Tire Pressure influences

[Yakaru]

So between my own research and reading SLOWn60's comments on my track thread I'm curious about something:

What influences a tire's preferred PSI for proper wear? In my tire there's unused tread where my suspension isn't loaded but...

http://biketrackdayshub.com/motorcycle-tyre-wear-guide/

From that link and my tires (see my Track thread: https://www.ninjette.org/forums/showthread.php?t=268586 ) it looks like I'm potentially getting some 'hot tearing' which is a sign of being under-inflated. Does that seem correct?

What would influence the correct pressure beyond the tire? I'm not riding that aggressively compared to some, but I am pretty light for example. Why would someone else on the same bike have a different ideal PSI than myself? Other than looking at the wear pattern, what might tell me about the direction I should take my pressures?

Thanks!
Yakaru

[csmith12]

Lemme ask you this... The order of rotation of groups went like this... I, A, N right?

[Yakaru]

Order was: Advanced, Intermediate, Relaxed, repeat until final session of relaxed.

[SLOWn60]

Originally Posted by csmith12

Lemme ask you this... The order of rotation of groups went like this... I, A, N right?

I was wondering how much of that might have been picked up off the track myself. I still think though there's an adjustment to be made (on that day, on that track, at the track temps that existed)

[csmith12]

Originally Posted by SLOWn60

I was wondering how much of that might have been picked up off the track myself. I still think though there's an adjustment to be made (on that day, on that track, at the track temps that existed)

Quite possibly, the pressures seem to be slightly upside down. On a "good" day at the track, the rear should raise in temp more than the front for a few different reasons. So you see riders with a slightly lower rear pressure than the front.

[sharky nrk]

IMHO, your going to have a bit of a hard time getting any kind of real tearing (hot or cold) on street tires at N pace. Even if your pressures are not perfect. One of the reasons for that is simply that street tires are designed to operate in a much wider range of temperatures than race tires. Your likely not riding the tire hard enough and/or far enough out of the operating range to have any kinda tearing. Now street tires can tear, but its MUCH less common than on race tires.

Typically as has been mentioned already, your front tire tends to be set a little higher in pressure than your rear, because out on track your going to be working your rear tire a little harder than the front. Most of the flex (heat generation) in the tire comes in the corner entry and corner exit (braking and accelerating) as the contact patch deforms. And in general, you spend more time with load on the rear tire due to the application of power as compared to hard braking.

[SLOWn60]

But; as I mentioned in your other thread: it is most important to spend your learning time at this point is on riding skills. Machine setup is far less important now. Lol! I should have never brought up the subject!

[alex.s]

the picture you showed has tire slag build up. doesn't look like any hot or cold indicators to me. if i had to guess i'd say you were close.

[RacinNinja]

Are you using tire warmers or not?

If not, 10% increase from cold to hot. Measure them when you go out. Measure them immediately when you get back in. There should be a roughly 10% increase. It's worked really well for me and what the "old school guys" taught me.

If the increase is MORE than 10%, add air.

If it's LESS than 10%, let out air.

For example, cold pressure is 30 PSI. You come in, and it's 35 PSI. Add 2 PSI to the tire before your next session.

[csmith12]

^^^^ that is the KISS method many use and it's pretty fair most of the time except for in the wet or for certain hamfisted riders. Weather, temps and surface are probably the biggest factors I run across for needs to adjust pressures. Aside of that, if the bike is not set up right or the rider has certain habits (late brakers, hard apexers and early pinners), the adjustments per rider/bike combo can help improve feel. A bad setup is a killer of tires, but I believe over/under inflated tires are sacrificed at the track more often.

Overall though, imho... if your bike is setup well AND you have good throttle control AND you are at least in the ballpark of tire pressure, then you can save some coin on tires throughout the season. Not to even mention that the bike responds, handles and feels more planted.

My n250 tires (sc1/rosso II) normally last around 40 track days and some odd races
My r6 tires (q3/q3) normally last at least 15 or so track days

Food for thought

[Yakaru]

Fair enough. I'll keep an eye on it.

Another question: I noticed my wear is much farther out on the rear than the front -- is that expected? I don't mind it but thought I'd bring it up.

