Chapter 7 with a Caterham SVT

[redursidae]

Good news! The fuel has stayed in the tank since the Autocross, and what was dripping didn’t smell like fuel, instead some sort of glue or residue in the underside of the aluminum shelf.

 

Since cleaning the shelf and the tank as best I could this hasn’t returned

 

As far as overall fuel smell, it is much better. I only smell the breather doing its job when I slosh the tank on a spirited drive and it subsides after some cruising.
 

Decided to do an LED swap with tail lights and indicators from Just Add Lightness, and headlights from Summit Racing. The headlights leave a little bit to be desired in their beam pattern but it’s decent. The tail lights are good and bright as needed. The indicators have not worked well so far, and cause all the lights to panic! With only one indicator on, all of the car's light flash, including the gauge lights. If I turn the lights on, then the buzzer is constantly on and the indicator bulb is lit. That’s a first. I tried disconnecting the tachometer to test the theory that the telltale could be the cause, but no dice, and not really sure where to go from here. This issue only happens with the LED indicators installed. Here is a video of the behavior with only the right indicator on:

 

 

 

 

Another interesting new quirk is that while driving with the lights on I can hear the buzzer and see the indicator bulb light up intermittently as I hit bumps. This is making me think there is a bad ground somewhere. 

[JohnCh]

I had something very similar happen with the Westfield many years ago. It turned out the ground on a rear taillight was bad. 

[Vovchandr]

Did you swap the flasher relay for an LED friendly one too? (JAL sells one I think but they are very easy to source anywhere)

Edited April 28 by Vovchandr

[redursidae]

1 hour ago, JohnCh said:

I had something very similar happen with the Westfield many years ago. It turned out the ground on a rear taillight was bad. 

 

Good to know. One of the original tail lights was working intermittently before, so I will start looking around there. Any idea if missing reverse and fog lights might have something to do with this?

 

47 minutes ago, Vovchandr said:

Did you swap the flasher relay for an LED friendly one too? (JAL sells one I think but they are very easy to source anywhere)

 

Yep, I did. The car already had an LED relay, and I also tried JAL's relay to be sure.

[JohnCh]

1 minute ago, redursidae said:

Any idea if missing reverse and fog lights might have something to do with this?

 

I don't know how the loom was set up in those days. I wouldn't expect it to matter, but it's always possible that the grounds were daisy chained and the connection at one of those missing points failed (e.g. they crimped those grounds together to complete the circuit and the crimp weakened over time). My understanding is that because LEDs draw far less voltage, they tend to expose weak grounds earlier than an incandescent bulb. I'd start by replacing the incandescent lights one at a time to see if the issue persists or goes away as a means of potentially narrowing down the location of the issue. You may get lucky. If not, then start methodically checking and cleaning all the ground connections in the circuit until you find the culprit. Don't forget to hit the grounds at the switch and relay.

[Croc]

The loom was essentially a crossflow loom with a custom engine harness for the zetec.

 

I bet this is a bad earth somewhere.  John's comment on LEDs exposing bad earths is spot on.  

[redursidae]

Understood, and thank you. Will inspect the grounds.

[redursidae]

 

Took the Cat to get an alignment today expecting it would be bad after raising it so much. It was kinda bad with -1.2* camber and 0.45* of toe-out up front, 5* caster. Rear was -1.5* camber and 0.1 toe-in.

 

To help eliminate understeer I asked them to set the front to -2 camber, 0 toe. Went for a quick blat and it feels better, but it still understeers when pushed hard enough. I’m going to shim it to try and get 6 or 6.5 caster and try again. Next step might be trying to stiffen the rear roll bar but I would rather not because likely that the tires have some blame in this. At any rate, I’m loving this thing  . 

 

 

Edited Friday at 07:42 PM by redursidae

[Croc]

16 hours ago, redursidae said:

... but it still understeers when pushed hard enough. 

 

 

 

I hate to ask this as it may be viewed as insulting but I feel I should check as most people new to these cars are expecting miracles from the car....    All Caterhams will understeer if you stuff it into a corner hard enough - even the very best set up ones.  The driver has to control the weight balance manually and put enough weight on the front wheels to get them to bite for crisp cornering.  These cars require more driver involvement to get the very best out of them.  Even then, high speed understeer is a thing you will run up against on very high speed corners (think 110mph+).

 

Apologies if you know this but I was reacting to what you said.  

[Croc]

Just thought I would add my starting spec for my various de Dion cars over the years.  This is intended to feel good for a track but I find it works well for road too although it can make the car sensitive to tram lining.  It does not matter what spring or shock combo you have for this.  

 

Front

Full caster on wishbone washers

Camber - For a LHD car on treaded tires you can go 3.2RHS and 3.0LHS. Full slicks will bring this down a little -0.2 -0.1.  This allows for weight bias of driver on side to side balance.  You may want to just be 3.1 both sides initially and then dial in divergently each side as you test.

1mm toe out

 

Rear

2.5deg ears with shim to get 2.6 camber.   Most people do not shim but I think it is essential - particularly on an SV.  

Start with no rear toe in.  Dial in after you baseline iniital spec - I bet you will end up at 0.1 as you mentioned in your post as that is where I usually end up.

 

Ride Height

Measure ground to chassis rail and not ali skin as older chassis and race cars have exposed tubes - the newer cars have ali skin.  If you are measuring to ali skin then modify measurement accordingly.

