Successful tire experiment – 2014 Breakout – but need tire expert psi advice
#1
08-14-2014, 07:25 PM
Successful tire experiment – 2014 Breakout – but need tire expert psi advice
I believe I have found a rear tire solution that improves the performance of the Breakout dramatically, but I need some advice on tire pressure from a “tire expert” if we have one on the forum. Let me explain.
I have been unhappy with the stock tire provided by HD, the Dunlop Elite 3 Custom Wide tire, for several reasons.
First, this tire is rated by its manufacturer for a maximum pressure of 41 psi, but HD, incredibly enough, recommends 42 psi on the Breakout with this tire. Since the capacity of this 79V (load index) tire is 963 pounds, this HD recommendation is very suspicious beyond the obvious fact that it exceeds the maximum psi specified by the tire manufacturer. The Breakout is NOT a very heavy bike – in fact, outside of the Sportster range of HD bikes, it’s one of the lighter HD models.
Secondly, the tire has an initial tread depth of 12/32 inch. After just 3400 miles of pretty easy riding (I average 42 to 45 mpg ☺ ), I was down to 1.5/32 inch, in the CENTERLINE ONLY area of the tire. A motorcycle tire is considered worn out when it hits 1/16” tread depth, so I have consumed 95% of the 11/32” of “usable” tread in 3400 miles, which means I would have hit the 1/16” limit by 3600 miles. This seems low to me, given that the Breakout is a cruiser, not a sportbike, and I ride it like a cruiser, not a sportbike.
Thirdly, the fact that the wear is concentrated along the “centerline” of the tire, despite the fact that I do mostly winding roads in the Texas Hill Country, reinforces the suspicion that HD’s recommended tire pressure of 42 psi is too high – at least for a solo rider who weighs 235 pounds with safety gear on.
Fourthly, this Dunlop tire is a very heavy tire. Per Dunlop, it weighs 21.75 pounds. I am very sensitive to tire and wheel weight. Heavy wheels and heavy tires have high moments of inertia. That creates multiple negative symptoms, including resistance to directional changes, a “cement overshoes” effect when accelerating (particularly when coupled with the bike’s ridiculously tall factory gearing), and significantly lowered power readings on any inertia drum type dyno (like the common Dynojet).
Since I have the already very heavy HD “Chrome Turbine” wheels on my Breakout, the combination of heavy wheels and heavy tires is particularly bad. In fact, when I had my bike in for dyno tuning at Mike Lozano’s shop, Mike commented that the combination of Softail engine balancer weight, heavy rear wheel, and heavy rear tire, is hurting both my bike’s dyno readings and its real world performance.
So, I went looking for a new rear tire. Since the Breakout is a cruiser, looking at “race spec” sportbike tires is not only a waste of race spec tire, but in fact, no manufacturer even MAKES a race spec type tire in the 240/40R-18 size. But, several manufacturers make that size of tire in what they refer to as a “sport street” or “custom” tire.
MY personally most important attributes for the new tire were a manufacturer with a history of high quality, light weight, good dry and wet traction, and reasonable tread life. However, despite my actively looking for information on all of these attributes for each tire available in the correct size, the only two attributes that I could DEFINITIVELY measure or verify for each tire, were the manufacturer’s reputation and the weight of the tire.
Since I have had great experiences with Pirelli tires on prior bikes (Ducati Monster and several 9XX series Ducatis), Pirelli satisfied the manufactuer history requirement. And, it turned out that Pirelli also offers the lightest weight tire in this size range: its “Diablo” series tire. So, I ordered the Pirelli Diablo in 240/40ZR-18 size (Pirelli part number 1682600).
