Dual calipers per rotor

[bettonracing17]

Not a secondary caliper for handbrakes/ parking brakes.

This is an idea more for discussion than for implementation.

Car: Circuit racer. 4lb+/hp. Wide slicks all round. Medium downforce. Short wheelbase.

Avg. Track: Low/ medium speed corners after long straights. Occassional stoplight after hwy offramp... jk.

Proposed brake setup: Front wheels only. Custom knuckle. Twin calipers mounted 180deg apart. Single master cylinder for all 4 front calipers (appropriately sized). Adjustable f/r wheel bias bar. Adjustable pedal ratio.

Intended advantages: A wider range of useful calipers and all the resulting advantages (read: cost).

Observed disadvantages: Complexity. More time consuming brake jobs. More parts to fail. Increased unsprung weight. I suspect a reduction in clamping effectiveness of each caliper (compared to a single caliper setup) but overall more brake friction overall and thus
calculations would be slightly more complex.

Assumptions: The designer has required resources to properly size all (6) calipers. The knuckles would be optimized for the proposed setup. The tuner & driver have good enough communication and knowledge to find the [presumably narrowed] f/r bias sweetspot. Adequate brake cooling.

I'm sure if this setup worked favorably, I'd be able to find something on the net or at the tracks. Searches proved fruitless.

If anybody's experimented with similar setups, as well as those of You more educated ones, please educate me.

Note: I may add additional points as I remember them.

Regards,

H. Kurt Betton

 

[GregLocock]

I suspect you'll run into a packaging problem - the outer tie rod balljoint and the calliper live in the same space.

Also activation might be interesting - would you run a separate circuit for each calliper?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[GregLocock]

Hit submit too quickly ! - it sounds like a reasonable idea, but you'll also lose some cooling area for the rotor as well.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Peter7307]

Kurt,

Rolls - Royce used a twin caliper brake system on the Silver Shadow cars built from 1966 onwards.

In their application one caliper set was fed from a high pressure hydraulic circuit. The pressure being supplied via an engie driven pump. The second caliper was fed via a non pressurised circuit.
The calipers were 180 degrees apart and as far as I know idential in design.
The disc itself was a conventional arrangement.

The intention was to provide the best possible level of "feeL and feedback" for the driver with the minimal level of effort required.

Cheers , Pete.

 

[bettonracing17]

Thanks for the replies.

Greg:
Packaging would be an issue but given the wide variety of mounting locations currently in existence, I feel it could be incorporated as one of the "concurrent factors" in suspension design.

My current thinking was to run the same circuit to all 4 front calipers (i.e. the front master cylinder feeds all 4) - for simplicity. Especially for a prototype. I'd hate to be troubleshooting any problems with any more circuits involved... Plus the prototype would have to have the option of easily going back to single caliper if a completely unexpected (and dangerous) problem were to arise. Cost advantages would also have to be reassessed (although I'm sure it would still be an advantage).

In regards to the cooling area, I feel this is where the price tag shows up for the free lunch... I debated to myself that having twice the heat in each rotor revolution would not allow enough cooling but one could argue that traveling at twice the speed has the same effect - except that twice the speed = [almost] twice the airflow (in a perfect world). So at 40mph, this setup would apply the effective heat of 80mph (actually considerably less), but with 40mph of airflow. (Consider the mph numbers for the effect being described, not for accuracy, as they neglect the squared effects of doubling the speed)

For both cooling issues (cooling area & cooling time), metallic pad compounds, variable inlet ducts (possibly thermostatic brake cooling fans) and other cooling strategies would have to come into play.

Pete
Thanks for the Rolls- Royce example. I'll look into it. Using their setup it seems like the non-assisted caliper would become somewhat of a 'trailing caliper' which I was trying to avoid (hence the 180deg) as I suspect the wear and heat issues introduced would create complexities in design (and testing). I suspect that even in 180deg config, there'd be trailing caliper effects but I feel that only testing would reveal those effects. Of course Rolls' design intent and application explains why the 'trailing caliper' would work better for them...

Any thoughts on trailing caliper (even in 180deg)?
>>>>>

You guys are making me consider a test bench setup using junkyard parts... I'll wait tho...

Keep 'em coming!

Regards,

H. Kurt Betton

 

[thundair]

I have considered doing that to a 65 Mustang that had the little one piston calipers. I was going to cut of two of the flange mount bolts on each caliper mount,, then siamese them at 180* apart...
That being said the extra mount is adding to the unsprung weight. So it seems you would be better of with a 6 piston (progressive) caliper,,, then mounting two of the 3 piston calipers..

