what is the optimal rim and tire size for 1/4 mile?

[NWFRS]

BBC TopGear challenge:

Build a GT86 drag car.

How hard can it be..?

[swarb]

205whp? what mods? dyno sheet?
time slip?
Can't really give advice if we don't know what mph/gear/60' etc you are currently at.

[Mike Brz]

I have already done all the power mod im going to do at this point. I just want to know what size is best. I appreciate all of the input amaya.

[Mike Brz]

My current mods are injen intake, agency power header, stock overpipe, 2.75 catless downpipe and exhaust, 3pc pulley kit, small tb spacer stock size, lightweight 17x8 35 offset all around with 245/45/17 all season tires, ecutek 93 octane tune. 186whp.

[Amaya]

Originally Posted by Mike Brz

I have already done all the power mod im going to do at this point. I just want to know what size is best. I appreciate all of the input amaya.

I may have gotten a little carried away with my recommendations. I was bored at work and suddenly I have an interesting problem presented :p

Originally Posted by Mike Brz

My current mods are injen intake, agency power header, stock overpipe, 2.75 catless downpipe and exhaust, 3pc pulley kit, small tb spacer stock size, lightweight 17x8 35 offset all around with 245/45/17 all season tires, ecutek 93 octane tune. 186whp.

The only tires I have any personal experience with is the Dunlop Direzza Z2's I put on a week ago with my new wheels. But so far I'm quite impressed with the grip they offer, much less spin when launching and hard shifting into second. I was surprised at how much quicker the car feels with them, if I get the time go back to the drag strip I will post the results. I'm running 245/40R17 in the rear which are 845 revs per mile versus 844 for the stock tires so practically no difference. To get a little more mechanical advantage I would say Z2's in 235/40 as they are 856 revs per mile. There may be a high performance tire in 235/35 that would be an even smaller diameter? Tirerack has tons of data, you just have to spend some time reading and taking notes.

[Amaya]

I really don't know about optimal rim size, personally I would sacrifice some weight reduction just to have wider tires because I like the look and don't plan on having a dedicated set of track tires yet. I would think that finding the smallest/lightest, grippiest tire and then getting the smallest/lightest wheels that will fit would be the formula for success since you aren't talking about adding a lot more power soon. Maybe even going to 16" wheels? Those should be lighter and the weight would be closer to the center keeping the rotational moment of inertia lower than an equal weight wheel in 17".

[dobbrz]

Originally Posted by Mike Brz

Hey guys. Wanted to know what the best rim and tire size for a 1/4mile. Brz is ~205whp naturally aspirated. Looking for best size for optimal gearing. i was thinking to go with 16x8 rims for the rear, (not sure what tire size, i was thinking to go with a smaller rolling diameter than stock) and fronts id get 16x5 rims. Thanks

Originally Posted by Mike Brz

My current mods are injen intake, agency power header, stock overpipe, 2.75 catless downpipe and exhaust, 3pc pulley kit, small tb spacer stock size, lightweight 17x8 35 offset all around with 245/45/17 all season tires, ecutek 93 octane tune. 186whp.

So...you don't have 205 whp then?

[venturaII]

Try a 225/45-16 in a DOT drag radial. It ought to be plenty sticky for a N/A motor, less weight than bigger tires, and the shorter gearing from the smaller overall diameter will be easier to launch and should improve your ET a bit. Or, a 225/50-15 would get you a little more sidewall with the same overall diameter as the 225/45-16, which will let you run a little less pressure, and would improve the launch a bit more. I also wouldn't go with a 8" wide wheel - it's a waste of size/money/weight if you're just interested in drag racing. 6.5 or 7 inches wide would be plenty for a 225 tire going in a straight line.


If you really want to do all you can, disconnect or remove the swaybar in front, and go for light, skinny 195/55-16s in front and air them up to 50psi.


And ignore the haters. They are what ruin forums. Do what you want with your car; just be aware that it's design emphasis on handling is going to be what defines it's ultimate limitations in other forms of motorsports.

[malave7567]

Originally Posted by dobbrz

So...you don't have 205 whp then?

you missed the post where he said he was getting an E85 tune soon. A good E85 tune should get him around there if he's already at 186.

[venturaII]

Originally Posted by Mike Brz

Smaller rolling diameter is going to be easier for the engine to turn the wheels. Also faster acceleration but lower top speed in 1/4 mile. Larger diameter would be easier to hook but slower acceleration with higher top speed.

Yes and no. If you had a single speed gearbox, then you'd be correct. But given that I doubt you're even going to be in 5th gear at the end of the 1/4 with stock gearing, your top speed, which is much more a function of horsepower, won't change much because you can just grab the next gear. Shorter gearing will definitely help your launch and ET.

[Mike Brz]

So smaller tire diameter?

[venturaII]

Originally Posted by Mike Brz

So smaller tire diameter?

Smaller tire diameter gets you shorter (numerically higher) gearing, which helps acceleration. Try to go smaller on wheel diameter too, as it makes the wheel lighter, and the additional sidewall and volume will allow the tire to launch better. I wouldn't go bigger than a 225 for width, if using a real DOT drag tire. Just my 2 cents. Good luck!

[Mike Brz]

Originally Posted by dobbrz

So...you don't have 205 whp then?

No. Im at 186whp with my current mods.
Im keeping the 3pc lightweight pulley kit and 2.75 downpipe and catback.

Adding driver and passenger side Speed Genius prototype ram air snorkels.
Speed Genius prototype air box.
Bye bye injen intake, hello Speed Genius prototype intake.
Stock tb out, Speed Genius big throttle body in.
Small tb spacer out, Speed Genius big throttle body spacer in.
Crawford power blocks? Yes please!
Swapping out the Agency Power header for a ported inlets/outlet HKS EL catless header.
Also ditching the stock overpipe for a Perrin 2.5 overpipe port matched inlet and 2.75 outlet.
Drive Shaft Shop aluminum driveshaft.
Flex fuel kit / e85 tune

Im sure 20whp wont be 2 difficult with these changes

[Mike Brz]

Originally Posted by venturaII

Smaller tire diameter gets you shorter (numerically higher) gearing, which helps acceleration. Try to go smaller on wheel diameter too, as it makes the wheel lighter, and the additional sidewall and volume will allow the tire to launch better. I wouldn't go bigger than a 225 for width, if using a real DOT drag tire. Just my 2 cents. Good luck!

Yea i was lookin for 15's but most have fittment issues. So i decided 16x8. I just dont want to change the diameter 2much and have to shift again cause that will kill the time also. Fronts im goin with 2 16in spares. (Like the ones from the trunk)