Comparing the specs of the Dunlop and the Pirelli was illuminating:
Dunlop Elite 3 Custom Wide
240/40R 18 79V (963 lb @ 41 psi)
Diameter = 25.91”
Weight = 21.75 lb
Initial tread depth = 12/32” (i.e. 3/8” or 0.375”)
$165 at Dennis Kirk
Pirelli Diablo
240/40ZR-18 79V (963 lb @ 41 psi) part no. 1682600
Diameter = 25.75”
Weight = 15.55 lb (confirmed by Amazon shipping weight = 17 lb, and Jim G’s postal scale measured the actual delivered specific tire as 16 lb 0 oz. This variance versus “stated weight” is very typical for tire manufactuers – they all slightly understate their tire weights, and all tires of a given model vary in weight around a target weight)
Rim used by Pirelli for its measurements: 8.5”
Acceptable rim width: 8.0 to 9.0”
Diameter: 654mm = 25.75”
Acceptable tire psi: 36 to 42
Speed rating = 168 mph
Initial tread depth = 5.5mm = 0.2165” = 7/32”
$171 at Dennis Kirk, $170 at Amazon
Note the following major differences:
The weight of the Pirelli is 6.2 lb less (i.e. 29% lighter!) than that of the Dunlop!
The initial tread depth of the Pirelli is only 7/32” versus the Dunlop’s 12/32”.
I am NOT knowledgeable enough about tires to say anything about “what these differences mean”. I am just pointing them out as obvious evidence of entirely different tire design philosophies.
Unlike Dunlop, Pirelli actually provides a recommended ACCEPTABLE psi range for the Diablo, and it is 36 to 42 psi. This means that Pirelli says this tire can work within that overall acceptable rnage, but naturally, within that acceptable range, the VEHICLE manufacturer is supposed to determine and provide the specific psi or range of psi that will result in the tire working properly WITH THAT SPECIFIC VEHICLE AND STATED OVERALL GROSS VEHICLE WEIGHT (which includes the wet weight of the bike, the rider, the passenger, and any luggage or accessories added). Sometimes, if a rider is lucky, the tire manufacturer publishes the recommended psi base don data from the vehicle manufacturer.
Since Harley does not offer Pirelli tires on its bikes, I could not get a recommendation from HD. And, while Pirelli does provide recommended actual psi for many different manufacturers’ models of bike, they do NOT include HD, as HD is not one of its target markets.
In the absence of a specific recommendation for psi from either HD or Pirelli, I went with Pirelli’s GENERAL guidance – the 36 to 42 psi range noted above. And, since the SAFEST starting point for tire psi is to go to the high end of the tire manufacturer’s recommended psi range, I started with 42 psi in the Diablo, and the HD recommended 36 psi in the front Dunlop tire.
Here are some critical data points that I would really appreciate getting some feedback on from someone who has really solid experience with determining correct tire pressures:
I started out this morning at 7am, at 73 degrees ambient temperature, with tires “cold” at 36F and 42R.
After 21 miles:
Front tire psi = 38 (+2 psi versus cold)
Rear tire psi = 42 (no gain in psi versus cold!)
Later, in 85 degree ambient temperature (note, this is 12 degrees hotter than when I set out on the ride), after 55 miles since the last stop on the 136 mile ride:
Front tire psi = 40 (+4 psi = 11% gain versus cold)
Rear tire psi = 45 (+3 psi = 7% gain versus cold)
I need someone knowledgeable on proper tire pressure determination to give me some guidance as to whether I should stay at the 42 psi rear, or whether I should reduce it, since the gain after 55 miles in 85 degree heat was only 3 psi or 7%.
That said, here’s the GREAT news on performance:
The bike feels like it has shed a pair of cement overshoes. No kidding. It feels notably more nimble.
In addition, Initiating turns is now FAR easier than it was with the Dunlop tire. I just have to “think” it now, and the bike goes there.
And, the combination of Mike Lozano’s careful dyno tune plus this Pirelli tire, has utterly eliminated the discomfort I used to feel on sharp right turns from a stop sign or red light. Now, the bike makes the turn willingly and precisely, without any manhandling or careful throttle/clutch work required. It’s a complete joy compared to before. It’s so much improved, that I am now considering forgetting about doing the gearing change (“shorter” gearing) that I have been trying to find the right parts to enable.
