Speedo Correction?

[Ted44]

If you have larger tires than stock, what have you done about speedo/odo correction. There are several devices on the market as well as replacement a speedo gear. Or do you do nothing?

 

[corsair23]

Wasn't a choice but I use my Scangauge II to show correct speed and a calculator to adjust for mileage

 

[Nay]

Wasn't a choice but I use my Scangauge II to show correct speed and a calculator to adjust for mileage

I think the Yellow Box is head and shoulders above the truspeed. The truspeed has no lights to show it's working, no diagnostics to show it is working properly, and costs twice as much. The Yellow Box has diagnostics/power on via embedded LEDs and it offers a greater correction range of +/- 28%.

Yes, you can flip a switch for a second set of tires with the Truspeed...but the yellow box is only a few switches and I can't see getting a truspeed unless you have two sets that come on and off regularly where you need an adjusted speedo.

Both of them require splicing into the vehicle electronics, though, where the Marks box is plug and play with a small hole drilled for wiring. For those who aren't comfortable with the cutting/soldering, Marks should be a great solution for an extra $100. Of course, you need to be comfortable with drilling a hole in the floor

I would not leave it alone - the shift points are hugely improved with a GPS calibrated speedo.

 

[corsair23]

I would not leave it alone - the shift points are hugely improved with a GPS calibrated speedo.

Good point Nay and one I always forget that I'm not taking into consideration...Maybe someday the Scanguage IV will be able to take care of sending a calibrated signal back to the ECU

 

[landtank]

When I corrected my truck there was only one option and it was the truespeed. It's been sitting on top of my heater box behind the glove box for about 5 years. Why anybody needs to see blinking lights is beyond me. The speedo either works or it don't. But the yellow box does seem to be a better bargain and a little easier to set up provided you get the correct one.

ScanGaugeII is a waste of time in this application as it is not interfaced with the ECU so you won't get the shifting benefits from actually correcting the VDO signal from the speed sensor.

If you are running 285s with stock gearing the gear from Slee is probably the best choice for that application but won't grow with future mods such as re-gearing or even larger tires.

 

[Nay]

When I corrected my truck there was only one option and it was the truespeed. It's been sitting on top of my heater box behind the glove box for about 5 years. Why anybody needs to see blinking lights is beyond me. The speedo either works or it don't.

It's just an install thing - you hook up a truspeed and it doesn't work and you have no way to know why. You hook up a Yellow Box and it tells you it has power, and then it confirms that each switch is functioning properly, and then you can set the dip switches to perform diagnostics if needed, and then it has a 10 year warranty.

All of which is probably pretty much a non-issue after install...but then the Yellow Box is $100 shipped so why not have the extra functions at half the price and half the size?

 

[woody]

45 minutes to change tires plus 1 minute to flip the TruSpeed switch...

45 minutes to change tires plus 3 minutes to find the dip settings and reset the YellowBox...

no complaints with the YellowBox in my rig, and should I ever decide to jump to 49" tires, I know I can set the speedo to read correctly

 

[landtank]

It's just an install thing - you hook up a truspeed and it doesn't work and you have no way to know why. You hook up a Yellow Box and it tells you it has power, and then it confirms that each switch is functioning properly, and then you can set the dip switches to perform diagnostics if needed, and then it has a 10 year warranty.

All of which is probably pretty much a non-issue after install...but then the Yellow Box is $100 shipped so why not have the extra functions at half the price and half the size?

I'm not saying the yellow box is a bad deal but unless they are supplying parts knowing why it's not working isn't going to help you. These things are real easy to install and about the only thing you can screw up is the polarity of the VDO signal.

If the yellow box was around when I needed something I would have definitely gotten it.

 

[Ted44]

the shift points are hugely improved with a GPS calibrated speedo.

That answers one question I had.

The next would be regarding the change in gear ratio caused by the larger tires. How does the loss of the stock 4:11 ratio effect performance? Seems as though there would be some increase in sluggishness and loss of power as you go up in tire size that is not only attributable to the tires, but to the increasingly taller gears.

At what tire size does the performance loss necessitate a regear?

regear = $$$$

 

[corsair23]

That answers one question I had.

The next would be regarding the change in gear ratio caused by the larger tires. How does the loss of the stock 4:11 ratio effect performance? Seems as though there would be some increase in sluggishness and loss of power as you go up in tire size that is not only attributable to the tires, but to the increasingly taller gears.

At what tire size does the performance loss necessitate a regear?

regear = $$$$

Ted,

There is some discussion in the FAQs but in general from what I have read most agree that if you go with 35" (315) or larger tires you will want to regear.

As for the effect on performance and the need to regear you are correct that it is due to multiple issues with going up in tire size. Tire size has an effect as does the weight of the larger tires, other mods (i.e. weight) you have done, and probably just as important, where you live. If you live in a high altitude area or one with a lot of hills/mountains IMO you will feel the impacts of larger tires even more.

I am running 285s with stock gears in Colorado and it is ok - definitely not bad enough for me to warrant the cost of regearing. Someday I'd like to go up to 315s, supercharge or turbocharge the engine, and regear. That is a lot of $$ so for now I'm perferctly happy with my setup. If I lived down at sea level then I don't think I'd even notice the performance loss from the bigger tires and mods - maybe I would...

As for regearing some go up to 4.56, some to 4.88s, and then there is Nay who said for years there was no need to regear if you ran 35s and then just recently he regeard to 5.29s

I think I'll buy a yellow box here in the near future just to see how big of a difference it really makes telling the ECU the true speed vs. the uncorrected speed right now. Based on what Rick and Nay say I should notice a considerable improvement.

 

[FJnAK]

I just ordered up 5.29's for my cruiser, it does ok with 315's but I notice a huge loss of power when I put my 37's on it.

 

[Ted44]

So...

Based on the poll, No Mark's 4WD and No Truespeed users? Landtank mentions his Truespeed, though.

I admit to being attracted to the Mark's 4WD Adaptor for two reasons, Slee sells it and I HATE the idea of messing with my ECU wiring.

At this point, I'm looking at 285s and OME medium, but I know I won't stop there. Now all I need to do is put the $$$ together...

Thanks for the input from everybody, so far.

 

[NorCalDoug]

no correction on mine...


running stock gears and 315/75 R16, my speedo is off by 10%. The math is simple to do.
when the speedo reads 60MPH, I'm actually going 66MPH.


I have my GPS to show actual speed...could that be considered "correction"?

 

[CycloSteve]

Thread revival.

Finally pulled the trigger for the Mark's 4WD Speedo correction box. 20 minutes, and it is installed and perfect. Plumbed the wires through the gromet on the right-hand side of the trans hump, and 3M taped it to the side of the heater box well out of sight, but reachable for adjustments. Plug and play, no cutting or tapping into any wires.

Gave correction for my 315's and 4.88's which were reading just about 9% over the actual, as confirmed by GPS...now spot-on. Not cheap ($200 from Slee), but happy that it gives me the flexibility to change tires, and fix things with the flip of a few dip-switches.

 

[Roc Doc]

Has anyone here had any experience with the Jet Performance Accu Speed module? It looks like it would do the job. I've got oversized tires but deep gears so I'm way off on my speedo.

http://www.jegs.com/i/JET+Performance/561/50110/10002/-1