Observations About Tire Wear and Mileage Under Severe Use

[David]

I recently had a really fun two days at the track on the new GS. I won't go into more detail here--it just sets the context.

 

I was very interested to see how dual sport tires would perform in that situation (by the way, no washing or sliding at all at fairly extreme lean angles from the Michelin Anakees), and I was especially interested in measuring wear, inflation, and temperatures as data points for our discussions here. So let me throw three interesting things at you about the tires, and then I'll throw a fourth in: gas mileage.

 

Temperature

 

At both mid-day sessions the ambient temperature was 87 degrees. The track surface was ca. 110 degrees. The front tire temperature (on the surface) was 121 degrees. The rear was 138 degrees.

 

Observation: as stressful as "pushing" a front tire is, constant heavy acceleration from the rear is even more stressful. I ought to brake quite a bit harder to pick up lap times.

 

Pressure

 

Cold inflation pressures were 32 lbs. front and rear. At the end of the fastest session the front had risen to 35 lbs. (9%) and the rear had risen to 37 lbs. (13.5%).

 

Observation: the front was probably good; the rear probably needed to start at 34 lbs. (Remember that pressure increases are largely from the heat generated from sidewall flex or surface to surface friction.) What I'd also say is that if we really believe the "10% rule" most of you are running pressures that are far too high. I'm not arguing for either--I'm just saying they are not consistent.

 

Wear

 

This is the really fascinating part to me. I have three sets of the exact same tire. One set is new. One has spent two days at the track for a total of 216.4 miles. And the last one has 4,500 miles of normal twisty riding (no interstate to speak of). I've measured wear in the center and at the same point on the sidewall for all three sets, and here are the results.

 

In 216 miles on the rear tire, I put 750 miles of wear on the center portion and 1,600 miles of wear on the side portion.

 

In 216 miles on the front tire, I put 214 miles of wear on the center portion and 2,340 miles of wear on the side portion.

 

Observations:

 

a) I'm not braking a lot (that uses the center front).

b) I'm cornering hard (that uses the center and rear side).

c) I'm accelerating hard coming out of corners (that uses the rear side).

d) A brand new rear would be worn out on the side in 600 miles.*

e) A brand new front would be worn out on the side in 415 miles.*

 

*Never mind the heat cycles, which will actually kill a tire sooner than actual wear.

 

Observation: In normal riding, your own style has a lot to do with how quickly your center/side rear wear out. Yes, inflation and surface are important, but flogging is a huge factor.

 

Here's a shot of the front after one session. Ahhhhh. The sweet sight of melted rubber!

 

 

Fuel Mileage

 

I've tracked mileage from the beginning and it's been an average of 48.6 mpg. For the first day I got 31.6 mpg for my best lap of 2:03. On the second day it dropped to 30.19 as I attempted to cut 2 seconds off my time.

[One]

Very interesting indeed, David ...but you should show us the picture of the Michelin Man down to his knees imploring you for mercy

 

Juan

[Paul Mihalka]

Very interesting numbers. It kind of confirms what my guess and gut feeling was that a good track day tire wear is like 2000 miles on the road.

[StretchMark]

I thought they started us out with 33 psi front/rear?

 

The experts say the track was designed to put more emphasis on the front end, so it looks like you were riding it like your supposed to.

 

I had one other observation:

Peg feelers an go as quickly as one lap

[Vagabond]

Cool. I have been wondering about this stuff. Now if I may ask a related question...

 

When riding at "low pressure" like 22psi for 700 miles at speeds up to 105........... (1)how does that affect wear, and (2)how does that affect traction in the corners (and therefore safety)?

 

I'm a....er..asking for a .... a freind. Yeh, that's it,...a freind who did that.

[David]

I thought they started us out with 33 psi front/rear?

 

You might be right and I wrote it down wrong.

[SteveB]

Pressure

 

Cold inflation pressures were 32 lbs. front and rear. At the end of the fastest session the front had risen to 35 lbs. (9%) and the rear had risen to 37 lbs. (13.5%).

 

Observation: the front was probably good; the rear probably needed to start at 34 lbs. (Remember that pressure increases are largely from the heat generated from sidewall flex or surface to surface friction.) What I'd also say is that if we really believe the "10% rule" most of you are running pressures that are far too high. I'm not arguing for either--I'm just saying they are not consistent.