Cheers

I don't know anything but the people that do.

 

[bettonracing17]

Thanks for the reply.

I have unsprung weight listed as one of the disadvantages. Considering a custom suspension with a custom knuckle and lightweight wheels, the weight gain would not be enough to make the car handle poorly on bumpy roads. Less poorly than if it had less weight, but not poorly enough to kill any hopes of winning the race. But to avoid that conversation of "how much does unsprung weight really affect a car's performance" let's assume that the car would race on smooth surfaces.

(I also suspect that the effects of the weight gain could be mostly tuned out with current damping technology).

Regards,

H. Kurt Betton

 

[thundair]

Unsprung weight causes weight...I drive a Z06 and at 145 the car feels like it weighs a couple of ton. My point is you will feel the weight.
You will need stiffer springs, bigger shocks, larger pivot joints, more bracing and the list goes on..That is why for some the inboard brake was the answer,, but you hardly see them now.

What you do see is aluminum calipers with light weight rotors even as they grow in diameter and some have made the hat section out of aluminum with the cast rotor bolted to it..

When you layout your design do it in 3D as you will see the shrouding of the rotor as this will add to one of the latest problems in disk brakes. Which is transferring heat into the rim and destroying the tire.

But don't give up on trying another solution there are plenty of people here that will keep you honest. Thats why I post, isolated thought is ignorance..

Cheers

I don't know anything but the people that do.

 

[revoltrise]

I've pondered this before myself, and I know it has been used in racing applications...Nissan Primera?...I think that in an ideal setup one perfectly sized caliper per corner has advantages, however, the perfect single caliper can will cost considerably more than say 2 Wilwood Dynalites for each front wheel. Plus the smaller calipers will probably resist heat-soak for a longer period of time, make this work and take some pictures!!

 

[revoltrise]

I've pondered this before myself, and I know it has been used in racing applications...Nissan Primera?...I think that in an ideal setup one perfectly sized caliper per corner has advantages, however, the perfect single caliper can (will) cost considerably more than say 2 Wilwood Dynalites for each front wheel. Plus the smaller calipers will probably resist heat-soak for a longer period of time, make this work and take some pictures!!

 

[patprimmer]

Brake performance depends mostly on heat rejection capacity.

Brake pad life depends mostly on pad area and compound and manner of operation.

Increasing pad area decreases the heat rejection capacity of the rotor.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bettonracing17]

Thanks for all the responses.

Thundair
For a custom application where weight reduction is already in mind,(read: custom knuckle, lightweight rims, etc), the quest of absolute minimum unsprung weight is approaching the point of diminishing returns. Data from FSAE and objective (lap timer) results from a tarmac rally car to support these statements. On bumpy tracks - especially in braking zones- or if the driver likes to ride brake strips, then it does have a significant effect on lap times, but I've found these not to be the case for majority of the tracks I've been to. We could discuss this in more detail another thread if You'd like.

The example of decreasing amount of observed inboard brakes also support the diminishing returns argument.

Revoltrise
If it continues to look somewhat promising, I might setup a bench rig to conduct some tests and see where it goes from there. I'm waiting to hear the compelling argument that makes it clear why nobody else is doing it currently (that I know of).

Pat
I think You've pinpointed a major flaw in the setup. However, heat rejection capacity of the rotor in a moving medium (air) is also related to the medium, it's thermal characteristics and blah, blah, blah (I'm sure You already know all that). Basically, with better cooling one should be able to remedy the 'heat soak' problem. Also, with relatively open design, one could aim to match the [pad area]: [rotor area] of the more conventional racing pad/ rotor combination, all be it at a significantly reduced cost (as opposed to just slapping two huge calipers and the biggest pads that will fit on there).

Anyone have any papers to recommend regarding pad area and heat rejection? (About to go search)

(And here I was thinking I wouldn't be using matlab for a while again...)

>>>>>

I'm starting to daydream about the Tyrrell P34 again... Keep me in check please.

Regards,

H. Kurt Betton

 

[MikeHalloran]

The simplest way to get more braking is with a bigger rotor, but as you increase rotor diameter, the wheel shrouds the airflow, and proximity heats the tire.

Two rotors interferes with both radiation and convection cooling of the rotor. Still it might be effective if you use a smaller rotor, so the wheel doesn't interfere with the air flow as much.

You can't afford big calipers, but you can afford special knuckles? That doesn't compute.

