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Sportster Motorcycle Tires, Wheels, and Brakes Discuss issues with Sportster motorcycle tires, wheels and brakes.

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View Poll Results: How do you adjust your tire pressures?
Use Manufacturers recommendations 22 57.89%
Go by the Max. air pressure on the tire 4 10.53%
Adjust pressure to my style of riding 12 31.58%
Only add air when tires look or feel low 0 0%
Voters: 38. You may not vote on this poll

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  #41  
Old 24th May 2020
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Quote:
Originally Posted by Folkie View Post
The opinions of 'experienced' riders are often over inflated!
probably very true!
i did not know any better.

today i set the front to 30 psi.
i saw 36 psi and 40 psi both quoted for the rear.
i looked up the owners manual, looked like it said 40 psi.
i split the difference, and set the rear to 38 psi.
tires were cold, used a quality milton gauge.

it is about to go for a test ride, to see if i like it, or even feel a difference.
thx for the advice from you, and gunner, and highly dangerous.
i can use all the help i can get, but i am slowly learning.
this is my first foray into much bike work on my own.
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  #42  
Old 24th May 2020
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Perhaps you are right.....I had not thought about ambient temperatures affecting it..,,,but on the other hand I have never seen it increase...it just seems to go very slowly down in pressure. I got interested in inner tubes and found this info....I assume it is correct. But I won't be changing my inner tube every 6 months as Dunlop recommends (in item 10)

(1) Synthetics. Inner tubes are a mix of natural and synthetic rubber. Natural rubber is more pliable and offers better resistance to punctures, but synthetic rubber is cheaper. Expensive racing tubes generally have a higher percentage of natural rubber to better form to the tire and to prevent flats. There are also solid foam inserts (called mousse tubes) that simulate air pressure from a foam tube.
(2) Thin versus thick. For a motorcycle manufacturer, the inner tubes are an easy place to save weight and money. Most bikes come stock with thinner and cheaper tubes. Since the entire mass of an inner tube is rotating mass and unsprung weight, it is a prime place to save weight. Conversely, almost every factory racer runs heavy-duty tubes (or mousses) to prevent flats.

(3) Sizing. Having the proper size inner tube for the tire is important for performance and preventing pinches. If you install a 110 inner tube in a 100 tire, the excess rubber will render it susceptible to being pinched with the tire irons. An inner tube that is too small for a given tire will have to be overinflated to make up the difference in size. Overinflation weakens the ability of the inner tube to resist damage. It is possible to run a smaller tube to save weight, but it isn’t recommended.
(4) Performance. Inner tubes play a large role in the feel and performance of the tire. Inner tubes must be the correct shape and size to sit flush against the sidewall to give a good, consistent feel. If there are places where the inner tube isn’t in contact, the tire will feel mushy.
(5) Heat. Inflating an inner tube to the proper pressure not only ensures more sidewall strength, but also prevents pinch flats. As a rule of thumb, 12 to 14 pounds per square inch (psi) is the standard recommended pressure. Keep in mind that as the tire heats up during operation, internal pressures can increase by as much as four psi. This can be lessened by using nitrogen in the tubes to avoid the water content and heat expansion.



(6) Weight. Inner tubes are available in a variety of thicknesses to provide the appropriate amount of protection against flats. The best known heavy-duty tubes are made by STI and distributed by Parts Unlimited. A thin inner tube is approximately 1.5mm to 1.75mm thick. A heavy-duty tube is around 2mm to 3mm thick. And a super-heavy-duty tube is 3.5mm to 5mm thick. The weight of a thin 110-90-19 inner tube is about 1230 grams (2.71 pounds), while a 3.5mm super-heavy-duty 110-90-19 weighs 1720 grams (3.79 pounds). For comparison purposes, a mousse tube tips the scales at 1950 grams (4.29 pounds).
(7) Baby powder. If an inner tube isn’t installed properly, it can fail. Using corn starch or baby powder on the inner tube during installation will reduce friction between the inner tube and the tire’s carcass to help the tube last longer. Adding a little air to shape the inner tube before mounting the tire can help prevent pinches during tire installation.
(8) Valve stem. The valve stem is the weak point of a tube. It is vulnerable to damage and leaks. The valve stem is vulcanized to the tube and can be torn off if the tire spins on the rim, so be sure the rim lock is properly installed. Never tighten the nut on the valve stem down to the rim. If you leave it loose, the tire can spin a little without ripping the valve stem off the tire. You can tell when the tire has spun on the rim because the valve stem will be cocked at an angle. Make sure to re-center the valve stem any time you see it angled.
(9) Contaminants. An inner tube is made to handle the abuse of a tire carcass, but not the outside elements. If water or dirt gets between the tire and tube, it will grate against the inner tube. Be sure that contaminants can’t get in through the rim lock or valve stem holes. The rubber grommet that comes stock on Hondas is a good idea. Replacing the standard rubber rim strip with duct tape makes it more difficult for water to get past the spoke nipples.

