# Bicycle Mechanics - Trimming Weight on Rims

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View Full Version : Trimming Weight on Rims

abm1213
01-28-06, 12:08 PM
I'm sitting here looking at my Deep-V rims and thinking blasphemous rational thoughts, again, without a whole lot of information. The rims are quite heavy. There are already some access holes in the rim for spoke installation. Why not carefully drill some more holes to trim off some weight? You could use one of those really strong rim strips like the plastic Michelin ones so that you wouldn't have a problems with blowing through. I'm sure it's been done. I'm also quire sure there are diminishing returns and increasing risks. Anybody ever do this?

I'm not saying I'm going to do it, I'm just wondering. There was another thread where the guy was thinking of trimming off the braking surface of his clinchers with vice-grips to make tubular rims and this post is sort of in that vein.

DannoXYZ
01-28-06, 01:42 PM
you guys are crazy...

CdCf
01-28-06, 02:33 PM

How much weight can you realistically save?
50 g per rim? Or for both...

Let's say you're an average, fit rider, weighing 70 kg. Your bike weighs, say, 7.5 kg. With a couple of water bottles, shoes, clothes and stuff, we'll make it an even 80 kg.

80 kg is 80 000 g.

If we say you saved 50 g, then you've reduced the total mass by a factor of...

50 / 80 000 = 0.9994

Yep, that's a whopping 0.06% you've saved!
Which would make you 0.06% faster if you were cycling vertically in vacuum. :)
At typical race speeds, on a mixed hilly/flat course over 100 miles, such a reduction would save you no more than about 10 seconds.

Worth it?

01-28-06, 02:45 PM
Which would make you 0.06% faster if you were cycling vertically in vacuum. :)

When you do this test, please make sure and get video and post it up so we can see it ;-)

Cheers,
Bill

wethepeople
01-28-06, 03:11 PM
Trials riders do this all the time... and they take a hellovalot more of a beating.

tartybikes.co.uk/products.php?product=rims_26

LóFarkas
01-28-06, 03:12 PM
I'm sorry, CdCf, that calculation is idiotic. Or lets just say, incorrect. First of all, 1kg on the bike != 1 kg on you. To take a trivial example, when you start from a red light and stand on the pedals, the heavier you are, the bigger weight is pushing down on the pedals (the more weight you have to get moving as well, of course). Now if that extra weight is on the bike, you will have to get more total mass moving, but not more power to get it moving with. A heavier bike is more difficult to bunnyhop and generally move around as well.
Now, as we all now (khm...) the outer perimeter of the wheels is where weight matters most, as you ave to spin them up every time you accelerate. Lighter wheels do matter.

To OP: I wouldn't do it. You sort of gave up on weight when you bought those silly heavy rims, and there's no going back. Sorry.

CdCf
01-28-06, 04:19 PM
I'm sorry, but you're wrong.
A commuter isn't (or shouldn't be if he/she is fairly sane) concerned with extreme weight savings. No normal race has more than one start from standing still. They're the only ones who would be stopping and starting regularly (traffic, red lights). And while it's true you accelerate and decelerate throughout a ride, the changes are very small. Besides, the extra mass on the rims isn't as big a deal as some claim. The more constant the speed is throughout the race, the less of a problem it is. At some point, you should actually benefit from it, because speed doesn't fluctuate as much if you have a larger rotating mass.

And you don't get extra power from pushing down with a greater body weight. You still have to do the work yourself, so being able to push down with a greater body mass, you also have to lift that mass up first. That means you have to do the same work, no matter what. This is only a factor when you start, and the first 3-4 seconds of the start aren't really important in a race over any reasonable distance.

So, in the end, the difference wouldn't be much greater than what I calculated. Even if I'm off by a factor of ten, it's still very little. And I know I'm not.

Retro Grouch
01-28-06, 04:27 PM
Think of how much water your wheel is going to collect every time that you ride in the rain.

abm1213
01-28-06, 04:31 PM
Lighter wheels do matter.

To OP: I wouldn't do it. You sort of gave up on weight when you bought those silly heavy rims, and there's no going back. Sorry.

I like my silly rims. If you look at the site suggested by a previous post, it turns out that, again, engineering innovation takes place somewhere else than traditional, euro-centered road racing. What a splendid and refreshing concept; reducing redundant and unnecessary weight to increase performance by altering the "production" unit. I really like the rims with the drilled out braking surfaces - those would be great on the track.