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post #1 of 7 (permalink) Old 04-07-2019, 01:14 PM Thread Starter
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Bigger front tire

I have a 98 Vulcan 800A...I don't like the skinny looking front tire. Stock 80/90-21inch....everyone asks me if it's flat and needs air! I want something a little wider and taller. What is the biggest size I can use without it affecting the handling?
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post #2 of 7 (permalink) Old 04-07-2019, 05:39 PM
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The tire specs will give you the diameter. You'll have to look at how much clearance you have between the forks and under the fender. You could then make an educated guess as to how wide you can go.

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post #3 of 7 (permalink) Old 04-10-2019, 06:23 PM Thread Starter
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Thanks...sorry but I should have asked how big of a tire can I use on the stock rim without it having any issues.Thought maybe someone has done theirs and had a tire size to show me.(pic?) I want to keep the fender on. I'm having trouble ordering one online because it always says, this will not fit your motorcycle.
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post #4 of 7 (permalink) Old 04-11-2019, 09:42 AM
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Measure your wheel/tire radius >> measure from garage floor to center of axle. And measure the amount of fender clearance. You can compare those numbers to the following math, but you'll have to investigate & determine whether or not a larger tire is safe to use. From the diagrams at Partzilla the 98 VN800-A4 rim is 1.85 x 21 >> 1.85 is the width of the rim in inches. 1.85 is a narrow rim, so this will limit what tire you can safely install. I tried the tire-rim search at Dunlop, but did not see mention of the rim width.

Wheel & tire math. 80/90-21 >>
21 = wheel diameter in inches
80 = the width of the tire in mm.
90 is the tire section height expressed as a percentage of the tire width.
Section width = 80 x 0.90 = 72 mm = 2.835"
Tire diameter = (section width x 2) + wheel diameter = (2.835 x 2) + 21 = 5.67 + 21 = 26.67"
Tire radius = diameter/2 = 13.34.

Math for a 90/90-21 tire.
Section width = 90 x 0.90 = 81mm = 3.189"
Tire diameter = (3.189 x 2) + 21 = 27.38
Tire radius = 27.38/2 = 13.69"
So a 90/90-21 tire should have about 0.35" larger radius >> larger radius = reduced fender clearance.

You can do the math for a different tire.

Circumference & speedometer. A larger tire will give a slightly different speedometer reading.
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Last edited by martin-csr; 04-11-2019 at 09:44 AM.
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post #5 of 7 (permalink) Old 04-11-2019, 09:55 AM
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If there is fender clearance for a larger tire, but a larger tire is unsuitable for your rim, you could get a different rim laced to your hub. probably expensive, but it is an option. You'd also need to check if the larger tire is too wide.

Circumference & speedometer. A larger tire will give a slightly different speedometer reading. The stock tire spins about 755 revolutions per mile, but a 90/90-21 spins about 736 times per mile, so it spins fewer times to cover a mile & I think it will give a lower speedo reading by about 3%. 736/755 = 0.97


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post #6 of 7 (permalink) Old 04-11-2019, 10:13 AM
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Edit for my first reply above: meant to type section height, not section width. the commonly accepted term is aspect ratio.







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post #7 of 7 (permalink) Old 04-12-2019, 02:39 PM
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I have seen an 800A with the 19" wheel and fatter tire from a Vulcan 500, not sure what years, think it had a 110/90-19 tire though, would be right at same overall height as stock. The 90/90-21 should make the speedo more accurate as they read fast to start with. stock 21" rim was 1.85" wide vs the 19" at 2.15, so the 110/90 should be good.

However, the 21" is same as used on a lot of Harleys, like a 2001 Dyna. MH21 tire, most cross ref charts say it's same as 80/90, don't know why they would pick on yours. (except that it looks better than theirs?)

p.s., I had an 800A for a number of years. friend also had one, he put well over 100k miles on his. I traded for an 04 Nomad. Still miss that 800A.
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