Changing gear size

[cbrown]

Hey everyone,

Long story short, sheared the pinion in my truck last week, after having it running for 6 days once I finally got a working transmission. Had two sets of stock gears at the house, but the carrier was damaged in mine also. Been kind of up in the air as to whether or not to go up in gear size. The truck is an 08 cclb, 40s and 20s, mainly driven on xrace that eric made on the dyno. I do take it to the track a few times a year and sled pull as well. The truck has always run strong on stock gears, pulls a trailer(even with another 10000 lb 250 on it) and gets good mileage- 14-16 mixed driving- for what it is. A buddy of mine with basically the same setup went with 5.13s, and the fuel mileage and drivability is garbage. Its obviously overgeared, but the combination of gear and tunes makes the throttle sooooo touchy(Aaron can attest, as when he drove it the other week when we were picking up my trans he said it was the most rediculous thing hes driven haha) Even with a smal tune its touchy, and with an empty deck over behind it its nearly impossible to drive without flooring it, coast, flooring, coast, etc.

Anyways, Im trying to figure out if I should get 3.73s and a locker or go ahead and step up in size. I doubt 4.10s would make enough difference to justify having to regear the front as well, but Im nervous going to a 4.56 would mess with mileage/ drivability and track times. Any insight/ experience with a particular setup would be appreciated.

Thanks,

Chris Brown

 

[sirnunya]

They also make a 4.30 gear.

I would just replace what broke. You said the truck always ran strong and did everything you needed it to do with stock gears.

 

[Spatel23]

Running a 40 inch tire definitely calls for regearing. The truck will be much happier and you'll have less chance of breaking things again (transmission).

I had 37s and 4.10s and it was ok. Basically put me back to stock if I remember right.

I think 4.30s would be your best bet.

 

[TANK'S 250]

for 40's you need at least 4:56's...NOT 4:30's....your tranny will thank you!


Gearing is a tough call....a lot of it has to do with preference, the type of driving you do(city/highway), and whether you tow or not.

The gear charts are a good start, but what people don't pay attention to is that even though the gear chart says ...for example...4:56 for 38" tire...it doesn't take into consideration that the wheel/tire combo weighs alot more....and with more rotational mass you should go up one more gear.


...so all the people that say " this puts me back to stock"...didn't think about the extra rotational mass over their old stock sizes...

....they may not notice the difference...but their tranny damn sure does!



I run 41" tires...but I'm geared 4.56's....because I have a manual transmission...which is another consideration.

I chose that differential gearing because with my manual trans I choose what gear I want,...if I'm mudding or towing...I use only 4 gears...but if I'm driving on a couple hundred mile trip at ...it's nice to have my top gear(6th) only running about 2,000rpm's @80 mph.

 

[Erikclaw]

4:56's may be good in a truck with a manual but I wouldn't go that deep on 40's. You will be tacking 2500 at 80mph I bet. I have 37's with 4:30's and at 80mph I am at 2250. I think I am geared too low, I would rather have 4:10's. But it is up to you and how you drive like Tank said. Tow a lot then different choices are needed.

 

[TANK'S 250]

4:56's may be good in a truck with a manual but I wouldn't go that deep on 40's. You will be tacking 2500 at 80mph I bet. .

I run 41" tires...but I'm geared 4.56's...only running about 2,000rpm's @80 mph.

for 37's a 4:10 is a decent match...but I'd go 4:30s to make the tranny happier.


He says he races, sled pulls, and tows heavy....if he only puts in 4.10's/30's with 40's......lets just say,...I hope he saved money for a new tranny...because it will fail sooner than later.

 

[TANK'S 250]

I would just replace what broke. You said the truck always ran strong and did everything you needed it to do with stock gears.

But his tranny blew up...that was BECAUSE he didn't regear....

It's all about making the tranny happy....unless you can afford a new one every couple years, then have at it...LOL LOL

 

[TyCorr]

How do we know thats why the tranny went? There are guys with tuning only that roach the trans.

I agree oversize tires and added power are a recipe for the trans to give it up but who knows if thats why his did.

Ive had 3.73's and 36+inch tires for 265k miles of which 180k was tuned, is mine gonna blow up too? I have a lowly 4r100 on top of it.

 

[Jeff@Spartan]

I have a buddy with 40/15.50/22 Toyo MT's on his 6.4. The truck is daily driven with the Spartan 275 tune. Stock transmission and 3.73 gears. He has no issues with over 50,000 miles on the odometer.

 

[cbrown]

You will be tacking 2500 at 80mph I bet.

Thats what Im concerned with. My buddys truck with the 5.13s is in overdrive at like 35 haha. I do race and sled pull, however its not an every weekend thing. Towing is occasional, if a friend ever breaks down or going to the sand drags or the beach with the other truck. So I dont want to gear towards that and sacrifice drivability. That said, I completely understand the reasoning behind that. I had plans to regear when I originally lifted the truck but it ran so good I decided not to.