I stopped by Mike Lozano’s shop during my 136 mile ride today, and walked him through the tire change and the spec differences. His very first comment was that I will surely pick up “several” horsepower on his Dynojet dyno. He says he had a slightly larger weight difference some time back when he changed from a spoke wheel to a carbon fiber wheel on a customer’s Harley, and the difference on the dyno reading was around 6 horsepower. He pointed out that in MY case, with the weight reduction being concentrated 100% in the tire, versus spread over the entire wheel diameter (rim, spokes, and part of the hub), the difference in moment of inertia is massive. We are both looking forward to dynoing my bike again during his next monthly dyno day.
Now I still have no idea how this tire will wear. That’s going to depend to at least some extent on identifying the correct tire pressure to run, since tire psi has so much impact on tread and tire life. That’s why I am asking for some knowledgeable assistance.
But, it seems clear that the PERFORMANCE of the tire has utterly transformed the feel of my Breakout. The performance is so much improved that even if this tire turns out to have WORSE tread life than the already unimpressive Dunlop tread life, it would actually be worth it to me. It’s that much of an improvement.
So, the experiment will continue. I hope some tire expert who reads this posting will step in and provide some guidance on what pressure to run.
In the meantime, here are some photos of this ridiculously wide tire:
Notice in the following photo how the width of the tire makes even a refrigerator look “small”:
Notice in the following photo how low the tire profile is (note that you are seeing the the tire bead of the opposite side of the tire “through” the donut hole. The “near side” tire bead is just below the “white spot” on the upper right portion of the tire):
Jim G
I have been unhappy with the stock tire provided by HD, the Dunlop Elite 3 Custom Wide tire, for several reasons.
First, this tire is rated by its manufacturer for a maximum pressure of 41 psi, but HD, incredibly enough, recommends 42 psi on the Breakout with this tire. Since the capacity of this 79V (load index) tire is 963 pounds, this HD recommendation is very suspicious beyond the obvious fact that it exceeds the maximum psi specified by the tire manufacturer. The Breakout is NOT a very heavy bike – in fact, outside of the Sportster range of HD bikes, it’s one of the lighter HD models.
Secondly, the tire has an initial tread depth of 12/32 inch. After just 3400 miles of pretty easy riding (I average 42 to 45 mpg ☺ ), I was down to 1.5/32 inch, in the CENTERLINE ONLY area of the tire. A motorcycle tire is considered worn out when it hits 1/16” tread depth, so I have consumed 95% of the 11/32” of “usable” tread in 3400 miles, which means I would have hit the 1/16” limit by 3600 miles. This seems low to me, given that the Breakout is a cruiser, not a sportbike, and I ride it like a cruiser, not a sportbike.
Thirdly, the fact that the wear is concentrated along the “centerline” of the tire, despite the fact that I do mostly winding roads in the Texas Hill Country, reinforces the suspicion that HD’s recommended tire pressure of 42 psi is too high – at least for a solo rider who weighs 235 pounds with safety gear on.
Fourthly, this Dunlop tire is a very heavy tire. Per Dunlop, it weighs 21.75 pounds. I am very sensitive to tire and wheel weight. Heavy wheels and heavy tires have high moments of inertia. That creates multiple negative symptoms, including resistance to directional changes, a “cement overshoes” effect when accelerating (particularly when coupled with the bike’s ridiculously tall factory gearing), and significantly lowered power readings on any inertia drum type dyno (like the common Dynojet).
Since I have the already very heavy HD “Chrome Turbine” wheels on my Breakout, the combination of heavy wheels and heavy tires is particularly bad. In fact, when I had my bike in for dyno tuning at Mike Lozano’s shop, Mike commented that the combination of Softail engine balancer weight, heavy rear wheel, and heavy rear tire, is hurting both my bike’s dyno readings and its real world performance.
So, I went looking for a new rear tire. Since the Breakout is a cruiser, looking at “race spec” sportbike tires is not only a waste of race spec tire, but in fact, no manufacturer even MAKES a race spec type tire in the 240/40R-18 size. But, several manufacturers make that size of tire in what they refer to as a “sport street” or “custom” tire.
MY personally most important attributes for the new tire were a manufacturer with a history of high quality, light weight, good dry and wet traction, and reasonable tread life. However, despite my actively looking for information on all of these attributes for each tire available in the correct size, the only two attributes that I could DEFINITIVELY measure or verify for each tire, were the manufacturer’s reputation and the weight of the tire.
