NX250 AX1 spoke wheel conversion

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jonathan
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Re: NX250 AX1 spoke wheel conversion

Beitrag von jonathan »

After what seemed like an age, my hubs came back from the powder coaters. I'm using a front hub from an XL125R ('86 on) which is a plug and play on the AX1/NX, but you will need the XL disc rotor and bolts. The Speedo drive, bearings, spacer, distance piece and spindle are all interchangeable.
The rear hub is from a KTM LC4 as you know (big thanks to Scrambler for sourcing a good one!) I had some new spacers made up (see above) which were modified to account for the AX chainline. I thought I'd also need a spacer plate for the disc rotor. KTM do these in 4 and 6mm as stock since this cush hub is used on a couple of different models. Turns out I didn't need one.

The bearings themselves weren't too bad as you can heat up the hub and tap them in, but they're more work than any other bike I've fitted bearings to. the spacers were a different matter. When I took the job to my local engineers' I'd taken the old bearings and spacers as a reference. The engineer made the new spacers to tolerance for these bearings, along with the modifications. The new bearings I fitted to the hub were much tighter, so I ended up having to freeze the spacers and warm the bearings in order to knock them in. With hindsight, I would fit the (frozen) spacers to the (heated) bearings first, repack the bearings with fresh grease, then chill both bearing and spacer to fit into the heated hub. There's nothing quite so demoralizing as pounding on a brand new bearing....

Anyway, once fitted, I threw the hub on with a sprocket and rotor to see how everything lined up.
IMG_20200531_185101.jpg
Front hub is plug and play but you need the XL rotor and bolts
IMG_20200531_185040.jpg
shows the resultant chainline and spacing (dimensions in previous post)


IMG_20200531_185025.jpg
shows the rotor spacing in relation to the caliper

Pleased with the results....now to find some rims!
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scrambler
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Re: NX250 AX1 spoke wheel conversion

Beitrag von scrambler »

looks great - I love the polished fork :)

The sprocket bolts look a bit too long - at my KTM rear wheel the bolts scratched the hub, for a different reason, tough: the previous owner forgot the spacer in the middle :shock:

ps. I was able to sell the KTM rim for a good price :)
NX250_AX1_sprocket bolts.jpg
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jonathan
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Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 AX1 spoke wheel conversion

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Yep...the sprocket bolts were not the proper KTM ones, just some countersunk bolts I threw in there while I checked the hub. The original powder coating on the forks wasn't too bad but there were quite a few chips and scratches. I thought I could always have them re powder coated in white if I decided to go back to stock look.
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scrambler
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Re: NX250 AX1 spoke wheel conversion

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jonathan hat geschrieben:Di Jun 16, 2020 1:13 am I've found a wheel builder locally and I'm about to have the hubs built up. When I fitted the rear hub, the chainline and rotor lined up really well, so the new spacers obviously work. When I look down the centreline of the hub it looks like it is in line with the centreline of the bike. I haven't taken any measurements yet but thought I'd ask you whether your KTM wheel has any off set? I assume the swingarm is centralized so I was hoping you might take a measurement from a fixed point between the rim and swingarm to see if the distances are the same?
I once took the dimensions of a KTM rear wheel. With a 2.50 '' wide rim, it is approx.3.7cm away on the brake side (without brake disc 3.3cm). And on the cush drive side about 2.9 cm (looks like the rim has a bit of an off set to the left?).

The distance in the swingarm is more difficult to measure because it is not straight. With my spacers, the KTM rim is about 5.5 cm away. Since the swingarm is curved, it would be 5.8 cm. For comparison, the original AX1 rear wheel. Here the rim is approx. 5.3 cm away. So there is a small offset of about 2-3mm to the left with the KTM rear wheel. In my opinion only a trifle but if you rebuild the wheel anyway you could correct this offset.

However, this is only measured very roughly, one would have to measure the exact rim widths (I'll try this today) and then measure the distance of the two wheels at the exact same place of the swingarm.

It would be even more precise to use the front wheel and the chosen rear rim and two long angled irons to determine the exact position relative to the KTM wheel hub ;) .
KTM rear rim_1.jpg
KTM rear rim_2.jpg
KTM rear rim_3.jpg
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jonathan
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Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 AX1 spoke wheel conversion

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Thanks for this Scrambler. So it looks like any difference in off-set would be down to the spacers used rather than deliberate off-set built into the hub. As you say, minor changes to centralize the rim in relation to the front wheel for proper front/rear alignment could be achieved by tensioning the spokes to suit. I'll double check today with the spindle at full torque. :D
jonathan
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Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 AX1 spoke wheel conversion

Beitrag von jonathan »

with the hub fitted without the disc rotor and sprocket, it's possible to measure the distance between the 'flats' on the swingarm (where the spindle goes through) to the centre point between the spoke holes. The spoke angles seem to be the same on both sides of the hub so this should provide an accurate reference point using a angle square ruler ('combination square'). Measured mine this way and it's the same both sides.
jonathan
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Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 AX1 spoke wheel conversion

