Tyres - is a 120/80 smaller than a 120/90...?

[Steam]

So I'm looking around for new tyres, and there's a good type which is 120/80 17inch.
What's on there now is a 120/90.

Is a 120/80 smaller than a 120/90? Smaller in diameter I mean.
Will my rear wheel need to go around very slightly faster to make up for that less 10mm?


I am new to this, hence my moron question.

Thanks!

[McJim]

So I'm looking around for new tyres, and there's a good type which is 120/80 17inch.
What's on there now is a 120/90.

Is a 120/80 smaller than a 120/90? Smaller in diameter I mean.
Will my rear wheel need to go around very slightly faster to make up for that less 10mm?


I am new to this, hence my moron question.

Thanks!

The dumbest questions are the ones that are never asked.

The 90 or 80 refers to the depth of the tyre. distance between the centre of the rim to the centre of the tread.

Someone else will probably be more eloquent so while they reply I will draw you a picture.

Mind you - I could be wrong......

[ElCoyote]

The dumbest questions are the ones that are never asked.

The 90 or 80 refers to the depth of the tyre. distance between the centre of the rim to the centre of the tread.

Someone else will probably be more eloquent so while they reply I will draw you a picture.

Mind you - I could be wrong......

Pretty much on the money McJim. It refers to the ratio between the width of the tyre and the profile, ie 80% or 90% of width. You see some of the cager hoons with 40% profiles where it is like an elastic band around the rim.

Cheers,

Phil

[Steam]

Thanks guys. So my wheel will have to go around a tiny little bit faster to make up for the reduced diameter / circumference, if I put on the 80.

[tommorth]

correct if ur speedo is driven off the front wheel may change it a little

[DEATH_INC.]

Pretty much on the money McJim. It refers to the ratio between the width of the tyre and the profile, ie 80% or 90% of width. You see some of the cager hoons with 40% profiles where it is like an elastic band around the rim.

Cheers,

Phil

40 profiles......they do 25's now....and 30's are real common.
But yer right on the rest of it....

[AllanB]

All correct ,also you engine will rev slightly higher for any given speed in top gear due to the lower profile. Also pull wheelies easier

If there is such a thing and it will fit the bike & rim a 130/80 will probably be stock re speed etc.

[Pixie]

40 profiles......they do 25's now....and 30's are real common.
But yer right on the rest of it....

Run over a sheet of newspaper and bend the rim

[megageoff76]

The 80 on the size 120/80, indicates the height of the sidewall is 80% of the width of the tyre...its not that the sidewall is 80mm tall.

[warewolf]

See the FAQs page on the tyre manufacturers' web sites.

Continental

Avon

etc

[Steam]

Thanks yep, all sorted now. I am now an EXPERT on what all the different numbers mean on the side.