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2021 Ninja 400, 1998 Honda VTR1000 SuperHawk
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I do all my own tire changes. In the one picture that’s why it was on the tire warmers. It was cold out and being warm makes the tire much more flexible. :)
Nice.
Maybe a pic or two on what tools you're using to change your tires etc.


BST carbon fiber.
It's hard to imagine how light they are. When you pull them out of the box they feel lighter than the box and your first thought is "I'm trusting my a$$ to this?" :)
View attachment 25437 View attachment 25438
I would have to have sex with those before they went on the bike, after cleanup of course. 😂😋🤫

I don't envy you but do appreciate excellent taste in upgrades. 🤙
 

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Nice.
Maybe a pic or two on what tools you're using to change your tires etc.



I would have to have sex with those before they went on the bike, after cleanup of course. 😂😋🤫

I don't envy you but do appreciate excellent taste in upgrades. 🤙
Changing tires does require a good water based lube 😂

Oh, I use a Nomar tire changer. They’ve changed a bit but like the Classic. Awesome tool!

 

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FWIW, a friend who has a Honda RS125 (about 1996 model) mentioned today that he's gone through several of the OEM tubular 15mm front axles. He said the center hole looked pretty small, and that's a very light (160-165 lbs I think) bike. So doubling the weight of the bike to an N400 is going to put even more load on the axle.
 

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I spoke to an engineer I met up with at the track day today, and I specifically asked about this axle talk.
His off the hip thoughts were shear strength may be more important than stiffness.
Steel wins over titanium there too.
 

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My 1971 TS185 Suzuki had some sort of factory-supplied stress raiser on the front axle between the main axle shaft and the spacer shoulder. Having the axle shear there made for a short period of very squirrely handling (and then I fell down).

I think for shear strength you just need "enough". After that, you can look at stiffness.
 

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Discussion Starter · #47 · (Edited)
I received the parts I bought from ebay for an R3. The rear axle is 17mm (measured about 16.90 each with my Harbor Freight cheapie digital caliper). The length is within 1/4" of the length of the stock ninja axle.

The weight is as follows (note that I'd estimate that my scales are perhaps within 5 to 7 % from an accuracy standpoint)
Stock Ninja Rear Axle: 570 500 grams without nut, cotter key or washers
Stock YZFR3 Rear Axle 270 grams without nut, cotter key (doesn't have one) or washers.

Difference - 230 grams, almost exactly 1/2 pound.

DISCLAIMER: I am not recommending that anyone swap the rear axle from an R3 to the Ninja 400.

However, for me, I am comfortable in my particular situation to try the R3 rear axle in my Ninja 400. Factors for this include:
The weight of my bike (around 328 lbs. vs R3 which is around 368 wet per Yamaha specs)
Lighter wheels and swingarm - should produce less forces on the axle
I weigh about 170 without gear - maybe 195 with gear. Bike is rated for about 390 lbs carrying capacity I believe.
Rarely ridden on the highway, just track days.

The front axle from an R3 is 15mm while the Ninja 400 front is 17mm. Not interested in making this work, as 15mm drilled seems like a big problem waiting to happen.
The swingarm bolt from an R3 will not work on the Ninja 400.

Wanted to post pictures, but my phone ratcheted up and won't take photos at the moment.

Next up for consideration is the swingarm pivot bolt from a DRZ400, just based of off of pictures on ebay. Seems to be 17mm as well and about the same length. It does have a funky head on the bolt that might not be so easy to tighten.

-K
 

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Discussion Starter · #50 ·
Inside diameter of the rear R3 axle is about 10mm on the threaded end and 12 mm on the end with the bolt head. I already installed and apparently didn't write down the lengths, so not sure which was longer. There are several threads sticking out through the axle nut on the R3 axle when it is installed on the Ninja 400.

The front axle IDs are roughly 5.5mm on the threaded end (although the first 1/2" or so is larger before it necks down) and the end with the bolt head is about 9 mm after it necks down a bit as well.

I located a place that will drill a stock Ninja front axle if I decide to go that route somewhere down the line.
 

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If the R3 rear is 17 OD x 12 ID (2.5mm wall) then that's basically the same area (for shear) as a solid 12mm axle (which seems a bit "moped-y" in size). That area is also a match for the 15mm x 9 (3mm wall) front. It seems like that should be OK (try shearing a 12mm bolt) but the rear is a 25% drop in stiffness compared to an N400 solid 17mm axle. If Yamaha is using "the usual axle steel" that may be why they are prone to bending. That makes the Kood higher strength steel axles seem like a good thing.

You may want to plan on pulling the rear axle after each of the first few track days to see if it is starting to bend.
 

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I looked up the axle size on my old 185 Suzuki and it appears to have been 12mm (12.6mm given for the ID of the center bearing spacer), so there's proof that a 12mm axle can shear. Granted, I was riding off-road and trying to be an MX star :) and the replacement axle saw similar use and didn't fail. My front axle is the only one I ever heard of that failed (and I worked at a Suzuki dealership at that time) so I suspect there was a flaw in the axle. But still . . . .

YMMV
 

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Discussion Starter · #53 ·
If the R3 rear is 17 OD x 12 ID (2.5mm wall) then that's basically the same area (for shear) as a solid 12mm axle (which seems a bit "moped-y" in size). That area is also a match for the 15mm x 9 (3mm wall) front. It seems like that should be OK (try shearing a 12mm bolt) but the rear is a 25% drop in stiffness compared to an N400 solid 17mm axle. If Yamaha is using "the usual axle steel" that may be why they are prone to bending. That makes the Kood higher strength steel axles seem like a good thing.

You may want to plan on pulling the rear axle after each of the first few track days to see if it is starting to bend.
Michael,

The inside diameter of the rear R3 axle is about 10mm on the threaded end and 12 mm on the end with the bolt head. I believe it "necks down" shortly after the bolt head to the 10mm size that continues to the other end of the axle bolt.
From earlier post: Inside diameter of the rear R3 axle is about 10mm on the threaded end and 12 mm on the end with the bolt head.
 

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The smaller ID under the threads would be because the OD there is smaller and the threads are cut into the metal. But that may not need to continue much past the threads. If the bolt head goes on the drive side of the wheel I'm not clear on why they'd want a larger ID there for only a short distance, since the chain pull is probably the big load that is seen. What might make more sense is a standard ID all the way through the unthreaded shank so that no matter from what side the owner inserts the axle there'd always be sufficient wall thickness under the sprocket.

You may want to grab some drill bits/rods and poke them in the axle to see where the ID changes, and then do a sketch to see if you can figure out what is going on.
 

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Discussion Starter · #55 ·
Michael,

Good idea on trying to map it out.

I also ran some searches on an R3 forum to see if I could find discussions about bent axles. The only ones I found were related to crashed bikes with bent forks and axles, salvage bikes being turned into track bikes etc. Search results are always hard to predict, but I didn't see much to indicate that axles are being bent while riding. One could however, wonder about the chicken/egg paradox... Did an axle bend causing the bike to crash? Or did the person crash and bend the axle?

I have seen instructors at track days beating the crap out of R3s with no issues observed.
 

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If I have a part in my hand I often will draw it in CAD or scan it. I may be unlikely to ever make one, but it can be handy to know "oh yeah, axle XXX is long enough to be used on bike YYY per my drawing/measurements." Sometimes when you measure and draw stuff you find that the manufacturer has done something clever/dumb that wasn't really obvious until you gave it a close look.

Some bikes just have parts that are usually a write-off in a crash. The old Yamaha XV550 Visions were like that when raced, drop it and there goes another heat exchanger (and maybe fork or steering stem/triple clamp). My friend's RS axles were crash damage. It is nice to have a track bike that does a good job of surviving crashes. :) It may mean the difference between going back on the trailer or getting spruced up and doing a couple more sessions before the track day is over.
 

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It seems to me that bent is bent. A soft failure is much better than a big one, but it would be nice to have no failure at all.

I wouldn't think that design of a non-failing axle would be a terribly complicated task for an OEM. Even if it was entirely empirical without any engineering calculations, they've got millions of axles that have been in service for decades that they could look at and say "nooo, maybe we better not make it quite that way for this application". :)
 

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Kirk, that Kood cartoon says "Kood axle shaft makes attached stiffness property better". I was looking at some project notes from a guy on my chassis list who is an engineer and builds chassis for Moto2, makes GP-replicas chassis for street RD500/RG500 2T four-cylinders, etc. About 12 years ago he built a very cool racer around a Kawa ER6/Ninja 650 engine and he had eccentrics at the rear axle for adjusting chain tension. The swing arm had clamps for the eccentrics. The thing that relates to Kood is he had the eccentrics integral with the axle, which is in left and right sections and held together in the middle of the wheel hub by a socket head cap screw (with some hardened dowel pins to keep the two eccentric ends in alignment). He said having the eccentrics (which also did duty as the wheel spacers) as a part of the axle made "a considerable improvement" in the stiffness of the rear of the swing arm. So that is probably what Kood is trying to say, they are improving stiffness to some degree by incorporating the spacers into the shoulder on the axle.

I hope you find that bit of information interesting.
 
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