RF-95 Tilton MC Conversion

[Rick Iverson]

Gent;

I bought a new remote Tilton three cup reservoir, simply because topping off the three factory Girling reservoirs is next to impossible.

LD20 ICP calipers, both fore and aft. Will anyone please help me with the math and suggestions on the correct Tilton MCs?

[alangbaker]

Gent;

I bought a new remote Tilton three cup reservoir, simply because topping off the three factory Girling reservoirs is next to impossible.

LD20 ICP calipers, both fore and aft. Will anyone please help me with the math and suggestions on the correct Tilton MCs?

I can't help with the part number for a particular master cylinder, but when I was asking questions about master cylinder sizes for my RF98 with LD20s all around, I was told that 0.7"F/0.75"R or or possibly 0.625"F/0.7"R

Those numbers would probably work provided your callipers are all the same slave cylinder diameter at all four corners.

[Mike B]

I can't help with the part number for a particular master cylinder, but when I was asking questions about master cylinder sizes for my RF98 with LD20s all around, I was told that 0.7"F/0.75"R or or possibly 0.625"F/0.7"R

Those numbers would probably work provided your callipers are all the same slave cylinder diameter at all four corners.

Rick,
I just emailed a spreadsheet calculator to determine your MC sizes. I'm using .70"F/.75"R on my P2 with LD20s all around, which agrees with Alan's suggestion.

[stvsxm]

Gent;

I bought a new remote Tilton three cup reservoir, simply because topping off the three factory Girling reservoirs is next to impossible.

LD20 ICP calipers, both fore and aft. Will anyone please help me with the math and suggestions on the correct Tilton MCs?

hi rick , this should be a very simple answer that you would certainly know so i guess i am not understanding the question.... so lets at at the beginning....

1) you are just changing cyls ? why not just install the same sizes you have ? or what am i missing ?

2) if you are changing lots of stuff and want to get back to the same place then thats a dif story.... the answer is to keep the hydraulic ratios the same and those ratios are defined by the area of the calipur pistons total divided by the area of the the master cylider.... simple example:

master cyl bore area is pi x r squared so if yo have a 3/4 master the area is .375 x .375x 3.1417 or .4418 sq inches.

now...( for this example ) if you have one single piston calipur of 2" diamer then the area of that piston is 1 x 1 x 3.1417 or 3.1417 sq inches...

the hydraulic ratio is the area of the piston divided by the area of the cylinder or 3.1417 / .4418 or 7.11 . in practical terms that means you have a hydraulic multiplier of 7.11 or if you apply 1 llb of force to the master you get 7.11 lbs of force at the calipur.

now... if you like the way the brakes have always worked yet you want to change one of the components then you have to make that ratio come out the same.... if you put cals on with larger pistons and keep the master the same to get a greater ratio and two things will happen.... first those brake will make more force per unit input because of the greater ratio and second you have a much longer and often softer pedal travel because you have to move a greater volume of fluid in the stroke to get the larger volume in the cal to move now.... the soft pedalo result is not a function of the hydraulics... its a function of the pedal geometry. the more the pedal rotates and gets over center, the less linear travel you get as a function of rotational angle... so to compensate you end up needing a starting angle more " leaning back toward the drive so that you get max stroke as the pedal comes to tdc and " locks up". remember... everything you change has a consequence somewhere else.

in general, but very specifically.... increasing the master size give you a much harder pedal but requires much more effort. decreasing the master size gives you a very sensitive pedal requiring light effort but a much longer stroke which scares the **** out of a lot of people. the same is true in reverse with calipur piston area. increase the area and that reduces the effort, increase the unit braking force but increases the stroke and decreasing the area increases the effort and reduces the both the braking force and stroke

so the answer you want is is first determined by the mechanical specs of what you have versus the mechanical specs of what you are going to all blended into the question... do you like the way the brakes work now ?

steven

adendum: don't lose sight of the mechanical aspects. yes ... its a hydraulic system but , using an absurd example.... lets say you end up with a 7/8 cyl on one side and a 5/8 on the other.... now you have to wind the balance bar all the way to one side and now one cyly... the 5/8 ... wants to travel all the way to the front bulkhead and the 7/8 wants to move about .001. that means you balance bar is now at some crazy angle and will make your pedal feel weird all the time. so... try to keep both masters roughly the same size... getting a big split can send you seriously down the garden path.

[bassracer]

Sharing my recent experience with this. I changed my RF95 (FF) from 0.7/0.75 to 0.625/0.75 because off too much rear bias I couldn't tune out with the adjuster.

During the change I also found that I did not have my pushrods set correctly to have the bias bar even under pressure. This was something I learned after reading a combination of instructions on bias bar adjusters as well as Carrol Smith books? Correcting this with the MC change has eliminated my concern - maybe too much front bias thru the adjustable range now. Through more testing I may return 0.7 Front.