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65. Pedal Setup

Whilst waiting for the collection and transfer to Caterham for the PBC and IVA steps, I started to think about the need for using heel & toe techniques once Tigger is on the road. I remember reading about the necessity for rev matching in order to avoid, shall we say, unwanted movements on the road. The point is (as I understand it) that because the car is so light a Caterham has much less momentum to overdrive the engine when changing down (and so there is no chance to use engine braking). Therefore, changing down without rev matching is likely to cause a wheel lock-up or skid, albeit momentarily.

To allow heel & toe action, the throttle and brake pedals need to be set up correctly in two dimensions. First, when the brake is pressed it should then be level with the throttle when it's in the rest position. Second, the two pedals should be an adequate distance apart from each other to allow the driver's right foot to blip the throttle whilst still modulating the brake.

There's a lot of information on previous builders blogs about setting up the throttle adequately - in particular the need to bend the throttle metalwork to get it to a position that simply creates the necessary travel for minimum to maximum throttle position. When I fitted the throttle cable, I was pleasantly surprised to find that no bending was necessary - but that was before I started to think about heel & toe requirements. Re-testing the pedals, it was quickly apparent that it failed the first requirement (accelerator being level with the brake when the brake is pressed). The first objective, then, was to fix this.

Inside the pedal box it is apparent that the brake and clutch pivot points were already assembled in their furthest position from the driver (of the two options available). However, the accelerator pedal was fitted in the closest position. I removed the pivot bolt and tried re-fitting it in the furthest position. This had the desired result of dropping the accelerator pedal a long way behind the brake pedal when the latter was pressed - but it was also going to create a huge amount of slack in the throttle cable, which could not be wholly taken up by the cable adjusters.

Having looked at the various other options, I decided the best approach would be to adjust the brake pedal so that it was higher (closer to the driver) when fully pressed, and to adjust the accelerator pedal in the other direction. The net result should create the desired position of the two pedal positions relative to each other when braking.

Adjusting the brake pedal was straight forward - crack off the retaining nut and then rotate the threaded shaft to pull the captive nut closer (and hence push the pedal away). This was a trial and error process of adjusting the threaded shaft and then trying the brakes to check there was still sufficient travel before the brake pads engaged. Once comfortable with that, the brake switch was adjusted and everything tightened up.

Before adjustment - when brake pedal is pushed it ends up below accelerator position; brake pedal adjuster

Adjusting the accelerator pedal was a little more difficult. Basically the range of motion had to be moved such that the minimum position and maximum position were further forwards. I started with the minimum (or idle position) of the pedal, which is set by a bolt with two nuts either side of a chassis flange - this would be very easy to adjust if it wasn't so inaccessible. To access it, I found I had to remove the accelerator pedal. It was a laborious exercise of trial and error to adjust the bolt head position, refit the accelerator pedal and test it's position relative to the compressed brake pedal. Eventually I found a position that was comfortable. With the pedal refitted and the throttle cable reattached, the amount of slack in the cable was immediately apparent. Moving to the throttle body, the cable adjuster was turned to take up the slack. Finally I could look at the throttle position when the accelerator was fully pressed. Of course the pedal stop needed to be adjusted forward by an equivalent amount, but this was straightforward.

As a final check, I wanted to make sure that when the accelerator was not pressed at all, the idle speed would not be affected by the throttle cable being too tight. I could see that the throttle body was not resting on it's end stop and so I took a tiny amount of tension off the cable. Starting the engine and letting it warm up produced a tick over marginally less than 1,000 rpm - higher than it was before these changes. I decided to let that go for now.

Minimum throttle position stop adjusted, cable adjuster at throttle body, final accelerator position.

Trying a heel and toe operation with the pedals adjusted in this way was much easier than before. I reflected on whether to bring the accelerator pedal closer to the brake pedal and decided against making any further changes - heel & toe was possible in this position, but I didn't want to risk getting to the point where my size 11's were inadvertently pressing both pedals. I reconnected the throttle cable to the accelerator pedal by pushing the cable deep into the slot and adding a set screw (which feels better to me than using a daub of silicon sealant). The final bit of tidy up was to add a bracket under one of the wheel arch bolts which would hold the tyre weld in position in the boot.

Throttle cable set screw; bracket for tyre weld.

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