18" or 16" rear tire?

SinisterMatti

SinisterMatti

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I'm in the process of starting a scrambler build. I went to the local yamaha shop and they told me I have a 19" wheel on the front and a 16" wheel on the back. I have a standard 1978 XS650 (spoked). I was about to order http://www.amazon.com/Bridgestone-Trail-Enduro-Motorcycle-100-19/dp/B005J8WX0S and http://www.amazon.com/Bridgestone-Trail-Enduro-Motorcycle-90-16/dp/B005J8WYZ2 when I saw some people saying they had a 18" rear tire on the standard. Can anyone confirm which size I would have? I've looked all over the tire I currently have and there are no dimensions on it and I'm not sure how to accurately measure tire size. Thanks!

my1ZXWd.jpg
 
Looks like an 18", but measure it. You definitely have a 19" front...so measure that. Then take those same points to measure the rear (If I recall, I think you measure right below the outside edge, where the lip flairs out).
 
The size you are referring to is just the diameter of the rim.

If its 16" across, you have a 16" tire.

Also, i thought all tires were required to have markings.
 
In 78 and 79 they made three models. The standard, the Special and the Special II. The standard had an 18 inch rear, the Special had the mag 16 inch, the Special II had an 18 inch front and 16 rear alloy with no flanges.
In your pic it shows that both wheels are flanged, they only made them in a 19 inch front and 18 inch rear.
All tires should be marked with the tire size on them. Something like 110/90-18 is the standard rear size. The 16 inch is a 130/90-16.
The first part of the number is the width of the tire, the second part is the aspect ratio, Or the percentage of tire height versus width. The last is tire diameter.
The aspect ratio is a percentage. as in the 90 means the height of the tire from the beads out to the tread is 90% of the width of the tire. Take the 110/90-18, this means the tire is 110 mm wide, the A/S of 90 means you take 90% of the width, as in 110 x 90% or 99 mm. This is how tall the tire is from bead to tread. The 18 is the diameter of the tire bead to beads. AS in 18 inches.
Leo
 
Last edited:
XSLeo said:
In 78 and 79 they made three models. The standard, the Special and the Special II. The standard had an 18 inch rear, the Special had the mag 16 inch, the Special II had an 18 inch front and 16 rear alloy with no flanges.
In your pic it shows that both wheels are flanged, they only made them in a 19 inch front and 18 inch rear.
All tires should be marked with the tire size on them. Something like 110/90-18 is the standard rear size. The 16 inch is a 130/90-16.
The first part of the number is the width of the tire, the second part is the aspect ratio, Or the percentage of tire height versus width. The last is tire diameter.
The aspect ratio is a percentage. as in the 90 means the height of the tire from the beads out to the tread is 90% of the width of the tire. Take the 110/90-18, this means the tire is 110 mm wide, the A/S of 90 means you take 90% of the width, as in 110 x 90% or 99 mm. This is how tall the tire is from bead to tread. The 18 is the diameter of the tire bead to beads. AS in 18 inches.
Leo
Click to expand...

Great info! thanks!
 
Is the different rear sizes have any effect on performance? I have a 16 currently and was thinking of going bigger. Any noticeable differences? Other than looks

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Going to a larger tire is often a problem. Some tires are wider at any given size than others.
When I got my 75 it had a Dunlop 120/90-18 on it. When I went to get new tires I put on Kenda Challenger tires, A 120 was to wide, rubbed on the swing arm. A 110 was just right, cleared the swing arm fine.
So the only ting I can say is try it.
On these old bikes going to a wider tire slows the steering response.
Leo
 
solo2racr said:
Going from a 16" to a 18" will change your overall gear ratio. It would have the effect of dropping a few teeth on the rear sprocket.
Click to expand...

I think that would only be the case if the 16" tire were significantly different in size...pretty sure that an 18" rim with a 110/90 and a 16" rim with a 130/90 are close to the same diameter...and different tire brands will vary.
 
It is based on both. The info came from this web site .....

http://www.gearingcommander.com/

They have the 650 Special w/ the 130/90-16 in their data base. One of the initial entries can be changed to a 110/90-18 to get comparison figures. I don't know what tire or tires they base their tire circumferences on but according to their figures, the 110/90-18 has about a 2" bigger circumference than the 130/90-16.
 
That's interesting, as my old tire...(130 on a 16" rim) and my new tire now on an 18" rim (110) is only about about 1/2" wider...not sure the brand of the old one...I sold it off...the new one is an avon.
 

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