tire pressure question

[Dan76spit]

recently ive been told something different about tire pressure than ive heard before. they told me not to run the tire at the pressure listed on the sidewall, but to run it about 5 to 7 lbs lower. the bridgestone tires on my spit say max pressure is 41 lbs, the door jam says to run tires at 29 lbs, what should i be running my tires at? all my life ive been told that you run tires at the pressure listed on the tire. I do this for all my cars and my motorcycles am i doing all of these wrong? thanks...

 

[martx-5]

To answer your question, yes you are doing this wrong. The tire pressure listed on the sidewall is the MAXIMUM pressure that the tires should be inflated to. This is not necessarily the pressure you should be running at. The car manufacturers pressures are a good STARTING point. The same tires on two different cars will most likely require two different tire pressures for optimum performance. So much depends on vehicle weight, suspension geometry, tire type and other factors, that it is impossible to come up with perfect inflation pressures without trial and error. When I get new tires for any one of my cars, I start off with what was working good for the last set I had on and then adjust a bit up and down, front to rear, to see where the car feels best to me. Most of the time it is fairly close to where the manufacturer suggests...unless it's a Ford SUV with Firestones. :laugh:

BTW, if you drop from the 41 psi you've been running to something closer to 32 psi, I'll bet you find a whole lot more grip in those tires. Then you can play with the pressures to find the real optimum for you car and tires.

 

[TR3driver]

I agree with Art, at least to some extent. Pressure on the sidewall is a maximum; the manufacturer's pressure is a minimum. Somewhere in the middle is a good starting point.

After all, your car doesn't weigh as much as the maximum weight listed on the sidewall, either.

 

[DrEntropy]

YAY!!

With the weight distro on a TR *eek* 6, running a MAX pressure in both ends oughta be plain SCARY. I'd start with a four pound differential, 32 front 35 rear and DECREASE it gradually a couple pounds after running the thing around the equivalent of an autocross test.

Increasing the front pressure and not touching the rears should increase "plow/push" or understeer.

In short, ya gotta learn to juggle. Final arbiter will be the car's reaction/feedback as you get to traction limits of the particular compound.

 

[3798j]

I actually think increasing front tire pressure will lessen under steer. Generally, a lower pressure will increase the tire's slip angle. Am I wrong? https://en.wikipedia.org/wiki/Slip_angle

 

[DrEntropy]

Increasing the pressure puts the tire into the center of the contact patch, less tread on th' floor. Less grip. There <span style="font-style: italic">is</span> a point of diminishing returns... That's why the "learnin' to juggle" remark.

Pumping them up to the sidewall "MAX inflation" figure on a car like a TR *gulp* six is taking them waaay past full width tread contact, IMO.

 

[DrEntropy]

The BEST way to determine proper pressures would (IMHO) be a tire pyrometer. Even temp across the entire width of the tread is what to shoot for.

Like this

 

[Dan76spit]

well thank you all! ive been running max pressure on my spitfire tires and my motorcycles tires for as long as ive had them. i will air down to 32 or so pounds on the spitfire and see how that is. im getting mixed opinions on a motorcycle forum about this same subject. seems to be pretty clear here though what the triumph people think. thanks for the thoughts...

 

[DrEntropy]

Two-wheel thingies are a completely diff'rent animal! :wink: