Speedometer correction........

[swi66]

I have a 98 Legacy Postal.

I'm adding the Outback struts to gain some height.

Already done the rear, fronts next weekend.

I was thinking about going to the 15 inch outback wheels and tires.

But was wondering how much off my speedometer would be.

How would I go about correcting it?

Would it read higher or lower than actual speed?

And by how much?

Would it affect anything with the computer????

 

Thanks for any info.................

 

160,000 finally got around to changing the struts.........

[lostinthe202]

Reveen just posted this great link to a calculator that will answer your question

 

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

 

Here is the original thread in case you were wanting to go to bigger wheels for MPG reasons

 

http://www.ultimatesubaru.org/forum/showthread.php?t=86384

[Rooster2]

I have done this on other cars, and have not found much of a spedo error. My guess is that you now have 14 inch wheels, so with larger wheels/tires, you get just a slightly greater distance per tire revolution, but not much. My guess is that your spedo will read 2 to 3 miles per hour slow. That is not much of a difference at all. Also, your car will accelerate just a tiny bit slower. Over all, it is not much of anything to be concerned about.

 

You will need to have the same size tires and wheels on all four corners, so as to not cause problems with AWD.

[idosubaru]

a 14" and 15" wheel could be the same exact size depending on the size of the tire. so if you want the 15" wheel just for looks and an upgrade then use that calculator to figure out what size tires mimic your original 14" wheel/tire combo.

 

or, i would just get larger tires for the 15" rim. your speedo won't be that much off, just use the calculator above. it's not uncommon for speedo's to be inaccurate by a few percent so new tires might make it MORE accurate since they often read too high (my legacy is about 3-4 mph high at highway speeds - roughly %5).

[swi66]

Thanks for the replies........

Our Legacy was a bit low, and the struts were shot.

Wanted to gain a bit of height for ground clearance.

That's why I used the Outback struts, they appear to be an inch and a half longer, and much more beerfier than the originals.

And my wife still uses it occasionally for mail delivery and the boxes are higher than her car.

The current 14" wheels look tiny in there now that it raised up.

A larger wheel/tire combo would fill the wheel well and gain a bit more height as well.

[stevetone]

Thanks for the replies........

Our Legacy was a bit low, and the struts were shot.

Wanted to gain a bit of height for ground clearance.

That's why I used the Outback struts, they appear to be an inch and a half longer, and much more beerfier than the originals.

And my wife still uses it occasionally for mail delivery and the boxes are higher than her car.

The current 14" wheels look tiny in there now that it raised up.

A larger wheel/tire combo would fill the wheel well and gain a bit more height as well.

 

Did you replace the springs with OB springs, or reuse the legacy ones? Thinking about doing the same (lift) on my '95 this summer.

 

Steve

[Reveeen]

Keeping in mind that the "sportier?" Legacys came stock with 15" wheels and in my case 195-60-15 tires. I am going to try outback struts once the snow goes from "God's garage" and 205-75-15 tires.

In this case, from a 195-60, to a 205-75 is a 12% difference (60mph=67mph).

[Barassa]

Hi folks - I just completed a strut/rims tires replacement on my 1997 Legacy L. I got some used OB 15" rims with 205/70/15 and used complete (struts and springs) from an OB.

 

The car had the original 14" steelies with 185/70/14's.

 

The lift was substantial and the car looks and handles great. Much more freeboard for my bike rack and MUCH less scraping due to lack of clearance.

 

I use a GPS to compare with my speedo and it seems to track approximately 10% lower (the speedo is lower than actual).

 

So is there a reasonable way to correct this (I know Jeeps have a quick gear change on the speedo, but I assume this is done less frequently).

 

Thanks!

 

Barassa

[idosubaru]

i've looked into it before and found no easy solution. you can google devises that run....i forget somewhere around $200-$400 to change it, and i don't know how compatible they'd be since they aren't subaru specific devices. i believe i started a thread about it a long time ago.

[johnceggleston]

ther are a couple of posible solutions:

 

1. use outback wheels but smaller tires, same diameter as the legacy L. the speedometer will not be off. you gain height from the struts, but none from the wheels / tires. but your wheels / tires may look small in your wheel wells.

 

2. swap in an outback TCU and/or ECU , (i think ECU, but TCU is probably cheaper ). i've never tried it, but one of them, or maybe the combination interprets the signal from the front speed sensor and converts it to MPH.

 

3. go to the tire size calculator, http://www.miata.net/garage/tirecalc.html , figure out how off it will be and then make a mental note to adjust your speed accordingly. at 60 mph you will really be going 65.2 mph or something like that. just go 10% slower than you want to, you want to go 75 mph, set the cruise at 67.5, want to go 66, set the speedo at 60, you'll be ok.