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Discussion Starter · #1 ·
For the longest time I did not understand why Suzuki engineers would design the SV650 with a 120/60R17 tire on the front and a 160/60R17 tire on the rear.

From the start, I wanted a different set up but I did not really understood why...

My first replacement front tire was a 120/70R17 Michelin Pilot Power. I did not know what that meant, except that I needed to adjust the ride hight a little. The bike felt a little different but I quickly got used to the change.

With time I ended up upgrading the rear wheel with a 2005 Bandit GSF1200S 5.50" rear wheel and a 180/55R17 Michelin Pilot Power... Later I upgraded the Bandit rear wheel with a lighter 2007 GSXR750 and a 180/55R17 Michelin Pilot Power 2CT... I still did not understand what that meant except that a larger tire = more rubber contact on the road.

Which a lot of people thought it was over kill, more weight than necessary, The stock wheels and tires do a fine job as they come.

The truth is obvious, Suzuki engeeners know more about design that I could hope to learn. But did they design the SV650 to be a standard bike... Or they design the SV650 be a race track bike to be railed on the corners of a canyon road or a race track?

All Super Sport Bikes come with 2 basic wheel and tire set ups... And this is not just Suzuki, We are talking Aprila, Ducati, Honda Kawasaki, Suzuki, Yamaha. etc.

  • 120/70R17 tire on a 17" X 3.50" front wheel, and a 180/55R17 tire on a 17" X 5.50" rear wheel.
or,

  • 120/70R17 tire on a 17" X 3.50" front wheel, and a 190/50R17 tire on a 17" X 6.00" rear wheel.
Now, I have done a little reading... Geometry: Wheel base, radius of the wheel and tires, radius of tires cross section, steering axis, caster angle, trail... Very interesting stuff...

Just after reading the importance of camber angle and its relation to trail, I realize that the SV650 is built more as a sports touring bike. However the shorter GSXR forks will put our SV650 in a competition race set up. Never mind the GSXR performance suspension and brakes. We are just talking geometry values.

OK now back to the wheels and tires... The 120/70R17 front tire and the 180/55R17 rear tire work together to make the bike corner... The wider rear tire cross section makes the bike pitch forward and tilt sideways when cornering. This is hard to explain. The point is that to mimic the super sport bikes wheel and tire set-ups changes the SV650 performance to a different sport level...

I have a lot more reading to do... Knowing the works of the bike will help understand what happens and why... I guess I am happy to inform that changing the Set up is not just for looks but it actually helps with performance on the bike... Will update more as I continue reading I am on page 32 of 360. ;D

Luis
 

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The difference between a 120/60 and a 120/70 is about 12mm of section height. Installing a 120/70 on the front raises the front end about 1/2". This will tend to slow down turn-in and increase straight line stability.

Raising the forks 1/2" will return the bike to stock ride height in the front. Raising the front relative to the rear or lowering the rear relative to the front has this effect because of the slight change in rake in the front end.

Lowering the front relative to the rear or raising the rear relative to the front has the opposite effect. Turn-in slows and straight line stability is compromised slightly. Since GSXR forks are shorter the turn-in speeds up. Racers like that feel because the transitional handling is quick.

The difference in geometry among all the sport bikes (and the SV) is tiny. Last I checked I couldn't find more than 1 degree spread in rake angle, similar small differences in trail. Very small changes in rake (like changing tires or even running different preload settings) make relatively large changes in the way the bike feels.

Having said all that, putting all the science into metal and rubber has unpredictable effects.
Some bikes feel better than others with virtually identical specifications. Most of this is due to compliance of the various systems and how they interact. Some bikes handle better when they don't feel as nice to the rider (race track performance). It's still very much an art.
 

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Discussion Starter · #5 ·
As Nexus pointed out, the SV650 is NOT a Super Sport... And that is why we modify it!!!

At least for me, I love the SV650 because it is a V-Twin. It is the under dog.... Everyone on a super sport thinks little of the SV650... Regardless if they even know how to ride their super sport. I feel good when I pass them on the corners... And have to wait for them to catch up at the top of the mountain. It's a pretty good feeling.

Andyauger,

See even if you adjust the ride hight, with the 120/70R17, you still have better stability because the fact that the front wheel is taller than the 120/60R17.

