Roman

Tech Spam thread - because 1/4" BSP gets 5 hand spans to the jiggawatt

Recommended Posts

Also more mass to absorb heat more surface area to shed heat 

as well as the leverage it's also more actual rotor surface contacting pad for every rotation under braking 

  • Thanks 1

Share this post


Link to post
Share on other sites

So would that mean that for a car to come to a stop, it requires X force, acting on Y distance of rotor? So the larger the rotor, the less rotations required to stop the vehicle, thus shorter stopping distance. All other factors remaining constant. That does make sense, but I hadn't thought about it in that way.

Share this post


Link to post
Share on other sites

Braking distance is relative to vehicle weight and/or speed as you probably guess, upgrading discs etc will give you better performance overall but to decrease distance you'd have to go abs or better grip through tyre selection etc.. 

  • Thanks 1

Share this post


Link to post
Share on other sites

Will be a combination of bigger brakes and decent tyres in this case. No ABS to be seen. The rotor sizing just had me a intrigued, due to conflicting info on the web. A bit of money to invest, so I just wanted to see what sort of improvements I might see if I went that direction. 

  • Like 1

Share this post


Link to post
Share on other sites

f1 car only uses 278mm rotors, just get your drill out for more cooling holes (1400 holes now)

Brembo_F1%202014_Special_1202-08.jpg

  • Like 1

Share this post


Link to post
Share on other sites

I think if you think of it in a dumbed down way it becomes clearer

Like if you try to undo a tight wheel nut with a short ratchet vs a powerbar. Same theory, you have more leverage the further away your hand gets the less pressure you have apply with your hand.

 

 

In my experience a car will always stop better and resist fade better with a larger disc.  

Have had examples where people have upgraded calipers,  ie one customer had a commodore with a v8 swap, it failed the brake test because it still had 6cyl brakes which are basically the same as v8 ones apart from the disc diameter. He put wilwood calipers on the 6 cyl disc and it still failed. Went to v8 size disc and it passed

  • Like 5
  • Thanks 2

Share this post


Link to post
Share on other sites

When I upgraded the brakes on my old mk2 golf gti I went from 239mm rotor to a 300mm rotor with Porsche 4 piston calipers. Obviously had a lot more stopping power but it also gave me far better feel and control of brakes, could easily tell when they were about to lock up

  • Thanks 1

Share this post


Link to post
Share on other sites

Theyll work better because a greater surface area of rotor passes across the pad per revolution.  

Using my old datsun clutch as an example. Stock disc was 180mm. I had the flywheel modified to take a 200mm clutch disc/cover etc.

that 20mm difference in O.D. increased the total friction area by 36%. (I don't remember what the minor diameter of the two discs was)  obviously because you're going to keep your stock pads, you'll know the height of the pad.

So Pi×R^2 subtract Pi×R^2 (where R is rotor OD less pad height) 

Then do it again with the larger rotor. Express the difference as a percentage and you'll see how much more friction is happening. Plus  more rotor mass to dissipate heat.  

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

That's some complicated formula!

Will be different pads / calipers, so thankfully I don't need to work that out. 

The heat side of things will be massive, 200mm solid disc vs 276mm vented disc, no more fade.

Share this post


Link to post
Share on other sites

On my 121 everything is the same as 929/rx4 except I have vented discs, caliper is the same albeit slightly wider to accommodate the wider disc.. I retro fitted 121 struts to my 929 coupe and by god it made a big difference to braking performance.. Not forgetting the 929 is 130kg lighter.. 

Share this post


Link to post
Share on other sites
On 13/03/2019 at 12:10, Bling said:

Brake theory query.

One of those "pop into head" ideas. Current discs are ~200mm diameter (hilarious). Looking at potential ~270mm rotors for an upgrade (ignoring caliper upgrade for this theory). Will the braking performance be improved purely by way of the brakes now clamping the rotor further from the center of the hub? The upgraded calipers are sized to match factory booster and that sort of thing. Lots of articles basically say that bigger brakes don't necessarily offer better braking performance. Except for the reduced fade with constant braking down a hill etc. I'm just thinking that if you're clamping the disc further out, it will brake easier, as in will be able to slow it quicker as it's applying more force by way of clamping location. But I have literally no idea beyond that theory. So engineers / mechanics, school me up on the forces involved, and whether or not i'm barking up the wrong tree with this idea.

Not sure what I can add to what has been posted so far but with brakes the rule of thumb is invariably ‘bigger is better’. 

As previously stated increasing the rotor diameter while retaining the original calipers (and  pad area) will in most cases improve  braking  simply through the point of friction being further away from the center of the hub (i.e. more leverage).  You will also increase the speed differential between the rotor surface and the pads which in turn will generate more heat (i.e. increased stopping power).

To break (excuse the pun!) it down to its simplest form, any friction braking system is a two stage process; 1: the conversion of kinetic energy into heat and 2: the dissipation of the heat.

For the 2nd part of the process using a larger rotor gives a significant gain by increasing the surface area where heat transfer (metal to air) takes place. Be aware that you will be increasing un-sprung weight, there could be a shift in brake bias and a change in pad material, and fluid type may need to be considered.

My own personal opinion is that for street driving there is possibly another gain from the larger mass of the rotor increasing the ‘heat soak’ capacity of a braking system in an emergency, single application scenario, (i.e. an emergency stop). I don’t have any hard data to back this up but would love to look at it further in a controlled environment.

Hope this helps.

  • Like 1
  • Thanks 3

Share this post


Link to post
Share on other sites

Thanks.

Lots of good information in this here thread that's for sure. All seems to lead towards it being a worthwhile upgrade in my case. 

Share this post


Link to post
Share on other sites

Well if you take it to the extreme (huge rotor), you will get less control with a big rotor compared to a small rotor. Just like if you put a huge vacuum booster on.

 

/Just remove mass from the car and eat less pies and you'll be fine with 200 mm brakes

Share this post


Link to post
Share on other sites

What would be the best plan of attack to repair this?

IMG_20190316_175843.thumb.jpg.f9cdb6e6edb018dfab4b022a35f20689.jpg

Three piece wheels have had the steel inserts removed and the stud holes slotted. I want to repair to original so thinking of a couple of options.

1- Weld up the slots, machine the holes and fit new inserts (if I can get new inserts).

2- Use the shank style wheel nuts and machine up a washer/spacer that locates on the countersunk and flat area around the stud holes but leave the slotted part as is.

Thoughts?

PS, I can weld ali and machine parts at little or no cost.

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now