Camber

Laser Alignment of Wheels Showing Camber

Having noticed the grease exiting my UJ bearings after the Worlds, I dismantled the front axle and found that half of the bearings were already quite rough. This is after only about 150 miles at the most. Dr Graham suggested that this could be caused by cornering forces. I probably did more, high load cornering over that weekend than the whole crossing of the USA during ROAM.
I ordered and now have received some sealed rather than shielded replacements but I am not sure that the problem is only caused by the loss of grease, I am sure they are overloaded as well. The bearings I am using at the moment are 696ZZ which are 6x15x5mm and have a static load rating of 655N. Unfortunately, I can’t increase the bearing size easily without a re-design, so I am stuck with them for the time being. The only interim solution could be to double up the same bearings within a modified housing.

UJ Assembly

While Quattro was in bits yet again, I decided on some more drastic action. For testing purposes, by adjusting (bending) my kingpins and modifying the lower wishbones, I am going to eliminate the camber on all four wheels. This will result in a narrower track of 600mm rather than 650mm but with the four wheels and low centre of gravity, Quattro will still be very stable.

From the excellent “The World’s Most Fuel Efficient Vehicle” (PACII) book.

The original idea for cambered wheels was to give maximum stability within the narrowest body. The 650mm track was chosen as it is one of the regulations required for pedal car racing in the UK. I was also influenced by the authors of “The World’s Most Fuel Efficient Vehicle” (PACII) book. In the section on tyres, they show a graph of rolling resistance versus camber angles. The curve is more or less flat between 4deg and 8deg, so I decided to go for 8deg. What I should have noticed was that this flat section of the curve indicated a 15-20% increase in rolling resistance. In fact, when I measured the camber on Quattro, it was closer to 9deg.
The other advantage of eliminating the camber will be that the UJs are running concentrically when Quattro is going straight, which should reduce friction losses considerably.

Camber Eliminated

Thinking positive, this could save me up to 20W in my tyre rolling resistance power at 35mph as well as reducing the side loads and therefore the friction in the wheel bearings. The power saving in the UJs is difficult to quantify but the angular speed variation I mentioned in an earlier blog should be minimised.

A couple of people mentioned the lack of shelter behind Quattro compared with other vehicles while racing at the weekend. Mike Burrows tried drafting me during the two hour event and said that there was no noticeable shelter. This is hopefully a sign of good aerodynamics and leads me to think and hope that any big gains in speed may well come from improved mechanical efficiency.

I should be able to get the modifications done over the weekend, so off to Reading for a testing session on the velodrome which is free Tuesday morning next week.