stupid tire question

[diffluere]

First: Yes, I searched it first.

Okay, so, I have the 120/80 front tire. I was wondering if the bigger tire requires a higher pressure than the standard 25psi. I have the Shinko tires,
This is probably a ridiculous question so try to be nice =)

[patrick_777]

Fill it to what it recommends on the side of the tire. FWIW, I keep all of my tires between 30 and 35lbs.

[bonehead]

I second what Patrick said. And good to see you back on the forum.

[Easy Rider]

Fill it to what it recommends on the side of the tire.

SIGH. :roll:

The number on the side of the tire is NOT a recommendation.

It IS the maximum safe pressure that the tire can be inflated to in ANY application.
That usually bears NO resemblence to what the correct pressure is in THIS applicaton.

So MY answer to your question is: NO, the slight difference in tire size will have little (if any) effect on what the ideal operating pressure is.

Running tire pressures more than 2-3 lbs higher than the "real" recommendation will cause increased wear in the center of the tread and reduced traction and possibly compromised handling. None of those effects will be drastic but they all are very REAL.

[mole2]

[quote="patrick_777":1v7jiqj7]Fill it to what it recommends on the side of the tire.

SIGH. :roll:

The number on the side of the tire is NOT a recommendation.

It IS the maximum safe pressure that the tire can be inflated to in ANY application.
That usually bears NO resemblence to what the correct pressure is in THIS applicaton.

So MY answer to your question is: NO, the slight difference in tire size will have little (if any) effect on what the ideal operating pressure is.

Running tire pressures more than 2-3 lbs higher than the "real" recommendation will cause increased wear in the center of the tread and reduced traction and possibly compromised handling. None of those effects will be drastic but they all are very REAL.[/quote:1v7jiqj7]

Didn't Ford recommend a lower pressure than what Firestone put on the side of the tires and cause premature failure? Firestone stated that the psi on the side of the tire was what was recommended by the manufacturer and should have been adhered to instead of the softer pressure Ford recommended to make the ride softer. I'm just asking...not being argumentative.


:)

[blaine]

I with "EASY' on this one!

[Easy Rider]

Didn't Ford recommend a lower pressure than what Firestone put on the side of the tires and cause premature failure?

Don't remember the specifics well but that was only part of the story. IIRC, the main problem was owners not paying ANY attention to the pressure and letting it get even below the Ford numbers; often WAY below.

The rest of the story, I believe, was mostly the lawyers argueing with each other. Maybe Ford did screw up their recommendation IN THAT SPECIFIC INSTANCE, but that one mistake with a huge SUV has virtually no bearing on this discussion.

While it IS true that some applications require the max. pressure to be used (the front tires on my tractor, for instance) the VAST majority of applications do NOT require that. Using the max. pressure when it is not required REDUCES the overall performance of the tire. Internet hype and subjective testimonials not withstanding, that is a well established fact.

[burkbuilds]

When the manufacturer of the bike specs the pressure for the front and rear tire that spec refers to that bike using the OEM tire. If you replace those tires with tires that have a significantly different set of specs I'd seriously consider that the original bike specs may no longer apply to the current tire. As an example, I owned a truck that OEM tires were max rated at 44psi and the mfg recommendation was for 40 psi which seems reasonable since it's about 10% less than max recommended pressure for those tires. I replaced those tires with a higher load rated tire that max pressure rating was 80 psi. If I had run those tires at 40 psi it would have seriously damaged the sidewalls and caused premature failure. I ran them at around 72 psi (about 10% less than max pressure recommended by tire mfg) and they wore evenly and held up well.
So, my thoughts would be that if your new tires deviated significantly above the OEM tires max rating, I'd adjust upward and keep a check on your tire wear to see if you are getting even wear across the tread or to much wear just in the center and adjust accordingly.

[Easy Rider]

I replaced those tires with a higher load rated tire that max pressure rating was 80 psi. If I had run those tires at 40 psi it would have seriously damaged the sidewalls and caused premature failure.

