Anyone tried 38mm rear calipers?
- Thread starter Ulix
- Start date
ianlawson
ian - NZ
Ulix, hopefully Pottsy may chip in here.......!
.....I seem to recall some of the guys in the UK X1/9 Owners Club have done this mod (Julian, Tiff, Pottsy himself maybe?).
I think they used rear calipers off Fiat 132's - but I may be mistaken.
Calling Pottsy - where are youuuuuu??
c:
cheers, Ian - NZ
.....I seem to recall some of the guys in the UK X1/9 Owners Club have done this mod (Julian, Tiff, Pottsy himself maybe?).
I think they used rear calipers off Fiat 132's - but I may be mistaken.
Calling Pottsy - where are youuuuuu??
c:cheers, Ian - NZ
kmead
Old enough to know better
Honestly there isn't much need for larger pistoned rear calipers. This would reduce the amount of braking done by the rear wheels. Without changing the master cylinder to one of a larger diameter you won't be moving enough volume of brake fluid to move them or apply as much pressure as you are today with the smaller pistoned calipers.
X's are setup with more front bias (the fronts will lock up before the rears) as it is really bad form to lock up the rear wheels creating a nasty skid opportunity. Now a little more rear braking bias would likely improve braking distances but would increase the chance of a rear lockup with weight transfer to the front.
Better tires, vented front disks (for sustained braking on race courses) and higher quality calipers in front would be the things to change up to not larger pistoned rear calipers.
Your opinion may vary...
X's are setup with more front bias (the fronts will lock up before the rears) as it is really bad form to lock up the rear wheels creating a nasty skid opportunity. Now a little more rear braking bias would likely improve braking distances but would increase the chance of a rear lockup with weight transfer to the front.
Better tires, vented front disks (for sustained braking on race courses) and higher quality calipers in front would be the things to change up to not larger pistoned rear calipers.
Your opinion may vary...
Pete Whitstone
True Classic
I was trying to work this out...
Which way this would go. I came up with the opposite, that it would increase rear braking. I have no idea if I'm right, but my logic is this:
You have not changed the pressure in the system, you have just changed the surface area that is acted on by that pressure. Greater surface area would mean less movement of the piston for a given amount of fluid, but at a greater pressure.
Do I have that backwards?
Pete
Which way this would go. I came up with the opposite, that it would increase rear braking. I have no idea if I'm right, but my logic is this:
You have not changed the pressure in the system, you have just changed the surface area that is acted on by that pressure. Greater surface area would mean less movement of the piston for a given amount of fluid, but at a greater pressure.
Do I have that backwards?
Pete
Mickey Dale
True Classic
I did it on my X and it was a deffo uprgade in my opinion. In fact at that time when I had Tarox drilled and grooved discs on the front and the G88's on the rear, with Ferodo racing pads all round, it was possible to not only lock up the rear wheels with very aggressive driving (not something I would contemplate now), it was possible to do handbrake turns.
I let a mate have a go so he could compare my brakes to his standard X. He was amazed that it was even possible in an X1/9!
Not sure how easy it is to get the larger calipers these days...
Regards,
Mickey
I let a mate have a go so he could compare my brakes to his standard X. He was amazed that it was even possible in an X1/9!
Not sure how easy it is to get the larger calipers these days...
Regards,
Mickey
Rupunzell
Bernice Loui
IMO, the exxe as delivered has too much front brake bias. This results in cooked front brakes when they are used HARD and often.
A larger piston rear caliper goes a long ways to correcting this problem.
IMO, yes a pair of 38mm piston calipers in the rear is definitely an upgrade.
The quick fix for this brake bias problem in a race car or any exxe that does not need parking brakes is to install FRONT BRAKE calipers on all four corners. They are a bolt-on direct fix to the brake bias problem.
We do this on the LeMons racer with Hawk pads (Mazda RX-7 rear) front and stock pads in the rear. The stopping power is enough to out brake just about anything on the track. We still have a braking problem due to heat capacity of the solid rotors. After a few laps of seriously hard braking, we cook the brakes and our braking advantage is significantly reduced... To be upgraded in the future.
Bernice
A larger piston rear caliper goes a long ways to correcting this problem.
IMO, yes a pair of 38mm piston calipers in the rear is definitely an upgrade.
The quick fix for this brake bias problem in a race car or any exxe that does not need parking brakes is to install FRONT BRAKE calipers on all four corners. They are a bolt-on direct fix to the brake bias problem.
We do this on the LeMons racer with Hawk pads (Mazda RX-7 rear) front and stock pads in the rear. The stopping power is enough to out brake just about anything on the track. We still have a braking problem due to heat capacity of the solid rotors. After a few laps of seriously hard braking, we cook the brakes and our braking advantage is significantly reduced... To be upgraded in the future.
Bernice
ianlawson
ian - NZ
Hmmm, kinda disagree there, Karl.....
