Tire Pressure

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Mar 28, 2014 | 09:28 AM

#31

dwoodlives

Cruiser

Joined: Nov 2013

Posts: 198

Likes: 17

From: Central Coast California

Quote:

Originally Posted by Fatbobiron

Your pressures could be off by as much as 3 to 4 psi low or high

[snip]

Do yourself a favor and invest at least 30 bucks on a quality digital tire pressure gauge.

It takes the guess work out of the pressure situation. The one I bought is accurate to .1 PSI

There is potentially a big difference between "resolution" [your 0.1 psi readout] and accuracy.

I became curious about my collection of tire pressure gauges. I also bought 3 new bourdon dial type gauges in three different price ranges: $75, $45, $18. Also bought a $13 digital gauge. These were added to my collection of pencil-type gauges.

These were tested against a calibrated mercury manometer capable of reading from zero to 32 psi.

Keep in mind the highest accurate test pressure available was 32 psi.

Of three "pencil" gauges: one was w/in 1 psi between 20 psi and 32 psi. The other 2 varied w/in 2-3 psi all over the place.

The $75 gauge was w/in .75 psi throughout the range [which was w/in advertised specs].

The $45 gauge was right on w/in the pointer width throughout its range.

The $18 gauge was off 1.5 psi on the low end, getting w/in .5 psi at the top end.

Amazingly the cheapo digital gauge was right on w/in its readout resolution [which was single pound increments].

Without the ability to accurately test higher than 32 psi might seem like a serious limitation. But for most auto/motorcycle tire pressures if a gauge read 'on' at 32 psi, I feel fairly certain that it is close at e.g. 40 psi [my Sportster rear tire, the highest pressure I care about].

These results were with the gauges I actually have. Another sample of the same models would likely yield different results [therefore I'm not mentioning brands/models].

BTW, with my recent obsession with tire pressures, I also tested tire pressure changes from 'cold' to 'warm'. It can be considerable. A discussion for another time.

Mar 28, 2014 | 10:38 AM

#32

Crazy Biker

Elite HDF Member

Joined: Jun 2006

Posts: 4,356

Likes: 1

From: Lansdale, Pa

40 40

Mar 28, 2014 | 11:24 AM

#33

AJSHOVEL

Seasoned HDF Member

Joined: Jul 2012

Posts: 9,511

Likes: 13,828

From: Pa.

Quote:

Originally Posted by Dusty Bones

Well the people who make my tires said do NOT use the psi in the book or on the frame, it will result in a dangerous ride. I kinda figured that out a long time ago. I still confirm every time I change my tires just to make sure they did not change something in the design.

I agree. Every tire is different. Always go by the max pressure and run 10% less solo for starts. Usually pretty close. The manual and the frame sticker have no idea what tires you're running.

Mar 28, 2014 | 11:45 AM

#34

Dusty Bones

Banned

Joined: Jun 2013

Posts: 1,461

Likes: 4

From: MI

Quote:

Originally Posted by AJSHOVEL

I agree. Every tire is different. Always go by the max pressure and run 10% less solo for starts. Usually pretty close. The manual and the frame sticker have no idea what tires you're running.

I go a step further. After new tires I allow for expansion of the tire that happens with all tires. After the scrub in and a day to expand I will drop 10% off max and go for a ride to warm them up, not around the block, atleast 35 miles and measure hot psi right away. If the hot psi is more than 10% over my cold psi then the cold psi is too low. I will add a pound cold and start over. When I hit the magical 10% rise in psi when hot I have hit the exact psi I need for my weight and bikes weight combined. Tires I use are always within a pound plus or minus but no two sets are exact. I am picky about my tire performance and just dropping 10% as a rule might work for some but I might only need 7% or up to 12% drop cold from max psi cold to get my perfect psi.

Do it on all rubber tired vehicles I have and tire wear and performance is perfect, never have delamination problems, handleing or performance problems. Psi is checked often and correct at a minimum weekly.

So really there is no set psi for everyone. If people are serious about being safe and making our over priced (not my brand lol) tires last we would all find that magic for us psi where hot psi is 10% more than cold psi.

I have seen my brand of tire be shot in 2500 miles on other bikes by riders who swear the frame psi is perfect for all tires, while mine last 8-10K of aggressive riding, hell I have to change my brakes when I get new tires so I aint got time for under inflated dangerous tires. Might make a soft ride for sensitive behinds while sniffing flowers, but dont expect good tire life unless you run rock hard OEM spec tires (dont matter who makes them, Harley tire specs are horrible).

Mar 28, 2014 | 11:54 AM

#35

shotgun1133

Intermediate

Joined: Mar 2014

Posts: 42

Likes: 1

From: Michigan

I have always ran Dunlops or Continetals with pretty good luck. I have discovered through experience especially with the Dunlops, they will cup if ran at HD's recommended pressure. It's best to run the tires at manufacturers max recommended cold pressure on the front to prevent cupping. Maybe a couple pounds less on the rear but no more than that. If you have ever followed a bike into a curve at speed and looked at their tires, an underinflated rear tire will pull out of line with the rim which is less than ideal.