Tire Gauge Calibration Tip - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 18 (permalink) Old 05-19-2010, 02:30 PM Thread Starter
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Tire Gauge Calibration Tip

I just installed new tires and want to get the best performance, gas mileage and wear. That means maintaining the proper tire pressure and an accurate tire gauge. I already have a digital tire gauge and the Kawasaki VN750 tool kit pencil gauge. Both gauges produce similar results, but I wondered how accurate those results were. So, I visited the local motorcycle performance shop and had the gauges tested on a calibrated master gauge (available at tire shops and some truck stops). Both gauges tested -2.0 pounds off. So, it appears that I have been under inflating my vehicle tires. The 2.0 pounds is not critical and is consistent with my research on tire gauge accuracy, but it is nice to know. Now, I can adjust for the inaccuracy by letting the gauges read 2.0 pounds over the reading I'm looking for (i.e., if the gauge reads 42lbs, then the actual pressure is 40lbs).

So, carry your tire gauge(s) with you and stop by a tire shop. Ask if they have a 'calibrated master gauge' for testing tire gauges and have them test your gauges. Bring a Sharpie to mark the gauge with any adjustments needed and the date it was tested. Note that some shops may claim to have a master gauge, but a master gauge must be calibrated at least annually in order to labeled certified. Usually no worries with a performance/racing shop (auto or motorcycle) since they need spot-on tire pressure accuracy.

Also, I would replace any gauge that was more than a few pounds inaccurate.


Chris Glennon - Portland, OR
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post #2 of 18 (permalink) Old 05-25-2010, 04:37 AM
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I have a Snap-On (almost all my tools are Snap On) TPGP50 pencil tire gauge for general use, and feel it is pretty accurate. It is calibrated 10-50 psi. I also have a super low pressure dial type gauge (just don't like digital) for my quad and my race car slicks.

I believe there are to things that are super important to long tire life. One is keeping them inflated to the proper pressure, and two, that the proper pressure is what is marked on the sidewall by the tire manufacturer, not what it may say somewhere on the bike, or in the manual.


The manual that came with my new EX500, which still has the stock tires, says 28 psi front, 32 psi rear. But on the tire sidewalls, it says 41 psi front and rear, and that is precisely what the tires are inflated to. Now, I've done some pretty hardcore (for me) sport riding on this bike, and the tires have performed very well for stock tires. I will get something better when they wear out. The last thing I want while doing aggressive sport riding is half inflated tires. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
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post #3 of 18 (permalink) Old 05-25-2010, 05:04 PM
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Here's my take on the PSI printed on the tire:

The PSI printed on the tire is the maximum pressure. The optimum pressure should be adjusted down from there based on how much weight you're hauling.

When you look at how the edges of your tires are wearing you can see if you're putting too much air (sides still look new). Ideally, you want to use some of that edge.

Mark
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post #4 of 18 (permalink) Old 05-25-2010, 05:36 PM
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Thumbs up Tire pressure

Quote:
Originally Posted by Mark View Post
Here's my take on the PSI printed on the tire:

The PSI printed on the tire is the maximum pressure. The optimum pressure should be adjusted down from there based on how much weight you're hauling.

When you look at how the edges of your tires are wearing you can see if you're putting too much air (sides still look new). Ideally, you want to use some of that edge.

Mark
I have to agree. On my 1 ton truck the tire pressure on the side of the tires is 85 psi. The duals in the rear I keep at 45 psi. if I'm not hauliing heavy. I adjust by the contact patch of the tire. At full pressure only the center of the tire touches the pavement, and the tire will wear the centers off and leave the edges unworn. By adjusting to the contact patch I got 89,000 miles from my bridgstones on a one ton dually truck.
Motorcycle tires as you know, are a completely different animal but, adjusting pressure to the load still applies and I think the suggested pressures in the manual and on the bike are a great place to start.
Checking calibration against a master guage is a great idea for accuracy too.

That's my 2 cents.

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post #5 of 18 (permalink) Old 05-25-2010, 06:32 PM
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True, the rating on the tire is the maximum rating for that tire for maximum load carrying capacity. Useful for trailering, towing, etc.

