Cyl Sizes and ratios
Discussion
Could anyone advise the following re the current factory spec Ultima brakes..
1. Pedal leverage ratio.
2. Model(s) of front and rear AP master cyls... and / or the cyl diameter(s).
3. The model of front and rear AP calipers... and / or the piston diameter(s).
The existing Wilwood brakes I inherited on my 1997 Spyder are somewhat 'wooden' with little travel - requiring heavy pedal pressure to stop/lock. There are no servos connected. Suspect master cyl to caliper piston ratio is the primary offender of the wooden 'feel'.
However, I'd like to ensure I'm looking in roughly the right place on paper before expending major effort and cost - so wish to compare against correct hydraulic advantage on the current factory AP set-up (accepting the actual retardation force will also be related to rotors, pads, wheel dias and tyres).
Tks,
Adam
1. Pedal leverage ratio.
2. Model(s) of front and rear AP master cyls... and / or the cyl diameter(s).
3. The model of front and rear AP calipers... and / or the piston diameter(s).
The existing Wilwood brakes I inherited on my 1997 Spyder are somewhat 'wooden' with little travel - requiring heavy pedal pressure to stop/lock. There are no servos connected. Suspect master cyl to caliper piston ratio is the primary offender of the wooden 'feel'.
However, I'd like to ensure I'm looking in roughly the right place on paper before expending major effort and cost - so wish to compare against correct hydraulic advantage on the current factory AP set-up (accepting the actual retardation force will also be related to rotors, pads, wheel dias and tyres).
Tks,
Adam
Can you not see what the cylinder sizes are? If not, why not phone Ultimas and ask. If they are the factory brakes you may have some other problem such as glazed pads.
edited, Sorry, just re-read your post and realise you probably know what you have already.
Do you have a bias bar and twin cylinders? You could just try a smaller master cyl
>> Edited by falcemob on Thursday 16th December 19:58
edited, Sorry, just re-read your post and realise you probably know what you have already.
Do you have a bias bar and twin cylinders? You could just try a smaller master cyl
>> Edited by falcemob on Thursday 16th December 19:58
Twin clys and bias bar. I'm sure I will need to go smaller but need to estimate how much.
I sent an almost indentical mail to the factory recently but they declined to assist - indicating they felt they could not get involved with any non-standard installation.
Was a little disappointed with their reponse as...
1. All I requested was detials on their standard products - as can be seen.
2. I've handed over £3K already to them this year.
They intimated it would be best for me to get a full AP set-up.... and I'm sure it would be the best for them also. However I'm reluctant to spend £3000 when £300 on a suitable master cyl might well satisfy my needs. At least I'd like to try it first, even if proved wrong later.
Hence turned to forums seeking assistance....
Basically I'm looking to calc a roughly equiv master cyl size / force to standard - given my different caliper cyl dimensions and pedal ratios.
I sent an almost indentical mail to the factory recently but they declined to assist - indicating they felt they could not get involved with any non-standard installation.
Was a little disappointed with their reponse as...
1. All I requested was detials on their standard products - as can be seen.
2. I've handed over £3K already to them this year.
They intimated it would be best for me to get a full AP set-up.... and I'm sure it would be the best for them also. However I'm reluctant to spend £3000 when £300 on a suitable master cyl might well satisfy my needs. At least I'd like to try it first, even if proved wrong later.
Hence turned to forums seeking assistance....
Basically I'm looking to calc a roughly equiv master cyl size / force to standard - given my different caliper cyl dimensions and pedal ratios.
Looks to me like you need to:-
Measure your pedal ratio.
Find your cylinder sizes, master and wheel.
Pad material type if known.
Take the above to Willwood for assistance.
The factory are quite right in declining help as they have no technical knowledge on the Willwood product. Moreover, the AP cylinder sizes probably bear no relationship with what you have so may even serve to cloud the issue.
Steve
Measure your pedal ratio.
Find your cylinder sizes, master and wheel.
Pad material type if known.
Take the above to Willwood for assistance.
The factory are quite right in declining help as they have no technical knowledge on the Willwood product. Moreover, the AP cylinder sizes probably bear no relationship with what you have so may even serve to cloud the issue.
