How close is your speedometer?
 

When mine is on 60 I am doing more like 64-65. I base this on several of those radar speed signs they have before sharp turns on the Interstate. I know these are probably not the most accurate radars, but there are 3 of them that I drive past routinely and they always agree, always the same.

Point is, I need to get new tires soon. Would I need a little taller tire or a little shorter to dial in my speedo?

Re: How close is your speedometer?
 

I'd say a little shorter.... mine is right at 10 mph off, but that didn't change with tire size...

Re: How close is your speedometer?
 

If you have a I Phone there is a free speedometer app It will show you exactly how fast you are going

Re: How close is your speedometer?
 

Yeap speedo app, mine is off 15mph with my 33s.
Posted via Mobile Device

Re: How close is your speedometer?
 

Once you fgure out how fast or slow your Speedo actually is via phone app, pace car or GPS, you can add a speedometer ratio adapter for about $40 between the end of your speedo cable and where the speedo cable screws into your tranny housing.
Tell them your actual speed and what the speedo reads(or distance for that matter) and they can build proper ratio adapter.
Did it with my Blazer, speedo and GPS reading are now within 1%
Thanks
Tbruz

Re: How close is your speedometer?
 

Mines about 1-2 mph off at 60... very close. But I have the truck set up pretty close to stock.

Re: How close is your speedometer?
 

You can also change the speedometer gear - here is a calculator to help figure out which gear you need:

http://www.tciauto.com/tc/speedometer-gear-calculator/

Re: How close is your speedometer?
 

FYI...On a th350, or any other trans with the small driven gear, 1 tooth difference = 1/2 tenth on the odometer. (or 5% change) On a th400, or anything else that uses the large driven gear, 2 teeth = 1/2 tenth.

Re: How close is your speedometer?
 

I buried my speedo one tme and figured I couldn't be going be going that fast cause the truck rode and handled perfectly. Got the GPS out and with my speedo showing 95mph the GPS showed just under 94.
Posted via Mobile Device

Re: How close is your speedometer?
 

Well if you buy a speed hut GPS speedo from them you will be spot on no matter what size tire. gear, transmission you have. I have a full setup in my 71 and love them.
U can also just buy the GPS speed o and hook the hot wire and ground up and your done. Instant speed directions 1/4 mile speeds;):chevy:

Re: How close is your speedometer?
 

I may be out of luck. No smart phone or GPS. Oh well.

Re: How close is your speedometer?
 

-
:agree: with what Andy4639 said.... Here is the install of mine. Doesn't matter what tire, rear ratio, trans, or anything else you are running it is always right on the money...

http://67-72chevytrucks.com/vboard/s...d.php?t=421745

LockDoc

Re: How close is your speedometer?
 

That is a good idea. Now I remember your original thread on this. I might do something like this on my Panel, but for my beater truck, I don't know if I want to go to the trouble. Thanks, for the reminder, though:metal:

Re: How close is your speedometer?
 

How close is my speedometer? From where,my eyes? I'd have to measure,but prolly right about 24" Is my guess.:confused:

Ok seriously,mine have always been accurate till I go to bigger tires,such as on my 4wds.

Re: How close is your speedometer?
 

Don't know, not connected. Bounces all over the place when I connect the cable. Just try and go with the flow of traffic and make sure some one is always passing me.
Posted via Mobile Device

Re: How close is your speedometer?
 

My speed-o was close -5mph when I had the TH400 and 3.08 setup.
Then I changed to a TH2004r and 3.73.. my speedo was a bit off.. +10-15 mph.
When I did my valve body & governor swap on the 2004r I got the correct speedo gear for my current setup.. Man now the thing is perfect at all speeds... well within 1 mph when tested against I-phone app.:metal:


I had to swap from RED TO GREEN on the trans gear... pretty easy fix if you ask me :)

https://lh6.googleusercontent.com/-r...52826%2529.JPG

https://lh6.googleusercontent.com/-E...52830%2529.JPG

https://lh6.googleusercontent.com/-e...52831%2529.JPG



Scott

Re: How close is your speedometer?
 

Good thread. I never thought about this :metal:

Re: How close is your speedometer?
 

www.speedhut.com has a small speedo also. I have been thinking about buying it for my golf carts so I can swap it out to whichever cart I'm using at the time. It's like a tach mounted on the steering column.;):chevy:

Re: How close is your speedometer?
 

Speedos don't get off by a set amount of MPH,they get off by a percent. So the mph difference increases with speed. When I put 37" tires on my 4.10 truck it reads 10% off,or says 50 when I'm doing 55. I pass 9 mile markers and my odo says 10 miles.

I got pulled over for doing 40 in a 25 going downhill the first night I put the tires on. I told the officers that and that I hadn't had a chance to figure the difference it made or have my speedo recalibrated. We discussed how it worked and the one was saying it would be off by a set amount of mph and I said the number would increase with speed. They offered to follow me to this less traveled road where they would have me drive by at 25 and they'd read my actual speed. So,I drove by doing about 36 on my speedo and they got about a 40 mph reading and let me off the hook :lol:
That was back when no one had tires that big yet.

Re: How close is your speedometer?
 

That's funny!
Mine is off about 7mph at 60/70
I downloaded one of the iphone apps and I paced my wife home one night...
I think when I put new tires on I'm going to go to 235/75 r15. If my math is right that should shorten the gap by about 2mph and put me 5 under at 70ish. I have worn out 225/75s on right now.

Re: How close is your speedometer?
 

did the exact same thing once with the local ticket writer after putting 35's on my bronco. let me go with a fixit ticket to have the speedo recalibrated.

Re: How close is your speedometer?
 

SWEET! Android has it too. This will come in handy because mine is way off - it shows at least 10 MPH under actual speed.

Re: How close is your speedometer?
 

Where did you get the adapter at? Thanks
Posted via Mobile Device

Re: How close is your speedometer?
 

Not sure where he got his but they are available here...

http://www.transmissioncenter.net/sp...n_______va.htm

Plus a lot of other stuff & info on the site.

LockDoc

Re: How close is your speedometer?
 

My GTO had about 5 mph difference. Wound up changing the speedometer gear in the transmission. can't remember if it's the drive or driven gear. It has a TH400, but I found something online that helped me determine which gear I needed. TCI has quite a few different gears to swap yours if that's what you want to do.

If you still want to change tire height, taller is faster, shorter is slower. Check out this website. http://www.rimsntires.com/specs.jsp You can compare a size you have with a size you will consider switching to. It even tells you how much difference the new tire will make in your speedo.