Tires

 

Tires are the last word in what you are doing with your motorcycle.

Many people do not pay them the proper attention they deserve. So many people just inflate them to the pressure stamped into the sidewall and leave it at that. Keep in mind when you take the pressure recommendation off the sidewall that the OEM has to cover their butts and has the worst case scenario in mind (a 250lb rider with a 300 lb passenger and carrying 200lbs of snacks across Arizona at 100 mph)

Tire Pressure:

Why not 42 psi? Probably the most common tire pressure used by newish riders is 42 psi because it is what is stamped on the sidewall. If you are sportriding, you want your tire to stick, it won't stick very well at 42 psi for a few reasons: with 42 psi your tire does not have much give so it will not take the shape of the road, it will make the tire "bouncier" so your damping so will need to work harder making setup more difficult, your tire won't heat up, and it will make for a smaller contact patch between your tire and the ground.

Tire pressure is so very important. It affects everything from heat to flex to contact patch. It is very simple and works like this: with less air the tire will flex more and provide a larger contact patch and will conform to the road better. The problem comes from the tire's inability to keep its shape, this flex makes heat through the friction of the material rubbing together. Too much heat and the oils in the rubber come to the surface of the tire and the tread gets "greasy" also when rubber gets hot it wears much quicker. Underinflation also lets the tire move laterally on the rim, giving a "loose" feeling and can lose traction if it rolls too much with the road. Overinflation makes a tire very cool because there is less flex, but without the heat there is less traction because the rubber compound is heat activated and with less flex the contact patch is smaller and cannot conform to the road, a bad thing for a sport rider. What you need is something in between (unless you are on a long distance trip) I find 34psi front and 36psi rear near perfect for sport riding on most of the radials I have ridden on (strangely enough, same for bias plies)

Track stuff:

On the track you want your tires to be hot so that you get optimum grip, but not too hot so that they overheat and bring the oils in the rubber to the surface.31psi front and 29 psi rear seem to be a good starting point. Some say you want a pressure difference between cold and hot to be between 2-4psi in front and 6-8psi in rear. In the olden days there was a 10% rule (suggestion) where the psi difference between cold and hot was 10%, I say olden days because the rims were similar size front to rear. It still works out pretty much bang on for the modern front. Why less pressure in the rear for track when on the street there should be higher pressure in the rear? The rear tire for modern bikes is wider than the front so there is a bigger chunk of air inside to heat up.To heat this up you need a bit more flex. As the air inside heats up the air molecules expand, bringing the pressure up to where it needs to be for the tire to keep its shape. If you use the above suggestions (31psi front 29 psi rear) and add the differences between cold and hot suggested above (2-4 psi front 6-8 psi rear) you come up with a hot psi of roughly 34 front and 36 rear, the same as I recommend for cold psi on the street. For the street riders reading this: you cannot get nearly the same heat in a tire on the street than the track, in fact the heat buildup on the street is negligable in comparison, that is why I suggest 34/36 cold psi on the street to keep the shape of the tire because the psi rise on the street is also negligable.

You can tell if you go too hot on tire because it gets a kind of look like a roller that has been rolled through a paint tray,and if it isn't hot enough it will look more like a tire that has been run on the street. A lot of track newbies think that because their tires have tons of shredded rubber on them they are newfound track gods, actually the opposite is the case, the faster you go the cleaner your tires get. The rubber the newbies have stuck to their tires is from the other bikes. (see Keith Code's "soft science of roadracing" for further details)

Profiles

The tire profile is very important to the way the bike handles. For the most part you want a constant radius of the tread surface. This gives a linear rate of turn. There are more triangulated profiles out there, especially race inspired or race tires such as the 190/55 sizes or any aspect ratio over 55. The advantage of the triangulated profile is for quicker steering and increased traction at extreme lean angles (think of a triangle sitting on its side, big contact patch). Be aware that by changing tire aspect ratios you are also changing ride height measurements and there can be consequences for that (see ride height section for details)

Keep in muind the circumference of your tire. If you do not have a ride height adjuster, be aware that putting a 190/55 tire in place of a 190 can reduce your trail and stability.

