Kawasaki Sportsbike Riders Club - Australia - Online Forum

I really wanTed To find ouT The science behind Tyre pressures so I could make informed decisions abouT whaT pressures To run, and low and behold I found iT righT here on KSRC

I've quoted this from Jonno's EPICSuspension Setup page here in case oThers wanT To learn Too.

viewtopic.php?f=21&t=24596

Really good facts and science for learning to choose correct tyre pressures.

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Tyre Pressure:
You'll get a lot of opinions on what tyre pressure to run, but the correct tyre pressure for you is not a matter of polling other rider's opinion. Here are the basics you'll need to decide for yourself. Dennis Smith of Dunlop's Sport Tyre Services recommends an increase of two to four pounds in front tyres and six to eight in the rear. While the most scientific means of determining if a particular pressure is the use of a pyrometer to assess whether the rubber has reached the manufacturer's recommended temperature, charting the pressure increase of a tyre after track sessions will give a good impression of how hard a tyre is working.

Stamped on the outside of many of your tyres is a recommended tyre pressure range. (At least an upper limit.) For longest tyre life it is my recommendation that you strive to keep them at the higher limit of those recommendations (regardless of what your motorcycle owner's manual might say to the contrary.) Further, this pressure should be determined while the tyres are cold - meaning, have not been used for a couple of hours.
Start with the bike manufacturer's recommendation in the owners manual or under-seat sticker. This is the number they consider to be the best balance between handling, grip and tyre wear. Further, if you're running alloy wheels on poor pavement, consider adding 2 psi to the recommended tyre pressure just to reduce the likelihood of pothole damage. Just as you would for a car, increase the pressure 2 psi or so for sustained high speed operation (or 2-up riding) to reduce rolling friction and casing flexing.
In order to get optimum handling a tyre has to get to its optimum temperature, which is different for each brand of tyre. Most of us don't have the equipment needed to measure tyre temperature directly so we measure it indirectly by checking tyre pressure since tyre pressure increases with tyre temperature. Tyre temperature is important to know because too much flexing of the casing of an under-inflated tyre for a given riding style and road will result in overheating resulting in less than optimum grip. Over-pressurizing a tyre will reduce casing flexing and prevent the tyre from getting up to the optimum operating temperature and performance again suffers. Sliding and spinning the tyres also increase tyre temperatures from friction heating.
A technique for those wanting to get the most out of their tyres on the street is to use the 10/20% rule.
First check the tyre pressure when the tyre is cold. Then take a 30-40 minute ride on your favorite twisty piece of road to get your tyre temperature up, then measure the tyre pressure immediately after stopping.
If the pressure has risen less than 10% on the front or less than 20% on the rear, the rider should remove air from the tyre (to increase heating affect of carcass flex). So for example, starting at a front tyre pressure of 32.5 psi should bring you up to 36 psi hot. Once you obtain this pressure increase for a given rider, bike, tyre, road and road temperature combination, check the tyre pressure again while cold and record it for future reference.
Each manufacturer is different. Each tyre model is different.

A tyre design that runs cooler needs to run a lower pressure (2-3 psi front) to get up to optimum temperature. Remember carcass flex to generate additional heat.

The rear tyre runs hotter than the front tyre on both road and track. So the rear tyre cold-to-hot increase is greater.

Dropping air pressure has the additional side effect of scrubbing more rubber area, and can additionally add more traction at the cost of a little stability
As an example for aprilia RSV Mille recommended starting temperatures for road use are.

Front Tyre 34.8 deg. Cold which in turn should be approximately 37.5 -38.5 deg Hot (3-4psi increase)

Rear Tyre 39.4 deg Cold which in turn should be approximately 45-47 deg Hot (7-9psi increase)
For the track you'll have to drop the cold tyre pressures an additional 10/20%. Track operation will get tyres hotter (increasing the cold-to-hot pressure range) so starting at say 32/30 psi now should bring you up to the same temperature (and pressure) that 35/39 psi gave you for the street.
Since track riding put tremendous stresses on a tyre the tyre heats up more than if it was on the street. run at a racetrack, unless of course you're running a race tyre. The lower the tyre pressure the more the tyre deforms. The more the tyre deforms, the more friction there is between the tyre and the road surface. The more friction, the more heat. The more heat, the greater the opportunity the tyre has to regenerate itself by shedding the 'used' layers of rubber (to a point). This deformation of the tyre also creates a bigger contact patch at the cost of a little stability.

