Just the basic facts about sportbike tires

The purpose of this page is to give the reader some key & commonly misconceived information about sportbike tires.

First off it is important to know how to read the numbers on the tire.

Example: 190/55/17

190 is the tire width in millimeters. These are not exact as you will find that no two manufacturers 180 or 190 size tires are the same width etc...

55 is the aspect ratio in that the sidewall height of the tire is 55% of the width (190*.55=104.5mm)

17 is the rim size in diameter

Now we'll put that into to use:

The RC51 (& most other current literbikes) come with equipped with a 190/50 tire. The first thing most owners do is throw it away & put on a 180/55 or 190/55 tire. The reason for this is the 180/55 tire is a taller tire than the 190/50 & aids in the overall handling of the bike making it turn-in easier. The 190/55 is an even better choice as it gives you an even taller diameter so you get all the benefits & then some of the 180/55 plus way more rubber on the ground when leaned over). The downside is that the 190/55 tires are more expensive sometimes WAY more expensive than their 180/55 siblings & the taller the tire is the more you will have to adjust your bikes suspension geometry to make it handle properly (i.e. hold a line without putting pressure on the bars, not want to stand up on the brakes & not run wide on corner exit etc...)

The current trend is even taller profile tires. We now have 180/60 & 200/60 series tires designed to handle the 200+ horsepower of modern literbikes. These tires put a lot more contact patch on the ground when leaned over allowing for much better acceleration out of the turns.

As you can clearly see the new 60 Series tires are HUGE

Next we will lay out some more general definitions:

DOT Street tire: a tire approved by the Department of Transportation for use on public roads

DOT Race tire: a tire approved by the Department of Transportation for use on public roads, but widely regarded as a purpose built tire designed to sacrifice longevity & wet weather grip for better adhesion under dry conditions only.

Race Tire: any tire that does not carry a DOT approval rating regardless of whether it has rain grooves or not (slicks) that is intended for use on competition road courses.

Contrary to popular myth the main difference between DOT street tires & DOT race tires is not the rubber compound. It is the construction of the belting plies in the tire carcass.

The belting in street tires is designed to give more stability & better ride when the bike is upright whereas the belting in race tires is designed for better grip & stability at high lean angles.

We have all heard the stories about Ricky Racer crashing his bike cause he was running race tires on the street & couldn't keep them warm enough etc & while there is some validity to those stories because the rubber compounds are designed to work in certain heat ranges, the overall statement is false & usually nothing more than an excuse for rider error. Cold race tires still stick better than a cold street tire. Race rubber being a softer compound than street rubber will be inherently more grippy than a harder street compound. Now if you have just recently abused your race tire or have installed a race take off then you may have either not enough catalyst left in the tire to provide adequate grip or you may need to put in a little time to scrub off the dead layer of rubber to get to some fresh rubber with good catalyst in it.

"What the hell is catalyst you say?" Well what really gives a tire its grip is a chemical catalyst in the compound that when heated makes the tire adhere better to the road surface. The reason racers sell race take-off tires even though they have more than half the tread left is because they have burned the catalyst out of the tires through either too many heat cycles or simply too much heat was generated in the tire period & now the tire no longer functions to their satisfaction or required level of grip. The hardness of the tire compound is only one part in the factor on grip as is the temperature range they are designed to run in. Tires pushed beyond their temperature range for extended periods will start to delaminate (seperation of the rubber from the carcass). Now I don't know about who you hang out with, but I know only maybe a handful of guys that can actually overheat a tire during street use... Street riders as a general rule simply do not have to worry about getting any tire race or street into the proper operating temp range as a normal sport riding pace will bring the tire into a useable temp range.  Racers on the other hand have to be concerned with selecting the proper temp range due to the fact that delamination can occur if the tire is subjected to sustained temps above it's operating range.

Another misconception is the idea that race tires are no good in the rain because of their lack of grooves in the tread. While it certainly is true that a tire needs grooves to channel water away to prevent hydroplaning, the real reason for lack of wet grip is again the compound. Street tires generally contain lots of silica in them to provide better heat dispersion (aids in consistent tire operating temps) & wet weather grip.

Something else that really needs to be discussed... I am to this very day in awe of how many motorcycle riders are ignorant to the simple fact that the recommended pressures listed in their owners manual for their motorcycle and on the sidewalls of the motorcycle tires are for the absolute maximum load capacity limit of the tires.

42 & 36 PSI are the max psi ratings for the tire. That means it is maximum pressure you should run in those tires for carrying the maximum load they are rated for. If you are not carrying the maximum load of the tires then reasonably lower pressures will offer you a better ride and more traction in all conditions.

Last, You can buy any gauge you want from $2 to $600, but if you don't at the very least check the calibration against a verified source you have no idea if it is accurate or not nor do you know if it is consistent.

I live in a world at the track where 1-2 psi can be the difference between a tire that lasts for a few laps or one that lasts for a few weekends. I have seen $12 Accu-gauge branded products produce consistent results for 2 decades and I have seen $450 liquid filled gauges be 6lbs off right out of the box.

You have to test them against a known pressure source. I mean it is no problem to use a gauge that reads 2lbs high as long as you know it always reads 2lbs high, but simply trusting a gauge without any type of verification is risk I am not willing to take and you shouldn't either. Every weekend I work at the racetrack tuning suspension I get at least 3-4 riders coming up to me with what they think is a suspension issue based on poor tire wear and when it turns out to be an incorrect tire pressure they are almost always flabbergasted. Never underestimate the value of an accurate and consistent tire gauge.


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