Adjusting Speedo to new tires ?
 

i was going to call the dealer on monday - but i did a small upgrade - that according to the tire-calculator changes the speedo by 1.5% -- so im wondering wouldnt the dealer be able to dial that back in easilly so that all the calculations on the computer and spedo are exact ? its not alot but wondering if anyone has done that ?

I'm not aware of anything the dealer can do to fix speedo error due to different sized tires from stock. 1.5% is a pretty tiny percentage anyways, you'll get almost that much difference going from a full tread new tire down to the wear indicators. Also, a lot of cars are off by a small percentage when new.

You can always check your actual speedo error with GPS, and just be aware of real vs indicated speed at various spots on the speedometer.

great idea about the gps check -- thanks.
im thinking about this too much... this might be a non-issue the more i think about it.

Over the past few years I've had quite a few sets of non-stock sized tires on my cars that have been up to 4-5% larger or smaller diameter than stock. The only time it has been an issue for me is with tires that were larger diameter than stock, which meant that the speedometer showed a slower speed than I was actually going. Specifically on our Forester XT, the calculated error was 1.6%, but the actual error was closer to 3%, as I found out when I was pulled over for speeding for 12 mph over the limit, when I thought I was only going 10 mph over, which should have been safe. When I later checked the speedometer error with a standalone GPS unit (as well as a speedometer app on my Android phone), I discovered that the speedo error was greater than what it calculated out to be.

The requirements for speedos here are that they must not under read but can be up to 10% over. So most of them read 5% over, right in the middle of the range required.
If it's the same in the US you can add up to 5% on the tyre diameter without worrying but I agree, a GPS will prove the point.

The electronic speedos can be recalibrated with an after market gizmo.

http://dccdpro.com/zcart/index.php?m...ea6683906157c9

It wasn't made for this application, but if you're that concerned about it I'd see what Jeff/Spiider/DCCDPro can do for you.

Exactly. The speedo should read higher than you're actually going, which is why I've never worried about taller tires that much.

I swapped the wheels and tyres on a Ford Courier[Mazda Bravo] single cab to get the gearing higher. The 14" were replaced with offroad 16" that were over 14% bigger so that 4th gear was the same as 5th had been before.

It was just right but I had to mark the speedo with liquid paper to save constant mental calcs on the move. Luckily no cops ever stopped me and saw that speedo.:thumbup:

That would definitely be a situation where you'd want a device as such, lol. I'll drive by some radars and see how accurate the speedo is; it should be reading higher BUT closer to actual speed due to my slightly taller tires. I should have appended my previous statement with "when you stay within 3-5% of stock tire diameter."

unless they sell the little pinion speedo gears at subaru? I dunno, sorta new to the brand myself