The o.e.m. Michelin Pilot HX MXM 4's on my Honda Civic Si will have maybe 35,000 miles on them by the time the wear-indicators are flush with the tread (31,000 now). Many people consider this unsatisfactory, and I certainly would for a general purpose all-season radial. But the they are grippy and I drive the car hard. It has done track tours and the Tail of the Dragon twice.
So it's about time to replace the Michelins. The Tire Rack website was helpful and easy to use for research. I couldn't find a grippier tire without going to "summer only." That's a non-starter because the car is a daily driver. Both rear rims leak air at a rate of about 5 lbs. over 2 weeks (sometimes one, sometimes the other!). And another Dragon run is coming up. So the leak problem is a good excuse to upgrade the rims.
The O.Z. Alleggerita HLT wheel weighs 15 lbs. according to Tire Rack (O.Z. says it weighs 13.8 lbs.). This is a significant improvement over other rims that typically weigh 18-22 lbs. The O.Z.'s are pressure-cast and shot-peened, which should make them stronger than gravity-cast rims (and, I hope, less leaky). Forged rims seemed too expensive: more than twice as much as the O.Z.'s, which themselves cost up to twice as much as some "name brand" gravity-cast rims.
I considered a 40 aspect ratio tire on an 18 X 7.5 rim. This would have been a no-brainer back in the day when I upgraded from 13 X 5.5 to 15 X 6, going from a 70-series aspect ratio to 50. But it's not so obvious when gaining only 10% in aspect ratio and at the same time adding weight. It doesn't help with the goal of reducing rotational inertia. A weight savings of 6 or 7 lbs. per corner is insignificant on a 3000 lb. car. But reducing the rotating mass (and thus inertia) by 25% seems like a worthwhile gain.
Finally, I have learned over the years that o.e.m. suspensions are engineered for a narrow range of unsprung weight. Increase unsprung weight at your peril if you want to keep the tires' contact patches in maximum contact with the road. Reduce unsprung weight and you increase the suspension's stiffness a bit.
So my baby's new shoes will be the o.e.m. tires on lighter wheels.
4 comments:
In mountain biking (and road cycling) you want the lightest, stiffest wheelset that you can get.
Recently bicycle wheel manufacturers started making carbon fiber rims which equaled a huge step forward, especially with the current crop of 29" wheeled mountain bikes.
The drawback is the admittance fee, which is between $1200 - $2500 per set (normal car parts start looking really cheap when compared to high end bicycle parts).
Just about anyone can tell a 100 gram difference in a bicycle wheel (lighter steering, better acceleration and hill climbing) whether it comes from the actual tire itself, or the rims and spokes.
In that same vein, 200 grams makes a huge difference, especially if it comes off the tires and rims (farthest away from the axis makes the most difference, which I know you know this, but I had to say it anyway).
Upgrading wheels and tires on a bicycle is the most bang for the buck, so I can see where this would be a likely place to gain an advantage in the sports car world.
P.S. Don't forget to post some pics when your wheels come in!
Didn't know about furthest from the axis, but it makes sense: most inertia.
Ever think about taking your bike to the Dragon?
"Ever think about taking your bike to the Dragon?"
I don't ride on the road anymore, there are just too many people texting and driving these days.
And although I doubt if many people are texting on the Dragon, it would still make me a little nervous what with all the 'English' (wrong side of the road) driving I've seen there : )
Yeah, I hear you. Sitting at stoplights around here, I'm surrounded by people yakking on cell phones. Assume the ones looking down at their laps are texting. Just KNOW am gonna get rear-ended one of these days.
But a 10-speed looks like fun on the Dragon from Killboy's pix. At least on the downhill parts. ;-)
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