Wilwood 16" kit caliper issues

[bobbrown]

Tyre grip is a very very complex subject to do with slip angles and a lot of other stuff
Simply saying a narrow tyre will lock up earlier against a wide tyre is simply not correct.
It has to do with friction and load
Heat is another thing that needs to be taken into account

F=uN,

where F is the force generated, u is the coefficient of friction, and N is the weight on the surface considered (in our case, the weight on the tyre).


Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability.

[RayD]

I understand what you’re saying Bob,

I was using it to bolster your point that it’s the tyres that stop the car.

I’d used up the “all other things being equal” phrase in another sentence.

Generally speaking, and all other thing being equal, a narrow tyre will lock up sooner than a wide tyre.

Ray

[DeeAitch]

I feel a lot of you are missing the point, the amount of braking that can be achieved on the front is no different on the standard brakes as it is on an upgrade it just takes more effort (pedal input) to achieve.
The amount of weight transfered during braking is down to the tyres you have fitted not the brakes.
It is the tyres that stop the car!!!!!!!!!!!!!!!!!!!!!!

With out the back brakes operating correctly then the cars stopping distance will go up, this is a fact not just a theory more so in the wet.

On a dry road you will get more weight transfer than on a wet road due to the extra grip from the tyres, note the tyres not the brakes.
The car would have been engineered to give good brake ballance in wet and dry conditions so this is always a compromise.
That is also why race and rally cars have adjustable brake bias to "dial in" the brakes for track/ stage conditions.

Bob

Bob, I agree - up to a point. I've often said that, ultimately, there are only 4 things able to keep you on the black stuff, and they are all made of rubber What you need to do is get the best rubber out there, keep them turning (cue another debate) and in contact with the road.
However on this one

the amount of braking that can be achieved on the front is no different on the standard brakes as it is on an upgrade it just takes more effort (pedal input) to achieve.

I feel this is only true if the stock system is capable of taking the wheel to the point of locking up before the pads heat up and fade. Once you get into fade then no ammount of additional pressure helps. An upgrade to RS4 pads for instance will increase the coefficient of friction thereby allowing the higher pedal pressure required before fade kicks in. Also I for one can not get the stock brakes to lock with my puny size 8's

I still feel I can now get access to a much greater rate of deceleration from say 70MPH than I ever could with the stock brakes, without locking up the fronts. The resulting weight transfer increasing the load on the front leads to even more grip from the tyre, probably due the larger forces acting on a larger footprint. Of course a higher pedal pressure on the stock brakes would also achieve this condition, assuming they were still operating within the constraints of the design / pad material.

Whatever, there is more weight transfer onto the front, and less on the rear, the harder I stop, unless I lock up, with a resulting decrease in the load on the rear tyres leading to less grip as this is proportional to load i.e. F = u R.
If the rears are already on the point of locking then any reduction in the load on them will tip them over the edge - happened to me once last year and it is scary if, like Geoff, you are dogging a Cow or, in my case, a Sheep

Lots of various parameters to consider in this so good luck in finding the ultimate solution.

Long time since I was at skool and all too much for me these days so I duck out now

[bobbrown]

I understand what you’re saying Bob,

I was using it to bolster your point that it’s the tyres that stop the car.

I’d used up the “all other things being equal” phrase in another sentence.

Generally speaking, and all other thing being equal, a narrow tyre will lock up sooner than a wide tyre.
Ray

Again this is not true, there are too many thing that need to be taken into account and selection of the correct tyre can effect so much.
Back in the mid 1990's we were rallying a MK2 BDG Escort (full group "A")and due to an earthquake in Japan could not Dunlop tyres for love nor money and our stage times dropped by 1 to 2 seconds a stage mile it was a case of the Dunlops suited the car.
The same is true on the road for example wide tyres do not stop that well in the wet, never mind snow where they are absolute rubbish, but going from say a 165 profile to 215 profile will not have that much effect asuming tyre temperatures and compounds are the same (narrower tyres usually have a harder compound due to the extra heat that is generated) but there are so many factors that need to be taken into account, in terms of pure stopping then the brakes need to be balanced but they do work within a band.
Go out side that band at your own peril

Bob

[bobbrown]

Not sure if this is relevant but the cost to purchase calipers from Rally Design comes down if you buy 4
I asked what the cost was for their Midlite (Dynapro) calipers if I ordered more than a pair and what volumes you need to buy in they said 4 calipers

So it would be worth while a couple of you getting together if you are going to replace the 16's with 06's as you could save some dosh probably around 15%.

