I know why the Sedans are faster than the Coupes!

[Tampa G35 Sedan 6MT]

Well I ended up buying a set of 19' coupe wheels of a buddy of mine that i go to school with.

This Kid has a lot of money so he didn't even know what they were worth!

He got new rims from the infiniti dealer for his 06 G coupe and gave the dealership his old rims.

I told him i would give him 100 bux per rim and he said ok go pick them up!

any how I love they way they look. I will post pics when i have it cleaned and it is a nice day outside.

I lost a lot of Get up and GO!

when accelerating and the RPM are from 2000-3000 the car is much slower.

I had the stock 18's that came with the sport package and at that point in each gear I had a lot more power.

I don't know if it much difference at higher RPMs becasue it seems very fast, It might be faster at the top end of each gear! but in the bottom of each gear under normal driving conditions... It is much slower!

I know that if i go to the track i will be putting my 18's back on!

any ideas on what this is?

I know the rims are an inch taller but that is the only thing. The rear tires are the same size as i had before 245-40

Do the 19's have more mass than the 18's



DJ

[gwoods]

with 19's you should be running 30 series rubber.. 40's are tall!!

Like 275/30/19 rear and 245/30/19 front?

You probably still gained some rotating weight at each corner replacing rubber with metal.

[Tampa G35 Sedan 6MT]

well they have the stock tires on them from the factory! 245-40-19 Rear and 225-40 19 Front

I like the taller tire! should give me better MPG on the highway! It also looks better with a little rubber on the Metal LMAO

I still have my 18's for the track. I probably will only be changeing the rears for the track.

DJ

[smockers83]

^ What he said.

The best way to go with bigger wheels is forged--really light weight. I don't know how the OEM wheels are made.

I'd really like to get the SSR GT7-Hs...they're over 50% off at tirerack (if any of you buy them out from me, I will ask for your complete and permanent resignation from this website). Each 19" wheel is only 22 or 23 lbs. What are the weights of the OEM wheels?

I'm just playin, you can buy them. I need a real job first and everything else before I can buy a set of new wheels.

[Tampa G35 Sedan 6MT]

They are Forged! they were mounted to the tires already! Maybe the rubber is heaver on the 19's than on the 18's I had BFG tires on the 18's 245-40-18

[RED_DET]

Next time around get some 245/35/19 tires all the way around. The 245/40 series 19" tire is a bit taller than the 235/45 18" tire. essentially you made the gearing taller, which diminishes acceleration.

[Andy_V35Sky_350GT]

^^

Huh? How does that work?

[joe603]

245/35 -19 front275/35 -19 rear

This size will fit on the 19" OEM forged rims. Not sure if it really makes that much of a difference from stock height wise, but they are wider.

[rn79870]

Unsprung weight has more of an affect on on acceleration than an equal amount of sprung weight. The car has to overcome the inertia of the wheel x 4 to accelerate from a stop. Overcoming that inertia takes power that would otherwise be busy accelerating the car down the street. In any event, I would guess it was not enough difference to really be noticeable but apparently it is.Suggestion. Take one off the car and weigh it. Weigh the stock wheel. Report the results.

The good news is that you've got 19 inch wheels.

[gwoods]

Next time around get some 245/35/19 tires all the way around. The 245/40 series 19" tire is a bit taller than the 235/45 18" tire. essentially you made the gearing taller, which diminishes acceleration.

Unsprung weight has more of an affect on on acceleration than an equal amount of sprung weight. The car has to overcome the inertia of the wheel x 4 to accelerate from a stop. Overcoming that inertia takes power that would otherwise be busy accelerating the car down the street. In any event, I would guess it was not enough difference to really be noticeable but apparently it is.Suggestion. Take one off the car and weigh it. Weigh the stock wheel. Report the results.

The good news is that you've got 19 inch wheels.

Exactly!

This is why I always cringe when I see people putting 20's on 22's on their car. The Hemi came with 20' rims I went down to 18's as soon as I could afford it. At the track I ran 275/40/17's just like on the G! One I was making over 450 hp though I went back to 325/45/18's for the track and 295/45/18's on the street. I light up the tires from a less the 15 mph roll... I miss that torque!

[C-Kwik]

Unsprung weight has more of an affect on on acceleration than an equal amount of sprung weight. The car has to overcome the inertia of the wheel x 4 to accelerate from a stop. Overcoming that inertia takes power that would otherwise be busy accelerating the car down the street. In any event, I would guess it was not enough difference to really be noticeable but apparently it is.Suggestion. Take one off the car and weigh it. Weigh the stock wheel. Report the results.

The good news is that you've got 19 inch wheels.

I think you have your terms mixed up. The concept is correct, but the terminology you are actually describing is rotational mass/inertia. Unsprung weight with respect to automobiles tend to repate to the wiehgt of the wheels and suspension pieces and their effects on the suspension movement.

As for weighing the wheels, it only tells part of the story. While it certainly has some relation, it is more important to know where the weight is on a wheel. Or more scientifically, you need to know the moment of inertia. If more of the wheel's mass is located further out from the center of the wheel, the more force will be required to move it. Think of it like a lever. using the same weight at various points on a lever will apply various amounts of force on the other end of the lever. The closer the weight is to the fulcrum, the less force it will apply. In a wheel of a specific design, a larger wheel will put more mass out further from the center of the wheel. Assuming the thickness of it's parts are the same, a larger wheel will have proportionately longer spokes which adds a little bit more mass. But the biggest mass increase will be in the rim as it is not only further out, but has to increase the amount of material to span the greater circumference of the wheel (which is 3.14 times the increase in diameter). Not to mention that a wider wheel will need more additional material than a narrower one. This is before we even add in the effects a tire might have in this.

Tires are the same way, but as you get into lower profiles, it becomes a bit simpler as there is less sidewall height to account for. But the same principle applies. But one consideration for a tire with respect to the moment of inertia is that with a larger diameter wheel, the inner diamter is further out than a tire with a smaller diameter. So if the tire is just as heavy or heavier than it's smaller diameter counter part, it is likely there is much more mass further out on the wheel/tire assembly than the smaller wheel/tire combo. This is true even if the outer diameter is the same. Just as a reference, the Bridgestone RE050A in the 245/40/19 are a pound or two heavier than a 245/45/18 of the same tire. On the other hand the Michelin PS2 has a 1 pound difference in the other direction. So it's not necessarily predictable by tire size. Of useful note about the PS2's is that they are 5 pounds lighter than the the RE050A's in the 19 inch size (245's). Just something to think about when tire shopping...

The stock 19's on the G35 are forged so they may be just as light as the stock 18s or lighter, but the tires may be an even bigger factor in this case.

[rn79870]

C_Kwik, Thanks for correcting my misstatement and adding to the discussion. Like I've said before the only thing I remember from Physics 101 and 102 is the cute little blond I sat next to and talked to entirely too much.

[Sentientbydesign]

I found a site recently that stated that the front 19"s were 19lbs and the rears were around 22.

I think the 18s might actually be heavier, but as kwik said, the moment of inertia matter more than the total weight.

The moment of inertia is the objects resistance to being rotationally accelerated.

So go get some forged gram lites 15s with light tires and you'll be starting in 2nd gear forever hehehe.

[Sentientbydesign]

Oh and only the 6MTs after 05 and the autos with the sports suspension/wheel tire package got the 19" rims.

The sedan is quicker because it is lighter!