 

Could you clarify the reason for increasing the rear pressure? If you started out 2# higher then you would wind up @ 39 which seems a little high and consequently reduces your contact patch. Which might result in lower temps and a resultant lower pressure or it could result in sliding off the track. When do you take your readings? Immediately after getting off the bike or after stripping down and getting a drink?

 

I have been riding with 32 on the track but have never tested post session temp with anything other than a bare hand which can get painful sometimes. I don’t think I have ever checked pressure post session. Interesting info. I’ll pick up a temp gauge for this weekend’s track day and see how my numbers compare.

 

When you have time I would like to compare notes on what you take to the track in addition to your pressure and temp gauge.

[DaveCinNO]

Nice write up, I have definately been guilty of over-inflation! How did you like these tires compared to others you're used from a performance perspective?

 

I've been tapping my calculator to get it to match your numbers, are you sure about the miles on the side and center or am I confused? Also, 48mpg avg? I'll be happy with a lot less than that, especially at speed.

[philbytx]

David,

 

VERY disappointed.....you still have a rubber tire "pimple" prominently displayed in your picture

[David]

Could you clarify the reason for increasing the rear pressure? If you started out 2# higher then you would wind up @ 39 which seems a little high and consequently reduces your contact patch. Which might result in lower temps and a resultant lower pressure or it could result in sliding off the track.

 

Steve, the theory behind the 10% rule is this: if you have the right amount of air pressure when cold it'll rise by 10% when hot. And since temps rise large from flex and surface to surface friction, the lower the cold pressure, the greater the rise when it gets hot. In other words, a tire with 32 lbs. will flex more than a tire with 34 lbs.

 

I know we've thrown that rule around here, and all I'm saying is that if we really followed it, we'd be using lower pressures on the road--pressures closer to what the manufacturer recommends. The high pressures you see listed here on the board are near the max cold inflation pressure. Early on they were used to prevent damage to soft rims; now it seems they are used to prevent cupping and achieve higher mileage from the tires. And what I'm saying is that either the 10% rule doesn't apply to our sport touring tires or we shouldn't be running these high pressures.

 

When do you take your readings? Immediately after getting off the bike or after stripping down and getting a drink?

 

Immediately, within 5 seconds, using an IR thermometer I kept by the stand.

 

This test was as scientific as I've ever been in terms of tires. But of course it's just one brand/model of tire, so it might not apply all that much. In fact, maybe the "large block" pattern promotes cooling. Who knows.

[David]

Nice write up, I have definately been guilty of over-inflation! How did you like these tires compared to others you're used from a performance perspective?

 

They were surprisingly good! Shocked the heck out of the corner workers and instructors to see dual sport block pattern tires on the track. Just goes to show how far tire technology has come, I guess.

 

I've been tapping my calculator to get it to match your numbers, are you sure about the miles on the side and center?

 

Yep, I'm pretty confident in the numbers, only because I built a big Excel spreadsheet to figure it out when I really should have been working yesterday afternoon. I measured everything in 100ths of an inch with a guage, at the same place on ever tire.

[SteveB]

I had great expectations of replicating your tire study at the track yesterday however I failed miserably at recording data after each session. At 97 deg. in the afternoon it became more important to strip down and get a cold drink.

 

I ran 32.5 on the front and recorded 35 after the session for an 8% increase after the 20 min. session. On the rear 33.0 increased to 37.5 for a 12% increase. I dropped the front down to 32 and increased the rear to 33.5 but failed to check it after the session.

What was really interesting to me was the disparity of surface temperature on the tire.

 

Front - left 142.5 - center 134.5 - right 130

Rear - left 150 - center 135 - right 127

 

As reflected by the numbers TWS has twice as many lefts as right turns.

[Z-Man]

David, Steve brings up something that could be important regarding temperature measurements. In sports cars, we measure the temperatures on the outside, center, and inside of all four tires immediately after every session. We also measure pressures at that time. It is from these readings that we determine whether to increase or decrease the starting pressure before the next session at that track.

 

I don't know whether race teams do the same for bikes, but if your objective is to optimize the balance of temperatures across the tire, it could certainly make a difference. On the other hand, the geometry and race dynamics for bikes are so different from what they are for cars, maybe it just isn't applicable for bikes.

[johncarves]

Ok, 33/33 cold on the track... just curious, what's your cold temps for mountain riding (all asphalt)?

[David]

Ok, 33/33 cold on the track... just curious, what's your cold temps for mountain riding (all asphalt)?

 

On these tires I've been using 35 front and 36 rear. At those pressures I'm happy with the compromise between traction and wear.