Car: 98 GS400
Q: If the stock final ratio is 3.26 and the stock wheel is 17 inches, does running a larger (19 inch) wheel effectively lower my gear ratio?

If so, would the Gs300’s 4.10(?) pumpkin be too much of a swing in the other direction?

 

Not if you run the correct tire size.

 

As mentioned, keep the circumference of your tire the same (or close) and you don't need to worry about gearing, or the more practical issue of your speedometer reading long or short. The "middle" (be it a 16" or a 20" wheel) won't matter. As you increase your wheel size, you reduce the sidewall of your tire to maintain a given total circumference. There are tire size calculators online that will give you the height of a given tire size. Also, websites like tire rack usually give the specs on the tires, including overall height.

I would not recommend a GS300 differential to someone with a GS400 for normal everyday driving. It will basically be a waste of 1st gear and you'll find the engine spinning much faster on the highway for no good reason. The gearing in these cars was done for a best compromise of power and efficiency.

 

compare tire sizes by checking the "rotations per mile" specification rather than height.

 

The ratio between a circle's circumference and its radius is always the same.

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Easy as pi?

 

Use a calculator like this: https://tiresize.com/comparison/ You can keep the same diameter by selecting a tire in say 19" or 20" that has a similar diameter to your 17's

 

Ya know, deep down the root of my question was whether it was possible to move my power band. Does that make sense? Now that I’ve got my ppe headers, srt intake and cat back exhaust the car is really fast.. on the top end above 70 is when it really begins to get in its zone so to speak.

Plus I already got one ticket because I just couldn’t “feel” how fast I was going.

So my thinking was that a higher gear ratio would move the “power band” and the higher rpm would kinda let me know/feel how fast I was going. (?)

Or maybe I should just toss a random wheel weight on the front wheel so it’ll “wobble” a bit at high speed and tune me into the fact that I’m starting to speed- lol.

Thoughts?

 

Looking at the speedo seems like the simplest method I could think of to alleviate your concerns. If you're worried about a ticket my advice would be to invest in a radar detector.

Your engine power curve won't be modified by gears or tire sizing. Your speed and fuel economy as well as your seat of the pants torque will be impacted as you change these other variables.

 

If you’re looking to jump out of the hole, add an aftermarket torque converter with a higher stall.

 

oh? Cuz there’s a kinda lag until the rpms and speed come up. I used to break the tires before I upgraded the intake and exhaust and went from 18’s to 19’s

 

Big fallacy that so many are negatively effected by.. Big exhaust. Loss of velocity/scavenging effect. Less torque for a little bit of top end. I rarely buy systems anymore. Unless you have plans for big power, it's best to keep stock pipe diameter and just move to free flowing mufflers. Headers are always good too. But you may be suffering from a loss of torque (as far as your off the line lag goes).

Going from 18s to 19s or even 20s means nothing besides a weight change, It's the diameter of the tire that will affect the effective gear ratio. I have to assume the tires on the 19's are not properly sized for the car. What size are you running now? I'll tell you if the diameter is too big or small (though they are obviously too tall). If they are an inch or more too large, then you will certainly suffer from an acceleration loss and a speedometer that reads less than you are actually going. Sounds to me like you've unfortunately really hindered the cars performance with your mods.. you can run 19's with the proper diameter tire and not have negative effects.

 

You can use www.willtheyfit.com and compare tire sizes and speedometer. You can compare stock size vs custom size to stay in the same perimeters. If your going from a 17" to 19"/20" gear ratios would stay the same the car would just be heavier and thus would change your 0-60 times if you were concerned about performance. Compromise and go 18's.. I think anything larger will negatively affect your power band.

 

Yea. I didn’t make the mistake of going with 3 inch exhaust piping. JBrady layer down the issues with doing so; Poor scavenging etc.

I'm running 255/40/19 in the rear w/35 offset.
Seems like just a bit taller (+.33 of an inch) than the stock 18 inch setup.

I’ve heard that performance headers will trade bottom end grunt for top end pull. But I’ve also noticed that once the tubes get warmed up the car seems quite perky at lower speeds.

Also those 19’s seem really heavy so I’m sure getting all that weight moving doesn’t help either.