Braake Caliper Placement

[Ian Anderson]

I have a question for those engineering guru types found in abundance on this forum.

What is the best? place for placement on the calipers on the front hub?

Reason I ask is that I was stuck in a jam a couple of days back and was looking at the placement on the higher range cars

BMW and AUDI have them at opposite sides - one at the front and one at the back, Peugeot had one mounted on the top and others at 45 degrees to front and rear

I did not see any on the lower side of the hub

Now the lower I can understand to avoid water in deep puddles etc

BUT is there a better engineering reason for the placement regarding moments etc? If so what is best? And why is this "best" not used across all marques?

Last thing can the explanation be made simple so an accountant can understand it?

Thanks and Marry Christmas

Ian

 

[Bob Putnam]

Caliper position has no effect on the net moment. Rotor-rotation resistance must ultimately be taken up through the upper and lower ball joints.

Calipers are located mostly by virtue of the space available: Usually opposite the steering arm, with a direct path for the air when bleeding. On race cars, there may be some thought to cooling.

 

[Phil]

Ian
I would echo what Bob said and add that bleeder location might be an issue, although most performance calipers have more than one bleeder. They seem to be easiest when the caliper is vertical with the bleeder on top.
I once worked on a GTD where the calipers were on the bottom, and we had to dismount the caliper, slide it around to the top, bleed it, and re-install, all the while fighting with limited flex line length. This was on the rear upright.
Cheers
Phil

 

[John P]

I read on another board where the builder mounted the caliper at the 5 o'clock position, said it would lower the CG. I personally don't think the caliper has enough mass to effect the CG by any measurable amount.

 

[speed220mph]

Re: Brake Caliper Placement

Although it doesn't seem to be a factor unless the wheel bearings are marginal, calipers mounted to the rear of the spindle centerline unload the bearings under braking and vice versa with front-mounted brakes. But as Bob says, it's more of a packaging consideration. Rear-steer setups have front-mounted calipers and the opposite for front steer. We did have a short-track stock car with rear steer that experienced right-front wheel-bearing failure when we ran it at a particular high-bank track that required hard braking for turns one and three. The cure was to install bigger wheel bearings. We never had a problem on that track with front-steer cars.

 

[Gary Kadrmas]

Very interesting topic and the replies so far are interesting reading.

For those that have yet to respond, please do. This is interesting information!

Thanks.............

 

[Jac Mac]

Bob has it right in my mind- in the instance Speed 220 mph has quoted the bearing failure could be as a result of extra heat soak in the wheel bearings from the sheilding effect of the caliper being in front or a deflection issue in the caliper mount, or a combo of several small differences. At the end of the day you have to have top/bottom ball joints or struts along with the steering arm and what space is left can be devoted to the caliper & mounting bracket. The thing must be rigid & many passenger car setups come up woefully short in this dept especially when fitted with large rotors wheels calipers etc, so choose carefully in your donor parts.

Jac Mac

 

[Iain]

Ian,

As per Jac Mac's reply we have put a lot of work into creating a stable platform for the whole front assenmbly, we are using quite large front rotors so the calipers are hanging a long way out in the breeze so to speak ! We have swung the mount down as low as possible, probably no significant advantage but it may as well be low as high ! What I find more interesting, and this may be a little off topic, is the relation ship between wheel weight and rotor weight. I am spending a kings ransom on superlight wheels yet the rotors will become really effective boat anchors when they have done their tour of duty ! even if I could afford the carbon alternative I just cant beleive that there isnt something between cast iron and carbon....

Iain

 

[Jac Mac]

Iain, while its a bit late in the process, the adaptor you have sandwiched between caliper and upright is a possible source of caliper deflection. As the two bolts that attach the adaptor to the upright are on closer centers and offset inboard from the rotor centerline the caliper will tend to deflect inboard @ the top & outboard at the bottom when the brakes are applied resulting in tapered pad wear & a long pedal . A better solution would be to redesign the upright using only the two original caliper bolts to mount directly to the upright, delection would then be minimal due to the larger center distance and elimination of the other two bolts.

The other thing I notice is the large amount of rotor surface @ the ID that may not be in contact with the pad surface & could be removed for weight reduction.

Jac Mac

 

[speed220mph]

Bob has it right in my mind- in the instance Speed 220 mph has quoted the bearing failure could be as a result of extra heat soak in the wheel bearings from the sheilding effect of the caliper being in front or a deflection issue in the caliper mount, or a combo of several small differences. At the end of the day you have to have top/bottom ball joints or struts along with the steering arm and what space is left can be devoted to the caliper & mounting bracket. The thing must be rigid & many passenger car setups come up woefully short in this dept especially when fitted with large rotors wheels calipers etc, so choose carefully in your donor parts.

Jac Mac

Jac: Brake heat soak into the wheel bearings is always a problem, unless of course the brakes are mounted inboard, i.e., Jag setup. We did a lot of playing with reducing heat transfer to the caliper on TransAm, Indy, CanAm and endurance cars such as those run at Daytona and Indy. Boiling fluid is one problem, but the one that really causes problems is the plasma condition being created by excessive heat at the pad/rotor interface.

