Reprogramming Speedometer ??

I'm starting to think about wheel and tire upgrades, so I'm wondering if there is any way we can reprogram the speedometer on our own.

 

I have an AP 2.0, but that doesn't do it. Do any of the open source software programs give you this ability? I'm assuming not since the ECU doesn't have direct control over the speedometer settings.

 

It would be nice to be able to switch between the stock 17's for winter a some new 18's for summer without having to go to the dealership twice a year for such a simple thing.

You're assuming your dealer would even know what the hell you're talking about. From the sounds of it most even doubt the existence of the SSM (I think that's what its called).

You're assuming your dealer would even know what the hell you're talking about. From the sounds of it most even doubt the existence of the SSM (I think that's what its called).

 

Oh yeah. It seems I give the stealerships too much credit some times. I've heard stories of botched oil changes at the dealership so I really should expect incompetence by default.

 

So does everybody here who has changed wheel size just live with a slightly inaccurate speedometer?

There is a setting for 17/18 inch wheel in BIU that can be changed with SSM.

It would be nice to be able to switch between the stock 17's for winter a some new 18's for summer without having to go to the dealership twice a year for such a simple thing.

There are devices that do such a thing, but its a recalibration of the speed signal to the speedo itself. Something like that won't work on the Legacy because of the CAN system... all digital.

 

There is a setting for 17/18 inch wheel in BIU that can be changed with SSM.

Yep, and just to be clear, the 18" setting is not a +1 scenario, which would be useless.

Oh yeah. It seems I give the stealerships too much credit some times. I've heard stories of botched oil changes at the dealership so I really should expect incompetence by default.

 

 

To be fair - for every dealer that screws up an oil change, there's a few hundred that don't. Nobody talks about the great oil change they got (and why should they), but everyone is quick to slam the joint that hosed it.

 

-

Jim

^^^

 

Very good point. And for every shop that botches an oil change, there are 10 do-it-yourselfers that botch the change as well, but you never hear about that either. Because honestly, who's going to admit they forgot the drain plug?

lol theres a whole thread on a guy who messed up BAD on an do-it-yourself oil change....ya'll need to read it its hilarious

i do the same, i have 18's for summer and 17;s for winter.....i never had an issue with my speedometer whay would u want to change yours?

Has anyone ever double-checked the accuracy of the speedo with stock tires?

 

I suspect mine reads a bit high, based on some interactive speed limit signs in my area, but I'm not sure how accurate those are either.

Has anyone ever double-checked the accuracy of the speedo with stock tires?

 

I suspect mine reads a bit high, based on some interactive speed limit signs in my area, but I'm not sure how accurate those are either.

Yes, there are a number of threads where those with GPS chimed on in actual vs. speedo. Mine was just shy of 2mph over when cruising at 75mph.

I suspect mine reads a bit high, based on some interactive speed limit signs in my area, but I'm not sure how accurate those are either.

I'm going with "Not very"....the ones around here tend to jump all around.

changing from 17" to 18" really doesnt change that much, especially if you the religous type that must follow the plus sizing rule.

 

even with the largest tire that you can possibly fit in the GT (regardless if it's 15" or 19", the largest tire you can put is a 25.4" tall diameter tire) which shouldnt throw off the speedo reading by 4 mph traveling at 60mph...

 

I do more wheel slipping and spinning in the cold, wet and on track that the tires probably register way more miles than I actually moved

According to my GPS, my speedo reads about 1-2mph too high in the 60-75mph range with the stock tires. With my 205/50R17 RSi winter tires, it is more accurate.

Thanks for the info, everyone.

 

It looks like it isn't worth the trouble and there really isn't much of an issue if the worst case scenario is a few mph inaccuracy at higher speeds.