Trackday at Mantorp - test of slicks

A very hot day at Mantorp Park again - with slicks for my first time!

The lap times where not that much better, only about a second. A bit disappointed actually. But probably it is my driving to blame, I'm (yet) not capable to take advantage on the extra grip! I felt the biggest difference in one of the high speed corners (the fast left before the hairpin), where I now could keep the pedal floored - when I dared!



Today's Best: 1:26.9
Most laps where constantly around  ~1:27.5
Previous all time best with ACB10: 1:27.9

The day that started with oversteer problems, especially when trailbraking into corners. Reduced when lowered rear pressure to 18.5 psi. A contributing factor could have been the new front discs and pads messing up my brake balance. Overall the car balance was good - I just need to learn how to drive faster!

Avon 15" ACB0 crossply slicks (see previous post)

Front: 19 psi
Rear: 18.5 psi

At the end of the day the engine started to sound loud! The reason was a cracked exhaust manifold. I left the car for the tech guys at Mantorp Park and hopefully they'll be able to weld it together in situ. The manifold cracked most likely because the rear silencer bracket went loose, again, which caused stress on the manifold.

Trackday slicks part #1

I've bought a set of 15" Avon crossply slicks!

For a while I've been tempted to try slicks. 15" slicks are expensive and hard to find second hand. Fitting 13" rims is not possible on the road version of the CSR without modifying the rear brake calipers. MOG racing sells a kit for conversion to 13" rears, but it is rather expensive. I've also considered to just shave the caliper with a grinder, but after a bit of measuring I thought it would be too much of shaving to feel comfortable.

I'd also like to keep my crossply-setup so I can go back to ACB10 without too much hassle, so crossply slicks would be of preference, but many people recommends radial slicks.

Anyway the urge for slicks became too great to resist so until I feel comfortable on spending money on new rims and conversion kit I bought a set of Avon 15" crossply slicks. A financial disaster and probably not a very good idea for the long run but I couldn't resist.

Comparison between my current ACB10 and ACB0 slick tyres:

	Tread	Diameter	Compound
ACB10 8.0/22.0-15 (215/40-15)	206 mm	561 mm	?
ACB10 7.0/22.0-15 (195/45-15)	180 mm	551 mm	?
ACB0 8.7/21.5-15	213 mm	561 mm	A56
ACB0 7.0/21.5-15	177 mm	561 mm	A24

ACB10 tread rear/front:	1.14
ACB0 tread rear/front:	1.20
ACB10 rake:	rear 5mm higher
ACB0 rake:	0 mm

More rubber on the rears and less rake. Maybe I'll get a bit of understeer?

Sources:
http://www.avonracing.com/
http://csr.informe.com/forum/csr-track-day-slicks-dt66.html
http://www.pistonheads.co.uk/gassing/topic.asp?h=0&f=101&t=1010028&mid=179024&nmt=CSR+Slicks
http://www.westermann-motorsport.com/shop/product_info.php?info=p300_Conversion-for-CSR-to-13-.html

Wheel alignment check

My current wheel alignment, measured in my garage. Cross-ply setup.

	Front	Rear
Toe	0.5° out	0.7° in	per wheel
Camber	-1.25°	-0.25°	±0.25°
ARB	Hard setting	-
Tyre	195/45-15	215/40-15	ACB10 road legal
Pressure	19 psi	19 psi	warm
Rims	6.5"-15	9"-15

Rear left wear

Front left wear

The wear in the middle came after running a bit too high pressure on Mantorp earlier this year. I think 19 psi is just right. I know that sounds low, but it works for me.

My rear 9" rims are too wide for the ACB10 according to Avon, but it works ok.

New front discs and pads

Pagid RS14

Apparently I didn't change the front pads in time, so one of the discs had some ugly grooves a bit too deep for my liking. They're probably fine but I changed them anyway together with the pads. I also had a brake judder I was hoping to finally get rid of.

I found my left brake caliper had scars from a wheel bearing miss-hap a couple of years ago. I suspect that could have caused the pads to jam and that the brakes did not take evenly on the fronts. The pads on the left wheel was only half as much worn as on the right! Glad I found it and was easy to fix with a rasp.

After a test ride on a dark highway I found all brake judder was gone! It seems the new brakes has a more distinct "bite-point" than before. I don't know why because I had exactly the same model of pads and disc before. Maybe that's just while they're new.

AP Racing 10" vented disc

PAGID Pads 20349-RS14 (for the AP-Racing CP7600 4-pot caliper) €177 + VAT from Nimex Motorsport in Germany.

Brake disc AP-Racing CP3707-103P from Caterham £150 * 2 + VAT

Brake disc to hub torque: 35Nm + loctite

Brake caliper torque: 47Nm

Castellated nut torque: hand tight

Wheel bolts torque: 74Nm

Clean the new discs with brake cleaner

Grease bearings with high temperature grease while you have the hubs removed.

It is also a good idea to air the brakes while you have the wheels off.

Both the discs and the pads need to be bedded in.

UPDATE: Meteor Motorsport now sells AP-discs for Caterham!