Its 120mm at back of front wishbone

+5mm rake at rear - Caterhams and Westfields are quite sensitive to rake. 

If you want higher ride height then same process to achieve right rake. 

 

This is start point and I then tweak one change at a time from there as no one chassis is the same - they all feel slightly different - at least on a track where I can replicate driving again and again to check feel on a standardized corner.  It is essential you baseline then change only one item each time thereafter otherwise you have no idea what each change is doing to improve or worsen the car.  

[redursidae]

Thank you, Croc. No insult taken, and I appreciate verification on anything I post.

 

I didn’t know understeer was the de facto behavior as this is the only Caterham I’ve pushed hard enough to find out, and I’m still learning how to dance with it. My expectation was that it would oversteer naturally and I would have to manage it. At Autocross I did a better job of balancing the weight, but didn’t do great every time and it showed. I’m no professional and still got much to learn. Yesterday I admittedly chucked it into a hair pin expecting Chapman’s hand to give me rotation. It’s good to know about the high speed understeer too, although that sounds like aerodynamics may be playing an effect too?

 

Greatly appreciate you sharing your specs! Good to hear that you shim the rear as well. Are there a set of recommended shim kits? Could I bother you with sharing a picture of where you measure the ride height? I thought I measured it at the right place but every time I look I get more confused. I set it to 145mm front and 160mm rear with me in the seat, mainly because of oil pan clearance but it will be lower with 13s once I eventually do that.

[CBuff]

3 hours ago, Croc said:

If you are measuring to ali skin then modify measurement accordingly

Is there a predetermined correction for measuring to the Ali skin?  Or just measure both front and rear to Ali and it’s consistent.  (I switched over from Avon zzs to Toyo r888r and I think there was a jump in front tire diameter vs the rears ).  Although I never check ride height and rake with the avons.  I feel like now is a good time to dial it in. 

[Croc]

22 hours ago, redursidae said:

I didn’t know understeer was the de facto behavior as this is the only Caterham I’ve pushed hard enough to find out, and I’m still learning how to dance with it. My expectation was that it would oversteer naturally and I would have to manage it. 

 

Its a big readjustment process but incredibly rewarding as a driver.  Most people come from bigger cars which have enough weight over the nose to just hammer the wheel left or right and the car just goes.  However, a Caterham (or Birkin or Westfield or Locost) just do not have the nose weight when under acceleration so a left or right turn in that state will just lead to scrub.  A brief lift of throttle or light tap on brake is nearly always enough to put more weight on the nose/front wheels to get them to bite for your turn.  Then you can play with throttle in the corner to adjust attitude. 

 

Think of it in a sequence.  Corner coming up.  Brake to get weight over nose.  Once weight is on nose then off brake and turn in.  Once turn iniitated then start to feed in power progressively to come out of corner quickly.  Slow in and fast out.   

 

Ross Bentley in his Speed Secrets series has a good section on managing weight transfer around the 4 wheels for varying outcomes.  Find his first book in the series and have a read.  Then go out and experiment - great opportunity for a track day since you can do it safely plus repeat corners to adjust technique and get a good seat of pants feel.  Also read his section on trail brake as this is a great technique for keeping the rear end controlled under late braking entry to corners - Caterhams respond well to trail braking.

 

 

 

22 hours ago, redursidae said:

It’s good to know about the high speed understeer too, although that sounds like aerodynamics may be playing an effect too?

 

Its more lack of weight on front tires under acceleration.  Its not a 50/50 weight distribution front to rear as a driver is a lot heavier than a 4 cylinder Ford engine.  Obviously with the aerodynamics of a brick, there is some front end lift which exacerbates the problem.  

 

The example corner for me is Copse at Silverstone.  Its the old turn 1 if you are using the old pits.  Its 60 foot wide track going and about 80 foot wide coming out.  I go in at 8600rpm in 4th and have 15 feet of available track on exit, even without braking or lifting.  And I scrub understeer the whole way through.  I do not need to tap or lift as the track is so wide.  But I have to do a lift to set the front tires up for a quick corner.  Frustrating.  

 

Luckily there are not many places where that is an issue - top corner just past the rising esses at VIR, Copse at Silverstone, two corners at Portimao, entry into corner 1 at double Gauche at Spa, etc.

 

 

22 hours ago, redursidae said:

Are there a set of recommended shim kits?

 

Caterham sell one for rear camber and toe:

https://caterhamparts.co.uk/de-dion-tube/6531-camber-and-toe-shim-kit-de-dion-cars.html

 

 

I would ping Josh at Rocky Mountain - I bet he has some in stock.  

 

You do need to know where you are starting from on rear alignment.  How much rear camber is dialed in from the standard de Dion.  Should be 2.5deg but that is not guaranteed - check will tell you.  

 

 

22 hours ago, redursidae said:

Could I bother you with sharing a picture of where you measure the ride height? 

 

Borrowing a photo from someone else since I am flying this month and won't be near my cars until June.  

 

Front - back of wishbone.  Photo shows a more recent model Caterham with ali skin.  The ruler points at measuring point.  My measurement was ground to chassis tube as not all cars are covered in ali there (e.g. older chassis and race cars) but you can deduct the right amount of ali skin cover from the 120mm. 

 

 

 

 

For the rear measurement point, do it ground to chassis tube at the rear axle point - no photo handy right now.  Its not much - only +5mm rake front wheels to back wheels.