Wilwood 16" kit caliper issues

[nitroman]

These are thicker: 1.25" VS the kit's .81".

I think you will find that it would be very difficult to get 1.25" thick discs to fit and to do so you would have to reduce the diameter of the disc or increase the wheel offset,
I prefer to stop, and have no inclination to fit drilled discs.

Bob

See the 10 Sept post on this page viewtopic.php?f=6&t=13356&start=80

[bobbrown]

I take it you are refering to the fact that F1 Lotus has 10.75” dia x 1.25” discs (but 10.75" is only 273mm) a fact I already knew, and he had to mod the caliper to get it in.
"Upgraded front brakes - 11.75"x1.25" rotors & Wilwood Billet Dynalite 120-5006 calipers" with standard 16" wheel will NOT fit
you run out of clearance to wheel.

Bob

[nitroman]

I take it you are refering to the fact that F1 Lotus has 10.75” dia x 1.25” discs (but 10.75" is only 273mm) a fact I already knew, and he had to mod the caliper to get it in.
"Upgraded front brakes - 11.75"x1.25" rotors & Wilwood Billet Dynalite 120-5006 calipers" with standard 16" wheel will NOT fit
you run out of clearance to wheel.

Bob

Brian has 11.75" (298.5mm) rotors with standard Fed wheels.

[F1 LOTUS]

I had to machine some clearance on the calipers

[nitroman]

I had to machine some clearance on the calipers

Mon sewer (my sewer?) Brian, would your 5006 bremsen fit within Elan S2 wheels, or do them there wheelies have even more constrictive confines?

[F1 LOTUS]

Je sais pas amigo? I don't have any means of comparing the different wheels?

[paulrwebster]

I replaced my 120-6816 calipers with 120-6806 calipers this afternoon. They definitely do not give the same sharp deceleration as the 6816 calipers, saying that, once I had done a few hard stops to warm them up and bed them in, they appear to be adequate. I braked as hard as I could from 30 mph, however could not lock the brakes. The biting point seems to be the same as the 6816, however I have never has a problem with low brake pedal travel.

[nitroman]

I replaced my 120-6816 calipers with 120-6806 calipers this afternoon. They definitely do not give the same sharp deceleration as the 6816 calipers, saying that, once I had done a few hard stops to warm them up and bed them in, they appear to be adequate. I braked as hard as I could from 30 mph, however could not lock the brakes. The biting point seems to be the same as the 6816, however I have never has a problem with low brake pedal travel.

Damn you Paul Webster, damn you! I was all set to order 6806 calipers. Does it feel like you have lost any tactile sense with the brake pedal?

Unlike the guys flinging their cars around on the ragged edge most of my rapid deceleration is done in a straight line when some idiot pulls out in front of me. I don't drive like a Loon in the wet either. The #2 thing after the great ability to modulate the "% of stop" with the Wilwoods is the sharp deceleration ("stand it on the front wheels") ability. I don't want to give either quality up for a little less pedal travel.

Perhaps this caliper mistake was the best mistake known to mankind?

[bobbrown]

They definitely do not give the same sharp deceleration as the 6816 calipers, saying that, once I had done a few hard stops to warm them up and bed them in, they appear to be adequate.

I am sure this is a perception issue, bit like coming off a fast clear motorway/freeway and straight in to 30mph zone, it seem like you are too slow, in this instance you have been used to the amount of pedal input on very large front calipers, yes the 6816 calipers are very large even bigger than the Brembo calipers fitted as stock to the Aston Martin DB9.
The brakes should be more than adequate but I feel you are missing the point, the reason to change the 6816 to 6806's is not just pedal feel it is also brake bias.
If you stick with the 6816 caliper just be prepared fron the car to swap ends under heavy braking and you do not always have the choice of where you have to brake hard, the animal in the road around the corner springs to mind.

Off to Hethel now

Bob

[nitroman]

They definitely do not give the same sharp deceleration as the 6816 calipers, saying that, once I had done a few hard stops to warm them up and bed them in, they appear to be adequate.

I am sure this is a perception issue, bit like coming off a fast clear motorway/freeway and straight in to 30mph zone, it seem like you are too slow, in this instance you have been used to the amount of pedal input on very large front calipers, yes the 6816 calipers are very large even bigger than the Brembo calipers fitted as stock to the Aston Martin DB9.
The brakes should be more than adequate but I feel you are missing the point, the reason to change the 6816 to 6806's is not just pedal feel it is also brake bias.
If you stick with the 6816 caliper just be prepared fron the car to swap ends under heavy braking and you do not always have the choice of where you have to brake hard, the animal in the road around the corner springs to mind.

Off to Hethel now

Bob

When did this kit originally come out, 2003 it seems? If that's true it's 5 years A-OK for me.

BTW what are the piston sizes on the OE calipers? I've read 35mm rear & 48mm front but can't substantiate that as it's not listed in any factory documentation I have.

