Different tyre sizes to manufacturer

[Hawkeye]

Hi,

I've got a 2007 GSX750F Katana.

Needing to change the rear tyre and on doing research, I've found that at some point, the rear has been changed to a different size.

The manufacturer spec shows a 120/90/17 yet I've got a 150/70/17 Sport Demon fitted.

Although I'm happy with the grip of the Demon, I didn't get a lot of life out of it as it has flattened off in the middle and is now bare. I've seen a couple of posts on here that mention the same thing.

So.... Anyone got any knowledge about what the change in the tyre size may have on tyre wear and handling. Currently looking at BT45's but not sure whether to stick to the same size or revert back to the manufacturers spec.
I'm also thinking the difference in size may have an affect on the speedo.

[oldiebutagoody]

Hi,

150/70/17 IS the correct tyre spec for your rear according to Haynes manual.

Front tyre is 120/70/17.

Stick with the original tyre profiles and try differing compounds / tyre brands. IE:if you use the bike for scratching go for that type of tyre, if you commute go for that type......etc etc.

[Hawkeye]

Strange you say that because I have found a couple of sites that quote different sizes.

This one shows 120/90/17. It also shows 100/190/16 for the front.
http://www.autoevolution.com/moto/su...atana-1998-747

Yet this one shows 150/70/17.
http://www.totalmotorcycle.com/photo...50-GSX750F.htm

Looks like I need to do a bit more research to find the correct size.

[nodrog:Me]

Here's a retarded idea, ask a Suzuki dealer.

[oldiebutagoody]

You are on the correct size bud. No worries.

Ask at the tyre shop/dealer or wherever you get re-rubbered. they will confirm for you.

I am running BT45's. They crossply bias tyres, touring type tyres with dual compound. Hard centre and softer sides. Not top of the range for sure but hold well enough for open road riding.

You can get a Bridgestone T30 for your rims that would be a step up, and go radial if you have the dosh.

[caspernz]

The 750 Katana of that vintage should have a 4.5 inch rear rim, and standard tyre is indeed a 150/70/17. When I had a bike such as yours, I found a 160/60/17 actually worked better for me. The change in tyre size merely reduces the optimism of the speedo a little, as rolling circumference is not that different.

The 150 width tyre saw me getting right to the edge of the tread, whereas on the 160 there was a little bit of chicken strip left. Michelin Pilot Road 2 and 3 worked nicely.

Front rim should be 3.5 inch with 120/70/17 the standard.

Needless to say having front and rear tyres that have similar life left in them benefits happy handling, matched sets are ideal if one can afford it of course.

[Erelyes]

Strange you say that because I have found a couple of sites that quote different sizes.

I tend to rely on this one for info.
http://www.motorcyclespecs.co.za/mod...gsx750f_07.htm

I find it strange you have over 2k posts and yet it didn't occur to you that a 150 tyre would be nigh-on falling off a rim designed for a 120 tyre; or that a 750cc bike with a 120 rear tyre would be rather sketchy...

[Kickaha]

or that a 750cc bike with a 120 rear tyre would be rather sketchy...

Bigger bikes used to run far narrower tyres than that, it all depends on rim width and what the bike was designed around not the size of the motor

[Hawkeye]

The 750 Katana of that vintage should have a 4.5 inch rear rim, and standard tyre is indeed a 150/70/17. When I had a bike such as yours, I found a 160/60/17 actually worked better for me. The change in tyre size merely reduces the optimism of the speedo a little, as rolling circumference is not that different.

The 150 width tyre saw me getting right to the edge of the tread, whereas on the 160 there was a little bit of chicken strip left. Michelin Pilot Road 2 and 3 worked nicely.

Front rim should be 3.5 inch with 120/70/17 the standard.

Needless to say having front and rear tyres that have similar life left in them benefits happy handling, matched sets are ideal if one can afford it of course.

I've used Pilot 2's in the past and was impressed with them. Can't remember when/why I changed. Probably something to do with cost/availability at the time. Looks like I need to go have a discussion with the dealers and get their input.
Only issue I have had in the past is they have tended to recommend whatever tyres they have in stock rather than discussing other options. Mainly because they are not your standard sizes they keep in stock.
These days, I don't ride hard enough to worry about chicken strips. Like to have fun but don't push the limits.
I used to ride with the boys quite a bit but tend to do more 2 up with the better half these days.

[Hawkeye]

Here's a retarded idea, ask a Suzuki dealer.

Thanks for that. Great input.

[caspernz]

I've used Pilot 2's in the past and was impressed with them. Can't remember when/why I changed. Probably something to do with cost/availability at the time. Looks like I need to go have a discussion with the dealers and get their input.
Only issue I have had in the past is they have tended to recommend whatever tyres they have in stock rather than discussing other options. Mainly because they are not your standard sizes they keep in stock.
These days, I don't ride hard enough to worry about chicken strips. Like to have fun but don't push the limits.
I used to ride with the boys quite a bit but tend to do more 2 up with the better half these days.

About the chicken strip thing, I'm not a hard rider by any means but I found the 150 was being stretched across the 4.5 inch rim and thus making you reach the edge of the tread quite quickly. If you're into 2 up riding then I'd suggest the 160 even more. The brand of tyre you buy is your choice, and if you're keen on a particular brand just get the dealer to order them in for you?

[swbarnett]

I've got a 2007 GSX750F Katana.

Mine's a K6.

The manufacturer spec shows a 120/90/17

Where did you find this?

yet I've got a 150/70/17 Sport Demon fitted.

150/70/17 on the rear is correct as far as I know. That's what was on the bike when I bought it and what I've run for the past 120,000km

Although I'm happy with the grip of the Demon, I didn't get a lot of life out of it as it has flattened off in the middle and is now bare.
...
Currently looking at BT45's

I've run BT45s both front and rear for the past 70'000km. I get around 10,000km from the rear and around 20 from the front. My mileage is mostly Auckland motorway (Tuakau to Auck CBD most days) and I find that even when the BTs flat spot they still handle pretty well in the corners (although I do notice the difference when I replace them).