John02Hawk

iTrader: (4)

..what the title says..

I currently have my gunmetal ZR1s on with 17x11 / 315s on the back, but have heard that it might cost me 5-7 rwhp/rwtq on the dyno.. Is this true?

Would I be better off just putting back on the 17x9 / 275 firehawks for the dyno?

I am getting the car dynoed this weekend, and would appreciate any feedback..

I guess I might as well also make this into a GUESS MY DYNO #'s thread, my mods are in my signature..

What do you guys think I will dyno?

-John

hoss 2000 z-28

iTrader: (1)

My guess is that wider tires will increase rolling resistance. I've read in other places that wider tires also hurt MPG a little. So to answer your question if you want to read the highest numbers possible then yes, switch back to your 17x9 wheels.

jmilz28

iTrader: (13)

You will lose a few ponies/pounds. Rotating mass takes more energy to move. The 5-7 is a fair estimate in my opinion for your power level, it's not a lot but you can feel it. Can you do before and after dynos with the 9s and 11s?

AU N EGL

Nope minimal if any difference. Contact patch of the tire is minimal.

The decrease in dyno numbers comes when you add wt, as going from a 17" to a 19" rear wheel.

cjg454ss

iTrader: (27)

it doesnt really make sense, if you make say 400rwhp with your 17X11s and then 405rwhp with 17X9.5s, then put your 17X11s back on you can say you ake 405rwhp but you really dont.you make 400rwhp. its like those supras that dyno on 120 octane and 45psi of boost and make 900rwhp, then never put 120 back in, turn the boost down to 21 and make 550rwhp, they just say that make 900rwhp

BriancWS6

iTrader: (18)

If you want to see a comparison of changes made since you were last there when you dyno'd with the 17x9s, then sure, throw them on, but if you wanna know what your throwing out back as your car will be run from here on out, leave em on.

95 Z28

iTrader: (21)

Hmm I'd really love to see a back to back dyno of a car with stock rims and tires, then with a 17x11 rim and tire out back. Seeing how much the heavier wheel and tire combo robs power in the real world would be really interesting.

spaz1

iTrader: (9)

When I put my 295 35 18/s on compared to the stock ones you could deffinatly feel the car was slower. I don't know if it was the weight difference or the change in gear ratio.

03 BUSA

iTrader: (25)

May lose hp but car should hook better causing the car to go faster.

BuBbABFP

iTrader: (3)

You will loose power, I think I read a thread about someone making 530whp? with stockers and 518 with TT 2's 17 by 11.

So I know I am loosing a few ponies due to my huge *** wheels.

SladeX

you will loose a bit of power, but at 375ft/lb and 381hp 315's don't hold a car on street. I roast 245 and 275 with tires with too much ease that it feels like the clutch is slipping when it's the tires giving up. In aug, I'll be going back to the same dyno for some comparison numbers if I get my heads in and I can possibly do a 315/245 rim comparison. I have 17x11 and the stock 16x8 for reference.

So if you are making more than my sig numbers, just go with the 315's on the dyno. Just think, you pulled those numbers WITH heavy rims...

Dyno numbers simply are for getting to know your car better, for shift points, health etc. Run it the way you drive your car 90% of the time, not the way that makes it sound the fastest. I'm sure we could all strip our cars to bare shells and then have a crazy power weight ratio in the process, but it's ridiculous at that point to enjoy the car.

AU N EGL

I help with some dyno tests like you ask about a year ago.

Wheel wt was the biggest deterrent, not wheel size.

The lighter the rotating mass the better the dyno results. Having rear wheel tire combo under 45 lbs each was best.
Over 55 lbs each killed power.

Rotating mass and wt hurts hp. Not only that but were the mass is located. If the mass is farther way from the center of rotation the less power is produced. ie 19" and 20" rims are horable to get your power to the ground.

Even it the O.D. is identical. Smaller rims are better. Drag wheels, have smaller rims and tires with larger side wall tires for several reasons. One is wt