[Motofool]

Originally Posted by sharky nrk

.......

Typically as has been mentioned already, your front tire tends to be set a little higher in pressure than your rear, because out on track your going to be working your rear tire a little harder than the front. Most of the flex (heat generation) in the tire comes in the corner entry and corner exit (braking and accelerating) as the contact patch deforms. And in general, you spend more time with load on the rear tire due to the application of power as compared to hard braking.

In my experience, the tire bearing the higher load (the rear tire) requires the higher initial pressure, .......always.

[Motofool]

Originally Posted by Yakaru

.......... Another question: I noticed my wear is much farther out on the rear than the front -- is that expected? I don't mind it but thought I'd bring it up.

That is normal, and a natural consequence of the different sizes of the transverse section of both tires.

The 45-degree red line in the schematic represents the surface of the pavement for max lean angle: the big profile is rolling on its edge, while the small profile does not (still has some distance from the edge).

[csmith12]

Originally Posted by Motofool

In my experience, the tire bearing the higher load (the rear tire) requires the higher initial pressure, .......always.

HEAT!!! The additional heat alone will compensate for a couple of lbs of more pressure in the rear at track pace vs street pace. The front gets more heat too, but not as "consistently" as the front and has time to cool before the next stress. The front only sees extreme loads/stresses under heavy braking and on exit.... doesn't even need to be on the tarmac.

[Alex]

Originally Posted by Motofool

In my experience, the tire bearing the higher load (the rear tire) requires the higher initial pressure, .......always.

Not on racebikes. Cold rear tire pressure is often significantly lower than the front. At the GP level, some of the rear tires called for 20 - 22 PSI cold.

Check out Bridgestone's page for their racing slicks: Front pressure 26 psi, rear pressure 20 psi

[csmith12]

Originally Posted by Yakaru

Fair enough. I'll keep an eye on it.

Another question: I noticed my wear is much farther out on the rear than the front -- is that expected? I don't mind it but thought I'd bring it up.

On the average bike at the track yes, completely normal. It takes a hell of a rider to make it to the edge of a front tire on an "average" bike.

The more "professionally/expertly" setup bikes I see... not so much. Professional riders need every nanometer of contact patch to enable their pace to scrape off that .001 of a second per lap.

To put it in perspective, and just make an educated guess... on any given average track day, only 1 or none of the riders can scrub a front to the edge (coaches included).

[Alex]

It's easy to scrub it to the edge of the tire (at one point, at one time). You just aren't expected to keep the bike upright afterwards.

[cbinker]

tire pressure is not as important for you as getting comfortable with the track and bike moving.

[sharky nrk]

Originally Posted by Motofool

In my experience, the tire bearing the higher load (the rear tire) requires the higher initial pressure, .......always.

Chris and Alex covered it

[toEleven]

Originally Posted by SLOWn60

But; as I mentioned in your other thread: it is most important to spend your learning time at this point is on riding skills. Machine setup is far less important now. Lol! I should have never brought up the subject!

If you're anything like me, you feel inclined to get all of the mechanical adjustments perfect so that you can isolate the factor you want to work on - the rider. But it may not be as possible as I (and perhaps you) would want. Get it good enough, focus on rider skills, go back to the mechanical bits when they start to pose a problem you (or a coach) can identify from the saddle.

[Yakaru]

Skills are the focus, but the engineer in me just wants to tinker with the mechanical bits too :P

[Motofool]

Originally Posted by csmith12

HEAT!!! The additional heat alone will compensate for a couple of lbs of more pressure in the rear at track pace vs street pace. The front gets more heat too, but not as "consistently" as the front and has time to cool before the next stress. The front only sees extreme loads/stresses under heavy braking and on exit.... doesn't even need to be on the tarmac.

Originally Posted by Alex

Not on racebikes. Cold rear tire pressure is often significantly lower than the front. At the GP level, some of the rear tires called for 20 - 22 PSI cold.

Check out Bridgestone's page for their racing slicks: Front pressure 26 psi, rear pressure 20 psi

Thank you both much.
I did not know that one.