Swapping Rear Wheel Advice Needed: From 16" to 17" or 18"

EvenmoreXS

EvenmoreXS

1981 XS650
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Looking for a little guru advice:

I am wanting to swap my rear wheel and tire. Currently im running 19 front spoked with disc, and a 16 rear, spoked with drums. I want to do this as easily as possible so going to a rear that has drum brakes and is spoked is the most likely candidate....

My original plan was to go to a 17 inch rear wheel but I don't think that's going to work out.....Next up would be the 18....Naturally.

I found that a Standard 18" rear tire should be a direct swap to mine...a special....frame is an 81. As long as I keep the drum in back I should just have to remove the old and replace with the new.....Is this correct.? Am I missing something. No new swingarm going drum to drum... right?


Does anyone have any pics of bikes running 19 front 18 rear with spokes???


I think Im going for a salt flats / board tracker type look...maybe Im wrong bout that.


This swap should raise my tail just a bit and I may need slightly longer / stiffer shocks, But I want to fill the wheel well a bit more in the back.

I want the back tire to appear the same size or just a smige smaller than the front.



If all is well.....does anyone have a 18" rear Standard in good shape to get rid of ? Barter, or for sale.


Also tell me If you think Im crazy.

Photo of the offending beast is attached.



Thanks Everyone !
 

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We have 2 XS650s and one has the 18 inch rear wheel and the other has the 16 inches and we can put either one on either bike with out changing a thing so it is a direct bolt on deal
 
Hi Evenmore,
of course you are crazy but no more than the rest of us, eh?
Like oldcoal sez, ALL drum brake rear wheels swap no hassle.
FWIW, you can swap a drum rear wheel into a disk rear bike by welding an extra torque stay bracket onto the swingarm and swapping in the drum brake torque arm and operating pedal hardware.
Disk rear wheel into a drum rear wheel frame is the same deal in reverse plus you have to weld a bracket onto the frame to hold the rear master cylinder.
I'd suggest you find a pair of the '75 thru '77 aluminum rim wire wheels because they look the best.
 
Big thing to watch is number of teeth on the rear sprocket since changing the rear wheel from 18 to 16 or the other way around does change the gearing of the transmission. So it can cause it to have a higher top speed but suffer lack of fast take off at the line
 
If you want pics look in the Sticky "ID thread" in the Garage

All Standard XS650's from 70-79 had 19F/18R wheels. The profile of the rims changed in 74 to alloy mud-catcher rims. If you want to keep the same profile rims as you have then any 70-73 rear 18" chrome on steel rim will work with your hub or a complete rear wheel will swap in. Any rear 36 spoke hub, (or whole wheel), from a 70-79 standard or a 36 Spoke rear hub from 79/80/81 Special II will match up with an 18" rim.

The difference in wheel circumference between the 16" and 18" is negligible. Going by Pancopetes gear ratio chart the 18" wheel has a 75mm, (3"), longer circumference when measuring for ground distance. This is why the 18" rear wheel and a 33 tooth sprocket, (euro standard combination), is considered to be the best gear sprocket ratio match for an xs650.
 
Last edited:
here is a pic of 72 xs650 with 16 rear 19 front. the forks have since been shortened to normal length.
 

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The 16 to 18 rim swap is simple if you stay with drum brakes. The profile of the 16 w/ a 130 and an 18 w/110 tire is just about the same... So no change in height. What makes the biggest difference in height would be a longer shock... 13.5" is what I've found to be a good cure for the lowered rear of a special.

Not sure I agree with any gearing issues, as the 18 and 16 rear rim had a stock 34tooth sprocket I believe... Unless you drastically change tires or the 80+ yrs had a different tooth count?

I've done this change on my '79 special II, you can check out my album for pics.
 
How long is a peice of string?

Will need a set of spokes as well so there is another $30.00, (from Mikes).

That is something you will have to weigh up.

They are getting harder to find but again $275.00, (with freight), + spokes and re-spoking and the rim is not in VG condition as can be seen in one of the pics, it has been rubbed and there are scratches on the chrome.

How desperate are yo to do this?

Could look for a long time for another or one could pop up tomorrow.

Mikes has an 18" rer rim in the profile to match your front but is is alloy and out of stock. $100 + $35 for spokes., could pick ip a hub for $50 or there a bouts.
 
Brassneck said:
The 16 to 18 rim swap is simple if you stay with drum brakes. The profile of the 16 w/ a 130 and an 18 w/110 tire is just about the same... So no change in height. What makes the biggest difference in height would be a longer shock... 13.5" is what I've found to be a good cure for the lowered rear of a special.

Not sure I agree with any gearing issues, as the 18 and 16 rear rim had a stock 34tooth sprocket I believe... Unless you drastically change tires or the 80+ yrs had a different tooth count?

I've done this change on my '79 special II, you can check out my album for pics.
Click to expand...


Thanks for the reply.

More rim and less tire sounds right....as long as I can fill just a bit more of the space under my rear fender. Everything else can stay as close to how it is as possible.
 
Brassneck said:
The 16 to 18 rim swap is simple if you stay with drum brakes. The profile of the 16 w/ a 130 and an 18 w/110 tire is just about the same... So no change in height. What makes the biggest difference in height would be a longer shock... 13.5" is what I've found to be a good cure for the lowered rear of a special.

Not sure I agree with any gearing issues, as the 18 and 16 rear rim had a stock 34tooth sprocket I believe... Unless you drastically change tires or the 80+ yrs had a different tooth count?

I've done this change on my '79 special II, you can check out my album for pics.
Click to expand...

Love the black and gold pin-striping. really makes the bike. Done a great job.

18" rear and 33 tooth sprocket was a Euro combination 18/34 was US
 
650Skull said:
How long is a peice of string?

Will need a set of spokes as well so there is another $30.00, (from Mikes).

That is something you will have to weigh up.

They are getting harder to find but again $275.00, (with freight), + spokes and re-spoking and the rim is not in VG condition as can be seen in one of the pics, it has been rubbed and there are scratches on the chrome.

How desperate are yo to do this?

Could look for a long time for another or one could pop up tomorrow.

Mikes has an 18" rer rim in the profile to match your front but is is alloy and out of stock. $100 + $35 for spokes., could pick ip a hub for $50 or there a bouts.
Click to expand...


I got some time to wait. No hurry. Other irons in the fire too. Also doing some frame work....some new side cover tabs.....fork oil needs new-ness.....clean carbs, been a year and a half since last cleaning......would love to redo the clutch... This back wheel is just part of the agenda. I can start at the front and work my way back.

I appreciate all the feedback though. Now I know WHAT to look for.

Thanks.
 
I had occasionj to revisit my RPM vs MPH Excel spreadsheet and corrected the nominal rolling distance for the 16" rear wheel. It is essentially the same as the 18" (1" difference)

Click here for the spreadsheet > RPM vs MPH

RPM at 60 MPH for the 18" wheel is 4117 vs 4170 for the 16" with stock 17/34 sprockets.

When calculating RPM vs MPH, you have to use rolling distance as there is no way to calculate or measure the effective diameter or the effective circumference of a motorcycle tire. Rolling distance is the distance that the motorcycle moves forward for one revolution of the rear wheel.
 

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