(10) Lifespan. Even if your inner tube hasn’t gone flat, it can wear out. Dunlop recommends changing tubes every six months. To know when to replace a tube, look for chaffing, strings of rubber, discoloring (an old tube gets darker) or fading of any writing on the tube. Amazingly, patched tubes will work as well as a new tube, but the patch is a weak point and ideally should only be used in a pinch (pun intended).

Last edited by glbsportster; 24th May 2020 at 20:32..
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  #43  
Old 25th May 2020
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I read a government study on tire pressure relating to trailer tires and load.
They said heat kills the tire and tire flex causes heat and you have to match tire pressure to load. Under inflation is the worst for tire wear. Over inflation you loose traction,...

I think additionally that tire pressure effects suspension.
You have to dial in your suspension for SAG for load but also tire pressure for load to get the bike to handle.

I start at the manufacturers spec. For my '11 Roadster I think the spec is too high in front and maybe too high in the rear

But year by year changes in tire size and individual riding style and rider weight means we're all dealing with unique to us tire pressure requirements.

If you're checking your lights, tire wear, air pressure, oil level, and drive belt before you ride you're WAY ahead of 95% of riders. Theoretically, you can always make air adjustments for load and air temperatures as part of your pre-ride checks.
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  #44  
Old 25th May 2020
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Quote:
Originally Posted by Toejam503 View Post
You have a 21" front wheel, don't you? This is normal, there's less tire/tube area. The air pressure fluctuates with the ambient air temperature and ground temps. It's not as noticeable on bigger/fatter tires. If your tire pressure gets more than an 8-10 PSI difference overnight, then you have a leak.
I've had periods of months, on my 21", where I've never had to add air but have noticed that when we have inconsistent weather, I usually have to add 5lbs or so every couple of weeks.
My guess is the air in the tire condenses and some air gets absorbed into the rubber.
agreed 100% mine does same thing with weather fluctuations.
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  #45  
Old 25th May 2020
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1 psi change for every 10 degrees F.
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  #46  
Old 25th May 2020
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In 2007 I was the car chief on an Indy Pro Series car. We had a hot tire pressure window of +/- 2 degrees (total of 4) from Firestones suggested pressures. This was due to a safety factor and was checked immediately after a qualifying run when pulling into pit lane, by a Firestone rep. I think they took it pretty seriously as we were bumped to the back and I recieved a $25,000 fine directly from the IRL.
A few lbs can drastically effect the tire characteristics.

**no, I did not pay it. It was taken out of a season accumulative payout**
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  #47  
Old 25th May 2020
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just took a short ride over our very bumpy local roads.
detroits roads are some of the worst in the country.
about 15 miles, between 25 and 35 mph.
lots of stop and go, and turns.
i can for sure feel the difference.
its quite a bit softer at 30 lbs in the front from 35psi.
the rear went up 3 lbs as well, i dont feel that difference much.
a more experienced rider might be able to feel the rear difference.
i will watch the pressures, and keep close to this.
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  #48  
Old 26th May 2020
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Quote:
Originally Posted by Joe_jeep View Post
just took a short ride over our very bumpy local roads.
detroits roads are some of the worst in the country.
about 15 miles, between 25 and 35 mph.
lots of stop and go, and turns.
i can for sure feel the difference.
its quite a bit softer at 30 lbs in the front from 35psi.
the rear went up 3 lbs as well, i dont feel that difference much.
a more experienced rider might be able to feel the rear difference.
i will watch the pressures, and keep close to this.
Perhaps the poor roads are why dual sport/off road cycles are gaining in popularity? I have considered a motorcycle of that type, with increased wheel travel, to cope with the roads around her!
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  #49  
Old 27th May 2020
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Quote:
Originally Posted by Iron Mike View Post
In 2007 I was the car chief on an Indy Pro Series car. We had a hot tire pressure window of +/- 2 degrees (total of 4) from Firestones suggested pressures. This was due to a safety factor and was checked immediately after a qualifying run when pulling into pit lane, by a Firestone rep. I think they took it pretty seriously as we were bumped to the back and I recieved a $25,000 fine directly from the IRL.
A few lbs can drastically effect the tire characteristics.

**no, I did not pay it. It was taken out of a season accumulative payout**
So how did the pressure go wrong? Was it the initial pressure or did the driver put enough heat in them to go over the limit?
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  #50  
Old 27th May 2020
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We were running close to the lower limit. Driver took a leisurly pace on the cool down lap allowing the tires to cool a tad too much. He was instructed to continue a rapid pace back to pit after his runn, but for some reason he did not. Tires cooled, pressure droppped. That quick.
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