Tire Pressures

I've read the posts on here about tire pressures, I see people run from the book's 36/36 to 42/42 and virtually every combination in-between. I've read the facinating discussions of temperature and pressure relationship, etc. I "think" I understand that underinflated tires will present a greater increase in temperature than an overinflated tire. Now, I don't have and am not going to buy a temperature reader for tires, heck, I don't even know what you'd use or how you'd take the temperature. I thought it would be interesting to discuss this while waiting for the snow to hit here in N. VA.

I've personally run from 36/36 to 40/42 (book calls for 36/36 at my weight solo and 36/42 with a pax). I've found that with Lorie on the back 36/42 works great. Any greater pressure in the front tire and ole Maxine wonders around on her own at slow speeds (<10mph/16kph). I usually run 36/38 or 38/40 solo, why, beats me, but both seem to work fine. I recently started a "Riding Notes" notebook (jotting down main points from "Sport Riding Techniques" for quick review) and think I'll try some rides at different pressures and make notes on the ride to include starting and warm pressure and ride charecteristics. That said:

Is there any temperature/pressure relationship (cold to hot) that can tell you when you're running the "right" pressures? Of course one must first define what the "right" pressure is. IOW, if I start at 38/40 cold, what should I see once the tires are warmed up? Is a 10% rise in pressure right, 20%? I'm not trying to bait anyone or throw a turd on the table - I'm really interested. For what it's worth, I think I read on the Avon site that my new Storms (did I mention how much I love these tires!) should be at 36/42. I'm not going to put nitrogen/hydrogen or synthetic air in my tires (dino air is ok), but would be interested in discussions of what effect those might have.

Thanks to any and all who take the time to mull, posit, and post their thoughts!

Should be looking for 5% to 8% increase.

Go through the suspension and make sure it is set up correctly for your riding style. Theres a flow chart thread you can refer to for set up info.

Directly from Metzler's web site:

Set the suggested inflation pressure on cold tires before riding. During service the tire's warming-up causes a pressure rise that must NOT be reduced. Check inflation pressure once a week. Increase rear tire pressure by 0,2 bar / 3 psi when riding with a passenger or with very heavy load. Insufficient inflation pressure causes tire flexing and overheating that may lead to internal damage. Overinflation impairs riding comfort and stability and can result in uneven wear.

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Pressure and temperature are tied together, when you talk about one, it implies a change in the other. A 10-degree-rise in ambient temperature equates to a 1 psi change in tire pressure. A 4 psi change in pressure implies a 40 degree rise in temperature. Tire manufacturers have a target tire temperature for optimum performance. Load and speed ratings are coupled to operating temperatures, as a result there is no one fixed and hard % of temperature rise value. We will ignore what happens to temperature rise when humidity adds a lot of water in the fill air

A temperature change of 10% isn't out of line for a DOT street tire, it is equal to ~4 psi. You only need to be concerned if tire pressure doesn't rise at all or exceeds more than a 6 psi rise.

All bets are off if you use N2 or Metric Air. Remember to change the air every 4k miles or 3 months, which ever occurs first. :lol:

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Jestal country --> For true tire temperature & pressure measurements the units used must be in degrees Kelvin and pressure readings should be compensated for ambient pressure which will vary with barometric pressure and altitude. I'm not going there…

Honestly, I had no idea that splitting hairs was a Winter Olympic Sport.

Jim, you are so close... mostly because you obviously are aware of the changes required when loads and conditions change, and because you are obviously taking the time to monitor your tire pressure.

If you really want to take it to the next level, spend $38 at Harbor Freight and buy yourself a laser point thermometer and a collapsible big-ass orange cone. The laser thermo is for reading the tire temp. The big-ass orange cone is to put on the side of the road because you will be pulling over every 30 minutes to read the tire temp.

Seriously, the number-one problem with tire pressure is when it's not monitored. Altitude changes, load changes, ambient temp changes are all the things that call for variation from the numbers that are obviously working for you.

Sorry, I guess I just (almost) turned this into a NEPRT. Can you tell I don't know the formula you are asking for?

I'll go away now.

Jeff

I have heard that a cold tire originally pumped to 40 lbs should read 44 lbs when hot. Not sure of the increase %... but that will always be my rule of thumb if I check my tire pressure while they are hot.

