I've been considering getting 18" or 19" wheels for my car, but have heard that your performance suffers when going with a larger diameter wheel. Can someone explain this to me a bit and maybe tell me if it is a noticable difference? Thanks!

Jeremy

 

keep the stocks and use them for the track if the performance is an issue

 

Here's an interesting dyno comparison that shows just adding 2" to the width of the wheel, and going from 275's to 315's cost 3.6rwHP. Not even a larger diameter wheel.

http://www.ws6.com/wheels.htm

The loss is caused by increasing the "inertia" of the wheels.... the more they weigh, and the further the center of mass is located from the axle, the more energy/HP is takes to acclerate the wheels up to speed. That eats up some of your rear wheel HP. Adding mass to the front will also slow you down.

The shop that tunes my car has seen changes of as much as 30rwHP due to changes in wheel/tire selection. They indicated that the tubes I added, and the larger section and tread width of my ET Drag 28x10.5-15W tires were probably costing me 10HP over my previous pulls.

 

Thank you! That is exactly what I was looking for. I think I might stick with my stock wheels. I really like the way they look, but the grass is always greener...

 

Yeah in fact you can put little mickey mouse wheels on like ricers and you will be uber racer. Whatever you do don't get big wheels with low profile tires, they are the devil I tell you.

 

Wha about the trade off w/ the traction loss of a smaller tire? Better traction for 6-10hp??

 

You do what you have to do..... if you can't hook with a 255/50-16 street tire, you have little choice but to look at a 275/40-17 or even a 315/35-17 tire. I can almost hook on the street with 315/35-17 drag radials - at least running NA, and I doubt it would hook at all on the OEM 245/50-16's. The added traction will easilly offset the lost HP. On the track, I figured if I ever get to launch it with the full 300-shot with a 5,000rpm flash stall off the line, and the 4.11's, I would need more than the tires I was running. And, maybe the larger tires would need lower air pressure, so I added tubes. If I don't get the results I wanted, I'll go back to the lighter weight tires, without the tubes and see if it helps.

He asked what the HP loss was, or if there even was a HP loss. I answered his question. But nowhere did I say he shouldn't use wider tires or larger diameter wheels. I just gave him the info he asked for, so he could make up his own mind.

 

i went up to a 18" and noticably different off line- granted i have much better traction especially shifting 2nd but definately takes off slower- ive heard every inch bigger take 1/10th off your gear ratio

but with better traction kinda washes out somewhat- meh guess have to upgrade gears and get a new cam to offset the rim difference

 

That's true if you are talking about going to a tire with a larger outside diameter. Going from the stock 25.65" diameter to a 26.65" diameter would have the same affect as going from a 3.42 gear to a 3.29 gear. But that's not what we are talking about with regard to going to a 17", 18", or 19" wheel. When you do that, you select the tire profile that holds your tire diameter constant. When you go to a 20" wheel, you are limited to the tire size/profiles available, and you will usually end up with a larger diameter tire than stock.

Even though you keep the tire outside diameter the same, going to a lower section height, and moving the rim portion of the wheel further from the axle, moves the centroid (center of mass) further from the axle, and absorbs more energy as the wheel/tire mass accelerates.

But let's keep things in perspective here... Monocoque advertises that they have the lightest drag wheels available, yet only claims a 0.05-second advantage over competing wheels.