pburchett Posted February 8, 2008 Share Posted February 8, 2008 Why does a Lariat, Crew Cab, 4x4, 6 ½ foot bed truck equipped with the 3.55 limited slip rear axle require the addition of 20” wheels while the 3.73 limited slip rear axle will allow for the 18” wheel option? Similar STX or XLT models do not require the larger 20” wheels no matter what rear axle it has. Is there a brake diameter difference on the 3.55 axle for the Lariat or is there some other difference? Quote Link to comment Share on other sites More sharing options...
xr7g428 Posted February 8, 2008 Share Posted February 8, 2008 I was under the impression it worked the other way: you could not get the 20" wheels with the 3.73. I also understood the tow rating went down with the 20's. I may be wrong about this as my information came from a sales guy that I think was trying to steer me to what was sitting on the lot. Which is why I didn't buy the truck! If you want to tow anything heavy, get the 3.73's. Quote Link to comment Share on other sites More sharing options...
betaiota Posted February 8, 2008 Share Posted February 8, 2008 I was under the impression it worked the other way: you could not get the 20" wheels with the 3.73. I also understood the tow rating went down with the 20's. I may be wrong about this as my information came from a sales guy that I think was trying to steer me to what was sitting on the lot. Which is why I didn't buy the truck! If you want to tow anything heavy, get the 3.73's. I think you're right. You can't get the 20's from the factory on XL, STX, or XLT. So when you order the 20's it puts you into the 3.55. But I think you can upgrade back to the 3.73 according to the Build-Your-Own. Anybody out there with 20's and the 3.73? Quote Link to comment Share on other sites More sharing options...
pburchett Posted February 8, 2008 Author Share Posted February 8, 2008 I was under the impression it worked the other way: you could not get the 20" wheels with the 3.73. I also understood the tow rating went down with the 20's. I may be wrong about this as my information came from a sales guy that I think was trying to steer me to what was sitting on the lot. Which is why I didn't buy the truck! If you want to tow anything heavy, get the 3.73's. According to Ford’s build it web site you can ONLY get 20” with the 3.55 rear axle, but with the 3.73 rear axle you can get 18” or 20” rims. My problem is that I want the 3.55 rear axle (A little better fuel economy) , but not the 20” rims. I want the 18 rims due to the fact that I will have to be off road at times. Quote Link to comment Share on other sites More sharing options...
F250 Posted February 9, 2008 Share Posted February 9, 2008 Get the 3.73 limited slip, I had the choice and did. This is a heavy truck with a 4-spped automatic, go to the dealer and test drive similar trucks with both axles before you decide. Compare the tow rating of the 3.73 vs the 3.55 even if you don't plan to tow anything the ratings illustrate the off the line acceleration advantage of having the 3.73s. If the 3.55s offer a marginal fuel mileage advantage on the highway they are not reflected in the offical EPA rating. As to why they offer a choice on the XLT but not the Lariat I don't know. Just like the only engine available in the STX is the 4.6L but you can get any engine you want in the lower priced XL. Quote Link to comment Share on other sites More sharing options...
jchkeys Posted February 12, 2008 Share Posted February 12, 2008 To hell with the 3.73s. I just dropped my F-150 off to have the 3.73 pulled and replaced with the 4.56 gears. The 3.73 gears would not allow the truck to stay in 4th. Unless downhill, the truck was hunting for 3rd too much. Pulling my camper from Suffolk, VA to Monterey, CA I will appreciate having the extra heavy gearing when I cross the Rockies. Quote Link to comment Share on other sites More sharing options...
xr7g428 Posted February 12, 2008 Share Posted February 12, 2008 To hell with the 3.73s. I just dropped my F-150 off to have the 3.73 pulled and replaced with the 4.56 gears. The 3.73 gears would not allow the truck to stay in 4th. Unless downhill, the truck was hunting for 3rd too much. Pulling my camper from Suffolk, VA to Monterey, CA I will appreciate having the extra heavy gearing when I cross the Rockies. I am thinking about doing the same thing. Could you please post back to this thread after you get your new gears with your opinion of how you like the truck with and without a trailer? I live in AZ so i am in the mountains a lot. I was thinking of going to a 4.30 or 4.10, but I haven't found any one running any of these gears. How did you decide on the 4.56 and also, what are you doing for the speedo? Can it be reprogramed? Thanks! Quote Link to comment Share on other sites More sharing options...
jchkeys Posted February 13, 2008 Share Posted February 13, 2008 I will give an update on the performance. I have an edge programmer. That is where you can change the CPU's gear ratio, tire size, and other features in about 2 minutes. All I have to do is clear the memory of the current program by re-loading the stock program, and then re-program it again with the new gear ratio. The speedo was only off by about 2 mph when I switched from the 30 inch tires to the 34 inchers, which is just as incorrect as it came stock. My GPS is always my speedometer. I chose the 4.56 after going to Ford Motor Parts and looking at the available gear ratios. There was a note by the 4.56 saying it was developed for f-150/Expedition towing. Then my truck place said they recommend the Precision Gear 4.56, they have put it in other F-150s that guys were using for towing. JCH Quote Link to comment Share on other sites More sharing options...
jchkeys Posted February 20, 2008 Share Posted February 20, 2008 The truck got the new gears today. I am still in the middle of the 350 mile break in, so I have yet to stomp on the accelerator or tow my camper. My impressions so far are great. The truck is no longer hunting for third at every overpass or hill. It is able to stay in 4th gear, at 65mph, ~2000rpm, and with about 40-45% load on the engine. It sounds happier because its in the power band, vice below it when the 3.73 was in there. It was a great decision, I just can't wait to get the camper behind it. JCH Quote Link to comment Share on other sites More sharing options...
xr7g428 Posted February 20, 2008 Share Posted February 20, 2008 Sounds good so far, let us know how she pulls... Quote Link to comment Share on other sites More sharing options...
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