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!

Another lonely day at Mantorp

A nice and sunny day at Mantorp Park! The day started out well being the faster of the two cars on the track.

...then this guy came along with his brand new Formula Renault...

The driver is only 15 years old and compete at european level against adults! As a comparison he had lap times around low 1:15 and I got at best high 1:27. When I was 15 I had a moped...

Anyway the day went on well and I had time to experiment with some toe settings. Previously I had neutral toe both rear and front. This day I first tried some toe-in on the rears which really made the car more stable and predictable. I didn't had the same problems with corner exit over-steer as before and my lap times went down. Later I also tried some toe-out on the fronts which made the car easier to rotate on corner entry. No difference on the lap times but it felt good and I think it is an improvement. My top speed was really low this day but I don't know if it depends on the toe settings or the fact it was a bit windy.



I polished my personal best with a few hundreds, but my tyres are long gone and I think with a fresh set I can really improve the time!

The day ended when I ran out of battery and the engine stopped! Apparently I have a bad connector to the alternator.

Tyre pressure 19 psi warm all around.

Mantorp

It was pretty lonely this day, three cars total

This years first track day was on Mantorp Park.

I had the opportunity to talk with a professional race team engineer about my wheel alignment and got the suggestion to make a small increase in negative camber all around, but overall the settings are good.

Best lap time 1.28,66 - No personal best but I blame the dirt after the long straight and in the the fast left after the hill. The race team I shared the track with said they lost 2-2.5 seconds because of the dirt and lack of rubber on the track. I doubt I lost that much time but maybe a second or so.

I experienced that when applying power after a corner that I lost traction on the rears, but when applying even more power I got the traction back!? Is it the LSD that locks up too late? Or is it just something to accept and learn to live with?

Avon ACB10
19.5 psi all around warm pressure  (It was too much! Remember until next  time)

New battery

My previous battery was a cheap Biltema gel battery. It worked ok in the beginning, even if I had a few anoying moments when there wasn't enough power to start the engine. Now one year later it can't even turn over the engine even when fully charged. So after an embarrassing incident at the grocery store a new battery was necessary, this time one with better quality - I hope.

Odyssey Extreme Racing 25

Found it on eBay for £97 inc tax.

The weight is 7.0 kg and about the same as my old battery, but a bit smaller.

Spring!

This years first drive! Still very chilly outside and the tyres never got temperature, but what a great feeling anyway! But why is that every spring you're about to wet your pants when you push the accelerator, but in the autumn all you can think of is how to make the car go faster?

I went by a scale: 600kg +/-10 kg with 1/4 tank of petrol and windscreen on.

I need a new battery! I couldn't start the car even if it was fully charged. No other problems found.

Front bump steer

There is plenty of information about bump steer to be found on the internet. Basically bump steer is when the toe alignment changes during bump, ie when the suspension compress.

Here is an article explaining how to correct bump steer on Caterhams. 

There are lots of different techniques to measure bump steer. I used a construction laser level which projects a line when you point it on a surface.

I jacked up the car, removed the wheels and disconnected the link to the dampers on the lower a-arm making it possible to raise (bump) the wheels by hand.

Then I put my laser level firmly on brake disc with one hand and pointed the laser to it to the wall in front of the car. When I raised the wheel with my other hand and watched how the line moved on the concrete floor. With zero bump steer the line should not move sideways. To  be more accurate you can reverse the level and look backwards. The movement (if any) should be the same backwards as forwards.

There are many other ways to measure bump steer. One is explained in the article above, another one of the more clever ways I've seen is by using a mirror to remove the camber-gain effect.

You adjust bump steer by adding or removing spacers under the steering rack. It turned out that I had quite a lot bump steer on the front right and I ended up by removing one big 4mm spacer. For me it was a bit of a pain to undo the steering rack clamps because the dampers is making it hard to access the hex bolts from above, but eventually I got it apart.

If you change the steering rack height, you have to reset the toe alignment! I aim for zero degrees front toe. Some say a bit of toe out won't hurt and will give the car better turn in.

Note to self: Never undo the rod-end-to-upright nut! It's a real pain to get back!

Cross-ply rear camber

Crossply tyres such as Avon ACB10 don't need as much negative camber as radial tyres, CR500, 888 etc.

On the CSR you adjust the rear camber by using spacers. But what happens if your bolts through the spacers are not long enough?

The wheels fall off!!! Well, almost. This is what happend to me at the "NGK"-turn at Knutstorp last spring. I'm glad I stayed on the track!


This is how the rear suspension looks like:

What happened was the threads on the two horizontal bolts ripped, which caused the two vertical bolts to rip as well.

So if you have a cross-ply set-up with a bit less negative camber, check that you have enough threads left on the horizontal bolts, and maybe replace them with something longer.

Brake fluid change

Replaced the brake fluid. Used the same fluid as last time - ATE Blue racing.
Because I accidentally got some air into the system I had to remove the rear callipers and shake them around to get all air out.

I use Pagid RS14 pads on the front, and RS4-2 on the rear by recommendations from Pagid technical support. It gives me a good balance, but next time I might try one step more aggressive on the rear.

