VFR Discussion Group -> Tire Pressure

I aired up my tires the other day and put approximately 40 pounds in the front tire. My Bike felt as if it wanted to be laid over in the turns. What tire pressure should I be running as the temps heat up here in Texas? Or does outside temps matter?

Thanks guys

Ron

TexasVFRman, Mar 23 2005, 10:55 PMI aired up my tires the other day and put approximately 40 pounds in the front tire.  My Bike felt as if it wanted to be laid over in the turns.  What tire pressure should I be running as the temps heat up here in Texas?  Or does outside temps matter?

Thanks guys

Ron

36 front , 42 rear. cold. if you have more than a 10% increase in pressure hot you are too low in pressure

767fixer, Mar 24 2005, 03:57 AM36 front ,  42 rear.  cold.  if you have more than a 10% increase in pressure hot you are too low in pressure

What he said..............and check them before EVERY ride!!

The VFR is a Sport Touring bike designed to carry a passenger and some luggage. The maximum load is 386 lbs., according to the "Tire Information" sticker on my '01. The recommended tire pressures are for the maximum load of 386 lbs. It's a safety and liability issue for Honda, so they post inflation pressures that accomodate the max load. Further, since most of the load weight is on the rear tire, Honda recommends a higher pressure for the rear tire (42 psi) than the front (36 psi).

If you check lots of other sports bikes, you'll see recommended inflation pressures considerably below the VFR numbers. In fact, the VFR has about the highest inflation pressure recommendations of any sport bike.

There are no hard and fast rules about what is the best inflation pressure for the VFR. It mostly depends on the load weight on the bike, and your riding style. For light weight guys that ride mostly twisties or track days, you'll find people that run as low as 30-32 psi both front and back. A lower inflation pressure causes the tire to flex more, thus generating heat in the tire, which increases traction..we all know about warming up the tires to get better traction!

There's a down-side to low pressure however. This significantly increases the wear rate of the tire, and it can be unsafe if you get too much load on an under-inflated tire. There's a whole analogy here about the Ford Explorer/Firestone tire debacle, but I won't belabor this thread with the story. Suffice to say, you need adequate pressure to support the load and generate some, but not too much heat in the tire.

For me, I weigh about 240# in riding gear, and I don't ride real aggressively. I'm running 36 psi front and back, and that seems about right for my weight and riding style. I can assure you that the bike has a lot better ride and traction at 36 psi in the back, rather than the recommended 42 psi. "Fixer" is correct; it's a good rule of thumb that anything more than 10% pressure buildup means the tire is underinflated for what you're doing.

If I were a 150# rider, I'd start with ~32-33 psi front and back, then use the 10% rule of thumb number to check pressure build-up during riding. Another rule of thumb is that the tire pressure should increase about 4 psi during riding, which is close to the 10% number "Fixer" mentions. The important think is to find the right pressure for your own weight and riding style! Don't just follow what everyone else does.

Lastly, some people recommend using nitrogen, rather than air in the tire. There is some scientific basis for this associated with water vapor contained in air, as well as chemical reactions between the rubber liner materials and oxygen. IMHO, the average street rider doesn't really get any benefit from running nitrogen, but it certainly doesn't hurt anything, either. IF the place that mounts your tires has nitrogen and it's free, go ahead and use it. It's slightly easier to regulate tire pressure with nitrogen.

The Lurkin Merkin

very informative, thanks.

PS: Outside temperature does matter. When it's hot outside, you will get more heat buildup in the tire, so you need to add a couple of pounds of pressure during summer riding.

The 10% number, or 4 psi number still applies.

The Lurkin Merkin

Lurkinmerkin, Mar 24 2005, 09:04 PMPS: Outside temperature does matter. When it's hot outside, you will get more heat buildup in the tire, so you need to add a couple of pounds of pressure during summer riding.

The 10% number, or 4 psi number still applies.

The Lurkin Merkin

This seem backwards to me. Higher tire temps means that the air pressure in the tire is going to increase more from cold so you should start with a lower pressure if you want to end up in the same place. <_<

Wallpiper, you're right..it's a bit counter intuitive. Here's the answer:

When the tire is underinflated, it flexes more, and you get some tread "squirm." This flexing and squirming generates heat in the tire. Excessive heat can lead to delamination, tread separation, etc.

So, an under-inflated tire will generate more heat buildup, and the pressure rise will be more than the 10% number. An over-inflated tire does not flex enough to get adequate heat build-up to achieve maximum traction.

On a hot day, you'll get more heat into the tire from ambient conditions, the sun, and road temperature, meaning that you cannot tolerate as much internal heat generation from tire flexing. So, to get the same pressure rise, you need to reduce the amount of tire flexing by increasing the initial pressure.

Hopefully, that's make sense. If not, PM me, and I'll try to answer.

The Lurkin Merkin