18" rear tire rim guru question

[soccer4m]

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. Anyone know what other model this came from?? I did a little checking and saw the old seca models had an 18" rear, other than that none of the xs,xj 1100 models had that size. The bike runs fun, no whining or weirdness. Its kind of cool to run at much lower rpms than my xj. So, just wondering if anybody knew what rim this came off of??????? Mike in Sun Diego

[John]

The 79 XS 750 SF had an 18" wheel, I'm not sure about the 850 SG though.

[prometheus578]

"I know you're busy, and all..."

But when you get a chance... maybe a picture would help us out.


XS850 special has a 16" wheel.

[SanDiegoMike]

Congrats on your find! I thought i read on here somewhere that the 18 incher was used on the 650's(?), but I could be wrong. Still looking forward to meeting you soon. My bike is down HARD right now for what I believe is an electrical problem w/the PUC...should be able to fix it this weekend though...I hope.

The OTHER Mike in SD

[AlanB]

Hi soccer4m,

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

[egsols]

What size tire would that be carrying and how difference in final diameter/circumference would we be dealing with as opposed to the 16" with a 130/90?

How bout a 18" combined with the 750 final drive?

[AlanB]

Hi egsols,

I don't know how the numbers work out, but Yamaha thought that the 750 could pull the 18" tire with the 750 bevel ratio........... I am SURE that the 1100 can manage the same ratios.

AlanB

[egsols]

Hi Alan,

What I'm wondering is, with the 750 final mod we are dropping the ratio...wouldn't it drop even more if we stick on a 18" with a larger circumference than the 16"?

[soccer4m]

My 18 inch tire

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. My xj has a radius of 12", center to outside of tire, this one has a radius of 14" to outside edge of tire. No clearance problems top or side. The engine revs are 15 percent lower. I verified by riding then calculated also, using 2 pi x radius for both sizes and the 18" tire has a circumference of 88" versus 75.4" to justify the 15 percent drop in revs. Maybe there will be a run on the xs750 and xs 850 rims for an easy way to drop the highway revs on these bikes. I will send pics as soon as I figure that process out....regards again, Mike in a HOT Sun Diego this weekend,,,,,pushing 100 F.

[egsols]

pushing 100 F

Better than pushing a 1100SF

BTW we have been blessed with mid 40`s and rain!!!!

[egsols]

On a serious note, that means you are gaining 2 inches in ride height and losing 2 inches in travel. 15% is a big difference especially if one combined that with a 750 final. I don`t know if I would want to sit up an extra 2 inches though. If I wasn`t over 6 feet I `d prefer mine even lower.

[John]

Wouldn't you only be one inch higher with the 18 inch vs the 16 inch wheel? The distance (radius) from axle center to the edge of the rim would olny be one inch greater.

[soccer4m]

rim

To John,,,that would normally be good thinking to have only one inch on each side of the rim but I measured by xj1100 versus the xs1100 special and that came out to a two inch difference in radius to the edge of the tire. So, I assume it would be two inches higher but the xs1100 special never had the smaller rim to compare. The xj is 16 inch rim size and this one is 18 inch rim size so two inches on the radius is correct, unless the radius gods are changing things? Anyway, the revs at freeway speed are way down compared with the xj, so it could be an easy modification for those to slap on a rim and drastically lower there revs. I wiil get back to what difference the mileage is, if any. Regards, Mike in Hot Sun Diego this weekend.
Mike-xs1100,xj1100, and other assorted bikes

[fredintoon]

Sloppy tape work?

Hi Mike,
I think your tape measure slipped or perhaps your astigmatism kicked in.
My mathbox says a 120/90-18 tire has a theoretical outside diameter of 26-1/2" and that a 130/90-16 tire has a theoretical OD of 26-1/4". That ain't no 15% difference, right?

[egsols]

My mathbox says a 120/90-18 tire has a theoretical outside diameter of 26-1/2" and that a 130/90-16 tire has a theoretical OD of 26-1/4".

Fred did you use the equation out of your math book that says the width is 120MM times 90%=the hieghttimes 2 plus rim diameter=26-1/2"? I like the disclaimer "theoretical".

I have bridgestone spitfires, the 130 should be 5.11" but measures 5.4" which coincides with Bridgestones chart,

http://www.totalmotorcycle.com/photo...pitfireS11.htm

On this chart the 130/90 16 has a width of 5.4" and an overall diameter of 25.1" giving it a theoretical ratio of 84% (Does the ratio include the bead height maybe?)

They list a 120/90-18 at 26.7" and 5.0" which gives us 87%

At any rate the difference in circumference between the 18 and 16 by Bridgestone is just over 6%.

If one where to go with a 130/90-18 it would increase to 27.4" and 5.3" for 9%

Wouldn't you only be one inch higher with the 18 inch vs the 16 inch wheel? The distance (radius) from axle center to the edge of the rim would olny be one inch greater

Yes it would but I was using soccer4m's numbers being 24" and 28" in diameter----4"/2=2"

Lastly, after looking at a few different charts I have come to the conclusion that not all tires are created equal. Depending on manufacturer you can get a 130/90-16 at 5.1" wide up to just over 5.4" wide. I quess the numbers on the side are to be used as a guide only and the author assumes no responsibility for any errors or omissions contained therein

My $0.02 worth.