barrman : Rolling Resistance

Rolling Resistance
Post by barrman on Aug 10, 2006, 3:10pm

It seems we have about 5 tire threads going on right now. I figured I would add another.

Fortune has smiled on me and I get to have 3 "Jeep Days" this week. Today is the second. While driving home yesterday, I decided to see how far I can coast. I have tried this with all of my vehilces from the same spot about a mile from my house to see how far they will roll when I put them in nuetral while going 40 mph.

The spot is a mile from my house and at the top of a gentle slope down. Then a slight rise, another gentle down, 90 degree banked turn to the left followed by a 90 to the right off the pavement and onto my dirt road. A long rise up, normal slope down and then a long (1/4) mile rise up to my driveway.

I have only had one vehicle make it from the neutral spot to my drive way. 1988 Mazda MX-6. The Suburban will almost make my property line if I do the turns right by basically sliding onto the dirt road. The Mini with its fat tires doesn't make it over the first rise. Neither does the '66 K20. The M715 with NDT's at 45 psi didn't either.

This was my first test with the XZL's on it. I was amazed when I passed the spot it stopped before at more than 20 mph. I took the dirt turn off in a slide and made it halfway between my property line and my driveway. In other words, further than my 2000 Suburban and almost as far as the Mazda.

I am sure someone will come on here and comment about the extra weight of the tires and how they effect momentum and stuff. I'm sure it does. As does the extra diameter. But, my XZL's with 80 psi in them rolled furnther than the skinnier with less tread NDT's at their max psi. They also ride smoother and look great.

Of course, the downside to having the big Michelins is stopping. I need to plan ahead a lot more for stops than I used to.

Just wanted to post about my little science project and brag on the tires somemore.

Re: Rolling Resistance
Post by compexp on Aug 10, 2006, 3:25pm

cool. guess i need to budget for some XZLs.

Re: Rolling Resistance
Post by kwai on Aug 10, 2006, 5:50pm

Your speedo is off. You were going faster than you think.

Re: Rolling Resistance
Post by mikel on Aug 10, 2006, 5:57pm

About the extra weight of the tires and the inertia. Sure, heavier tires will carry you farther from a fixed starting speed, but keep in mind that it will take extra energy to get those heavier tires spinning in the first place, cancelling ALL your gains

Re: Rolling Resistance
Post by 40grit on Aug 10, 2006, 6:07pm

kwai might be onto something, how many have stock size tires? Did you use a GPS to check speed?

Re: Rolling Resistance
Post by mikel on Aug 10, 2006, 6:16pm

Yes, his speedo is probably off by quite a bit...


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">kwai might be onto something, how many have stock size tires? Did you use a GPS to check speed?</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

Re: Rolling Resistance
Post by jeepistdougiowa on Aug 10, 2006, 7:02pm

Harder tires flex less....opposite of trying to push a car with a flat tire. That's my theory anyway...LOL

Re: Rolling Resistance
Post by barrman on Aug 11, 2006, 8:10am

I adjusted for the speedometer difference. I was indicating 35-36 mph when I started the test. Which in theory should be 39-40 mph actual speed.

I agree about the "balance out" of the bigger/heavier tires. It is just like a tail wind in an airplane. It never balances out with the headwind you had going the other direction. You end up with a net loss.