Bob

[a5gcd]

Those of you who bought from Rally Design when I arranged the group discount will all have 120-6816s as I have.

I have spoken to Lee at Rally Design and explained the "mistake" and they have offered us the same deal as before. 120-6806 calipers for £69.50 instead of the normal price of £89.50 + VAT of course. Give him a call, quoting Lotus Elan group buy, if you intend to take up his offer.

01795 531871

[nitroman]

A5, good news for UK!

I feel a lot of you are missing the point, the amount of braking that can be achieved on the front is no different on the standard brakes as it is on an upgrade it just takes more effort (pedal input) to achieve.
Bob

Bob, just for shits & grins I'll agree with you, and add: It takes far stronger legs than I have to stop an Elan with "normal" stock brakes. Even in an extreme condition where human physiology moves into panic mode, which is the only instance when more than 1/3 of the fibers in a muscle can be employed at the same time, a person cannot generate enough force to stop an Elan's wheels from spinning without hitting the object before them. The Wilwoods, regardless of caliper, solve the problem of human inadequacy.

[paulrwebster]

Those of you who bought from Rally Design when I arranged the group discount will all have 120-6816s as I have.

I have spoken to Lee at Rally Design and explained the "mistake" and they have offered us the same deal as before. 120-6806 calipers for £69.50 instead of the normal price of £89.50 + VAT of course. Give him a call, quoting Lotus Elan group buy, if you intend to take up his offer.

01795 531871

Thanks for sorting that out for us. As Geoff has already ordered his, it might be a good idea to hold off a little while and get his feedback on the performance of the replacement calliper.

[Paul.P]

Does anyone know if the 6806 calipers use the same pads as the 6816 ?

[tigerdog]

Does anyone know if the 6806 calipers use the same pads as the 6816 ?

Wilwood's web site has a single spec sheet for all Forged Billet Dynalite Calipers. That specsheet lists 7112 pads as appropriate to all. I therefore believe the answer is "yes".

[algirdas]

Dear All:

Ditto Tigerdog. I confirmed with Wilwood today that the pads for the 6816 and 6806 are interchangeable.

I should have the group pricing information from Wilwood Monday or Tuesday next week.

Sincerely,

Algirdas

[nitroman]

As Geoff has already ordered his, it might be a good idea to hold off a little while and get his feedback on the performance of the replacement calliper.

I've now owned 3 separate Elans bought with anywhere from 11k to 19k miles, which in succession have been modified from:
3 cars with standard brakes to:
1 car changed to EBC Greenstuff pads
2 cars with Wilwood 120-6816 calipers

I've also driven Doug's former car with the 120-6806 calipers in spirited mountain driving. His car had I perceived, somewhat less pedal travel. If there was any less gripping force with his calipers, it was inconsequential, as his brakes could still easily lock the front wheels, IF you intended to.
===============================================
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tele 0 1525 636057
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You get 3 (so 1 to screw up with) large ones for Wilwoods, and
6 (4 to screw up with) small ones for the rear calipers.



He lists decals on EBAY too, just no LOTUS: http://shop.ebay.com/items/__Brake-Cali ... .m63.l1177
He previously stated to me (in March): Hi Matt, We gave up marketing LOTUS decals as the response was so poor. If you would like a set, please use item number 250184148960 to place the order (Renault Decals ) and add a note to your PayPal payment that you want Lotus and the colour you want. Best regards, Adam.

===============================================
This post made by me in another thread dated 20 Apr 2008:
(This also explains why, when Ekapol ordered 1.75" seals to rebuild Doug's old calipers, the new seals were far too big to use!)

