Author Topic: Tire Pressure Question  (Read 13034 times)

Offline Kiwi_Roy

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Tire Pressure Question
« on: June 08, 2015, 04:53:55 PM »
I heard a comment over the weekend referring to tire pressures on old bikes. A friend stated suggested that
"the manuals are out of date, modern tires should run much higher pressure"

I had never given it a thought before but it made perfect sense to me, who knows best, the bike manufacturer or the tire manufacturer?

Is there a site somewhere that calls out the pressures for different tires?
 
What should I run in my 72 Eldorado?

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Offline atavar

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Re: Tire Pressure Question
« Reply #1 on: June 08, 2015, 04:59:13 PM »
Everything about tire pressure is a rule of thumb.  In general tires should be run close to their rated pressure to protect core and plys and other structural elements, but having said that I would suggest using what is printed on the tire as a starting point and experiment to find what works best for you.

As a fallback you can always write the manufacturer, tell them exactly what tire you have, the width of the rim it is mounted on, and the loaded weight on the axle (a bathroom scale will tell you that) and the speeds you ride at. 
The manufacturer should respond with the correct pressure to use.  Having said *that* their reply will probably come through their legal office and tell you to use the values printed on the side of the tire.

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Online Chuck in Indiana

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Re: Tire Pressure Question
« Reply #2 on: June 08, 2015, 05:12:29 PM »
Here's the 10% rule.
Pick your starting pressure, say 30 lbs. Go for a spirited ride, enough to warm up the tires. You are looking for a 10% pressure increase. You get 33 hot? Pretty darn close. 
Chuck in (Elwood) Indiana/sometimes SoCal
 
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Re: Tire Pressure Question
« Reply #3 on: June 08, 2015, 05:15:01 PM »
 All depends on what wheel bearing grease is being used  :shocked: :huh:

 Seriously , I don't remember recommended pressures changing all that much . My /5 manual was in line with modern wisdom , as is a Triumph manual from 1970 or so that was just consulted .

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Re: Tire Pressure Question
« Reply #3 on: June 08, 2015, 05:15:01 PM »

Offline hooah54

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Re: Tire Pressure Question
« Reply #4 on: June 08, 2015, 05:59:26 PM »
Roy, a bike mechanic friend of mine gave an answer similar to Chuck's ...between hot and cold should be less than 5lbs...still question what the starting point should be myself.
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Offline Waltr

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Re: Tire Pressure Question
« Reply #5 on: June 08, 2015, 06:06:47 PM »
10% rule makes sense as long as outside temp remains consistent.  Measuring the tire pressure in the garage at 70 degrees and then riding while in the 90's has to be figured into the picture.
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Online Chuck in Indiana

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Re: Tire Pressure Question
« Reply #6 on: June 08, 2015, 06:19:37 PM »
10% rule makes sense as long as outside temp remains consistent.  Measuring the tire pressure in the garage at 70 degrees and then riding while in the 90's has to be figured into the picture.

That's pretty complicated.. makes my head hurt..  :smiley:
Chuck in (Elwood) Indiana/sometimes SoCal
 
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Offline Antietam Classic Cycle

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Re: Tire Pressure Question
« Reply #7 on: June 08, 2015, 07:03:23 PM »
On an Ur-Eldo, I think you'll find 32 psi front and 36 psi rear to be a good starting point. That's what I use in all Loops.
Charlie

Online Kev m

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Re: Tire Pressure Question
« Reply #8 on: June 08, 2015, 07:17:21 PM »
Metzeler used to give specific recommendations for their roles ON PARTICULAR bikes on their website. Not sure if they still do.

The 10% rule is better than looking at "capacity specs" since most tires I've seen (except maybe trailer tires) aren't generally loaded to capacity anyway.
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Offline Wayne Orwig

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Re: Tire Pressure Question
« Reply #9 on: June 08, 2015, 08:03:39 PM »
Make sure you use the right air.


 :azn:


Since motorcycle tire widths have generally been getting wider over the decades, wouldn't that mean that there is a larger contact patch, and less air pressure is needed, generally? (Edit...)But I haven't noticed that.

« Last Edit: June 08, 2015, 10:15:02 PM by Wayne Orwig »
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Online Kev m

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Re: Tire Pressure Question
« Reply #10 on: June 08, 2015, 09:44:45 PM »
Wayne, I can't say I've noticed a trend downward in pressures that corresponds with the upward trend in size.

More importantly I've seen two tires from different manufacturers have different recommendations on the SAME bike. So I suspect it's more material/design driven.

