I've seen approximations on the equivalent hp gains with lighter wheels. I understand that lighter wheels do not create more hp in and by themselves, but certainly a car will accelerate faster with lighter wheels. There are many variables with rotating mass such as diameter, offset, etc. If anyone has ideas on this I'd be interested.

The reason I'm now thinking about lighter wheels for the G in the spring is that I was shocked today changing my wifes 05 Honda Odyssey tires to a winter package. She has the Touring model, and as such, has the Michelin PAX system. For those that don't know, the PAX is regarded as one of the best run flat systems out there and is used on some very expensive sports cars that don't have room for a spare. But when I took the first wheel off, I couldn't believe how heavy they were. The Tire Racks steel wheels with Blizzacks seemed like a feather in comparison. I had to weigh one. 77 lbs each So now, with about 25 lbs per tire lighter, I swear I can feel a difference. Maybe it's pychological , but I don't think so. The only thing I don't understand is that the exotic sports car applications certainly use much wider tires. I can't imagine the weight.

Anyway, as much as I like the 7 spoke wheels on my 05G, I'm thinking about SSR Comps in the spring to save weight. And I would not go above 18's, and maybe stick with 17's, as this will be a perfomance mod for me, not a looks thing.

Any thoughts?

 

I know it's not a G35, but I did a test with my 96 Maxima at the track. I had lightweight aftermarket 17s that weighed 42lbs. I also brought my OEM 15" rims that weighed 42lbs. I made 4 passes with the 17s and then made 4 passes with the 15s swapped on the front. With hardly any measurable difference in 60' (+/- .03 seconds), the car averaged about .1 and 1mph faster with the 15s. While the weights were the same, the narrower 15" rubber and more of the mass centered around the hub netted better times. Most of the gain was realized in the 1/8 mile. If I would have swapped 15s on all four corners, I might have seen a few more hundreths improvement, but most of the gains come from the drive wheeels. With the 15s on, the car felt far more lively, but the 1/4 mile numbers revealed there wasn't a huge difference.

All I can say is go for the lightest you can afford and go no larger than 18s. I'm looking into 18X8 ASA AR1's from the Tirerack. They cost ~$210 each and weigh 21lbs. That's a steal and I've had great luck with ASA rims.

 

Thanks Dave. I'll take a look at them. The SSR's are lighter but also more expensive.

When I was racing the Camaro, I used Weld Draglite wheels and they were rediculously light. So much so I questioned whether they'd be able to take the torture of the launch (front wheels in the air) but they never failed me. It's all in the quality.

 

There is a LOT of physics involved to determine the effect on acceleration and such. But there are common approximations that can be used.

For the G... approximately each pound per wheel, is about 1 HP. For the Odessey, probably about the same, maybe less.

It has to do with vehicle weight and original power, among other things.

For example, using traditional computations that the weight reduction of the wheel/tires is about equal to about 4.5 times in standard "sprung" vehicle weight reduction.

If the originals are 50 pounds, and the new setup is 45 pounds... then you save 5 pounds per wheel/tire. Times 4 (each corner) equals about 20 pounds total weight reduction from all wheels/tires. Times 4.5 equals about 90 pounds similar weight reduction of the vehicle.

My G35 6MT is ~3500 pounds. Reducing that weight by 90 pounds would be about a 2.6% reduction in weight. Which would also be equivalent to avbout a 2.6% increase in power, as far as straight-line acceleration... about 8 HP for a 298 HP G35.

If you took off 25 pounds per wheel/tire from the Odessey... yeah, you'd be able to feel it. That's about the same as taking 450 pounds off the weight of the car! That's about 10%! (Those things are heavy.)

Lighter wheels/tires also help with braking and suspension tracking/response.

Dave - also, if you are comparing 15s vs. 17s... did they have the same outside tire diameter? If not, you were also changing the effective gearing with smaller tires.

 

Same diameter. The advantage came from more of the rotational weight being centered around the hub. The closer the weight is to the hub, the easier it is to accelerate.

