1975 KZ 900 , ZRX Swingarm, 89 GSXR front end

Oh man tire scientoligy...

The theory I think carries the most weight is this..

On the racetrack, the tire builds a great deal of heat, which in turn expands the air inside it. When the starting pressure is higher, the elevated temp is high, increasing the volume of air inside, and decreasing the contact patch size. There is no doubt somebody out there who can explain this better. But thats the way i get it.

Also, the tire builds heat quickly with lower pressure, thereby sticking better mechanically, when it is at a lower pressure. So you get the best traction early.

Both of these rules, are not really in play on the street, at least at the 26-28 lb. range. I run 30--31. Kind of a compromise.

After 20 minutes on the track, the tire gets hot enough to be uncomfortable to the touch (150 degrees). The next time you ride hard in the canyons, stop and lay your hand on the rear tire across the profile, I bet you'll be suprised to find it warm but not hot.

When you talk to tire guys they get figity unless they really understand it. I "think" it's more about the volume of air as it expands, than the pressure. After a session the pressure may not be all that high, but the air inside has expanded, reducing the contact patch.

So if anybody has a better explaination, I am all ears!!

Your only is as smart as you is good at listening. When you think you know it all you stop learning. Yup..I am all ears...

Thanks for the explanation.
I did quite a bit of reading on suspension last night. I'll try to set it up today.
At least i have a plan now.
i think i must be out of wack on the settings, rather than having a rake issue.
I hope so. that would be an easier fix than the rake.
I will check my tire pressures too. Thanks.

tk11b40 wrote:

Oh man tire scientoligy...

The theory I think carries the most weight is this..

On the racetrack, the tire builds a great deal of heat, which in turn expands the air inside it. When the starting pressure is higher, the elevated temp is high, increasing the volume of air inside, and decreasing the contact patch size. There is no doubt somebody out there who can explain this better. But thats the way i get it.

Also, the tire builds heat quickly with lower pressure, thereby sticking better mechanically, when it is at a lower pressure. So you get the best traction early.

Both of these rules, are not really in play on the street, at least at the 26-28 lb. range. I run 30--31. Kind of a compromise.

After 20 minutes on the track, the tire gets hot enough to be uncomfortable to the touch (150 degrees). The next time you ride hard in the canyons, stop and lay your hand on the rear tire across the profile, I bet you'll be suprised to find it warm but not hot.

When you talk to tire guys they get figity unless they really understand it. I "think" it's more about the volume of air as it expands, than the pressure. After a session the pressure may not be all that high, but the air inside has expanded, reducing the contact patch.

So if anybody has a better explaination, I am all ears!!

Your only is as smart as you is good at listening. When you think you know it all you stop learning. Yup..I am all ears...

want a visual explanation... you know those balloons you buy for birthdays that are filled with helium? well, if you keep it for a while they start to loose their flotation right? this is because the helium molecules start to break down. well, if you take that same balloon and put it into a room that is at a higher temperature it seems to have inflated back to somewhat its original size. This is because those helium molecules that are still in tact begin to move around again and bump into each other to form new molecules, but since these new molecules are not stable they will quickly break down once again after they either reach room temp or are moved to a cooler area. This same action happens with tires. You not only get better traction with a race slick tire because of its bigger surface due to its lower psi but it allows for the tire to expand so it don't pop (which could be BAD on a strip!). this is the best way I can explain it. Ahh science, you got to love it...

Contact area has jack to do with traction unless your talking loose surfaces in which paddles and knobs help grab more material to throw. In sand low pressure does not get a better grip by producing a larger contact area, rather it lowers the cars pressure on the ground and reduces the tendency of the vehicle to sink into the sand. In rocks it helps more of the knobs wrap around a rock which is different than driving up the rocks.

Ok, that was to answer all of the replies that may be spawned by my first sentence.

When you lower pressure on the street the contact area increases which decreases the pressure exerted by your tire on the ground in direct relation to the increase in area.

The only ways to get more traction are to eat ice cream more often, heat up your tires (increasing the friction), or buy stickier tires.

Lowering pressure on the track just helps the tire heat up faster (increasing traction due to heat regardless of contact area). The tire heats up faster because of sidewall flex from the low pressure. Sidewall flex allows your rim to get that much closer to the ground. If the rim hits the ground your traction goes way down.

And yes, hotter tires at the track will increase in pressure, just not that much. Blowouts in under pressured tires occur because the additional sidewall flex breaks down the sidewall until the slight increase in pressure blows out your tire's sidewalls. Which is why blowouts usually leave a nice long strip of tread.

badboie wrote:

tk11b40 wrote:

Oh man tire scientoligy...

The theory I think carries the most weight is this..

On the racetrack, the tire builds a great deal of heat, which in turn expands the air inside it. When the starting pressure is higher, the elevated temp is high, increasing the volume of air inside, and decreasing the contact patch size. There is no doubt somebody out there who can explain this better. But thats the way i get it.

Also, the tire builds heat quickly with lower pressure, thereby sticking better mechanically, when it is at a lower pressure. So you get the best traction early.

Both of these rules, are not really in play on the street, at least at the 26-28 lb. range. I run 30--31. Kind of a compromise.

