Just got 20s put on today,I'll post some pics when I get a chance to take some. Anyways imediately I feel that the car doesn't respond as quick as before from stop to go. Just wanted to get some knowledge from you guys. The rims are chrome, so I'm thinking maybe because the rims are heavier or could it have something to do with the bigger circumfrence?

 

Think of it this way: That extra 2 inches of metal in rim diameter is essentially displacing 2 inches of rubber and air. Unless you opted for some expensive light alloy wheels that weigh no more than the stock rims, you've added unsprung weight. It will not only take longer for the wheel mass to get rolling, but the heavier wheels will probably worsen the ride.

RainMeister
'04 G35C 6MT, brilliant silver, premium, nav

 

yea. If you wanted performance, i wouldnt go bigger than 19's on this car. Forged 20's would be ok depending on which brand you went with, but other than that, chrome 20's will slow the car down..

 

Yep, he's absolutely right. As a matter of fact - there is an interview (I think in SuperStreet Mag) where the owner of Giovanni Wheels states that 19" is the largest you can go in regards to performance. The reason is the aspect ratio of the tire is at the performance envelope limit...or something like that. Also, the weight is much greater and sometimes you even have to upgrade your brakes because of the additional inertia.

 

Unsprung weight is really a big deal as far as performance goes. I went from the stock 6MT 18s to the Nismo 18s. Nismos are about 18 lbs per wheel, stocks about 30. The larger tires are heavier, but with the lighter wheels, I can feel the difference. I didn't think I would, but I definitely do. BTW, IMO, 18s are the way to go. I believe they offer the best compromise between looks, ride, handling, performance, weight and etc. I love my Nismos.

Lou

 

Unsprung weight (as opposed to suspended weight) has nothing whatsoever to do with acceleration. Of course, the lighter the car the faster it will accelerate, but this is absolutely unrelated to whether or not that weight is sprung or unsprung.

Going to a larger wheel affects your final drive ratio, which directly impacts acceleration. The smaller the drive wheel(s), the quicker the car will be. The converse of this is that you lose top-end in the trade. If you have enough power, you can get a good mix of both.

Now, going to a larger wheel does not necessarily make your total diameter larger, but it usually does. Ive seen some coversions that also change the tire to an insanely wide profile, making the overall gearing change negligible. Measure the final diameter of the mounted tire (rubber to rubber), then measure the stock one. That difference can easily be calculated into the final drive ratio change and the expected acceleration performance change can be accurately estimated.


Black/Willow 03.5 6MT, Premium, Navi, Aero, SAT
350Z Nismo CAI

 

Increasing unsprung weight WILL DEFINITELY hurt your acceleration.... Unsprung weight has more of an effect than suspended weight on acceleration.

This is common knowledge to drag racers who spend money on super-lightweight drag wheels.

 

Lou,

Do you have a pic of the NISMO wheel that you can share? That's one mod that I'd be very interested in.

RainMeister
'04 G35C 6MT, brilliant silver, premium, nav

 

20" are all for show, not GO! If you want to keep your cars power and speed specs the same, I wouldn't have gone anything larger than a 19" wheel, keeping in mind the "up-sizing" rule where it's within 10% of the OEM spec ratio.



"See, the problem is that God gives men a brain and a *****, but only enough blood to run one at a time."

 

Yeh I'd like to see the Nismos too, please post a pic. TNX
GSM

<font color=red>GSM</font color=red> <font color=black>Silverstone Coupe</font color=black>

 

Unsprung weight is only important for acceleration purposes when traction is significantly compromised during that acceleration. For top-fuel dragsters and other VERY fast cars this is important since tire skipping, hop, suspension loading, frame twisting, and other handling issues compromise traction at that performance level. This not the case for the G35, rest assured.

I used to drag 11-second Pontiacs and GTOs, and changing to lighter wheels and suspension components was solely for the gross weight loss benefit and to prolong the life of the moving suspension parts by reducing gross stress. The unsprung weight loss did not have any appreciable affect on the traction gain, and traction gain is the ONLY way unsprung weight reduction affects acceleration. In fact, reducing the unsprung weight in the front (with tiny wheels and tires) was far more effective by helping us steer the damn things. But again, this was not an acceleration gain except through the loss of gross mass.