For instance Metzeler tends to recommend higher pressures for their tires used on Harleys than OEM Dunlops.
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Offline rodekyll

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Re: Tire Pressure Question
« Reply #11 on: June 08, 2015, 09:46:10 PM »
I go with the theory presented above and start with the recommended pressures.  I decide from there if I need to go up or down.  The handling and harshness of the ride make my final determination.  I try to run the front a few # lower than the rear, like a car.

Offline Sheepdog

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Re: Tire Pressure Question
« Reply #12 on: June 08, 2015, 09:59:24 PM »
I also use 32 front and 36 rear for unloaded solo rides on my Vintage. All loaded up, I bring the rear up to 40...
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Offline Wayne Orwig

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Re: Tire Pressure Question
« Reply #13 on: June 08, 2015, 10:19:45 PM »
Wayne, I can't say I've noticed a trend downward in pressures that corresponds with the upward trend in size.

I edited my comment. I meant to add that I have not noticed pressure requirements going down with wider tires. But as originally mentioned, pressure are a bit higher now then spec'd decades backs. Maybe it is just the bikes getting bigger/heavier. Maybe just the bikes getting bigger. For sure the generally population is getting heavier.  :boozing:
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Offline SED

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Re: Tire Pressure Question
« Reply #14 on: June 08, 2015, 10:21:34 PM »
The front/rear difference is important.  I worry less about the absolute pressure as long as the front rear difference is maintained.  Front-rear difference of a few pounds was really noticeable autocrossing a 4 wheeler - it must be as important on bikes.

The Ariel minimum recommendations are 20F and 26R for 3.25x19 tires and I run up to 10psi more with the modern tires.  BTW Ariel recommended a minimum was 16 psi for 4.00x19s!

Strangely the Monza pressure recommendations are hard to figure out.  The frame tag lists 28F and 36R which is a BIG difference.  The owners manual shows 3 pressures for low speed, high speed and two-up.  The frame tag shows the low speed for the front and the two up pressure for the rear. 

Solo high speed recommendations are 31F and 34R for the Monza.
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Offline atavar

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Re: Tire Pressure Question
« Reply #15 on: June 08, 2015, 10:25:42 PM »
this is true, make sure to use the full synthetic air.. 
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Offline Aaron D.

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Re: Tire Pressure Question
« Reply #16 on: June 08, 2015, 10:34:23 PM »
They have gone up, and it makes a big difference.

Offline leafman60

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« Last Edit: June 09, 2015, 03:53:57 AM by leafman60 »

Online balvenie

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Re: Tire Pressure Question
« Reply #18 on: June 09, 2015, 04:09:10 AM »
Thanks for those links, leafman60, I just happen to be using an Avon front :grin:
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Offline John A

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Re: Tire Pressure Question
« Reply #19 on: June 09, 2015, 07:20:01 AM »
I didn't look at the links Leafman provided yet but wear patterns need to be monitored when choosing pressures
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Offline Testarossa

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Re: Tire Pressure Question
« Reply #20 on: June 09, 2015, 11:00:32 AM »
http://www.drivegreen.com/Motorcycle_Tire_Pressure.htm

I seem to recall an article (by Kevin Cameron?) explaining that vintage tires (Dunlop K70 for instance) with stiff bias-ply sidewalls need less pressure (25 psi) than modern bias-belt tires with more pliable sidewalls (32 psi and up).
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Offline Dilliw

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Re: Tire Pressure Question
« Reply #21 on: June 09, 2015, 12:25:11 PM »
Michelin has a little tool on their website but the oldest Guzzi on the list looks like late 80's.  For the Pilot Activ and my EV they recommend 2.2 bar front and 2.4 bar rear (32/35psi).   Play with it and maybe you can find something close to your Eldo.

http://motorcycle.michelinman.com/tire-selector#s=0

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Online Kev m

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Re: Tire Pressure Question
« Reply #22 on: June 09, 2015, 12:41:15 PM »
Michelin has a little tool on their website but the oldest Guzzi on the list looks like late 80's.  For the Pilot Activ and my EV they recommend 2.2 bar front and 2.4 bar rear (32/35psi).   Play with it and maybe you can find something close to your Eldo.

http://motorcycle.michelinman.com/tire-selector#s=0

Thanks for posting that, it reminded me that I never checked when I changed from the Pirelli to the Pilot Activ on the V7 Stone.

Interestingly enough Michelin is recommending a lower pressure on both front and rear than the OEM recommendation for the Pirellis.

Sport Demons - 36 / 36 solo - 38 / 38 2-up or with load
Pilot Activ - 32 / 36 no mention of adjustment for load.

I've been running it at 38 and always felt is a little hard. Maybe I'll test it at 36 just to see.

