Dropped Tire Pressure to Improve Ride

[atomsplitter]

Correct. Plus race bike tyres get extremely hot which effectively increases pressure. Road riders take pressure readings when cold. Track riding pressures are calculated on running temperatures when racing.
If you put 42 psi in your tyres in the cool of the garage, after a vigorous ride it'll be more like 52 psi. Hence my 38/24 will be more like 40/38 when ridden.

Plus, manufacturers pressures are an average to cover all bases: solo riders, heavy riders, riders with luggage, riders with pillions. IMO you need to match your pressures to your type of useage and style of riding.

Good point. The actual tire pressure under load can be calculated using a thermodynamic formula P1V1/T1 = P2V2/T2. In this case the volume (V) remains constant (change is insignificant) so pick a happy cubic inch number like 100. The temperature has to be converted to absolute temperature (Rankine) so add 460 degrees to ambient. and pressure must be converted to absolute as well so add 14.7 psia to guage tire pressure (psig). Assume your cold tire temperature is 75 degrees F and your riding tire temperature is 150 degrees F, so the cold temp is 535 degrees R and the riding temp is 610 degrees R. If the tire is inflated to 42 psig cold then the absolute pressure is 56.7 psia. So you solve the equation for P2 (riding pressure) now that you have P1V1T1 and V2/T2. When you do the math you have to remember to convert the absolute pressure back to guage pressure (subtract 14.7 from the result) and that should yield about 50 psig in this instance.

 

[Idaho Red Rocket 3]

I was running the Triumph recommended PSI F/R. My little 2.3L Rocket would develop a weaving at high speed. After talking to the forum, a rider suggested using 38/38 F/R. Weaving disappeared. I've been using 38/38 ever since. Very happy with my ride and cornering.

 

[HarryBo]

Correct. Plus race bike tyres get extremely hot which effectively increases pressure. Road riders take pressure readings when cold. Track riding pressures are calculated on running temperatures when racing.
If you put 42 psi in your tyres in the cool of the garage, after a vigorous ride it'll be more like 52 psi. Hence my 38/24 will be more like 40/38 when ridden.

Plus, manufacturers pressures are an average to cover all bases: solo riders, heavy riders, riders with luggage, riders with pillions. IMO you need to match your pressures to your type of useage and style of riding.

Well said!

 

[HarryBo]

Good point. The actual tire pressure under load can be calculated using a thermodynamic formula P1V1/T1 = P2V2/T2. In this case the volume (V) remains constant (change is insignificant) so pick a happy cubic inch number like 100. The temperature has to be converted to absolute temperature (Rankine) so add 460 degrees to ambient. and pressure must be converted to absolute as well so add 14.7 psia to guage tire pressure (psig). Assume your cold tire temperature is 75 degrees F and your riding tire temperature is 150 degrees F, so the cold temp is 535 degrees R and the riding temp is 610 degrees R. If the tire is inflated to 42 psig cold then the absolute pressure is 56.7 psia. So you solve the equation for P2 (riding pressure) now that you have P1V1T1 and V2/T2. When you do the math you have to remember to convert the absolute pressure back to guage pressure (subtract 14.7 from the result) and that should yield about 50 psig in this instance.

Omg! I'm not worthy!

 

[Jagster]

I'm no scientist. I go by feel. I use my senses and practical experience. Seat of my pants, is a suitable phrase.

Just for context:
I ride on the road and not on a race track.
I'd rather wear the tyres prematurely than my skin.

One thing I feel is:
- Better to ride on below recommended pressure than above. A bigger contact patch is better than a smaller one.
- In general, more flex/compliance in the tyre gives more feel than a more rigid set up. More feel gives more survival information. That said, tyre compound is a huge factor in all of this too, so i'm generalising rather than making my comment as a hard rule.
- Too little pressure is of course dangerous for a number of reasons, so i'm highlighting that point without hesitation.

and finally....
- If I was riding at proper high speeds and riding on the ragged edge, I would for sure, be paying far more attention to not be running too low pressure. In fact i'd be data logging my tyre pressures like i'd got an obsession but what I call fast isn't really 'fast' ......I'm a road rider. Sure, I ride progressively, but I ride country roads with cow droppings and liberal sprinklings of loose gravel on random corners. Corners, lots of them. Many of them blind corners.
Generally not smooth tarmac stretched out for miles ahead like I can imagine being the case in some regions/countries.

So, a bit softer is better than too hard. (That's not always the case in some things in life, but hey...)

 

[Gimlet]

So, a bit softer is better than too hard. (That's not always the case in some things in life, but hey...)

True. And by the same token, a motorcycle final drive chain is one of the very few things in life that's better being a little slack than too tight...

 

[Jagster]

Just to round off my thinking about the subject raised at the start of this thread....

So. We're discussing ride comfort and how that comfort is affected by tyre pressures.
I note that we haven't really talked much about suspension, but I think we probably should, if the subject is primarily about ride comfort.

Firstly, I think it's worth stating that if I was starting off with a new bike, I would put the tyre pressures at the recommended pressure before I then dialled in the right suspension settings to suit my weight and ride requirements, just so I know that the tyres are at a specific reference point that the manufacturers tested and validated the bike to having.
Only then, would I allow a bit of slack in the tyre pressure department.

So....I admit that this bike has got me a bit foxed, when it comes to finding a suspension setting that i'm happy with, comfort-wise.
I can get the bike to be composed yet compliant as a cornering tool at speeds which frankly shouldn't be possible in my head. These bikes handle amazingly for what they are.
However, ride comfort at the rear end is most definitely something that has me a bit stumped.

I would like to have a suspension technician help me to resolve what I can't seem to be able to achieve easily myself before I start chucking away the stock suspension and raiding the piggy bank.
If, in the meantime, dropping a few psi in the rear tyre helps me to not loose a tooth filling or bite my tongue clean off, then I think it's worth a shot, at least as a safety measure.

I bottomed out the other week on a short but apparently deep dip in the road. It wasn't something that was at all visible, but I suppose I was trucking on a bit for the over all road/landscape situation, but I REALLY hit the deck big style and it wasn't a nice experience at all.
It must have been as bad as it felt because it cracked my licence plate around the lower fixing, and my licence plate is mounted on the body of the bike, not on the swing arm thing. I reckon that if i'd been running with the stock set up, my licence plate and turn signals would have been left behind at the scene.

Without doubt, the rear suspension is the most frustrating aspect of ownership. Which is a shame because it's so much fun to ride in the twisies, rolling on and off of that delicious torque.

 

[TURBO200R4]

I have a system
I pump them to 38 then in about a month they are down to about 33 and then I take them back to 38
Did not like 30 it felt a little weird.

 

[A1A Rider]

My tires hold the pressure well, probably losing only a half of PSI a month.

Generally, you get PSI sudden changes with weather temps. But where I am, it stays more or less stable, temp wise, well, also giving a whole year riding weather.

 

[Kiwicol]

Tire pressures would also be influenced by rider weight, correct? A 50kg (110lb) bean stalk is going to get away with lower tire pressures over a 150kg (330lb) bear.