Posts
110
Joined
9/19/2017
Location
Chattanooga, TN
US
Edited Date/Time
7/31/2021 12:31pm
Someone in the KTM thread in Moto-Related made a comment that if the Japanese 450s could shed 10lbs, maybe they would be more competitive with the Austrian brand
"If Honda/Yamaha and Kawi could remove 10lbs off each bike and still be less expensive (in my parts a KTM will command over $1000 more then anything from Japan) it would probably really put a dent in KTM sales..." - @Monk
What modifications would it take to lose 10lbs off of a 2019 KX 450? According to the Vital 450 shootout, the kx is 9lbs heavier than the ktm. I know this is well-trod territory, but I'm curious to hear others' opinions.
"If Honda/Yamaha and Kawi could remove 10lbs off each bike and still be less expensive (in my parts a KTM will command over $1000 more then anything from Japan) it would probably really put a dent in KTM sales..." - @Monk
What modifications would it take to lose 10lbs off of a 2019 KX 450? According to the Vital 450 shootout, the kx is 9lbs heavier than the ktm. I know this is well-trod territory, but I'm curious to hear others' opinions.
The engineers did a very good job of centralizing the mass weight while in motion which is what counts & not it being on the stand or the scales.
If you read some of the 19 shootouts the riders made comments about the KTM / Huskies feeling heavier vs. some of the Japanese brands. What's on the scales could be deceiving to how the bike feels on the track.
In my case as a consumer I'm looking for performance, durability, longevity, quality & not necessarily what the weight is. At my skill level the weight of the bike is not even a concern.
then I bought a 19 husky TC250 now that feels like a bicycle
Titanium or aluma steel hardware including steering stem, axles, and swingarm bolt. I'm making an aluminum front axle and maybe rear axle and swing arm bolt for my vintage bikes but I would use something stronger on the newer bikes.
Titanium springs if they are currently steel.
Titanium exhaust head pipe.
Aluminum and/or carbon fiber muffler.
Lighter rims like dirt stars or there is one other brand.
Aluminum spoke nipples, but these would need to be tested for reliability.
Starcross or Hoosier tires.
Standard thin wall inner tubes.
Lighter rim locks if they have heavy ones.
Titanium valves and valve springs if they are currently steel.
Drill a large id on camshafts.
Magnesium engine cases if they are currently aluminum.
Possibly titanium or powdered metal connecting rod.
Ceramic bearings.
Drive chain with titanium rollers and possibly hardened hollow pins.
The Shop
To be fair, remember that KTM uses an air fork, so that's something like 2 lbs in itself. But a 7 or 8 pound reduction is easily attainable if the engineers look at every single part of the motorcycle as an opportunity for weight reduction, that's exactly how KTM did it. The real question is whether or not the trade-offs are worth it. In general (but not always) a weight reduction also comes with a reduction in stiffness and/or durability.
@ 230lbs. I can certainly shed that amount & as you mentioned it's free..
That is the last place I would skimp on strength to reduce a few ounces.
What's the budget? Certainly attainable, but with a price. However, as mentioned, comparing apples to apples means you add appx. 3lb to the KTM/Husky instantly for a comparable dual spring fork; not to mention replacing their THIN oe-specification tubes with something you can actually ride...
-Tires are a good place to start. Have heard the Michelin's and new Hoosiers are almost spec tire light. Even Pirelli's weigh less than Dunlop and Bridgestone competition. ≈.25-1lb.
-Exhaust. Replacing the bazooka yields significant weight savings. ≈2.9lbs.
-New triple clamps. Ride Engineering advertises .25lb. with their 19' design.
-Guts Phantom seat foam; Don't forget the PulpMX discount code. ≈.25-.50lb.
-RaceTech titanium advertises 6.5lb. decrease with ALL their trinkets. Can usually get ≈1.5lb. decrease with just axles and swingarm pivot.
-DRC sells aluminum bolts that are a good replacement for LOW STRESS applications. ≈.25lbs.
-LightSpeed and PC should be selling a carbon chain guide which aids in alignment and loses some ounces...
Links so you know I'm not blowing too much smoke...
https://www.keeferinctesting.com/offroad-testing/2018/8/14/fmf-41-rct-t…
https://ride-engineering.com/products.php?d=1&p=bm&pn=KX-TBK22-G9&t=kx
http://www.gutsracing.com/Kawasaki_KX450_Phantom_Seat_Foam_p/680-ph.htm
https://racetechtitanium.com/product-category/motocross/kawasaki/kx450f/
https://www.ebay.com/p/DRC-Hard-Ware-Aluminum-Flange-Bolts-Titanium-M6x…
Good read here for KX450F ideas: https://motocrossactionmag.com/bike-test-we-ride-ride-engineerings-2016…
Ti shock springs are lighter weight, and I personally LOVE the feel, but come with some hiccups. HSS may shave some weight with steel spring benefits: https://motocrossactionmag.com/bare-bonestitanium-shock-springs-vs-stee…
This isn't touching anything internal yet, utilizing ceramic bearings, going back to 240mm rear rotor, removing rear brake protections (which the KTM/Husky don't even have) and chopping the rear guard mounts off, or discussing the longevity merits of a heavier aluminum frame over the lighter steel offerings which may not go through the same R&D durability cycles of the Japanese bikes...
