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Bigger MC's with uprated calipers

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Re: Bigger MC's with uprated calipers

Post by kevhaywire on Tue Nov 11, 2008 4:42 am

Yep, the difference between 0.38 to 0.45 is what you're feeling.

On such a small scale (0 to 1), little differences have a big effect.

The DS2500s are a constant 0.5 but that doesn't mean it bites the same hot and cold. That's just the pad's friction coeffecient. The disc itself still needs to get hot Very Happy We've all felt the effect of a sopping wet disc giving no braking power at all until the pad has wiped the water off......

My old Pagid RS15s were ridiculous. 0.5 when cold, 0.6 when hot. They were fun with 330mm APs Very Happy

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Re: Bigger MC's with uprated calipers

Post by jmc on Wed Nov 12, 2008 1:30 am

Interesting Kev. Is the friction coefficient not indicative of bite then? I would have thought the poor initial braking on a wet disc was due to the water acting as a lubrication layer, rather than it being a disc temperature thing...

I really do like the sound of the RS15s, but the last time I asked they didn't make them for my callipers. Might have to check again though.
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Re: Bigger MC's with uprated calipers

Post by mic_VR on Wed Nov 12, 2008 2:44 am

My EBC redstuff's have a co-efficient of 0.5 and I've been very impressed with them so far. Good bite from cold but just get better and better as things get warmer.

And a huge range as well
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Re: Bigger MC's with uprated calipers

Post by kevhaywire on Wed Nov 12, 2008 3:56 am

Yeah the coefficient is indicative of bite strength, but mostly in controlled lab conditions.

The same pad can behave differently "out in the field", depending on disc surface type and material, aswell as temperature.

The water analogy was a poor one, sorry Very Happy I meant to try and explain that a cold disc won't bite aswell as a hot one.

The DS2500s bite well enough from cold, but they're certainly a lot better when there's a lot of heat in the brakes.

The RS15's performance against temperature is a lot more noticable than the DS2500s, but you could really feel them torturing the tread blocks Very Happy
Amazing pedal feel aswell, being so soft.

Regarding the original query of MC size etc, most 4 pots work well with stock MCs. Increasing the MC size reduces pedal effort, but increases travel.

I'd really like that solid pedal feel modern Vauxhalls have. There's just no slack at all in the pedal and bites right at the top of the travel with very impressive initial bite.....but it's deceptive. A typical Vectra TDI will put my head through the screen if I use the same pedal pressure as I do with the AP brakes, but try and haul that Vectra down to 30mph from 100mph, and the braking isn't so impressive after all. That's where big 4 pots come into their own, resisting fade supremely well.

I suppose it's (as always) a trade off between initial bite strength which boosts confidence, or braking that throws you into the seat belt where it matters most.

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Re: Bigger MC's with uprated calipers

Post by jmc on Wed Nov 12, 2008 10:53 am

Cool, cheers Kev. It definately points to pad choice rather than MC size then.

I take it then that if I can get RS15's for the Porka callipers (I seem to recall we've had this conversation before Laughing) they should be as impressive when cold as the Ds2500's. Last time I was buying pads they didn't do them (although even then there was a lot of 'we do', 'we don't', 'we do', 'we don't' emails and phone calls) but having checked the website now it seems they do.
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Re: Bigger MC's with uprated calipers

Post by kevhaywire on Thu Nov 13, 2008 8:47 am

It's been a while since I used the RS15s, but from what I can remember, the DS2500s are a bit better from cold. But the RS15s only need a few moderate pressure stops to get enough heat in them.

They're not a cheap pad, mine were about £165!

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Re: Bigger MC's with uprated calipers

Post by jmc on Thu Nov 13, 2008 9:19 am

Ah right, so it looks as though the DS2500 would be better for from cold. I've got someone looking to see whether they can actually get them for my callipers (the information from different sites is contradictory). I know what you mean about price. One site where I was looking (which said they were available) had them down as £202 for the set for a pair of callipers Shocked
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Re: Bigger MC's with uprated calipers

Post by jmc on Fri Nov 14, 2008 5:10 am

Oh my lord, the DS2500 are £204 for the set for the front Shocked
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Re: Bigger MC's with uprated calipers

Post by mrbeige on Fri Nov 14, 2008 6:05 am

jmc wrote:Oh my lord, the DS2500 are £204 for the set for the front Shocked
holy mother of god, I wasn't expecting that. The ones I had on the 256's were nowhere near that, I remember something around £60. I might have a word with a mate and see if I can arrange some sort of forum discount with a supplier.....

