Tier1Terrier

I just purchased a complete set of Sebro slotted one-piece front & rear rotors and am a little perplexed about something. Just out of curiosity, I decided to weight the rotors out of the box. I fully expected the fronts to weigh more than the rears but what surprised me was that the right rotors weighed more than the left rotors, and not insignificantly. To be sure I wasn't making a mistake, I weighed them and reweighed them to ensure that the reading were consistent, even switching back and forth. Each time I weighed each individual rotors, even when switching back and forth, the reading I got were exactly the same for each rotor down to the tenth of a pound. I believe the scale to be accurate as it always gives very consistent readings.

Here are the weights for the fronts:

• Left Front: 26.4 lbs
• Right Front: 27.0 lbs

That's .6 lbs difference from left to right. Over a half pound. That doesn't seem like an insignificant amount. (That is a 2.23% difference in weight)

Here are the weights for the rears:

• Left Rear: 22.6 lbs
• Right Rear: 22.8 lbs

Not as big of a difference from left to right but still .2 lbs or almost 1/4 pound. (That's a .88% difference in weight. So less than 1%)

Interesting to note that in both cases (fronts vs rears) the rights weigh more than the lefts.

These differences in my opinion are too significant to be unintentional, yet I can't understand why they would be. It's hard to imagine that there could be a quality control issue that would produce such unintentional differences. We're not talking about and ounce or a few grams difference.

I'm perplexed by this because to the best of my knowledge, replacement rotor rings from companies like Girodisc & AP are the same weight from left to right. On the Essex website, it lists the AP 350mm replacement rings as 21.2 lbs for left or right. And my guess is that the rotor hats are the same from left to right too.

Any ideas why there would be such significant difference in the weight of these Sebro rotors?

quickboxster

Interesting, I just weighed my brand new set of spare Sebro slotted rotors still in the bag and the right rotor is 0.6 lb heavier than the left.
That's for a 987 and the total weight of the right rotor is 14.6lbs.

Kein_Ersatz

amurph182

clearly these are NASCAR rotors built to withstand the greater forces on the high side of the banking.

stownsen914

I think he might be right!

Seriously, while interesting to note, I think I wouldn’t be too concerned about it. Since the lefts and rights come from different molds (I’m assuming they are directional), there could be some difference. I’d be more concerned with measurement tolerances than weights being off by 1-2%.

Speed2k

Check out a video on corner balancing on YT and you'll see that each axle could have a massive difference in weight, then you'll realize the difference in weight between the rotors is not really that significant.

One other exercise that you should try is to pull your current rotors off and weigh them. I've never tried but I suspect there's a difference in weight for those too.

Tier1Terrier

Thank you all for your comments. Based on these comments and others from another thread I posted about this in, I'm beginning to think that not only is it common for rotors to not be exactly the same weight, but that the weight difference that I'm seeing (~2%) may not be very significant after all. I appreciate everyone's input.

GlenL

Between the molds and the machining, 3% doesn't seem excessive.

FWIW... I got some discs from Sebro that were machined poorly and pulsated right out of the box. Now I only use Zimmermens. And I've have had those crack through. For track weekends, I tote along a full set of new discs along with assorted new/old pads.