BTW any las vegas people want to go Tomorrow, Dec 1st, to the drag strip her in vegas let me know. Now to the question.
Say im gonna drag race my car. And I obviously want the fastest time. Which set of wheels would be better to use or would they yield the same times.

The 18" wheels/tires
225/40/18 front
255/35/18 rear.

The 19" wheels/tires
245/35/19 front
275/35/19 rear

The 18's and 19's both weight the same with the wheels and tires (18's are heavy stocks & 19's are forged)

I read somewhere that bigger wheels (19's) would still be slower even with the same weight cause the wheel and tire combo is taller than the original size. Is this true? And if there is a diference it shouldnt be more than a .1 of a sec difference right?

TIA

 

The smaller diameter the rim, the more wrinkle in the tire, the better the traction. Generally rear rim's for drag cars are 15"ers,but you can't go any smaller than 18's because of the calipers Also weight wise, 100 lbs is generally considered to be 10 ponies. I don't know about the time difference though.

 

Wheels:
Even though your 18"s and 19"s weigh the same, all other things being equal, the 19"s will be slower. This is because there is more mass further away from the center or axis. Think of an ice skater that pulls his/her arms in when they go up for their jumps and then pushes them back out to slow the spin for a hopefully controlled landing. His/her weight remains constant but the distribution of weight in relation to the axis of the spin is what makes the difference.

Tires
you have a couple of competing concerns here. As mentioned above, you want a taller aspect ratio for better traction. You want a little flex in the sidewall here. However, the overall diameter of the tire affects the final gearing of the car. The larger the diameter, the higher the gearing (which is bad for acceleration in general unless you have a car that has so much power that it's a not an issue.) So, the goal here should be to shorten the gearing by going with a tire with a smaller overall diameter but keep the aspect ratio relatively high by going with smaller diameter wheels. You can probably fit a 16" wheel back there relatively easily as the rear rotors are ~12" IIRC.

Another concern is the actual gearing of the car in relation to what the new overall diameter of the tires will be. Ideally, you'll want to be very close to the redline in the lowest gear possible as you trip the lights. If you go with tires that are too small, the car may have to upshift to a higher gear before reaching the 1/4, which will naturally take time.

Weight
As a general rule of thumb, 100 lbs equals .1 in the 1/4.

Rotational weight is another big concern here. Rotational weight must be accelerated on 2 planes: around the axis and laterally (forward or backward.) This is why 1lb of rotational does not equal 1 lb of dead weight dynamically when accelerating. The key here is to get ultra light weight wheels AND tires. If you go all out and get some 16" forged wheels that weigh ~12 lbs with lightweight tires, v. the 24+lb stockers, you might shave a couple of tenths in the 1/4. You're reducing rotational mass, you're reducing the wheel and tires moment of inertia (it's resistance to spinning) because more mass is closer to the axis, and you're probably lowering the overall gearing of the car with a smaller overall diameter but getting better traction with a taller than stock sidewall.

Hope I've made sense.

 

That pretty much says it all on the tire issue. The only other things you can do is get as much weight out of the car as possible. To what extent you do this is up to you. The basics would be to remove anything that is not "bolted" on to the car. Also be sure to run with no more than a 1/4 of a tank of gas and if you are feeling up to it run the car almost dry and put high octane racing fuel in it at the track.

I would personally leave the wheels on the car and just give it a run. Get a feel for the car on the drag strip and then by the next time you go you can work some things out and see how making changes, such as weels, improves your times.

 

Also turn off as many electrical devices inside the car, including dimming interior lights. After you do enough runs, you may only realize that .0x0 change in time, but every bit counts.

 

I thought you can put 17s on the back, I think Roro did it.

 

You should be able to fit 16" on fairly easily.

 

Thanks for the info. So how much faster do you think the stock 18's will save me in the 1/4 mile vs the 19's? .1? .2? Also stiffening the coilover wouldnt do anything would it?

BTW I pulled out the spare, the tools/jack in the trunk, my subwoofer box and amp, the back seat, and all the stuff in the glove box etc. Anything else I can remove?

 

You can use narrow / light weight 17" wheels and tires on the front to reduce unsprung weight even further, but it may be difficult to find a wheel that has the right shape center dish (to clear the calipers).

 

You should soften the dampers in the coilovers to increase weight transfer to the rear, and the front passenger seat should be pretty easy to take out. It should just be 4 bolts, and a couple electrical connectors.

 

has anyone tried it on the back?

 

If 17" will fit on the front (standard stock IS350 wheels are 17"), then 16" will easily fit on the back. The rear brakes are almost a full inch smaller than the fronts. If I remember correctly, some IS250s in other markets come with 16" wheels, and their front brakes are about the same size as the rear brakes on the IS350.

 

Someone on the my.is forums said not to do a burnout on street tires. Why would you not want to do a burnout? Its been 37 - 45 degrees here in las vegas the last few nights, shouldnt I do a burnout to warm the tires up?

 

I don't think that there will be that much of a measureable difference. MOI will be less and the sidewalls will be a little taller for better traction but I doubt it would add up to anything more than a few hundredths.

 

For some weird reason when I put on the 19's the car "feels" faster in a straight line. Probably just me though.