New Shoes on the Speedster


Our 1957 Porsche 356 Speedster replica conversion has been getting a bit of attention lately as I posted it on eBay at auction. A lot of interest, but it remains a price sensitive market and the bids fall woefully short of both our investment in it and the reserve. But it has caused a bit of attention.

Meanwhile, I had recently found a better way to present videos on our website. This is not only better than the way we were presenting them, but significantly better (I think) than they appear on YouTube. But I also have gotten smarter on some of the tools out there to monitor what people are viewing and why (Google Analytics and Web-Stats). The interest seems to be overwhelmingly in favor of the Speedster over the Mini Cooper.

We’re going to complete our Mini Cooper Project, hopefully before the end of the year. And in fact, I posted a new video today. This 1:48 minute mini-series in its own right, only covers battery selection issues, layout of battery locations, box design in general, and the construction and installation of two boxes that will be placed where the original gas tank was beneath the rear seats. Despite it’s length approaching two hours, these were NOT the hardest of the boxes, by a lot. So at least two more such monsters just to cover the box design and installation.

But that’s not as outrageous as it sounds. While batteries and their installation would seem to be the most straightforward issue in an electric car conversion, in actuality it is at least half the effort you will spend on the project and probably a good deal more than half on many projects.

But looking at life after Mini, I am struck by the absolute ROMANCE of the Speedster. I’ve just never owned a car that causes so much attention everywhere I’ve gone (and I had one of the first civilian Hummers ever built). There just is no head turner like it. Not a Ferrari. Not a new Porsche. Nothing.

And the attention of the viewers to the web site would seem to confirm it. The Mini makes a much more practical daily driver, and certainly has its own allure as evidenced by a strong, nearly cult like following for some 50 years. It has modern amenities such as air conditioning, bluetooth for your iPhone, heated seats, hell it has windshield wipers for the headlights. It’s an all weather year round car and it is truly a GREAT little car.

But it’s not a Speedster. And it can’t ever be a speedster.

Anything done once is worth doing again. And in these kinds of efforts, when you get done, you ALWAYS have a list of what you might have done differently. In this case, less might have been more. Less batteries. Less range. Less weight. And maybe a less muscular, but more flexible AC drive system with regenerative braking. A little neater battery layout. And some better thought to the wiring. Not the battery and motor wiring so much, but the instrumentation and other wiring that accumulated as we solved problems. I think a second run at a Speedster could be done in much neater fashion, at signficantly less expense, and at a reasonable range of 60 or 65 miles.

But range is the hot button in this game. I don’t really need it, but its an easy target. Friday, we changed the tires on the existing Speedster. It had sported some very nice 195/60R15s. Like almost everything in ICEland, the evolution has been toward ever better performing components – for ICE vehicles. But generally to LESS well performing ones for electric drive applications. Tires are a good example.

We looked at the new “low rolling resistance” tires from Michelin, BF Goodrich and others. And we noticed a curious thing, we could do better than they were doing by going retro on the tires.

Briefly, our 195/60R15’s are NOT stock tires from Special Editions Ltd. These tires are “sport” tires with a wider tread (195 mm instead of 185 mm) and a lower profile. The 60 refers to the ratio of tread width to sidewall height – the distance from the rim to the tread. So the tires we had were 195 millimeter wide, and 60% of that or 117 mm in the sidewall. They were also a relatively soft sticky rubber to increase grip and traction, all the things you want to hold those curves when grossly overpowered by a 180 hp CB Performance engine.

Well, the problem is “grip” and “traction” are antithetical to rolling resistance. If you want to decrease rolling resistance, you go to a NARROWER tread, higher tire pressures, and a larger diameter. Think of the very narrow hard racing tires the bicycle guys use on the Tour ‘d France. There’s a reason for them.

Back in the fifties and sixties, volkswagens used 165R15 tires. The sidewall ratio wasn’t listed at that time, but was nominally an 80. A 165 is 30 millimeters, well over an inch narrower than the sport tires we had on. And because of the taller sidewall, larger in diameter by over an inch as well. This helps our gearing with lower RPM at higher speed in 4th gear – increasing our torque at that speed and so increasing our top speed.

The higher sidewalls provide more flex, and so a better ride. We can trade that for some more tire pressure, raising it from 40 lbs to 45 lbs.

And to wear well, the tires are made from a harder rubber. It’s not as sticky, but that means it will roll with less resistance.

These original tires were bias ply. Radials do perform better in almost every respect, but we found this size in a radial. Better, or perhaps comically, depending on your taste, they were in wide whitewall. I had to try it.

