what gears?

I have a 97 f250HD 5spd 4x4. The truck has a 60 swap and currently has 3.55 gears with a limited slip and 37s. Currently at 65-70 mph I am turning between 1900-2200 rpm. It seems a little high to me. Every gear calculator I have found says with the 5spd and 37s I need to get 4.30s. Same with plugging in the final drive ratio of the zf6 i want to swap in. not sure if these would be too low or not. Just trying to find the best ratio for hauling and daily driving. 4.30s are a bit more expensive as well. many people have told me to run 4.10s and be done with it. Suggestions and opinions are welcome.

why not just stick with what you have? those rpm's are optimal for mileage and power

I have 35's with 3.55's. It is great empty, but a bit high geared with a load.
Look at it like this. If you put 4.30's in and get tired of the 37's, you will be re gearing it again. If you go 4.10's, you will be perfect with 35's and slightly less than perfect with 37's. So you have flexability.

Another idea to go with it. Swap in a complete 99-04 rearend with a little machine work and custom wheel studs to run OBS bolt pattern. SD's came with 4.10 and even 4.30 in the V-10 trucks. For the cost of a gear set and install you could be along ways to having rear disc brakes.

The zf6 swap is a waste BC it only splits up the middle gears a little bit.

if he wants to bring rpm down he certainly does not want 4.10 or 4.30s

i was planning on using the 99-04 rear end and doing the machining at my school. was just curious about what to do with the gear ratios because the numbers i was getting seemed off to me. did the 99-04 trucks come with a limited slip rear. that's something i would definitely miss from my rear end. i've read more good reviews than bad reviews on the six speed swap. most seem to love it especially when hauling. plus it has a massive cool factor to me.

i don't necessarily want to bring the rpm down. it would be a nice byproduct but the main thing is i want to be able to stay in the optimum rpm range for daily driving and towing. driving the truck right now first gear is almost unusable . i'm already hitting second by 5-7 mph. seems a little soon to me. still learning a lot about thee motors too.

The 6 speed swap is not worth it for any coolness factor. It is just parts, money and work. It may be worth it to someone who tows at heavy GVW often. For me I found the ZF5-42 trans is a better street trans and the ZF5-47 better with higher gears or heavy loads because of the lower first gear.

That rpm seems awfully high for 37s at 65.

My thoughts too, seems like with 3.55 and 35's I have to drop out of 5th sometimes to keep RPM up where not lugging. Especially before the 1.0 and WW2, it would get under the turbo and get hot (egt's)

so 4.10s would probably be the way to go then?

With 3.55s and stock sized tires I was at 1950 rpm@65
Swamped 4.10s in and was now 2300-2350@65 With stock tires
With 4.10s and 35s I'm at 2200-2250@65

All GPS verified

Op will you be doing performance mods? My pickup is still stock performance wise and changing from 3.55s to 4.10s was well worth it for me. After I do efuel, injectors etc. Maybe I would be ok with 3.55s but on a stock pickup 4.10s help keep the rpms from dropping way out of the powerband, esp. When towing. I do miss getting 19-20 mpg consistently though!

the SD axles come with 3.73, you arent supposed to use 1st gear in the zf5 for regular driving, its a granny gear

MJ, not in the mood for a pissing match here. I know your in the mood today.

I'm driving a 2002 F250 that came with 4.30's stock. There are plenty of trucks that came with 4.10's too. Yes 3.73 is more common.

As far as 1st being a granny, that depends on the trans, and the set up.

ZF-42 (95 and earlier) no granny gear. 2nd too high for takeoff. Pretty much that way stock, gets worse with bigger tires or higher gearing. With 4.10's and stock tires you CAN take off in 2nd. Add bigger tires or have 3.55's and no second gear launch.

ZF-46 96-97 has a lower first gear but weather it is a granny still depends on a lot. With 4.10's and 31" tires 1st is useless, good for 15ft before shifting. With 33's it is still too low. With 3.55 and 33's it is a good takeoff gear, with 3.55 and 35's it is almost too high.

97strokerHD said:

so 4.10s would probably be the way to go then?

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To the OP: that statement based on the amount of time discussing it is kinda silly. Like saying "ok so painting it green is the way to go" As a newby you need to discuss and think a while. Every gear choice is a compromise. 4.10 is one choice with one set of compromises.

I spec trucks for 80,000 gvw with 13speeds and 33,000 GVW with Allison 6speed autos pretty regular, and there are very well thought out performance planning programs that attempt to plot all variables and predict performance in gears etc. They are pretty close but not perfect either. And it is always a compromise.

Other factors that come in is speed in gears. If you have a favorite or just necessary grade you have to climb towing, sometimes it is the choice between revved high in 3rd or lugging in 4th. In that case dropping the rearend one ratio gets you in the sweet spot in 4th in the same situation. Not that it will be right for a different load or grade.

Turbo diesels with drivers who pay attention can afford to be over geared (too low rpm) a bit more than gas engines. But my current set up is on the bottom of being unusable in 5th loaded

i do plan on doing upgrades. s366 turbo,e-fuel, injectors, intake, exhaust, and idm upgrade. just trying to build a fun reliable truck.

Are you going to pull or haul anything with it? Want that door open for when you buy a toy to haul or just worry about it later?

Garbage Mechanic, sorry about the premature statement. Tend to get a little ahead of myself trying to plan things out on a super tight to nonexistent budget. Not complaining though because we all have life to deal with. thanks for the advice.

By the way, if you are going to be around awhile and want us to help, fill out your sig. That way we don't have to remember what setup you have everytime we start a conversation. Mods, what trans, what gears, tire size, maybe goals.