New 285's. Effect on speedo?
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New User
Joined: Sep 2005
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From: Saratoga, NY
New 285's. Effect on speedo?
Just put new 285's on the X and I'm wondering what effect it has on the speedo. It seems like quite a few of you have gone up in size. I know that I'll actually be traveling faster than the speedo shows, but I'm wondering if the ECM uses speed as one of it's operating parameters. I've also seen the products that compensate for the larger tire size. Do they address any other issues, like the ECM, or do they just show actual speed?
Senior User
Joined: Jan 2005
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From: Monterey Park, California
When I tested mine using odometer check mile markers, with the stock 265's, my indicated speed was faster than actual. If I get 285's think my speed will be right on. Maybe yours is right on now.
Did you keep the spare at 265?
Did you keep the spare at 265?
Last edited by Hello; Sep 23, 2005 at 02:45 PM.
Junior User
Joined: May 2005
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cficare are you running 305-70R-16s on stock rims and did you do a lift? I read in past posts about people going with this tire size with out a lift but none of the threads I read said anything about stock rims. thanks for any help
Logistics Pro
Joined: Feb 2005
Posts: 3,529
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From: SEVA
VodkaMan - (prefer scotch myself) No, not stock rims. I got a great deal ($75 ea) for a set of new Panther 16x8 rims on eBay. No lift either. The only rub I get is at full-lock AND simultaneously hitting a bump ... which usually happens when I enter my parking garage at work. That minor rubbing occurs between the tire and the rear face of the fenderwell panel (plastic) inside the front fenders ... no contact with anything made of metal. Otherwise, no rubbing or clearance issues at all.
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Joined: Sep 2005
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From: Saratoga, NY
Originally Posted by Hello
When I tested mine using odometer check mile markers, with the stock 265's, my indicated speed was faster than actual. If I get 285's think my speed will be right on. Maybe yours is right on now.
Did you keep the spare at 265?
Did you keep the spare at 265?
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New User
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From: Saratoga, NY
Originally Posted by bterry
I'm not positive, but pretty sure speed is an ECM parameter. Take it to the dealer, and they will reprogam it for the larger tires. Many people here have done it.
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New User
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From: Saratoga, NY
The 265's that I had were listed at 31.7" diameter and the 285's are listed at 33" diameter. I'm assuming that's tall enough to make a difference in the reading on the truck. When I went from 26.5" tall slick on my Z28 to 28" slicks there was a world of difference in my 1/4 mile trap RPM.
Tuned
Joined: Aug 2004
Posts: 499
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From: Laguna Hills and Payson
I have a GPS in-dash on my '05 X.
The stock 265/75/16 ~31" tires read 3-4 mph too high at 70.
My Current 295/75/16 ~34" tires read 0.5-1 mph low at 70.
I would bet your tires are *spot* on.
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2005 EXCURSION Eddie Bauer 4X4 PSD
4" FabTech lift/level, Bilstein mono-gas shocks, Rancho Steering Stabilizer
Silverstars, BFG 295/75/16 AT KO's on Factory Mags
LANDYOT Generation II Radius Rods, Ford factory hood insulator
The stock 265/75/16 ~31" tires read 3-4 mph too high at 70.
My Current 295/75/16 ~34" tires read 0.5-1 mph low at 70.
I would bet your tires are *spot* on.
__________________
Quietman
www.roenation.com
2005 EXCURSION Eddie Bauer 4X4 PSD
4" FabTech lift/level, Bilstein mono-gas shocks, Rancho Steering Stabilizer
Silverstars, BFG 295/75/16 AT KO's on Factory Mags
LANDYOT Generation II Radius Rods, Ford factory hood insulator
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New User
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From: Saratoga, NY
It's beginning to sound like I got lucky on the size choice. One can only hope. Thanks for the info and keep it coming guys.The more opinions the better. I've learned a hell of alot reading the forum for the last month.
Fleet Owner
Joined: Jan 2004
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From: Brentwood,CA
Originally Posted by EB03PSD
The 265's that I had were listed at 31.7" diameter and the 285's are listed at 33" diameter. I'm assuming that's tall enough to make a difference in the reading on the truck. When I went from 26.5" tall slick on my Z28 to 28" slicks there was a world of difference in my 1/4 mile trap RPM.