I've decided to go with a AGM battery.
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Also, If I use larger drive tires, will I get more speed? The reason I would like to use a CVT is to get the higher speeds without having to run the motor at it's max rpm.
I'm no expert, but if my research is correct, you're probably better off with flooded batteries. Your original requirements seem to stress range and top speed over acceleration. AGMs are better for acceleration, but worse for range. Like others have said, freeway speeds for 70 miles is pretty tough to get, especially with bad aerodynamics. For my project, I'll probably go with AGMs, but my requirements are for better acceleration and lower range than yours.
As far as acceptable depth of discharge and number of cycles goes, that's going to vary with the type of battery. IIRC, flooded is more robust than AGM and will handle abuse better. If you can, get batts that are designed for EVs (eg golf carts) or make sure they're tough enough for EVs. Other types will not do well with the extreme demands of an EV.
Larger tires might get you better top speed, but it might not. Larger tires are heavier. Either way, you'll probably have to have some kind of gear reduction, whether it's sprockets and chain or a car-type differential.
Gearing an EV for direct drive (no transmission) and high top speed can be tough. CVT sounds interesting. One thing I think you might have wrong is you seem to not want your motor to run at high RPM. From what I understand, most EV motors run cooler at higher RPM than lower, because of internal cooling that's less effective at low RPM and the higher current needed during acceleration. What I've heard is that people use transmissions in EVs to minimize accelerating at low RPM. Accelerating obviously stresses the motor, and when it's at low RPM, it's worse.
If you haven't already, you might want to spend some time checking out EV sites. There's more than one DIY-type forum. You'll find a lot of info about what vehicles need to get freeway speeds and long range. Your original post asked about 48V and Etek. IIIRC, motorcycles with 48V and Eteks do about 45 mph and maybe 30 miles-no where near your target. For a lot of examples of EVs, check out the EV Photo Album. Watch out for predicted performance. Results don't always measure up.
It sounds like your goals are similar to mine. I hope your project works out for you!