.....IMHO, larger pistoned rear calipers would definitely result in increased braking effect on the rear wheels , as there would be an increase in the rear brake piston surface area (given that the brake pedal PRESSURE remained the same).
However, the offset of this would be an INCREASE in brake pedal stroke, as the master cyl. would need to displace MORE brake fluid as a result of the increase in rear brake chamber capacity.
That's how I see it, anyway.
cheers, Ian - NZ
.....IMHO, larger pistoned rear calipers would definitely result in increased braking effect on the rear wheels , as there would be an increase in the rear brake piston surface area (given that the brake pedal PRESSURE remained the same).
However, the offset of this would be an INCREASE in brake pedal stroke, as the master cyl. would need to displace MORE brake fluid as a result of the increase in rear brake chamber capacity.
That's how I see it, anyway.
cheers, Ian - NZ
fiatfactory
Steve Cecchele
X19 all types and 124 all types, 34mm piston rear calipers (type 124 cast into caliper body)
Lancia beta scorpion/montecarlo, Fiat 132 and Fiat 125, 38mm piston rear calipers. (type 125 cast into the rear caliper body)
Results in a shift rearwards of the hydraulic bias, the larger piston giving more pressure to the rear pads.
IMO a worthwhile change.
SteveC
kmead
Old enough to know better
Just so I understand:
By changing to a larger rear piston, you increase your mechanical advantage at the rear by increasing the volume of fluid needed to displace the piston. This is accomplished by increased stroke at the pedal to move the increased volume of fluid.
So the displacement at the rear will match the front (presuming the front calipers have the same diameter pistons) and as a result equalizing the brake bias on the car front to rear.
Is this correct or am I missing something else?
By changing to a larger rear piston, you increase your mechanical advantage at the rear by increasing the volume of fluid needed to displace the piston. This is accomplished by increased stroke at the pedal to move the increased volume of fluid.
So the displacement at the rear will match the front (presuming the front calipers have the same diameter pistons) and as a result equalizing the brake bias on the car front to rear.
Is this correct or am I missing something else?
fiatfactory
Steve Cecchele
It doesn't have anything to do with displacement, it pressure and force we're talking about.
An example...
Assume we have a master cylinder that has a piston area of 1 square inch, we have a pedal/fulcrum arrangement that has a mechanical advantage of 5:1 and we apply 100lbs of force to the pedal, the fluid (which is incompressible) "sees" a line pressure of 500lb per square inch.
This pressure (which is equal in all parts of the system) is transferred to our caliper piston, which for this exercise we will say has an area of 2 square inches, it's "seeing" a line pressure behind it of 500lbs PER SQUARE INCH, it has an area of 2 square inches, so it's applying 1000lbs of force to the rear of the brake pad... it hydraulic multiplication.
So if we up the caliper piston size to say 3 square inches, and all else stays the same, the fluid pressure stays the same (with the same MC size and pedal ratio and force applied) at 500 lbs per square inch but the force applied to the back of the pad increases to 1500lbs of force.
Increasing the master cylinder size and displacing more fluid per inch of stroke doesn't equate to more hydraulic force, it actually lessens it....
Another example, using the same pedal ratio of 5:1 and pedal force of 100lbs as the first, if we double the master cylinder size to 2 square inches, the force applied to the master cylinder piston is the same at 500lbs, but the line pressure will halved to 250 lbs per square inch because the piston area has doubled, even though for the same stroke we will shift more fliud.
SteveC
An example...
Assume we have a master cylinder that has a piston area of 1 square inch, we have a pedal/fulcrum arrangement that has a mechanical advantage of 5:1 and we apply 100lbs of force to the pedal, the fluid (which is incompressible) "sees" a line pressure of 500lb per square inch.
This pressure (which is equal in all parts of the system) is transferred to our caliper piston, which for this exercise we will say has an area of 2 square inches, it's "seeing" a line pressure behind it of 500lbs PER SQUARE INCH, it has an area of 2 square inches, so it's applying 1000lbs of force to the rear of the brake pad... it hydraulic multiplication.
So if we up the caliper piston size to say 3 square inches, and all else stays the same, the fluid pressure stays the same (with the same MC size and pedal ratio and force applied) at 500 lbs per square inch but the force applied to the back of the pad increases to 1500lbs of force.
Increasing the master cylinder size and displacing more fluid per inch of stroke doesn't equate to more hydraulic force, it actually lessens it....
Another example, using the same pedal ratio of 5:1 and pedal force of 100lbs as the first, if we double the master cylinder size to 2 square inches, the force applied to the master cylinder piston is the same at 500lbs, but the line pressure will halved to 250 lbs per square inch because the piston area has doubled, even though for the same stroke we will shift more fliud.
SteveC
Pete Whitstone
True Classic
Rupunzell
Bernice Loui
It is basically a lever... think of the smaller cylinder as the long arm of the lever and the larger cylinder as the short arm of the lever..
