cloudy
|
| posted on 24/1/08 at 10:28 PM |
|
|
Reducing brake rotor weight..
Just after a sanity check on this one. After fitting wilwoods all round, I find the bulk of my unsprung mass is now generated by the discs
themselves...
I'm dead against home drilling of rotors due to the high risk of failure. My plan is however remove material on the face of the disc where it
mounts which in my opinion is completely overengineered given the load is being transfered through two fairly piddly sierra caliper mount lugs!
Thoughts? 
[Edited on 24/1/08 by cloudy]
|
|
|
|
|
cloudy
|
| posted on 24/1/08 at 10:33 PM |
|
|
Also what are your thoughts on drilling the unswept area like so?
[Edited on 24/1/08 by cloudy]
|
|
|
StevieB
|
| posted on 24/1/08 at 10:38 PM |
|
|
If you machine down the surface of the disc where you intend to, would the wheel not be mounted slightly more inboard.
Not much, but I'd think about whether the few mm you machine down would mean the caliper fould the wheel.
|
|
|
cloudy
|
| posted on 24/1/08 at 10:48 PM |
|
|
Sorry, badly explained - I would be removing material by drilling. I don't want to interfere with the relatively high tolerances in the
thickness
|
|
|
jambojeef
|
| posted on 24/1/08 at 10:55 PM |
|
|
Its certainly a heavily over-engineered part and weight could be safely removed as you say.
The concern is, it being a rotating assembly, that if modifications are made then the part is balanced afterwards. With cast items, you cant assume
that just drilling a balanced part evenly will leave a balanced part because of natural density variations in cast parts.
iirc there are some pictures of Champion's race locost in the book with drilled brake rotors but around the bell rather than the disc itself.
The other concern is that if you leave the holes undressed that stress cracks could propagate from the rough edges. I would perhaps read up on what
treatment is best to minimise the chance - perhaps some shot peening or just finishing of the hole with smooth files and emery?
Hmm, does that help? I hope so!
Geoff
|
|
|
RazMan
|
| posted on 24/1/08 at 11:00 PM |
|
|
Why stop there?
Bikes are getting a bit radical nowadays - very dodgy imo.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
|
|
|
indykid
|
| posted on 24/1/08 at 11:29 PM |
|
|
i was going to say i'd happily machine down the thickness of the disc itself, but i wouldn't do the drilling because of the balance
issues.
i guess the same applies to thinning the disc though. i'd still turn down the disc as that would be worn down under normal use, but
wouldn't do the drilling due to the stress raisers caused by the holes.
how much are the lightweight thinned and drilled raceleda discs?
tom
|
|
|
Ivan
|
| posted on 25/1/08 at 06:01 AM |
|
|
I'd guess that you wouldn't save much more than 3/4 lb by these mods which on a safety critical item is to my mind hardly worth the
risk.
There are much safer ways to save that amount of unsprung weight like disc skimming, careful wheel choice, tyre size, tyre choice, tyre skimming,
caliper choice, alluminium bells etc.
Maybe there's room for a manufacturer to look at producing and testing ultra-lightweight discs along the line of what you are proposing - if
properly done I for one would buy them as not only do they save unsprung weight but look cool.
A sensible alternative would be to produce an aluminium bell to allow bolt on discs without the large unswept area of iron. Similar to the one shown
by Razman above.
|
|
|
britishtrident
|
| posted on 25/1/08 at 07:46 AM |
|
|
Really not a good idea, the thickner material gives a better heat conduction path which helps even out the temperature variations around the disc
prevent disk warping.
Warping occurs when the vehicle is stationary with the brakes very hot, a hot spot forms in the area of the disk covered by the brake pad.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
dan__wright
|
| posted on 25/1/08 at 08:58 AM |
|
|
what about inboard brakes (for the rear) its something im interested in doing, like on the zcars Monte Carlo.
for the front i will be looking at ali bells and light callipers.
FREE THE ROADSTER ONE…!!
|
|
|
Mave
|
| posted on 25/1/08 at 09:02 AM |
|
|
I wouldn't dare messing around with discs. Sure, they are way too heavy for such a light car, but how much can you take away safely? Do you
trust your "feeling" when it comes to those safety critical parts?
How much can you safe anyway; perhaps a couple of hundred grams. That won't be noticeable.