Since I have had great experiences with Pirelli tires on prior bikes (Ducati Monster and several 9XX series Ducatis), Pirelli satisfied the manufactuer history requirement. And, it turned out that Pirelli also offers the lightest weight tire in this size range: its “Diablo” series tire. So, I ordered the Pirelli Diablo in 240/40ZR-18 size (Pirelli part number 1682600).
Comparing the specs of the Dunlop and the Pirelli was illuminating:
Dunlop Elite 3 Custom Wide
240/40R 18 79V (963 lb @ 41 psi)
Diameter = 25.91”
Weight = 21.75 lb
Initial tread depth = 12/32” (i.e. 3/8” or 0.375”)
$165 at Dennis Kirk
Pirelli Diablo
240/40ZR-18 79V (963 lb @ 41 psi) part no. 1682600
Diameter = 25.75”
Weight = 15.55 lb (confirmed by Amazon shipping weight = 17 lb, and Jim G’s postal scale measured the actual delivered specific tire as 16 lb 0 oz. This variance versus “stated weight” is very typical for tire manufactuers – they all slightly understate their tire weights, and all tires of a given model vary in weight around a target weight)
Rim used by Pirelli for its measurements: 8.5”
Acceptable rim width: 8.0 to 9.0”
Diameter: 654mm = 25.75”
Acceptable tire psi: 36 to 42
Speed rating = 168 mph
Initial tread depth = 5.5mm = 0.2165” = 7/32”
$171 at Dennis Kirk, $170 at Amazon
Note the following major differences:
The weight of the Pirelli is 6.2 lb less (i.e. 29% lighter!) than that of the Dunlop!
The initial tread depth of the Pirelli is only 7/32” versus the Dunlop’s 12/32”.
I am NOT knowledgeable enough about tires to say anything about “what these differences mean”. I am just pointing them out as obvious evidence of entirely different tire design philosophies.
Unlike Dunlop, Pirelli actually provides a recommended ACCEPTABLE psi range for the Diablo, and it is 36 to 42 psi. This means that Pirelli says this tire can work within that overall acceptable rnage, but naturally, within that acceptable range, the VEHICLE manufacturer is supposed to determine and provide the specific psi or range of psi that will result in the tire working properly WITH THAT SPECIFIC VEHICLE AND STATED OVERALL GROSS VEHICLE WEIGHT (which includes the wet weight of the bike, the rider, the passenger, and any luggage or accessories added). Sometimes, if a rider is lucky, the tire manufacturer publishes the recommended psi base don data from the vehicle manufacturer.
Since Harley does not offer Pirelli tires on its bikes, I could not get a recommendation from HD. And, while Pirelli does provide recommended actual psi for many different manufacturers’ models of bike, they do NOT include HD, as HD is not one of its target markets.
In the absence of a specific recommendation for psi from either HD or Pirelli, I went with Pirelli’s GENERAL guidance – the 36 to 42 psi range noted above. And, since the SAFEST starting point for tire psi is to go to the high end of the tire manufacturer’s recommended psi range, I started with 42 psi in the Diablo, and the HD recommended 36 psi in the front Dunlop tire.
Here are some critical data points that I would really appreciate getting some feedback on from someone who has really solid experience with determining correct tire pressures:
I started out this morning at 7am, at 73 degrees ambient temperature, with tires “cold” at 36F and 42R.
After 21 miles:
Front tire psi = 38 (+2 psi versus cold)
Rear tire psi = 42 (no gain in psi versus cold!)
Later, in 85 degree ambient temperature (note, this is 12 degrees hotter than when I set out on the ride), after 55 miles since the last stop on the 136 mile ride:
Front tire psi = 40 (+4 psi = 11% gain versus cold)
Rear tire psi = 45 (+3 psi = 7% gain versus cold)
I need someone knowledgeable on proper tire pressure determination to give me some guidance as to whether I should stay at the 42 psi rear, or whether I should reduce it, since the gain after 55 miles in 85 degree heat was only 3 psi or 7%.
