This is why people spend so much money on lightweight rims, it has to do with rotational mass. Try spinning a bucket 1/4 full of water and then do the same with one 1/2 full... Remember that hp and torque are relative to the amount of weight being "pulled". Now before anyone gets jumpy and says weight doesn't affect hp, remember that the factory dyno's the engine on a stand and NOT in a car, where the rotating mass is a predetermined constant. Higher weight wheels affect performance, everyone knows that, I'm just trying to explain why. If you really want 18's on a RA spend that much more and get lightweight ones if you want performance to go with it. I put my 17's on and realized that my stockers weighed less. I could feel that the car was slower, I didn't need a dyno to confirm it. Hope this helps.

 

You seem pretty knowledgeable Recommend me a Rim brand to go with, and some lightweight tires, hehe.. I'm getting my car in ~1 1/2 weeks or so and want to put some new rims/tires on it. I have some ideas, but not sure. I'm keeping 16's

 

volks, gram lights, racing harts. go look it up man. lol. its not that difficult

 

Ya I know its not, lol. I just like input of other people. More then what *I* think, because i'm a newb

 

thanks man, that makes a lot of sense. what's funny though is that the 18's i have now actually weigh almost a pound less than my factory ones. i'm gonna get it dyno'd again later on but this time with the stock rims and see what the difference is. on a positive note, at least everything was hooked up right

by the way, when i go back to the dyno with the stock rims on, what would you predict the numbers to be? blk-majik got 159whp and 163 torque with fewer mods, that's why i'm curious. thanks.

 

Is the diameter of the whole thing the same as the stock rims/tires? If the wheels and rims together make a bigger diameter than the stock ones, it will take more power for the engine to turn em. Same with the weight. Larger diameter+more weight=loss of power. Same with the brakes, it's harder on the brakes to stop those bigger wheels.

 

This couldn't have been said any better... ever wonder why honda guys but 22's for their slicks?? Stock tires are around a 24... the bigger you go the more you affect the final gear ratio in relation to the dyno. Same on the track... bigger is makes the gears longer... smaller makes them shorter getting you into the upper gears faster and making your mph increase dramatically.

 

215/35/18's are actually a little bit smaller diameter than 205/50/16's (sorry didn't see it in your sig, actually I wasn't paying attention to it...) Otherwise, I'd have to guestimate around 190~195whp on 91-93 octane gas if everything works as claimed by RRM along with everything else in good working order. If you allready have blow-by or your clutch is toast, who knows? I still don't understand why Blk isn't making more hp than he is, he should be making ALOT more power. I haven't asked him but I'm wondering if everything went back okay when he tore down his top end to PC it.

 

Big diameter gives you top speed, small diameter gives more acceleration/horsepower to the wheels
But from the post below, these rims/tires together are actually smaller diameter? They must be heavy rims. The poster could try dynoing with the stock rims/tires hm?

 

could always just be a bad dyno run, too. even if the ECU is faulty, the DP should have helped. what exhaust work do you have done? just muffler? i know i lost some low end torque /w mine, but im also sure I gained peak HP and that my peak tq is about the same, just further up in the powerband. how many runs did you take? I did 3 runs when I got my numbers, 1 after another /w about 5 mins between. the got better as the car warmed up and jumped about 10hp/12tq on the last run because of the heat. our cars run well at running temp. bad cold and bad hot.

 

also, was it dyno'd in the same gear both time? 4th gear should give the best results.

 

Even more good points... keep them coming guys!

 

thanks for the input guys. the rim/tire combo i have now is actually about a pound lighter than the stock rim/tire combo, and like amg dragon said they're actually a little bit smaller diameter.

blk-majik, the only exhaust work i have done is the downpipe and the muffler. i did 3 runs on the dyno, all in 4th gear. well, 5 runs really, the first 2 were short test runs to make sure everything was good. we didn't wait 5 minutes between runs though like you did, more like 30 seconds.

like i said before, i'll probably try it again in a few weeks with the stock rims/tires. i hope that's all it is, and not a bad piggyback.

 

ok maybe this is a stupid point Im not sure about this. but a bigger rim and tire though is a smaller over all dia. You also moved more weight further out correct?

I mean Im sure if someone here was awesome at math we could figure this out good. but even if something is slightly lighter but you move that lighter mass further from the point that the energy is produced. That would also effect it as well? maybe?

But im gonig to say if it effected it not that much. it jsut doesn't seem right how you dyno'd out on that one.

but you got me worried. I got 17's that are slightly smaller the the overall of my 16's I wonder how much they weight. Time for some research.

 

i have a set of 17's in the mail. they weigh 14lbs each, so i should see overall gains. double check on the dyno antoher day. if u have the same results, call rock =)