Either one oughtta work fine. 10 mm = .39 inch.

 

Just remember one thing, when you change the tire size you also make the speedometer give out an incorrect reading.

 

I considered that already. I figure that There is approx 3% difference in size from the stock. I can live with that much error in the odometer. When I bought the bike (approx 25 years ago) the speedo needle was reading approx 20 mph fast. I had to dissasemble my speedo & re-set the needle on the shaft to get a correct spped reading. I can do that again, now that I have a GPS I should be able to get it spot-on

 

What is more important is this, going wider on the front increases the standup when braking in corners. Be prepared for that when you brake hard in the first corner with 120s on and the bike wants to tilt up all of a sudden, having said that, i would go for the 120

 

What is more important is this, going wider on the front increases the standup when braking in corners. Be prepared for that when you brake hard in the first corner with 120s on and the bike wants to tilt up all of a sudden, having said that, i would go for the 120

And just to be a contrarian, I'd go with the 100. Because: The front will feel lighter, and turn in better, AND the fronts are usually a bit too wide from the factory, IMHO. I suspect it's an attempt to keep a large contact patch so the front end doesn't wash out on inexperienced riders. If you look around at bikes, particularly ones that the rider has used all the tread on the rear, there's always a bit of virgin rubber on the fronts.

 

Either one oughtta work fine. 10 mm = .39 inch.

Which is about 3/8". That doesn't sound like a lot until you consider something like a wheel trap (those little canyons that open up when two ribbons of pavement start to pull apart), which can suck a thinner tire into it.

Further, since the choice is 120 or 100, the difference is really .78 mm or just over 3/4". That's a lot of real estate.

Given the choice between a bit oversized or a bit undersized, I'll take the extra meat.

 

Thanks everyone. This is the kind of info that I'm looking for to make an educated decision.

What is more important is this, going wider on the front increases the standup when braking in corners. Be prepared for that when you brake hard in the first corner with 120s on and the bike wants to tilt up all of a sudden, having said that, i would go for the 120

GPZ600R, How much of an issue is this condition? I would assume that it would also happen with the stock size tire. How much difference will one size larger be?
I should also add that my riding style is not aggresive. I do not attempt to drag my pipes in the turns, but I have been known to run the speedo needle pretty high (just because I can).

 

Which is about 3/8". That doesn't sound like a lot until you consider something like a wheel trap (those little canyons that open up when two ribbons of pavement start to pull apart), which can suck a thinner tire into it.

Further, since the choice is 120 or 100, the difference is really .78 mm or just over 3/4". That's a lot of real estate.

Given the choice between a bit oversized or a bit undersized, I'll take the extra meat.

This is the reason that I was leaning to the larger size.

 

I'd do the 100 just because you didn't tell me the size, but knowing the Spitfire S11s I am guessing your bike would most likelytake the 100 over the 120, but more than likely there is a 110 available. They didn't make a 120 in a 16 and I'm not sure they did in an 18. But I do know they do the S11 in both a 19 and an 18 in 100 and probably in a 19 too.

I would stay with a smaller size if I couldn't get the right size just because it would give me more responsive steering and that's usually better than slower steering.

 

GPZ600R, How much of an issue is this condition? I would assume that it would also happen with the stock size tire. How much difference will one size larger be?
I should also add that my riding style is not aggressive. I do not attempt to drag my pipes in the turns, but I have been known to run the speedo needle pretty high (just because I can).

How much an issue depends really on your riding. Lets try to make a visual example. Take a nice neat righthander, lets say 45 degree turn. You approach the turn at 100km/h and in the corner you apply the front brake. The 100 tire will probably do nothing, other than slow down. the 110 tire is going to start to want to stand up, you will feel the bike uprighting a little. the 120 tire will have a more increased effect, making you push the bars down to keep the bike in the corner. If you don't keep the bike down, it will high-side you. All sounds bad, but it is only a minimal effect and shouldn't sway your decision. there are more pros than cons.

 

Take a nice neat righthander, lets say 45 degree turn. You approach the turn at 100km/h and in the corner you apply the front brake.

OK... 60 mph curve, leaned over a bit, grab the front brake. Am I the only one here who thinks this is a Bad Idea regardless of what size tires you're running?

 

i didn't say Grab, i said apply, there is a subtle difference. You never ever apply brakes in a corner ?

