i remember hearing that having 20 in wheels will cause there to be a loss in power bc of more rotating mass? is this true and if so, how much power loss we lookin at here, a noticable difference? thanx.

 

I've heard the same but I was told that it wouldn't be that much of a differance... now if you have 2 cars that are evenly matched up then thats where it matters and counts. I really dunno though.

 

It depends on the weight of the wheels and of course the tire size if you go with a tire/wheel with a larger diameter than stock. If your rear wheels with tires weigh 30lbs more than the stockers then that's the same difference between the stock driveshaft and a 1 piece aluminum driveshaft. I think anyone with a 1 piece shaft will tell you there is a noticeable difference.

So I would say yes the difference is noticeable.

 

yes you will see a noticeable diff in power, but i'd be more concerned about your LSD. according to the manual, running tires other than 17" or 18" will cause a permanent loss of effectiveness in your LSD...

 

A typical set of 20's is significantly heavier than the OEM wheels. You should expect to see a loss of 10-15 HP at the wheels on a Dyno.

Of course, there are some 20's which are even heavier than that, and there are some which are lighter.

If you go with larger diameter TIRES (outside diameter) that has the same effect as changing your rear-end gears, but this won't show an HP change on the dnyo. Also, keep in mind that this is an uncommon practice. When one buys 20's, you generally get very low-profile tires so the OD is the same as stock.

I don't belive the line in the manual about loss of LSD effectiveness with different wheel sizes. It just doesn't make any sense.

 

My 20's aren't that much heavier than stock bullits, and I couldn't feel any noticeable difference in the switch...

 

jay
That is just it! MOST of the people that are claiming 20" lose all this performance HAVE NEVER BOLTED A SET UP!

Yes IF there was a substantial weight increase with 20โ€ rims over the stock rims one would lose some performance! But if the weight between the different size rims is close the added traction with a bigger foot print that most 20" can give you over stock tires is easily over shadows any performance loss one could feel because they have inadequate or marginal horse power! Is every 20โ€ rim made the best rims we can bolt on our cars? Absolutely NOT! There is always a trade-off. One must ask what they want from their car or the add-ons that they install. And anyone that will boldly make a statement that โ€œAll 20โ€ rims will make your car lose performance has no more of a clue then the guy that states 20โ€ rims are the best size rims for ALL performance aspects. Neither of those ends of the spectrum is correct. Somewhere in the middle lies the truth about 20โ€s and performance!
05SDI

 

Erm I got some actual dyno #'s from when I just got bigger tires when my mustang was rather new. I had the stock crapellis 235/50/17 and I did 306.8 rwhp, I changed to 255/40/17 hankooks and my rwhp dropped to 298. Remember if I am not mistaken every lb you add in rotational weight is = to 4x non-rotational weight.

Att. Andrew

 

every lb you add in rotational weight is = to 4x non-rotational weight

Well, it changes with speed = inertia

I believe that you could have seen a change in the dyno numbers. But assuming the tire sizes are correct the 235/50/17 Pirelli was not the stock tire the stock tire was 235/55/17 and they were 27.1โ€ tall. When you changed to 255/40/17 Hankooks you tire height dropped to about 25โ€ tall. What did you change on either the dyno set up or calibration to make up for the 8% difference in the two tire sizes? (if your 235/50/17 tire size was correct then it is closer to 5% difference in tire size) Now the HP numbers you have given are within 3% and that can be the difference in either weather or a clean air filter.
Now IF you had stock 18โ€ wheels and you mistakenly typed 235/50/17 instead of 235/50/18 and you lost HP when you bolted on a set of 17โ€ wheels, this would be quite humorous to me!

I have always said dynos donโ€™t win races!! They are just a tool to inform you of one aspect of how a vehicle could perform.

 

you will likely lose 10-20rwhp, depending on what wheels, how wide, and how much rubber is on them...not the end of the world by any means, but quite noticeable when pulling hard to redline