55 profile in the back. Ok... but why?

[martin_14]

hi,
we've read from several forum members and journalists that a 55 profile in the back helps with the turn in and holding the line in the curve without so much push on the inner grip of the handlebar.
Fine, say I believe it; but can somebody explain the why? Because I keep scratching my head...
So far I had the OEM Bridgestones (no no), the Pirelli Angel ST (nice when new), and the Pilot Power 3 (great grip), all in 50 profile, and they all require effort to keep a line compared to other motorcycles I test.

[The Pope]

Think of the 50's cross section as a "U" and the 55's as a "V". Yes, these aren't the exact shapes, but it's the only way that I was quickly able to describe the differances. 

Turn in - Which shape looks like it would fall over easier, "U" or "V" ?  I'd say "V" The easier the tire will fall over, the easier the bike can turn in.

Holding the line in the curve - If you were to take these "U" & "V" shapes and rotate them over onto their sides like when you're leaned over in a curve, the "V" will have a slightly larger contact patch than the "U".

Well, that's how I "think" it works, but I'm sure that there will be others to chime in here that may have a better understanding than I.

But the only way for you to truly understand is to put a 55 on your bike.

[gPink]

It also raises the rear of the bike which changes the rake slightly. Similar effect to sliding the fork tubes above the top fork clamp.

[VirginiaJim]

I couldn't tell the difference..

[Rembrant]

It also raises the rear of the bike which changes the rake slightly. Similar effect to sliding the fork tubes above the top fork clamp.

Yup, it's like a jack-up kit for the back of the bike, which changes the rake of the forks. This makes the turning a little more aggressive.

I couldn't tell the difference..

I could, but not in a positive way. I tried the 55 series rear tires, twice, and didn't like them. I just found it made the bike feel like it had a bigger tire on the back...lol. On a good note, the 55 series tires do have a higher load rating and do last a little longer, at least in my experience.

Rem

[gPink]

I'm running a 180/55 Angel right now. A friend who owns a local indie bike shop runs a 180/60 on his track bike. That has a seriously round profile.

[Deziner]

Generally speaking, the closer you have the front and rear contact area profiles, the more "neutral" the handling.  I don't know why, but some folks are able to discern differences like that than others are. Think Darkside. If tires on a high performance motorcycle had a cross-section that was basically half of a cirxle, most folks would find it really "twitchy" . It would, however, make directional changes really well. Think Moto GP chicane.

[clogan]

I couldn't tell the difference..

Nor could I.

 The difference between a 50% and a 55% aspect ratio for our rear tire is too small for me to notice, especially when you consider that the comparison would be typically made between a worn-out tire of one size versus a brand new tire of another.

[stevewfl]

I can't tell a difference either unless I'm railing the bike in the turns so hard I can reach down and touch the road with my glove, and keeping up with guys on track bikes with proper suspensions hitting their knee pucks.  Thats when there's no comparison, 55 eats the 50 alive 

[Daytona_Mike]

It also raises the rear of the bike which changes the rake slightly. Similar effect to sliding the fork tubes above the top fork clamp.

That is exactly why. Just doing the proper sag settings  for the bikes ride geometry (and/or re-spring the bike for your weight) will change the rake.
If I was on the track then ok- a 55 it is but I am not on the track and I prefer the bike's handling to be neutral.
When I  first got my C14 it would not lean into a corner easily. I had to keep pushing on the handle bars to keep in a turn  other wise it wanted  pop right back up. I very much disliked that.    It was because the bike was not set up for my weight and the sag settings were incorrect. I re-sprung the bike's suspension (for my fat @ss) and then did  my sag settings.
Now when I put it into a corner  it stays put  but I also want it to come back up easily and the 55 would not do that. The 55 wants to resist coming back up so I went back to the 50.
I like the 50's  round profile  for the street and it handles like your rolling the bike over and back up on a basket ball- effortlessly.

[sailor_chic]

Everybody has mentioned the handling pros and cons.  How about the benefit of the 55 correcting the slow speedo. This alone I feel is worth going bigger.
Remember guys... Size does matter

[jwh20]

Tire size and profiles is not an exact science by any means and size is not exactly universal among all tire manufacturers.  But you can expect some differences between tire profiles like 50 vs. 55.

Here is a link to a good resource that gets you an idea of the expected dimensions of a tire:

http://tire-size-conversion.com/tire-size-calculator/

So the stock rear tire for C14 is a 190/50-17.  According to the calculator you have:

Diameter = 24.5" Width = 7.48" Wheel = 17" Sidewall = 3.74" Circumference = 76.9" Revs/Mile = 824.3

A 190/55-15 will be:

Diameter = 25.2" Width = 7.48" Wheel = 17" Sidewall = 4.11" Circumference = 79.2" Revs/Mile = 799.8

So you can see that a 55 tire is a bit "taller" and therefore also will turn a bit slower at the same speed.  As far as effect on the speedo, since the C14 speedo comes from the drive shaft and not the front wheel, the net effect will be a higher actual speed for a speedo indicated speed.  So if your speedo is reading LOW as most do, this will correct that somewhat.