Also the radius of the 120/70R17 front tire cross section is different... Specially if you have a wider 180/55R17 rear tire... When the bike its lean at an angle... The wider rear tire makes the bike tilt the narrower front tire toward the inside of the corner... Also, makes the front end pitch foreword.

Now if you get on the gas... The gyroscope of the rear wheel gives the bike more stability... Also, the rear tire slides a little toward the out side... Helping the bike corner... And also, lifts the front end slightly giving you a little more trail which ads stability. The bike corners smoothly... On left handers I can let go of the inside clip-on and touch the asphalt... The bike feels really stable.

Trail is 102mm on the SV650, and 100mm on the SV650S

Trail is 96mm in the 05-06 GSXR1000 and 96.4mm in the 07-08 GSXR1000

I do understand the art statement... What feels good to me may be crappy and bumpy for you....

After doing the SV650 suspension, Penske double click on the rear. GSXR 1000 front with Traxion Dynamics springs and softened valving... I think the 5.50" rear wheel and 120/70R17 front tire, and a 180/55R17 rear tire modification is the next best performance upgrade...

I am getting a little faster at the track... And, I am not riding scared either... Luis
 

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You guys sure do sound like you know what you are talking about....SVX keep talkin. Let us know about your proposed "ideal" setup. I am always looking for stuff to do to my bke. Changing stuff and tweakin it is half the fun of owning an SV :)
 

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A 120/70 is not appreciably more stable than a 120/60. If you're referring to extra mass farther from the center of rotation, that may be true, but the difference is very small. Down in the decimal places a zero certainly. Weight distribution in the tires themselves can have an effect just a big or bigger. Net weights have a bigger effect, usually.

Similarly, the difference in gyroscopic stability of the rear tire from the 160 to the 180 is pretty small in general. Remember that the wheels and tires have to change direction as you go through a curve, so more gyroscopic stability isn't necessarily a good thing. If you look at MotoGP bikes of various cc classes you will note that they use the smallest tires possible, not the biggest.

Gyroscopic forces are quite small compared to the magnitudes of the forces involved in keeping a bike stable in a curve.

As you lean over with a wider rear tire lots of stuff is happening. The angle of the centerline relative to the ground does have a slightly greater slope, but the line of drive is also altered. The effect is that the line of drive is "off" the front to back center of mass more as the tires (front and/or rear) gets wider. Wider and narrower tires will sideslip pretty much the same. The contact patch isn't that different.

When comparing contact patches "squirm" is just as important as net area. Compounds and tread design (in the case of racing slicks, compounds) are developed to control squirm as much as possible.

The rake and trail differences you mention are pretty small, and over the years the numbers go back and forth around a fairly narrow range on sport bikes. The SVs all have geometry that is in the supersport design range.

The bottom line is that the science is great, and can point you in directions you may not have thought of. It's always good to have an understanding of how stuff works. Also, if it works for you, it works. Another rider might climb on your bike and think it stinks. That's the nature of racing. That's why there isn't one setup that works for everyone.
 

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70 is the sidewall height as a percentage of the width, an the 17 is the rim size in inches
 

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70 is the sidewall height as a percentage of the width, an the 17 is the rim size in inches
no,it is not.that is why you all wrong here.it is ratio between width and height(not sidewall but part you ride on).
reason you can have 120/70 same diameter as 120/60 or even race tires like 16.5.
diameter change would apply only if all have identical sidewall,which they don't.
reading numbers on tire will only tell you width and ratio for that particular tire.even than it does not have to be right.there are tires stamped 180 but measure at 175 or 185 or ?.
 

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napkin, 120/70-17 tires do have a larger diameter than 120/60-17

and a fat rear tire on the sv wont make your bike corner harder. fat tires are for putting power down. that applies to straight line and cornering.

you can say whatever you want man, but all you are doing is adding weight and spending money.

look at the 125 and 250 cc racebikes.
 

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Let's clarify some terms. Diameter is the rolling radius times 2. The width is the measurement from the left side to the right side. A 120/70 will have a rolling radius 12mm greater than a 120/60 [(120*0.7)-(120*0.6)=12mm, or if you like (0.7-0.6)= 0.1, 0.1*120 =12]. The diameter (twice the rolling radius) of a 120/70 is 24mm more than the diameter of a 120/60. They have the same width.

