What Tire Pressure To Run?

Hi guys, I've got a 1978 KZ650D and my manual says to put 25psi front and 28psi in the rear based on my weight and luggage. ive been trying to find out what i should run but, everyone has a different say and im not sure what to do. when i was riding my bike on the highway around 80 or so, it would sort of sway and bounce a little on the corners. so im thinking maybe im running the wrong shock reload and tire pressure. i lowered the shock preload to #2 position which is second to lowest setting after the ride. before it was on #4 second to highest. im also a 240lbs rider. any recommendations?

those tire pressure seam low. I ran 32/32 on mine I'm 250lbs. Tire pressure is very much personal taste, not to mention those numbers were created for tires that don't exist anymore. These bikes are not super rigid. Its not uncommon to feel a little flex during high speed cornering, however they can be made pretty good. Are you running the stock shocks? they are way undersprung for 240 pounds.

Maybe needs new fork springs & Rr shocks?

I go with about 28-32 PSI. owners manual says 25 Fr & 21-25 PSI Rr depending upon the load.

Dave Moss is pretty amazing. Great channel for suspension setup.

You probably have to measure your static sag to see if you have enough range on your springs.

But there are so many variables here.
Have you changed your fork oil in the last year?
How much luggage and where is it placed on the bike?
How old the tires are?


Start with the tire pressure video first.
 

Most tire manufactures post recommended tire pressures on their websites. I think that is a great place to start.  DO NOT USE THE MAXIMUM PRESSURE LISTED ON THE SIDEWALL!  That is a government requirement maximum pressure allowed, and assumes you are running at maximum speed with a maximum load.

Part, or maybe all, of the problem is the suspension. At its very best, when it was brand new, it was crap. Forty three yeas later, it is tired old crap. New, high quality shocks and fork springs, with some fresh oil, will make a world of difference.

Yup, check the tire manufacturers recommendations.

Modern tires are much better than they were 40 years ago and the inflation recommendations from back then don't apply anymore.

It is interesting that Moss says nothing about different front to rear pressures in that video.

A Z1 recommended tire pressure is 26 front and 32 rear, or 36 rear for two up riding.  But my tires leak a bit and I'm lazy so I will run them a couple of psi above that when filling them.  And because I'm like you...a big guy, I run the rear at 38 +-.

wrote:

Most tire manufactures post recommended tire pressures on their websites. 

This just doesn't seem to be the case very much anymore. More and more manufacturers seem to be removing this info from their sites. I'm sure it probably is looked at by their legal departments as a potential liability. I know Avon used to list 33F/36R for their Roadriders, but not anymore that I can find.

wrote:

It is interesting that Moss says nothing about different front to rear pressures in that video.
 

I think the key take away is that you need to perform tests yourself as there is no exact numbers that will be correct for everyone.

The stock pressure was too low.  Then out of curiosity I tried the Max listed on the tires >> felt like I was riding on glass.  So I chose a number in between. very scientific.

wrote:

wrote:

Most tire manufactures post recommended tire pressures on their websites. 

This just doesn't seem to be the case very much anymore. More and more manufacturers seem to be removing this info from their sites. I'm sure it probably is looked at by their legal departments as a potential liability. I know Avon used to list 33F/36R for their Roadriders, but not anymore that I can find.
 

Well, that sux. Nothing like making life more difficult for customers.