Interesting discussion of environmental effects on tires/pressures. I’m a retired artilleryman and to compute firing date we take into account “non-standard” conditions. A “standard” day (all basic date is corrected to this standard day) is 59 deg F, no wind, 100% humity and air pressure, no rotation of the earth (yup, you compensate for the rotation of the earth dependant on what direction you’re firing), and powder temp of 70 degrees. You take your basic data, shove in your corrections, and whack away. Same thing is done in trying to compare ¼ mile times (for instance) of bikes running at different times and places. An FJR running the quarter in 20 degrees wx at an altitude of 10k will run a different time than the same bike running at 100 degrees at sea level. Sooooooo, environmental considerations are shoved into the equation and you get “corrected” times. I’ve seen two reported times in different mags for the FJR – 10.67 and 11.02 “corrected.” Interesting that there isn’t more general use of “corrected” time when mags do their tests on bikes. When you stop to think about it, if they report other than the corrected times you’re not getting an accurate and comparable performance number. Interesting stuff.

Pressure and temperature are tied together, when you talk about one, it implies a change in the other. A 10-degree-rise in ambient temperature equates to a 1 psi change in tire pressure. A 4 psi change in pressure implies a 40 degree rise in temperature. Tire manufacturers have a target tire temperature for optimum performance. Load and speed ratings are coupled to operating temperatures, as a result there is no one fixed and hard % of temperature rise value. We will ignore what happens to temperature rise when humidity adds a lot of water in the fill air

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Hmmmm, assuming your tire maintains pressure (up and down w/ambient temp) does the humity in the tire actually change from whatever was present when you filled the tire? And Jeff, I agree I'm close. I do check my air pressure "usually" before each ride starts. Within the limits of 36-40/38-42 I can't say I've ever noticed any significant difference in handling. Only occasion is with mi amore on the back with pressures >37 in the front.

Still, just because I'm a curious shit I'll note details of ambient temp/cold and smokin' tire pressures just for the fun of it.

And, metric air is just too hard to find, I'm going to stick with American standard!

JeffAshe said:

The laser thermo is for reading the tire temp. The big-ass orange cone is to put on the side of the road because you will be pulling over every 30 minutes to read the tire temp.

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Or you could just install a Smartire monitor and get realtime pressure and temperature for both tires while cruising down the road... big orange cones not required...

I believe the formula is Charles Law from my scuba diving frame of reference.

P1 x V1 P2 x V2

_______ = ________

T1 T2

(which doesn't paste over very well at all).

I did find this Tank Temperature/Pressure calculator that should work for our FJR's. Try changing the 3200 psi of a scuba tank to 42 psi for our tires and it's the same physics.

For example, a tire at 50 degrees with 42 psi will have 50 psi if the air inside the tire is 120 degrees. (Notice I say air inside and not tire tread temp)

Yup, you got the correct formula and used it correctly! The formatting is flubed up, but that is the limitations of this Forum's text management. I left the formula out of my reply so Jestal would have something to chime in with, but look who showed up instead :lol:

Or you could just install a Smartire monitor and get realtime pressure and temperature for both tires while cruising down the road...

Click to expand...

Are short, sensible answers allowed here? :blink:

Hmmmm, assuming your tire maintains pressure (up and down w/ambient temp) does the humity in the tire actually change from whatever was present when you filled the tire?

Click to expand...

Humidity doesn't change, the water quantity is fixed, it is just a matter of how much can be held 'in solution'. However, the humidity effects the way the tire pressure changes as the temperature rises.

Sooooooo, environmental considerations are shoved into the equation and you get “corrected” times. Same thing is done in trying to compare ¼ mile times (for instance) of bikes running at different times and places

Click to expand...

And true for dyno compensations too.

Two things I've noticed: riders don't check tire pressure often and often ride under-inflated -- maybe?, increasing tire temp.; riders ride w/max air pressure in their tires (just to be on the safe-side?) -- and, maybe? their tires don't get up-to temp.?

JimLor: let us know your results/determinations -- if any.....

On a side note: I've been told by my friend with an '07 FJR, that Yamaha now recco's more air pressure in the tires than they did for the Gen-1s.

Allow me to "officially" report from the 07 manual in my grimey little hands...

Yamaha has done a superb job of defining what appears to be three(3) different load ranges.

Rider Weight (0-198 lbs.)

Rider Weight (198-467 lbs.)

High-speed riding

All three ranges specify exactly the same pressures, 39 Front, 42 Rear.

