What have you done to your Tacoma today? 1st Gen Edition

That's how mine is. One piece.

 

Will do, Mike! Is your speedo reading fast or slow right now?

I would think so too, but I'm more than a little overgeared with 5.29s. But that's exactly where I wanted to be. This truck is worlds better off the line, even with the added rotating mass of the 35s.

I'm no expert, and I don't pretend to be, but I'm guessing that is the issue. Roughly speaking, a 4.7 gear set would put me right back to factory performance, but of course you can only get 4.88, which is slightly overgeared, and would cause the speedo to be slightly off by the same percentage. 5.29s would just make that percentage larger.

Again, that's just what 'seems' plausible to me.

 

It's reading slow. So 65 on the speedo means I am doing 70. I think... it's been a while since I've driven it with the new DD lol

 

This. Think about it in percentages. (rounded)

I went from 4.10s to 4.88s, that's a 19% difference.

I went from 31" tires to 33" tires, that's a 6.5% difference.

Speedo will read 19% higher because of the gears, and 6.5% lower because of the tires: net of 12.5%

Stock speedo gear is a 30 tooth, times 112.5%, get's us a 33.75 tooth, but 33 is the biggest Toyota makes.

 

I like math!

 

Sorry, I'm gonna get a little pedantic, hopefully not dickish.

You can't subtract ratios, they're multiplied. The gears cause a 19% increase in revs (or 119% revs) while the tires decrease revs, the inverse, so 31/33 = 93.93%, not 106.5%. Multiply those suckers 1.190*0.939=1.117 (11.7% increase).

Check out this gear ratio calculator to corroborate the point.
http://www.grimmjeeper.com/gears.html


None of this really amounts to much in our situation, seeing as the difference of 0.8% equates to....bupkis (0.5mph difference @ 70mph). Just an FYI, because for instance my total gear ratio from trans/tcase/rear axle would be 38.72 being multiplied, not 10.53 from being added which is a lot bigger of a deal than in our case.

 

This ^^^

Larger tires lowers the indicated speed. A regear raises the indicated speed.

FWIW, I am on 33s (33x10.5r15), regeared to 4.88s and have the 33 tooth speedo gear. With the auto trans, at 70 mph (GPS), the tach reads 2500 rpms, and the speedo reads 72 mph.

 

Close enough. I'm an accountant, not an engineer, so I normally just plug numbers.

 

I hate math!!!

 

I see. I just assumed everone went with 5.29s because it would match the factory ratio.

 

No 5.29's are quite a bit overgeared. I plan on going 5.29's because I am hoping to avoid a crawl box since I am a manual.

 

Good stuff, fellas! That's pretty much what I thought.

WARNING: Nerding out to follow...

I just used my stock tire size (30.5, I think) and my new size, 35.

35/30.5 = 1.15

Stock gears are 4.1, so

4.1 * 1.15. = 4.70 (ideally)

Closest gear set is 4.88, and I'm running 5.29, so

4.88/4.7 = 1.04, or a +4% error with 35s
5.29/4.7 = 1.13, or a +13% error with 35s

All assuming the stock speedo gear is used, of course. Stock speedo gear is a 30 tooth, so to mitigate that 13% error,

30*1.13 = 33.76 tooth, ideally. 33 tooth actual.
33/30 = 1.1, which is only a 2.72% difference from ideal case to actual.

So using a 33 tooth with 5.29s and 35s should get me pretty close, I think.

Or my math is bogus and I'm completely full of shit.

 

I don't know math at all.
However, you need the 33 tooth.

 

Guess and check method works well too.

 

Since your speedo might be off from the factory, the only way to really be sure you get it spot on is to determine how off it is with a gps and real testing. Read.

https://web.archive.org/web/20101201145208/http://ttora.com/wiki/index.php/Speedometer_error


But if you would like to do maths,

http://www.celicasupra.com/forums/showthread.php?67982-The-end-to-speedometer-gear-questions

 

I don't get to use my math skillz much anymore, so I saw the opportunity to need out and took it! Thanks for your help, man!

Did your get your speedo gear from the dealership?

Yep, I might as well just throw that thing in there and see what I get. Now I just need to get a GPS...

Thanks, Tim! I'll check that out tonight!

 

If you want to do the math check out the 2nd link I added. Since the TTORA page says each tooth is "about 3%" I guess that isn't too accurate of a method either haha.

But the 33t speedo gear is what will get you closest with 35s/5.29s. Pt# 33403-39415

 

These are the kinda math problems we need in high schools!

 

Yes, just took a day to get it in. It might be local stock to the Denver dealers.