This afternoon, with the new shoes and pumped up to 45 lbs, I duplicated the run we made last month of 101.85 miles on a single charge. Incredibly, it made a very significant difference. This afternoon, I drove the car 107 miles on the nose. And we were able to eliminate a small, but tricky calculation we had previously had to do on mileage because of the smaller diameter tires. These tires are very close to what the speedo is actually set up for.

This 107 miles is pretty precisely the max range. I ended the run with all cells actually quite nicely balanced at between 2.8 and 2.9 volts per cell at rest. But that’s essentially it. We’re over the edge of the discharge curve which drops off precipitously below 3.0 volts resting voltage. The official cutoff voltage is published at 2.5 volts. But I don’t believe there are 2-4 miles range in the difference.

This was radio going full blast and some headlights on the last 15 minutes of the trip, but no heater of course. The absolute max range of this vehicle is 107 miles. But that’s over 6% better than our previous best. Can tires make a 6% difference? Apparently so.

I guess I would rate the ride noticeably stiffer than the previous tires. Not bad, and not pronounced, but I could tell the difference. The sidewalls and 5 lbs were not a wash. But I think we could do 42-43 lbs very comfortably.

Actually, I LOVE the retro look on the white sidewalls.

Check out the new mini video at http://evtv.me. It’s bottom row on the left.

Jack Rickard
mjrickard@gmail.com

http://EVTV.me

5 thoughts on “New Shoes on the Speedster”

  1. Hi Jack,

    I just recently opened your conversion video on youtube and I am fascinated by the electric Porsche and now the mini-E. You mentioned in one of the videos that you are thinking of placing a microswitch on the “gas” cap so that the car would not run with the cord plugged in. If I may suggest, a small 110V AC relay connected across the input 110VAC outlet at the car can also be used. The relay contact can then be connected to an alarm or in series with the control. Only in the rarest occasion that there is a power outage that this arrangement will not work.

    Please continue sharing your mini E conversion work to the public.

    Best regards,

    JohnM

  2. Hello,

    I read your post from early last year about regen. Having tried to set a braking regen (actuated by switch on brake) thats acceptable to all users I’ve always wondered if some sort of pressure transducer in the brake line might allow for modulatioon of regen braking. The harder you press the more the regen braking comes in. I’ve never had an opportunity to try this so it might be no good, but it might be worth a try. The next question is how much you really get back from regen braking and does it make this sophistication worth it.

    I’ve read as much of your comments about battery charging as I can. Challenging the status quo and forcing people to defend it always helps determine what ideas truly make sense and what ideas are bogus. I will first admit I am completely devoid of Li experience, but just purchased some TS cells for testing. I like your idea of not balancing the cells and the simpliciation in circuitry it allows. I plan to use an amp-hr counter in my system as my lead experience shows that it works to help controll the DOD. I will have to develop some amp-hr capacity versus lifetime amp-hours removed data so I can account for battery aging in my amp-hr system. But one question: Does the weak cell as determined by amp-hrs have a cell self discharge that is also the slowest? I’m concerned about long term storage of cells (say over the winter) and if balancing the cells will be needed. My fear is that self discharge rates and cell capacity aren’t related resulting in scenerios that will force periodic balancing after long periods of storage. Because this will require some longer term testing (which I will be doing) and because you appear to have a large amount of experience I wanted to ask your opinion on this subject to speed up understanding of how to treat the batteries properly.

    I appreciate any advice you can offer.

  3. A pressure transducer in the brake line is entirely feasible and most controllers have a 5K pot input for degree of regen that could easily be interfaced. The problem would be how to select the transducer, they are available for a little over $200 typically but for a wide array of pressures. And trimming all that might be difficult.

    We’re rethinking our regen strategy somewhat. We’ve talked to a number of people who VERY MUCH LIKE the feel of regen triggered by a decrease in accelerator pressure. So we’re going to have to play with that.

    The “book” on regen would tend to indicate a 10-12% extension of range from regen. I was a little skeptical as well, but at least one person has measured actual regen gains over time and seems to believe it is more like 22% average. It rather depends on topography and driving habits obviously.

    Amp hour counting appears to be the only viable strategy for any accuracy at all in determining SOC, so you are definitely on the right track. Accounting for cell aging is an unknown area. My plan is to have a variable for DOD in the software. Then once a year I’ll just pull a cell and capacity test it. I can then adjust DOD to correspond. 79% insttead of 80% for example.

    I just really don’t have any hard data on self discharge and would probably be out of bounds to comment on it. I can tell you we have some THundersky’s that have been sitting in their original boxes for 18 months. I pulled one out the other day and it was in perfect condition, and with the usual 60% charge on it. I charged and discharged 4 cells, and they seemed as good as any in the shop. I’m thinking calendar/self discharge is overstated for these cells. But I have not done any serious testing, and the time element rather precludes anything definitive. No effective test scenario presents…

    Jack Rickard

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