Drilling and rotor venting helps reduce these problems as does certain materials. Further, rotor-to-hub mounting is a big factor as is ducting and routing cooling air over and through the caliper. We even tried water spray, which really worked well, but tech and rules put a stop to that practice.

Check out those weird hubcaps on the Ferrari F1 cars. We also used this with John Greenwood's Vette. Same goes for Porsches of that era. BBS supplied those pieces. Airflow down the side of the car and behind the wheel to create a depression--low pressure--is critical. Pumping air in doesn't work well unless a way out is provided, preferably into a depression.

Ah, then there are carbon/carbon brakes. Problem "solved." LOL

 

[Fran Hall RCR]

The Turbine wheels on the Mk4 were supposed to help brake cooling but were proven to be totally ineffective ....especially when a certain race team installed the wheels on the wrong side and noticed no difference in performance,..... whoops.

 

[Jac Mac]

Im fortunate (or unfortunate) depending on what the problem or question is at the time to have some close contacts with a varied group of motorsport competitors. One such incident was with a well known truck racer ( large like Kenworth-DAF-Volvo etc ) with water spray to the front rotors, the spray nozzles had residual check valves in the lines to prevent water loss when not in operation- unfortunately on this occasion the valve must have had a small piece of debris in it and the nozzle had slow dribble when not in use. at the completion of the meeting after the final race the truck was left standing in the pits, a few minutes later there was a huge 'bang' like a shotgun being fired & everyone ducked for cover thinking a tyre had exploded. No one had a clue what had 'exploded' & it was not until they tried to move the truck that the reason was discovered, the culprit being the leaking nozzle on only one portion of the red hot brake rotor which had split in a radial direction.

The centrifugal fans on each wheel arrived down under on the Aussie Touring cars fairly quickly- I remember reading an article on Greenwoods Vette and noting the same setup on cars at Bathurst that season. I also note that many Auto Manufacturers incorporate a fan design into the alloy wheel centers and blurb on about brake cooling, then fit the same wheel to both sides so that air is being moved into the wheel arch on one side & extracted out on the other

Sorry Fran , slow typist- When you consider that the wheels are only ever going to turn at around 2000 rpm max it takes a fairly efficient centrifugal fan design with a large exit OD to be of any use.
Jac Mac

 

[Iain]

Jac,
Thanks for your ideas on the caliper mounts, we have tried to make the base of the mount as wide as possible and the upright has a shoulder milled into it to accept the adaptor, both done on a CNC machine so they should be a tight fit, I think the fact that the upright has been designed to be ambidexterous may have driven some of the design compromises, only time will tell. One of the iterations of brake set ups we had on my Cobra generated excessive pad tapering with the resulting "long" pedal. If this occurs again then we may have to go back and remachine as per your recommendations.

Iain

 

[speed220mph]

The Turbine wheels on the Mk4 were supposed to help brake cooling but were proven to be totally ineffective ....especially when a certain race team installed the wheels on the wrong side and noticed no difference in performance,..... whoops.

Fran: I was at KarKraft "in the day". The vanes looked good, but came at a huge cost to us, requiring two more sets of tooling, or two sets for the front and two for the rear. The red and blue knock-offs was a more practical idea--red for left and blue for right. How is that for a political statement way before its time?

 

[Jac Mac]

Jac,
Thanks for your ideas on the caliper mounts, we have tried to make the base of the mount as wide as possible and the upright has a shoulder milled into it to accept the adaptor, both done on a CNC machine so they should be a tight fit, I think the fact that the upright has been designed to be ambidexterous may have driven some of the design compromises, only time will tell. One of the iterations of brake set ups we had on my Cobra generated excessive pad tapering with the resulting "long" pedal. If this occurs again then we may have to go back and remachine as per your recommendations.

Iain

That puts a different perspective on it Iain , with 5 bolts & that large 'footprint' of the adaptor I dont think it will deflect any direction in a hurry, I'm always telling people not to jump to conclusions, might have to start listening to myself!

Jac Mac

 

[Russ Noble]

Fran: I was at KarKraft "in the day". The red and blue knock-offs was a more practical idea--red for left and blue for right. How is that for a political statement way before its time?

Speed,

Sorry about the thread drift here but WRT the knockoffs. Did you see the discussion here?

http://www.gt40s.com/forum/gt40-tec...eding-knock-off-wheels.html?highlight=feeding

Do you know or remember which side the spinners were fitted "back in the day"? Did the red spinners indicate LH thread or LH side or both?

Might be more appropriate to reply on the spinner thread.

Cheers

 

[speed220mph]

Knock-offs tighten in reverse direction of normal wheel motion, right, or clockwise, on the left (red) and left on the right (blue). Brain teaser, right?

 

[Chuck]

Just remember the phrase "ass backwards". Works every time.

 

[Rob]

Eh.... Ian.... finally a topic I know something about...... but unfortunately have nothing to offer because Bob already hit it with all the explanation it truly needs.

Beyond that....there is really only aesthetics and any contribution there could possibly be to CG (very nominal).

 

[Chris Duncan]

As regards to caliper position. Always thought that centralizing weight is better for inertia concerning direction changes. So front calipers in back of front axle and rear calipers in front of rear axle.

Is the battery better at the back bumper or behind the driver seat?

It might not make much diff but that's what race cars are all about, every little bit counts.