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Old 05-09-2015, 05:38 PM   #1
Stick_man OP
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tire sizes old vs. metric

Can someone tell me tire sizes? I have harley sx 175. My manual calls for 3.00 x 19in. (front) and 3.50 x 18in (rear). When I first bought the bike years ago a mechanic installed 100/90-19 (front) and 110/80-18 (rear).
I needed a rear tire and found a cheng s 3.50 x 18in on ebay and took the wheel and tire to mechanic. After bringing the wheel home from the shop and mounting it - it looks so small. Is this OK?
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Old 05-09-2015, 08:02 PM   #2
Andy-Gadget
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The joys of mixing metric and imperial together, made to order stuffup like landers into Mars

The old designation, 3.00 x 19 is the width of the tyre across the widest part of the side walls, in inches, when the tire is fitted to the correct width rim and inflated to the correct pressure, so 3 inches wide. On older tyres, the aspect ratio, the shape of the tire, is assumed to be 100%, on bias belted tyres, so the modern metric equivalent would be (3" x 25.4mm = 76.2mm) 75/100 x 19, not an easy size to find.
The back is 3.5" x 25.4mm = 89mm, so 90/100 x 18 is as close as you will come.
This is a very skinny tyre, trust me.

The modern equivalents you have quotes as 90% and 80% aspect ratio tyres, so the crown (centre) of the tyre to the rim is 90% (or 80%) of the width, so 110mm x 0.8 = 88mm, so the rolling diameter is close, but the bike will handle differently due to the tyre being wider than the old bias belted tyre.
The front tyre is greater in diameter than the old one, 100 x 0.9 = 90mm.

Clear as so much mud?

Quote:
Originally Posted by Stick_man View Post
Can someone tell me tire sizes? I have harley sx 175. My manual calls for 3.00 x 19in. (front) and 3.50 x 18in (rear). When I first bought the bike years ago a mechanic installed 100/90-19 (front) and 110/80-18 (rear).
I needed a rear tire and found a cheng s 3.50 x 18in on ebay and took the wheel and tire to mechanic. After bringing the wheel home from the shop and mounting it - it looks so small. Is this OK?
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Old 05-09-2015, 08:22 PM   #3
ctfz1
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Tire Size

Most tire Brand web sites offer official conversion charts.
From one:
2.75/3.00 tire 18/19" MJ/90 90/90
3.23/3.50 tire 18/19" MM/90 100/90
3.75/4.00 tire 18/19" MN/90 110/90

There are variations on mounted wheel size dependent on actual rim width and actual tire size.
Some tires run small some large.
Some tires before my time I think were 1:1 aspect ratio, before /90, /80 arrived. Some OEM rear tires were /80 profile. When to when I do not know.

If you can check original rim and tire specifications, and mounted tire diameter. Proper size for rim width is important. For a long time back when people tried to fit the largest tire sizes they could get away with.
Today most people try to fit to rim width.
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Old 05-09-2015, 08:58 PM   #4
fxray
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Quote:
Originally Posted by Stick_man View Post
Can someone tell me tire sizes? I have harley sx 175. My manual calls for 3.00 x 19in. (front) and 3.50 x 18in (rear). When I first bought the bike years ago a mechanic installed 100/90-19 (front) and 110/80-18 (rear).
I needed a rear tire and found a cheng s 3.50 x 18in on ebay and took the wheel and tire to mechanic. After bringing the wheel home from the shop and mounting it - it looks so small. Is this OK?
Probably not. They quit importing/selling Cheng Shin motorcycle tires in the U.S. in about 2008. That would make your eBay tire at least 7 years old, so it is past its shelf life.

You can buy those original sizes from Heidenau. Those are the same sizes that were original fitment on my CL350 Honda. I put a set on last year and have been happy with them except the rear is about ready to be replaced already after only about 3400 miles.





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