Changing tyre size?

[danw]

I have a 1982 Suzuki GN250.
The current (and I believe, factory) tyre size is 120/90 - 16.

I changed the front tyre earlier this year, and I love the new Michelin Pilot Activ that was fitted.
I now need to replace the rear tyre, and was hoping to match it with the equivalent Michelin Pilot Activ.

However, it doesn't come in a 120/90 - 16.
The closest match is a 120/80 - 16.

I realise that this adjustment of aspect ratio will negatively affect top-speed, and therefore fuel-efficiency.

Is there anything else I would need to consider in changing rear tyre size?

[sugilite]

The difference between supposedly same tyre sizes from manufacturer to manufacturer can differ greatly. When I ran a supermoto bike, I found I could run a Michelin 160 tyre and it would not foul the chain, where as I could not get a dunlop 160, or a metzler 160 anywhere near that bike. I'd not sweat it too much and just fit the Michelin to match the front. Having a matched pair designed to work together will most likely trump any small issues that may arise by not fitting another brand tyre in an attempt to have the exact specified oem profile.

[Mike.Gayner]

It's a GN250, it really doesn't matter.

[spanner spinner]

I have a 1982 Suzuki GN250.
The current (and I believe, factory) tyre size is 120/90 - 16.

I changed the front tyre earlier this year, and I love the new Michelin Pilot Activ that was fitted.
I now need to replace the rear tyre, and was hoping to match it with the equivalent Michelin Pilot Activ.

However, it doesn't come in a 120/90 - 16.
The closest match is a 120/80 - 16.

I realise that this adjustment of aspect ratio will negatively affect top-speed, and therefore fuel-efficiency.

Is there anything else I would need to consider in changing rear tyre size?


use to work for large motorcycle tyre shop, did this profile change to about half the gn's we fitted tyres to due to supply issues (when the canvas is hanging through your tyre you need a new one NOW!) it is not a issue and most customers could not feel and difference in handling. as for change in gearing it is so small it is not worth worrying about, if you really want to correct the gearing we worked out the difference in gearing and it amounted to one tooth off the rear sprocket.

[Akzle]

It's a GN250, it really doesn't matter.

this. .

[spanner spinner]

The difference between supposedly same tyre sizes from manufacturer to manufacturer can differ greatly. When I ran a supermoto bike, I found I could run a Michelin 160 tyre and it would not foul the chain, where as I could not get a dunlop 160, or a metzler 160 anywhere near that bike. I'd not sweat it too much and just fit the Michelin to match the front. Having a matched pair designed to work together will most likely trump any small issues that may arise by not fitting another brand tyre in an attempt to have the exact specified oem profile.

The tyre manufactures like just changing the numbers on the side of there tyres but using the same mould for a couple of different tyre sizes. The 160 Michelin was most likely a 150 with 160 on the side so that they have a 160 in there line up. This is because some customers are more hung up on the numbers on the side than the true tyre size or how well the tyre works.

[danw]

It's a GN250, it really doesn't matter.

It obviously matters enough to you that you felt you had to say this.

And of course it matters to me, because, whether I like it or not, it's all I've got to ride, right now.

[danw]

use to work for large motorcycle tyre shop, did this profile change to about half the gn's we fitted tyres to due to supply issues (when the canvas is hanging through your tyre you need a new one NOW!) it is not a issue and most customers could not feel and difference in handling. as for change in gearing it is so small it is not worth worrying about, if you really want to correct the gearing we worked out the difference in gearing and it amounted to one tooth off the rear sprocket.

Thanks! That's helpful.

I made some rough calculations and determined that the difference in overall diameter between a 120/90 - 16 and a 120/80 - 16 is about 12mm, making for a difference in circumference (and therefore speed/distance measurement) of about 2% less than factory. I guess that's not particularly major.

Thanks again for your advice.

[Wiki Drifter]

To avoid starting a new thread, i've got a question also..

My front wheel is designed for 110/70 -17. Are there any issues in fitting a 120/70 -17 tire? Reason being i want put on PR4s next time, but they don't have 110 size like the Pr3s.

[spanner spinner]

To avoid starting a new thread, i've got a question also..

My front wheel is designed for 110/70 -17. Are there any issues in fitting a 120/70 -17 tire? Reason being i want put on PR4s next time, but they don't have 110 size like the Pr3s.

Yes there are lots of issues, you need a 3.5 inch wide for a 120 section tyre to shape up correctly. Your bike I am thinking is a 400 to have a 110 on the front which means it will have a 3 inch rim so the 120 won't work. Put a 120 on a 3 inch rim and the tyre will be peaked, which means it will less contact patch than 110 and will have overly steep sidewalls which will lead to bad handling.