When you are accounting for your riding style and the way different days, streets, tracks can be accounted for. All bikes will have different characteristics which means my starting riding temperature is different than yours.
Additionally with the colder months of the year tyre pressures and the effect of temperature can greatly affect the overall pressure.
Time and outside temperature effect the pressure within your tyres. It is NORMAL for a tyre to lose about 1 pound per square inch (psi) per month. Outside temperatures affect your tyre pressure far more profoundly, however. A tyre's pressure can change by 1 psi for every 10 degrees Fahrenheit of temperature change. As temperature goes, so goes pressure.
For example, if a tyre is found to have 38 psi on an 80-degree mid-summer day, it could lose enough air to have an inflation pressure of 26 psi on a 20-degree day six months later. This represents a loss of 6 psi over six months and an additional loss of 6 psi due to the 60 degree temperature reduction.
At 26 psi, your tyre is severely under inflated and dangerous!
What is being illustrated here is that you MUST check your tyre pressure on a regular basis (about once a week is reasonable) and to be particularly aware of it on cold days
Reference of James R. Davis, sportsrider.com, Larry Kelly mad-ducati.com
Suspension stroke
A sportbike should normally not use its full suspension stroke, although on some circuit one or two big bumps or hollows can cause the suspension to bottom. Also landing of front wheel after wheelies can cause excessive use of the front fork stroke. If suspension bottoms in big bump or hollow, it should not automatically mean that the suspension should be set more hard. However, if suspension bottoms at the place were the maximum grip is essential the tyre cannot create the best traction, because it also has to perform as spring. Adjusting the setting is necessary. During every riding session the suspension stroke should be carefully checked. When tyre grip and lap times improve, the suspension has a harder job. So, setting must be set harder. On the opposite, when it starts raining tyre grip and lap times go down, in that case a softer setting should be applied.

I've read this article about tyre pressures before and I've debated whether to say anything. Basically, I don't like what it says at all and I don't think it's good science.

It's stuff that an average corner tyre store owner would tell a truck driver or a guy loading up his four wheel drive (to go round Australia) to do with tyre pressures on their vehicles. For that type of application it's fine.

Anyway, sorry if it causes offence to some peoples belief, but there you go.

no offence taken none of us wrote it thought it was worth posting becsuse it actually gives reasons for the advice it gives..... I know it's not actual "science" but there seems to be method to the madness...

So what's the 'real deal' if this isn't it?

I don't think you could get the right tyre pressure for the road ever.... to many variables... road surface, road temperature, stop start traffic

99% of people would only push their tyres on the road to maybe 70% being generous also as each brand tyre works in different ways, sticking close and just under the manufactures pressure is the best option, they would have done x1000 more hrs testing than anyone else...

On track a complete different story....

Tyre Science?

Road Tyres
36 36 for the road
30 30 for the track

then ride.............................simple really

This'll start a debate.

Ha ha

Depends what track tyres?

The first thing to understand is how a tyre generates heat.

To see how heat is generated you need to look at the tyre footprint temperature as the tyre is ridden around the race track. To do this you use three infrared sensors per tyre and a data logger. One infra red sensor points at the middle of the tyre and the two others point at each side of the tyre. The data logger receives a signal from the sensors and records the temperature of the tyre in real time as the bike is being ridden.
When the bike is ridden out of the pits and onto the circuit you will see that the temperature of the tyre down the straight will be slightly higher than track temps (assuming you haven't used tyre warmers).

As you accelerate out and tip the bike into the first bend you will see the tyre temperature on that edge of the front and rear tyres increase slightly. As you straighten up, and start accelerating hard, you will see the middle of the rear tyre increase temperature, however you will see the tyre edge that you just cornered on lose some temp. Then as you head down the next straight, with the throttle wicked up, you come to the first hard corner and you brake hard. Suddenly, you will see the footprint temp on the middle of the front tyre shoot up dramatically. Say, the on track footprint temp out of the pits and down the straight was 36 degrees C, well under brakes on the first corner, (remembering that you are still being a bit cautious, cold tyres and all) you might see the temp shoot to 50 degrees C!

