how bad can tall tires kill your rear ratio?

[D347643]

ok i am gonna go with 3.73's in the rear but im also going to be running something like a 305/50/15 or maybe a high 200 like 295/50, would getting those taller tires affect the 373's? would 410's be equivalent to 373's in that manner? thanks for any info

Drew

 

[mike93lx]

if you're looking to do 3.73's with those tires, you'll prolly want to go a 3.90 and get speedo gears for a 3.73. the 3.73 will perform somewhat like a 3.55.

what kind of mustang do you have? a 305 will be very heard to get under the back end of a fox.

 

[mike keirstead]

Check the height of the tires. They must be on the website of the brand of tires. I have 3.73s and i went from 245/50/16( 24.75 inches) to 275/50/15 (26 inches) and I noticed a difference. It actually helped the car hook in low gear a little better. These are drag radial specs. The 325/50/15 BFG drag radial is 28 inches high. So 305/50/15 would be 27.5 or so. Thats alot of tire for 3.73s. Unless your making real good power. Depends on what you use the car for really. If its just a street car they would be fine. You would lose a little gear but nothing to worry about. At the track it may take a bite out of your 60 foot versus a shorter tire.

 

[D347643]

i have an 86 hatch, ill prob just go with 295/50/15 but from the measrements its like 11.6 inches wide and that sounds small for some reason, maybe its just me. like i expect it to be huge but 11.5 doesnt sound too huge.

Drew

 

[mike keirstead]

We are talking Height not width. 11.5 inches is not that wide your right. But 28 inches high is a different story.

 

[mike keirstead]

Sorry guys I posted before i saw the width talk.
Mike93lx is correct . They will perform like 3.55. I would say go with 4.10s. You will have to roll the fenders for 305/50 to fit. 295/50 may require a spacer. Make sure you have atleast 5.5 backspacing on an 8 inch wheel and 6.5 on a 10 inch wheel.

 

[D347643]

yeah i know about the backspacing, i already have my 15x10 draglites with 6.5 backspacing. I had planned to roll the lip anyway and ditch the quads and also the ditch tailpipes for sidepipes. I just want a tire that willl be pretty big but not ridiculously tall and wouldnt squat at 100mph and start rubbing, ya know what i mean?


Drew

 

[Michael Yount]

D3476..... All this you can calculate with a little math - it's all simple ratios. We'll start with tire size - to calculate the height (diameter) of a tire you take the section width -- Let's use your 305/50/15 example - 305mm and convert it to inches (divide it by 25.4 mm/in), you get 12.01. Multiply that times the aspect ratio (the "50" in the tire size) -- 12.01X.50= 6.00. That is the sidewall height. Since you have a side wall at the bottom and at the top, you multiply that by 2, and add the diameter of the wheel - 15, that gives you (2X6) + 15 = 27". That's the approximate height of a 305/50-15 tire. If you do the same calculation on the stock Mustang tire you'll see it's about 25.7" tall. So, putting the taller tire on has the effect of reducing the axle ratio by the ratio of the tire heights. 25.7/27=.95.

.95X3.73=3.55 So, your 305/50-15 tire makes the car behave as if it had stock height tires with a 3.55 gear. If you want to it to behave like it really has 3.73's -- 3.73/.95=3.92 -- you'd have to put something like a 3.90 gear in it.

So, you can play all kinds of games with tire sizes/heights, and see how the effective gearing will be impacted. It's just simple ratios.

 

[D347643]

wow~!!! thanks a million man!

 

[final5-0]

ok i am gonna go with 3.73's in the rear but im also going to be running something like a 305/50/15 or maybe a high 200 like 295/50, would getting those taller tires affect the 373's? would 410's be equivalent to 373's in that manner? thanks for any info

Drew

http://www.allfordmustangs.com/Detailed/608.shtml

Later
Grady