tongy89

I am just about to get some new tires and i was just wondering what my new gear ratio is going to be after i put them on

I have the stock tires right now with 4.10 gears

I am getting 295/45/18

Does anyone know how to figure out what the new ratio will be?

SirKnightTG

The formula is:

new_ratio = ( new_tire_diameter / old_tire_diameter ) * gear_ratio

See here for more formulas: http://www.4lo.com/calc/geartable.htm

So stock size is 27.18" and the size you're getting is 28.45"

This works out to: 4.29:1 ratio. But, at the same time, your RPMs will drop by about 100 or so if I remember correctly.

Norm Peterson

Depends on what answer you're looking for. Either you're matching the speed vs rpm or you're matching the expected acceleration.

Speed & rpm - the new gears required to match your 4.10's and whatever OE size are as above (about 4.30).

Acceleration - what the car will feel like if you left the 4.10's alone and went to the bigger tires would be like OE tires with 3.90's.


Norm

MTAS

I have the same setup, it's roughly 3.90:1. I have the Predator set for 4.09 gear ratio and 734 revs/mile (straight from the Nitto web site). I tracked it the other day with a friends car (bone stock) and it was dead on.

tongy89

Thanks guys,

i figured it would probably be around 3.90.

MTAS, How do you like the nitto tires? Im looking at the NT-555 and am reading a lot of mixed reviews on them

157dB

63360 inches in a mile.
Do the math backwards from there...

chopper_man

Why would you change the gear ratio from what the actual gears in the rear end are? The tires RPM would do the correction for that. Am I missing something here? I have basically the same setup except running 3.73's with the over sized tires. I just put the correct RPM in there, gears set at 3.73 and it's right on the money.

Thanks,
-Brian

kpaulhus

He has it set to 4.09 because the predators dont have 4.10 setting i guess? He is just saying that with the bigger tires and 4.10 gears the actual ratio works out to something like 3.90's

MTAS

kpaulhus is correct - the Predator doesn't have 4.10 as an option, only 4.09 which is strange to me. But oh well, like I said, with it set for 4.09 and the revs/mile set per Nitto's page, the speedo is dead on. Tongy89, I really like the Nitto 555 tires and will probably go with them again in December when I'm ready for a new set. Great steering response is one of the main things I notice with them. No wet traction issues as long as you drive sensibly.