So unless the G in question has problems with traction, reducing the unsprung weight will do nothing for straight-line acceleration. Now, reducing unsprung weight does do wonders for handling, and in fact is one of the very best things people do to improve that.

That said, I always marvel at how tiny the upper A-arm is on the G. It looks like I could take it off and break it in half with my hands.


Black/Willow 03.5 6MT, Premium, Navi, Aero, SAT
350Z Nismo CAI

 

Without taking into account traction thresholds, even if your 20"s were the same weight as the stock 18"s, they'd be slower, because the larger diameter impedes changes in inertia. Your braking distances will be longer too. The weight of the wheels also impacts this, and I suspect your 20s are much heavier. It shouldn't be a HUGE difference, but all other things being equal, your stock wheels would be faster in a quarter mile run. Some Autocrossers go to smaller wheels because they're advantageous on a short, tight course. But the faster you go, the less of a performance loss (except for the braking part).

-Jack
Obsidian '03 G35 Sports Coupe
Titanium '03 MX-5 Shinsen #532

 

You know shader your really full of old shoes. As I said, I didn't expect that unsprung wheight would really make that much of a difference, but the Nismos made a believer out of me. My G now accelerates faster at a standstill or at speed. I didn't believe the things I'd read about the importance of unsprung weight before, but I do now.

About pictures. I don't own a digital camera yet, but I have ordered one (a Cannon A70). Hope I made a good choice. It got a good writeup in MacWorld. I've never used one before, so it should be interestinng. The Silver GT4s look great on my DG Coupe. I will post pictures when the camera comes, and I learn how to use it. BTW, I put Dunlop SP9000s on the Nismos. 245/40 and 275/40.

Lou

 

I laugh sometimes when I read these posts where everybody thinks that 20's are slower than 18's. I mean really, come on guys, do you really think that the axle knows if it's an 18" or a 20" wheel? All the axle sees is the final weight of the whole object (wheel and tire). The only loss with a 20" rim, with everything else being equal and I mean tire diameter and tire width, is the amount of flex that the sidewall of the tire will provide on the launch and in the corners. The lower profile tire on the 20" will have less give causing a "tighter" and more bumpy ride and on the drag strip it will cause more tire spin. That's it, tire spin is the only downfall for drag strips which is why nobody run with 20's because they need the best launch they can get.
I'll admit, I bought 20's because I wanted my G to look good but also I got them much wider than stock in hopes that they would give me as much traction as the stock tires or better.

No flames please, just my opinion and I hope it makes sense to all of you.


Silverstone 6MT Maya DTM 20's

 

Lowrider, as I said, removing weight is always a good thing for acceleration. My point is that dinstinguishing between sprung and unsprung weight is only advantageous when considering handling. Not only is your G 50lbs lighter with the Nismo wheels, but that weight loss is from the unsprung total, which will improve your cornering and steering among other handling benefits. Your supsension can react more quickly and deftly to keep your tires flat with the road since there is less inertia at 12lbs less per wheel. However, if you had cut that same weight (about 50lbs) from a sprung position in the same car but kept the stock wheels, you would have seen a similar performance gain. The handling would not have improved, but the straight-line acceleration would be the same.

Sammy, the driveshaft doesn't know the size of the wheel/tire combo on the end, but the engine and transmission certainly do. The final diameter of the drive wheel(s) help determine the final gear ratio which is directly related to acceleration. That's why drag tuners gear the cars from the tranny all the way to the tire to maximize power output across the rev range. Wheel sizes and tire diameters are not selected randomly; they are part of the final drive ratio. Larger diameter wheel/tire combos increase the top speed at redline, making you shift later to meet the optimal torque curve. The trade-off is that your acceleration is slower due to the higher gearing.


Black/Willow 03.5 6MT, Premium, Navi, Aero, SAT
350Z Nismo CAI