jtmiller92

iTrader: (42)

I am buying a set of Weld DragLites for my RS in hopes to run a little quicker at the track this year. My plans are to run a 15x9 in the rear with 5.5" BS and the 3.5" front runners. My question for the guys who race more than me at the track is this. I ran an 11.86 at 122(this isnt a debate on my MPH) with a 1.67 60 ft on 18" Wheels and 275/35/18 Drag radials. Would it be better for me to stick with a 26" or go to a 28" tall tire. i plan on running MT ET Street Radials, either the 28" 275/60/15 or 26" 275/50/16. Will running the taller tire hurt me or help me?

The Boyd wheels were heavy so if nothing else I am atleast removing some weight from the car. The rears came in it 53lbs each with the front 18x8's at 51lbs each with tires mounted of course.

Trevor86TA

You might loose a bit of performance by running a taller tire if it puts you out of the powerband for more of the pass. But why not run bias ply slicks on your second set of rims? Guys haven't had great luck with the radials on manual tranny equiped cars.

jtmiller92

iTrader: (42)

Only reason for the radial at this time is it will be serving as both a street and strip set until i get another set of street wheels. I sold the 18"s and wont have another set until late spring or early summer. I was just thinking the 15" drag radial tire would perform alittle better than the 18" which i still cut a 1.67 60ft on. Just hoping for a little improvement. When i get the new set of wheels, the ET street radials will probably be close to replacement time and i can get true bias ply slicks then. Just thinking out lous for the moment.

AlkyIROC

Choosing a tire height is only part of the equation. For a street/strip car it's not as important but for a drag car, you want as tall of a tire as you can stuff under the fenders. This gives a bigger front to rear footprint on the ground. Then you pick a gear ratio so that your engine is maxed out at or just before the finish line in high gear 1:1. That might not sound like much but most drag cars have shift points well above 6500 rpm. Building an engine with a higher rpm limit means you'll stay in each gear a little longer. To bring the time you're in each gear back down, a deeper gear is used in the differential which will depend on the tire height.

Back to your car. Assuming you still have a factory gear ratio, you should stick with the 26" tall tires. Guessing you shift at 5500 rpm, at what rpm are you at when you cross the finish line? That can determine if a taller tire could be used or a taller tire and some deeper gears to go with them.

Lets say you cross the finish line at 4000 rpm. You would need a deeper gear to cross the finish line at a higher rpm while keeping the same tire size. If you install a taller tire without changing the gear ratio, you'll run out of track before you run out of rpm.

Originally my car had 3.27 gears and 26" tall tires. I was running out of track before I was out of rpm. I swapped to 28" tall tires and 4.10 gears and it made my finish line rpm and performance much better. I then went to 29.5" tall tires and 4.56 gears which made my shift points 6800 and finish line rpm 7200. I now have 32" tall tires and still have 4.56 gears although I may switch to 4.89 depending on how well this combination performs.

On the other end of the scale, you could have a very tall tire, 30", and some highway gears in the diff, 2.73 etc. The car would be dead slow off the line but would probably be able to easily reach 150+ mph on the highway.

jtmiller92

iTrader: (42)

I'm running 4.10's and shift light is set at 6500 (Rev Limiter at 6800)so most likely I am shifting around 6600 RPM by the time i go through the movements. I am in 4th gear somewhere between 6400 and 6500 RPM when i pass the finsh line.

Trevor86TA

Stephen - LS1s can do more than that on the highway bone stock. At 1:0and with a set of 2.73s and 30" tires he would have the gearing to do 222mph. In 6th, well, you get the picture.

jtmiller92 - MT also makes a 275.50.15. Just make sure you put it on a decently wide rim. I think that a short tire will help you as long as you can hook up on it.

AlkyIROC

So technically, your gearing is almost perfect for the 26" tall tire. You could use slightly more gear but the next ratio option is 4.56 which would be too much.

Installing 28" tall tires would mean you'll cross the finish line at an even lower rpm but then 4.56 gears would make that better.

jtmiller92

iTrader: (42)

Thanks Guys, i think I will go with a 26" tire for now. I can always change it out later if need be. I appreciate the explanations given. Makes a lot of sense. Thanks, Jt

68Rat

What gears do you have and what is your max trap RPM ?