which speedo gear do i need?

if switching from the stock 16" rims and 30.6" tires to 15" rims and 28.6" tire, which gear do I need to correct the speedo readings? how do you figure out what you need?

oem 16" rims with 265/70R16 tires that are 30.6" high ( = 30.6x10.4R16)

new 15" oem rims with 225/75R15 tires that are 28.6" high ( = 28.3x8.9R15)

 

Interesting. According to this, they should be darn near the same diameter actually: https://www.tacomaworld.com/tirecalc?tires=265-60r16-225-75r15

Are you sure about the diameter of that 265/60R16 ?

 

ok well sorry about that, it should read 265/70R16 not 60


anyway then, I can also go with a 215/75R16 that's supposed to be 28.7" high so I don't need different rims

my main goal is to put on tires that are 2" shorter at around 28.3"-28.7" high instead of the stock oem 30.6" high tires

basicly im looking to do a 2" drop by using tires sizes

 

Can't answer but you may also be interested in electronically correcting it instead. More accurate, more money.

http://www.yellr.com/yb_home.htm
http://www.dakotadigital.com/index....t_id=126/category_id=287/mode=prod/prd126.htm

And besides, if you calculate based on the assumption that stock size tires provide the accurate baseline speedo reading, it could actually be wrong.

Verify with your phone's or standalone GPS what your current speedo accuracy is like. The navigation should report your speed. And don't make a speedo correction until after you buy the tires.

 

well every car or truck I ever road in, the actual gps recorded speeds said you were really going 5mph slower then the speedometer said you were actually going when going between 55-70mph

it was the same for motorcycles so I just came to the conclusion all vehicles had a built in 5mph discrepancy to keep you from speeding

 

You are aware that most 15" rims won't clear your calipers right? That includes old 15" Toyota steelies and alloys. Only 95-97 Tacomas can wear 15" wheels without the worry of them contacting the caliper. There are a few 15" wheels that do fit though, and most others will fit with the use of wheel spacers.

 

@keakar, whats with all the upgrades and need for more power lately??

Also this may help: I upgraded to 265/75R15. Im on stock Prerunner 15" alloys. So my speedo is under reporting about 4mph at 60mph (so really 64mph). Luckily have not had to explain it to a CHP yet. Then again i drive faster than i should.

 

thanks for the info, I saw 15" rims mention for 02 so I thought they would fit 03-04 as well but I guess not.

looks like I have to go with the = 28x9.3R16 then, it's supposed to be 28" high so that will give me a 3 1/2" height difference that should lower the truck to about an 1 3/4" drop and I still be using my oem stock 16" rims

well its two fold, one is I want to get about a 2" drop for the truck so its easier to get in and out of (5"7" and short legs) but I don't want to mess with the suspension doing it, plus flipping axles requires minimum 3" drop (which is more then I wanted) and it involves readjusting driveline angles with shims and all I need is 2" drop for my short legs lol. an added bonus is smaller tires will alter the gear ratio to pavement slightly so its like a small mini regearing as well.

secondly its about better mpg not hp and speed but they do go together. the more hp it has the less it strains under "normal" driving conditions, so if you drive it gingerly (and I drive like a grampa) it "should" get better mpg and when towing you have that extra power if you need it. im not looking to race or 1/4 mile times and wont be "blowing the carbon out" anytime soon no matter what lol.

I actually think my SC fantasy is just that unless I find a really really great deal on one for like $1000 for everything but I do need to drop the truck 2" and tires are the cheapest and easiest way to do a small drop like that but then the speedo gear change has to be figured into it and I am not sure how large an error it will have