Advice Request: Keep the 305/45R17's or drop down to a 275/40R17

Last June I bought a set of M/T ET Street Rs in the 305/45R17 size. Last summer was my first real serious effort running this car at the drag strip.

My car is a stock '15 GT Premium Automatic with the 3.55:1 axle ratio.

This being my first experience with DRs, these Street Rs are an outstanding tire, for my application, they may actually work too well.

With the tires heated up, I launch at 1500 rpm and do not experience any wheel spin. Plus, the car bogs a bit around the 60 foot mark.

My best time for the 1/4 has been 12.678 @ 111.26 mph with a 1.888 second 60 foot. In general, my 60 foot times are in the 1.9 range.

I'm thinking that maybe this tire size is a bit much (width and diameter) for this stock configuration. Versus the stock 235/50R18 tires, these 305/45R17's make the overall axle ratio taller by about 2% (numerically lower).

Looking at the M/T catalog, they offer a Street R in the 275/40R17 size. This tire will have a smaller diameter than the 235/50R18 stock tire and will result in a 6% shorter overall axle ratio (numerically higher).

To help with my 60 ft times, I'm thinking I need some level of wheel spin off the line that a narrower and smaller diameter tire should provide.

Any comments or suggestions?

Run the 305's one more season and try to improve the launches or switch to the 275's? I have a buyer for the 305s and the out of pocket switch would be minimal.

I'm stuck with the 17" tire diameter as I want to keep the Race Star Bracket Racer wheels.

I'm thinking about only adding a tune, either the Ford Power Pack 2 or a Livernois tune. Not sure if the tunes would add low end torque to help with the launches. No other mods planned as I will be updating to another S550 in the next couple of years.

One thing to note is that when I run the line lock with these 305s, after a few seconds of wheel spin, the tires start to grip and actually push the whole car forward. When running on concrete, I end up with 4 tire patches; two from the DRs and two fainter ones from the front 235s.

Thanks.

I have basically the same question below. I have a GT A6 3.15 Rear car. The general consensus seems to be stay with the 28" tall tire. Once you do add power then you will be glad you stayed with the 28" tire. It looks like you have the same 18" Factory 5 Star wheels that I have. I was thinking of getting those Racestar Brackett Series wheels. Do you have any pics of your car with those wheels and the 28" tire on it? Thanks.

Jasmo123 said:

I have basically the same question below. I have a GT A6 3.15 Rear car. The general consensus seems to be stay with the 28" tall tire. Once you do add power then you will be glad you stayed with the 28" tire. It looks like you have the same 18" Factory 5 Star wheels that I have. I was thinking of getting those Racestar Brackett Series wheels. Do you have any pics of your car with those wheels and the 28" tire on it? Thanks.

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Here are some photos. No rubbing issues.

Note that I only install the Racestar wheels when I go to the strip, usually install the day before and remove them when I return home.

Thanks for loading up the Pics! Those wheels look great! The bracket series wheels are cheaper than the Chrome or Dark Stars and since I only plan to run them at the track as well. I figured they would work well. I intend to buy a set of wheels and tires just like these. I think I will go with the 28" tire and just live with the times in prep for more power!!

One more question on those wheels and tires.

Do you do anything to protect the paint when you have the slicks on? I have seen guys at the strip put like plastic around the fenders and wheel wells when the slick are on. From my past experience the slicks do pickup everything and you hear the rocks hitting the car. Also there is usually rubber thrown up on the fenders. Do you just clean it off and not worry about it? Or have you ever tried protecting the paint?

Jasmo123 said:

One more question on those wheels and tires.

Do you do anything to protect the paint when you have the slicks on? I have seen guys at the strip put like plastic around the fenders and wheel wells when the slick are on. From my past experience the slicks do pickup everything and you hear the rocks hitting the car. Also there is usually rubber thrown up on the fenders. Do you just clean it off and not worry about it? Or have you ever tried protecting the paint?

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Last summer I got over 25 runs in with these DRs and have not noticed any debris on the rear fenders. That being said, bluebeastsrt's suggestion of using painters tape is a good idea. Will probably be doing that going forward as I was probably tempting fate.

One thing to note about the the Drag Star Bracket Racer wheels.

They were designed for the pre-S550 1/2" (12.5mm) wheel studs. The S550 has 14mm wheel studs. The 1.5mm difference in stud diameter makes installation difficult unless you hand start each lug nut. The wheel hub bore is larger than the axle hub so you will need to move the wheel around a bit when you hand start the lug nuts.

Since you will be installing and removing these quite frequently, you will get a lot of practice. I can now install or remove them in about 20 minutes with hand tools.

Use the special lug nuts that come with the Race Star wheels, don't get lazy and try to use the OE lug nuts.

I bought a Harbor Freight aluminum floor jack, placed under the aluminum rear control arms at the spring seat area, to help with the process versus my old Sears floor jack.

Lastly, these DRs are directional, so to avoid mis-installation, I have marked each tire with a white arrow indicating the correct rotation (sidewall direction markings can be hard to read).

bluebeastsrt said:

Keep what you got. Launch it at 1800rpms. Your sixty should improve to low 1.8s on the stock converter. Painters tape.

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Thanks, bluebeastsrt, I will be staying the course with these tires.

guy at the track yesterday had a new 17 with just a tune. He was running a set of 245/45/17 ET R's and they were perfect for his 3.15 auto car. He was cutting low 1.8 60'. I would step down a size if it were me. Less rotating mass and weight should help you 60' better. I ran a 275/40/17 Nitto dr on my 15 with the stock stall and 3.15 gears. It pulled low 1.8 60'. The tires would not take the 4c stall so I stepped up to a 27" drag radial