I have a question for the tire experts.

I use my '04 mainly for commuting year around as much as possible.
It currently has BT45's on it and I'm happy with the wear and handling.
My question is.. What effect changing tire sizes will have on handling?

I'm thinking of going to a 120-70 or maybe a 120-80 on the front and a
140-70 on the back. Last time I checked these were available in the BT45's

If I understand it correctly, the larger front tire would make the bike a bit less eager to turn. Would that mean a bit more stable on the Highway or would it be a total pig?

The reason for going up on the back. is to keep the size ratio more or less the same from front to back. Is that required? Or, can I stay with stock on the back?

I don't really ride aggressively and don't need the bike to be as flickable as it is. However, I don't want to make it dangerous either.

Thanks for any help.
BeSafe.

I'm not sure a 120 will even fit on the front.  The handling wont change much at all, no matter what size rear.

I've run 110/70 and 110/80 front tires and 130/70, 130/80, 130/90, 140/80, and 150/70 rear tires and all of them on the OEM 3.0" front and 3.5" rear wheels and quite frankly I've noticed little or no effect on the handling that I'd attribute directly to the different sizes. 

There were more noticeable changes to handling that could be attributed to different types of tire, namely sport touring or supersport radials to replace the OEM bias ply tires.  These radial tires don't come in our OEM sizes so it's necessary to go to the 140/80, 150/60, or 150/70 rear tires to get the advantages of these radials.

One possible exception was when I put a 130/90 rear touring tire on with a 110/70 front and the resulting raising of the rear axle by 1" resulted in noticeably quicker steering response due to the steeper steering head angle.  So in theory if you put a taller front tire on with the 130/70  size rear tire you will slow steering response and make it a tad more stable on the highway if even noticeable.

Some here have run a 120/70 front without a problem but I'm almost sure a 120/80 front won't have adequate clearance to the fender.  My 110/80 front just clears the fender.

If you like the performance and tire life of the BT45s, it would be best to stick with the OEM sizes in my opinion.  The only BT45s in the 110/70 and 130/70 sizes that Bridgestone lists now are the G spec tires that come as OEM on the GS-F models and these are selling at bargain prices right now.

Just checking at AMT, the price of the G spec BT45s are $66 front and $72 rear and the 110/80 front is $82 and the 140/70 rear is $92.  Can't see any advantage to these oversize tires that would warrant the greater cost.

http://www.americanmototire.com/

My tire log showing the tires I've used on the GSs:

http://img.photobucket.com/albums/v443/jcp8832/GS500tirelog.jpg

GSjack knows all about tires. In my personal opinion, I wouldn't go too far from the stock sizes especially on the front. I doubt a 120 will fit on there anyways. As far as the rear goes I know 130 and 140 will fit absolutly problem free and I think that 150s will usually fit without problems, but you don't really gain much with the wider tires except that you can get stickier tires that don't generally come in the stock 130 size.

When you get away from the standard 70 profile and go to a 80 or 90, in the front you change your speedometer reading (it'll read slower with a taller tire) and in the rear you change your effective gear ratio (taller tire = less rpm for a given speed)

If you're happy with the stock tires traction, I'd recomend the Kenda K671 tires as a replacement. In my experience, they stick as well as or slightly better than the stock rubbers but they have deeper tread and last longer. As a bonus they're some of the cheapes tires I've found. Available in the stock sizes and larger (I went with a 110-70 front and a 140-70 rear)

There are plenty of tires that stick better than stock but they're generally more expensive and don't last very long.

Thanks for the response guys!
That answers my questions. I'll probably stick with the OEM's then.
My front is still good but the back is beginning to get kind of squared off.
I haven't been able to make it to the twisties for quite a while now.

My bike has just under 6K miles. I'm the second owner. These are the original tires. I'll just get a new rear so I can finish up the front.

I might try some of the new Roadrunners ( I think that's right) next time.
Thanks again.
BeSafe.

thanks Ducati.
I guess we were typing at the same time.
I'll check out the kendas.

A friend of mine tells me that I come close to touching the pegs down when we ride the twisties around here. ( Western Arkansas ).
When I ride with him, I usually push it harder than I normally would. I stay inside my comfort zone though.

Most of the time I like to go easy.
So, I don't think I would want to give up any wear for extra stickiness that I wouldn't use any way.

Thanks for the help guys. I really like all the info that is available on this site.
BeSafe.

Yeah I usually go sort of easy as well, but once I leaned it way over and drug the centerstand with the kendas on there  I was probally pushing them a little farther than I should have but I didn't crash. Not bad for $70 tires.

Think you might mean the new Roadriders, they replace the old discontinued HKM, Roadrunner, and Supervenom tires from Avon.

http://www.tiresunlimited.com/ALL%20TIRES/AVON/AVON%20MC/avon_am26_roadrider.htm

I've had a couple Kenda tires and found them to be about as Ducati describes them.  Worth considering but I think the new Roadriders might be a better buy for just a little more cost. 

I wore out a pair of the HKM AM51/52 Avons and they were good for about 10k miles, the new Roadriders should be better tires but it's too early to report on them yet. 

Yep, Roadriders.
I read about them in one of your posts a few weeks back.
I guess I could take one for the team and order a set to see how they do, and give a review. I hate to not get all the miles out of my current front tire though.

i have 110/70 front and 140/70 rear and that is what i am going to replace them with.

i am thinking of going with the avons but kings tire is super cheap and look really good.

here is a link to them.    http://www.kingstire.com/Sport.htm

what does everyone think of these. thanks

First I've heard of them, looks like a Chinese outfit and many of the tread patterns look like copies of well known tires.  The ones your looking at look like the Dunlop GT501 tires.  Have no idea of the quality or performance of these tires.  Somebody's got to try them first.   

From search:

"Kings Tire Group, the manufacturers and exporter of tires, tubes and flaps, established in 1988,from TAIWAN. With three factories in TIANJIN, CHINA .

Our service is global for every customer, main market is Europe, U.S.A, Australia and New Zealand."

http://www.dunlopmotorcycle.com/tirecatalog_tire.asp?id=8

The Avons look like a better choice to me unless someone has more info on Kings Tire.

I had a MEtzeler MZ2 in from 110/70 and Previous owner (had not noticed until I blew it the other day) a 130/90 continental Blitz in the rear.... Just dont do it.... wow what  abad combo... and like jack say, I was weirded out the 1" difference in turns.

I spent the $$ for a set of Avon AV45 110/80 and AV46 140/80 azero's and I can tell you 2 things...

1) I feel a real difference on the ride quality
2) I feel more comfortable attacking the corners with good quality tires

PS: I commute to work every day 116 miles round trip to work. Good tires = safe, cheap cheung sung tire = dangerous on wet.