SO I have done my fair share of performance tuning since i bought my car last year; nothing major you can read my list below, but enough to want to see the results of my money spent. But i just bought 20" Shine's in March. And everywhere I look and hear peopel say that the larger the rim, the bigger the impact on HP numbers on the dyno.

SO I am asking around here how MUCH of an impact do larger/heavier rims have on readings? Has anyone ever maybe actually tested it out by running two different pulls on differnet size rims to compare the results? Just curious on other people's experieince with this. Any advice will help and would be much appreciated.

 

When the Big wheel craze started years ago, all the magazines did quarter mile test with oem and big 18-19" [at that time]...............the results were noticable but the science was poor statisically.

Generally the rotating wheel weight gets multiplied, dynos are unnatural [in the real world] since the front wheels don't move.

Do you really care what the dyno reads vs real world performance where one might lose 0.1 second in quarter mile or 0>60?

Unsprung wheel/tire weight shows up more in handling/braking than acceleration.

Tire friction is the biggest individual loss item on a drum dyno so hard to quantify wheels vs tires in a change diameter..............

 

Solid. Thanks for the info. Let's see if i get more insight.

ChicagoZ here usually has a dyno meet with one of our sponsors. The promo for the day is a discount on three pulls. Maybe I will run it with my 20's then switch the rear tires with a friends' 18's and do a pull and chart the differneces if any.

 

I really noticed my sedan pull harder when I switched my stock 23 lb six spoke wheels to the 18 lb 5Zigens. It felt like a noticable HP bump.

 

It actually makes a very big difference on the dyno. I did a comparative dyno test of three sets of wheels.
1- light weight 17" enkis with R compound race tires.
2- stock 18" wheels
3- 20" Big Bling chrome plated wheels.

Although the peak power numbers were nearly unchanged, the area under the curve was substantially changed.

I can't post the dyno plots just yet because I am writing up a technical report on the testing but the results were essentially as follows:

Throughout the majority of the midrange the race wheels/tires gained 5-7 HP over almost the whole curve. As an average, this is a significant increase. It also explains why the Z felt so good when driving.

Throughout the majority of the midrange the Big Bling wheels/tires lost as much as 14.5 HP over almost the whole curve. As an average, this is a loss in power. It also explains why the Z felt like a dog when driving.

Unsprung weight makes a big difference while driving and while on the dyno. There was also a difference in wheel diameter which changed the effective final drive ratio and this must also be considered when evaluating the differences of wheels. But in any case, the wheels you select for your car can make a big difference in handling, performance and dyno results.

 

My 20's are within 0.2" of the oem diameter so that is close. The rims even weigh about the same as my stock 17's but the wider tires weigh a good 5lbs more and it does slow you down a bit. I need them for traction anyway and the looks are worth it.

 

Great information, Tony.

 

Bringing a thread back from the dead so that I don't get the "Use the search" quote

Tony,

Need your insight on this dyno result. Just got a dyno after installing a few items and i got the attached dyno result (I know the dates are quite far apart but the conditions now are worst, hotter and humid). Didn't expect that much TQ gain at low-midrange nor did i expect to lose so much HP at topend (car stopped making power pass 6k). I really wasn't expecting any gains whatsoever, but rather some minimal loss. The shop said the loss is normal with such larger rims in both width and diameter, do you think that is the cause? I previously had stock 18". These are the stuff I installed in between dynos.

-Interstate Battery, finally had to replace my 6 year old OEM one.
-MD Coolant Control Valve
-UR lightweight underdrive pulley (-5.2lbs)
-UR lightweight flywheel (-15lbs)
-Southbend OFE stage 3 clutch, just to replace my 90k old one.
-Girodisc 2-piece rotors (-9lbs rear and -11lbs front)
-Axis 20'' Rims (+???)
-SxExCx ground kit

EDIT: Is it possible that there is some settings on the Mustang Dyno?

 

well no stock G makes power past 6k.
plus the widely variable conditons between pulls could be + or - 20% of your original numbers.

and without matching AFR curves, who knows what the stock ecu was doin to compensate for the higher temps...

and honestly, even if you did lose some power, are your going to sell the wheels?

 

The RPM shown on the dyno are not from the tach but based on the settings of the Mustang dyno machine. I know that the stock Gs don't put out any more power past 6krpm, but it's like I said it's all based on the cutoff setting on the dyno machine. I looked at the AFR for the most recent dyno and nothing seemed abnormal or too different then my previous one, hence the reason i didn't opt to get a print out.

Given the current curve it's hard to say, in general terms, whether or not I lost or gained power. The new dyno shows a significant improvements in the more common and usable rpm range, with the penalty near redline. There is no doubt that most of us that uses our car for daily use will spend more time in the lower to midrange, but if you track your car then it's a different story.

Though the wheels are much heavier then my stock 18'' they provide much better traction for acceleration and handling, so then again it's not a win win situation if I were to move back to stock. Of course I am not going to sell my wheels, but it's a curiosity I would like to be answered. The more knowledge the better decision we can all make for latter projects.

 

Same car, same day, same dyno.

The only variable is the wheels.

 

Thanks for the chart.

On the X-axis, the variable is time in second, is this the time progression of the car on the dyno? Therefore if I take your previous statement that the Max HP hasn't changed much in all three cases then your curve shows roughly a 0.5s quicker acceleration to redline for the 17" when comparing it to the 20". Is this correct?

If it is readily available, do you have a chart with RPM on the X-axis?

For my case, I show a drastic loss in power in the topend. Do you think this can be solely attributed to the 20" wheels? The total diameters of my wheels with the 18" and 20" rims are identical.

 

This is the data as produced by the Dynajet. The dynajet owner did it all on a time scale.

 

Thanks again for the graph Tony, based on this, it seems that my problem lies somewhere else. Perhaps the lightweith Al pulley or flywheel. Any ideas? Or is it perhaps that I'm on a Mustang Dyno that considers load whereas most Dynojet machine don't?

 

Here is a possibility.

Not only dynos are know to show different absolute values when it comes to HP and TQ, I'll also bet that they can produce different slope angles on the power curve.