Funky Pilot-Road-3 wear.. front tire..

[mogu83]

I wore out a set of PR2s, then went on to PR3s, on my third set and they will be replaced with PR3s. For the record I also run 36/42.

Funny how you come to dislike a particular brand of tires. A few decades ago I had a set of Pirellis on a car and they were terrible, I'm still holding a grudge against that brand (I'm Irish we hold grudges a long time) and wouldn't put them on a wheelebarrow.

[deilenberger]

I actually believe the tyre manufacturer might also know a bit about it; after all, they design, test & eventually produce them.
Anyway, it was only a suggestion offered from experience. My PR3's, at 36/42 aren't cupping. Yours at lower pressure are.

Thanks for the suggestion! How many miles on your PR3's?

I have yet to see Michelin give a recommended pressure chart.. does one exist I haven't seen? There is a maximum inflation pressure marked on the tire, but that's different from a recommended pressure.

Cupping can be caused by more then pressure (and actually I believe it probably is usually caused by braking as mentioned above by Kirby. I do tend to brake rather aggressively (but also rather infrequently.) One Michelin website illustration for the PR3's actually show the tread-blocks distorting under braking force, and I believe they claim that is a good thing since it enhances tire/road friction. Would higher pressures reduce the distortion? Perhaps - but I suspect at the expense of friction and comfort.

[Bill Stevenson]

Nominal tire pressures are based on assumptions about weight of bike and rider and load, speeds, and ambient conditions such as temperature, wet or dry and so on. I offered this advice once before and was challenged on it so I backed off. But I did check again after the challenge and was encouraged by a client of mine who is an executive with a major tire manufacturer and a motorcycle enthusiast and by another friend of ours who is a top level amateur time trials rider. Both advocate this method. According to my tire executive friend his advice works for cars too, and is valid for radials as well as bias ply tires, and either tube or tubeless.

Set your cold pressure at the vehicle manufacturer recommendations. Go for a nice long ride. Check tire pressures immediately upon dismounting. A properly inflated tire for the conditions of use will gain approximately 10% pressure. If your pressure gain is more than 10% the initial pressure was too low for the conditions of use. If your pressure gain is less than 10%, then the tire was overinflated for the conditions of use. Adjust for your next ride. Note, small changes in initial pressure are all that is necessary most of the time and there is room for variations ( the word approximately is the key). Also note, if you use this approach you might change tire pressures before riding depending on loads, expected conditions for riding (i.e. back roads, highways, slow, fast, rain, dry, summer, winter etc.) and get away from one setting fits all conditions. On a tour you might even change initial set points as you move from one geographic region to another. Also, allow yourself room for discretion in terms of use and to account for personal preference. What you like in terms of feel and so forth can be different from others. I am much more sensitive to front tire pressure than back, for example, and find the frequently suggested 36 psi front makes my bike feel skittish especially under heavy braking or on a twisty mountain road. I like somewhere between 30 psi and 33 psi much better. I can be happy with my back anywhere between 36 psi and 42 psi most of the time. For me, how I ride, what I prefer. Your results may vary. So the 10% gain target should be viewed as a starting point only.

Regards,

Bill

[deilenberger]

Bill,

I agree the 10% "rule" is only a starting point. I think it was more valid before radial tires became the norm.

I have full-time display of my tire pressure and temperature on my R12R. That allows me to easily see what the pressure change is AS I ride it, and also to see how ambient conditions can change this. The problem with the 10% rule is - at what temperature is it valid? You can see a 10% change in tire pressure with a 40F temperature change in the internal tire air temperature.... and for lots of people - the range of ambient temperatures they may experience can exceed 40F in a single day, so sitting still, without the wheels turning the tire pressure can change more then 10%.

Sometime I'll start recording exactly what pressure readings I get for what tire-air temperature I read, but it isn't unusual for me to start the day with 32/36 and during the ride see 38/44 as the tires warm up (and also see a >40F change in tire air temperature just due to heating when riding.)

This makes the 10% rather difficult to use IMHO. I go much more on how the tire feels to me, and as you note, above 34PSI (measured at 72F) in the front starts feeling loose or skittish or just less stable to me.

