Brake Calipers for use with 10" wheels?

[IanFlaherty]

Hi all,

I'm new to this forum, so I'm really sorry if this is a repost. I've searched and searched, but couldn't find an answer to what I assumed would be a common question!

I'm a 3rd year student at LJMU in Liverpool, UK, and this is our second year at Formula Student. Last year we entered class 3, but I was not a part of this. This year we will be entering class 2. I am responsible for the brake setup of the car.

Basically I could do with some advice as to what brake caliper/pad setup can fit inside a 10" wheel? All the calipers that I have looked at on Wilwood.com and APRacing have a minimum disc size of around 10", which is obviously too big to fit inside a 10" wheel.

Also, I have specified the use of two APRacing CP2623 Master cylinders (one for front brakes and one for the rear, central brake) and the APRacing CP4226-2S0 caliper for the rear, please could you comment on their suitability for use with whatever calipers you mention.

I really am cursing last years team for specifying 10" wheels. I realise they have there benefits, but for a first year team, it really doesn't seem sensible.

If this has been posted before I would appreciate it if you could provide me with a link to it.

Thanks,
Ian

[IanFlaherty]

Hi all,

I'm new to this forum, so I'm really sorry if this is a repost. I've searched and searched, but couldn't find an answer to what I assumed would be a common question!

I'm a 3rd year student at LJMU in Liverpool, UK, and this is our second year at Formula Student. Last year we entered class 3, but I was not a part of this. This year we will be entering class 2. I am responsible for the brake setup of the car.

Basically I could do with some advice as to what brake caliper/pad setup can fit inside a 10" wheel? All the calipers that I have looked at on Wilwood.com and APRacing have a minimum disc size of around 10", which is obviously too big to fit inside a 10" wheel.

Also, I have specified the use of two APRacing CP2623 Master cylinders (one for front brakes and one for the rear, central brake) and the APRacing CP4226-2S0 caliper for the rear, please could you comment on their suitability for use with whatever calipers you mention.

I really am cursing last years team for specifying 10" wheels. I realise they have there benefits, but for a first year team, it really doesn't seem sensible.

If this has been posted before I would appreciate it if you could provide me with a link to it.

Thanks,
Ian

[Alastair Clarke]

Hi Ian,

We (Cardiff) moved to 10" wheels last year, and found a few calipers that fit easily inside this size of wheel. At the front, we used some Brembo calipers (P34) which have 34mm diameter pistons. They were used with no issues on 170mm diameter disks at the front. At the rear we used a single disk mounted on a spool (I wouldn't do this if we were running a diff) - the caliper was the AP CP4226 with a 200mm rotor so I'd guess you could make this caliper fit inside wheels as well. The Brembo calipers were a bit big and heavy, but Brembo do a really sweet fully CNC'd version of the same caliper which is about half the weight (and more than twice the price!). The AP calipers are really nice though.

We used AP CP-2623 master cylinders, they're available in a wide range of bore sizes, so simple hydraulic calcs with an assumed tyre coefficient of friction should help you select suitable bores and caliper piston diameters. It's worth doing a bit of sensitivity analysis on anything where you've assumed values like tyre and pad friction coefficients, unless you've got measured data to back these assumptions up.

Hope this helps

Alastair

[IanFlaherty]

Thanks for the quick response Alastair, it's much appreciated!

So, looking around for the P34 Brembo calipers, I've come across them for in the region of £1500. I take it that is for the fully CNC'd version? Otherwise it seems a lot of money to pay in comparison to the AP products.

Would you recommend using the AP CP4226 for all three calipers then? Is there anywhere that states the minimum disc size for this caliper, i.e. any smaller than 200mm? I will get in touch with AP again if not, but it sounds promising. Oh and we will be using a LSD at the rear.

I have all the calculations set up, but it's just a case of finding the right components. I seem to be going round in circles replacing one component and then having to replace another because of it. Hopefully I may finally be sorted if the CP4226's work though.

Lastly, did you machine your own discs, or purchase them?

Thanks again,
Ian

[J.R.]

Try the Wilwood PS1 or GP320. I believe we had the GP320 last year (I'm sure someone from my team will correct me if I'm wrong), and will be using the PS1 this year.