 

I'd do the 100 just because you didn't tell me the size, but knowing the Spitfire S11s I am guessing your bike would most likelytake the 100 over the 120, but more than likely there is a 110 available. They didn't make a 120 in a 16 and I'm not sure they did in an 18. But I do know they do the S11 in both a 19 and an 18 in 100 and probably in a 19 too.

I would stay with a smaller size if I couldn't get the right size just because it would give me more responsive steering and that's usually better than slower steering.

My bike takes a 110/90-18 on the front. Someone posted a link which showed a 110 in Raised White Letters is manufactured, problem is no one stocks it and I can't seem to find anyone that can special order it. Since I have found several retailers that stock the 110 & 120, both in RWL and at a good price, it is going to be less hassel to go with one of those.
How noticable will the steering change be if I go to the larger of the 2? As I stated previously, I'm not an agressive rider. Stability on "rain-grooved" pavement & linear cracks is important to me. If I went with the smaller tire to make the steering more responsive, will it come at a price of reduced stability?

 

If I went with the smaller tire to make the steering more responsive, will it come at a price of reduced stability?

Probably not.

The normal upright contact patch doesn't increase linearly with the aspect of the tire. In other words, an aspect that is 10% larger doesn't yield a 10% larger contact patch. Tires of the same type (front wheel, traditional motorcycle tires), generally all have a similarly sized contact patch at proper inflation - something not much larger than a nickle. All a larger aspect does is reduce the "ten speed skinny tire effect" when encountering something that a narrow tire can fall into. As noted above, 10mm won't really do anything, though I wouldn't want to swing 20mm to go down a size if something in the middle isn't available. There again, we aren't talking moped tires here. There are few wheel traps out there than can swallow a real motorcycle tire.

Further, most traditional front motorcycle street tires in popular sizes have roughly the same PSI rating, meaning you aren't going to see any added ride comfort or protection for the rim should you hit something like the lip of blacktop coming off a construction zone. A bigger sidewall can do that, but it has to be a lot bigger (like the difference between a traditional car sidewall and those low profile stupid tires that the kiddies all like on their rolling boom boxes).

Finally, on wet pavement, the very tiny increase in the friction would do nothing noticeable to decrease hydroplaning or affect water shedding. Dropping your speed 5MPH would make way more of a difference.

In other words, on a flat road with the bike upright, it does essentially nothing for you with the sizes you're talking. All it does is affect the measurement of the curve of the tire from edge to edge, which can affect response in a lean. Even that's very small and something you can adapt to. The amount of fuel in your tank likely has more affect on the handling of the bike. How well you keep up on your tire pressure will also have more effect.

To sum up: if you can get the size called for with your bike, get it. I would only go larger verses the only choice being smaller based on the measurements I cited in my post above. Up 10mm won't likely do anything for you, but I wouldn't want to trade 20mm to go smaller than recommended.

 

Not if you know what you're doing and there is a legitimate reason ahead to slow down a bit - road kill, gravel, or a car in a blind corner. I've done it probably thousands of times mostly without really thinking about it beyond ingrained response. It's part of the rider skills that should be developed. Would you not try to stop if there were tree limbs down just around a corner, because you "don't brake in corners"? Personally I've learned the skills and would be on the brakes, no problemo.

Every bit of what he said is true, but not just under braking. The same is true when simply backing off the throttle too. It's all about leverage, geometry, and physics. Who cares about the exact science, it happens. Wider tires will require more effort to turn in and also more effort to stay turned in on a corner much the same as a raked out front end will too.

 

Bridgestone does not make the RWL in the 110/90-18. I looked for it. The 120 is calling for a 2.5-3.0 inch rim, the 110 calls for 2.15-3.00. The 120 tire is rated at 5" wide and 26.5" diameter on a 2.50 wide rim, where the 110 is at 4.4" and 25.9" diameter. If you insist on the Bridgestone 120/90-18 RWL be aware you may also run into fender clearance issues due to the size difference. That was the same size tire the GL1100 GoldWing ran (I know, I had two of them and went down in front tire size on both, to a 110). You could take your chances on the 120, but I'd be measuring the tire on the bike in width and diameter to be sure the 120 will fit. If it was me, I'd just do black walls to have the right sizes, having done the oversize and undersize changes and reading what you want.

