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What makes you say that? Wheel diameter has nothing to do with tire diameter. What are you currently running? 37s & 4.88 or 37s & 5.29?
Because I've tried both. I tried on my buddies 37x12.5x17 before getting my 37x12.5x15 purely to check for clearance in my fenders. His setup was a perfect match for my 5.29s. My 15s have been dogs with a 37" tire. However I get a lot more sidewall wrapping around rocks so it is a give and take.
15" wheel has more rubber = more weight.
Toyota matched diff gears to trans and tire size, assuming you are going with 3rd gen or older drivetrain, that would be 4.10's for 5-spd w/28's, or 4/3?'s w/28's. 37's are 24.3% bigger than 28's, 5.29's are 22.5% taller, while 4.88's are only 16% taller, 6.5% isn't a lot, but then 37's will weigh more and have a greater rolling resistance, so that needs to be considered as well. If you are buying new gears, go with the 5.29's, if you already have the 4.88's run them and see if the performance is tolerable, then decide if regearing is needed/wanted.
Hmmm.. thanks for all the input. I hadn't considered the extra weight. I'll stick with the 5.29s. I'll be going with a 17" wheel for more choice in tires... and bigger brakes.Now I just have to decide on a tire! On my FJ40 I was using 38x14.5 Super Swamper TSL SX. While great off-road... I'm ready to trade in a little toughness for some tread life and better freeway manners.
I run 5.29s with 33s with a 3rz. for me it's a trade off. I have single case gearset so my crawl ability is increased in 4low. The real benefit for me is a very usable 4hi for sand and mud. The only drawback is higher rpm's on the freeway which means less mpg's (if I want to go real fast)and the need to shift sooner especially from 1st gear(2wd). If I had dual cases I think 4.88's would be perfect for my 3rz w/33's. In regards to the original question, I wouldn't even consider anything but 5.29's for 35's and especially 37's for the 3rz unless it's a trailer queen. If you were going with the 3.4 swap, the 4.88/5.29 decision would be more difficult.
4.88s match up pretty much perfectly with a 35 inch tire. The math give you 34 inches, but between many of them being less than 35 plus the rolling diameter is even less from the weight of the vehicle. I think my speedo on my 4Runner is more accurate with 4.88s and my 35 inch Cooper SST Pros than my Sequoia is with one size taller tires.
A 3RZ, 33s w/5.29s you must be pulling on everybody up the passes.
And full throttle in 5th gear isn't a good idea for transmission life........
Good discussion here, not much to add.One thing to note that many seem to forget is that a 35" tire rarely measures thirty-five inches, and even if it did, after a season or two it will be closer to 34". I built a nice Engine RPM and Truck Speed Calculator on our R&P page: https://www.marlincrawler.com/differential/ring-pinion Plug in some numbers, write down the resultants, and then go drive your truck how it sits now and compare. See if the RPMs vs speed is what you're looking for. If the calculator calls for 3,500 RPM for 65 MPH on the freeway then run your truck in 4th gear at 65 MPH to see if those high of RPMs is something you'd want to live with.... etc.Regards,BigMike
The results make it look like 5.29's would increase the rpm's by 170 at 70/5th gear, when they would actually only be increased by 60-70rpm's, on the other hand it looks like the the 4.88's would only lower the rpm's by about 70, when they actually lower the rpm's by about 170.
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