KnifeySpoony

Really, nobody?

I used sikaflex 221 on my recent build, applied as instructed in the current build guide. No issues with multiple track days with Vmax of 124mph.

My car is mostly a track car, I really only drive it to/from the track. I had considered this upgrade for maximum performance during my 420R build last year, but decided to see how the stock setup was. I found it a little over-braked in the front, but upgrading the rear pads to DS3000 has pushed the bias rearward enough that I am happy with the braking performance. However given my recent issues with interference between my rear calipers and watts linkage arms (/forum/techtalk/rear-brake-caliper-contacting-radius-armwatts-link), I am thinking about this upgrade yet again. Presumably the lower profile rear calipers won't have any interference issues. I'm OK with the handbrake delete (I'm in the US and in my state the car will never be inspected again). This setup seems to need a proportioning valve, although my calculations of brake bias don't seem to suggest the bias moves all that far rearward compared to the standard setup. I'm wondering if anyone has done this upgrade, or driven one of the R300/420R race cars with this setup and can comment on performance. I have never plumbed brake lines, and I would have to get the appropriated line flaring tools etc, but it seems not too difficult to learn. Also I would need to decide on a cockpit-mounted prop valve vs one in the engine bay (much easier to install). Wondering if the easy adjustability is really necessary, as I won't racing in the race.

Definitely check the lambda and TPS. From my understanding lambda sensor failure is more rare, but it's easy to check. My 420R is on roller barrels, so it simply won't run without the TPS (different mapping strategy), but my TPS recently started failing after about 3000mi. Replaced and all is well again.

I checked and there's maybe 4mm of clearance between the caliper and watts arm at ride height. There a little bulge on the inside of the caliper that appears to be making contact. I've read that the Sierra calipers modified by Caterham to fit our application. I wonder if this is the interference that is corrected. That also makes me worry that it would be impossible to remove more metal from the caliper safely, otherwise wouldn't Caterham have removed more?

Ah... hadn't thought of that. I recently changed out the standard 1.5deg ear for a 2.0 ear. That would certainly account for it. I'd have to take out the damper to run the suspension through its travel to really assess static clearance. I know that there is a lot of side/side flex in the rear end under load. Given that it just seems to be grazing the watts arm, I guess it's safe to continue running like this, but I will consider a spacer under the dedion ear if need be. I trashed a set of wheel bearings disassembling the rear end to swap out the dedion ears, so I'm not super excited to go back again right away, as I'l probably have to replace them again. I'm in US and shipping from Caterham is $$$.

I have a 420R with watts linkage and standard rear calipers. I noticed that there are witness marks on the forward watts link from the rear caliper on both sides. They appear to be relatively light scratches, not big gouges or dents, so it seems like the contact is light. Wondering if this is of any concern, or a case of TADTS.

With my setup (raceline sump), there's probably about a liter that drains from the finger filter hole.

I'm not sure about draining the sump (my 420R sump is a little different), but most of the oil is in the tank. You will need to drain it - you can use the drain plug at the bottom, but most people don't use it as it is prone to stripping, as it's in soft aluminum. Many people use a fluid extractor to suck the fluid out of the tank.

TBH I don't think we have enough info to really diagnose the problem. Is the understeer during corner entry, at steady state, or on exit? Damping can make a difference on transitions for sure (ie more of a factor on entry/exit), but certainly the relative roll stiffness front to rear will be the primary determinant of handling balance. Hence I would look at spring rates and ARB. And also agree about tire temps - if you're not even getting heat in the tire than all bets are off regarding suspension.