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SportTrac Discussion
Engine & Drivetrain
Anyone here re-geared their ST? Likes? Dislikes? Advice?
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<blockquote data-quote="Yardsale " data-source="post: 790096" data-attributes="member: 58988"><p>I had my 3.73:1 changed to 4.10:1. I did this to compensate for larger tires (265/65-17). The difference between the stock tires and the new is about 5.5%. The difference between the 3.73:1 and the 4.10:1 is about 9%. So the gearing change "over shot" the tire change by about 4.5%. This is a bit more raise in engine RPM at a given speed than needed to compensate for the tires (at least, by the math), but the new tires and rims weigh almost twice what the originals did and, for acceleration, this needs to be compensated for as well.</p><p></p><p></p><p></p><p>The biggest difference is pulling typical freeway hills (4 or 5%). I can now stay in overdrive and remain at the same speed, or accelerate if I want with no down-shifting.</p><p></p><p></p><p></p><p>With the larger tires and without the gear change, the engine RPMs were below the engine power band and I always had to cause a down shift to remain at a steady speed. The shifting costs in mileage.</p><p></p><p></p><p></p><p>As for mileage, it seems to vary, but perhaps a decrease by about 0.5 MPG.</p><p></p><p></p><p></p><p>Pitfalls - as Bill notes, this is not a do-it-yourself unless you have dome this before and were successful. If you have someone else do this, be sure to get an agreement <u>in writing</u> that the warranty includes no differential noise with the new gears (also, as noted by Bill - proper gear setup is a science). Oh and that estimate is per differential plus about $100.00 more for the front, which has to be removed.</p><p></p><p></p><p></p><p>All in all, a good change for me.</p><p></p><p></p><p></p><p></p><p></p><p>Edit: Just read your tire size - the 4.10:1 will be plenty (IMO). If not, add a nitrous system.</p></blockquote><p></p>
[QUOTE="Yardsale , post: 790096, member: 58988"] I had my 3.73:1 changed to 4.10:1. I did this to compensate for larger tires (265/65-17). The difference between the stock tires and the new is about 5.5%. The difference between the 3.73:1 and the 4.10:1 is about 9%. So the gearing change "over shot" the tire change by about 4.5%. This is a bit more raise in engine RPM at a given speed than needed to compensate for the tires (at least, by the math), but the new tires and rims weigh almost twice what the originals did and, for acceleration, this needs to be compensated for as well. The biggest difference is pulling typical freeway hills (4 or 5%). I can now stay in overdrive and remain at the same speed, or accelerate if I want with no down-shifting. With the larger tires and without the gear change, the engine RPMs were below the engine power band and I always had to cause a down shift to remain at a steady speed. The shifting costs in mileage. As for mileage, it seems to vary, but perhaps a decrease by about 0.5 MPG. Pitfalls - as Bill notes, this is not a do-it-yourself unless you have dome this before and were successful. If you have someone else do this, be sure to get an agreement [u]in writing[/u] that the warranty includes no differential noise with the new gears (also, as noted by Bill - proper gear setup is a science). Oh and that estimate is per differential plus about $100.00 more for the front, which has to be removed. All in all, a good change for me. Edit: Just read your tire size - the 4.10:1 will be plenty (IMO). If not, add a nitrous system. [/QUOTE]
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SportTrac Discussion
Engine & Drivetrain
Anyone here re-geared their ST? Likes? Dislikes? Advice?
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