As you tip in, this time using more lateral G's than the first corner, and you will see the tyre edge of the front and back tyre temps increase dramatically also. Depending on how hard you corner, the tyre temp might jump from 33 degrees to maybe 42.

As you start to throttle on, the weight transfers more to the rear, the rear tyre gets more weight (load) the tyre edge gets a bit hotter, you straighten up apply more power, more weight transfer, more heat generated, pick the bike up, middle of the rear tyre gets hotter....hard down the straight, maybe a little wheel spin...see a temp spike on the middle of the rear tyre. Hard down the straight and brake hard for the next corner...middle of the front tyre has cooled slightly and is now approx 46 deg C and you break hard and late...temps spikes to 65 deg C! Tip in...more confidence, more speed, more corner g’s........... this time it’s a left hander and the other two corners out of the pits were right handers......tip in..ohhh...bit of front end slide...ohh ohh..bit greasy...yeah because the left side of the tyre hasn't had any load yet...no load to generate the heat in the tyre footprint to counter the g’s.

The left side of the tyre might have been at about 36 or 37 deg C before you enetered the corner however, after tipping in and load the left side of the tyre, you’ll see the LHS tyre temp shoot up to about 43 – 44 deg.

Anyway, round you keep going, each corner, each braking application generates more load, more heat and the tyre temp increases and then loses some down the straight until you hit and an equilibrium between atmospheric temp, track temp, tyre construction, tyre compound, track design, track grip(co-efficient) and how hard you ride.
If you keep going round you will see the middle of the tyre running at about 80 deg C and shoot to 120 to 130 under brakes. At Phillip Island you will see the left side of your tyres hit 115 to 125 then drop back to about 80 on the straight. If you’re a pro rider on the same tyre and bike then you’ll generate more heat, more load, more cornering force and you’ll cook the tyre(make it greasy and slidy), blister it or even delaminate it. The tyre chooses the wizard.

Tyre heat is generated by the shearing, tearing, distorting and flexing of the microscopic layers of the tyre surface as determined by its chemical compound. Soft compound tyre = greater wear, more temp because there is more tearing shearing and distorting of the fibres of the footprint with the road. Thus, high speed circuit like Phillip Island means more load, more G’s greater tearing shearing and distorting of the footprint and therefore....greater heat is generated. When the tyre is not under “load” it loses temperature. This is what happened to Rossi and caused his broken leg!

So it’s a constant increase decrease thing. That’s what you have to picture as the tyre goes around the track. Not one temp. However, the inside of the tyre, where the air is...reflects an average of this fluctuation..depending on tyre construction and heat dissipation, through the footprint surface, THROUGH THE SIDEWALL and the rim!!!
The inside air temp increases with carcass temperature but doesn’t fluctuate like the tyre footprint temp does. It’s like a little oven. Convection causes the air to increase temperature. As the temp increases it expands.

But air isn’t necessarily air. Air has other things in it...moisture is one of them. Water causes a greater increase in pressure. Depending on the amount of water that is in the air you blow into your tyres will determine just how much greater your tyre pressures will increase. That’s why you should use dry air or even nitrogen. But these also expand with heat...nitrogen expands about half that of atmospheric air.

Just as a guide, air pressure will increase by 1 psi for every 4 deg c of internal tyre temp

The thing is that tyre pressure is a function of tyre construction. The two factors determine how the carcass will behave under load for cornering, braking manoeuvring etc and importantly it determines the size of the tyre footprint. Increase the tyre pressure gives a stiffer carcass and a smaller footprint and vice versa. Smaller footprint size changes grip.

In the tyre industry, tyre carcass construction and the tyre pressure work together to carry weight. The idea is that the more weight you carry, the stiffer the tyre construction and the higher the pressure (eg a truck). The pressures written on the side of the tyre indicate the tyre pressure at the tyres maximum allowable load carrying ability. They are obsessed with making sure the vehicle doesn’t crash due to a tyre failure. Thus they worry about weight on the tyre causing the tyre to basically disintegrate because the tyre generates too much heat and explodes killing thousands of innocent children and dolphins and cute butterflies. The low pressure or over weight heat that is generated flexes the ENTIRE carcass not just the sidewall. Thus they explode into a mass of rubber strewn down the highway...usually its just the tread that delaminates off the tyre and then the tyre sidewall flogs itself to death because you keep driving on it. But there it is to see when you pull up...the sidewall of the tyre is trashed....it must have caused the heat and caused the tyre to explode.