That said, here’s the GREAT news on performance:
The bike feels like it has shed a pair of cement overshoes. No kidding. It feels notably more nimble.
In addition, Initiating turns is now FAR easier than it was with the Dunlop tire. I just have to “think” it now, and the bike goes there.
And, the combination of Mike Lozano’s careful dyno tune plus this Pirelli tire, has utterly eliminated the discomfort I used to feel on sharp right turns from a stop sign or red light. Now, the bike makes the turn willingly and precisely, without any manhandling or careful throttle/clutch work required. It’s a complete joy compared to before. It’s so much improved, that I am now considering forgetting about doing the gearing change (“shorter” gearing) that I have been trying to find the right parts to enable.
I stopped by Mike Lozano’s shop during my 136 mile ride today, and walked him through the tire change and the spec differences. His very first comment was that I will surely pick up “several” horsepower on his Dynojet dyno. He says he had a slightly larger weight difference some time back when he changed from a spoke wheel to a carbon fiber wheel on a customer’s Harley, and the difference on the dyno reading was around 6 horsepower. He pointed out that in MY case, with the weight reduction being concentrated 100% in the tire, versus spread over the entire wheel diameter (rim, spokes, and part of the hub), the difference in moment of inertia is massive. We are both looking forward to dynoing my bike again during his next monthly dyno day.
Now I still have no idea how this tire will wear. That’s going to depend to at least some extent on identifying the correct tire pressure to run, since tire psi has so much impact on tread and tire life. That’s why I am asking for some knowledgeable assistance.
But, it seems clear that the PERFORMANCE of the tire has utterly transformed the feel of my Breakout. The performance is so much improved that even if this tire turns out to have WORSE tread life than the already unimpressive Dunlop tread life, it would actually be worth it to me. It’s that much of an improvement.
So, the experiment will continue. I hope some tire expert who reads this posting will step in and provide some guidance on what pressure to run.
In the meantime, here are some photos of this ridiculously wide tire:
Notice in the following photo how the width of the tire makes even a refrigerator look “small”:
Notice in the following photo how low the tire profile is (note that you are seeing the the tire bead of the opposite side of the tire “through” the donut hole. The “near side” tire bead is just below the “white spot” on the upper right portion of the tire):
Jim G
The following users liked this post:
LuvdemBobberz (08-23-2019)
#2
08-14-2014, 08:02 PM
Jim,
Great write-up! It's refreshing to see , on this forum, an in-depth review of a product or an experiment. I'm tired of reading post "What did you do to your bike today", or "Look at my new mirrors".
Here's my 2 cents. Tire manufactures cannot stamp the optimal PSI on the side of their product because of the many variables. They provide Max PSI at Max Weight. Experimentation must be performed to find the correct PSI depending on weight of the bike, weight of the rider, riding style and road conditions. I like Metzeler's which provide me with the best overall riding performance in all weather, wet or day. On Metzeler's web site they post a helpful chart to determine proper PSI depending on size of bike and single or 2 up riding. I've found my sweet spot to be 39 front and 41 rear.
It's interesting that Harley recommends a higher PSI than what is posted on the side of the OEM tire. I believe Harley is not even aware of this.
Great write-up! It's refreshing to see , on this forum, an in-depth review of a product or an experiment. I'm tired of reading post "What did you do to your bike today", or "Look at my new mirrors".
Here's my 2 cents. Tire manufactures cannot stamp the optimal PSI on the side of their product because of the many variables. They provide Max PSI at Max Weight. Experimentation must be performed to find the correct PSI depending on weight of the bike, weight of the rider, riding style and road conditions. I like Metzeler's which provide me with the best overall riding performance in all weather, wet or day. On Metzeler's web site they post a helpful chart to determine proper PSI depending on size of bike and single or 2 up riding. I've found my sweet spot to be 39 front and 41 rear.
It's interesting that Harley recommends a higher PSI than what is posted on the side of the OEM tire. I believe Harley is not even aware of this.
#3
08-14-2014, 08:23 PM
Jim,
Great write-up! It's refreshing to see , on this forum, an in-depth review of a product or an experiment. I'm tired of reading post "What did you do to your bike today", or "Look at my new mirrors".
