are 4:30 gears too low for highway use?

That's getting awfully tall. I would say a 3.90 would be the limit especially with the 18 speed.

 

Hi Dustin: This subject has been discussed many times with just as many opinions. I perfer gears low enough for any job encountered. Sometimes at the expense of some extra fuel, but it is a good feeling knowing the truck will do it.
Present truck has 4.30 gears. Alittle slow on the highway, for good fuel mileage. IIRC, around 1650 rpm's at 65 mph? A majority of time i am on secondary roads and usually heavy, by a considerable amount. So i buy extra fuel to have the "correct gears". Worth the trade knowing driveshaft and clutch arnt being destroyed. If you have to givethrottle when letting clutch out, it isnt geared low enough.
At present time, on a month long job nearly all highway work, grossing -80K. Alittle faster gears would be nice, but cant have it all. And as said, it is for a month, so...

 

How heavy? At 80k or less OTR the 4:30s are low. The 430HP Detroit and big weight would bother me alot more than the gearing. The 525 Cummins has 1850 torque. The 430 Detroit is only 1450 or 1550 torque. It could be either. I have run 100k+ with gears from 3:70 to 4:33 and found little to no difference in fuel milage. If you were hauling freight your 3:58s would be alot better on fuel but over weight B trains, Dont be afraid of the 4:30s.

 

I look at it this way: How much extra fuel could you have bought with the money you spent replacing drive line components you tore up because you didn't have the proper gearing at the work site?

Gotta spec the truck to do the job.

 

I wouldnt be scared of the 4:30s. for what its worth I have a 2011 pete 388 isx 600 18 gear with 4:30s and it gets better mileage than our 389 (spec the same right to wheelbase) with 3:90's. only difference is the 4:30's let u pull the hills a gear higher without losin speed. probly where its makin the mileage up

 

wonder how 4.30 would go with a 15 over and a 3406 c over the rd im guessin it would cut my top speed back alot

 

4:30s are more of a heavy haul off road gear. Any thing under 100k on the pavement dont need a gear that low. With a 15 over your RPMs would be even higher than with any other overdrive trans. The 15 is only.79 over. The other Roadrangers (8LL 9s 10s 13s and 18s) are .73 or .74. Not a huge difference but still enough to be to low for me. 3:70s or 3:90 with tall rubber would be better for the road.

 

It comes down to how fast you are going to drive on pavement. Arrow had a bunch of 450 Mercedes on their chip haul out of Kamloops, 18 speeds, 4.30's on 11/22.5 tires. But they only drove 90 km/h.

My Columbia, also with a Mercedes, came on 11/24.5's. I put LP's on it and effectivly turned the 3.90's into 4.11's I gained a whole lot of drive ability and didn't loose any fuel economy.