tyre are so low profile, they might have failed to absorb impacts of bumps/potholes.

[man_of_steel]

Originally Posted by abhishek46

I am no expert, but my 2 cents here,
I feel that the low profile tyres have a role to play here. Because the tyre are so low profile, they might have failed to absorb impacts of bumps/potholes.

The tyres used by KTM currently are NOT low profile ones. The fact is that only the side wall of the tyre seems small.

If you see the specification of the tyre it is 150/70-17. Which means that the aspect ratio is 70. Which means height of the tyre is 70% of its width(150mm) which comes to a meaty 105mm when the bike is upright.

Now, for comparison sake, lets take the tyre specification of the Yamaha FZ-16 which is 140/60-17 which makes the tyre height 84mm. And if you take the Conti-Gos(140/70-17) of the CBR250R the tyre height of 98mm.

In car tyres where the tyres are flat in cross section, the sidewall height will be same as the profile of the tyre and the tyre wall height and strength will be the contributing factor for ride comfort and impact absorption. But that is not the case with motorcycle tyres with a rounded profile.

[giri1.8]

I still can't believe that they have not come up with a solution, I have hit very deep potholes at very good speed on my hunk, yet to face any issue so far. Bikes release for our market should suit our condition, ironically no one has reported any serious issue on 200 NS alloy. I would have purchased 390 with my eyes closed if it didn't have so many issue!

[abhishek46]

Originally Posted by man_of_steel

The tyres used by KTM currently are NOT low profile ones. The fact is that only the side wall of the tyre seems small.

If you see the specification of the tyre it is 150/70-17. Which means that the aspect ratio is 70. Which means height of the tyre is 70% of its width(150mm) which comes to a meaty 105mm when the bike is upright.

Now, for comparison sake, lets take the tyre specification of the Yamaha FZ-16 which is 140/60-17 which makes the tyre height 84mm. And if you take the Conti-Gos(140/70-17) of the CBR250R the tyre height of 98mm.

In car tyres where the tyres are flat in cross section, the sidewall height will be same as the profile of the tyre and the tyre wall height and strength will be the contributing factor for ride comfort and impact absorption. But that is not the case with motorcycle tyres with a rounded profile.

My Bad. Thanks for the eye opener.

[Sheel]

Just asking - After a mod job, are not the alloy wheels of cars powder coated? And if powder coating is causing this, can someone please explain the reason for this to happen?

[man_of_steel]

Originally Posted by Sheel

Just asking - After a mod job, are not the alloy wheels of cars powder coated? And if powder coating is causing this, can someone please explain the reason for this to happen?

As mentioned in the first post. It is not the powder coating that weakens the alloy but it is the process. If the alloy is not properly cured while manufacturing, there is a chance that the curing that happens during powder coating could lead to premature aging of the alloy.

[PratikPatel]

Looks more like a metallurgy or a process problem. I have a set of similar style rims by Brembo on my Ninja 300. These are forged and extremely light weight. The rims are so optimised for weight that they have a hollow centre hub to reduce weight. These rims are extremely tough and durable.

It is interesting to note that the rims under discussions have been modelled and influenced by the Brembo Marchesini wheels (M10 series). KTM has traditionally used Brembo wheels on all its street bikes. While the 'original' is designed as a forged product, the KTM rim is designed as a cast wheel to keep cost down.

The KTM rims are at least 2 to 3 times heavier than the ones I am using. So it is unlikely that this is a design problem.The powder coating angle does not make any sense. It unlikely to compromise the structural or metallurgical properties so throughly to lead to such damage.