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Sportster Motorcycle Suspension, Frame, Forks, Handlebars, Fuel Tank, Oil Tank, Fenders Discuss Sportster Motorcycle Suspension, Frame, Forks, Handlebars, Fuel Tank, Oil Tank, Fenders problems, advice, and/or how tos.

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  #1  
Old 20th March 2010
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Default Lower Tire pressure ???

Has anyone run lower than recommended??? I am running 30# in my 19" front and 36# in the rear, and it just seems a bit road harsh to me, and I was thinking about trying 28# in the front and 32# in the rear, as I thing it would soften the harshness a bit, plus the slightly larger patch might increase traction...
Anyone else run simuliar pressures, or have any warnings, or input...???
Thanks and have a good one...Tater...
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Old 20th March 2010
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Tater, I try not to. I can really tell the difference when i'm nearing 30psi in both tires. There is a wishy washy feeling in the turns.
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Old 20th March 2010
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running too low causes the tire to flatten out and you'll end up running only on the edges of the tires, instead of the entire tire. you'll lose contact patch, heat the tires more then normal sometimes to the point of failure.

Not recommended.
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Old 20th March 2010
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The pressure marked on the side wall is maximum pressure and should be used if carrying the maximum weight (also marked on sidewall). This is not a likely scenario. So, in real life, we have to do a little simple math.

A simplified version of the formula the tire reps use at the race track....

1. Add max weight ratings from tire
2. Add actual weight (bike's weight+your weight+cargo weight)
3. Divide actual weight by max weight
4. Multiply sidewall pressure rating by factor determined in "3"
5. That is your starting point.
Note: this starting point calculation does not account for temperature or riding style.

Important: Use actual weight - your bike full of gas and your butt full of taco's wearing that fancy leather weighs more than you think.

Real life
Rear tire rated 761#@41psi
Front tire rated 507#@41psi
max = 1268#
bike weight 570#
butt weight 200#
cargo 20#
actual 790#
770/1268 = .62
.62*41 = 25.4 psi starting pressure.



THIS IS NOT TO LOW. The rule of thumb is a 10% rise in pressure before/after ridinga track session. This also applies to street riding for best grip and longevity.

With a typical South Texas day in the high 80's, we run about 27psi cold in the sportster and will measure ~30psi after 20 miles or so in the saddle.

ride safe bros
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Old 20th March 2010
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Quote:
Originally Posted by TripleDuck View Post
The pressure marked on the side wall is maximum pressure and should be used if carrying the maximum weight (also marked on sidewall). This is not a likely scenario. So, in real life, we have to do a little simple math.

A simplified version of the formula the tire reps use at the race track....

1. Add max weight ratings from tire
2. Add actual weight (bike's weight+your weight+cargo weight)
3. Divide actual weight by max weight
4. Multiply sidewall pressure rating by factor determined in "3"
5. That is your starting point.
Note: this starting point calculation does not account for temperature or riding style.

Important: Use actual weight - your bike full of gas and your butt full of taco's wearing that fancy leather weighs more than you think.

Real life
Rear tire rated 761#@41psi
Front tire rated 507#@41psi
max = 1268#
bike weight 570#
butt weight 200#
cargo 20#
actual 790#
770/1268 = .62
.62*41 = 25.4 psi starting pressure.



THIS IS NOT TO LOW. The rule of thumb is a 10% rise in pressure before/after ridinga track session. This also applies to street riding for best grip and longevity.

With a typical South Texas day in the high 80's, we run about 27psi cold in the sportster and will measure ~30psi after 20 miles or so in the saddle.

ride safe bros
nice math lesson, however, According to all the tire manufacturers this tire pressure you're recommending is to low..

Dunlop (OEM replacement tires) Typical is around 30psi front.. 36 rear.
Metzeler recommends at least 36 front and 38 rear (SOLO riding)
Avon is also similar.

Now Maybe a racing tire has different results but for street riding, I recommend following the manufacturers recommendations.
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Old 20th March 2010
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Quote:
Originally Posted by TripleDuck View Post
The pressure marked on the side wall is maximum pressure and...
Actually, on Metzeler tyres, the number is the recommended normal pressure, not the max.
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Old 20th March 2010
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Thanks Folks, so I am running about what I am supposed to be running, and for sure not too high pressure @ 30# Frt. & 36# rear, and you agree with the owners manual...
Thanks, I'll stick with that, as tire wear & non-cupping (so far)(3K) looks pretty darn good... (BTW-tires are Dunlop originals)...
And I do try to ride the twisties, got in 220 mi. of pretty good riding yesterday (wore me out though)...lol...
I do run the max on the tire sidewall on my PU & car...
I was just thinking that it might help the ride & traction a bit, but I guess
the best thing besides that or a Mustang seat would the buns of steel work out like the wife does...lol...
Thanks Folks and have a good one...Tater...
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Old 20th March 2010
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Quote:
Originally Posted by FoxsterUK View Post
Actually, on Metzeler tyres, the number is the recommended normal pressure, not the max.
I don't have a metzler in the garage right now...you could be right.

However, the tire manufacturer has no idea what bike a specific tire will be mounted on. The bike/rider may weigh 400# or they may weigh 700#. If you want to ride the same tire pressure regardless of load.....knock yourself out.

I've got a few track laps on my butt and have attended more than a couple tech sessions on tire pressure - its a topic of constant discussion in the performance bike arena. The public information has liability all over it - because the manufacturer cannot predict what tire the bike is to be mounted on. Go talk to a tire rep - a manufacturer's tech rep (not a minimum wage tire salesman). In public forum, they will talk the "published pressure". Out of media ear shot (like at the race track) you will get a different story....and yes street tires are developed on the track....the same rules apply.

my suggestion is do what makes you comfortable and feel safe. I'm just sharing a little bit of info gleened over the last 42 years of motorcyling and works fine for me and my loved ones.

ride safe bros
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Old 20th March 2010
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most manufacturers have a chart for their tires for different bikes i use what they say
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Old 20th March 2010
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Low tire pressure causes sidewall failure. Can any one say Firestone tires and Ford SUVs and Trucks. Remember, it was not that long ago.
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