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Originally posted by cywelchjr
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These bikes came out just as they were transitioning from the 'old' inch system to the new metric sizes. If you look at the factory brochures from the day, they show the special as having the 130/90-16 as OEM with the '79 model. I'm not sure when the metric 17s came in, as the inch size was still being sold as a replacement after the XS was out of production. The one I have I got in '83 or '84...Fast, Cheap, Reliable... Pick any two
'78E original owner - resto project
'78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
'82 XJ rebuild project
'80SG restified, red SOLD
'79F parts...
'81H more parts...
Other current bikes:
'93 XL1200 Anniversary Sportster 85RWHP
'86 XL883/1200 Chopper
'82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
Cage: '13 Mustang GT/CS with a few 'custom' touches
Yep, can't leave nuthin' alone... -
Got a chance to clock my tall final/tire combo. Reads 65 MPH at 3.4K, with a light 5 MPH tail wind.
2H7 (79)
3H3
"If it ain't broke, modify it"
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I think I've figured just what the difference was...
A 130/90-16 tire is 25.16" in diameter (Dunlop 404 as per their website). I know there's variations between brands and even models in the same brands (the EliteII in the same size is 25.7"), but for comparison purposes I'm using this 'tire line' as Dunlop also offers a 130/90-17 in the 404, which is 25.97". So, figuring circumference on the 16", you come up with 79.05". Add 5% to that and now you have 83.0". Figure diameter, and that works out to 26.42" for a 4.50H size. A 'modern' 130/90-17 is only 81.6" in circumference, for about a 3% difference. So...
4.50H-17 tire = 3.3:1 ratio; original XS standard.
130/90-17 replacement = 3.4 ratio.
130/90-16 'special' wheel = 3.47 ratio.
I couldn't find a 130/70-17 in a Dunlop, but their closest size (140/70-17) is still smaller than a 16" tire by 1%, so that would put gearing down to to nearly 3.5:1. That's why your motor was buzzing....
Also makes sense in comparing my new 160/80-16 to the old 4.50; as I've noted, even worn this tire is still slightly larger, and diameter spec on this size is 26.2". So even this is 1% small compared to original; I'll have an effective ratio of 3.33:1.Fast, Cheap, Reliable... Pick any two
'78E original owner - resto project
'78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
'82 XJ rebuild project
'80SG restified, red SOLD
'79F parts...
'81H more parts...
Other current bikes:
'93 XL1200 Anniversary Sportster 85RWHP
'86 XL883/1200 Chopper
'82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
Cage: '13 Mustang GT/CS with a few 'custom' touches
Yep, can't leave nuthin' alone...Comment
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Rpm
I am around 3750 at 60mph indicated. My speedo in kilometers reads about 3km over actual, according to the speed radar signs we have on the highway.Originally posted by bikerphil View PostGot a chance to clock my tall final/tire combo. Reads 65 MPH at 3. K, with a light 5 MPH tail wind.
My big white numbers show kilometers and the smaller yellow numbers show MPH. My tach wanders after in gets warm and or the revs increase.
But I seem to be turning a few more revs than you. I have not checked the rear tyre size.
Your message quoted above may have been altered by a mistroke on my part.
Please blame the Piper's Pale Ale on special at the local watering hole.
Uncle Crusty ( wifi at Starbucks )Comment
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