Can you get _enough_ braking with a more conventional setup?



Mike Halloran
Pembroke Pines, FL, USA

 

[bettonracing17]

Thanks for the reply.

To ensure we're on the same page, I'm talking about using dual caliper per rotor per (front) wheel, not dual rotors per front wheel. Off the top of my head, can think of 3 reservations against using dual rotors...

You can't afford big calipers, but you can afford special knuckles? That doesn't compute.

That's not the case but here're two legitimate examples that could justify it if that were the case:

1) Access to a fabrication & machine shop with relevant computer software and experience for knuckle manufacturing. No experience with caliper manufacturing.

2) Within a specific finite budget, gains in the suspension department may be more effective than in the braking department. Budget allocated accordingly.

I'm sure I could acheive the same (probably better due to available data) braking ability with a conventional setup. I'm also never content with conventional

The purpose of my question is more for exploration than for a particular application.

Please feel free to critique the details proposed.

Regards,

H. Kurt Betton

 

[MikeHalloran]

I meant to write "two calipers" of course.

But I had been thinking about two rotors, also. I.e. with 4WD type spindles, you could put another rotor on the inboard side of the knuckle, where it could have better cooling than the one on the outboard side. Sort of like inboard brakes without the u-joints and halfshafts.

I'd rather trust my bones to homemade calipers than homemade knuckles. YMMV.



Mike Halloran
Pembroke Pines, FL, USA

 

[bettonracing17]

I'd rather trust my bones to homemade calipers than homemade knuckles. YMMV.

Lol! I wouldn't trust my bones with niether! (given the implication of 'homemade'). Of course if the design includes sound engineering logic and is being designed on a computer in a home office, I'd be willing to reconsider...

Interesting idea of the 'inboard side' mounted rotors. Sounds potentially obtrusive to the suspension members for most performance oriented double wishbones. Of course my thoughts are undeveloped regarding that setup.

Regards,

H. Kurt Betton

 

[patprimmer]

Several Japanese and I am sure some European high performance mass production road cars have 4 spot callipers standard.

Why not just buy a set from a junk yard.

Things that spring to mind are Mitsubishi Lance EVO, Nissan Skyline GTR, Subaru WRX, Nissan Pulsar GTI-R etc etc

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IceStationZebra]

Bettonracing17 ".. I debated to myself that having twice the heat in each rotor revolution would not allow enough cooling but one could argue that traveling at twice the speed has the same effect - except that twice the speed = [almost] twice the airflow (in a perfect world). So at 40mph, this setup would apply the effective heat of 80mph (actually considerably less), but with 40mph of airflow. (Consider the mph numbers for the effect being described, not for accuracy, as they neglect the squared effects of doubling the speed)"

Doubling the number of pads does not create more heat. You are changing the kinetic energy (motion) into heat. So at the same speed and nearly the same mass (probably a slight increase with the 4 caliper set-up) you would generate almost the identical amount of heat. And I will assume that the current calipers generate the forces you require - so in reality each of the four calipers will only be doing half of the work your current ones are.

So from a performance stance you are decreasing your rotor cooling and increasing your sprung mass to run a more complicated braking system that may be cheaper. Doesn't sound like a road I would take.

I agree with Pat - look for production 4 pot calipers instead.

ISZ

 

[bettonracing17]

I interpret Your reply as recommending calipers from performance vehicles to be used in single caliper per rotor configuration.

If this is the case, I think I may have incorrectly created the impression that I'm asking about this setup due to lack of funding and looking for a cheap setup.

Please discard this interpretation and look beyond the cost advantage.
>>>>>

It seems the primary disadvantage is the decrease of rotor heat rejection (increase in pad area) with unsprung weight coming in a close second.

I'm now considering a test rig...

Regards,

H. Kurt Betton

 

[bettonracing17]

Apparently You posted while I was typing last night. The previous reply was directed to Pat.

Pretty compelling argument regarding not doubling the heat. The excerpt You quoted was more in regards to the amount of time (or degrees of revolution) the rotor has to cool before being reheated by the next set of pads but I guess Your argument explains that only half the energy is being converted per set of pads (as opposed to doubling it).

I'm also concluding that even in an application designed to create more braking force, the heat rejection issue multiplies and the [theoretical] braking force advantage of the proposed setup starts rapidly approaching zero...

I'm starting to understand why nobody's doing it (publicly)...

Thanks for Your time and inputs.

Regards,

H. Kurt Betton