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Re: Bigger MC's with uprated calipers

Post by jmc on Fri Nov 14, 2008 6:11 am

Neither was I - to be fair it was the first place I looked (balancemotorsport) so there may be other suppliers, but even so, I nearly fell off my chair Laughing I was expecting about half that.

Out of interest what is the friction coefficient of a standard pad under cold conditions?
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Re: Bigger MC's with uprated calipers

Post by junkie on Fri Nov 14, 2008 3:12 pm

Cant remember the exact price but they were around £110 for mine from Jabbasport but dont hold me to that.
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Re: Bigger MC's with uprated calipers

Post by kevhaywire on Fri Nov 14, 2008 4:06 pm

£204!!!

I think it's that Brembo / Porsche caliper branding stinging you there mate Very Happy

DS2500s for my AP calipers are £140 Very Happy

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Re: Bigger MC's with uprated calipers

Post by jmc on Sun Nov 16, 2008 1:57 pm

Yeah I think you might be right there Kev. I mean who would put Porka callipers on a Corrado - oh, yeah. One thing I have found with the 421's - they may be a bit pants when pottering around and slowing me from 30mph, but they don't half hawl the speed of when slowing down from 80. It's like chucking an anchor out the back Very Happy
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Re: Bigger MC's with uprated calipers

Post by kevhaywire on Mon Nov 17, 2008 7:03 am

Yep, now imagine throwing another anchor out and that's the RS15s Laughing

TBH I've never found the MK2 / MK3 / Corrado to have a good pedal at low speeds with ANY breaks, and imo, the VR6's standard brakes are shockingly bad to the point of being completely useless / dangerous.

I remember when I bought my VR. I drove into the dealer's yard in a complete beater of a D reg 325i worth £400 tops. Drove home again thinking the VR was not only slower than the 325i, but the brakes were so schitt I over shot a few junctions before I got used to the modulation pressure required. What was it with VW and brakes and headlights in the 80s?

Anyway, I digress Very Happy I guess the 421's low speed behaviour goes hand in hand with the Corrado's useless pedal behaviour, well, certainly with the VR in any case. I think G60s didn't have too bad a pedal?

Get in a MK4 Golf with 256mm discs and stock pads, and you go through the screen with the same pedal effort, so they obviously completely redesigned the pedal box and MC arrangements.

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Re: Bigger MC's with uprated calipers

Post by jmc on Mon Nov 17, 2008 1:37 pm

I seem to recall my G60 brakes as standard were pretty good. However that was I just got the car, and anything was better than my previous 1.4 Polo. It wasn't long after I got the car that I uprated the brakes, and I think my driving style has become more 'spirited' as my ownership has progressed which probably explains why I am now picking holes in the brakes performance at slow speed. I didn't know that about the VR6's brakes being so bad as standard though - thats not good Sad. Mines a late G60 BTW - I wonder whether they share the same problem?
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Re: Bigger MC's with uprated calipers

Post by mrbeige on Mon Nov 17, 2008 1:50 pm

jmc wrote:Mines a late G60 BTW - I wonder whether they share the same problem?
Same original brakes, if that's any help.

Going on what Kev said, is it possible to change say the Pedal box, MC and servo over to the mk4 setup to try and improve things? If the brakes are much better in a mk4 it follows that that set-up in a Corrado (which is lighter) along with the brakes you have Jonathan, would give you a much better pedal and greatly improve overall braking?? It's probably quite a job to do, but matching the leverage provided by the mk4 pedal box with the mk4 MC and servo rather than just the MC, would be a fair better solution. Obviously go for the earlier cable throttled pedal box though.

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Re: Bigger MC's with uprated calipers

Post by Toad on Mon Nov 17, 2008 1:51 pm

I far prefer the brakes in my early 16v to the VR. Admittedly the ABS sat not working all the time I drove it.
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Re: Bigger MC's with uprated calipers

Post by jmc on Tue Nov 18, 2008 3:06 am

I'm sure it's 'possible' Stualthough given my question about how to change the pads, probably more possible for someone that knows what they're doing Laughing. If it's a question of leverage, then can the pivot points be moved on the brake pedal - presumably it's just a lever?
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