18 inch rear mag with disc

Im having a super hard time trying to find an 18 inch rear mag with disc. I am building a 79 650 and i know they dont come on the xs but they do on the rd 400 and various other bikes. I have checked everywhere i can think of, could anyone point me in the right direction. I already posted in the classifieds. Thanks.

I have a set I was going to use but ended up going with spokes. I was planning on putting them up on ebay with in the next couple of months. I have had them nfor a couple years now. thay are 1979 or 78. rd400 mags .look just like the xs wheel but are 18 front and 18 rear with rear disc. If your interested in them send me a message.

Look for an SR500 rear wheel.

i have even one the sr500 forum

Oh I thought you were just looking for bikes that had a matching 18" mag with disc.

Let people know where you're located - is it Maryland?

The RD400 wheel will work but it's a bit on the narrow side, plus the spokes are not shaped exactly like the XS spokes. I used an SR500 rear wheel, it's wider than the RD wheel and has the same spoke shape as the XS. It worked fine, I had to shift it .400 to the left by machining that much off the stock 650 sprocket side spacer and then making a similar thickness spacer for the right side from round aluminum bar stock. I also had to make a 3/16" spacer to go between the disc caliper mount and the right inside bearing spacer so that the caliper mount was centered over the rotor. The hardest thing was finding a steel 33 tooth sprocket, I wound up using a JT sprocket which was originally for a Honda CB500T and having the stud holes reamed.

For sprockets its surprisingly inexpensive to have custom ones cut. Number of sources - I had a 44t 520 sprocket made for $60 all in if I recall. Mine was by Rebel Gears www.rebelgears.com

My wheels are Honda CB750 front hubs laced to 19" vintage dirt track racing rims with a custom sprocket carrier for the rear that also has a 3rd bearing to carry the load. FZR1000 rotors on both wheels (same 6 bolt pattern as the Honda hubs which is also the same as Yamaha - 80mm on center).

Oh and yeah that's a 'front' tire on the rear hence the rotation arrow. Shinko 705's are all rated to run either front or rear, at least the bias-ply versions.

I'm in the same process right now. I've got the sr500 wheel and a xs400 wheel. The GIANT cush drive on the sr500 convinced me that the easier solution was to go with the 400 since the smallest sprocket I could find for the 500 wheel was something like 40 tooth. I thought that the rd400 wheels were the same (as the xs400), but I don't see any shape difference like 1974jh5 mentions, and the sprocket options are a lot closer.

I haven't solved all the problems yet, but the most significant seem to be the offset between the sprockets which by my measurements is 1/4". I've read some threads that suggest it is 3/8 per side, but it looks more like a 1/4 on the sprocket side and 1/2 on the disc side to me. By switching to 520 chain and sprockets and turning the offsets toward each other I can cut that 1/4 down to 1/8, so I see no need for a spacer on the sprocket side.

I'm thinking that I may run a different caliper, so that side I haven't worked out yet. The 400 has a 5mm disc, so that opens up a lot of options, but the bolt pattern is the same, so I could use the 7mm 650 disc as well. I'd prefer to use the lighter disc and a lighter caliper as well. My 500 wheel has the 5mm disc as well.

I can get bearings with the 400 od for the 20mm 650 axle, so that isn't a problem. Google will get me dust seals that will work with whatever axle spacer I use, I'm still not 100% what I'll use for those spacers, but I may just drill some round stock with a 20mm hole. The 500 wheel also has the 17mm axles, so this problem would have to be worked out as well.

Sorry for the wordy post, but I've spent the last week wrapping my head around this problem and I might as well share.

Thanks for all the info on the swap guys and yes I'm located in Maryland I think it says it under my name on the left. Marvel if u have two rear rims and u are only using one would you like to get rid of one

I'm holding on to it for now. SR500 stuff holds a lot of value to the flat track crowd, so I'm keeping it as trading stock. Plus it would be hard for us to be much further away and still both be in the continental US...

The spoke shape difference is right where the spoke 'flares' into the rim. The RD400 has a straight spoke in that area, the XS/SR spoke has a radius. In all honesty, if you don't look close you will probably never notice it.

There are bearings readily available which have the 20mm XS axle ID and the correct OD for the SR wheel. I don't recall the numbers off the top of my head but they are very common.

I did my rear wheel alignment by clamping a straight edge (angle steel) to the rear sprocket, then putting the other end against the countershaft. I had put the axle back in place and already had the distance from side to side with the stock XS rim with spacers axle etc torqued down. I dropped a plumb bob from the center of the frame and lo and behold, shifting the rear wheel .400 to the left not only aligned the sprockets but at the same time it centered the rim in the frame. Cool.

awsome news, i found a 18 in rear sr500 mag at a locale salvage place. Now i am using the david bird hardtail. Would anyone know the compleate bearing set and seals that i need by chance? I am gonna do some research on here obviously but i was just curious if anyone knew every oring seal and bearing that i needed. Alson i wanted to run a 33 t rear sprocket so i have to come up with something to get it to work. ill have to post some pics of my build.

Yes you do gotta post up some pics it's making me curious because I was thinking running a 18 mag too in the rear

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1974jh5 said:

The spoke shape difference is right where the spoke 'flares' into the rim. The RD400 has a straight spoke in that area, the XS/SR spoke has a radius. In all honesty, if you don't look close you will probably never notice it.

Click to expand...

I wonder if there weren't more than one design of 18 used on the 400. I can't find a difference in shape from it to my 16 off my 650 to the 18 off the 500. Also, I notice you mention above that the 400 was narrower than the 500. Mine are both 2.15. I'm betting some 400's came with a 1.85, and maybe that had the shape you're talking about.

1974jh5 said:

I did my rear wheel alignment by clamping a straight edge (angle steel) to the rear sprocket, then putting the other end against the countershaft. I had put the axle back in place and already had the distance from side to side with the stock XS rim with spacers axle etc torqued down. I dropped a plumb bob from the center of the frame and lo and behold, shifting the rear wheel .400 to the left not only aligned the sprockets but at the same time it centered the rim in the frame. Cool.

Click to expand...

I haven't done this yet as the frame is gutted right now - engine work. I got my measurements by measuring from a straight edge on the rim edge to the sprocket center, then measuring rim width. I'll have to do bearings first and fake it together before I build spacers and try your method, see where it looks right.

The sad part is this is all simple compared to the nutty plans I've got for the front end...

Hi.

Here´s a setup with a xs400 front wheel. Homemade spacers and such.

BigBoreSwede

Rear from an xs500 also fits in, with the required adaptor. It is 2.15, wide with the same spoke radius as the front.

kiwi said:

Rear from an xs500 also fits in, with the required adaptor. It is 2.15, wide with the same spoke radius as the front.

Click to expand...

Researching what it takes to fit an XS500 rear mag wheel with disc into my 1980 XS650 disc mag rear and wondering if this adapter is an off the shelf item and if so, who sells it ?

TIA

I made an RD400 wheel fit some years ago: http://www.xs650.com/threads/lets-see-the-xss.170/page-160#post-355798
Custom spacers, new bearings, stock rear disk with custom offset spacers to align the brake caliper bracket and the rubber sprocket bolt thingys replaced with aluminum bushings.