Steve
Though my orginal mail was clear but possibly need to clarify further...
I'm not requesting any assistance with any non-standard compoents. I'm not asking for any direct assitance with Willwood nor any other non-standard braking system.
I'm requesting detials only related to standard componets - I'll do the rest.
My minor frustration is I cannot grasp why anyone inc the factory would be relucant or unable to give me info on standard components!
Maybe I'm missing something??! Clearly I'm missing something!
I'm not requesting any assistance with any non-standard compoents. I'm not asking for any direct assitance with Willwood nor any other non-standard braking system.
I'm requesting detials only related to standard componets - I'll do the rest.
My minor frustration is I cannot grasp why anyone inc the factory would be relucant or unable to give me info on standard components!
Maybe I'm missing something??! Clearly I'm missing something!
layada said:
Could anyone advise the following re the current factory spec Ultima brakes..
1. Pedal leverage ratio.
2. Model(s) of front and rear AP master cyls... and / or the cyl diameter(s).
3. The model of front and rear AP calipers... and / or the piston diameter(s).
The existing Wilwood brakes I inherited on my 1997 Spyder are somewhat 'wooden' with little travel - requiring heavy pedal pressure to stop/lock. There are no servos connected. Suspect master cyl to caliper piston ratio is the primary offender of the wooden 'feel'.
However, I'd like to ensure I'm looking in roughly the right place on paper before expending major effort and cost - so wish to compare against correct hydraulic advantage on the current factory AP set-up (accepting the actual retardation force will also be related to rotors, pads, wheel dias and tyres).
Tks,
Adam
Layada
I never liked Wilwood brakes they flexed under stress, I always used AP or Brembo in my racing days due to the better feel ...
G MAN
The GTR´s pricelist describes the brake setup:
Set of four 12.7" vented disc brake and callipers comprising X drilled 320mm x 30mm AP Racing curved vane vented discs with alloy bells and AP Racing four pot callipers (1.5" & 1.625" pistons with double
seal) with Mintex 1166 pads.
As I have my pedals lying around at the moment I can
do some measures for you if this helps.
Michael
Set of four 12.7" vented disc brake and callipers comprising X drilled 320mm x 30mm AP Racing curved vane vented discs with alloy bells and AP Racing four pot callipers (1.5" & 1.625" pistons with double
seal) with Mintex 1166 pads.
As I have my pedals lying around at the moment I can
do some measures for you if this helps.
Michael
Hi G-MAN,
Agree with you. Cannot substantially defend the quality of Wilwoods, they would not be my first choice or recommendation either (actually neither would AP - Brembo would probably my preferred brand). Unfortunately it's what I have to work with for now unless I spend a fair amount more money. However, they do work and at present it’s the opposite of spongy / flex - they are too firm on the pedal. So some tinkering is required.
Hi Michael
That’s some v.useful info thanks – I’m assuming that the front and rear callipers are the same model? (and the 1.5 and 1.625 refer to uneven piston sizes in a single calliper, smaller at the leading edge?)
Would be great if you could also provide some pedal dimensions - the distance of pedal pivot point to master cyl attachment point and the distance of pivot point to middle of pedal pad. (provides pedal ratio)
NB I use 1166s on the Wilwoods now – they came with EMC Greenstuffs!! that I duly cooked. As you can see several mods are required to get the whole set-up even to be acceptable for road use – acknowledging they will never be ideal… but ‘good enough’ will do for now.
Thanks again
Adam
Agree with you. Cannot substantially defend the quality of Wilwoods, they would not be my first choice or recommendation either (actually neither would AP - Brembo would probably my preferred brand). Unfortunately it's what I have to work with for now unless I spend a fair amount more money. However, they do work and at present it’s the opposite of spongy / flex - they are too firm on the pedal. So some tinkering is required.
Hi Michael
That’s some v.useful info thanks – I’m assuming that the front and rear callipers are the same model? (and the 1.5 and 1.625 refer to uneven piston sizes in a single calliper, smaller at the leading edge?)