Here's my 2 cents. Tire manufactures cannot stamp the optimal PSI on the side of their product because of the many variables. They provide Max PSI at Max Weight. Experimentation must be performed to find the correct PSI depending on weight of the bike, weight of the rider, riding style and road conditions. I like Metzeler's which provide me with the best overall riding performance in all weather, wet or day. On Metzeler's web site they post a helpful chart to determine proper PSI depending on size of bike and single or 2 up riding. I've found my sweet spot to be 39 front and 41 rear.
It's interesting that Harley recommends a higher PSI than what is posted on the side of the OEM tire. I believe Harley is not even aware of this.
Great write-up! It's refreshing to see , on this forum, an in-depth review of a product or an experiment. I'm tired of reading post "What did you do to your bike today", or "Look at my new mirrors".
Here's my 2 cents. Tire manufactures cannot stamp the optimal PSI on the side of their product because of the many variables. They provide Max PSI at Max Weight. Experimentation must be performed to find the correct PSI depending on weight of the bike, weight of the rider, riding style and road conditions. I like Metzeler's which provide me with the best overall riding performance in all weather, wet or day. On Metzeler's web site they post a helpful chart to determine proper PSI depending on size of bike and single or 2 up riding. I've found my sweet spot to be 39 front and 41 rear.
It's interesting that Harley recommends a higher PSI than what is posted on the side of the OEM tire. I believe Harley is not even aware of this.
#5
08-14-2014, 10:06 PM
YES!! I put on only 136 miles today only because it gets so HOT here in Austin this time of year, usually by 11am. If it weren't for the darn heat, I'd be taking longer rides to places like The Three Sisters and Bandera. I love the feel of a slightly cool wind at 60 mph, the beauty of what God built versus what Man built, and the pleasing sound and feel of a bike that has been configured and customized to my specific needs and preferences.
But, I'm also a scientist by affliction, so I am continually running experiments that have the potential to make a good thing better.
And, as you may have gathered, I am very detail-oriented. Think about it: if I was NOT so detail oriented, I'd have never tried to find a different rear tire, but the anomalies I noted at the start of this thread were just inviting examination and solution.
You think I'm obsessive? Try Thomas Edison. He had it so bad that he tried literally thousands of ways before he successfully got a working light bulb. And the light bulb changed everything. He also developed the phonograph and the motion picture camera.
Like it or not, we need obsessives like me.
I'm trying to talk my wife into letting me do a Polaris Slingshot project. That 2.4 liter GM Ecotec engine in it is making only 177 hp right now, but GM actually published an entire book on how to soup that particular engine up to 250, then 300, and then up to over 1000 hp. The Slingshot weighs 1700 lb. Who can resist? She says I need to get a new job first (lost the last one 2 weeks ago).
So many potential projects. So little time.
Jim G
But, I'm also a scientist by affliction, so I am continually running experiments that have the potential to make a good thing better.
And, as you may have gathered, I am very detail-oriented. Think about it: if I was NOT so detail oriented, I'd have never tried to find a different rear tire, but the anomalies I noted at the start of this thread were just inviting examination and solution.
You think I'm obsessive? Try Thomas Edison. He had it so bad that he tried literally thousands of ways before he successfully got a working light bulb. And the light bulb changed everything. He also developed the phonograph and the motion picture camera.
Like it or not, we need obsessives like me.
I'm trying to talk my wife into letting me do a Polaris Slingshot project. That 2.4 liter GM Ecotec engine in it is making only 177 hp right now, but GM actually published an entire book on how to soup that particular engine up to 250, then 300, and then up to over 1000 hp. The Slingshot weighs 1700 lb. Who can resist? She says I need to get a new job first (lost the last one 2 weeks ago).
So many potential projects. So little time.
Jim G
#6
08-15-2014, 12:39 AM
Jim,
You and I are much alike. I live in a country which doesn't have road side assistance. No calling for help. No tow truck. We Harley owners in my area have to do our own wrenching and roadside repairs if we break down. I analyze every engineering aspect of my bikes and always try to build the better mouse trap. Like you, I've posted on this site, lengthy reports concerning Modifications, Fabrications, and Product Testing only to be criticized by my attention to detail.
