Tire pressure...follow spec or follow tire rating?

[jbs80106]

Sorry if this is a simple question but my k75s current has Dunlop 491's on it, great wearing tire by the way!

But curious about tire pressure.  Specs on Dennis Kirk say 40 psi, front and back.  The tag on the side of the bike says 42 psi rear, 38 psi front (if memory serves).  I know I've been running 42 psi cold on the rear.

Which should I follow?  Can't tell on Dennis Kirk if the PSI rating for load is a cold temp or a warm temp?

[kevin_stevens]

Sorry if this is a simple question but my k75s current has Dunlop 491's on it, great wearing tire by the way!

But curious about tire pressure.  Specs on Dennis Kirk say 40 psi, front and back.  The tag on the side of the bike says 42 psi rear, 38 psi front (if memory serves).  I know I've been running 42 psi cold on the rear.

Which should I follow?  Can't tell on Dennis Kirk if the PSI rating for load is a cold temp or a warm temp?

None of the above.  Follow your bike manual or your best judgement.

What's printed on the tire is the *maximum* safe pressure - and the maximum permissible load at that rating.  That may be more than the axle rating of your bike.  It may not be optimal for single-up riding.  It may not be the best pressure for handling, or wet weather, or anything else.  I never understand why people think the tire manufacturers know the best pressure over all the hundreds of bikes their tires will fit.

If you run X pressure - cold, hot, it doesn't matter - at that instant, the tire is guaranteed to support Y load.  And don't run the tires higher than that pressure - cold, hot, it doesn't matter.  That's *ALL* that the sidewall tells you.

KeS

[denydog]

None of the above.  Follow your bike manual or your best judgement.

Exactly!  KeS said it well.  But to say it again, the tire may fit a variety of bikes, and bikes vary widely in their design, gross weight, handling characteristics, solo or two up, etc...   Who do you think knows more about the variables of each bike the tire might be fitted to, Dennis Kirk, the tire maker, or the bike manufacturer?  Hint, Dennis Kirk and the tire manufacturer generally don't have a clue.

I only repeated this point because I have been amazed over the years by how many people insist the sidewall (max) pressure is the only correct pressure, and must be used at all times.

[jbs80106]

Got it!  Thanks!

SO....the tires on the bike from PO are listed as OEM replacements obviously and came in the right size.  BUT, bike sticker says something like max load of 639 lbs at 42 psi for rear tire.  I don't weigh anywhere near that.  Tire is only rated up to 40 psi.....


So what to run?  What is 'too low'?  Clymer says 36 psi for 1 up riding.  

So....go with Clymer and see how it goes.  Bit worrying to think I was A) runnig with it 2 psi above actual tire rating and B) running 6 psi over what manual says...

Hail mary etc. etc. etc........

[kevin_stevens]

Got it!  Thanks!

SO....the tires on the bike from PO are listed as OEM replacements obviously and came in the right size.  BUT, bike sticker says something like max load of 639 lbs at 42 psi for rear tire.  I don't weigh anywhere near that.  Tire is only rated up to 40 psi.....


So what to run?  What is 'too low'?  Clymer says 36 psi for 1 up riding.  

So....go with Clymer and see how it goes.  Bit worrying to think I was A) runnig with it 2 psi above actual tire rating and B) running 6 psi over what manual says...

Hail mary etc. etc. etc........

Tire is only rated to 40 psi on the sidewall?  That sounds unusually low.

I would consult the various flying brick sites.  I have new BT45s on my K100RS and I'm running them at 36F/38R.  If I let them get down to 34/36, which is closer to where I'd run radials, they start feeling mushy and sloppy.  But the bike isn't going to fall over or blow up as long as you're withiin a fairly broad range of, say, 30-45 psi.  It's a matter of rider preference and priority.

KeS

[jbs80106]

Well the all knowing internet reveals this:

Load Capacity/Inflation Pressure: 910 lbs./40 PSI Load

Empty bike, 1 up, no where near this.

When I started running inflations to spec (by the bike specs that is), notice a difference in handling for the worse but figured it was within spec so all the better.

Will try running with the lower inflations to see if the difference goes away. If not, perhaps something else is amiss?

Had the bike for 1.5 years. Put 10k miles on it.  Tires are solid with lots of tread left.  Perhaps over inflation is what I'm noticing?  The trouble in dealing with 2nd hand bikes with little docs on the equipment effects.  

Also has a rear shock dampener(?)...fox preload thing attached.  Haven't messed with it to even know what it does exactly.  PO was of similar build to me so figured good for him, okay for me....

nice, eh?

[kevin_stevens]

Well the all knowing internet reveals this:

Load Capacity/Inflation Pressure: 910 lbs./40 PSI Load

Empty bike, 1 up, no where near this.

When I started running inflations to spec (by the bike specs that is), notice a difference in handling for the worse but figured it was within spec so all the better.

Will try running with the lower inflations to see if the difference goes away. If not, perhaps something else is amiss?

Had the bike for 1.5 years. Put 10k miles on it.  Tires are solid with lots of tread left.  Perhaps over inflation is what I'm noticing?  The trouble in dealing with 2nd hand bikes with little docs on the equipment effects.  

Also has a rear shock dampener(?)...fox preload thing attached.  Haven't messed with it to even know what it does exactly.  PO was of similar build to me so figured good for him, okay for me....

nice, eh?

The shock is probably dead.  I just replaced the Fox double-clicker on my K100 because they can't get repair parts for them anymore.

Too much pressure will make the bike feel very nimble, but the ride will be harsh and the wheels will "patter" and skip over washboard surfaces.  Everything will feel more abrupt.

Too little pressure will make the bike feel mushy and unresponsive; but quite plush on all but biggest bumps.  The bike will feel like it is moving on the tires when you are in a corner.

The canonical way to set pressure empirically is to set them cold, then go ride them until they are as hot as they are going to get for your type of riding, and look for a 10% rise in pressure.  If you get more than 10%, RAISE the starting pressure (low pressure tires heat up more and build more pressure).  If you get less than 10%, lower the starting pressure.

KeS