Yeah right...go to any race track and measure the footprint temp of a bike that comes in hot. If the footprint temp is 80 or 90 degrees C then you’d be lucky to see 40 degrees in the sidewall temp (if you measure the actual sidewall not the side footprint). It would be a scientific breakthrough if the low sidewall temps generated the higher footprint temps. Heat travelling from low to high.

cool thanks well written!

ok, so safe to say 30 track 36 road it is then? which is what I'd been doing, but a bit lower front than rear on the road or same front and rear?

why do manufacturers say lower for the fronts? smaller tyre radius, therefore less deformation and less heat generated and smaller contact patch, so lower pressure required to boost patch and temp?

The best way to approach pressures is to ask an experienced knowledgeable rider with the same bike and same tyres what they run. If they are a good rider and a bit faster than you then you might have to run sligthly higher pressures..one or two psi...as they will generate more heat and thus slightly higher pressure rise.

You can help yourself if you record your pressures before a run and then after. From cold to hot....the rise for different ambient and track temps etc.

But really it's all relative. The question is: "how fast do you want to go".

If you go out on a track with road tyre pressures and you ride slow then it ain't gunna matter one bit.

If your real fair dickum then you go testing and you prove what pressure is best, you learn how to calculate pressure rises and you get real good at knowing everything about your tyre, its number of heat cycles, it s construction, it's compound operating window etc. The stop watch and the seat of your pants become your indicators....and i forgot...your wallet tends to dictate things too.

tim wrote:

why do manufacturers say lower for the fronts? smaller tyre radius, therefore less deformation and less heat generated and smaller contact patch, so lower pressure required to boost patch and temp?

Depends on construction and sometimes the bike. You will find that on some bikes the tyre pressures are the same depending on how the front tyre is constructed compared to the rear and on the bikes weight distribution etc so it's not a cut and dry thing.

Tyre pressure affects contact patch size and affects the "balance" of the bike front to rear. Too high a front pressure, can cause the front to slide, or more correctly, increase the tyre's slip angle which means the bike runs wide or won't turn back into the apex or the thing won't turn at all etc. If you lower the tyre pressures you can "balance" the front to rear grip. This makes you go faster. It doesn't generate more heat it simple changes the contact patch size.

What your looking for is confidence. Riding fast is a confidence thing. A well balanced predictable bike gives you more confidence. The more confidence you have in the bike the faster you go. Well set up suspension gives you more balance and predictability, more confidence and you go faster.

Grand prix riders live on confidence.

One thing though, I was trying to tell you that the tearing, shearing and deforming of the tyre tread is what generates the heat. The tyre tread on a microscopic level is like the hairs on your head. If you could imagine that the road surface, on a microscopic level, is full or rocks and boulders and crevices and if I were to stick all the hairs of your head to all those little rocks and boulders etc and then pulled head quickly away....first it would hurt...but secondly...all the hair I pulled out of your scalp causes heat in your head!
If your scalp was the tyre surface and your hair was the fibres on the the tyre surface and it happens a million times a second...thats a lot of heat generated.

Look how much movement is in the this Ntec
Photo of Ripper at EC on his super light CBR1000

Tack, while I would love to challenge your thinking, I can't. You are spot on.

FMD!!! You people are fuked !! Just lean the Karrn !!

hoffy V2.0 wrote:FMD!!! You people are fuked !! Just lean the Karrn !!

I learnt from the Troy Bayliss School of motorcycle engineering......

he teaches you one thing.....










just ride the fukker....

Strika wrote:Tack, while I would love to challenge your thinking, I can't. You are spot on.

Nice of you to say Marty but i can hardly take credit for it. All this stuff comes from years of working directly with Japanese tyre engineers, international race teams and technicians etc.

I just collected the information.

The problem is there is so much disinfromation which has become "gospel" around the place which makes making any comment on this stuff difficult.

So I'm happy if it helps someone.