I do agree that lightened discs look cool though....
|
|
|
MikeRJ
|
| posted on 25/1/08 at 09:11 AM |
|
|
I don't think balance would ever be an issue, I've certainly never seen any balancing marks on new discs. Due the the relatively small
diameter and weight compared to the wheel and tyre, any slight imbalance is going to have negligible effect at road speeds.
However, I personally wouldn't bother going to such lengths. The weight saving will be minimal, and you may introduce a risk of warping or
cracking between holes, even on the unswept area. As someone else has said, going for alloy bells would be your best bet.
|
|
|
cloudy
|
| posted on 25/1/08 at 09:30 AM |
|
|
I think the potential savings are far more than a few grams, I would guess a brake disc weighs something around the 3-4kg mark? A 1kilo saving is
probably possible
Anyone have any good contacts for brake disc thinning? I understand it's probably unwise to do so on a 'normal' lathe...
James
|
|
|
tegwin
|
| posted on 25/1/08 at 09:59 AM |
|
|
I would imagine you would want to grind the disk rather than put it in a lathe...
If you know what you want doing, any engineering company should be able to help you out!
|
|
|
RazMan
|
| posted on 25/1/08 at 10:04 AM |
|
|
A 30% weight saving??? Even with some radical thinking I doubt if you will achieve even 10% - and then have a think about the safety issues of
thinning a disc a little TOO much and having it disintegrate when you need it most.
Two words - alloy bell 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
|
|
|
v8kid
|
| posted on 25/1/08 at 10:05 AM |
|
|
I've never heard of brake discs being ballanced but anything is possible I suppose - bit unlikely though as hey are concentric, the mass is
relatively close to the center and the rotate relatively slowly..
Most automotive machine shops will regrind brake discs all you have to do is specify how thick the final item has to be.
Brake discs are designed for heavy production cars with high milage and litigation in mind so they are massivly over engineered.
With less inertia to dissipate and a shorter lifetime radical alterations should be possible.
I had not considered the idea of drilling the non swept area but will certainly di it now!
With regard to feeling and safety critical parts if we can't trust our common sense and what engineering knowledge we have gleaned to lighten
some rotors we should not be building our own cars. Period.
Safety critical? Yes but how safety critical? What will happen if it fails? Will it kill us?
I don't think so. In all likliehood the rotor will jam in the caliper and we will come to an embarrasing halt. As a risk it pales into
significance compared to the other "acceptable" risks we take when building our own cars.
P.S. Where the hell is the spellcheck button?
|
|
|
02GF74
|
| posted on 25/1/08 at 10:32 AM |
|
|
I am pretty sure the catalogues show callipers for thinner discs as used by Caterham and Westfield so thinning the disc is an option.
Drilled and slotted discs are common so afain an option.
Alloy hugs come slotted so again you can slot/drill out the central part, whatever that is called.
How much you will save? Dunno without doing some sums but if you are able to make the modifications safely at reasonable cost then go for it.
|
|
|
hughpinder
|
| posted on 25/1/08 at 11:07 AM |
|
|
willwoods do lightweight rotos and aly hubs - the link from rallydesign.com (iirc) gives the dimensions and weights of the items (from
'standard' discs to aly hube etc.
|
|
|
short track 123
|
| posted on 25/1/08 at 11:12 AM |
|
|
If you let me know what disc's and the sizes i can work it out the weight savings for any one that might be interested.
Jason
[Edited on 25/1/08 by short track 123]
|
NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
|
Bob C
|
| posted on 25/1/08 at 12:00 PM |
|
|
I went the ally bell route - helps to have a lathe & CAD
http://freespace.virgin.net/bob.carter/images/frbrake.jpg
all up saving c.f. mx5 original is a couple of kg/corner of UNSPRUNG weight. The discs are modified ford galaxy rear (front) and skoda estelle front
(rear).
Bob
PS the cast iron of stock brake discs is lovely stuff to machine in a lathe - but you end up covered in black kak...
|
|
|
Phil.J
|
| posted on 25/1/08 at 12:19 PM |
|
|
'PS the cast iron of stock brake discs is lovely stuff to machine in a lathe - but you end up covered in black kak...'
It helps if you have a heavy magnet adjacent to the job (old speaker bits are good) when machining cast iron to catch most of the dust/swarf.
It's not the sort of thing you want on the lathe slides as it is so abrasive.
|
|
|
.jpg)