Would be great if you could also provide some pedal dimensions - the distance of pedal pivot point to master cyl attachment point and the distance of pivot point to middle of pedal pad. (provides pedal ratio)
NB I use 1166s on the Wilwoods now – they came with EMC Greenstuffs!! that I duly cooked. As you can see several mods are required to get the whole set-up even to be acceptable for road use – acknowledging they will never be ideal… but ‘good enough’ will do for now.
Thanks again
Adam
BigAl1 said:
Front MC = 0.75" dia.
Rear MC = 0.625" dia.
Brake pedal ratio as it was given to me was 142mm/60mm.
I don't know the caliper cyl sizes except from the website info available.
Allan
Just read that again - that's interesting. Unless there is some fiddling with the balance bar from its central point, this implies there will be a greater line pressure (and breaking force) in the rears than the fronts. Travel on the rear MC stroke will be greater though, due to its smaller size.
A 3/4-inch master cylinder seems excessively large for the fronts given the size of pistons.
I have had 4 pot front callipers with 41mm pistons (about 1.65in.) and when I had a 3/4 cylinder fitted I had to really stand on the brakes to make the car stop.
I tried 5/8 and found that to be the best pedal feel but the travel was a tad to long for my liking, short legs and the fact I race the car. In the end I settled for .70in front and rear (my rear callipers are 2 pot) and that was a good compromise.
I have now changed to the same size callipers as you have (AP racing copy but half the price) but haven’t tried them yet so can’t comment.
As you have callipers with 2 sizes of piston (one of which is smaller than my old ones) you may find that the 5/8 cylinder will be OK for the front.
The size of the rear callipers will affect what rear cylinder you need but generally it will be larger than the front so you have more pressure to the front brakes.
You could try swapping the cylinders round to see how they perform, that way you wont be spending any money although if you use Wilwood/Girling cylinders they are only about £25 each.
>> Edited by falcemob on Friday 17th December 19:04
I have had 4 pot front callipers with 41mm pistons (about 1.65in.) and when I had a 3/4 cylinder fitted I had to really stand on the brakes to make the car stop.
I tried 5/8 and found that to be the best pedal feel but the travel was a tad to long for my liking, short legs and the fact I race the car. In the end I settled for .70in front and rear (my rear callipers are 2 pot) and that was a good compromise.
I have now changed to the same size callipers as you have (AP racing copy but half the price) but haven’t tried them yet so can’t comment.
As you have callipers with 2 sizes of piston (one of which is smaller than my old ones) you may find that the 5/8 cylinder will be OK for the front.
The size of the rear callipers will affect what rear cylinder you need but generally it will be larger than the front so you have more pressure to the front brakes.
You could try swapping the cylinders round to see how they perform, that way you wont be spending any money although if you use Wilwood/Girling cylinders they are only about £25 each.
>> Edited by falcemob on Friday 17th December 19:04
Somewhat agree. If I had not heard that the standard brake config works well, I would have thought 0.661 on the fronts would have been nearer the mark given the piston sizes.
Also surprised that the rear MC is smaller dia than the front - rear line pressure (braking force - all other items being equal) would appear to be ~30% higher than the front (without any balance bar fettling)
However, I'm sure the Factory knows what they are doing and I've not heard any complaints - so I guess the safest apprach is to make the Willwood set-up approximate their specs for now and see how it goes.
Adam
Also surprised that the rear MC is smaller dia than the front - rear line pressure (braking force - all other items being equal) would appear to be ~30% higher than the front (without any balance bar fettling)
However, I'm sure the Factory knows what they are doing and I've not heard any complaints - so I guess the safest apprach is to make the Willwood set-up approximate their specs for now and see how it goes.
Adam
Interesting this as I have TWO clys at .75 which is what the factory issued and said are STANDARD. I do have the older FORD brakes, but I still have not got a real answer to this either. Why are most people running two sizes of clys and yet all the early cars had two of the SAME size? I find I need more bias to the REARS as the fronts can lock up very easily as there is no weight there. I cant lock up the rears at all.
So, should the clys be the same size regardless of the brake setup or would you expect them to vary in size no matter what?
So, should the clys be the same size regardless of the brake setup or would you expect them to vary in size no matter what?
The fronts should lock up before the rears.. but only just before.
