Rear end question...

bocefus · January 27, 2006

Hello all, This is my first post and I have to say this is an excellent forum and I've seen some great ?'s and info. Anyway, I have a 2004 Sierra 5.3 and threw some 22's under it and I'm concerned about the drivetrain. I've heard that changing the rear end gears would help by reducing wear on the tranny. Any suggestions with ratios or anything else to look at? Thanks. Mike

bowtie_pasta · January 27, 2006

Do you know what gears you are currently running? Do you notice any performance difference with the new wheels?

trever1t · January 27, 2006

It's not the wheel size alone that will determine the proper gearing but the overall tire diameter.

If you went to 22"'s but are running the same tire OD then there is only the added weight to be concerned about. If your overall diameter went from 31" to 34" then a gear change probably would be a good idea.

What size tires are you running. Steel wheels or alloy?

Ted_Grevers · January 27, 2006

Hello all, This is my first post and I have to say this is an excellent forum and I've seen some great ?'s and info. Anyway, I have a 2004 Sierra 5.3 and threw some 22's under it and I'm concerned about the drivetrain. I've heard that changing the rear end gears would help by reducing wear on the tranny. Any suggestions with ratios or anything else to look at? Thanks. Mike

<{POST_SNAPBACK}>

Don't forget that if you have a 4WD, you have 2 differentials to change out. You also need to consider that with that much more wheel weight spinning, you should consider larger brakes for safety.

-Ted

bocefus · January 28, 2006

The new wheels did help with handling. It has less roll than before. My truck is two wheel drive and I'm not sure of the ratio in the rear end. I thought I read somewhere that 4.10 gears would help but I thought that would be a bit drastic. I use my truck as a daily driver and I want it to be practical to an extent, such as highway driving, towing here and there. Thanks for the replies.

Mike

redvett · January 28, 2006

Did you get a speedo calibration change for the new tires? If not your engine,transmission, ABS & SDM system are why out of wack. Fuel economy, transmission shifting, antilock brakes & airbag deployment will suffer.

bocefus · January 28, 2006

No I haven't tuned it...yet. I'm still debating between a Diablo Programmer or to send my comp in for a tune. I also am planning to install new servos but I have to finish installing the rest of my drop kit. Too much to do with so little time.

pm26 · January 28, 2006

If you had standard rear end, you will have 3.42 gears, which were standard in '04 on 2WD silverados with 5.3 engine. 3.73's would be the next possibility. not very many 2WD 1500 series trucks came with 4.10s.

In order to determine what gear ratio you need to compensate for the new tire size, measure the circumference of an old mounted tire, and then do the same for the new tire/wheel. Determine the percentage difference. If that difference is about 10%, and you have 3.42 gears, you need to go to3.73s. For 20% difference, you need 4.10s.

bocefus · January 29, 2006

Will these work for my truck? Just curious if all types were applicable and if I should be concerned about highway driving, tranny issues, etc. Thanks a bunch for your info. Mike

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fossil · January 29, 2006

I would go up in ratio 1 size from what I presently have. ie: if you have a 3:42 then I'd go with a 3:73. My syock 05 4x4 has 4:10 gears and 17 inch rims and revs out at 2200rpm at 70mph if that helps.

Tree_Hugger · January 29, 2006

I would go up in ratio 1 size from what I presently have. ie: if you have a 3:42 then I'd go with a 3:73. My syock 05 4x4 has 4:10 gears and 17 inch rims and revs out at 2200rpm at 70mph if that helps.

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This advice is completely irresponsible because he still hasn't said what size tires he's running. (And neither did you). The wheel size has nothing to do with the gearing!

pm26 · January 29, 2006

The wheel size has nothing to do with the gearing!

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That is very true.

I have an Army deuce and half with 20 inch rims and 9.00-20 tires. The mounted tire diameter is 40 inches! For a low profile car tire mounted on a 20 inch rime, the mounted tire diameter is something like 24 inches!

bocefus · January 30, 2006

I'm running Cooper Xeon XST 305/40R22's with a 31.61 daimeter. The stock wheels are 94.42 inches in circumference with a 30 inch diameter. I still need to measure the new wheels circumference. An online calculator says it's 99.27 inches. Also, I took a look at GMC's site and it says that 2WD models have a 3.23 stock rear end.

Tree_Hugger · January 31, 2006

I'm running Cooper Xeon XST 305/40R22's with a 31.61 daimeter. The stock wheels are 94.42 inches in circumference with a 30 inch diameter. I still need to measure the new wheels circumference. An online calculator says it's 99.27 inches. Also, I took a look at GMC's site and it says that 2WD models have a 3.23 stock rear end.

<{POST_SNAPBACK}>

So your new tires are 5% larger than your old ones.

This will result in 5% lower indicated speeds than actual and about 5% less 'perceived' power on the road. Also 5% lower rpms for the same speed.

It's probably not enough to notice (Do you feel like your truck is sluggish now?).

But if you want to 'return to the stock 'power', 3.42 final drive would return you to the exact same effective final drive you had with the old tires.

Personally, I'd leave it alone...

If you wanted to get even more 'zip' than you had before, then 3.73 gears would give you about another 10% more zip (and more rpms for the same speed, probably higher fuel consumption etc... ).

Hope this helps.

bocefus · January 31, 2006

Thanks for the info. I think I'll go ahead and get the programmer and change out the servo in the trannny. I've had drive train issues before with my '86 700R4 tranny so I just wanted to make sure that I wasn't damaging this one that I'm not really familiar with.