quick question

[JCATON]

does anyone know how much 285 55 20 tires & 4.10 gears will throw off my spedometer? please help.

[true4.2]

A lot without a chip.

I'm not expert by any means, but I'd say a good 15 - 20 mph anywhere over 35 to 40 mph. Anything below 35 I'd guess decrease amount by about 5 to 10 mph until you hit 0 mph. Does that make sense? Like I said...not an expert, but it should be fairly close.

I had stock 16" tires and 4.10's, and at 80 mph on my gauge, I was actually doing 70.

[BrianA]

Pick a number, any number. Now divide by 2, add the square root of the number, multiply by.....


Uh, actually I have no Earthly idea.

[BlueOvalFitter]

Quick question? Are we suppose to read it quick or answer it quick? Sorry,I just had to!

[4.2manster]

it all depends on your current setup. a 285/55r20 is a big tire, if you plan on lowering your truck then that is way too big.

285*.55*2/25.4 = 32.3"

My stock 235/70r16 comes out to 28.9"
My current 274/45r20 comes out to 29.7"

much closer.

It all depends on your stock tire size. If you have stock 235/70r 16, and go to a 285/55r20 with 4.10's, you probably wont even notice a difference in MPG/odo (sorry joe, but most ppl with 33"s re-gear to 4.10)

So you'd be pretty close to the stock EFFECTIVE gear ratio, but forget about lowering the truck with that setup. I don't even know if it'll fit under the front wheel wells unless it's a 4x4. That's the tire size most people with Expeditions use when they throw on 20's.

FYI: the HD pickup uses 275/45r20

[JCATON]

sorry i was off ive got 285 50 20 tires. i found out im off by 7.8% on my spedo with my wheels. does putting on new gears mess up your spedo to?

Originally Posted by 4.2manster

it all depends on your current setup. a 285/55r20 is a big tire, if you plan on lowering your truck then that is way too big.

285*.55*2/25.4 = 32.3"

My stock 235/70r16 comes out to 28.9"
My current 274/45r20 comes out to 29.7"

much closer.

It all depends on your stock tire size. If you have stock 235/70r 16, and go to a 285/55r20 with 4.10's, you probably wont even notice a difference in MPG/odo (sorry joe, but most ppl with 33"s re-gear to 4.10)

So you'd be pretty close to the stock EFFECTIVE gear ratio, but forget about lowering the truck with that setup. I don't even know if it'll fit under the front wheel wells unless it's a 4x4. That's the tire size most people with Expeditions use when they throw on 20's.

FYI: the HD pickup uses 275/45r20

[4.2manster]

285/50r20 is 31.22"

still a bit taller, 4.10's will give you some umph still. Expect an increase in what your speedo reads compared to what you are actually driving at.

[six shooter]

Just get a programmer when you get your gears so you can calibrate your speedo with your tire size. I know the microtuner has that capability.

[4.2manster]

with any (good) chip, you can tell them your gears and tire size and they will program/flash the chip so that your odo/speedo works properly

[true4.2]

sorry joe, but most ppl with 33"s re-gear to 4.10

Correct, but I thought that was just to help power and acceleration. Does the added gearing help with 33's instead???

[4.2manster]

b/c you are increasing the overall diameter, it's the same effect as putting taller gears. So to offset that, you actually DO put on shorter gears, to try to balance it out.

if at 3000 rpm you are going 10mph
on 33's you would go 12mph
throw 4.10's and you are back at 10mph

And no, those are not actual values!

[true4.2]

Ah I see, thanks for the correction. I = retarded