Your experience indicates that your rears need more breaking force. However I dont know if the Ford setup uses different (smaller) piston sizes in the rears than in the fronts (it's not uncommon to add an inherent bias this way, rather than via MCs). Before any kind of comparison re MCs can be done, this would need to be established.
Do you happen to know the font and rear caliper piston sizes? Are the front and rear rotors the dame dia? Also are you running 15 inch front tyres and 17 inch rear tyres like I have on he Spyder? (Last two questions are just matter of relative torque applied.)
Your experience indicates that your rears need more breaking force. However I dont know if the Ford setup uses different (smaller) piston sizes in the rears than in the fronts (it's not uncommon to add an inherent bias this way, rather than via MCs). Before any kind of comparison re MCs can be done, this would need to be established.
Do you happen to know the font and rear caliper piston sizes? Are the front and rear rotors the dame dia? Also are you running 15 inch front tyres and 17 inch rear tyres like I have on he Spyder? (Last two questions are just matter of relative torque applied.)
Thanks for the assistance in providing the brake system specs for the current models- very helpful of you all and much appreciated.
Now time for some feedback on the calcs to show the results of your efforts…
On paper at least, it would appear that to get an almost exact pedal-to-piston travel as the factory set-up, I’d be looking at something like 0.661 on the front and 0.551 on the rears. However, the actual pad-to-rotor pressure will be 12% higher with an identical pedal pressure.
My wheels are smaller than current models but the rotor diameter is not that much different. Interestingly this would appear to make a significant increase on the rubber-to-road braking torque compared to the current model - resulting in less pedal force to lock-up the wheels. With this in mind it might be worthwhile considering increasing the MCs one size to balance things out. That would make 0.590 on the rear and 0.7 on the front but I’m still a little undecided – any comments here?
The apparent 30% greater rear breaking effort is still bothering me a little. I’m assuming it has little to do with the font to rear weight distribution - as the difference in relative tyre widths evens this out on the road – i.e. the tyre widths distribute a similar weight per unit contact area at each wheel… and so would generate a similar braking traction for each wheel. (Given my tyre dimensions it would infer roughly a 40-60 front to rear weight ratio for the car.)
The only thing I can muster up with is that the rear disks are also slowing the rotating mass of the engine & gearbox – possibly this accounts for some but 30% still seems a little high to me. Put you foot on the clutch and this would disappear, potentially locking up the rears under heavy braking. Did I see Richard lock up the rear at the very end of the 0-100-0 run video? Putting a foot on the clutch before stopping? Just grabbing at straws - thoughts on the 30% anyone?
Thanks again to all!
Adam
Now time for some feedback on the calcs to show the results of your efforts…
On paper at least, it would appear that to get an almost exact pedal-to-piston travel as the factory set-up, I’d be looking at something like 0.661 on the front and 0.551 on the rears. However, the actual pad-to-rotor pressure will be 12% higher with an identical pedal pressure.
My wheels are smaller than current models but the rotor diameter is not that much different. Interestingly this would appear to make a significant increase on the rubber-to-road braking torque compared to the current model - resulting in less pedal force to lock-up the wheels. With this in mind it might be worthwhile considering increasing the MCs one size to balance things out. That would make 0.590 on the rear and 0.7 on the front but I’m still a little undecided – any comments here?
The apparent 30% greater rear breaking effort is still bothering me a little. I’m assuming it has little to do with the font to rear weight distribution - as the difference in relative tyre widths evens this out on the road – i.e. the tyre widths distribute a similar weight per unit contact area at each wheel… and so would generate a similar braking traction for each wheel. (Given my tyre dimensions it would infer roughly a 40-60 front to rear weight ratio for the car.)
The only thing I can muster up with is that the rear disks are also slowing the rotating mass of the engine & gearbox – possibly this accounts for some but 30% still seems a little high to me. Put you foot on the clutch and this would disappear, potentially locking up the rears under heavy braking. Did I see Richard lock up the rear at the very end of the 0-100-0 run video? Putting a foot on the clutch before stopping? Just grabbing at straws - thoughts on the 30% anyone?
Thanks again to all!
Adam
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