[Rhino]

Tire size and profiles is not an exact science by any means and size is not exactly universal among all tire manufacturers.  But you can expect some differences between tire profiles like 50 vs. 55.

Here is a link to a good resource that gets you an idea of the expected dimensions of a tire:

http://tire-size-conversion.com/tire-size-calculator/

So the stock rear tire for C14 is a 190/50-17.  According to the calculator you have:

Diameter = 24.5" Width = 7.48" Wheel = 17" Sidewall = 3.74" Circumference = 76.9" Revs/Mile = 824.3

A 190/55-15 will be:

Diameter = 25.2" Width = 7.48" Wheel = 17" Sidewall = 4.11" Circumference = 79.2" Revs/Mile = 799.8

So you can see that a 55 tire is a bit "taller" and therefore also will turn a bit slower at the same speed.  As far as effect on the speedo, since the C14 speedo comes from the drive shaft and not the front wheel, the net effect will be a higher actual speed for a speedo indicated speed.  So if your speedo is reading LOW as most do, this will correct that somewhat.

This confirms my experience. On stock rear tire, when my gps says I'm going 71 mph my speedo says 75. When I put on the 55 profile it corrected this error by about half. 824.3/799.8 * 71 = 73.17mph.

[jwh20]

This confirms my experience. On stock rear tire, when my gps says I'm going 71 mph my speedo says 75. When I put on the 55 profile it corrected this error by about half. 824.3/799.8 * 71 = 73.17mph.

Bingo!!  I see you were paying attention in class.   

And I did say "reading low", what I meant there is just what you said, your speed is lower than indicated.  So I guess the speedo actually reads high.  For some reason every motorcycle I've ever owned does this.  If you check it with a GPS, which is extremely accurate, you're always going slower than indicated.  Is this a way of fudging the top speed or something?

[Daytona_Mike]

I wonder if  the rear tire stretches out. With the 50 series at 170mph indicated I am really only doing 167 via GPS.
That is not much of a difference.

[Rhino]

I wonder if  the rear tire stretches out. With the 50 series at 170mph indicated I am really only doing 167 via GPS.
That is not much of a difference.

ZOW! That's moving right along. At that speed I would be afraid to look at my GPS and speedo long enough to read them. gen1 or flashed gen2?

[Daytona_Mike]

Gen1 - Full AreaP- flies out and PCV with Autotune and my friend on his ZX1400 walks away from me easily-- and then he is gone!

[jwh20]

I wonder if  the rear tire stretches out. With the 50 series at 170mph indicated I am really only doing 167 via GPS.
That is not much of a difference.

I'm sure there is some stretching out but it's also possible that there is added down-force from wind that might counteract that.  Mount a GoPro so it can film your rear tire contact with the road and take a few 170 mph runs so we can all know the results.   

[connie14boy]

I've have owned and ridden many bikes in 45 years, but none have been so sensitive with tires as "Black Bear", my 2009 C-14 ABS. As the stock 021 Crapstones wore out, the bike became unstable in high speed sweepers and low speed parking lot maneuvers, and got really weird if below 40 psi. I was thinking of trading it in or selling it because it was destroying my riding confidence. This forum recommended Michelin PR's with the 55 rear profile, and it was a night and day difference for me and the Bear. I can now play with the Porsches and can't get the ****-eating smile off my face! Thanks guys. (PS- Kawasaki made a big mistake with the stock 021 Crapstones- I'm sure it hurts the resale value too, as I have heard other bikers comment on the "clumsy" handling.)

[jwh20]

I've have owned and ridden many bikes in 45 years, but none have been so sensitive with tires as "Black Bear", my 2009 C-14 ABS. As the stock 021 Crapstones wore out, the bike became unstable in high speed sweepers and low speed parking lot maneuvers, and got really weird if below 40 psi. I was thinking of trading it in or selling it because it was destroying my riding confidence. This forum recommended Michelin PR's with the 55 rear profile, and it was a night and day difference for me and the Bear. I can now play with the Porsches and can't get the ****-eating smile off my face! Thanks guys. (PS- Kawasaki made a big mistake with the stock 021 Crapstones- I'm sure it hurts the resale value too, as I have heard other bikers comment on the "clumsy" handling.)

That is a familiar story but personally I think 80% of the difference is going from (and you said it) "Crapstones" to Michelin PRs.  The remaining improvement might be from the profile change but you'd have to compare PRs with 50 and 55 back to back to be a valid comparison.

My C14 came from the PO with Michelin PR2's installed and I find them to be excellent tires even if the "2" models are superseded.  I do have PR3's on my ZX-14 and I find them to be an excellent tire as well.  But both my bikes are using the stock size 190/50-17.  So I don't really have any experience using a 55 profile on either bike.

From what I've read, however, you tend to get the biggest change in handling by using a narrower (or wider) tire.  So going to a 180 width either with or without a profile change will get you more responsive handling.  Going to a wider tire, and I understand a 200 width is the widest you can fit on a C14, will tend to give you heavier handling in the turns but probably a better ride in the straightaways.  As always, tire sizing is a compromise.