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I am wishing to go to a significantly taller profile on rears. Any known recipe for correcting speedo?
2015 SXT 8-speed auto trans.

Thanks
 

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I am wishing to go to a significantly taller profile on rears. Any known recipe for correcting speedo?
2015 SXT 8-speed auto trans.

Thanks
I'm told that the 15 and newer cars take their speedo signal from the front tire, so no correction is needed. But, the gear ratio (effective) changes with a taller tire and you will loose bottom end pull. If you go to a taller tire, I'd recommend lower gears also. You can get a 3.09 using the stock setup, but if you go lower you probably need to change out the differential and axles to the 230mm or 250mm versions. I'm no expert. I'm doing research now for my own car. I'd love 3.55 but I don't think I can do it without changing to the larger axles, meaning differential...axles and who know's what else.
 

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Discussion Starter #3
Thank you for the info that's awesome.
I just installed an Eibach kit and though it performs great the wife thinks the rear looks too low now.
I'm going to try to run taller profile rears with matching fronts the correct profile, as some of my other sporty cars do.
It will be fine as the minor performance tweaking I am doing is geared (no pun intended) towards highway performance, not digs.
Thanks again
 

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I'm told that the 15 and newer cars take their speedo signal from the front tire, so no correction is needed. But, the gear ratio (effective) changes with a taller tire and you will loose bottom end pull. If you go to a taller tire, I'd recommend lower gears also. You can get a 3.09 using the stock setup, but if you go lower you probably need to change out the differential and axles to the 230mm or 250mm versions. I'm no expert. I'm doing research now for my own car. I'd love 3.55 but I don't think I can do it without changing to the larger axles, meaning differential...axles and who know's what else.
I don't think that is 100% correct, if the speedo signal was taken from the front wheels then how are the guys logging rear wheel speed on the dyno? When I use the line-lock feature of the tazer my speedo still functions. I think the front wheel sensors are used by performance pages for 0-60, 1/4 mile....., but the speedometer uses info from the trans.
http://www.challengertalk.com/forums/f181/tazer-awesome-401666/index120.html?401666=#post7891553

BTW if you go with bigger tires in the rear, they should not be more than ~5% bigger than the fronts as it could cause issues with ABS.
http://www.challengertalk.com/forums/f79/will-275-35-20s-throw-codes-635754/?635754=#post8105234
 

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I don't think that is 100% correct, if the speedo signal was taken from the front wheels then how are the guys logging rear wheel speed on the dyno? When I use the line-lock feature of the tazer my speedo still functions. I think the front wheel sensors are used by performance pages for 0-60, 1/4 mile....., but the speedometer uses info from the trans.
http://www.challengertalk.com/forums/f181/tazer-awesome-401666/index120.html?401666=#post7891553

BTW if you go with bigger tires in the rear, they should not be more than ~5% bigger than the fronts as it could cause issues with ABS.
http://www.challengertalk.com/forums/f79/will-275-35-20s-throw-codes-635754/?635754=#post8105234
What I was told, is that they use the ABS sensor on the front wheels. I did point out that I'm not an expert on the subject, and this was second hand. But I've read that several places in threads here and other places. There is an ABS sensor in all four wheels however, so that might explain your comment. Again, I don't know 100%.


Looking on Rock Auto, I can find a speed sensor on 2014 models, but 2015 and up I only see the ABS ones. That might just mean they don't have it though. Same thing at Autozone, they have the trans speed sensor, but only for 2014 and down.


Best bet is to ask the service department at your dealer.
 

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What I was told, is that they use the ABS sensor on the front wheels. I did point out that I'm not an expert on the subject, and this was second hand. But I've read that several places in threads here and other places. There is an ABS sensor in all four wheels however, so that might explain your comment. Again, I don't know 100%.


Looking on Rock Auto, I can find a speed sensor on 2014 models, but 2015 and up I only see the ABS ones. That might just mean they don't have it though. Same thing at Autozone, they have the trans speed sensor, but only for 2014 and down.


Best bet is to ask the service department at your dealer.
Yeah, I see what you mean. I know the automatics have input and output speed sensors, but I can't find anything on the manuals and the wiring schematics don't yield any insight. Mopar parts list show nada as well. I guess it's possible that the VSS is obtained soley from a combination of the wheel speeds sensors (e.g. performance pages uses front and speedo uses rear?) and feedout from the ABS system. :dunno:

I see the post that states the speedo gets it signal from the front tone ring.
http://www.challengertalk.com/forums/7429377-post4.html

But as you can see in this vid (0:36 car is stopped but speedo is at ~20mph), when the line-lock is activated the speedo still moves.

But then again, I saw a charger vid with linelock on and the speedo did not move.

Now I gotta do a burnout vid (or just log with HP tuners) to see if the tires are not the only thing smoking something. :grin2:
 

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