Almost never inflate any vehicle tires to that, normally much to harsh a ride. The owners manual for whatever the vehicle is the best source for correct tire pressure.

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post #6 of 18 (permalink) Old 05-25-2010, 06:42 PM
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While it is listed as the "max" pressure, tire companies tend to be a bit conservative about such things, so even at the "max" recommended pressure, you still have some room to play with, at least on the high side. You don't have to worry about the tires being overinflated if you have them at the sidewall pressure. Almost every vehicle that comes into our shop (about 30 a day) has drastically underinflated tires, and when they leave, they all have the tires inflated to the pressure on the sidewall. I have gotten 20,000 miles out of the stock Bridgestones running them at the pressure on the sidewall. I can see no advantage to underinflating a tire, other than maybe for a softer ride.

My '66 Ford F100 pickup has 16.5x8.75 10 ply commercial tires on it (I got a killer deal on the tires and wheels, it has an 8 lug Dana rear axle and 8 lug front discs) and the tires (Firestone Trans Force HT) say 81 psi on the sidewall. And that is exactly what they are inflated to. As close as I can reasonably get to it anyway. 45 psi would be half flat. Of course it has a bumpy ride, with a 3/4 ton suspension and commercial tires, but I never intended it to be a Cadillac. I'll bet those tires never wear out. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #7 of 18 (permalink) Old 05-25-2010, 06:53 PM
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Quote:
Originally Posted by 93VN750 View Post
True, the rating on the tire is the maximum rating for that tire for maximum load carrying capacity. Useful for trailering, towing, etc.

Almost never inflate any vehicle tires to that, normally much to harsh a ride. The owners manual for whatever the vehicle is the best source for correct tire pressure.
Ah yes, the "harsh" ride thing again. Like I said, a "soft" ride is the "only" reason for inflating tires under their recommended inflation pressure, and it comes at a high price. Underinflated tires not only wear out much faster, but they don't handle very well either. Tire companies are fanatics about safety. They have to be. They probably get sued more often than any other company that makes vehicle parts. Do you really think they would put that pressure on their tire if they felt it was not safe? Not likely.


If I remember correctly, the big Ford Explorer/Firestone tire fiasco happened mostly because Explorer owners were seriously underinflating their tires, by following the recommendations in the "manual". There was nothing actually wrong with either the Explorer or the Firestone tires. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #8 of 18 (permalink) Old 05-26-2010, 03:25 AM
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I'm getting ready to buy a set of Metzlers and when I did reviews on them most people said they need to be over inflated from what the factory recomends for their bikes. Any truth to this?

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post #9 of 18 (permalink) Old 05-26-2010, 08:43 AM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
If I remember correctly, the big Ford Explorer/Firestone tire fiasco happened mostly because Explorer owners were seriously underinflating their tires, by following the recommendations in the "manual". There was nothing actually wrong with either the Explorer or the Firestone tires. Jerry.
You are right, Exploder owners complained about how hard the vehicles rode so Ford took action, lowered the recommended TP to compensate for two things, too hard a suspension and too cheap a tire. Ford told Firestone we will pay you $8 a tire, no more, so that's what they got, an $8 tire. They were both as at fault as each other.

Tires should be inflated to generate the correct contact patch when at temp under the maximum TP rating. This obviously will vary greatly with driving conditions, temperature, highway, local, etc. It will always be a compromise.

Jon

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post #10 of 18 (permalink) Old 05-27-2010, 12:07 AM
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I'm not going to get into another long drawn out argument here either. Obviously owners are free to inflate their tires to whatever pressure they want, and they are the ones who will deal with the consequences, if any.

I have always inflated all my tires, including bicycle tires, and even the tire on my wheelbarrow, to the pressure on the sidewall, and have never had any problems doing so, either with handling or tire wear. So, I know it is safe to do it that way. I'm not one of those that likes a mushy ride, so that is not an issue for me.


As for the Ford/Firestone thing, I can't help but think that had owners inflated their tires to the pressure on the sidewall, none of that would have happened.


Here's the way I see it. Inflate the tires to the pressure on the sidewall, and everything will be ok. Anything else is a gamble. Jerry.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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