Mods feel free to move this if its in the wrong place,


I am going back to get dyno tuned again and I am going to be on a dynojet, so I want to try and squeeze out as much power as I can.

I have two sets of rims

Coupe 17's with 245 45 dunlop starspecs ( I think they are 24 lbs each for the rim)
and 4 coupe rear rays 19's with 2454019 falken 452's on them.( I think they are all 21 each around)


I wanted to know what you think will eat up more power, I am trying to squeeze every fraction of hp that I can.

I know the 19's are lighter but do have a over all more mass to turn.

opinions please!

 

Unless its a track car your totally wasting your time worrying about it, with the ECU in the G35 you can loose 25BHP by driving style

 

Thats why I race everywhere! That ECU must think I'm jeff gordan!

 

LOL! should have no problem three then, seriously though i very much doubt that there would be any discernible difference between them, i would always tune for torque over max BHP in any case, torque has far more impact on drivability and *** dyno

 

I've always been under the impression that a smaller wheel will be better.

 

hahahah Id go with 19s, distance from the axis isn't as critical as pure mass... Speaking from an engineering aspect.

 

Because?



Actually more mass will sap more power, until it reached maximum acceleration, but you might as well argue the roiling resistance of the type of rubber used in the tyres, the whole subject is pretty pointless anyway, as if you did see 1/2 or BHP or ft lb of torque difference, the only thing that might notice is the dyno, certainly not you.

 

I suppose because all of the test I have seen conducted with the sizing of the wheel has always slowed a car down. However iirc it was all based on stock wheels. So I suppose if the bigger wheel was lighter it would be easier to get to rotate.

But then again if the overall radius of the wheel is longer wouldn't it take more force to get that going regardless of the weight?

 

Generally speaking, in theory, the tyre size should be adjusted to make the overall rolling radius the same or very close to the std wheel overall radius, no matter what size the rim is.

 

Smaller wheels with larger tires are generally lighter than bigger wheels with lower profile tires. Another important factor is polar moment of inertia - if the mass is farther from the axle, it's harder to spin something. So, bigger wheels are both heavier with a higher polar moment of inertia, so they require more power to spin up than lighter wheels, and you end up accelerating more slowly. On top of that, if you make the wheel too big, the tire ends up being too low profile, and can't deform enough under cornering and acceleration loads, so it's not as grippy as a taller tire. This is why race cars generally have smallest wheels they can which are big enough to cover the brake rotors and relatively thick tires.

I agree, that for a street car it really doesn't matter, but it's very important if you care about absolute performance.

 

The reason why I ask is because I need to break 300WHP, and before people start to talk crap I do have a built na, nothing on the engine is stock, I was very close to it, but now I have a few more tweaks down and will be going to a better tunner so yes that .5 hp can be from me going 299.5whp to 300 whp. I care because its cooler to say I broke the 300 whp point.

I dont want this to be a vq debate, there is over a hand full of guys NA on my350z that makes over 300whp, and the one from kaz0 something we have 98% same build and he made over 305 whp.

I do feel that my car handles a lot better with my 17's rather than 19's in cornering and acceleration, but the butt dyno is full of lies so I wanted to see if anyone knew scientifically what is better.


Thanks for the inputs so far

 

Thanks for that explanation, cleared up a lot!

 

Why aren't you going to tune on what you drive on? That makes the most sense...

 

This is so true. Race cars use 18" or 19" whichever is big enough to clear BBK and I think they would prefer 18" over 19" as long as 18" clears their BBK. And yes higher profile tires are lighter than low profile tires.

If you wanna squeeze out every HP/TQ, then go with 17" wheels. But for street use, or for the look, 19" is the way to go.

 

Because he want's the biggest numbers