Matt#498

i have a 01 silverado z71 1500 on 35's i have heard 4:56 but i think it sounds a little low but all the shops say it will run good and get better gas milage.

can yall tell me if my speed will be affected?
and will it help gas milage?

therewolf

Hi Matt#498,

Welcome to the Chevy Forums.

If you've got 35s, 456s would probably be the gears for you. 410s would work, but you'd probably not have the low end power you want.

As to "affecting speed" are you referring to recalibrating your speedometer, will you have more low end dash, or are you referring to top end speed ?

For gas mileage, I imagine around town, having gears which match your tires will help a little. I DNK what kind of mileage you're getting or expecting to see with 35s, but I'll hazard a guess that long highway trips are a thing of the past for you in that truck.
At 65 MPH with 456s and 35s, you're engines taching what? @3800 RPMs?

Matt#498

right now i get around 12-13 but the people at the shop said i will be getting better milage around town and while towing

and i was wondering how it would affect my top speed

nauticstar87

Your top speed will drop. You can prolly still govern out, but your engine will be screaming. You'll get to that top speed in no time. i had an ol' ford 4-speed with granny 1st, when i slapped in a new axle with 4:56s, i could smoke anything of the line all the way til i hit 55. i was scared to push it any more than that.

mudmaniac

If you already have the 35's on the truck the 4.56 gears will bring it back to almost stock gearing, you will have more low end and will be able to hold a higher gear at highway speeds when going uphill.

therewolf

And those 12-13 people are right. Given that you're ALREADY LOSING a massive amount of gas mileage to the 35s, matching gears will help your MPG by not allowing your engine to bog down.

You'll lose your top end speed, period. If you're towing something local or to the lake, fine, but I wouldn't recommend taking the 456-35s show on the road cross-country.

Those gears are designed to give you gobs of low-end torque and power which you need with 35s. You gain that advantage at the cost of top end speed.

Matt#498

thanks everyone im getting the 456s put in monday ill let yall kno how i like it and does anyone know how to get pics on here?

therewolf

Be sure they reprogram your PCM for the gear change, so your speedometer will read correctly. It will also reset the ABS sensors so you're not getting brake warnings on your dash.

There's a section up in the beginning of the forums which handles pictures.

BTW, mudmaniac and a couple of the other guys here (as well as your 12 or 13 experts back home) should be able to break down exactly how much top end you lose when you change to 456s.

BassinProf

Going from 4.1 to 4.56 will give you better low end torque but worse MPG (especially on the highway). It will also give you lower top end speed. Unless your truck is underpowered and bogging down when you try to tow I wouldn't make the switch. I have 4.1 gears and run 35s with no problem but my truck has the 6.0 liter engine.

mudmaniac

rivereye is correct, you will lose some top end. Here is a link to a rpm calculator, you will need to know the trans ratio, tire size and diff gear ratio. http://www.ringpinion.com/Calc_RPM.aspx
I don't drive mine on the road much anymore, but as I remember I would be at about 2000 rpm at 60 mph. With the stock 3.73 gears and 285x75x16 tires, I would be at about 1500 rpm at 60 mph.
I assumed that if you have 35's you don't drive on the interstate that much.