Okay so why is that now that I've got lighter wheels, so therefore more unsprung weight, I feel like I'm much slower? At least slower off the launch? I bought a set of kosei k-1's which are supposed to be very light weight and I went with the 17's since I am planning on at some point putting in some serious braking power if I can find a system that won't drive the ABS nutty, and of course I have the spare change for it. But I certainly wasn't expecting to feel a decrease in hp/tq. is it because now so much of the weight is further out that it was on my stock 14" rims? Oh well they look damn nice and the Potenza RE730's seem to hold nice in the corners. I'll post pics as soon as I get a chance.

 

It's not all about the weight, but about the effective change in gear ratio that the bigger wheel gives you. It's like putting in a taller final drive when you go to plus sized wheels.

 

even though the wheel and tire are essentially the same size diameter as the stock wheel and tire? that's the part that I don't understand.

 

How are they the same diameter? are you running super low profile tires?

 

Larger diameter wheel = more centripidal (physics people correct me if Im wrong) force. It takes more force to get that larger diameter wheel going.

As for superlow profile, thats an understatement! 1inch is ~25mm, so you do the math Like he says, youve essentially increased the final drive. At least they look good, and youve gained a few mph up top for those trips down the Autobahn

 

Well I've got 17" wheels and then 205/40/17 tires. I did the math before and the difference in total diameter was like 2mm or very close to that. I'll try to work it out tomorrow and post what the difference is. Stock was 14" and 195/65/14. It's basically a 3 plus sizing moving up three sizes in wheel and down the corresponding size in tire. Maybe I'm confusing myself. I'll do the math tomorrow at work though and see what the difference works out to be.

 

I think stock LS size is 195/60/14 not 195/65/14. The 205/40/17 are almost the same size (maybe a little more than 1%). I'd like to see pics of your car since I am debating the Pro-Kit and maybe 17's.

 

I'll try to have some posted by the weekend, depends on if I can borrow my friends' digital camera. They do look sweet and tomorrow I'm putting on a new set of brembo rotors, just the flats but they'll look much nicer behind those wheels.

 

i think 17" tires are heavier, since they are lower profile they have to support more weight. the tire may be made out of more metal wires inside than a 15" tire. please correct me if im wrong heheh

 

that may be true but there's still less tire isn't there, so even if the tires were essentially denser, there's less tire material than on a normal profile tire

anyway I did the math and my new wheel/tire set up is about 6mm larger than stock coming in at 595.8mm versus 589.6mm. guess that little bit makes a difference.

 

When considering vehicle acceleration, you must consider more than wheel/tire mass. The overall rolling radius must be considered (which you have done) as this affects overall gearing, as well as the rotational inertia of the wheel/tire.

The rotational mass moment of inertia of a body decides how much torque needs to be applied to that body to accelerate it at a given rate. If you take 2 discs of the same mass, one with the mass concentrated at the center and one with the mass concetrated at the perimeter, the second will have a larger moment of inertia, and thus be harder to accelerate. The low-profile tire is most likely much heavier than the stock tire, and you've concentrated that mass to the perimeter of the wheel.

So, you're being penalized in 2 ways: once with the decrease in overall gear ratio, and again by increasing the rotational inertia of the wheel/tire system.

 

thats very true dude

 

Unfortunately, it's NOT a lot simpler than my previous explanation.

When referring to vehicle acceleration, rotational inertia is the DOMINANT component, not mass. It is important to understand the theory and how it affects the vehicle.

Mass matters, but not nearly as much. Vehicle/tire mass matters more to handling (when referring to unsprung weight) than it does to acceleration.

 

I went with 17's from my stock 15's & measured a 2.25" increase in rolling diameter & thats where you will notice a differance. Get a set of stockers for the races & let them rip. Also you won't rag out those nice expensive 17" tires

 

if the rolling circumference of the tyres are the same then there is no difference to the gearing.

however.... with a larger and lower profile rim and tyre combo, the mass is pushed further from the centre of the rotating object. so you are moving the mass a larger distance, requiring more energy, slowing you down

it's like... u watch figure skating in the winter olympics, when they are spinning on the spot and their hands are out in the air the spin relatively slowly compared to when they move their hands closer to the axis on which they are spinning. this is despite the overall mass of the ice skater remaining the same.

 

good eye buddy. the mugen MF10L i plan on buying might be small...but they will get me off the line quicker.

 

17" lightweight or not will take away from the car.


More wheel, simple