2007 FZ1 55’s on back instead of 50’s

I

ilawrence111

Member
Visit site
I see there are a bunch of threads on this from 5 plus years ago but can’t get any definitive answers. Anyone out there running 55’s on the back tire and not change the bike’s geometry after installation? If so, is handling the same or am I gonna slide out on the freeway on my next ride? Also if anyone is aware, how much would I need to adjust my forks and in which direction in order to stabilize the bikes geometry?
 
When I bought my bike a year ago, it had a 180/50 on the rear. I am now on my second 190/55 and have only noticed two very minor differences: it puts the speedo right on point and my pegs scrape before I can use up the last half inch or so of rubber on the very edge. Ran it at Summit Point (Shenandoah Circuit) with no problems!
 
Doc Samson said:
When I bought my bike a year ago, it had a 180/50 on the rear. I am now on my second 190/55 and have only noticed two very minor differences: it puts the speedo right on point and my pegs scrape before I can use up the last half inch or so of rubber on the very edge. Ran it at Summit Point (Shenandoah Circuit) with no problems!
Click to expand...
Excellent. I’ve only hit the track maybe 5 or 6 times here in Texas but have been provided a bike each time. I just want to keep my brain in my skull and my skin covering my bones coming out of corners lol
 
Last edited:
You should be fine! I never felt as if "lean" was out of control or unstable. If I recall correctly, I even raised my forks through the triple tree just a hair. Keep in mind that I am considered an "advanced" Novice, so not an top level rider by any stretch...
 
Doc Samson said:
You should be fine! I never felt as if "lean" was out of control or unstable. If I recall correctly, I even raised my forks through the triple tree just a hair. Keep in mind that I am considered an "advanced" Novice, so not an top level rider by any stretch...
Click to expand...

This is the correct direction for the forks. The 55s will be about a 19mm bigger diameter than the 50s. So the rear of the bike will come up and if it is desired to maintain the same relationship the front will have to come up as well.
 
Erk,

Timeout! The tire profile is designed (rubber characteristics, reinforcing strand wrap/angle, etc.) for a specific width rim. Unless you have a GEN I or purchased an old Satan machine with an R6 wheel conversion, you are running a tire (180/55) designed for a 5.5" rim on a 6" rim. Not a good option for consistent handling. If you indeed have a 5.5" rim you are undersized for a 190/55.

The FZ1 (with stock size tires) was designed with a 25 degree steering head angle. This puts handling characteristics in the 'mild' column. Stable, but takes some countersteer force to 'dip' into turns. Changing the front-to-rear ride height relationship by 1" (either way), effectively alters the head angle by 1 degree.

The R1 (a somewhat more radical handling bike) has a 24 degree head angle. This makes for easier/quicker turn-in. However, when the steering head angle begins to drop below 24 degrees, high speed handling becomes affected by the tendency for fork oscillations (caused by imbalance, road surface, front tire unloading, rubber/pressure/bump resonance, etc.) to increase to the point of uncontrollability (tank slappers). The R1 has a steering damper to reduce this condition.

For the FZ1 increasing the rear height by 1/2" (13mm) or so improves the turn-in without significantly affecting COG or high speed issues (IMO). This can also be done by dropping the fork tubes in the front if ground clearance is not an issue.

The static ride height relationship can also be affected by spring weights and preload. This is matched to the weight of the bike, weight of the rider and add-on load and front-to-rear loading. Do you notice a handling difference when you move your body to the rear?

When you change tire characteristics, you also change unsprung weight. This affects the amount of damping needed by the shock absorber. The stock FZ1 shocks were designed with a minimum range of adjustment and, in the case of the GEN II, springing for fairly zaftig riders.

The rear tire choice is designed to provide an optimum contact patch needed for engine output and match the projected load weight. The 180/55 works fine for up to 150 HP. The 190/55 is good to 200 HP or so. The newer 'super' bikes in the 200+ HP range are using the 200mm profiles. Changing to a tire size larger than required has many side effects. Include inflation pressures.

The moral of the story is that one change may require others to optimize handling, comfort, safety, etc. This is matched to your needs. Are you a street rider or race on a track? Do you want comfort or maximum performance? Size the tire for the ride but do not ignore the massive amount of engineering that chose the stock tire sizes.
 
You must log in or register to reply here.
Back
Top