speedometer

[mud slinger]

I have 33x12 tires on my 1978 Bronco, Does anyone know .would this make my speedometer be slower or faster than what it shows

 

[Seabronc]

I have 33x12 tires on my 1978 Bronco, Does anyone know .would this make my speedometer be slower or faster than what it shows

Change your speedo gear. Attached is a chart from Jeff's Bronco Graveyard on how to calculate what speedo gear you need.

Good luck,

>-

 

[Yardape]

It would show a faster speed than actual

 

[Mach1s]

I believe it would be the other way around. When your speedo read 55 mph. you are probably going about 60. You have more tire rotation than your stock tire which would move your truck further per rotation showing you are going slower than you actually are.

 

[gte959s]

That is correct with a bigger tire you have a larger circumfrance (3.141593 x diameter=circumfrance).

3.141599 x 33"= ~103.6" circumfrance

while

3.141599 x 29"= ~91.1" circumfrance

91.1" / 103.6" x 100%= 87.9%

The 29" tire making one rotation would only make 87.9% of the 33" tire's full rotation. So a 33" tire would spin fewer times at the same MPH showing you a lower speed than you are actually going.

 

[89Bronco58]

wow listen to the newbie go!

 

[brandcole73]

wow listen to the newbie go!

I put 32's on my 95 and, according to my GPS, The spedo showed about 5 mph slower at 55. (If my spedoe showed 55, the GPS said I was doing 60) I never changed adjusted the spedo because I would change back to smaller tires in the winter.

 

[racebreedbronco]

they are correct.. it will read slower, give me your old and new tire sizes and I will post the correct gear part# to get, also advise veh info, a/t or manual trans

 

[Broncobill78]

Just call your local speedo shop or Jeff's or *any* off-road shop, tell them what you have & what tires you're running and they'll be happy to sell you the gear. Takes maybe an hour to change it if you've never done it before

 

[BroncoBrett913]

I always thought that it would read faster than you are actually going. Thats crazy, but the math works out! huh.... Thats why it seems like i am flying by people when I go five over the limit. LOL I guess the only way to find out is to find a speed checker in your town (The ones that flash when you are going to fast and it gives your speed readout) and see what that tells you. I guess that is a more redneck way to figure it out, but it seems like the easiest way!

 

[gibs0n06]

it true it does read slower on the speedometer and i put 33 on my stock bronco and when im doing 65 im actually doin 73

 

[Foul Al]

it true it does read slower on the speedometer and i put 33 on my stock bronco and when im doing 65 im actually doin 73

you also rack fewer miles with the bigger tires onit. only a good idea for the exemption sticker fanatics...