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Do You Need A Bigger Master Cylinder Or Braided Lines With A Big Disc Kit?
This question comes up on nearly every big disc kit enquiry, and the honest answer is usually no. A bigger disc does not, on its own, ask more of your braking system. It is the caliper, not the disc, that decides how much brake fluid gets pushed around and how the pedal feels underfoot.
The confusion comes from the fact that we sell two different things under names that sound similar. A big disc kit fits a larger disc and a bracket to relocate your original caliper over it. A full big brake kit replaces the caliper too, usually with more pistons and a bigger total piston area. Only one of those changes the fluid volume your master cylinder has to move, and it is not the disc.
- A big disc kit keeps your original caliper, so fluid volume and pedal feel do not change and a bigger master cylinder is not needed
- Pedal feel and fluid volume are set by caliper piston area and count, not by disc diameter
- A full caliper conversion with more or bigger pistons raises fluid demand and often benefits from braided lines
- Braided lines fix hose expansion under pressure, which is a different problem to master cylinder sizing, so the two are not interchangeable fixes
What is on this page
- What actually changes when you fit a bigger disc
- Big disc kit or full big brake kit: check which one you are actually buying
- Why the master cylinder usually stays exactly as it is
- When braided lines actually earn their keep
- When a bigger master cylinder is actually worth discussing
- Common questions
- What we would actually fit
What actually changes when you fit a bigger disc
Braking force at the wheel comes from clamping force multiplied by the effective radius of the disc. Make the disc bigger and you increase that radius, which increases the torque the same clamping force can generate, and you add thermal mass to cope with heat. Neither of those changes has anything to do with how much brake fluid the caliper needs to move to close the gap between pad and disc.
That gap, and the volume of fluid needed to close it, is set by the caliper: how many pistons it has and how big they are. Swap the disc for a bigger one and bolt the same caliper onto a bracket over it, and the caliper’s piston area has not moved. The master cylinder is still pushing the same volume of fluid into the same pistons. Pedal travel and pedal effort stay where they were before the disc went bigger.
Big disc kit or full big brake kit: check which one you are actually buying
The two names get used loosely, including sometimes by us, so it is worth being precise about what each one is. Take our Tarox Audi S3 (8L) 300mm rear big disc kit: the listing is explicit that it uses a relocation bracket to keep your original caliper, handbrake included, over a larger two piece disc. Nothing about the caliper changes on that kit, so nothing about fluid volume changes either.
Compare that with a full conversion such as the Brembo 355mm 6 piston kit for the Mercedes C-Class (W204). That kit replaces the caliper with a 6 piston unit as well as fitting a bigger disc. Six pistons means more total piston area than the standard caliper it replaces, and more piston area means more fluid has to move to take up the same running clearance. That is the situation where the master cylinder question is actually worth asking. The disc-only kit is not.
Why the master cylinder usually stays exactly as it is
A master cylinder is sized against caliper piston area and pedal ratio, not disc diameter. A given pedal effort produces a given hydraulic pressure at the master cylinder bore, and that pressure acts across whatever total piston area sits in the calipers at the other end. Change the disc and leave the caliper alone, and that relationship has not moved, so there is nothing for the master cylinder to catch up with.
This is standard brake engineering, not a house opinion. Master cylinder sizing guides used across the performance and race brake industry work the same way: bore gets matched to caliper piston area and pedal ratio, and disc diameter does not enter the calculation at all.
When braided lines actually earn their keep
Standard rubber brake hoses expand slightly under pressure. That expansion absorbs a small amount of your pedal travel before it ever reaches the pads, and it is more noticeable the harder and more repeatedly you brake, which is exactly what changes on a full caliper conversion built for track use. Braided, PTFE lined hoses resist that expansion, so more of the pedal travel you put in reaches the pads instead of stretching a hose.
On a disc-only big disc kit, the caliper and its hose have not changed, so there is rarely a pedal problem to fix, which is why braided lines are not something we push on that kit. On a full conversion, particularly one with more pistons and a harder pad compound for track use, braided lines are the upgrade that is actually worth having. Some brands, Tarox among them, fit braided hoses as standard on their complete conversion kits. Others price hoses separately so you add them to the order and choose the spec yourself.
When a bigger master cylinder is actually worth discussing
The exception is a genuinely large jump in caliper piston area, for example moving from a stock single or twin piston caliper to an 8 piston conversion with a lot more total piston area behind it. That much extra volume can outrun a stock master cylinder’s stroke, leaving the pedal feeling long even with braided lines fitted. That is a real conversation to have before you order, but it is about the size of the caliper jump, not the size of the disc, and it is not the situation most big disc kit buyers, or most six piston conversion buyers, are actually in.
| Big disc kit | Full big brake kit | |
|---|---|---|
| Caliper | Original caliper retained on a relocation bracket | Caliper replaced, usually with more pistons |
| Disc | Larger disc and bell | Larger disc, matched to the new caliper |
| Fluid volume needed | Unchanged | Increases with piston count and size |
| Master cylinder | No change needed | Occasionally needed on a large piston area jump |
| Braided lines | Rarely necessary | Worth having, some kits include them as standard |
Example prices correct on 6 September 2026: Tarox Audi S3 (8L) 300mm rear big disc kit, 1,179.60 pounds inc VAT. Brembo Mercedes C-Class (W204) 355mm 6 piston conversion kit, 4,271.40 pounds inc VAT.
Common questions
Does a bigger disc on its own make the pedal feel different?
Not normally. If the caliper is unchanged, the fluid volume the master cylinder has to move is unchanged, so pedal travel and effort stay the same.
What is the real difference between a big disc kit and a full big brake kit?
A big disc kit fits a larger disc and keeps your original caliper on a relocation bracket. A full big brake kit replaces the caliper too, usually with more pistons, which is what actually changes fluid volume and pedal feel.
When should I add braided lines?
When you are fitting or already running a full caliper conversion, especially one used hard or on track. They stop the hose expanding under pressure, which tightens up a pedal that would otherwise feel long.
When would I actually need a bigger master cylinder?
Only on a genuinely large jump in caliper piston area, for example moving several piston sizes and counts up in one go. It is a conversation to have with us before you order, not something a disc-only kit needs.
Do all kits include braided lines and pads?
It depends on the brand. Some brands, Tarox among them, fit braided hoses as standard on their complete conversion kits. Others price hoses and pads separately so you choose the compound. Check the specific listing rather than assuming.
Will a big disc kit affect my ABS or handbrake?
A genuine big disc kit keeps the original caliper, and where the listing says so, the handbrake mechanism works exactly as before. Confirm this against the specific listing rather than assuming it, and check with us if in doubt.
What we would actually fit
If you are fitting a straight big disc kit, leave the master cylinder alone. Nothing about the caliper has changed, so nothing about fluid volume or pedal feel has changed either. Braided lines are a nice to have here at best, not a fix for a problem the kit does not create.
If you are fitting a full caliper conversion, budget for braided lines, particularly if the car sees track use, because that is where hose expansion actually costs you pedal feel. Only start asking about a bigger master cylinder if you are jumping a long way up in caliper piston area, and even then, talk to us first. Call Garreth or Cameron on 0115 9893488 with the kit you are looking at and we will tell you honestly whether the master cylinder needs to change or not.