I've still got the Pirelli up front... probably for the rest of this year.
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Offline rodekyll

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Re: Tire Pressure Question
« Reply #23 on: June 09, 2015, 01:43:18 PM »
I ran a mismatched pair of tires once -- MZ88 on the front and Tourance on the back.  At rated pressures they acted like they were on different bikes -- insisted on taking different tracks, even when going straight.  I almost kilt myself in a sweeper when the bike refused to follow the line.  It kept steering to the outside of the curve.  I managed to stop it before I was too far off the roadbed.  I had to play with tire pressures for the rest of the trip trying to dial in some stability.  I finally found a combination of significantly lower rear pressure and proportionately higher front pressure that let me feel confident to about 65.  Beyond that speed it never did get better.

Offline Dilliw

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Re: Tire Pressure Question
« Reply #24 on: June 09, 2015, 03:53:49 PM »

I've been running it at 38 and always felt is a little hard. Maybe I'll test it at 36 just to see.


Yeh I just put the rear on there (I've had the front) and I aired it up to 40 just like I did my ME880 since I do a lot of 2 up.  I ended up dropping it back down to 36 and I might try their recommended 35.  That tire might like a little less pressure.
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Offline Lannis

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Re: Tire Pressure Question
« Reply #25 on: June 09, 2015, 04:09:58 PM »

The Ariel minimum recommendations are 20F and 26R for 3.25x19 tires and I run up to 10psi more with the modern tires.  BTW Ariel recommended a minimum was 16 psi for 4.00x19s!



My original manuals for my old bikes (1955, 1961, 1969, 1975) recommend WAY lower pressures than I'd be comfortable running today.    Like most have indicated, I boost them to what "feels" right and then see how they wear and handle there.

Sort of like setting timing advance.  On an old BSA, burning good leaded gas with a clean combustion chamber, 31 degrees max advance worked well in 1961.   Today, burning adulterated crap 89 octane and with 50 years of wear, there's no sense insisting on setting it to exactly 31 degrees with a timing light - you set it to where it will run without hammering a hole in the piston top ....

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Offline oldmxdog61u

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Re: Tire Pressure Question
« Reply #26 on: July 29, 2018, 05:18:54 PM »
I prefer to add helium to reduce sprung weight and increase freedom of motion while excerbating rotational stability.  Notable difference over air.

Whatever you do, never use ambient air with politicians in proximity as the fecal matter will destroy the rim band inside tire, corrode aluminum, and reduce luster of the rubber.

I know thi# is all true as I read it on the internet, and after switching to helium, I waxed a geezer in the Walmart parking lot on a electric cart. The old eldorado really handles those speed bumps, although you get a lot of air on those awesome jumps with helium.
Honest.  Really.
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Offline rodekyll

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Re: Tire Pressure Question
« Reply #27 on: July 29, 2018, 05:24:43 PM »
Ummmm...... Your mic is hot ........

Offline RinkRat II

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Re: Tire Pressure Question
« Reply #28 on: July 29, 2018, 05:51:58 PM »
I prefer to add helium to reduce sprung weight and increase freedom of motion while excerbating rotational stability.  Notable difference over air.

Whatever you do, never use ambient air with politicians in proximity as the fecal matter will destroy the rim band inside tire, corrode aluminum, and reduce luster of the rubber.

I know thi# is all true as I read it on the internet, and after switching to helium, I waxed a geezer in the Walmart parking lot on a electric cart. The old eldorado really handles those speed bumps, although you get a lot of air on those awesome jumps with helium.
Honest.  Really.

    THIS^^^^^^^^^^^^^ I know it's true as I've read it on a FORUM on the internet and these trusted individuals would not lead me astray :copcar:


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Offline redhawk47

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Re: Tire Pressure Question
« Reply #29 on: July 29, 2018, 11:59:01 PM »
Everything about tire pressure is a rule of thumb.  In general tires should be run close to their rated pressure to protect core and plys and other structural elements, but having said that I would suggest using what is printed on the tire as a starting point and experiment to find what works best for you.

As a fallback you can always write the manufacturer, tell them exactly what tire you have, the width of the rim it is mounted on, and the loaded weight on the axle (a bathroom scale will tell you that) and the speeds you ride at. 
The manufacturer should respond with the correct pressure to use.  Having said *that* their reply will probably come through their legal office and tell you to use the values printed on the side of the tire.
I feel that setting your tire pressure to what is molded on the tire is bad advice. That pressure value is what you should use if the load on that wheel is as much as what is molded on the tire.

The 10% rule is good advice. I have also had recommended 4 psi increase. Start with the value recommended by the motorcycle manufacturer. After riding 15 miles or so, if the pressure has increased more that 4psi, increase your cold pressure. If it has increased less than 4psi, decrease your cold pressure. Each time you change pressure and test you must start with cold tires.

Dan
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