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Everything went a bit mad during the covid crisis, including rim manufacture and import times, so after finally settling on a 3.50 x 17 rear and 2.5 x 19 front I placed an order in late June. There was/is a five week lead time if they don't have the rims sizes/colours in stock since they make them up in batches. My plan was take the bike over to the Classic TT in the Isle of Man this August but the races were cancelled due to covid, so there was less impetus to finish the rebuild. I didn't fancy rebuilding the wheels myself. I've built dozens of bicycle wheels for road and MTBs and I'm assured that the process is exactly the same, but I don't have the tools or the confidence to tackle a motorcycle rim, since the consequences of getting wrong could be much more dangerous. So I enlisted the services of a pro wheelbuilder who does all sorts of unusual rims including customs, classic cars etc. I'm picking them up on Monday but here's a preview pic...
blingwheels.jpg
they're not the matt gold as used on the japanese DID rims commonly fitted to Honda trail bikes, which would have been my preferred choice if they were still available, but I have a gold SM Pro platinum rim fitted to the rear of my transalp and they're a nice looking rim. will post more pics when I get some tyres on and the wheels are back on the bike.

They should look great....they'd look fantastic on a 'Black Beauty' Dominator :D

It will be interesting to see the total weight of these rims + tyres compared to the stock cast wheels. I imagine they'll be heavier, which won't help the AX1 acceleration wise, but once they've spooled up it shouldn't make much difference. the AX1 was never a performance bike anyway, and it'll roll faster downhill :lol:

I've gone up a 3 or 4 teeth on the rear sprocket (will check and re post) so the gearing should be (theoretically) unchanged, although the chain will obviously need to be extended. Tyre clearance should be OK but it may be on the rear limits, so a sprung chain tensioner might be required. We shall see....
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scrambler
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Re: NX250 AX1 spoke wheel conversion

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The rims look great! I like the shine - blingbling :D Do these rims have a certificate about the load capacity? Unfortunately, this is usually required by the German TüV.

I also think the wheels will be a bit heavier, but what the heck - the driver might lose a bit of weight to compensate :)
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jonathan
Beiträge: 127
Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 AX1 spoke wheel conversion

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I don't have the load rating but I'm fairly sure I could get the specifications from the manufacturer and do the maths. If the KTM rim was originally an 18 inch, these have shorter (stainless) spokes so theoretically stronger. The XL hub is the same as stock, aside from the rim being slightly wider. Honda used this hub on several models from the 125 upwards. Going off the weight and torque of an LC4 KTM, the rear wheel will be well over specced for a little 250cc with 30hp, and the load rating will no doubt be greater than the oem cast rim, especially with a larger volume tyre, but being able to demonstrate that to the Scheise-meisters at the TuV is another story :roll:

I offered both rims up this evening to check clearances etc. With the hub spacers I've used for the rear, I specced zero offset for the rim, based on my measurements (pieces of string, bits of masking tape, a long straight edge, two combination squares, some basic trigonometry and lots of re checking).
With the rim & spindle at full extension (back of the slotted holes), it measures 45mm on the chain side, from the very outside edge of the rim to the swingarm

and on the rotor side it measures....45mm, exactly :D :D :D

I was reasonably confident it would be central but there's always a nagging doubt...especially when you use bits of string :lol:

so now it's on with tyre shopping.

when I've sorted some tyres out I'll try to borrow my mates phone and take some decent pics and post the dimensions for the spacers, clearances etc for future reference. It's been quite a journey...you have a lot to answer for Scrambler ;) :D

remind me to treat you to a Masskrug or two if we ever meet
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scrambler
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Re: NX250 AX1 spoke wheel conversion

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Hi Jonathan,
haven't heard from you for a long time. Hopefully you're doing well and can enjoy your AX1 with the spoked wheels. In the meantime, I'm thinking of giving my AX1 a spoked wheelset too, but with an original 16'' rim at the rear. Tüv issues and what not ;)

Inconveniently, I can't find my drawings from back then anymore (since we Germans are soooo organized), so I have to measure everything apart again. This time, however, I'll document it in the forum so that it doesn't get lost again.

From left to right we start on the left, with the spacer for the cush drive. The 24,9mm must be strictly adhered to when turning the spacers. Too much and the spacer is difficult to drive into the wheel bearing, too little and the spacer sits too loosely in the wheel bearing. It's best to give the mechanic a wheel bearing / KTM spacer as a template for measuring. It's hard to measure so accurately with the cheap calipers I have. So it could be really 24.85mm, so please always measure yourself.

The second diameter of the KTM spacer is 40mm, but it rests on the narrow AX1 chain tensioner, so I guess one can take the smaller diameter of 34mm of the Honda spacer.

Bild
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