Speedometer 10mph off - too slow??

[tsi1991awd]

So I bought a 1990 AWD, the trans is a 91+ and the speedometer reads 10mph too slow (about 10mph slow anyways)...is there anything I can do to correct this or am I screwed?

It has 17" wheels with low pro's on it. This may be causing it to be off, but nonetheless....is there anything I can do to adjust it?

 

[DSM-Hottie]

Mine is like 5-10mph off too idk what to do about it, its annoying. Was on my way to BOTI and my buddy was like "why were you doing 55" i said i wasnt I was doing 65.

 

[Guzman08]

just take off the clear part on the gauges and take off the needle for the speedo . and get a gps . and once it says your going 10mph or 20mph . put on cruise control and try to put it on exactly. this is what i did when i had the same problem. its not that hard to do. its pretty easy.
you can search this:
gauge cluster removal. or even led gauge cluster.

remember rate me.. want to be helpful.
your rims should have effect on it a bit. but easy fix maybe like 15-20 mins or less depending on you

 

[gingerbredman00]

Just pull your cluster apart and pull the needle off and put it back on pointing a little higher..

 

[knochgoon24]

Mine reads about 4mph too fast, but the logger also reads the same amount off. Have you compared those 2 values?

What size are the tires? That's really what determines the final speed. I've seen a few people use tires that were a size or two smaller in diameter.

 

[Melbowski]

Mine reads about 4mph too fast, but the logger also reads the same amount off. Have you compared those 2 values?

What size are the tires? That's really what determines the final speed. I've seen a few people use tires that were a size or two smaller in diameter.

Same thing here, but I'm about 5mph off. When the speedo shows 60, the logger also says 60, but I had my friends pace me and I'm only doing 55. Changing the needle around sounds more like a band-aid to me than an actual fix. Anyone know if the actual formula in the computer can be changed to fix this? I'll have to check and see if it scales with speed, or if it's just always off by 5mph. Probly doesn't help that my speedo tends to die on a regular basis either, like they say about DSMs: 60% of the time it works every time!

 

[Aproductions]

Basically when you get new tires and rims your supposed to use the tire calculator which keeps everything right.

stock setup 2g....205/55/16 at 60mph

rims i was looking at were 17s and it said to get 225/45/17 and that would make my cars speedo say 60.4mph when i was actually only doing 60...thats really close

If you don't use the calculator and just get rims and tires and go with like 235/50/17 or something, then things may be off pretty bad, but like stated...you can just reset it.

 

[Guzman08]

dude its not a band aid fix. its a accurate reading. dam. what is it covering up!! nothing exactly.

 

[97gst_spyder]

Every model dsm came with different rim/tire sizes. So changing the rims/tire sizes are going to change how fast the car is moving, but the engine/trans will be spinning the same amount as before.

For instance.

Stock tire diameter is 25in. So the engine at 3k in 5th gear, the car is going 50mph.
New tire diameter is 27in. So the engine is at 3k still in 5th gear, the car is now going 55mph. Vis-versa for smaller diameter tires.

The VSS - Vehicle speed sensor is on the trans, thats why you logger and speedo state the same amount.

The only 'real' ways to fix this is to change the ratio on the VSS gear to match your setup (impossible), or change the value that the ecu displays the speed ( ie- Superchips for trucks/Suvs can do this). But idk if dsmlink for chip burning can do this. The easiest why to do this is to check your speed with a bone stock newer car, radar, or something that you know is damn near perfect, and pace it and change your needle to match it.

Here's a link to the best tire/rim size comparison.

http://www.miata.net/garage/tirecalc.html

 

[tsi1991awd]

You guys talking about computers this and that....this is on a 1g, it is a cable driven speedo. I guess I could do the needle thing...wouldn't it read 10mph when I was actually stopped though?

 

[97gst_spyder]

The cable is driven off the trans. The trans rpm to engine rpm ratio does not change. So your speedo is showing the speed you would be going if you had stock rims/tires.

 

[tsi1991awd]

Right, so as I was saying, how do I correct that?

I don't know the exact measurements of the tires because the car is in the shop right now. I know the wheels are Evo 7 wheels. I want to say the tires are 235/45r17. I know they are 235's for sure, and they are 17s.

 

[97gst_spyder]

Other than change the gear ratio on the vss/speedo cable gear. move the needle to the correct speed.

 

[tsi1991awd]

Also, I don't know if this has anything to do with it but my car is a 1990...the tranny is from a 1991+...I am not sure if the speedo gear or speedo cable is different between the two or not, but the 1990 gauge cluster reads in 5mph increments, while the 91+ reads in 10mph increments....would this be a problem?

For example, the 90 has 5, 15, 25, 35, 45 marked....while the 91+ has 10, 20, 30, 40, etc.

 

[Codester]

You could use GPS to find your correct speed. I've used it several times and it's accurate enough