This page covers the work I performed to the suspension system in my Toyota MR2 EV. Suspension work was necessary to allow the car to handle the substantial extra weight from the batteries. Since work was needed anyway, I also modified the suspension to lower the car for an improvement in aerodynamic drag.
|Old and New front springs|
Since the original curb weight of my car was about 2200lbs, and the final weight of my car is 3140lbs (weighed at the local dump) I had to upgrade the shocks and springs on the car to handle the extra weight. I also upgraded the brakes, see my EV Braking System for more details there. The rest of the chassis and suspension did not need modification for the weight (It did for fitting the batteries and such, see my Chassis Modifications for details). One of my reasons for picking a sports car was that its suspension and chassis are fairly solidly built.
I decided (based on the weight change data on my EV Weight Change page) to go for a set of springs that would lower the car by about 1" (for better aerodynamics) and add 200lbs of carrying capacity per coil, for a total gain in GVW of 800lbs. The 800lbs represents the overall weight change from what the car weighed before conversion.
I looked at aftermarket springs from a variety of sources, (See EV Reference Material page) and while several of them had spring rates that were probably about right, They were also designed to lower the car. If they had been designed with those spring rates, but for stock height they probably would have come out right with the added weight on my car, but with the designed-in lowering they would have come out too low. The only spring manufacturer that probably would have provided an off-the-shelf system that would have worked is Ground Control. They make height-adjustable custom springs. Those springs are really aimed at racing applications, but since you can get them with most any spring rate you want, they could be customized. I was unable to get ahold of them however, so I got annoyed and tried a different supplier.
I ended up having springs custom made. I went with a local outfit named Gitt's Spring. Their price was good, but they weren't the best to deal with in that they were rather disorganized. I probably won't go to them again. First they made a completely wrong set because they lost the sample springs and then just guessed. Then they forgot about me for a couple weeks. Finally I got my springs, but they still haven't returned my samples. Despite all that, in the end I did get a set of springs that come pretty close to what I asked them to make. (I just gave them a front and rear original, and told them to make new ones with 200lbs more capacity per coil and a 1" drop).
The shocks on the car needed upgrading too. The MR2 originally had the integrated oil damped shocks inside the strut assemblies. I replaced these with aftermarked Tokico performance shock cartridges. These seem to be working well and are a good match for the springs.
Both conversion books I have (see the EV Reference Material page) suggested measuring the ride height before you start, so you can try to replicate this with heavier springs and shocks. So I did. All four corners of the car measured 10.25 inches, from the peak of the wheel well to the top of the trim ring on the aluminum wheels.
After all was said and done, the ride height measurements for the rear are now 9.5", and the fronts are still at about 10". So the rear springs came out almost perfectly, while the fronts are a bit stiff. However, it is plenty good enough for now. Handling is good. The car doesn't lean in corners, nor does it bottom out on bumps. The spring rates seem to be well balanced to the weight of the car. I'm sure the car doesn't feel as light as it would have as a gas car (never drove it that way) but it is still very manageable as an EV.