 

Thanks a lot guys. That's exactly the stuff I was looking for.

 

What matters is called rotational moment of interia. It's a measure of how difficult it is to change the rotational speed of an object. A wheel/tire combo is a very complex object and it's not easy to calculate the rotational moment of interia, but you can make educated choices based on simpler shapes that a wheel/tire combo is close to. For example, the rotational moment of inertia of an ideal hoop where all the mass is at the outer edge is equal to the mass times the radius squared. The rotational moment of interia of a uniform disk is equal to 1/2 times mass times radius squared. A wheel tire combo will likely lie somewhere between these values. So what does that tell us? Well it tells us that the most important thing is radius, as that factor is squared and consequently has a much greater impact on rotational moment of interia than mass does. It also says that mass itself is important and where that mass is located is important as well. So in order of decreasing importance for acceleration and braking performance, you want the smallest diameter wheel/tire combo that gives you enough contact patch to use the available friction on the road, you want the lightest possible tires as that mass is farthest from the center of rotation and lastly you want the lightest rims you can find. Since we can't deviate much from the stock overall diameter of the wheel/tire combo without affecting the speedometer (and hence odometer, VDC, TCS, airbag trigger speed, etc) that means the biggest bang for the buck would be with using the stock rims with the lightest tires available. Next would be going for lighter rims with those lighter tires.

 

Another issue with the smaller rims is fitment over the brakes.

 

Well... and the "bling" police might come arrest you for not running 19s like everyon else.

 

I have had my 18 by 8 wheels on for 1.5 years now with 245/45 18. Wheels are 19lbs each and my tires are 29 lbs each. My stock 17s were definitely lighter no question. With the 17s my best 1/4th was 14.61@97.98 this was in low 80 degree weather. I recently went to the track with my 18s and my best time was 14.63@97.3, this was in much colder weather. Now my 18" tires in 245/45 are taller then stock. My new tires are going on next week that are 245/40 18 and they are 23lbs each compared to my current 29lbs each. My overall diameter will be 2.3% smaller then stock and a wheel/tire package weighing 42lbs. Do you think I can expect a sub 14.6 or even 14.5?

BTW it is an 03.5 Auto, borla exhaust, z tube, stillen CAB.

 

Good insight, but not exactly correct. The best combo would be lighter 17's (need 17's to clear the brakes), not the stockers. That's why I originally stated that 17" SSR Comps were on my list. Rims vary greatly in weight. Tire much less so.

 

I can tell that I've done what you're considering. My Maxima came with 15s as stock. I first did 17s (pretty heavy) and loved the look, but the added weight really slowed the car down. I went with super light 16s (Kosei K1s, 15.5lbs) and super sticky summer rubber. The overall combo weighed 38lbs. The car felt far more lively, but after a year, I just wasn't happy with the smaller 16s. I went with 17s again, but this time I went with light 17s to reduce the gain in rotational inertia, but gain some looks back. I've heavily considered light 17s for my G, but since the car already has nice 17s which look big for 17s (Sport 5 spokes), I decided I'd just be more happy with trading a fractional amount street acceleration for a good looking light 18. All the light 17s I've seen, while sexy looking, just don't look big enough to justify the expense and minimal increase in acceleration. If my G came with 16s, then I'd do 17s, but since 17s are OEM I want something that will "pop" a bit. Just my opinion.

 

I completely agree, and I'll probably decide with the lightest 18's I can find. Like you, I have a real problem spending big bucks for the same diameter as the stocks.

On an off note, most of these guys that are doing 19" or above have no idea how rediculous the wheels look with the "tiny" brakes inside. It should be mandatory, IMO, that brakes be upgraded with anything above 18's. I've actually seen 20's on ricer cars with drum brakes. Dreadfull....

 

+1

I have even seen an escalade with such a setup. Large expensive Wheels, tiny stock breaks. A large cross drilled rotor really finishes the look on any car

 

I guess if I bought cheap rims, I would have had some money left over for the brake upgrade