Speedo gear change help

[talkstometal]

I just put on different wheels and tire sizes and have the wrong speed due to size change. can you guys help with my math?

car:
1999 4runner, 2.7L auto, non-abs, 2wd
stock 225/75/r15

now has:
265/70/r17

online calculator states: speedo reading 70, would actually be 78.21mph. so, 10.49% off? what gear should I buy?

 

[talkstometal]

Best speedo correction approach for larger tires

Ive searched with no luck. the above link is a close match with no answer. minus the dakota digital type box, which I do not want. Ive used those types in the past. since toyota makes different tooth gears I would like to go that route.

But...I dont know if going 1 tooth or 2 tooth less would be accurate

partsouq states I have part: 3348259015 GEAR SUB-ASSY SPEEDOMETER DRIVEN (ATM) 33403G RZN180..4FC N=17,MARK 17:6 01 11.1995 - 08.2000

 

[phattyduck]

Use a speedo-healer type product. That way when you (inevitably) re-gear the rear, you can just change a number on the computer rather than find *another* speedo gear to match.

-Charlie

 

[talkstometal]

Use a speedo-healer type product. That way when you (inevitably) re-gear the rear, you can just change a number on the computer rather than find *another* speedo gear to match.

-Charlie

thanks for the reply. I, for some reason, did not want a dakota box. Ive used them in the past. going to rethink that since you mentioned rear gear change. last night on the highway she kept downshifting. maybe a gear will help.

anyone with input on less teeth? 1 or 2 to make up for that %?

 

[phattyduck]

thanks for the reply. I, for some reason, did not want a dakota box. Ive used them in the past. going to rethink that since you mentioned rear gear change. last night on the highway she kept downshifting. maybe a gear will help.

anyone with input on less teeth? 1 or 2 to make up for that %?

What's your current tooth count? You need to adjust by the same % difference as the tire diameter.

Also, if you know your current gear ratio, it might be worth changing that instead of the speedo gear... The 4-cylinder needs the right gearing to drive decently at speed.

-Charlie

 

[talkstometal]

thanks for your thoughts on the rear gear. never entered my mind. Ive only driven her on the highway once so far(after tire/wheel change) and like I said, kept downshifting. that was on the slightest uphills. this is my around the town car and rarely drive on the highway.

I looked up door code, diff reads: a02a
online lookup seems like its a: 3.58 2pinion open diff

does anyone know which gear would fit and be best to attain oem ratio based on the new wheel diameter being 10.49% off?

 

[phattyduck]

thanks for your thoughts on the rear gear. never entered my mind. Ive only driven her on the highway once so far(after tire/wheel change) and like I said, kept downshifting. that was on the slightest uphills. this is my around the town car and rarely drive on the highway.

I looked up door code, diff reads: a02a
online lookup seems like its a: 3.58 2pinion open diff

does anyone know which gear would fit and be best to attain oem ratio based on the new wheel diameter being 10.49% off?

A02A is unlikely to be that low. It is probably 3.90, but I'm trying to find a reference. I'd bet either a 4.10 or a 4.30 would get you back your power AND speedo gear. You might need to do a 'spin test' to verify your rear gear. Then just multiply that by 1.105 to see what the ideal new gear is.

Then again, maybe you want more power? Then a 4.56 or 4.88 might be worth it. You'd have higher RPM on the freeway, but it would be much peppier around town... You'd have the opposite problem though (speedo reading higher instead of lower).

-Charlie

 

[talkstometal]

more searching, I think you're right. 3.90. I will do a driveshaft test and see. if it is 3.90 then 4.30 would put in the correct band?

3.90/4.3= 0.90

Is that the math? and if correct, can I just swap the gear?

 

[phattyduck]

more searching, I think you're right. 3.90. I will do a driveshaft test and see. if it is 3.90 then 4.30 would put in the correct band?

3.90/4.3= 0.90

Is that the math? and if correct, can I just swap the gear?

Rear gear is easy to swap since it comes out as a complete 3rd member (like a Ford 9-inch) I think the challenge you will have is that the 4.3 gears generally came on the e-locker rear diffs of 4WDs - which are not mechanically compatible with the non-e-locker housing and are (obviously) much more expensive than a standard open rear diff.

But yes, your math is correct. A 4.3 will be correct if your stock gear is a 3.9.

-Charlie

 

[talkstometal]

counted the tire vs driveshaft rotations. I have a 3.9

such a bummer that 4.3 are only elocker. wouldnt mind changing out the whole axle if it was free. ha, ugh