exodus_gs1

iTrader: (3)

So im not new to the drag racing game, but this is something i have never either noticed or paid attention to. I was reading and some guys where talking about how depending on tire size depends on what gears to get or what gears depends on tires. Can someone explain it a little more in depth without being a douche... I have 4:11's a little 265/35-40 but that's how the car came. Haven't had money for bigger tires. In my neck of the woods its big gears with big rubber powered by big numbers. Not to much science to it from what i have noticed.

I8UR4RD

iTrader: (16)

yeah static and dynamic gear ratio. you have some steep *** gears already. im sure if you search youll find the formula somewhere. i dont have it on me.

RPM WS6

iTrader: (3)

I'm not sure that I can do this without being a douche, but I will try my very best.

As you increase tire diameter, effective gear ratio is reduced. In other words, if you have a 4.11 gear with a 25.66" tall tire (stock 4th gen height), but then go up to a 28" tall tire, you have then lost some of the mechanical advantage of the 4.11 gear that you had with the shorter tires. Taller tires will also reduce your cruising rpms at a given speed, versus the shorter tires.

Ideally for drag racing, you'd want to have a gear and tire combo that will give you the best possibile launch (without bog or spin), allowing you to cross the traps as close as possibile to your peak horsepower rpm (rather than having to upshift right near the end and cross the traps at the basement of your powerband).

Hopefully you will find that to be a douche-free reply.

exodus_gs1

iTrader: (3)

Ok yea that was good lol. I just didn't want someone popping off about saying"what are you dumbass"... Blah blah. But ok that kinda makes since, so is it all trial and error? And also you said the bigger tire lowers cruising rpm... Meaning now im at 3 grand at 80 mph bigger tire say 325/40r18 it will be less then that like below 3 grand.

RPM WS6

iTrader: (3)

Yes, a taller tire will definitely lower your cruising rpm for a given speed. To play around with specific numbers and combos, here is a link you might find helpful:

http://www.pszweb.com/car/gears.htm

If you read through the instructions on the main page of that link, it will explain how to use the calculator for different purposes (such as ideal gear ratio for 1/4 mile racing, or necessary tire diameter to maintain a given speed below a certain rpm, etc.)

exodus_gs1

iTrader: (3)

Ok cool, I found one but didn't give me any results for my setup... But thanks I'll give it a look after work

exodus_gs1

iTrader: (3)

Yea that one did the same thing maybe its my phone. I did it on my lunch. Idk I'll try again at the house thus evening

RPM WS6

iTrader: (3)

I just tried it and it works perfect from my desktop. So yes, try again when you can.

exodus_gs1

iTrader: (3)

Did you do it with 4:11's 6500 redline and a 28" tire?

exodus_gs1

iTrader: (3)

probably not seeing how I never mentioned that. I have 4:11's and the car shifts at 6500 and im trying to figure out if I should go 26's or 28's. I have heard both so idk. It will either be a 295/35r18 or a 325/40r18. All tho I like the 335/30's but it's a 25" tire. And taller is better then wider I am coming to find out. I feel like a newb all over again fml lol

exodus_gs1

iTrader: (3)

ok got it to work, i put in the tire of 325/40 18 and saying my redline is 7000 and traping 140 (all hypothetical) said my gears should be 4:13. so my understanding is with my 4:11's trapping at 7000 with those tires I should be at roulghly 140 mph? is this correct?

RPM WS6

iTrader: (3)

There are some issues with this, let's review:

- First off, "4:11" is not a gear ratio, it's a time of day. Your gear ratio is formally expressed as 4.11:1 (the basic explanation for this is 4.11 turns of the driveshaft for 1 revolution of the tire), or simply "4.11". If you enter 4:11 in the calculator it won't work because this is not a gear ratio. You must enter the correct number, which is 4.11.

- Secondly, why are you using 7000rpm as your redline or shift point? Based on the mods in your sig, I imagine you should be shifting at 6000-6200 at most.

- If you go with the 295/35/18 tire, then your max speed at the top of 4th gear would be 117mph at 6200rpm. Based on your mods, you won't be trapping at nor beyond 117mph. So while this isn't perfectly ideal, this should leave you some room to grow.

- The taller 325/40/18 would make the situation worse, and put you near the bottom of 4th gear as you cross the traps (since the top of 3rd would be 97mph).

- All of this is assuming you have an M6 trans.

exodus_gs1

iTrader: (3)

HAHAHA damn im a dumbass... That explains so much. wish someone would hav said something sooner. and no sorry i am an A4 and the car shifts at what seems to be 6500 but havent paid that much attention to the exact spot. and I put 7000 because I have been talking with some people. but ill give it a go again. thanks for the help

exodus_gs1

iTrader: (3)

Re did it and with the 28" tires and 4.11's ill trap 130 @6500 rpms which is where I shift. thanks again for the help and the calculator