Best,

[mogu83]

Sometimes when I read these oil/tire pressure/suspension threads I think I'm missing something. When I read about riders (not pros just regular guys) feeling the difference in 2/3 pounds extra pressure in the tire, one or two clicks of dampening on a shock or the difference in engine temperature and performance between using 10w60 or 20W50 oil - I just don't see it.
Don't get me wrong I know I'm old and a lot slower than I used to be, but I don't get left behind in the twistys and I'll drop the reins and let the bike run on a long lonely stretch of road, before it had 10K on it I knew what 'flat out' was.. Am I the only one that is so insensitive to these items which it seems others find so critical ???.

Here's an interesting case of too much information. I recently put a tire pressure monitor on the bike (like the one Don has), it gives pressure and temperature. On a recent trip out West the rear tire pressure was 42 and 77 degrees ( also ambient temp) in the morning, in the mid-afternoon after running in the mid to high 80s with ambient temps in the low 100s the pressure was 50 and the temp in the tire was 133. Throw a 5/7K+ foot elevation change (up) into the equation. I just noted it and watched it, the next morning the pressure was back at 42.
I guess if you used the 10% rule I should have started off with more than 42 pounds in the tire.

[deilenberger]

Here's an interesting case of too much information. I recently put a tire pressure monitor on the bike (like the one Don has), it gives pressure and temperature. On a recent trip out West the rear tire pressure was 42 and 77 degrees ( also ambient temp) in the morning, in the mid-afternoon after running in the mid to high 80s with ambient temps in the low 100s the pressure was 50 and the temp in the tire was 133. Throw a 5/7K+ foot elevation change (up) into the equation. I just noted it and watched it, the next morning the pressure was back at 42.
I guess if you used the 10% rule I should have started off with more than 42 pounds in the tire.

That's the reason I suggested the 10% rule might actually be obsolete now. Radials heat up a lot differently from bias ply tires (which have a much stiffer tire body..) so pressure changes can be a lot more extreme. I can't recall ever seeing 50 PSI on a rear tire, but I've also never seen 133F tire temp either.

See you at the meeting tomorrow Harry..

[Bob Ain't Stoppin']

I agree with you Harry. People are putting way too much thought into the tire pressure thing. Pick one . . . and have a great ride.

[Bill Stevenson]

Whether I am putting too much emphasis on tire pressure or not is a decision each person should be encouraged to make for him or herself. For me it is not a big deal, something that is routine and doesn't require much time or thought. I share it for what it is worth and assure you that it is not new and comes from several reliable sources. it is not perfect. I do agree with Harry that it is not something that I feel on my rear tire, but it is more critical for me on my front. Here in South Florida, where I reside, the tire pressures are typically set somewhat higher in the morning than they are when I am riding on trips up north. The reasons are clear from Harry's post. Using his example, I would have set the cold tire pressure up from 42 to 44 psi and see what happens on day two, assuming another hot day. The max tire pressure would be expected to drop from 50 to perhaps 46 or 47 and voila there is the 10% rule. It is no big deal to me to do this. Could I feel this difference in the back tire? I doubt it. Would the tire be operating in a safer margin? No doubt. Suit yourself.

With respect to Don's thoughts, I don't see any inherent reason to doubt the 10% rule for radial vs. bias ply tires. I do agree that the amount of change would be different, in fact I can confirm that Don is correct from some older bikes that I ride that are fitted with bias ply tires. That implies that to stay within 10% requires different initial cold tire pressures for different types of tires, but it is still very possible to apply the rule.

Again this information is not meant to be taken as the only way to figure out what works best for you. But it is a good way and potentially a more accurate way than taking figures out of the owner's manual without giving consideration to the way you ride, on the roads you ride, with the loads you carry, and the weather conditions you encounter and so on. One last point. It has been my observation that the recommended pressures in our BMW owner's manual often keep within the 10% rule for most riders in typical conditions. So they are not a bad place to be for those who think the 10% method is too cumbersome. And if you check your tires inflated in compliance with those recommendations you are probably in the 1-2% of riders who are doing anything at all. Every service tech I have ever asked has told me that it is normal and expected that bikes come into the shop on seriously under inflated tires due to owner neglect. Stay safe out there and have fun.

Regards,

Bill