Gearing for a TBI

[sreidmx]

I got the wifes truck.. trying to get the gearing setup proper. It has 33 inch tires and a 700r4 I was thinking 4.56 or 4.88. basically putting the motor back to what it was stock.. Its a lugger now, spins 1800 or so at 70.. I think. Its got 3.73 in it now.

 

[riflerk20]

I have 4.56 and 285/75 16 tires on my 87 k5 . The only motor upgrades are headers and dual exhaust. I don't have a tach but it cruises at 75 without shifting out of OD much

 

[paratrooper307]

That RPM sounds about right, although you'll want to check your ring and pinion to be sure.

A 4.10 gear with 33s would put you right about where you would be with a 3.73 and 31s. Probably the best overall choice for a vehicle that sees mostly street time. However, since you've got OD, you can go deeper without major issues. A 4.56 only adds about 200 rpm@70 over a 4.10, and 4.88 would put you about 400 rpm higher. Deeper gears also give you some flexibility if you want to upgrade tires later. A 4.10 is probably the cheapest option, since 3/4 ton axles in that ratio are easy to find. You can play around with this calculator and get an idea of the effects of your choices.

https://www.ringpinion.com/Calculators/Calc_RPM.aspx#TireHeight

 

[tRustyK5]

here is the new math:

700R4 = 5.13's

 

[blazinzuk]

I think you'd be happy with 4.56s or 4.88s

4.10 meh not enough of a change for me.

 

[paratrooper307]

here is the new math:

700R4 = 5.13's

I like your math, but might get tiresome on the highway and your wallet. The OP did state that he wanted to regear to compensate for the tires and get stock-level gearing.

 

[tRustyK5]

33's and 70 is ~2500 rpm, and when the inevitable 35's go on it'll still be A-OK.

 

[sreidmx]

I need to check the gear charts but I want to be in a decent range for towing in 3rd. I checked again and 70 is about 2krpm on the nose. If I could bump that 400 I think I'd be golden.