The Pagid part numbers are 20349 for the front AP-racing 4 pot calliper and 1158 for the Audi (?) rear.

Thanks to Levin Racing for their patience.

Cracked clutch disc - engine out!

I always had troubles downshifting at high RPM. Always when trying to engage second gear when going into an hairpin I had to struggle until the revs dropped. My upshifts weren't that fast either, but within reason. After consulting lots of people I just couldn't diagnose what the problem was. Everything went smooth when standing still and at normal road driving.

One day I had enough and decided to take the engine out and investigate what the problem was.

Cracked clutch disc. At high RPMs the centrifugal force would make the loose part of the disc move outward and touch the clutch cover, making it not fully disengage.

So what I learned about taking the engine out was:

• Write down and take photos of all connectors and hoses, and where they should be.
• Take your time and have someone to help you!
• You need a crane.
• Be sure that you put the gearbox mount at the right way when the engine is going back in, or you have to take it out again (ask me how I know this).
• There is a way to get the engine out. The exhaust outlet is really in the way, but if you rotate the exhaust so the cat points upwards/forward there is enough room. Take your time to avoid any damage to the body panels. If your exhaust manifold is not welded together it will be much easier because it can be removed completely.
• You have to remove the steering rod.
• Engine oil and coolant will be all over the floor, be sure to drain as much as you can before disconnecting anything.
• You don't have to drain the engine oil if you take the gearbox out with the engine.
• The engine mounts are hard to put back. Small hands would help.

And what a change! The new clutch completely transformed the car. What a relief!

Differential support

There are reports on broken differential mounts on the CSRs, so I have mounted support brackets to avoid a future disaster.  Some say they're not necessary if you have steel spacers on the diff mount, but all race CSRs have support brackets mounted, it is even in the regulations, and if they're not necessary I wonder why it shouldn't be necessary on the road models which are used on the track with sticky tires.

Caterham sell support brackets for race CSRs. Unfortunately they don't fit the road version! The reason is that the race CSR has the differential mounted in the center but the road version has the diff a couple of centimeters to the right. MOG racing also have an adjustable diff support kit but take quite a lot of money for it. Others (Gunnars garage) weld mounts onto the frame and bolt the diff through there.

EDIT 2011-10-11: Caterham now have a road-version of the diff strut available!

The original - doesn't fit

I didn't want to modify the frame so I bought the race support brackets from Caterham and modified them. Since I don't have any tools nor the skills about welding I went to a local firm to and asked them to do the welding for me.

I took the Caterham support brackets and cut the ends off. I let the welder make a L-profile with some angle to the sides. They are bolted on the existing diff cover holes and the seatbelt mounts.

Fitment check, then back to the welder

Removed excessive metal with a grinder, and then some black paint.

In place!

New holes in the trunk-plate.

Thanks to Tyresö Svets.

Mantorp trackday movie

Movie clip from Mantorp this summer. Personal best 1:27.94!

Avon ACB10 tyres
Filmed with a GoPro HD

About using nitrogen in tyres

There are different opinions about using Nitrogen in tyres instead of ordinary air. I did some research and here are my conclusions regarding nitrogen and track driving:

The Ideal gas law says there are no difference between different gases regarding temperture vs pressure relationship. Many people use that as an argument for that air works just as fine as nitrogene.

However, if the gas contains moist, the number of mol of gas changes when the water changes state between liquid and vapor. The Ideal gas law also says pressure is relative to number of mol of gas and the amount of vapor a gas can carry is relative to temperature. So with a gas containing moist, the pressure relationship to temperature is not linear!

Any gas can carry moist, even nitrogen. The difference is that nitrogen is produced by cooling air, removing any possible moist. Diving air is also completely dry for the same reasons.

Air for divers and tyres

So my conclusions are that any dry gas is more predictable than humid air. Dry air works just as good as dry nitrogene. The benefit with a completely dry gas is a linear temperature-pressure relationship. Remember that you have four wheels and the chance you have exactly the same amount of moist in all of them is not very likely.

With that said, I did try nitrogen once instead of my normal gas-station air and couldn't find that much difference, but I tend to drive a handful of laps and then check and re-adjust my tyre pressures over and over. For those who have to start a race with cold tyres I can clearly see the benefit.

To be able to fill a tyre with nitrogen or dry air you must do it several times before all humid air is out. With stiff side-walls and low tyre pressure it not easy to get all out.

Silencer mounting bracket

When I bought my Caterham it was equiped with a big heavy rear silencer. Last winter I decided to remove it and modify the side silencer. After a couple of bad attempts with cracked welds and brackets I once again went to my local garage and extended the exhaust and welded a new mounting bracket. Hope it works this season!

Yes, the red spot is blood from my fingers

In order to decrease the bending force on the welds I have put rubber bushes between the brackets.

Thanks to Stefan Andersson Bil & Plåt

Spark plugs

Finally I changed the spark plugs. About time I'd say!

NGK BR7EFS
Gap 0,64mm
12 Nm