[Drew Price]

J.R.,

Make sure you can get the pad compound you want for the PS-1's, at least last year when we were doing things there was only one or two compounds available from Wilwood, with very little data about them.

We ended up cutting down a set of Ferodo DS3000 pads, which worked great.

Several teams have custom linings bonded to new or custom backing plates.

As of last year, there were no aftermarket companies making pads for the PS-1's, but don't take my word for it.

We will probably use the Wilwood compounds this year with little bitty masters, since we have a set already, and machining down the Feroros ate 3 or 4 end mills. http://fsae.com/groupee_common/emoticons/icon_eek.gif

Best,
Drew

[Asymmetric]

I don't see how you went through so many end mills. I have pads machined almost on a daily basis at work and they cut like butter.

[fixitmattman]

http://www.hayesbrake.com/stan..._products_4ldhc.html (http://www.hayesbrake.com/standard_products_4ldhc.html)

Great calipers, fairly inexpensive. Back in Baja we used these with 10" rims and had room to spare. They were bullet proof in BAJA even despite our uber heavy cars and passed brake first time every time. May need custom linings for FSAE duty though, we were lucky to get top speeds 1/3-1/2 of FSAE.

[Alastair Clarke]

Hi Ian,

Try these guys for Brembo calipers

http://www.iane.co.uk/brembo_R...E%20CALIPERS%20.html (http://www.iane.co.uk/brembo_ROAD%20FRONT%20BRAKE%20CALIPERS%20.html)

You've been looking at the billet calipers (i.e. the expensive ones) which are a lot lighter, but try the road versions (P34C) which have cast bodies and are a fraction of the price.

As to the suitability of the AP CP4226 for all 3 calipers I can't say without looking at the calcs. They're quite small pistons so you may end up with high line pressures (try to keep them under 1000 psi to avoid squishy brake lines etc). They're very light and small though, and I remember seeing one team a few years back running twin calipers on each front wheel which may be a solution. However, you really need to do the calcs and see what you can come up with - I found a spreadsheet with the calcs useful so you can quickly change parameters etc and see the effect. If you're using a LSD at the rear I'd be very tempted to look at having a brake on each wheel - there's lots of discussion in the archives here as to the pro's and con's of a single rear brake with a diff.

Our disks were machined in house - we got some cast iron blanks from a sponsor (Alcon) and took it from there. If you machine them in house, rough them out then normalise (stress relieve) the material before finish machining and grinding. That said, I know of many teams running laser cut disks of mild steel (would give high attrition rates of pads I'd expect) or stainless. I think it's one of those cases where you pays your money and takes your choice!!!

With ref to the Wilwood calipers, we used the PS1's a while back and found them to be good and widely available, so that's another avenue to explore.

Can you tell brake design was one of my pet projects whilst I was in FS??

Alastair

[HenningO]

These two calipers are very well-suited for 10"

http://www.isr-brakes.se/produ...alipers/22-048.shtml (http://www.isr-brakes.se/products/calipers/22-048.shtml)

http://www.isr-brakes.se/produ...alipers/22-036.shtml (http://www.isr-brakes.se/products/calipers/22-036.shtml)

Good selection of brake pads as well!

[Tim.Wright]

Just in case you think machining brake pads is craziness, we have been doing it with the Wilwood PS1 for a few years now as well. As has been said before the standard compounds were limited.

+1 vote for Wilwood PS1
+1 vote for machining pads

If your man hours are limited though, it may not be the best way to go.

Tim Wright
Curtin Uni FSAE
Compulsory Life Member

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Asymmetric:
I don't see how you went through so many end mills. I have pads machined almost on a daily basis at work and they cut like butter. </div></BLOCKQUOTE>

Asymmetric,

Let me clarify. We cut the pads to the profile we needed to fit in the calipers with a bandsaw, and it did go very smoothly.

Where we had problems is the PS1's require very very thin discs, and the street pads we purchased had ~0.1875 thick backing plates, and easily 0.5" of friction material, so we had to cut down the thickness of the friction material by about half.

Machining the abrasive linings was what chewed the cutters up, but we also did not want to risk using any of our carbides in case it messed up one of those. We have a large (very large, hundreds of cutters) drawer of dulled or chipped cheap Chinese HSS endmills, and just destroyed some of those. We had to go at a pretty slow spindle speed too to avoid putting too much of the dust coming off into the air, so we didn't use a carbide in a flycutter.