I got no real problem with that theory but I've been exactly there before and had somewhat different results.

The higher rated tire was VERY likely an entirely different construction.....like a REAL 4 ply (or 4 belted or maybe even 6 ply) instead of 2 ply belted. It also likely had thicker and stiffer sidewalls; a true "truck" tire instead of a heavy "car" tire.

Assuming that the original tires were actually apporpriate for the total load of the vehicle, it probably wasn't really necessary to increase the pressures NEAR that much. I don't remember my exact numbers but I tried mine about 90% of the new max. and it road like a TANK; bounced my kidneys out of place. When I ran them back to 5 lbs over the original recommendation, it rode 1000% better and there were no problems with wear. Given your numbers, that would have been 45-50 lbs instead of 72.

I don't think you will EVER find that much difference in max. ratings on motorcycle tires unless you do something really wierd.......and then all bets are off.

[diffluere]

Well if I recall, the max psi for the OEM tires was 33psi. Maybe this is totally wrong. The new max for my new tires is 45 psi. I think running at 40psi would be insane!

I'm going to pump them up to 27 instead of 25 and see if that feels any different. 25 feels fine to me but I was just wondering. =)

[blaine]

I am running 100-90.I tried it at 25psi bike wanted to follow cracks in the road.Increased psi to 30 lbs bike feels alot more stable.I have 17000kms on same tire.Still not down to wear bars.I also run 30psi in the rear.These are CHALLENGER tires.I get good mileage from these tires.

[dhgeyer]

diffluere,

I think you are on the right, common sense track. Here's what I know on this subject, some of which has already been stated. The pressure in the owner's manual is almost always lower than the max pressure on the side of the tire. There was one bike I owned where they were the same, but that was a very heavy bike. The GZ is a very light bike.

As a general rule, ideal handling will be achieved with the pressures listed in the owner's manual. Maximum tread life will be achieved at a pressure somewhat above that, but handling will be affected. A somewhat increased pressure will delay, in particular, "cupping" on the front tire. This is a kind of scalloped pattern that develops on the area between the center and the sides of the tire, and is noisy in turns, and makes the bike not feel "right".

Increasing the pressure will give a bit harder ride, and will tend to make the bike's steering more negative (it will have more of a tendency to want to go straight and pull out of turns requiring a little more countersteering effort). Increased pressure also decreases the contact patch between the tire and the road a little bit, thus decreasing traction slightly. None of these effects are dramatic, and most knowledgeable riders keep their tire pressures somewhat above what is listed in the owner's manual so that they don't have to buy tires as often. Generally, the higher pressure you run them at, the longer they'll last, within the safety limits.

Two cardinal rules are: 1) never go below the pressure listed in the owner's manual, and 2) never go above the max pressure listed on the tire.

Always measure tire pressures cold, before riding. Bear in mind that, as ambient temperatures rise, so does tire pressure - roughly 1 psi per 10 degrees F.

There are dealerships and service centers that inflate motorcycle tires to 40 psi front and rear no matter what the manual says. Other go by the book, others go somewhere in between, so you're not going to get agreement on this even among the "experts".

Knowing the parameters, you make your own choice.

By the way, putting a different size tire on the bike will definitely affect handling, so please go easy until you learn to what degree this has occurred in your case. It may be barely noticeable, or quite pronounced. When I went with a larger diameter tire on my BMW R850R, it required a lot more steering effort. I was quite surprised at the difference.

And it's not a stupid question. :)

[diffluere]

I've actually had the 120/80 tire since August, I just never thought about the pressure being different until now! I've just been riding around, keeping it at 25psi. I didn't really notice a difference when I got it, but the old tires were OLD (like..original 2002 tires) so they probably didn't feel the best anyway. Plus, I was a brand new rider so I wasn't really used to my bike yet anyway. It feels just fine now, and other people that have ridden my bike haven't mentioned anything weird.

Thanks for the help guys!