80/90-21 vs 90/90-21

[JoelH.]

My front MT21 is getting pretty worn so I'm looking to replace it. I'm not vary well versed on tires sizes, I mean I understand the numbering system, but I don't understand what decides wheather you would use a 80/90 vs a 90/90 etc.. Can someone give me a primer on the subject.

Thanks Joel

[10guy]

Pretty much any 21" front tire that I know of will fit on the drz.

[JoelH.]

Yes, but is there any reason too go, or not too go, 90/90.

[bushwhacker]

Since both tires are the same width handling should be about the same so we are only talking about the diameter of the tire.

Stock 80/100 has an 80 mm sidewall. 90/90 has an 81mm sidewall. basically the same diameter tire.

80/90 has a 72 mm sidewall. 18 mm or about .7 inches smaller diameter. This translates to about 2.25 inches smaller circumference.

This will throw your speedo off a little more and your tire will wear a little quicker.

Is it enough to notice. Probably not. You are talking about approximately 2.5% difference. That's .025.

With everything else being equal (which it never is), if your speedo was off exactly 10 mph at 90 the difference would mean that your speedo would be off 10.25 mph at 90. If you got 2000 miles out of the 90/90 you would get 1950 miles out of the 80/90.

Bottom line - 6 of one, half dozen of the other.

-

[OldDualSporter]

My front MT21 is getting pretty worn so I'm looking to replace it. I'm not vary well versed on tires sizes, I mean I understand the numbering system, but I don't understand what decides wheather you would use a 80/90 vs a 90/90 etc.. Can someone give me a primer on the subject.

Thanks Joel

Basicly, the first number is the tire width, and the second number is the "aspect ratio" or percentage of sidewall height versus tire width.

So, *roughly*, an 80/90 would be 3.20" wide, with sidewall height of 90 percent of the width.

A 90/90 would be 3.60" wide, with a sidewall height of 90 percent of that width.

Since 90 percent of 90 mm is higher than 80mm, the 90/90 is a taller tire overall.

Hope that helps in your tire choice.

[GuyGraham]

Since both tires are the same width handling should be about the same so we are only talking about the diameter of the tire-

You're mistaken I'm afraid. The tyres are not the same width.

The first number is the width of the tyre in mm's. So the 80/90 is 80mm wide and the 90/90 is 90mm wide

The second number is the height of the tyre (technical term is aspect ratio) and it is a percentage of the width. So the 80/90 tyre has a height of 90% of 80mm which is 72mm. The second tyre is 90/90 and therefore has a height of 90% of 90mm which is 81mm.

Stock tyre is 80/100 which is 80mm wide and 100% of 80mm high, meaning 80mm high.

Yes the 90/90 tyre will fit, it is little wide for the front rim (which is 1.60ins I believe and the maximun recommended width tyre for this rim is an 80mm wide tyre). Speedo accuracy will be slightly affected but you probably won't notice it.

I run a 90/90 with no problems.

[OldDualSporter]

Guy -- looks like we were both typing a similar answer at the same time!

[Spud786]

an 80/90 is a skinnier tire and smaller diameter than a 90/90

I would go with the 90/90

[MotoChris521]

Hold on to ypur hats boys ! They now have 90/100 sized tires ! I've had a Bridestone M-401 on the front of my DRZ for the last 1,000 miles.I like it alot.I have a Dunlop D742 90/100 (wanted to try both) that's going on soon.Niether are DOT,but i'm not a DOT kinda guy.

[JoelH.]

Thanks for the input guys. I ordered a 90/90 this morning. $53.00 to my door.

[Eugene Brown]

I have a question about rim width on a 21’ wheel and tire size. Can I run a mt80/90- on a 21’-3.5’ wheel?

[bumtarder]

17 hours ago, Eugene Brown said:

I have a question about rim width on a 21’ wheel and tire size. Can I run a mt80/90- on a 21’-3.5’ wheel?

3.50" front wheel? Where did you get that? A normal DRZ 21" front is 1.60 wide for a 80/100-21 factory spec'd tire. 3.50" wide rim is what a SM model runs in the front 17" wheel for a 120/70R17 tire which is about 4.75" wide.

So you want to put a too narrow tire on a too wide rim? Don't think that's going to work very well if at all.

Edited October 1, 2021 by bumtarder