You can't have a 120/70 with the same rolling radius as a 120/60.

Also, before you get too hung up with theory you should understand the relative magnitudes of the various forces and how they change. An example is "bigger diameter = more stability". Suppose you have a 30# wheel and tire combination (120/60/17) rolling along at 50 MPH. Now suppose that you move the radial center of mass 1/4" further away from the axle (not just part of the tread as in a 120/70/17 combination). The difference in centrifugal force is about 4%. So moving just part of the tread is inconsequential, educated estimate 0.02% change in centrifugal force.

If you could produce a super rubber that would be super sticky and super strong all the MotoGP bikes would be on 1" wide tires.

And still, in the end result, if it works for you it works.
 

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You can't have a 120/70 with the same rolling radius as a 120/60.
... unless you have differnet rim sizes. Just nitpicking. :)

If you could produce a super rubber that would be super sticky and super strong all the MotoGP bikes would be on 1" wide tires.
For now I´m fine with 110/50 and 150/70 and wouldn´t mind radically slimmer tires. Would be a major mental readjustment process, probably. :)

Ciao
Jan
 

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Let's clarify some terms. Diameter is the rolling radius times 2. The width is the measurement from the left side to the right side. A 120/70 will have a rolling radius 12mm greater than a 120/60 [(120*0.7)-(120*0.6)=12mm, or if you like (0.7-0.6)= 0.1, 0.1*120 =12]. The diameter (twice the rolling radius) of a 120/70 is 24mm more than the diameter of a 120/60. They have the same width.

You can't have a 120/70 with the same rolling radius as a 120/60.
search what those numbers mean.it is ratio for tread not sidewall.
take 2 different brands with same numbers and they will not be same diameter.
60 is just more flat and round while 70 is more V shaped.it is profile that changes.
120/60 in one brand can be bigger diameter than 120/70 in other.it can simply have taller sidewall.
 

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search what those numbers mean.it is ratio for tread not sidewall.
take 2 different brands with same numbers and they will not be same diameter.
60 is just more flat and round while 70 is more V shaped.it is profile that changes.
120/60 in one brand can be bigger diameter than 120/70 in other.it can simply have taller sidewall.
Sorry wrong.....not that complicated

3 digit number: The "nominal section width" of the tire in millimeters, from inner sidewall edge to outer sidewall edge
/: Slash character
2 or 3 digit number: The "aspect ratio" of the sidewall height to the total width of the tire, as a percentage.


Yes..... differant manufacturers tires will have slightly differant diameters for the same size.... pure tolerance issue....
 

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it is not sidewall height,it is height of tire(tread you ride on+sidewall).try measuring different tires and you will see it is not simple 12mm difference.
[/IMG]http://www.amadirectlink.com/roadride/Riderresc/images/tiresection_sml.jpg[/IMG]
 

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Discussion Starter · #19 ·
SVX What book if you dont mind my asking, may be somthing to fun to put on the reading list
The book is Motorcycle Dynamics... By Vittore Cossalter...



Luis
 

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Discussion Starter · #20 ·
The point is that a taller 120/70R17 front tire in combination with a wider 180/55R17 rear tire (with adjusted ride hight...) Makes no difference in a straight line...

However, when lean over, makes the bike Pitch Forward more and also increases the Yaw Angle. This helps the bike corner better. That is because the change affects the bike's geometry when lean over. The change happens progressively as the bike leans into a corner.

Once the bike is mid corner the bike feels more stable because the change to the geometry of the bike. This inspire confidence and it is easier to get on the throttle sooner witch further increases stability.

So as ANGREESHEEP said... Adding weight and spending money...

Well my 07 GSXR750 rear wheel weights less that the stock SV650 rear wheel... And spending money on an upgrade that will help make you a more confident and faster rider... Is worthed...

Again the change was not done for looks, It was done for performance. I do not commute on my bike and I do not do long touring rides. I ride the canyons one corner at time and do track days so sharpen up my riding ability.

If you commute or tour the canyons at the posted speed limit... spending $400. to $600 on a rear wheel upgrade may offer no benefit to you. I still recommend suspension upgrades first. The wheels and tires is probably the next step...

Luis
 
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