[paulrwebster]

[quote="bobbrown
The brakes should be more than adequate but I feel you are missing the point, the reason to change the 6816 to 6806's is not just pedal feel it is also brake bias.
If you stick with the 6816 caliper just be prepared fron the car to swap ends under heavy braking and you do not always have the choice of where you have to brake hard, the animal in the road around the corner springs to mind.
[/quote]

Oh I do get it, that is why I have changed them, and I am not going to change them back. The braking is better than the stock setup, however I have just been out again and out in a Vauxhall Zafira. The Zafira brakes are slightly sharper, try as I might I again could not lock the brakes on the Elan. They are, however, OK, but that stand on the nose feel is gone.

[nitroman]

Stats to help make sense of changes to expect
Assuming the stock caliper’s piston sizes are 35mm/rear, 48mm/front, here are some calculations for comparing stock brakes to the 3 possible (i.e., bolt on) Wilwood calipers. This is based on total square piston size alone (the most important stat) and does not include other factors like swept area & the increased mechanical advantage of a larger caliper (these 2 factors are the same on all 3 Wilwood calipers). The chart below shows mathematically the decrease in braking Paul witnessed. The middle field (Increase Over Stock) represents both increased braking ability & increased pedal travel. The #6806 caliper essentially makes Brian's statement about the 15" brakes applicable to the 16" system, as 15" & 16" pot sizes are now equal: "This is not a system that is designed to give a big increase in braking torque at the front. It will almost precisely match the designed braking torque of the stock system."

Code: Select all

Caliper  F&R piston   Incr/Decr     sq-mm     Braking %
 Type     area sq-mm    VS Stock   Front/Rear  Front/Rear
=======  ==========   =========   ==========  ==========
OE          6172         --       4248/1924     69/31
#6806       5795        - 6%      3871/1924     67/33
#6811       7231        +17%      5307/1924     73/27
#6816       8146        +32%      6222/1924     76/24

* stats recalculated to reflect a 52mm piston OE front caliper.

[bobbrown]

I have just double checked my figures while in the process of making the Wilwood upgrade with dust seals.
I was at Lotus yesterday, and while chatting with some of the members re the Dynapro caliper it was noted that the piston seals were not on the full piston diameter.
I have checked on the standard caliper and the same is true, the piston diameter on the standard caliper is 52mm!!!!!!!!
This gives an effective area of 4248 square mm, now both the 15” and the 16” are specified with 35.1mm pistons giving an effective area of 3871 square mm.
So what does all this mean, the calipers are too small to give any increase in clamp loads and in effect mean they are no better than standard and in the case of the 15” slightly less!
Wheel loads read like this at 15Bar line pressure
Tyre load (this takes into account clamp load, disc diameter, and tyre size)
Standard 1,600N
Wilwood 15" 1,584N
Wilwood 16" (120 6806) 1,792N

The good news, if you can call it that, is the brake bias will be very close to standard

I would ask that some one checks these figures.

I will now be looking at the Dynapro setup using a caliper with a larger piston size than the 35.1 pistons specified in the original Wilwood upgrade and in this instance will opt for the 38.1mm piston as this gives an approx 30% increase in clamp load and increases the tyre load to 2112 Newtons at 15bar line pressure.

[bobbrown]

I have changed the calculations with in the graph to allow for the Standard caliper piston being 52mm

Does not change the fact that the 120 6816 caliper is too large but shown the rest follow the standard setup
The original 15 Wilwood is very close to standard so the brake bias will be correct, the 16" with 120 6806 calipers slightly above this.
I have checked with Hi-spec and they use 38.6mm piston size and the calculations are done on a 285mm diameter disc
Bob

tyre force1.jpg

[paulrwebster]

I have just double checked my figures while in the process of making the Wilwood upgrade with dust seals.
I was at Lotus yesterday, and while chatting with some of the members re the Dynapro caliper it was noted that the piston seals were not on the full piston diameter.
I have checked on the standard caliper and the same is true, the piston diameter on the standard caliper is 52mm!!!!!!!!

I may be missing the point here, but I have just measured the piston on the stock calipers and it is 46mm. Are you saying that the piston is bigger out of sight behind the dust seals?

[bobbrown]

Yes it is

You have made the same mistake I did, I have removed the piston and it is 52mm
You can feel the step behind the boot

Bob

[RayD]

...

[F1 LOTUS]

FWIW - I was guided by the AP kit developed for our cars [which I would have fitted had it not been too costly to import].

[nitroman]

FWIW - I was guided by the AP kit developed for our cars [which I would have fitted had it not been too costly to import].

Dude, I understand projects... Grab five or ten bucks of material then add a million man-hours!

[tigerdog]

Even with the feedback above, since I already have all the other wilwood bits I plan to move forward with 6806s. I like the graph results of the dynapro better but can't afford to start from scratch. Since I am able to lock the fronts with my current EBC rotors and greenstuff pads, I expect I can do the same with the 6806s. Bob, if I can't, would you chock it up more to pad selection than mechanical issues?