just made a video to show how bad the speedo lags and why i love the RPD.

take a note of when the RPD hits 80 and when the speedo does.

cobalt ss speedo lag - YouTube

 

It's a known issue, the stock boost gauge and instrument cluster are both on the low speed CAN bus, RPD is on the high speed CAN bus.

If you wanna see a huge lag put a stock boost gauge next to a mechanical one for a 2.5k punch, it's depressing.

 

wish i could fix it, its so annoying.

btw this is on my old 20psi tune.

 

Yeah I wish we had boost gauges like the SRT-4's haved, those things like peg as soon as you hit boost.

 

Ya.. SRT-4 gauges were nice... and it looks like the lag is between 5-8 mph difference lol... I coulda sworn that my rpd was about the same tho.. I'll hafta check again when I get it back :P

 

Is there a way to fix the speedo and boost gauges?

 

Speedometer.. no

Boost Gauge.. Yes.. buy a good mechanical gauge

 

I hate it too. My speeding was worse than I thought lol.

 

hmmm i gonna do a pull with interceptor to see what happens

 

this is bs. i never knew this

 

hmmm never noticed this, ill check mine out lol

 

... what size are your tires...... I know it is off, but thats ALOT. if your tires are bigger your speedo would be slower...

 

i was gonna say that looks slow as ****

nope, difference is even greater on e

 

Regardless of tire size the speedo will still be off compared to the RPD.

And that was on my 245 40 18 tires.

 

well ya you have taller tires, which means they turn less relative the speed they are going compared to stockers (you know this I dont have to explain that to you)

Yes there is a lag, and I know its considerable, but that is REALLY bad lol, think some of it is your tires, and are you dropped how you get that to fit?

 

Tire size will have nothing to do with spedo lag.. period

It will however obviously effect the accuracy of your displayed speed

 

Im dropped on pedders and have 18x8 +35 rims. I have 255 35 18 in the fronts now.

Also, tire size will throw off speedo accuracy, not lag. My cars just quick.

 

^^oh i know mine is off by about the same amount, also on 18x8 and pedders, i dont know offset tho its the me too 045's, and I know mine is off, so depening on situation i have my rpd on

 

they lag bad watch my vid on you tube and you will see the boost gauge drop and the speedo climb 10mph lol. When i get time i'll make a vid of a hp log and speedo and it will look just like Dart SI's.

 

^^ i know I am agreeing, i just never realized it was THAT bad, same happens to me. But uh, when im doign that im not completely paying attention to how off it is, and a bit more focused on whats in front of me lol

 

There was this video on a thread where this guy was makin a rpd+ stock boost gauge pillar.. He did a pull with both of em side by side an they read the Same everytime.. Jus sayin... I have no rpd, so I can't comment on speedo lag, an all the gps's I've used always lag a Lil bit 2 so I never really noticed it.. I'm on 245/40/18 btw..

 

Being that everything in your instrument cluster and external stock gauges is just a large network if the address assigned to boost is say 0145, the stock boost gauge will read that address the same number of times the RPD will. The only way to fix the lag on any of it is to use gauges that do not use the stock wiring and sensors such as a mechanical boost gauge.