Tire size and RPM

[dwmobz]

Its time for tires. I have a 98. 5 24V with 3. 54 gears and automatic. I two a 24' TT that weighs about 6,000 pounds. I have the typical problem of low RPM (~1600 RPM) at 60 mph (out of power curve) and therefore little or no capacity to climb hills when towing. I'm looking at going from the stock 30" diameter tires to about a 33" diameter tire. I used the RPM calculator (TDR link) and it looks to me like I could turn off the overdrive and cruse at about 2000 RPM at 60 MPH with the 33s. This would virtually make the O. D. useless while towing (low RPM). Are there any long term disadvantages to running in 3rd as opposed to O. D. over the long term? Any feedback from those with similar setups would be appreciated.

 

[Rob Thomas]

You shouldn't be towing in OD anyhow, I ruined a auto trans doin' that a few years back, live and learn.



Later, Rob

 

[LSMITH]

First, welcome to the TDR. Second, that is the combo of gear and tire I run, you will be just over 2000 at 60 MPH, and it tows like a locomotive at that RPM. Third, you can tow in OD with no ill effects if you do it correctly. You want the RPM over about 1700, and you want to shift down if boost goes over about 20 PSI on a stock transmission. For flat land towing there is no reason to tow in drive.



Remember that the higher the RPM the easier you are treating your automatic transmission, so yes towing in drive is easier on it, just not necessary.



Beware, the combo you are thinking about is really high geared. You will sacrifice some low end grunt, and OD is useless completely below 55 MPH.