viperbob

There were some discussion in the past on the merits of the Euro RS Red calipers for the rears of our cars. As I have upgraded to 14" rotors with Brembo F50s, I needed something to balance the rear. With the help of Brembo making sure the balance was proper, I went with the factory RSs. I thought I would post a picture of the difference in piston sizes between the TT and the RS. Much more of a diff than I would have thought. Actually, even the smaller piston on the RS is larger than either of the TTs.

Enjoy


Factory TT





Euro RS

DJF1

Nice... Thxs for posting!

nels415

Bob,

I have to show you how to set your dig cam on macro mode.

-nelson

JohnM

Bob,

Would you mind measuring the piston diameters on the TT rear calipers? Are they 30 & 28mm or both 28mm? There has been some conflicting factory info on that, they were 30/28 at one time but curious to know what is used on current parts. Since the smaller RS piston is 30mm your comment suggests that TT caliper is 28/28.

Roygarth

Does this mean the RS brakes are more powerful than the TT?

clubsport1

Piers, factor in the difference in weight and the answer is a resounding YES!

viperbob

John M,

Sorry, but the TT calipers left earlier today for the home of another Rennlister. Maybe he can measure the pisons before he installs them. I did however try to install the brake spider from the TT (which fit equally into both pistons) and did put it into the RS caliper and it did not fit as it was too loose. This would leave me to believe that the 30mm of the RS was larger than both pistons on the TT..

Nelson,

Yeah, Yeah. I was boxing them up late on Monday and did not look at the pictures until last night to make the post. By then it was too late as they were winding (or driving) their way to South Carolina...

Roygarth

Yes, but are the actual brakes/calipers more powerful?

Gert

The rear calipers of the Turbo have 34/28mm pistons while the RS has 34/36mm.

JohnM

Hi Gert,

Did you mean to write 30/28 and 30/36 respectively? I know those are the workshop manual figures, but from Bob's pic both pistons on the TT rear look like they are the same size, and smaller than the RS's 30mm piston.

Greg Fishman

Here is a chart http://www.pelicanparts.com/MotorCity/wmv/brakes.htm. If accurate it shows the measurements of the rear pistons: RS with a 36/30 and the TT with a 30/28.

chris walrod

The larger the piston diameter, or area, the more working pressure needed to produce a given amount of work. However, I dont think in a brake-boosted car (all 993's) this is an issue. Brake balance and the feel for modulation is the advantages gained by going to larger piston diameters and/or larger master cylinder diameter.

My 95 car's brakes are stock C2 calipers and I feel I could use more rear brakes. I would like to creep the bias aft, but havent decided which route to this with (different calipers or higher pressure rated relief valve)?

JohnM

Hi Greg,

When I last coresponded with Bill he was similarly unsure re the rear caliper specs as some data says 30/28, some says 28/28 - I think his page used to say 28/28, can't swear to that though. Wish I'd remembered to measure mine before they went on. Doh!

Viken

Gert's figures are correct. Turbo/C4S big reds rears have 34/28 mm pistons while the RS's had 34/36 mm. Also, cars equipped with big reds (Turbo/C4S), had an additional proportioning valve.

JohnM

Odd, as that is not the data that is listed in the 993 workshop manual which states 36/30 for the RS rear, 30/28 for the C4S and TT, 30/28 for the C4 and 34/30 for the Carrera. The RS Information Technik supplement also says 36/30 for the RS rear, and from Bob's pic of the TT rear there is no way those pistons are as different from each other as 34/28.

Has there been a change in the spec at some point?