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Opinions vs math on gear ratio

Armo325

By Armo325
in Engines & Drivetrain

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Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
5 hours ago, Darksky said:

Just the tire

 

Bridgestone Dueler H/T D684 II 255R70-17 mounted on stock steel wheel 63.5 lbs. including cap and TPMS.  The General HT, GM's other go to tire on this rim just under 60 lbs. Your tire weighs more than my entire assembly!! Yea, that's going to have a HUGE impact in inertia moment. 

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aseibel Senior Enthusiast

aseibel

Posted
Posted

Maybe if one is actually concerned with towing performance, then he shouldn't install 35" tires on a truck that came with 31.5" tires?

 

The vast majority of lifted trucks with big wheels out on the road are solely for looks. I don't get all this discussion about spending a couple grand to make a truck perform well again after throwing all that money on looks that just seriously hampered the performance. I wish I had that disposable income.

 

But I do agree that if you want to go the big tire + re-gear route, then you do need to account for both the change in your ground speed relative to the driveshaft, as well as the extra angular momentum of the big heavy tires. The OP is on to something. I got a C in dynamics, so I'm not going to attempt to calculate it.

Darksky Enthusiast

Darksky

Posted
Posted
On 3/19/2019 at 1:59 PM, Grumpy Bear said:

Bridgestone Dueler H/T D684 II 255R70-17 mounted on stock steel wheel 63.5 lbs. including cap and TPMS.  The General HT, GM's other go to tire on this rim just under 60 lbs. Your tire weighs more than my entire assembly!! Yea, that's going to have a HUGE impact in inertia moment. 

Part of it may be that they’re ten ply.

ic3man5 Enthusiast

ic3man5

Posted
Posted

I would be worried about the driveshaft rotational speed first. I can't find it anymore (if someone knows where its at that would be great) but I remember the 3.73 gearing and 100MPH they like to shred apart. I was told by a driveline shop my critical point of failure is 200MPH with the 3.42 gearing and 32" tires.

 

Of course if your 6th gear RPM is the same as stock 3.42 on stock tires to your new gear ratio and tires then I wouldn't worry about it.

Carversonline Enthusiast

Carversonline

Posted
Posted

Did you guys figure out the perfect ratio for 35s yet...... My set-up is a little heavy

Tires weigh 80lbs each 35x12.50 20 trail grapplers

Wheels 44lbs. Each 20x12 fuel.

I will throw this out there...my shop said 90% of the guys with the newer truck and 35s go with 4.11s

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