Imagine that! Oh, the manual is still blue too.

luvtoride said:

I have heard that a cold tire originally pumped to 40 lbs should read 44 lbs when hot. Not sure of the increase %... but that will always be my rule of thumb if I check my tire pressure while they are hot.

Click to expand...

That's exactly what I get and stick with. 10% increase in pressure hot.

JeffAshe said:

Allow me to "officially" report from the 07 manual in my grimey little hands...
Yamaha has done a superb job of defining what appears to be three(3) different load ranges.

Rider Weight (0-198 lbs.)

Rider Weight (198-467 lbs.)

High-speed riding

All three ranges specify exactly the same pressures, 39 Front, 42 Rear.

Imagine that! Oh, the manual is still blue too.

Click to expand...

Sorry Ashe, can't trust ya no mo. You no longer bleed blue. Traitor cherry fella. If the tire ain't flat on the bottom side, ride it! :blink:

Come on D. It's still the same ole me, just incognito in Black Cherry colors.

I found it humorously amazing that Yamaha has not taken the time to define tire pressure changes for the three different load ranges they specified. Obviously, somebody lacked complete data and decided to fill in all three with the same specs.

Or perhaps those Metzler tires have a new load sensing feature that I am not aware of. Guess it will be a shame when I cut them off the rims for the 600 mile service.

Jeff - what differences do you feel from the 05? Faster/slower/heavier/lighter/etc.

JimLor said:

Jeff - what differences do you feel from the 05? Faster/slower/heavier/lighter/etc.

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Jim,

I have not put many miles on it yet. It's just been too damn cold with some ice and snow around. But Saturday looks good and I plan to make a post specifically about the differences. But this is what I think I have observed thus far:

* I don't feel the immediate need for risers. I assume that's because the seat height in relation to the bar height is different. At least the 07 feels close to the same as my 05 with 1" risers. I was running 1.5" risers the last few months.

* Suspension feels more solid. In fact, the 07 at stock settings feels almost identical to my 05 with my "special" settings. But it will take some time for the components to break in and then I can start on suspension settings.

* The stock wind screen works MUCH better than the 05 stock screen. But you can bet that I am putting my modified CB flip on before riding this weekend. I do think the stock screen would be nice in very hot weather. I'm just spoiled and not used to all that noise in the helmet.

* The seat comfort is much better for me. I found the same thing on the 06 rides I borrowed.

* Mirrors are a big improvement. Not enought time yet to say if they function as well as the Multivex.

That's about all I can comment on so far. I need to get a few hundred on her before I twist and push the corners.

Jeff

Not to take this thread sideways, but....

I am also a member of Warchild's other hangout, CBRXXcom. Recently a new forum vendor (Vancosport), offered a discount on a slightly more expensive, yet wireless, tire pressure/temp monitoring kit. I have purchased the Smartire system, and this one seems superior, in terms of installation ease and function.

It's worth a look.

Dale has mounted one on his bird. I bought one for my FJR and my XX.

The laws relating the pressure, temperature, and volume of an ideal gas, derived from Charles' law and Boyle's law.

P is Pressure of a 'gas'

V is the volume

T is temperature (in Kelvin)

n is the number of moles of the gas

R is the universal gas constant.

PV = nRT

Or

k is Boltzmann's constant

N is number of atoms:

PV = NkT

Note that these relationships are for ideal gas, and 'dry' air is 78% nitrogen, 21% oxygen, and the remaining 1% is { argon, carbon dioxide, water vapor, and other trace gases}. So the relationship from pressure to temperature is linear with a fixed volume

JeffAshe said:

<snip> "officially" .... 07 manual ... three(3) different load ranges.

Rider Weight (0-198 lbs.)

Rider Weight (198-467 lbs.)

High-speed riding

All three ranges specify exactly the same pressures, 39 Front, 42 Rear.

Click to expand...

Thanks -- well, being one of the high BMI types, I've decided to up my tire pressures. Previously, I've sorta taken what was written in the manual as gospel -- but now I've become a dis-believer.

I've added a couple psi to what I'd thought was maximum and rode a couple hundred miles and it feels just fine -- maybe better? I've never gotten great tire mileage -- so, maybe that'll improve too?

Seems this new revelation from MamaYama throws a 'whole-new-light' on FJR tire pressures...? :blink:

Guess now -- I need to get cold then hot tire pressure for an accurate determination.

Can't just 'go-by-the-book' anymore. :huh: