18" rear tire rim guru question

[soccer4m]

rim and tire info.

Hi Nortonrider and egsols,,,,I do not understand the left of center or whatever you said for the 17" rim,,,I never had that rim on. The tire on the 16" rim is a Metzeler me880 130/90-16 and the 18" rim has a Kenda Challenger 120/90-18.
The Metzeler tracks and is an outstanding tire. I bought it for my daily rider, the xj1100 and the Kenda is also very good, but I wasnt sure if the Metzeler size would fit in an 18" so I got the Kenda, plus I am cheap and thrifty. Anyway, for anyone looking to drop the revs, like a sixth gear it is an easy project....I think the original rim on the 80 xs was a 16" but when I picked it up it already had the 18" so started the thread to find out what it was off of.

Regards, Mike in Sunny Diego, xj and xs refined beasts of machinery

[oldnortonrider]

soccer, you said~~ "18" rear tire rim guru question
Fellow xs,xj'rs, I picked up an abused, 80'midnite special,1100 with an 18" rear rim. This is not the factory 16 incher..........."

and later mentioned~~ "..........Thanks for the replies,,,,the tire is the straight cast spoke, and says-mt2.15 x 18. I am running a kenda 120/90-18........."

What I'm thinking~~is that the original 16 inch wheel which was on it before the 18 inch wheel was put on~~was an mt2.50 x 16, which would have been 2 and half inches between the inside of the metal part of the wheel rim that holds the beads. That line in the center that would run forward to front of the machine would be different, after the mt2.15 was installed. Center line of the rear wheel, rim, and tire has been moved to the left. Wouldn't line up with the center line of the front wheel rim. Geometry. mt2.15 means two and 15/100 of an inch measured on inside of wheel rim (when tire is off).

May have confused you more; hope not.

[fredintoon]

Offsets.

I gotta simple mind, let me try?
Let's say the original 16" x 3" (well, mine is 3"wide) rear wheel ran it's tire directly behind the front one. So we put on a narrower 18" rear wheel and so long as it fits it don't matter to this discussion what it came off.
The next thing we say is that the new rim was also made to run directly behind it's front one.
Now we must ask ourselves, is the offset from where the wheel plugs into the final drive to where the middle of the tire is the same for both those rear wheels?
If yes, the tire on new wheel will be where the tire on the old wheel used to be.
If it ain't, the new wheel's tire will be offset by that difference.
But finally, who gives a toot? There's Beemers that are deliberately built with their rear wheels offset.

[soccer4m]

rim size offset

You guys are figuring out all the variables for the larger rim,,,,the new 18" rim sits exactly centered between the rear swingarm and is the same distance from the arms as my 16" xj1100. So, the rim must have the same distance from the final drive unit as all the xs, xj1100's. Its too hard to measure without pulling off both rims and using a big caliper. Measuring with a tape, while mounted it measures the same. Yamaha must have made that overall width the same for both rim sets. So,,,,I see no problem for those inclined to pop on a 18" xj rim and drop the revs overall. Only difference is that the xs 18" is a bit slower off the line, so I just gun it more and after first its still a beast.....regards Mike, xs,xj1100's

[soccer4m]

pics of the measurements

pics of the measurements.................

[oldnortonrider]

Yer gettin' closer..................; that 120/90 (x18) tire would be about 10mm skinnier than the 130/90 on the wider original rim. IF the 120/90 is centered with the "motorcycle centerline", the tire should be about 5mm extra clearance out away from where it misses the inside of the driveshaft housing. Eyeball it and see if it appears to have a good bit of clearance; original is just a bare miss. You might look at the "miss" on your other machine, that has the 130/90 to see what the clearance originally would have been (roughly) on the one that now has the 18 inch~~MT2.15 on it. If they're both about the same....................not centered on your MT2.15 .

Another way you can tell , and this is the way we did it, back in my boy racer days (as in road racing)~~have somebody sit on the machine, cuz they're gonna need to move the front end teeny tiny bits, while you get down in front of the machine on a flat level cement floor~~getting down on yer knees, in front of the front wheel, at a right angle; bend over about 3 feet in front, head down, eyeball at ground level~~line up the bottom of the front wheel with the bottom of the back tire. On a driveshaft machine that back wheel doesn't get cocked at an angle, like all the chaindrive jobs do, after a bunch of chain adjustments, and this is how we got 'em true. You can get 'em right on the money.
When you're doing this with the one that has the 18/MT2.15 on it, you can tell when both wheels are dead on straight ahead. Back wheel already is. Now when you've ascertained front one is pointed in the exact same direction as the back one, CENTER the front wheel in your line of sight with the back one. You've got to concentrate. I was a sniper shooter, in my younger days, so it may come natural to me. One of the ways that I remember that I could really fine tune the alignment, was to see if I could see some of the wall of the rear tire on one side........you'd have to get the side wall picture the same ........., and then check/glance at the front tire.

I guess I could write 5000 more words, to explain better, how to do this. When these chaindrive guys see that "offset" on the rear; where it's either to the left or right of alignment with the front one, when pointed exactly straight ahead, it makes 'em sick. Hard job to change it; usually can't.

OK, see what you can come up with. I figured you'd like to know, when I saw the pics.

When you've got your head down, doing that alignment~~zoom in and zoom out~~sorta change that distance that you have, to get a better feel for any possible offset.

[fredintoon]

7%

Hi Mike,
in the photos your tape sez the tires measure 83-5/8" and 78-1/8" My mathbox sez that's a 7% difference.
OTOH you previously posted that the tire change reduced your revs by 15%.
How's that work?

[oldnortonrider]

heh-heh ~~handy, dandy pocket tool for offset alignment ~~

[/IMG]

.........cheap; $1500.00!

http://www.ascycles.com/detail.aspx?ID=1239

[soccer4m]

final diagnosis of 18" rim

After riding 1100 miles to the Yosemite rally, side by side partly to measure, the specs are in for this 18" rim conversion. The speedo on my 16" rear xj shows 4100 rpm's at 60 mph,, and the 18" rear on the xs reads 3800 rpm's at the same 60mph. But the speedometer reads the same driving me to finally figure out the front wheel drives the speedometer and the engine,rear drive drives the rpm's-tachometer. So, the savings is "7.8%" simulating a 6th gear for those comtemplating a quick rim switch for the bikes{info, thanks to Alan B in England and the prodding of Fred in Canada}So, I rest in peace knowing how and why the 18" rim reduces the engine rpm's. Again, a 18" xj750 rim pops right on and works well,,,,,,,,,,regards, Mike in hot S.Diego this week

[AlanB]

Hi Guys,

Typing mistake in soccer4m's last post; A swirly 18" rim from an XJ750 will NOT fit straight into an XS11!!

XJ11 fits with its own spacers, as does the straight Spoke 18" rim from an XS750.

XJ750 goes in, but needs a lot of work; no easier than fitting the 4.00x17 from the euro XJ900......



And I am in SCOTLAND, the British country above england on the map.......

It is a bit like us calling all Americans Texan, just because Texas is quite a large part of America..........

AlanB

[soccer4m]

rim

Sorry about that Alan, I didnt look at past post carefully -

{Seca wheels don't fit the XS11 without serious work.
The XS750 and 850 Standards used an 18" rim which is a straight fit for the XS11.That is probably your source.
As a check, our Seca had Swirly/Girly wheels, the 750/850 range had straight spokes.XS650 Standard did use an 18" rear rim, but it was chain drive. Does NOT fit the 1100.My info comes from UK; apologies if it does not fit with US bikes!
AlanB}
Here is a pic of the straight spoke xj750 rim on the 1980 xs1100 midnite spec.

[fredintoon]

And I am in SCOTLAND, - - -

" - - - the British country above england on the map.......
It is a bit like us calling all Americans Texan, just because Texas is quite a large part of America.........."

Hi Alan B,
OTOH, back during WW2 in Somerset UK my very Christian uncle would give Bible classes to the (at that time segregated) coloured US troops stationed in the area.
Those Alabama baptists would go into fits of laughter whenever we called them "Yankees".

[AlanB]

Hi soccer4m,

If that pic does show an XJ750 rim on your XS, then we obviously got different bikes with the same names on opposite sides of the pond; none of the XJs had the "artillery" (straight) spokes on this side.

AlanB

[soccer4m]

XS 18" rim, not XJ 18" RIM

I stand corrected thanks to Alan B of the great nation of Scotland, The conversion is an xs rim, 18", not the xj rim.So, those running off getting all the xj rims on ebay, get the xs rims,

http://i291.photobucket.com/albums/l...maha_xs850.jpg
18"





So, after all the info. sharing and measuring to find out what I had on the xs1100, were back to around an 8% drop in revs with the rim switch, late 70's750, or 850 rim, easy swap for those inclined.....regards, Mike in Hot S. Diego