"I have a 6" rear rim, 180 or 190?" Most (if not all) 180 size sport tires have an aspect ratio of /55 giving a triangulated profile, and the majority of street tires in the 190 size have an aspect ratio of /50 so they are a flatter profile (their advantage is at lesser lean angles you can use more power because of the rounded profile because they have almost as much contact off center as they do when vertical. I think that is probably why all the big power bikes come with them for ham fisted street riders). The 180/55 was designed for a 5.5" rim, the 190 was designed for a 6" rim. Now for the less obvious. A 180/55 is taller in the center than a 190/50 even if you fit it on a 6" rim (180 x 0.55= 99mm, 190 x .50= 95mm), with the horizontal stretch you you take out even more of the rounded profile making it even more triangulated. Another advantage is that a 180 is lighter than a 190 so you get a major advantage of increased acceleration and ease of change of direction. Another insignificant theory (mine) is that the carcass is a bit tighter because it is stretched horizonatally that little bit on a 6" rim. Some proof that there is a noticeable advantage of the 180 is that a large percentage of club racers with 6" rims use 180s and also that in a Sport Rider Magazine tire shootout the tire makers that did not make a 190/55 (notice the 55) sent 180/55s to be used on the GSXR1000 they were using. In conclusion, if you have a 6" rim and want the best street/sport tire size, go with a 190/55 (notice the 55, pirelli and Metzeler make them, hopefully more will join in) or a 180/55.If you have a 5.5" rim, the 180 is the only tire, period, full stop, even for pose purposes.

 

Heat cycles:

Every time a tire heats up it does a thing called "outgassing", this is where the chemicals in the rubber release and the rubber loses some of its sticky compound. After too many of these the tire hardens up and loses its available grip. A sport rider would want to discard these.

What the numbers mean:

When you see say: 190/55/ZR17, this is the size of the tire in this format:

tread width/ aspect ratio (width vs hieght)/speed rating, Radial, diameter of the wheel.

you can know when they were made by the lot number, the lot number starts with DOT and then goes on. the last four #s are what you are lookin for, the last two are the year and the two before that are the week (remember 52 weeks in a year)

 

this from the michelin site:

WHAT IS A SPEED RATING? The speed rating, represented by a one- or two-letter code in the tire size [100/90-19 (57H), for example], indicates the maximum speed at which a tire can be safely operated when it is properly loaded and inflated. Please refer to the safety information area of this website for important advice regarding the use of Michelin motorcycle tires and tubes. Code mph km/h Code mph km/h Code mph km/h

(B) 31mph or 50kph, (P) 94mph or150kph, (H) 130mph or 210kph (J) 62mph or 100kph (Q) 100mph or 160kph (V) 149mph or 240kph (L) 75mph or 120kph (R) 106mph or 170kph (W) 168mph or 270kph (M) 81mph or 130kph (S) 112mph or 180kph (W) >168mph >270kph (N) 87mph or140kph (T) 118mph or 190kph

 

 

1998: Won a WSMC Formula One Race. Won several CMRRA (Southern California)

Championships.

1999: Won Aprilia Cup Challenge Championship, winning three of four series

rounds and taking second in the fourth round. Joined Team Valvoline EMGO

Suzuki. Won Suzuki GSXR600 Cup Series Final and finished second in Suzuki

GSXR750 Cup Series Final, at Road Atlanta. Won four CCS Championships at

Daytona Race Of Champions, including Unlimited Supersport Expert,

Middleweight Grand Prix Expert, GTU Expert, Heavy weight Superbike Expert.

Finished 10th in AMA 600cc Supersport debut and 5th in AMA 750cc Supersport

debut, at Loudon.

2000: Won AMA 750cc Supersport Championship with three race wins and a total

of six podium finishes in nine races. Won seven out of 12 races in Formula

USA Unlimited Superbike Championship and finished second twice, finished

second in series points. Won Formula USA Sport Bike races at Daytona and

Road America.

2001: Won the AMA Formula Xtreme Championship and two Xtreme races and

regularly was a top contender in the AMA 600cc Supersport Series. Tested and

gained a ride on Red Bull Yamaha MotoGP team for 2002.

Signed with the Factory Suzuki motogp team for 2003-2006