Laced a 21" rim to disc brake hub today

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deacon883

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I wanted to run a 21" rim on my otherwise stock '81 XS front end. I printed out the Fong Bros article and studied on it awhile. I cheated a little cuz I labeled each spoke hole, numbering the inside spokes 1-18 and the outside spokes 19-36. The 6:30-6:28 drill threw me but I checked it and because I numbered everything before:) I took it apart, it lined up just like they said. Finished lacing it up, took it over to a friends shop, (Wiccid Sickles in Phoenix) to have him true it. I'll get it back on Tuesday, have it reshod and mounted back on my front end by Wednesday night. Oddly enough, the difference in tire profile doesn't gain more than a half inch in height at the front axle. Pictures will be posted next week.:)
 
I've ben telling people that all along. The overall height between the 19 and 21 inch tire is close to the same. Not enough to make much difference. Under the engine you will get about 1/4 inch difference in ground clearance.
 
Same with 18" and 16" rear tires, not a really big difference due to the tire heights.
 
There's more of a difference in the rear. The tires are closer to the same width so the over all height is more on the 18 inch tire. If you have the 18 rear, 19 front and go with the 16 rear, 21 front, what you raise in the front you lower in the rear. If you run a speedo off the front wheel I think it will make the speedo read closer to correct. Most 19 inch the speedo reads about two mph faster than you are actually going. The extra height of the 21 inch makes the speedo read almost exactly the same speed as you are actually moving.
The 120/90-18 is about 26.5 inches tall. The 130/90-16 is about 25 inches tall. It won't be too noticable as far as ride height, but it will gear the bike a bike lower. About like changing the rear sprocket 1 or 2 teeth.
If you have a 120/90-18 on then put the 130/90-16 on it's like making the rear sprocket a 35 or 36 instead of the stock 34.
I think thats why the standards get better top end and slightly better 1/4 mile times.
 
Ok, here's a couple pics... The third pic is of the monstercraftsmen.com chain tensioner. I messed up when welding the brackets to the frame rail so I had to wind a wire spring by hand in the reverse direction. Worked ok, especially for my first attempt at spring making.
 

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Hey Deacon,
I was wondering if you could hook me up with some more information.
What make is your rim? Would any 36 hole rim work?
Also, wondering where you got your spokes from? Buchanan?

I love the look of a tall front tire, thanks for any info you can throw my way.
 
Mike's does carry 21" rims, but I went to my local motorcycle boneyard here in Phoenix and found a front wheel for $20. Bought the spokes from mikes. The first rim I found did not work, even though it was an Akront shouldered rim. Upon closer inspection, Yamaha used shouldered DID rims on my year XS. But it wasn't the manufacturer, since rims are delivered without spoke holes, it was the patterns not matching. So my advice, for what it's worth, is to take your current 19" rim with you to the junkyard and match it up with any 21" wheel with the same spoke pattern. The donor wheel I got had slightly smaller nipples so I did have to drill the spoke holes one size larger.

As a side note, Mike's XS has been sold and prices have risen as a result. There are several vendors on E-Bay selling spokes by the millimeter length. I will look into assembling some kits, provided I can spec the inside and outside spokes.
 
Cool, I might be hitting a salvage yard next weekend, time to Hunt!
So all I need is to source out a 21"rim with the same pattern. Pardon my ignorance, but does that mean the same number and inside/outside order, or am I missing something more about deciding if it will work?
I have a 79, are the hubs different by year? (therefore different pattern?)
 
Assuming it's a standard lacing patter, you need to measure the rim diameter at the spoke hole. To measure to the hub you need to have the width of the axle between the forks, the distance from the left flange to center of the hub and from the right flange to the center of the hub. Last, you need to know the diameter of the hub flanges at the spoke hole and what cross pattern desired.

Punch those numbers into a spoke calculator and bam.

As the OP said, you need to make sure the lacing patter in the same as the stock XS.
 
I realize you have acknowledged a mistake with the tensioner, but it still looks incorrect to me??

Shouldn't the sprocket be in the trailing side of it's pivot?

Am I loopy?
 
Tad, you are correct. If the unit were less stout, I would have had second thoughts about reversing the trail. It has sealed ball bearings, it's lined up within ten thousandths and if the chain ever gets loose enough for it to roll past 90 degrees, the fender will stop it before it gets into the tire. I expect to deal w/ a little chain stretch, but I have enough room under the fender to adjust axle position slightly. Good eyes, by the way!
 
Beau is right about the spoke calculations. I went up to my local harley speed shop and measured the Drag Specialties spokes that I posted earlier. Exact match to what I got from Mike's XS, so he may be buying them and marking up slightly.

RevD, one more thing to look out for: Make sure the rim you buy comes from a wheel whose hub was the same diameter on both sides. For instance, the typical drum brake hub from a later model dirt bike has a shorter spoke on the drum side. A disc brake hub would have the same length spokes on both sides. This means the angle of the nipple holes will be the same on the left and right sides of the rim. Confused yet? You won't be after you pick up a couple wheels and compare them to each other.
 
Deacon,
You used spokes for a 19" rim to lace a 21" one to a xs hub? Is there really exactly 2" difference in the diameter of the hubs?
Not wanting to cast doubt, just really stoked to do this too and want to make sure I have everything straight!
 

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