*Don't forget, most of the things we change on a new bike adds weight. Skidplates, aftermarket wheels, oversize bars and clamps, foldable levers, seat covers (over the stock cover most of the time), stiffer springs, etc...
A shit ton of my KTM's weight went up when I added the following: cone valve spring forks, A60 rims with Talon hubs, proper inner tubes that were less likely to go flat and ruin my day, skid plate to protect the metal down tubes. Add all that up and i'm it's probably around 7-9 pounds.
Well, I have been working in Aerospace industry for 22 years. I'm very familiar with ALL types of exotic alloys and metals. IE, tensil strength, shear strength, HT, normalize,RC, Stress relieve, all of these play a factor when determining what type of metal to use.
Also, very familiar with all types of metal finishing and plating specs.
barnett468 Please tell me your metallurgy history/background.
Pit Row
What is your background to tell me that I know absolutely nothing ????
So when you tell someone that they know absolutely nothing, I would think you could answer a simple question as to what your background is that makes you the expert ? Remember ?
Or do you just like to talk shit ?
.
It was your claim I know nothing. I simply stated my background, and then you never answered my question ??
Never said I was an expert, but I am very familiar with all aspects of metal. To be an expert, you would have to be a certified metalurgist, I am not.
So do tell us, whats your back ground in this field ??
Peace
Also, the word "metallurgist" has 2 l's, not 1 like you spelled it.
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He said running an aluminum axle would give him the willies :-)
Galling would be another big concern, but a Nicotef coating would help prevent that.
Clearly you have no background since you cant answer the question. Until then, just quit responding.
It obvious that explaining something to you would require a lot more time than I have!
Good day MATE!
If there was, then ......... well you know, everyone would have them.
I wouldn't be afraid of it breaking, just more fatigue, bending, galling, with zero gains.
Who wants to try one out ? Front or rear, What bike ?
I will make someone a set, I could do YZ 250, I have some of those, or KX 85
Any other bike, you will have to supply the dimensions and I will make them.
Peace!
.
7068 in the T6 condition is indeed a very strong aluminum alloy. But ultimate tensile strength is hardly the only qualifying metric in its suitability as an axle. As the article and other people have already mentioned there are many factors to consider. Strength, fatigue life, stiffness, hardness, corrosion resistance, stress corrosion cracking resistance, etc. are all at play here.
Yield Strength:
My bet is 7068 would be plenty strong for the application. But for how long? This leads us to fatigue.
Fatigue Strength:
Hard to say without a thorough analysis and proprietary knowledge of the manufacturer, but I'm betting the stock axle is made from a rather strong alloy steel such as 4340 or similar, that has a strength suitable to keep the stress levels below the endurance limit. So fatigue is a non-issue there. But it absolutely is an issue with an aluminum axle. So how many cycles can it take at the design stress before failure? A front axle sees a lot of load cycles. Luckily for the fatigue world they're not fully reversed cycles, but they're certainly relevant. Most likely an aluminum axle of any alloy will require a fixed service life to be safe, e.g. it requires replacement every year or similar.
Stiffness:
No argument here, aluminum of any alloy will have a stiffness 1/3 that of steel. You can overcome this to some extent by making things thicker, but that has quickly diminishing returns as the bending stiffness of a tube is related to the outer-most layers. You're also adding weight as you make things stiffer to compensate. Even if you went with a solid aluminum axle, you wouldn't be anywhere near the bending stiffness of a stock steel axle. And you'd probably be heavier as well!
Corrosion/Stress Corrosion Cracking:
I don't know the data off-hand for 7068, but for 7075-T6 there are stress corrosion cracking issues. It's advisable to run the over-aged T7 temper to avoid these issues, but then you have a little less strength. Maybe 7068 also has this issue, maybe it doesn't, but it needs to be considered.
Hardness:
Aluminum is soft relative to steel. You're going to see surface wear pretty quickly due to the flex in the system and just from normal use/maintenance. You can overcome this with a hard-anodize, which will also help with the corrosion issues, but a hard anodize has a negative impact on fatigue strength. So all that needs to be considered as well.
Availability/Cost:
Good luck finding this alloy, I have yet to see it from any of our normal suppliers. It may only be available in full 12' lengths and in limited diameters. Fine if you're manufacturing a lot of axles, not so much if you're making a one-off part. Also, it's likely to be expensive.
So all that said, assuming you have a high budget and can replace the axle every so often to alleviate the fatigue concerns, a 7068 axle may work fine. But (and that's a BIG but) there's always going to be the stiffness concern. To realize the weight savings of an aluminum axle, which was the whole point to begin with, it's going to be 1/3 the stiffness of stock. Depending on the arrangement of your hub, spacers, fork lugs, etc. this may not be a big deal.
Assuming the stiffness isn't that big of a deal, and after all the concern over strength, fatigue life, etc. you've only managed to save 0.36 lbs vs. a stock steel KTM axle. I'd argue there are better places to look for weight reduction.
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