Great stopping power, but longer pedal travel.
I can feel another mod coming round the corner.
Regards
Jim

Jim,
Ever since i did my wilwood up grade Pinky has a longer/soft pedal travel, i've ordered a new master cylinder from the USA to see if that'll make a difference

I dont think just replacing the MC with a "like for like" item will assist this. Surely this pedal travel is down to the size of the pistons now being moved and a greater amont of fluid moving more quickly. Perhaps a Cylinder with a greater capacity might help?
Regards
Jim

Got this from a site discussing BMC needs when converting from single-piston-calipers to 4-piston-calipers:
...multiple (caliper) pistons will need more fluid displacement to make them work properly. This generally means a larger bore master cylinder is needed for any given application. However, as this component can be very costly to replace, most folk stick with the standard one. It will work OK, but means that on the multi-piston calipers there is more pedal travel than normal. The good news is that the smaller bore (more but smaller pistons in the caliper) means higher line pressure for any given pedal pressure - less driver input for same braking effort, and better ‘feel’. 'Feel', incidentally, is the sensation of what the brakes are up to, and is an important part of our thought process as to how much pressure we need to apply to the pedal in any given situation.

For information sake, a great deal of pressure may be needed to slow a car down with its original (large-bore) single-piston calipers, but the same car would probably be ace on a four-piston caliper set-up. Also, the amount of hydraulic pressure produced at the pedal is INVERSELY proportional to the master cylinder bore. So if you are locking the brakes up too easily, you need to INCREASE the bore size. Consequently if you are standing on the pedal, pulling off the steering wheel and gritting your teeth together to lock the brakes, a smaller bore is the order of the day.

With these thoughts in mind, would it not be possible to use a smaller piston-size Wilwood caliper to address the concern of pedal-travel? The calipers below use the same bolt-pattern, they are just bored for different piston-sizes. I believe this will result in less overall pad-pressure being possible, but should further-increase pedal-feel. I am thinking of doing this when switching to Wilwoods on my Yellow M100, but would like the opinion of others before doing so. The 1.75" bore is the caliper advised for the kit, so there are 2 smaller bore sizes.

Code: Select all

Bore Size     Disc Width Blk Part# Polish Part#
1.75" 44.5mm  .81" 20.6  120-6816
1.62" 41.1mm  .81" 20.6  120-6811  120-6796-P
1.38" 35.1mm  .81" 20.6  120-6806  120-6791-P


Note that for Brian's development 16" Wilwood kit (retained on his personal car), Wilwood caliper # 120-5006 with 1.38" pistons was used. He also utilized/utilizes 11.75x1.25 rotors VS the 16" kit's 12.19x.81 rotors. When I asked about that 3-years ago Brian replied "That’s right, for my installation it was okay to custom-machine the calipers in a couple of areas and run things a tad tighter but I figured off-the-shelf parts would be better for the kit." Hence the switch to the thinner disc, but I don't understand why the switch to a larger-piston caliper was made. Note that the 15" Wilwood kit uses a Powerlite caliper with 1.38" pistons (and a smaller 11" rotor). The 15" kit also has a smaller swept (disc/pad contact) area, which is expressed as roughly equating to the OE brakes. However the 16" kit offers an improved/increased friction area. All Dynalite calipers use the same pads, so as long as they're used with the same diameter rotor the swept area remains unchanged regardless of the caliper's piston-size. However, ultimate pad force exerted upon the disc increases with a larger piston. Wilwood states "A larger piston provides greater clamping force." Huh? See chart. Pad contact area per caliper for the Powerlite (aka 15" kit) is 22.8 SqIn VS 29.9 SqIn for the Dynalite (aka 16" kit), translating to a front-brake swept-area of 45.6 VS 59.8 SqIn. In addition (referring to the chart below) the smaller-piston size of the 15" kit only offers 62.5% the clamping-force of the 16" kit. Can those with the smaller 15" Wilwood kit still lock their wheels?

Things to remember:
1) A bigger bore master cylinder means higher pedal effort.
2) A bigger bore master cylinder means less pedal movement.
3) The larger the MC diameter, the less hydraulic line pressure you will have. (think of a shorter lever, you lose the mechanical advantage. That is why the pedal effort is higher.)
4) Bigger pistons in the calipers mean more force is exerted on the disc, but less pedal effort is required by your foot.
5) Bigger pistons in the calipers means your foot must move the pedal farther.
6) Bigger rotors generate more brake torque, which makes the pedal effort feel lighter.

Hmm. All that said I may have talked myself out of this. Whilst initial application of the pedal would yield a quick response, the reduced clamping-force (and therefore stopping-ability) could be extremely dissapointing.

