Hello,
I would have loved to take pics and done a write up but my buggy is in my garage with out a rear axle under it currently so I had to do the swap in the driveway. Which meant doing it quickly and getting it done.
The swap I did was just pulling out a complete stock 2010 third member and replace it with a stock (lower geared) 2009 third member.
Why lower the gearing?
I went from stock 215/65-17 tires to 285/40-20. Which is a change in outside diameter (height) from 28 inches to 29 inches...1 inch taller or 3.6% taller.
The stock rear gear ratio of a 2010 SE with a 5 speed auto is 2.87:1 (sucky). So to get my gearing back to stock I'd need 3.6% lower gearing (0.10332), making my new gear ratio requirement 2.97:1.
Well, since we live in reality...for the most part, there is no such animal as a 2.97:1 ring and pinion for a 198mm Chrystler rear end. The next closest option is a 3.06:1. It would be a good option as it is 6.62% lower the then stock ratio which would help over come the added rolling resistance of the significantly wider tires. That would keep the car pretty close to the stock feel of acceleration and general drivability.
That wasn't really as low as I wanted to go. If I was going to do the swap, I really wanted the added benefit of lower then stock gearing to assist in getting off the line and general acceleration performance increases. So I went with a 3.64:1 ratio which is almost 27% lower then stock.
A gear ratio of 3.64:1 compensates for the increase in tire size and rolling resistance of the wider tires and then some. The reduction almost makes poor low end throttle response a thing of the past because it puts the motor in its power band quicker. It's still there but is masked by the nearly instant thrust into the power band.
Is it worth it?
OH YEAH!!! It's like a whole new car again. After the install, I put 300+ miles on the car that day because it was just to much fun to get out of it.
So...what are the down sides?
Minor fuel mileage decrease on the highway.
I'm not sure exactly how negatively it will impact my highway mileage but it surly will. I've been mashing down on the go button more then normal because it's way fun. In theory it should actually help my city mileage because it takes less effort from the motor to make the car move from a dead stop (as long as you're not romping it all the time). That's what I've found to be true on all the other vehicles I've re-geared after tire size increased.
Data I can report is the RPM's at 70MPH in 5th gear:
2150 RPM's with 215/65-17 tires and 287:1 gearing (stock/stock)
2000 RPM's with 285/40-20 tires and 287:1 gearing
2500 RPM's with 285/40-20 tires and 3.64:1 gearing
To my knowledge, the gearing options for a 198 rear end are:
2.87:1 (5 speed 3.5L Challenger, Charger, Magnum & 300)
3.06:1 (AWD Magnum)
3.64:1 (4 speed 3.5L Challenger, Charger, Magnum & 300)
3.90:1 (2.7L Charger, Magnum & 300)
***Please take the above gearing options as a guide,
not as fact. I'm not an expert in what gearing came in what model. It's info I gleaned via on-line searches. Please investigate for yourself before buying a third member.)
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As a reference, my car is a 2010 base model SE with a 3.5L motor & a 5 speed transmission. The only other "performance" type mod's I've done are the stupid big tires and wheels (245/45-20 tires front on 20X9 wheels & 285/40-20 tires rear on 20X10 wheels) and a complete SRT8 suspension swap. I've also re-tuned the car for 91 pump gas, firmer shift points, the tire size change, raised the allowable top speed and now the gearing change.
Happy motoring.
-Scott
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