Read here.. Unit one & Pascal's Law:
http://www.edgeroamer.com/sweethaven/mechanics/hydraulics01/
One requirement, fluid must not compress under pressure or the force transmission will be significantly reduce. Transmitted force will be absorbed by the fluid compression or any other part of the system that can compress. This is why those Teflon / braid brake hoses result in firmer brake pedal feel over rubber.
Bernice
Read here.. Unit one & Pascal's Law:
http://www.edgeroamer.com/sweethaven/mechanics/hydraulics01/
One requirement, fluid must not compress under pressure or the force transmission will be significantly reduce. Transmitted force will be absorbed by the fluid compression or any other part of the system that can compress. This is why those Teflon / braid brake hoses result in firmer brake pedal feel over rubber.
Bernice
Rupunzell
Bernice Loui
No, no brake proportioning valve required. The resulting brake balance might surprise you.
This is another one of those under spoken advantages of a mid engine car. Weight balance helps braking and acceleration.
The stock brake bias is desirable to prevent rear brake lock up which could result in some drivers loosing control of the car under difficult conditions. Lock up the front brakes.. sort of stay in control, lock up the rears, and the car might swap ends.. bad.
Bernice
This is another one of those under spoken advantages of a mid engine car. Weight balance helps braking and acceleration.
The stock brake bias is desirable to prevent rear brake lock up which could result in some drivers loosing control of the car under difficult conditions. Lock up the front brakes.. sort of stay in control, lock up the rears, and the car might swap ends.. bad.
Bernice
Mark Plaia
True Classic
Interesting.....
No, no brake proportioning valve required. The resulting brake balance might surprise you.
Building the Dallara racer, we also put front calipers in the rear. However, for that car, the proportioning valve was needed. I took a best guesstimate of the setting when the car was built (limiting pressure to the rear calipers) and tested later. When it was time to change tires, I did a series of brake lockup tests to evaluate the various settings. (Did not want to take a chance on flat spotting good tires) I ended up leaving it where it was originally set.
Ciao,
No, no brake proportioning valve required. The resulting brake balance might surprise you.
Building the Dallara racer, we also put front calipers in the rear. However, for that car, the proportioning valve was needed. I took a best guesstimate of the setting when the car was built (limiting pressure to the rear calipers) and tested later. When it was time to change tires, I did a series of brake lockup tests to evaluate the various settings. (Did not want to take a chance on flat spotting good tires) I ended up leaving it where it was originally set.
Ciao,
thorpeyx1/9
thorpey
its a great upgrade,well worth it changes the front/rear brake bias by 8% to the rear,i got them on mine
paul
XjunkieNL
Thanks for the explanation, Steve.
Hydraulics seem to have its own logic.
If it was a test I would have many wrong answers
Hydraulics seem to have its own logic.
If it was a test I would have many wrong answers
kmead
Old enough to know better
Thanks Bernice, although I said it differently that is what I meant. Thanks for the link.
The smaller MC pushing its fixed amount of fluid per distance of stroke with a relatively fixed force applied, your leg, you are increasing the force applied to the pad by the larger caliper piston as it moves less but with greater force.
The multiplication of applied force is a function of displacement of the one (the MC) to the other displacement of the other (caliper piston).
http://www.edgeroamer.com/sweethaven/mechanics/hydraulics01/default.asp?iNum=0102
In any case, thanks to all for the lesson, I understand this much more clearly and hopefully others do as well.
As someone who has had a car with an issue with rear brake bias, I caution folks about making this change as the results can be very problematic, particularly in wet weather. I stand by my other points regarding tires and so on despite my clear error in logic/application.
The smaller MC pushing its fixed amount of fluid per distance of stroke with a relatively fixed force applied, your leg, you are increasing the force applied to the pad by the larger caliper piston as it moves less but with greater force.
The multiplication of applied force is a function of displacement of the one (the MC) to the other displacement of the other (caliper piston).
http://www.edgeroamer.com/sweethaven/mechanics/hydraulics01/default.asp?iNum=0102
In any case, thanks to all for the lesson, I understand this much more clearly and hopefully others do as well.
As someone who has had a car with an issue with rear brake bias, I caution folks about making this change as the results can be very problematic, particularly in wet weather. I stand by my other points regarding tires and so on despite my clear error in logic/application.
brakes
Hi
I got 132s fitted on the back and braided hoses both are a good move, one question i lost my rear brakes, hit something and pushed the rear brake hose against the tyre, but i lost the front brakes as well i thought they were dual circuit so if youn lost one set you kept the other.
Or is this normal one out all out
Cheers
Hi
I got 132s fitted on the back and braided hoses both are a good move, one question i lost my rear brakes, hit something and pushed the rear brake hose against the tyre, but i lost the front brakes as well i thought they were dual circuit so if youn lost one set you kept the other.
Or is this normal one out all out
Cheers
