I believe the general consensus is that most of us run close to the max. pressure as stated on the tire (within a few lbs. anyway). That gives an acceptable ride with maximum tread life. The max pressure on the tire is the "cold" pressure - they expect it to be more when the tires are warm, so as long as you're not exceeding the recommended max when your tires are "cold" you are OK, IMHO. I run my Metzeler ME880s at 38-40 psi both front and rear.
I read somewhere that tires normally wear more on the left because roads slope to the right to let water run off. I don't know if that explains what you are experiencing, though. I do know that most of us run much higher psi than what you stated. I know the manual says 28 lbs. or something like that, but the general consensus here is to run 38-40 instead. Gives much better tread life with little (if any) difference in handling.
I run 34 front, and 36 rear, and use pressure caps to keep them at the right inflation.
I would recomend within 10% of the TIRE manufacturers' rec. pressure. The Kaw manual says something like 28/30 IIRC. My Dunlops and Metzlers have always been at 36/39 (plus/minus one). The stock Flintstones recomend a good bit lower, I think, but not nearly as low as Kaw.
I recommend going to the tire brand web sight and looking up the specs for tire pressure for your particular bike; i.e., on the Metzeler web page, since I run ME880's, there is a lookup for the particular size ME880 we run and or a lookup of our bike by name with a pressure for "normal loads" and "greater than 200# load" which is people plus gear plus cargo. I run 36 front and 40 rear per the chart. The OEM pressures shown in the owner's manual or service/repair manuals are ONLY for OEM tires like my original Bridgestones. rgds Mike
Stock Tire Pressure-REAR
Ihave finished completing tests on using different pressures in the stock tires of my bike. My findings may contradict earlier reccomendations I have made conserning rider weight and shock settings.It should be noted that I am refering to the stock Bridgestone tires and not those that have tires by other manufactures. I belive there was some confusion there anyway looking at the tire pressure poll. The test bike was my 2002 Vulcan 750 with aprrox. 3,500 mile on it. the tires are nowhere near being worn and have excellent tread left. The first series of tests was on the rear tire.
After trying out pressures from 26 to 36 psi. I determined that the rear tire should for solo riding/and passengers under 150 lbs.. have 30 psi. Cornering tests indicate that more pressure than that for a rider under 180 pounds makes the rear a bit jumpy. However..riding with a heavier passenger/luggage weight in most cases will only require 2 more pounds of air. If you and your passenger total more than 300 pounds, I can see going as high as 34 psi...but that should be the maximum you ever use.( Passenger/luggage/rider total weight should not exceed 397 pounds according to the manual) So here..the pressure reccomended in the owners manual seems fairly spot on.Tests at lower pressures (26-28) , showed adverse handling charateristics. although the book does say that 28psi is fine for riders under 215 pounds...I got faster times through turns with the extra 2 pounds of air I added , and I weigh 148lbs.
I believe that some riders have found that the bike "rides" better with lower or higher pressures in the rear...but I am certain that this is just a bad fix...when the real culprit is the rear shocks.( See my mext post on "SHOCKS!!") Although 28-29 psi does not effect the handling that greatly and may be a good pressure to use for some riders, I myself have taken into account the fact that every time I have a passenger I don't want to keep adding air and then taking it out for just myself...I have found that the 30psi is a very good comprimise.Given the fact that sustained highway speeds also require a firmer tire...that is why I picked 30psi as a good all around pressure..even for those that never have passengers. I detected no adverse handling problems with it and hence that is my new recommendation. Knifemaker
Stock Tire Pressure - Front
The past few weeks I have been experimenting with diffrent tire pressures to determine what works best and seems the safest. After coming up with a workable pressure for the rear tire...( see post on Rear tires)..I began testing the front. the problem here is that it is very hard to detect odd handling attributes from the front end of a bike. Especialy ours , as the rear and front tires are diffrent sizes (widths being the important reason)..and the front forks playing such an important role also. The reason the widths make a diffrence is that the contact patches of the tires form more of a triangle than a rectangle. When the bike leans over..the front being thinner than the rear takes a moment longer to "set-up" for a turn...compared to tires that are closer to the same width. Most of you never notice this..but it happens and makes spotting problems a bit harder. Tire makers know this..and that's why they usualy sell front and rear tires as matched sets...they have a computer to figure out lean angles and design the tires to work as a pair...The way I solved this dilema was to devise a test where the front forks played a much smaller role and the transition time for the bike to set up for a turn was not a factor.
What I did was to test for front end slide in very slow but sharp turns. To do this, you enter a sharp turn, like a right turn from a stop at an intersection. Halfway through the turn..you abruptly make the turn tighter and roll on the throttle a bit. The bike will try to "push" the front tire in the dirrection it was orriginaly going..if all goes well , your new lean angle and countersteer will take you on the new path. If the front tire seems to slip a small amount first..this is dirrctly the fault of the tire loosing a good grip on the road. This was the basis for my test.
Everything else being equal..your tires shouldn't slip. Starting with Higher pressures first..34psi...I found that I could get the front end to slip quite easly at fairly low speeds making a right turn at a certain intersection. The road was not real smooth and was slightly crowned right near the curb.Waiting for the front tire to reach the top edge of the bank..and then executing the slight change..I found that I could repeat this without much trouble everytime I circled around and went through again. Now it was just a matter of slowly letting off some pressure for each run. ( Even though I knew what was sgoing to happen , it was still hard not feeling my heart skip a beat as the front end chattered sideways a few inches...so kids..don't try this at home....lol) After letting off one pound and repeating the test I slowly noticed the bikes reluctance to skip and found the transition going much smoother. When I got to 29 psi in the front tire I couldn't get it to slide at all. Based on this , I would have to conclude that this is the highest pressure I should run in the front end.
Tests at lower pressures than 26 psi exibited diffrent problems, unwilingness to take the turn smoothly and harder steering inputs requried to get through the turn at all. These being common indications of insuficiant tire pressure. The maual lists 28psi as the pressure to use in all load requirements...this seems to be quite logical from my tests...although I did find the bike did seem to go through fast turns..sweeping lefts and rights at 60 to 70 mph... just a bit more steadily at 29 psi than 28. Iv'e also noted posts about running much diffrent front tire pressures here...some seeming to say that the "higher" pressures gave a better ride or seemed to make the front feel "tighter"...and again I must point out that first...adding more than reccomended pressure does not absorb bumps better...higher pressures should tansmit shocks faster...not slower. And that any changes from the 28-29 psi are simply masking problems with the front suspension...Which in my opinion is in need of slightly stiffer springs and better dampening.( see my next post on shocks) Knifemaker