I will mention Dunlop does a RWL in a 110/90-18 in the F20 model, which is an OEM style replacement tire.

You may end up with less rubber on the road with the 120 since it possibly will pinch up on the same size rim as intended for the 110. That might cause more tracking issues. Even if it doesn't pinch up it will slow steering response significantly. In neither case will the 120 give you any wear advantage to speak of. Go with the 110 since it is what the bike was designed to use. It will handle the best for your needs. It's incredible what just that little bit can do either up or down.

 

Bridgestone does not make the RWL in the 110/90-18. I looked for it. The 120 is calling for a 2.5-3.0 inch rim, the 110 calls for 2.15-3.00. The 120 tire is rated at 5" wide and 26.5" diameter on a 2.50 wide rim, where the 110 is at 4.4" and 25.9" diameter. If you insist on the Bridgestone 120/90-18 RWL be aware you may also run into fender clearance issues due to the size difference. That was the same size tire the GL1100 GoldWing ran (I know, I had two of them and went down in front tire size on both, to a 110). You could take your chances on the 120, but I'd be measuring the tire on the bike in width and diameter to be sure the 120 will fit. If it was me, I'd just do black walls to have the right sizes, having done the oversize and undersize changes and reading what you want.

I will mention Dunlop does a RWL in a 110/90-18 in the F20 model, which is an OEM style replacement tire.

You may end up with less rubber on the road with the 120 since it possibly will pinch up on the same size rim as intended for the 110. That might cause more tracking issues. Even if it doesn't pinch up it will slow steering response significantly. In neither case will the 120 give you any wear advantage to speak of. Go with the 110 since it is what the bike was designed to use. It will handle the best for your needs. It's incredible what just that little bit can do either up or down.

Here is a link that someone else dirrected me to. Bridgestone Spitfire S11 It shows that a 110/90-18 is avalible in RWL, but I'll be darned if I can find one. I have considered going with blackwalls just to retain the stock size, but I do like the white letters.
I also found the Dunlop F20 in the 110/90-18 RWL. Problem there is I can't find a rear tire to match it. If I'm going to have the white letters, I would like to have the same brands front & rear. Maybe I'm just too fussy about the appearance.

 

If I'm going to have the white letters, I would like to have the same brands front & rear. Maybe I'm just too fussy about the appearance.

I'm shocked at this show of vanity.....

(Goes back to polishing every crevice of my engine with Q-Tips...)

 

Here is a link that someone else dirrected me to. Bridgestone Spitfire S11 It shows that a 110/90-18 is avalible in RWL, but I'll be darned if I can find one. I have considered going with blackwalls just to retain the stock size, but I do like the white letters.
I also found the Dunlop F20 in the 110/90-18 RWL. Problem there is I can't find a rear tire to match it. If I'm going to have the white letters, I would like to have the same brands front & rear. Maybe I'm just too fussy about the appearance.

I'm kind of surprised, there was no listing on Bridgestone's actual site, which was the one I had on the short cut. Maybe there's an error with Bridgestone's site. If you can get it, definitely buy it!

As for the Dunlop, there is a match, they will both say "Qualifier" on the sidewall, but the actual tire model number will not be the same like the Bridgestones. You just need to look at their site and see what the raised white letters say.

 

I'm shocked at this show of vanity.....

(Goes back to polishing every crevice of my engine with Q-Tips...)

Finally, someone else that understands!

 

I'm kind of surprised, there was no listing on Bridgestone's actual site, which was the one I had on the short cut. Maybe there's an error with Bridgestone's site. If you can get it, definitely buy it!

As for the Dunlop, there is a match, they will both say "Qualifier" on the sidewall, but the actual tire model number will not be the same like the Bridgestones. You just need to look at their site and see what the raised white letters say.

Thanks, I'll have to give that a try. That's what I have on the bike now, Qualifiers w/ different model#s but they still both say Qualifier on the sidewall. So far, I have only
found the F20 front w/ RWL and the Elite II rear in RWL in the size that I need, but they don't match.

 

Get the Bridgestones if you can. I've used them and sold a few hundred sets since they first came out back around 1986 when I was in bike sales. They work well for the money for sure. The only other tire I'd recommend over them would be the old Tour Elites in RWL which I thiink are still made for the Harleys, but maybe not in RWL. They get really great wear, but the 'stones are a better tire for more spirited riding.