im pretty happy with my 1/4 mile times but was told im being slowed down by my tires. there bfg 315's. i have the 3:73 gears and was told 285's would help my 1/4 mile time by 3 or 4 10 th's. is there any truth to this? thanks justin

 

I don't know if they would help you 3 or 4 tenths but they will definately help you. The bigger tires weigh more so it takes more power to turn them. Now, there is a balance. Wheel spin. The bigger tires will be harder to break loose and spin than the smaller ones so you can launch a little harder on the bigger tires.

 

i was thinking that also. i launch in 4wd now and have a hard time keeping it from spinning.

 

I just had this same question arise on a dyno.I have always had bfg 285/70/17 on my truck,recently I put a set of 305/55/20 nitto terra grappler on 20x10 wheels.The 20's weighed 23 pounds more per wheel than my 17's did.The result I lost 40 horse on the dyno,really confused I put the bfg's back on my numbers are back to normal.Now here's the strange part,Chris at Relentless Diesel just finished a 06 mega cab on 315 bfg's,the truck dynoed 687hp.The 315's weighed 30 more pounds than the stock 17's.Thinking the truck would dyno more on a lighter tire we took the 315's off and put the stock tires on .The result,the truck lost 40 horsepower on the stock tires.It sounds weird but I think the bfg's are the best tires ever,no matter what size you have.

 

I'm sure the physics gurus can provide all kinds of dynamics and formulas to explain what the optimum tire size/weight/width/pressure would be for truck based on gear/weight/hp/torque, etc.. I have had 315s since new, so I don't really know what smaller/liter tires would do. Before my money tree died, I had planned on looking for 32-33" street slicks for my spare set of stock alloy wheels to use for racing. I would guess that something smaller than 315s on liter wheels would help some, but I doubt it would be more than a 1/10 or so. There has to be a point that the tires would be too easy to spin given the high hp and torque. Breaking loose all 4 in 4wd would not help trap times that's for sure. Kind of expensive and PITA to swap 3 or 4 different sets to find the optimum for racing and I doubt they would be the optimum for street. Just my .02.

 

I had 315's before. Now I have 36/13.5/20 on 20x10" wheels and it slowed me down about two seconds in the quarter. Dont know if its cause my tranny slips more or what. I used to light those 315's up. It takes all I have to turn these 36" over...

 

315`s will definitely slow you down......i went from 265`s to 285`s,and went from 9.10 to 9.40`s in the eighth.....it doesnt feel like that much of a difference,but it is.............bama

 

I went from 285's to 35's and I believe that the 35's made the truck a lot slower, maybe it's in my head, but it sure feels like it. I never timed it with the two though so I dont know the true difference. Oh I have the 3.73 gears too.

 

You have to remember that what you lose on the dyno, you might not lose on the track. Numbers are worthless unless you can lay them down.

 

You guys need to realize that changing the diameter(which changes the rolling circumference) changes your overall final drive ratio. Without taking the time to do the math, if you have 3.73s and 285s and then go to 315s, it's just like leaving the 285s and dropping the ring&pinion to 3.23s. If you went to 38s, it would be like leaving the 285s and changing the gears to 2.93s. Again, I didn't do the math, so these numbers are not likely accurate, but you get the idea.

Many years ago (too many) I had a 72 rs camaro. It had 3.23 gears, and when I got the motor built like I wanted, it only ran about 14secs. I changed the gears out to 4.56s ( no tire change, no horsepower change) and it ran 11.90s to 12 teens.

Conclusion - yes the weight makes SOME difference, but gearing (and tire sizes - also the width due to rolling resistance) make a bigger difference.

This is, of course, MHO.

 

makes sence to me. thats however is a big differnce from 14 sec to 11.90's. i doubt ill see that kind of improvment. im at 12.80 right now and would like to get to low to mid 12's.

 

Obviously wou won't see that kind of increase, but that is an example of a HUGE change. It was my daily driver. Premium fuel, 8mi/gal, and 3500rpms on the interstate at 60mph. Just one of the stupid things I did when I was young. But at 19, who cares!

I'm bettin' you'd be lucky to pick up 2 tenths. Also, if traction is an issue, you may actually slow down. When I had my autocross car out at the strip playin' around, I tried two different tires. One was 25" tall and one was 26.5" tall. I ran the exact same e.t., but 3mph faster with the taller tires. The short tires got me aff the line quicker, but the taller ones helped at the far end.

Find someone to let you bolt there tires/wheels on for one or two runs and then you'll know for sure.