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Answer a friendly bet...(7 posts)

Answer a friendly bet...manicoti
Aug 8, 2003 4:21 AM
My friend, a mechanical engineer, and I, a biologist with much more riding experience, have had the discussion about wheelset weight and rotational mass. He junked his rear wheel in a crash and doesn't want to spend alot on a new wheelset (<$500). He is looking at the Shimano's and I told him to just go with Ultegra/Open Pro's. I don't have any numbers, but I need help justifying to him that the rotational mass on the factory built wheels will be greater than on the conventional wheels. He weighs about 210 and is pretty solid, so I believe that the conventional wheels will be better for him since they are stronger and more easily servicable(sp). They will also be less expensive. He said that since the spokes are J-bend, they do not need any reinforcing in the rim so they are not heavier rims. They are if they are aero. Anybody have any help or links to past discussions to clear this up one way or the other.
moment of inertia...C-40
Aug 8, 2003 5:48 AM
What you're comparing is the moment of inertia, something that very few companies, with the exception of Nimble, bother to advertise. This is kind of amazing, considering that everyone seems so obsessed with wheel weight, they don't bother to advertise the moment of inertia.

To answer your question, two wheelsets may have the same weight, but if one has heavier rims and lighter hubs it will not accelerate or decelerate as quickly.

For someone that weighs 210, it probably doesn't matter much what he uses (he's way beyond competitive cycling weight). If he doesn't want to spend a lot of money, then conventional custom-built wheels from Excel sports or Colorado cyclist are the way to go. Personally, I'd go up to CXP-33's at that weight.
re: Answer a friendly bet...Chen2
Aug 8, 2003 6:09 AM
One of my riding buds weighs 225 - 245 and he has trouble bending Open Pros hitting bumps.
~Al
what?burdiman
Aug 8, 2003 7:52 AM
I weight in at 240 and have never had this happen and the roads I typically cover range from good to horrible. Sounds like a build problem. I run Open Pro, 36 hole, on an American Classic hub. Wheel weight comes in right around 900g (not bad I think).
Rough roads.Chen2
Aug 8, 2003 9:05 AM
It surprized me too, I ride two sets of Open Pros. We've got some really bad chug holes in Oklahoma, maybe that's the difference, I don't know. But this guy has bent 3 OP's that I know of. He's not very good at maintenance and loose spokes may also be to blame.
~Al
Rough roads.xcandrew
Aug 8, 2003 12:47 PM
"loose spokes may also be to blame"

I'm assuming you're not talking about denting the rim from riding underinflated tires. I wouldn't say just "may be to blame". The load carrying capacity of a wheel is directly proportional to the tension in the wheel. Specifically, if the "hit" causes a load on the wheel that is greater than roughly the sum of the tension of the 4 or 5 spokes in the region of the "hit", the rim will bend or collapse. Stiffer rims will distribute this load over more spokes, so they will be a bit stronger. Stiffer rims can also be stronger because they can take higher tensions in the build, but obviously the actual tension in the wheel is the important factor... the builder needs to take advantage of this. Your friend will bend any rim if the spokes are loose.
some links....divve
Aug 8, 2003 7:04 AM
You'll find that the weight variance amongst the lightest and some of the heavier wheels is of little importance. When including the total weight of bike and rider, wind resistance, rolling resistance, the wheel inertial matters the least of all factors. Sure, you can feel the difference. It adds very little to your performance however.

http://www.bike.com/template.asp?date=8%2F1%2F2001&lsectionnumber=6
http://analyticcycling.com