Type-R rear brakes on Si

[circuit.heart]

The thinking here was to do a basic cheap parts swap upgrade on the rear to balance out adding a BBK to the front. Not on its own.

If the BBK was designed properly for the car as a standalone product, it shouldn't be increasing front brake torque to begin with. Adding the large rear rotor is still going to throw off your brake bias.

My FK7 has been within 0.2s of a Type R track record and it has never had an issue running 100% stock rear rotors, calipers and pads paired to basic DC5R Brembos up front. You can upsize the rear rotor all you want, paired to whatever front brakes you want, but you either have to math out (piston size, rotor size) how to set the correct bias for the car's grip level or compensate with compound choice.

Sponsored

 

[KingOfBrussels]

If the BBK was designed properly for the car as a standalone product, it shouldn't be increasing front brake torque to begin with. Adding the large rear rotor is still going to throw off your brake bias.

I agree with you, and OP has a not exactly properly designed Genesis Coupe 4-piston Brembo conversion. Those calipers were chosen because they happen to bolt up to the hubs, not because they provide correct brake bias.

Not going to do a full brake bias calculation because I don't have numbers like booster ratio and coefficients of friction of the pads and tires. But on a basic level, any of these BBKs go to a larger diameter front rotor which would need less front axle piston area to maintain stock-like brake bias.

Plugging the specs for a few calipers into this calculator gives the following results.

https://brakepower.com/help_abc_27_PAC_t.htm

Si - sliding caliper w/ single 57mm piston = 10,202 mm^2 front axle piston area
Wilwood 6-piston - 2 35mm pistons; 4 28.5mm pistons = 8,947 mm^2
Genesis Brembo - 4 42mm pistons = 11,078 mm^2

So for example the Wilwood kit does go down in piston area vs. the stock Si calipers but the Genesis Brembo caliper does not.

The Genesis Brembo and Acura RL caliper conversions, which both have 4 42mm pistons in their calipers, are relatively cheaper than actual BBKs. But it's not ideal brake bias vs. something with properly sized caliper pistons.

In theory a bigger rear rotor could help bring the bias of the Genesis Brembo or RL caliper kit back closer to stock but the parts don't exist for that.

Me personally I'd rather go for a properly designed front BBK and stick to upgrading the pads/rotors in the stock rear size along with proper hi-temp fluid. But hey this is at least an interesting thought experiment.

 

[Hondanickx]

The easiest way would be to redrill the CTR rotors which can be done really easy cause it's also a 5 holes disc ,just redrill in between the 5x120 holes.I'm doing the same with some Mercedes rotors which are 5x112.You need to look at the rotor height ,that determines the offset of the disc and also the offset of the caliper.

As far as the brake bias goes ,yes most cheap BBK kits people make here they don't look into the increased brake bias they have.But also most don't really have any problems with the front brakes locking up either.So i don't know if the abs unit regulates this or not.

The genesis calipers are 8.6% larger in piston area compared to the SI/or regular civic 57mm piston. Using the nissan rogue rotor which is 320mm afaik ,makes the disc 13.5% bigger then regular civics and 2.6% bigger on a Si. Total would be a front brake increase of 22.1% on a regular civic and 11.2% on a Si .Ideal piston sizes for a single 57mm piston is 36/40mm which the DC5 integra has , and porsche Boxster S (3.2L) ,renault megane RS 3 in europe,and some other.

Another thing to look into is the SI has bigger brakes in the front 312/282mm and also uses a different brake proportion valve .The regular civics have smaller brakes and they are more matched being 282/262. So using the for example genesis calipers on a Si or on a regular civic will effect more on a regular civic then on a SI.The SI allready has an abs unit that compensates for the bigger brake bias in the front.

PS: The european 10thgen civics all have 293mm disc in front and 282mm discs in the rear.

 

[teders]

Very interesting thread you guys have here, and particularly relevant to me right now. I just upgraded to the 27won BBK after finding the limit of the stock Si calipers on track. I had tried a few different pad compounds, and even the most aggressive i found (Raybestos ST43) was not going to be an ideal solution because it would wear so unevenly. This was mostly due to the nature of single piston calipers. The piston side pad would be significantly thinner, unevenly worn, and also warped at the end of a hard day on track. Additionally, the stock Si calipers just dont have many pad options as far as race applications.

I was considering the Genesis Brembo conversion, but ultimately found a pretty good deal on a 27won kit, which has yet to be delivered. Would be interested to see if 27won took the piston surface area factor into account when they designed their kit. I'm not seeing piston dimensions online, so i'll take measurements and post in here when they arrive.

The other thing that ultimately swayed me towards the 27won kit is the fact that the rotors are 330mm/28, which is a significant increase in size over the stock rotors. After speaking with Kevin Boehm a little bit about his car (fyi hes a pro Honda racer who races a 10th gen si in SCCA STU class, and also races the Honda TCA car), i learned that his ideal rotor size for the civic is 330/30, as everything else he tried would just overheat and get worn too quickly. Now granted he's a pro driver who is asking a LOT more from the car than most enthusiast level drivers, myself included. The Genesis conversion uses 320/28 rotors i believe.

Here are some pics of the Raybestos pads Ive got. This was after one day on Summit Point Circuit. Not terrible wear pattern, but at $260 for the front set, using these on a single piston caliper seems wasteful.

 

[Hondanickx]

Very interesting thread you guys have here, and particularly relevant to me right now. I just upgraded to the 27won BBK after finding the limit of the stock Si calipers on track. I had tried a few different pad compounds, and even the most aggressive i found (Raybestos ST43) was not going to be an ideal solution because it would wear so unevenly. This was mostly due to the nature of single piston calipers. The piston side pad would be significantly thinner, unevenly worn, and also warped at the end of a hard day on track. Additionally, the stock Si calipers just dont have many pad options as far as race applications.

I was considering the Genesis Brembo conversion, but ultimately found a pretty good deal on a 27won kit, which has yet to be delivered. Would be interested to see if 27won took the piston surface area factor into account when they designed their kit. I'm not seeing piston dimensions online, so i'll take measurements and post in here when they arrive.

The other thing that ultimately swayed me towards the 27won kit is the fact that the rotors are 330mm/28, which is a significant increase in size over the stock rotors. After speaking with Kevin Boehm a little bit about his car (fyi hes a pro Honda racer who races a 10th gen si in SCCA STU class, and also races the Honda TCA car), i learned that his ideal rotor size for the civic is 330/30, as everything else he tried would just overheat and get worn too quickly. Now granted he's a pro driver who is asking a LOT more from the car than most enthusiast level drivers, myself included. The Genesis conversion uses 320/28 rotors i believe.

Here are some pics of the Raybestos pads Ive got. This was after one day on Summit Point Circuit. Not terrible wear pattern, but at $260 for the front set, using these on a single piston caliper seems wasteful.

27won is 36/40mm Piston ?

 

[PSPEC]

I am making a rear bbk conversion if anyone is interested. Uses stock caliper and CTR rear caliper brackets. I made a custom cast iron rear rotor that fits fk7 hub and CTR (fk8) caliper bracket. You can use any 10th gen rear pad.

Any 10th gen non type r rear hub
Any 10th gen rear caliper
Any 10th gen rear pad
fk8 / ctr rear caliper brackets
My custom cast iron rear rotors

Upgrade to 305mm x 11mm rear rotor from stock 262 x 9mm rear rotor
Retains electric parking brake

Turns non type r rear brakes into type r spec rear brakes.

Sponsored