After 20 minutes on the track, the tire gets hot enough to be uncomfortable to the touch (150 degrees). The next time you ride hard in the canyons, stop and lay your hand on the rear tire across the profile, I bet you'll be suprised to find it warm but not hot.

When you talk to tire guys they get figity unless they really understand it. I "think" it's more about the volume of air as it expands, than the pressure. After a session the pressure may not be all that high, but the air inside has expanded, reducing the contact patch.

So if anybody has a better explaination, I am all ears!!

Your only is as smart as you is good at listening. When you think you know it all you stop learning. Yup..I am all ears...

want a visual explanation... you know those balloons you buy for birthdays that are filled with helium? well, if you keep it for a while they start to loose their flotation right? this is because the helium molecules start to break down. well, if you take that same balloon and put it into a room that is at a higher temperature it seems to have inflated back to somewhat its original size. This is because those helium molecules that are still in tact begin to move around again and bump into each other to form new molecules, but since these new molecules are not stable they will quickly break down once again after they either reach room temp or are moved to a cooler area. This same action happens with tires. You not only get better traction with a race slick tire because of its bigger surface due to its lower psi but it allows for the tire to expand so it don't pop (which could be BAD on a strip!). this is the best way I can explain it. Ahh science, you got to love it...

AHh..

Ok I knew this would happen.

If contact patch has nothing to do with traction why has increased in size over the last 30 years?

Rsdials. try cornering on a set of bias ply tires, then switch to redials, see how much different that feels.

Anyway my comments refer to raodracing, or roadcourse.

There are a thousand opinions out there. I can tell you the old Bias tired 80's bikes did not stick to the pavement like the new tires do. Yup...crashed a time or two, saved a few bad ones, all slides.

Rare to get a bad slide on the street any more. It used to happen all the time for me. Maybe I am just old and slow now.:laugh:

"RADIALS"

TYPO..sorry

tk11b40 wrote:

The roller is done, well roller prototype. Thanks to Mark for heading off a problem I would have had later. No doubt been all upset about it.

The ceramic coating is done on the header, Performance Coatinfs in Seattle, nice work. Good service.

Brilliant!

-KR

tk11b40 wrote:

AHh..

Ok I knew this would happen.

If contact patch has nothing to do with traction why has increased in size over the last 30 years?

Rsdials. try cornering on a set of bias ply tires, then switch to redials, see how much different that feels.

Anyway my comments refer to raodracing, or roadcourse.

There are a thousand opinions out there. I can tell you the old Bias tired 80's bikes did not stick to the pavement like the new tires do. Yup...crashed a time or two, saved a few bad ones, all slides.

Rare to get a bad slide on the street any more. It used to happen all the time for me. Maybe I am just old and slow now.:laugh:

Under this logic I would be well ahead to put a 220/90-16 on my bike. Trust me, been there, done the tests, checked results, experiments, etc. Results show area doesn't matter, it is about the load on on area (pressure) that affects traction. There are lots of opinions, but the fact remains that area doesn't matter. If I had tires a foot wide made out of PVC I'd slide out of any corner.

Wide tires present a larger radius for cornering which allows the rider to lean the bike over more without reaching the edge of the tread, and then sliding out of the corner. You have just as much area as before touching the ground with wide tires as old tires.

Why do stock car tires get trashed compared to F1? Because the wider tires in formula racing lower the stresses on the tire allowing faster corners without tearing apart. Also why my driving style caused my radial car tires to tear in the middle. Too much cornering on tires and suspension meant for casual driving. Lead to heavy sideways loads and eventually a nice groove around the tire with metal bands showing.

Radials just keep the tire in its proper shape compared to bias plies that deform and offer odd edges similar to reaching the edge of your tread. You can lean further, and go a bit faster so long as your tire stays in a round profile.

Contact area doesn't affect traction??!!?? :ohmy: Completely and utterly inaccurate...period.

hmmmm. i wonder why they make wider tires (slicks) for dragsters if contact area doesn't matter. I guess I was mistaken.

79MKII wrote:

Contact area doesn't affect traction??!!?? :ohmy: Completely and utterly inaccurate...period.

Find me a source saying that contact area between two objects increases traction, excluding the things like mud, sand, and rocks.

badboie wrote:

hmmmm. i wonder why they make wider tires (slicks) for dragsters if contact area doesn't matter. I guess I was mistaken.

Again, see the post about formula cars. Increased area of tire on a dragster lowers the stresses on the tire and the temperature. The tires are sized to get hot and stick to the pavement without melting into a puddle of steel and wire. If they were smaller the car would have great traction if it could ever get out of the puddle of smoked rubber.

Unless you frequently do burnouts on the track, do what you want if your paying for your own tires, lower air pressure will not increase your traction.

With one stipulation, if you ride slow and don't work the tires enough to keep them warm, then yes, low air pressure will help keep your tires warm and stickier. If you push the bike and really work the tires you are better off with a stickier tire kept at the proper pressure. Less tire flex and better traction. Just reduced tire life.

On a side question, if I can lift up 250lbs with my arms and I weigh 125lbs, why can't I pick myself and a chair up into the air while sitting down? Do I need a chair with arms or a reclining back?

OK tire discussion all done now...

you win.