tires

When I first took delivery of my 2005 GEM I thought I would drive it to see how I would like the 25MPH speed restraint that is built into the vehicle. I also was aware of the possibility of modification.

After driving it a few times I felt the need to have more power. Not to go crazy but to navigate the 35MPH streets more effectively. I have to deal with some inclines on a regular basis and the stock 2005 GEM that I drive will slow down to about 20mph when tackling it, with a full charge.

Now I'm a fairly curtious driver with my GEM. I make sure I take the side roads when traveling in the business district as not to slow things down and I tend to pull over whenever I can to let cars pass.

Having said that it basically is no fun when I have to go up and over the local freeway and slow all the traffic. It would be very nice to be able to at least do 25MPH up the hill and perhaps close to 35 on the flats when needed.

One of the ways to increase speed is to increase the tire size. Going from my stock 12" rims with 165/65/r12's to 175/65/r14 will result in a increase of 3 mph according to the Gem speed options spreadsheet. It may not seem like much (and can be a pricey upgrade) but coupled with a motor upgrade from ride-4-fun the my GEM could get close to 35mph

After some very helpful replies to my posts on the Yahoo NEV forum I found out the following:

24" or just under total diameter tire size seems to be the magic number. Anything more then that may rub, especially with the rear spat and when turning. It also depends on the year of your GEM (the earlier GEMs had 10" rims and the chance of rubbing is greater, however you will get a larger speed increase when oversizing the tires on these models plus they have a lower gear ratio so that adds to the speed increase.

What are the options
The goal is to increase the diameter of the wheel. When you increase the size of the tire you gain more distance per axle revolution. The GEM uses a 4x4 lug pattern, this is common to trailers and golf carts

• The least expensive option is to purchase 13 trailer rims with 4x4 lug pattern and "0" offset. The offset is the amount that the mounting portion (the part with the lug holes) is offset to the inside or outside of the rim. GEM's have "0" offset as do standard trailer rims (alloy wheels made for trailers may have an offset). Rims and tire combos can be purchased from companies such as Northern Tool and etrailerparts.com. You can find them with and w/o tires. The largest size in a 4x4 lug pattern is 13" & generally you can put a 175/80/r13 tire on the rim and have 24" diameter. With this option you can probably keep the cost to less then $100 a wheel. The down side on the cheap ones is they are made of steel.
  

• The other option is to simply use alloy wheels that you would normally put on a car. It is more expensive but arguably cooler looking. You can even go to a low profile wheel / tire combo as pictured right. Most alloy / sport wheels have some sort of offset and do not come in a 4x4 lug pattern. This requires the use of wheel spacers /adapters. The adapter will go from one lug pattern to the other and return the wheel to a "0" offset. All wheels will say what their offset is.
  

I saw the wheel kits and thought perhaps I could put something together myself and save some dough, especially since I found out later that I paid too much for the GEM - I didn't get taken but I could have done better with an old model - that's a different blog.

To keep cost and weight down I decided to keep the rim size at 14" and go with a higher tire (175/65/r14) resulting in a total height of 23" even. Intially I thought I would go for a 23.5" total height with a 185/65/r14 tire but since I was mostly buying over the net I wasn't going to be able to return the items practically if there was aproblem I decided to keep it conservative. There is only a 1/2 mile per hour difference between the 23 vs 23.5" wheel height.

I decided to purchase pep boy wheels choosing the 950 series. I think the low profile wheel/tire packages look cool but may not provide the best battery life (distance). I wanted to keep the weight down and not go with an overly wide tire, as these tire/wheel combos tend to have. I also heard about something called "Low Rolling Resistance" Tires. Based on the yahoo users group I decided to go with a Bridgestone Ponteza RE92 on the pepboy rims from Tirerack.com.

I was also directed to contact wheeladapters@aol.com. They are an ebay vendor and evidently have the best price on the correct adapter/spacer needed for what ever rim one purchaes. Although the correct wheel spacer for the 38mm offset that these new rims have is 1.5" I was told that the 1.3" is close enough. They also ship with lug nuts

Another option is to simply go to Craigslist.org and find a used set locally but I found that most rims were not going for less then $50 each and did not have the tire I wanted on them.



INSTALLATION
Installation is fairly straight forward. The only thing I did that was different was I used the OEM lug nut for the adapter and the adapter lugs for the new rim. The reason was because the bevel on the adapters lug (right) fit the Pep Boys rims better then the OEM lugs. This eleiminated some play that was present.

The adapters went onto the rear wheel of the GEM with out a hitch. I had jacked the GEM up so that both rear wheels were off the ground. This was OK since the parking brake kept the wheels locked while tightening the adapter onto the brake drum.

However, when doing the front wheel I did the same thing - lifting the whole front so that both wheels were off the ground. The problem with this is that when one wheel is spun the other wheel spins. This makes it difficult to tighten the lug nuts. To stop the wheel from spinning I placed a screwdriver in between the studs that hold the disc brake & lug plate. In the process of doing this I think I dislodged the disc for the brake on one of the wheels because it squeaked when I finally drove the car. I intially thought I bent the disc support studs. I eventually applied the brakes very hard in quick succession (partially out of frustration) and the noise stopped.





BUDGET

Potenza RE92 175/65/14 - $61 each (4x61=$244 + $47 shipping) = $293
wheel adapters - $129
Rims - $218
mounting/balance - $45

TOTAL: $685

Ride-4-fun's comparable 14" kit is $799 (plus $150) shipping. Their's is a low profile tire and probably not a LRR tire. They did tell me they use a 1.5" spacer / adapter. In the end I saved about $250 and perhaps got a better tire.

WEIGHT
The difference between the old tire/rims and new ones is approx. 6lbs each. The particular rim I bought is made of aluminum. I don't remember what the adapters weigh but I want to say the grand total of additional weight was around 40-50lbs.





























New Tire on left















Size difference