I read every word of your report and enjoyed it. Keep'em coming brother. There are still a few of us Gear Heads around.
Bob
You and I are much alike. I live in a country which doesn't have road side assistance. No calling for help. No tow truck. We Harley owners in my area have to do our own wrenching and roadside repairs if we break down. I analyze every engineering aspect of my bikes and always try to build the better mouse trap. Like you, I've posted on this site, lengthy reports concerning Modifications, Fabrications, and Product Testing only to be criticized by my attention to detail.
I read every word of your report and enjoyed it. Keep'em coming brother. There are still a few of us Gear Heads around.
Bob
#7
08-15-2014, 01:23 AM
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#8
08-15-2014, 08:43 AM
Thanks, guys! I still need a tire pressure expert to chime in with psi advice!
With the rear tire set at the 42 psi starting point for the experiment, the ride is just a bit stiffer than I suspect it needs to be (still better than the Dunlop!), and of course too much psi will cause the same rapid tread centerline wear as I got on the Dunlop.
Jim G
With the rear tire set at the 42 psi starting point for the experiment, the ride is just a bit stiffer than I suspect it needs to be (still better than the Dunlop!), and of course too much psi will cause the same rapid tread centerline wear as I got on the Dunlop.
Jim G
#9
08-15-2014, 11:03 AM
#10
08-15-2014, 11:32 AM
I have found a couple of articles online which seem to agree on a methodology for determining proper tire psi.
What they basically say is that you stay inside of the maximum psi as published by the tire manufacturer, and try to get the air pressure setting that produces EQUAL TEMPERATURE at the centerline of the tire as at the outer edges of the working tread.
Apparently, if the centerline temperature is higher than at the outer edges, the psi is too high (the centerline of the tire is making most of the contact with the road, and is hotter as a result).
If the temperature at the centerline is lower than at the outer edges, the psi is too low (the edges have better contact with the road than the centerline does).
The idea is to get the tire up to normal working temperature by riding the way you would normally ride, and then quickly stopping the bike and measuring the temperature at the 3 points (left edge, centerline, right edge). By the way, if the left edge differs in temperature from the right edge, there is either a misalignment or a weight distribution issue.
The trick is getting the right equipment to do the temperature check.
One writer suggested an infrared gun type temperature reader that you aim at the points on the tire is adequate. Another one pointed out that more accurate results are obtained via a device that uses needle probes that you ***** right into the tire tread, since the temperature INSIDE the rubber even a bit loses temperature more slowly after you stop than the exterior surface of the rubber does.
I have neither type of course, and given my current unemployed status, I doubt my wife would like the idea of buying a $100 infrared gun temperature reader for another one of my (many) experiments.
Any expert opinions out there?
Jim G
What they basically say is that you stay inside of the maximum psi as published by the tire manufacturer, and try to get the air pressure setting that produces EQUAL TEMPERATURE at the centerline of the tire as at the outer edges of the working tread.
Apparently, if the centerline temperature is higher than at the outer edges, the psi is too high (the centerline of the tire is making most of the contact with the road, and is hotter as a result).
If the temperature at the centerline is lower than at the outer edges, the psi is too low (the edges have better contact with the road than the centerline does).
The idea is to get the tire up to normal working temperature by riding the way you would normally ride, and then quickly stopping the bike and measuring the temperature at the 3 points (left edge, centerline, right edge). By the way, if the left edge differs in temperature from the right edge, there is either a misalignment or a weight distribution issue.
The trick is getting the right equipment to do the temperature check.
One writer suggested an infrared gun type temperature reader that you aim at the points on the tire is adequate. Another one pointed out that more accurate results are obtained via a device that uses needle probes that you ***** right into the tire tread, since the temperature INSIDE the rubber even a bit loses temperature more slowly after you stop than the exterior surface of the rubber does.
I have neither type of course, and given my current unemployed status, I doubt my wife would like the idea of buying a $100 infrared gun temperature reader for another one of my (many) experiments.
Any expert opinions out there?
Jim G