This is really interesting. How did you measure the tire footprint size?

Jim G

 

After riding wet the ground on part of your driveway and pull straight in to the dry part of the driveway for about 3 to 4 feet don't lean and full weight get off and you will see your footprint. When I first did it it was much thinner then now.

You also could do it in soft dirt and see it on your tire.

No science to this just my way of looking.

Again I'm not an expert but I got 6500 on my first rear tire and that was with part of the 65k at 42 psi and now I'm hitting 4500 on my second and it looks goooood. Hows your milage??

 

Double post.

 

On the advice of another Breakout owner, 24v, I reduced the tire pressure on my Nightrain and ended up with 34 on the rear and 32psi on the front.

I too noticed the very narrow wear band (footprint) on the rear tire and things improved on the tire that I had on at the time, and my new tire has close on 3k miles and will most definitely last 2 ~ 3k longer than the previous one.

While I was trying lower air pressures, at no time did I feel reduced performance, but then I'm not a street racer.

 

Not a motorcycle tire expert but did own an auto tire store for 25 years. That kinda makes me know a little about tire pressure. I always aired my customers tires up to the lowest recommended pressure for normal driving. This will allow for maximum tire wear. Always cautioned the customer that if your running an extremely heavy load to air up to the maximum. Never ran into any problems over the years. I practice the same methodology on my bikes. 10,000 miles from the last dunlop on my old dyna. Still had a little to go.

 

jim, I was on the dennis kirk motorcycle website looking at tires for the breakout. Out of the five that were available they all start with around 8/32 - 7/32 max tread depth, except for the avon brand which was said to have 12/32 tread depth. I found that to be interesting. I thought no way, but its also 5 lbs heavier roughly.

 

wow, keep the data coming guys! We'll figure this out.

Jim G

 

Completely wrong. I ride like an 80 year old women. No burnouts, no fast take off's, no hard cornering, solo riding only, 175 lbs, always maintain 42 psi.

 

I had an interesting chat with one of the technicians at my local HD dealership this morning, about tire pressure in these 240mm wide tires.

He told me that the dealership staff always run far less than the 42 psi recommended by HD for the Breakout. In fact, I found when I checked the tire pressure in my new Pirelli Diablo the next morning after getting it installed at the dealership and then driving home and letting it cool overnight, that the psi was 35. I bumped it up to the recommended 42 as a start point for my testing, but notice that the dealership staff completely disregarded the HD recommendation.

The technician told me that their disregard is based on a simple idea:

If the bike plus rider weighs "x" pounds, and the psi is "y", then the contact patch is x/y.

But the contact patch is the product of contact length times contact width. A 240mm tire is much wider than the narrower tires typically used on cruisers. So, the contact width will be much greater. Which means that the contact LENGTH will be much smaller. The logical question is WHY would you deliberately make the contact length smaller? Extra contact length is a traction plus, provided you don't achieve it by dropping the tire psi below the tire's recommended working range.

The technicians' reasoning is that if "x" psi is recommended for a narrower tire, why would you insist on "x" psi for a much wider tire on the same weight bike? He says he would never run 42 psi in a 240 tire on a bike as light as the Breakout, because if he did, it would wear only along the centerline, and consume its centerline tread too quickly while the sides would show only minimal wear. This of course is the exact symptom I got by running the Dunlop tire at 42 psi for only 3400 miles.

Now let's use some real numbers. My Breakout weighs about 710 wet, and I add 235 lb with my safety gear on, so the total weight is 945 lb. Let's assume 65% of the weight is on the rear wheel. That means the load on the rear tire = 945 x 65% = 614 lb.

If I run 42 psi in the tire like HD recommends, my contact patch for that tire is only 614/42 = 14.6 square inches.

If I run 36 psi, my contact patch is 614/36 = 17 square inches, which is 16.4% larger. That means better traction.

Pirelli says that the Pirelli Diablo tire can be run anywhere in the 36 to 42 psi range and still be within the acceptable design psi.

Now it is theoretically possible that if you ran 36 psi but also loaded the tire to its full 963 lb capacity (that's its conservative load capacity per Pirelli), you might generate too much heat due to the extra rubber deformation going on with each revolution. But, you should be able to identify that kind of excess heat buildup by seeing a very large gain in psi between when the tire is cold and when it has been ridden sufficiently to reach equilibrium internal temperature.

But my current temperature rise at 42 psi is ZERO after 21 miles at steady ambient temperature, and only 3 psi even after the ambient temperature has increased by 12 degrees (from 73 to 85 degrees - see the data in my first posting in this thread). This seems to indicate that 42 psi is too high, since the psi SHOULD increase by a few psi when the tire goes from "cold" to "operating temperature".

I am going to do some research on how MUCH a motorcycle tire should increase in temperature and psi in STREET versus track use. (Racers on a track deliberately run very low psi to expand the size of the contact patch, and so experience a very high increase in temperature and psi, but race tires are specifically designed to handle those high temperatures and large psi swings, and street tires are not).

Jim G

 

You should be a writer for some bike magazine. I like how you compared every thing with percentages, measurements, and weights. And it has been my experience that Pirelli tires wear a little faster due to using a softer rubber. But that's okay with me as I prefer traction to tire life any day.