More about tire pressure.

[Guest]

I recently got Reg. Pridmore's book and I've been generally impressed with the content. Unlike some of the other experts he does have some differing ideas about some of the standard concepts and procedures, however.

One thing that I read but don't understand, as he doesn't explain his reasoning, is tire pressure. He states that while most tire manufacturers advocate pressures of around 40 psi, he suggests 32 psi (front & back) should be the correct setting for street tires. With two up or with heavier bikes he says back tires should be boosted by 2 psi or so. He doesn't differentialte between radials or bias plys.

I found this confusing and I wonder what the advantage is. Wouldn't the tire sidewalls get more "flexi" and wouldn't this result in premature wear or even tire failure in extreme useage?

Would anyone have any knowledge to share on this subject. Anyone taken Mr. P.'s CLASS courses?

Thoughts folks?

Cheers all,
Spyug.

[49er]

You should be running higher pressures on modern tyres. The tyres of our bike's era were designed to run around 32 psi. Pressures around that figure were recommended by the bike manufacterers.
However, IMO you need to set your pressures using your bikes suspension set up and your personal riding styles as guidelines.
I run Sport Demons and found 34-35 psi front and 38-40psi rear to suit me best. Because of the progresssive spings, increased preload and 15 grade oil, any pressures over 34 psi up front cause the front wheel to sart to loose adhesion during tighter, more undulating turns. The rear wheel is more stable at higher pressures, so isn't so sensitive to changes in psi.
The higher the pressure, the greater the side wall stability. It is a great advantage when running higher pressures, to be using a stickey conpound.
Just my 2 cents worth.

[Steve]

Yep, you have to look at things in context. When he was suggesting 32 psi, what was the maximum rating on the tire? Many (most?) manufacturers were selling comfort about as much as performance, so they suggested the softest pressures that would safely carry the intended load. If the maximum suggested pressure on the sidwall was 32 psi, then you run at 32 or less, depending on the load and speed. If another tire says it can carry the same weight, but requires 40 psi to do so, then that's what you run in it.

A general guideline I have always followed is the 10% rule. Measure and record your cold tire pressures. Go for a ride. Make it a spirited ride of at least 50 miles to ensure that the tires are properly warmed up. Measure and record your warm pressures. You are looking for a 10% increase in pressure. If it was less than 10%, your cold pressure was too high. If it was more than 10%, your cold pressure was too low. If you frequently ride two-up, you will need higher pressure, especially in the rear tire. Yes, you need to check the pressure rise again. Darn, another excuse for a ride.

Oh, if you change tires to another brand or model with different weight/pressure ratings, you get to do this all over again.

.

[simon kuether]

I'm with the 49ER.Bridgestone Spitfire's at 34 psi front and 38 psi rear and getting a grippy 15,000 km rear and ++km front.Cheers,Simon.

[Sandy]

A general guideline I have always followed is the 10% rule. Measure and record your cold tire pressures. Go for a ride. Make it a spirited ride of at least 50 miles to ensure that the tires are properly warmed up. Measure and record your warm pressures. You are looking for a 10% increase in pressure. If it was less than 10%, your cold pressure was too high. If it was more than 10%, your cold pressure was too low. If you frequently ride two-up, you will need higher pressure, especially in the rear tire. Yes, you need to check the pressure rise again. Darn, another excuse for a ride.
.

Excellent advice! This is the way we always checked for proper tire temperature/pressure back in my sport riding days and track days. We didn't have low cost pyrometers then. I haven't heard this method mentioned for quite some and thought that most folks either forgot about or just didn't know. If the tire is heating up too much you'll be over the 10% and likewise if the tire is not getting hot enough for the rubber to work properly, especially on soft compound tires, you'll be under the 10%. For general street riding you could however use as low as about 8% but softer tires don't seem to work great until they get nice and hot.

[chef1366]

I run 40psi in the rear and 35 in the front. Bike is stable and I get more miles from the tires.

[posplayr]

Great Tip

Hey Bill why didnt U tell me that before. U know I run 20 psi all around

[Billy Ricks]

Yep, you have to look at things in context. When he was suggesting 32 psi, what was the maximum rating on the tire? Many (most?) manufacturers were selling comfort about as much as performance, so they suggested the softest pressures that would safely carry the intended load. If the maximum suggested pressure on the sidwall was 32 psi, then you run at 32 or less, depending on the load and speed. If another tire says it can carry the same weight, but requires 40 psi to do so, then that's what you run in it.

A general guideline I have always followed is the 10% rule. Measure and record your cold tire pressures. Go for a ride. Make it a spirited ride of at least 50 miles to ensure that the tires are properly warmed up. Measure and record your warm pressures. You are looking for a 10% increase in pressure. If it was less than 10%, your cold pressure was too high. If it was more than 10%, your cold pressure was too low. If you frequently ride two-up, you will need higher pressure, especially in the rear tire. Yes, you need to check the pressure rise again. Darn, another excuse for a ride.

Oh, if you change tires to another brand or model with different weight/pressure ratings, you get to do this all over again.

.

Ditto on this advice. The maximum pressure stamped on the tires is for the maximum load rating. The amount of weight you carry and riding style makes the correct pressure different for everyone.

[Carter Turk]

I did four track days back in 2000-2001 on my Kat. Reg Pridmore's Class schools came up to Pacific Raceways formerly SIR (Seattle International Raceway)for a 2 day course.

When it came to tire pressures on the track with morning temps in the upper 40's to low 50's, he suggested 30-30 psi. I put in 125 laps of the 2.25 mile course over 2 days.

I had a 591 bias up front and a radial MEZ2 out back before they discontinued it.

I still mix with a Harley 591 up front and a Dunlop 205 radial out back. 31psi front and 31-32 out back. I get about 10 months out the tires and ride year round.

[salty_monk]

I ride with 28 - 36 in the 1000's but I'm not very heavy.. (165lb) Seems to be working ok so far. I haven't really tried any other pressures to compare. I'm running Avon RR

Dan

[chef1366]

Hey Bill why didnt U tell me that before. U know I run 20 psi all around

I thought it was 10psi.