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Blazer Forums >> Mechanical & Maintenance >> General Tech Help >> 1st Gen S-series (1983-1994) Tech >> VSS

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VSS - 3/25/2008 11:00:47 PM

Doran

Posts: 19
Joined: 3/23/2008
From: Bedford, Tx
Status: offline

What axel does the VSS read to determine speed? How does it configure speed? I have different size tires and need to know if my speedo is off for the front tire size or the rear tire size, thanks.

Post #: 1

RE: VSS - 3/26/2008 5:00:09 AM

swartlkk

Posts: 15304
Joined: 5/1/2005
From: Waterloo, NY
Status: offline

I am assuming you are 2wd due to the front tire size or rear tire size statement. It uses the sensor in the back of the transmission . I'm not sure if your vehicle will have parameters in the PCM for a tire size difference or if it would be a speedo gear swap in the back of the transmission. Really need to know the year so I can look up some things.

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Kyle-

My Restoration Projects
Please Do Not PM for Tech Help

(in reply to Doran)

Post #: 2

RE: VSS - 3/26/2008 9:39:06 AM

Doran

Posts: 19
Joined: 3/23/2008
From: Bedford, Tx
Status: offline

sorry, forgot my signiture on that post. And yes 2WD, I'm wondering because the tires in the back would have me going 66 while my speedo reads 60 while the fronts are more like 61.5 when the speedo says 60, and I can't seem to find, anywhere on the net, something that explains how the VSS works as far as tire sizes go.

I appreciate your help. All the truck info is in my signiture.

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1991 Blazer Tahoe 4DR 2WD
VIN Z 4.3L TBI

(in reply to swartlkk)

Post #: 3

RE: VSS - 3/26/2008 9:57:30 AM

swartlkk

Posts: 15304
Joined: 5/1/2005
From: Waterloo, NY
Status: offline

What is the stock tire size (can be found on the door sticker or your RPO code list) and what is the size of the tires you have on it now? I can tell you the speed difference, but I will have to look up the VSS information when I get back home tonight and have my references available.

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Kyle-

My Restoration Projects
Please Do Not PM for Tech Help

(in reply to Doran)

Post #: 4

RE: VSS - 3/26/2008 10:20:26 AM

Doran

Posts: 19
Joined: 3/23/2008
From: Bedford, Tx
Status: offline

I've actually been using this website http://www.kouki.co.uk/Utilities/tyresizer.asp to determine the speed differences, but maybe you can prove it true or false on it's calculations.

Stock - 205/75-15
Front - 215/70-15
Rear - 235/75-15

I know the fronts are only a tiny bit bigger than stock, but the rears are a little more. Needing to know which difference applies to the VSS and my speedo.

_____________________________

1991 Blazer Tahoe 4DR 2WD
VIN Z 4.3L TBI

(in reply to swartlkk)

Post #: 5

RE: VSS - 3/26/2008 10:32:46 AM

swartlkk

Posts: 15304
Joined: 5/1/2005
From: Waterloo, NY
Status: offline

Actually, your front tire is just a bit smaller than stock. That is unless you mean 215/75R15...

205/75R15 == 27.1 OD / 744 revs/mile - stock
215/70R15 == 26.9 OD / 751 revs/mile / speedo is 0.9% too fast
215/75R15 == 27.7 OD / 728 revs/mile / speedo is 2.2% too slow
235/75R15 == 28.9 OD / 689 revs/mile / speedo is 6.5% too slow

With the 235/75R15 tires on the back, at 60MPH as indicated by your speedometer, your actual ground speed is 63.9MPH. To me that isn't much to worry about, but I don't really push the +10 rule when I drive...

_____________________________

Kyle-

My Restoration Projects
Please Do Not PM for Tech Help

(in reply to Doran)

Post #: 6

RE: VSS - 3/26/2008 10:54:01 AM

Doran

Posts: 19
Joined: 3/23/2008
From: Bedford, Tx
Status: offline

That's what I meant, my bad. I don't really either but I will do 65 in a 60, just not right now so much because I don't know exactly what my speed is compared to my speedo. So you're saying the VSS takes the speed based on the rear tires? That's good to know, thank you very much Mr. Admin dude ;)

(in reply to swartlkk)

Post #: 7