Im sure the abuse the truck sees combined with the fact its pulling around extra weight had something to do with the transmission. first time I toasted the converter, but was pulling a trailer in a race tune and kind of kept bumping in and out of converter lock. Had no intentions of pulling a trailer, but got in a bad situation and sorta had no choice. Chit happens. Second time broke low/ reverse out on the beach pulling a guy I know out with locked up hubs.

So, what would 4.30s put me at compared to stock? Would the ratios be about the same?

Also, Shone could you shoot me a PM with the info you have on the powdercoat?

Thanks

 

[TANK'S 250]

I have a buddy with 40/15.50/22 Toyo MT's on his 6.4. The truck is daily driven with the Spartan 275 tune. Stock transmission and 3.73 gears. He has no issues with over 50,000 miles on the odometer.

LOL...his odometer isn't right

 

[Erikclaw]

Thats what Im concerned with. My buddys truck with the 5.13s is in overdrive at like 35 haha. I do race and sled pull, however its not an every weekend thing. Towing is occasional, if a friend ever breaks down or going to the sand drags or the beach with the other truck. So I dont want to gear towards that and sacrifice drivability. That said, I completely understand the reasoning behind that. I had plans to regear when I originally lifted the truck but it ran so good I decided not to.

Im sure the abuse the truck sees combined with the fact its pulling around extra weight had something to do with the transmission. first time I toasted the converter, but was pulling a trailer in a race tune and kind of kept bumping in and out of converter lock. Had no intentions of pulling a trailer, but got in a bad situation and sorta had no choice. Chit happens. Second time broke low/ reverse out on the beach pulling a guy I know out with locked up hubs.

So, what would 4.30s put me at compared to stock? Would the ratios be about the same?

Also, Shone could you shoot me a PM with the info you have on the powdercoat?

Thanks

With my 37's and 4:30's it is close to being in the stock range if I remember right. But I don't like the high rpm's at 80mph. It is 2250-2500, I don't remember exactly right now. I don't tow much and my dd driving can be over an hr on the hyw each way. I want 4:10's but don't think the cost makes it beneficial.

 

[pog]

with 35s and 3.73 im at 2-2100 @80mph. 37s and 4.10 would prob be very close to stock. is there no 3.90 gear available? big jump between 4.10 and 3.73

 

[Jeff@Spartan]

LOL...his odometer isn't right

I think he has figured out what the mileage really is, and it's somewhere around 50-55,000 miles. The hand calculated odometer. lol

 

[AKHILF]

Not trying to jack the tread but is there an equation for figuring out true milage?

 

[Wayne]

With my 37's and 4:30's it is close to being in the stock range if I remember right. But I don't like the high rpm's at 80mph. It is 2250-2500, I don't remember exactly right now. I don't tow much and my dd driving can be over an hr on the hyw each way. I want 4:10's but don't think the cost makes it beneficial.

Ran my truck at 80 on the way home tonight with 3.73's and factory 20's/ 265's which actually measure near 35 (largest factory option tire) I was pulling a steady 2100 rpm's. Now I see Erik why you were complaining about too many rpm's at 80. I'd still put the same setup you have on mine if I had the money and 37's, but for you (a guy who goes 80 all the time and seldom tows heavy) those 4.10's should be perfect. When I recommended you the 4.30's back in the day I failed to take in to account that you started out with the tallest available stock tires. Sorry about that. I sure do love your truck though. The power on that thing is crazy!

 

[cbrown]

So is the general consensus that a 4.30 would be ideal for 40s without running too high of rpms? thanks for all in the info again.

Chris

 

[TANK'S 250]

4:56 gets you closer to stock...but Like I said...you still have to take into consideration of the extra rotational mass of the tires and wheels...so 4:88's...

....I would still recommend 4:56's for 40's

 

[tbsimmons]

To get you back to stock, but remember what Tank above said, rotating mass will play a much bigger role than tire size.

(New Tire Size / Old Tire Size) * Stock Gearing = New Gearing for Stock.
I would round up.

 

[cbrown]

Ok, so using that equation, I get 4.26 calculated with a 35" stock tire and 4.39 with 34" stock tire. I had the lariat 20s stock, so not sure what the stock ones exactly were, but if I recall they are between that. Is there a way to calculate what rpms I would be turning at a certain speed depending on gear size? Also what effect would larger gears have on fuel mileage? Im certainly not overly concerned with it, however I do like being able to cruise around without watching the gauge drop. It would make sense to me that regearing to a stock ratio would improve the mileage? Stock gears + larger tires = dropped mileage. Gears to compensate+ 40s = stock truck mileage?

Thanks,
Chris