Mark, I just put two lengthy posts on the SubaruVanagon Yahoo Group about my experiences with larger tires and gearing changes up with Suby 2.2L and, now, a 2.5L engine. My experiences are all with Syncro Vanagons with Subaru 2.2L and 2.5L engines....but you can use the spreadsheet for an autobox also... Use the Excel Calculator in the SV Yahoo Group FILES area called "3 Ratio Tire and Gearing Calculator"...(a modified version of Tim Smiths original spreadsheet.) Just plug in the R&P ratio and the gear ratios for the autobox into the first 3 gears. Ignore the 4th gear column. Be sure to get the "revs per mile" specs from the manufacturer for the size tire you are considering. With a Subaru 2.2L in my Syncro Westy with 14" wheels and stock tires, I very quickly got used to being able to climb medium sized hills in 4th ...and liked that ability....and I found it annoying when I lost most of that 4th gear climbing bility when I installed new 215/75-15 size tires. Some who read this may find that comical..since a Suby 2.2L in any Vanagon model can climb almost all hills in third. ...but it's just my preference. It's very easy to get accustomed to extra power/torque quickly..and hard to vive it up. The gearing calculator showed the 215/75/15 size tires to give me 77mph @ 4000 rpm (stock was 71mph)..so about an 8.5% increase, overall. But from my experience with a Syncro Westy, I don't think I would recommend a tire size that would put your automatic's 3rd (top) gear over 75mph in 4th. Your lighter van may not lose as much as a Syncro Westy. You could try this....In a 2wd drive van, it's pretty easy just to borrow a couple of larger tires/wheels from someone, slap them on the rear and give them a try. This will give you an idea of how the gearing works out..on the driving wheels...but will not tell you much about handling overall...since you'll have a missmatched set. I'm thinking of experimenting this way with this out...experimenting with a set of 30" tires on the back of my Syncro...decoupled, of course. You need to drive around on them for a week or so...in different terrain ....to see how you like the gearing effects. A run around the block won't do it. T Good luck. Warren Chapman Moderator SubaruVanagon Yahoo Group |
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