New rims with stickers on

New 13" rims from Force Racing, 7" and 9" wide with brand new Dunlop slicks - "stickers".

I bought the rims directly from Force Racing this time and they were very easy to deal with and I can really recommend them.

The rims are very lightweight - only 3792g/3528g according to my kitchen scale* and look stunning.  If you want to order yourself, refer to this post and they know what to do.

Note that you need to modify your rear calipers to fit 13" rims on a CSR!

The slicks are the same dimensions I usually run - used Radical PR6 slicks 230/570/13 and 190/535/13 - but this time in soft compound instead of medium which the Radicals run. We'll see how that goes. I bought them from HP Tyres. The rims are a bit narrow for these tyres, but I think they work ok.

I plan to practice on worn used slicks and put these on when I really want to go for it. I've already started building a simple rack for my trailer.


* - my kitchen scale is known for messing up recipes 

Mantorp - slicks vs CR500

Mantorp, again. A new personal best, again - 1.21,8!!! That is 1.5 seconds faster than last time, and I haven't changed anything except put on a new set of (second hand) rubber. I never thought I could reach laptimes like that!

At the end of the day I mounted a set of standard 15" rims with Avon CR500 tires just to see the difference compared to the Dunlop Radical slicks. 1.24,8 or 3 seconds. That is a big difference, no questions about it, but with the CR500 the car suffered tremendously from understeer and I think the difference would be less if I took the time to adjust the suspension to suit the tires better. Not to mention tires with better dry performance than CR500.

Slicks in red, CR500 in blue.

I also put zip-ties on the damper rods and that confirmed my suspicion that the front dampers bottoms out onto the bump stops. I don't know if it is while cornering or while braking, but that is something I should look into next time.

Riding on the bump stops is not necessary a bad thing. Read an article here.

Mantorp and two new sets of slicks

Back to Mantorp. It may appear as it is the only track I go to, and yes, that is sadly true.  I wish I could go to more tracks but Mantorp is both convenient and economical for me. 

Increased front neg camber with 0.5 degrees (two turns).
Little more tyre pressure than last time. (about 22-23 psi. 19.5 psi cold.)

And I shaved off another big second from my personal best! - 1.23,3.

I ended the day early because I didn't want to ruin a good day by breaking something.

I found a new source for second hand Radical slicks from whom I picked up two complete sets on the way home.

Trackday slicks part #4 - how did it go?

During the winter I modified the rear calipers to fit 13" rims, and this weekend was the first test how it worked out.

Well..

First impression was that it didn't. Lots of scrape marks on the inside of the rims and I was really concerned that the rims were ruined.

After a closer inspection, I believe the scrape marks are not from the calipers themselves, but from gravel trapped between the calipers and rims. They are very shallow and I don't think it's anything to be bothered about except maybe for visual appearance. Brake dust, old tire rubber for sure doesn't improve the look of things...

I might give the calipers another go with the grinder just in case.

UPDATE:


After another track day I did have another go with the grinder. After trying several different ways to measure clearance I found the best way was to tape a small drill on the inside of the rim and see where it touches the caliper. Now I'm certain I have at least 2 mm clearance everywhere.

I also took a black pen and painted the edges of the caliper, so if it touches the rim again I can see exactly where I need to grind some more.

Trackday slicks part #2

I emailed Avon asking for recommendations regarding slicks on the CSR.

Hi Niclas,

As you probably know, the racing CSR run 9”X13” front wheels and 10.5”X13” rear, we developed some radial slicks specifically for this application for use in the CSR Eurocup.

195/530R13 A24 compound

250/570R13 A24 compound

With 15” wheels things are a bit more difficult. I would recommend using radials on a CSR as the car was designed to work best on them (most other Caterhams work better on a cross-ply) but unfortunately we do not make any radials in suitable constructions and compounds for this car in 15”. The cross-ply tyres you have a probably the most suitable we have available but again, these are not perfect due to the split of compound front to rear (A24 front A56 rear).

The cross-ply tyres will only require a small amount of camber, far less than the radial set-up the car would have been built to.

Sorry I can’t be more helpful.

Regards,

Xxxxx

And after a follow up question:

Hi Niclas,

I’ve done a little digging and you are absolutely right, they did run 7” and 9” which were a little bit narrow but seamed to work well.

We have replaced the 175/550R13 front with a 195/530R13 spec number 13800S – it’s actually the same size (don’t ask).

The rear 250/570R13 spec number 9906S is still current.

I’d go with the 7s & 9s and get the necessary rear brake changes done.

Hope this helps.

Regards,

Xxxxx

See also Trackday slicks part #1

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