raven_ghostwolf

Here are some numbers to help you draw your own conclusion;
Height (over all diameter) & Width are computed from tire size and will have some variance between manufacturer.

Stock size
225/60-15 H = 25.63" W = 8.85"

Your current tire size
245/45-17 H = 25.68" W = 9.64"

Option you listed
255/40-17 H = 25.03" W = 10.03"

Project 5.GO!

The deal is for 4 tires, so I'll be doing the back to match. I would imagine that if the wheel is shorter, the tires will turn faster, so the speedo would register that I was going faster than I was in reality. The question is, how MUCH faster? It soulds like I'll see a reduction in the number of speeding tickets in my future! LOL Now, would I be right in assuming that they have a driven gear to match the shorter tire?

Project 5.GO!

So they are only a half inch wider overall, and half an inch shorter. That is not too much of a difference. A difference of nearly 2 inches per revolution. That adds up over a mile. Unless my basic math has suffered in the 20 years since middle school, I have the 245/45/17s coming up to 785.8 revolutions, and the 255/40/17s coming up to 806.1 revolutions. Is that enough to warrant a speedo gear?

OnyxCobra

you should just be running 245/45-17 up front and 275/40-17 in the rear. 255/40 is a noticeable difference to stock size.

raven_ghostwolf

Ok here are some more numbers to compare using the stock rear gear ratio of 2.73, in 4th gear which would be a 1:1 ratio on a 5 speed, and using 2000 rpm for motor speed.

225/60-15 = 55.85 mph

245/45-17 = 55.96 mph

255/40-17 = 54.54 mph

As you can see not a huge difference, but would be noticed in mpg performance if you track it closely. Hope this helps out some.
(yes I'm some what of a nerd and I have created spreadsheets to quickly calculate these kind of things)

Project 5.GO!

225/60-15 = 55.85 mph

245/45-17 = 55.96 mph

255/40-17 = 54.54 mph

As you can see not a huge difference, but would be noticed in mpg performance if you track it closely. Hope this helps out some.
(yes I'm some what of a nerd and I have created spreadsheets to quickly calculate these kind of things)[/QUOTE]

Well, the opposite side of the coin is that it would be like getting a mini rear gear job, right? A minute change in acceleration? LOL What if I went with some 295/25/13s? Hahahaha!

But seriously, is that enough of a difference to change the speedo driven gear, or do they only come in 5MPH increments?

absolutbspec

Now the thing is your running 9" wide in front... i am too. People are saying they have 245 up front with no issues..on ponies (8"). 9" wide will rub. I think i have 255/40 nitto nt555's up front. Perfect with tire clearance but my rims shave alittle. It looks like it rubs the control arm with my 1-1/2" drop up front. Id like to know how to stop it too. 9" wide up front sucks...if i had to do it again i wouldnt. Steering is limited compared to before plus the sound when you hit the arm sucks.

crusin92red5.0

i have 9 inches up front, lowered 1.5 and mine too hits my stock a arm. i wonder if it would hit a tubular a arm though? to fix the problem: buy rack limiters or shave the a arm. (mine only hits the left wheel when i turn all the way left.

raven_ghostwolf

Here you go just for laughs

295/25-13 = height 18.81" width 11.61"

2000rpm/4th gear/2.73 = 40.98 mph

absolutbspec

i was thinking the same thing about the a-arm but that will only change when i switch to coilovers. I wonder how much shaving it will actually give..and if its even worth it. Rac limiters would seriously limit the steering. Good luck getting into a parking spot in one shot.