Two or One rotors?

[Shawn Durette]

What are most teams using for rear brakes? What are the advantages to one vs. two rotors on the rear?

Shawn

[UNB f4i tats]

http://fsae.com/groupee_common/emoticons/icon_frown.gifhey just add one on the rear

[Agent4573]

I don't think we have ever used dual rear rotors on our car. Our rear rotor this year is basically the same design as our front rotor, but a little thicker.

Some of the added benefits of only one rear rotor are less rotating mass, less mass in general, it moves the mass of the rotors from unsprung to sprung weight, you only have to make one....

[Erich Ohlde]

We've run a single rear brake (quaife diff) for several years. Although in testing our 04 car we noticed that if you got hard on the brakes one wheel would begin to rotate backwards and kick the ass-end out. I think we have decided on running two rear brakes this year.

[Nate Notta]

If you run outboard rear brakes you can use a small simple open differential. We did it once, and dynamically it was fine.

[Shawn Durette]

Nate,
So you say you did it once and it worked fine dynamically, but what? You switched to one to rear rotor to save weight? Or what other issues should I be considering or looking into. I want to pick and order some MCs soon.

Thanks,
Shawn

[Nate Notta]

Yeah went inboard the following year to save weight (and unsprung weight in particular).

[Courtney Waters]

With one inboard brake your axles will have to deal with the braking torque. Usually not a big deal, but something to consider. Also, an inboard brake acting through a limited slip tends to add understeer. If you lift the inside wheel, you will only see the transfer torque at the outside wheel. Packaging-wise, which works better for your car? With 13" wheels it's not too bad to do outboard brakes, but with 10" it gets more challenging. As for weight, how much would two small outboard calipers weigh vs. one larger inboard? How would the inertia of a larger single disc compare to two smaller outers? Talk to drivers who have driven both types to get their feedback as well.

[Daves]

1. 2
2. 1
3. 1: less unsprung mass if inboard
2: better braking & control

[Buckingham]

If you take a single disc system, and convert to an inboard dual disc system of equal rotor mass, you can significantly decrease rotating inertia.

[Nate Notta]

...braking on the sprocket has the least rotating inertia and total mass http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Garlic]

That depends.... you can definitely make a lighter sprocket if you don't have to brake on it, and a smaller rotor if it's size isn't determined by your final drive ratio.

[Nate Notta]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Garlic:
That depends.... you can definitely make a lighter sprocket if you don't have to brake on it, and a smaller rotor if it's size isn't determined by your final drive ratio. <HR></BLOCKQUOTE>

I have to disagree there... we braked on a 7075 aluminum 520 bike sprocket last year (with significant material cut out for weight savings). It worked like a charm. You can't get any lighter than that.

[Garlic]

It could have been lighter if you weren't braking on it. It would have seen less loading and needed less material for heat transfer.

7075, wow that stuff hates heat. Sounds like a recipe for disaster.

[Nate Notta]

Well, the proof is in the pudding.

Sorry these pics aren't the best resolution, but you can get the idea. Most teams run sprockets heavier than this even when braking on a seperate rotor, so I don't think anyone can argue there is a rotor braking setup lighter than this.

http://zeus.uwindsor.ca/fsae/gal1/images/wedding%20009.jpg
http://zeus.uwindsor.ca/fsae/gal1/images/wedding%20016.jpg
http://zeus.uwindsor.ca/fsae/gal1/images/wedding%20018.jpg

[GTmule]

When the sproket isn't the brake disc, where does the disc go? Pictures would be nice http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Frank]

can i ask these people with "sprotors"...

do you lubricate the chain, and how?

does the lubrication mess with the friction material?

[Garlic]

Sorry and don't mean to knock on your design Nate. But even if 'most' teams run a heavier sprocket then that, I can tell you ours was a lot lighter and most top teams are too.

Did you do any FEA on the sprocket? including normalized 7075 strengths? If you are getting it as hot as you ought to with heavy braking it is going to be approaching 7075-T0 which is quite weak, of course if you designed for that it's not a flaw.

[me_george]

For sure, one rear rotor will reduce the rotating mass. but there are lots of other factors should not be ignored. It really depends on what kind of dif. you use. also, where are you going to mounted, just ,make sure the brakes have enough air flow otherwise it will over heat and fail.. this year, we are using 2 rear rotor , but with smaller OD, which almost as heavy as the one rotor, but with better air flow to cool the rotor during racing..

[Nate Notta]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Frank:
can i ask these people with "sprotors"...

do you lubricate the chain, and how?

does the lubrication mess with the friction material? <HR></BLOCKQUOTE>

We used a RK Chain X-Ring chain with no lubrication.