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MAX Update No. 7: Science Marches On

8/28/2008 12:43:14 PM

Tags: Auto X Prize, gas mileage, 100 mpg, MAX

We hit one teeny snag in final assembly. As you recall, the original MAX got a significant swat from behind, which we feared might have affected the rear axle. Well, when we drained the lubricant from the axle, chunks of differential fell out. 

That’s not too big of a deal, since we had a replacement rear axle assembly waiting in the wings (I'll tell you why in a minute). But we hadn't wanted to use it just yet. In my opinion, the best way to do this "rebuild" would have been to make the new car exactly like the old car. Then we could have driven it, tested it and made sure our baseline hadn't changed — we'd know that any differences between the two cars were the result of a mistake. If there was any difference in performance or economy, we could sit down and figure out what we did wrong. If there were no differences, we could go back to our development plan of making changes one change at a time and testing the results. 

MAX Version 2.0But the clock is ticking: summer is whizzing by and we have quite a long to-do list. The top job on that list is to install a taller rear end. That's hot rod slang for a final drive ratio that takes fewer turns of the engine per turn of the wheels, so at any given engine RPM, the car covers more ground. It turns out that the automatic transmission version of that Toyota Corolla wagon (aka the Corrode Warrior referenced in this article) has just what we need, a 3.30 (3.3 revolutions of the drive shaft = 1 revolution of the wheels) axle, so we went ahead and put it in MAX. 

I expect we'll see a higher top speed than with the original MAX — about 75 mph — and an improvement in fuel economy at cruising speeds. But maybe not. We may need to make streamlining changes before we see any benefits from the gearing changes. 

Meanwhile, we'll just have to trust ourselves that we haven't accidentally introduced any new variables, and the only difference between MAX version 1.0 and MAX 2.0 is the gearing. We should know soon. As you can see, the parts are falling into place.

Photo by Jack McCornack

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