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For the 38, Lotus continued with the offset suspension design. While it theoretically provided better handling (with less weight transfer to the outside tires), the design proved too quirky and was eventually dropped. Only NASCAR Late model cars and Sprint cars still use offset tracks like the Lotuses did. Modern teams have tamed the weird suspension and it still works in oval only cars. The track width of the 38 was widened slightly compared to the 34.
Pretty familiar isn’t it? The 38’s control arms seem to be made of thinner tubing than on the 34 and 29. The driveshafts are also different, though they may use the same sliding joint used in the older cars, obscured by the tail panel. 
For 1965, the major changes were in the chassis, underneath the tinwork. The 38 is a full monocoque car, with no steel trussing whatsoever. This shaved even more weight off the already light 34 design. Minimum weight for 1965 was 1,250 lbs, and it’s safe to say the 38 was as close to that minimum as possible. The intake runners were also covered in ram air scoops to gain just a tiny bit more horsepower at speed. USAC also made a few rule changes for 1965 in response to the Sachs/MacDonald crash. Changes included a switch to methanol fuel (which was easier to extinguish) and a mandatory minimum of two fuel stops. This gave teams the chance to run smaller fuel tanks and would help prevent the inferno caused the year prior. Chapman, once again looking for every advantage possible, planned to run Clark with the same set of tires throughout the entire 500 miles! He would stop for fuel only but save time in the pits by not having to lift the car and replace wheels.
Only the British would design such a stylish cockpit. Who says racecars need to be function only? The seat too is trimmed in this stunning red leather. What you can’t see however, is the water pipes running between the engine and front mounted radiator. Stylish? Yes. Comfortable? Far from it! Still, Clark was the first man to turn a lap at over 160 MPH, but would miss out on the pole to AJ Foyt by 0.5 MPH. Clark would start second.
Slight aerodynamic changes also differentiate the 38 from the 34 including fairings over the front rockers, and a narrower radiator opening. This was possible because the use of methanol made the Ford engine run cooler and Lotus could use a smaller radiator to adequately cool the car. Unlike both the 29 and 34, the 38 featured twin refueling and vent ports. This would double the speed of pit stops. A new, gravity fed fueling rig would also speed pit stops. For 1965 Lotus planned to run the race on a single set of tires, speeding up pit stops even more. 
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It was NOT Parnelli Jones who convinced Colin Chapman to design the Lotus 29. It was Dan Gurney.