The total clamping force in a brake system is a function of three factors:
1) Line pressure - Provided by the pedal ratio (leverage) and master cylinder size.
2) Effective radius - A factor of the overall diameter of the disc.
3) Piston area - The effective size of the calipers pistons.


This article explains things a wee bit better http://www.sportcompactcarweb.com/edito ... index.html

[Doug]

wow, the great caliper discussion thread continues

where's ESM with his scientific graphical analysis -- (probably keeping quiet on purpose )

[nitroman]

wow, the great caliper discussion thread continues

where's ESM with his scientific graphical analysis -- (probably keeping quiet on purpose )

I'm in favor of the 6806, but I thought others might find some of these caliper facts relevent. Hey, I had already done the research!

[algirdas]

Dear All:

A pair of 6806s should be delivered to my house tomorrow afternoon. I'll try to get them on this weekend and do some comparison testing (assuming I get the system bled properly) while sensations are fresh in my mind (and right foot).

Matt-I held off ordering a set for you since you appear to be vacillating on making the switch. If everything falls into place, you should be able to order directly from Wilwood and get the discount pricing. I'll keep you posted.

Sincerely,

Algirdas

Matt-How do you keep that undercarriage so clean? After seeing yours, I look at mine and just want to hurl.

[tigerdog]

Matt-How do you keep that undercarriage so clean? After seeing yours, I look at mine and just want to hurl.

Matt's attic holds a painting of an Elan slowly metamorphosing into a rusty, crumbling Lada.

[bobbrown]

Dear All:

A pair of 6806s should be delivered to my house tomorrow afternoon. I'll try to get them on this weekend and do some comparison testing (assuming I get the system bled properly) while sensations are fresh in my mind (and right foot).

Matt-I held off ordering a set for you since you appear to be vacillating on making the switch. If everything falls into place, you should be able to order directly from Wilwood and get the discount pricing. I'll keep you posted.

Sincerely,

Algirdas

Matt-How do you keep that undercarriage so clean? After seeing yours, I look at mine and just want to hurl.

If you remove the cap off cover brake fluid reservoir and cover it with cling film then screw the cap back on, if air tight you should then be able to replace the calipers with out the need to drain the whole system.
It is then just a case of bleeding the front, the rears should stay as they were as I think this is where most of the bleeding issues stem from.

Bob

[ailwyn]

Matt-How do you keep that undercarriage so clean? After seeing yours, I look at mine and just want to hurl.

Matt's attic holds a painting of an Elan slowly metamorphosing into a rusty, crumbling Lada.

Not another Grey member?

[dapinky]

Matt-How do you keep that undercarriage so clean? After seeing yours, I look at mine and just want to hurl.

Matt's attic holds a painting of an Elan slowly metamorphosing into a rusty, crumbling Lada.

Not another Grey member?

My, what a lot of Literary well-educated members we seem to have........

(either that, or they have seen the kids film about the League of Extraordinary Gentlemen)

[John_W]

... the smaller-piston size of the 15" kit only offers 62.5% the clamping-force of the 16" kit. Can those with the smaller 15" Wilwood kit still lock their wheels?

... I may have talked myself out of this. Whilst initial application of the pedal would yield a quick response, the reduced clamping-force (and therefore stopping-ability) could be extremely dissapointing.

Matt,
I'd say you're spot on.

I have the 15" kit (same piston size as the 6806 Dynalites, but smaller disc than the 16" kit) and your description fits the behaviour of my brakes, ie:
- The brakes always work, they never stick like the standard ones, and I don't have to take the front brakes apart every month to service them like the standard ones.
- for normal stopping, response is very quick, with good feel and a hard pedal with little travel.
- when you really need to stop a bit quicker than normal, you need to push the pedal a lot harder, and it goes a bit further down. The brakes do not give their full stopping effect unless you push the pedal hard. If you just press half-heartedly, there is the definite feeling that "I'm not going to stop" (this tallies with your reduced clamping "disappointment")
- I can lock my brakes, but only when I really try to push the pedal hard (like yesterday when a 40-ton lorry coming the other way decided to overtake a bus).

John

edited to say: Of course with the 16" kit you have a larger-diameter disc and a greater pad area with the Dynalites, so even using the 6806's with the same diameter pistons as I have you should be able to stop better than I can.