Best,
Drew

[IanFlaherty]

Thanks for all the replies, it really is a great help.

However! As I half expected, today it was proposed by the team leader and lecturers that we change to 13" wheels. I'm slightly frustrated that it has happened so late in the year, but fortunately it's not too much of a problem for me, or as it turns out, anyone else on the team. I would have been much further ahead by now if the decision had been made before Christmas though.

Anyway, it is what it is and I've already changed most of the components over to those suited for a 13" wheel setup (mostly those recommeded by APRacing.. I figure it's a bit late in the year to start messing again and it will leave me more time for analysis and testing). I do have a spreadsheet as you suggest Alastair, so the calculations have been adjusted. The only thing I'm now struggling with really is getting the brake bias about right, but I'm hoping that won't take much work to sort out.

Just as a side note, does anyone know if Solidworks models are available from APRacing for their components? I'm sure I read somewhere that they are. I'll get in touch with them directly if no-one knows for sure.

Thanks once again for the help, hopefully there shouldn't be as many problems now the wheel switch has been made.

Ian

[J.R.]

Why switch pads on the PS1's? (I know NOTHING about brakes)

Does anyone have recommended pads for the PS1's?

[Drew Price]

When we purchased ours there was no published data on the friction coefficient or a 'mu vs. temperature' curve, like is available from most of the other manufacturers, even if you had to ask for it. It makes optimizing the system a little more difficult, since you don't know exactly what clamping pressures you need to be generating to guarantee you will pass brake test, for instance.

Mu can vary by 30% or more depending on temp, and we wanted to use a pad that came on and had generous friction at low temps so that we could:

1) Test safely and reliably when it's cold here in IL (many early test mornings were in the low 30's F)

2) Pass brakes if it was cold and damp at comp, which it was.

Best,
Drew

[J.R.]

Those pads are ridiculously expensive! Did you really pay ~$300 for them???

[Asymmetric]

Use a carbide face mill and you wont even know your cutting the friction material. We make our own prototype pads at work and hence do a lot of custom chamfers and slotting. If we are going to take a lining down to half of its thickness or a full worn condition for certain testing we will take off the lining in about 3 passes. Make sure you have a shop vac near by to suck up the majority of the dust. I don't think we have even rotated the carbides in a few years and probably do at least 30 pads a day.

[SamB]

We're on 10" wheels and have CP4227 front and CP4226 rear. We had no problems at Silverstone last year so would reccommend these. Sticking to them again this year.

Hope this is useful

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Asymmetric:
Use a carbide face mill and you wont even know your cutting the friction material. We make our own prototype pads at work and hence do a lot of custom chamfers and slotting. If we are going to take a lining down to half of its thickness or a full worn condition for certain testing we will take off the lining in about 3 passes. Make sure you have a shop vac near by to suck up the majority of the dust. I don't think we have even rotated the carbides in a few years and probably do at least 30 pads a day. </div></BLOCKQUOTE>


Thanks Asymmetric, will do that next time around!



<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J.R.:
Those pads are ridiculously expensive! Did you really pay ~$300 for them??? </div></BLOCKQUOTE>

We got a discount on them from the supply house we purchased from, but I think it was 40%-50% off the list price, still not super cheap, but the brakes on our past car were one of it's best features. Once the bias was dialed in we had no problem passing brakes (except that the car had trouble getting up enough speed by the time it got to the test lane!), great modulation.

I think it was a 4:1 or so pedal ratio, 0.700" and 0.625" masters, and 1" calipers all around on pretty big diameter rotors with the DS3000 pads. I will be interested to see how it compares to what we're gonna do this time around, with much smaller dia rotors to get the unsprung and rotating masses down.

The DS3000's are making nearly their full mu from 200*C up, with a very flat curve.

Ferodo Race Compounds (http://www.raceshopper.com/ferodo_compounds.shtml)

They have come out with a new DS3000 version, DS3000 +03, with nearly 0.7 coefficient, pretty damn bitey.

Road pads stick around the 0.3 to 0.4 range for longevity.

Best,
Drew