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Light Wheels & Sticky Tires For Launch...?

7398 Views 44 Replies 14 Participants Last post by  WarBaby
I'm trying to arrive at an ideal combination of tires and rims for launching my `11 RCSB 2WD Hemi ST. Curiously, the factory 17 X 7 steel rim weight seems very elusive--I've read numbers from 23 to 33 pounds each. Does anyone know with certainty?

To the point, I have a K&N CAI and 14" straight-through muffler. I plan on 4.10 factory LSD gears, Y-pipe, removal of trailer hitch/spare tire/tailgate plus an Edge 2800 stall TC (it is also my daily driver). My truck is lowered 2" in the rear. I would like to use M&H 275/50R17 drag radials that are 28" tall (stock height is 31.6"). M&H specifies a 9" rim for that tire. I have found several 17 X 9 Ultra wheels that weigh between 24 and 25 pounds that are "supposed" to fit. I am thinking about using General Grabber UHP 275/55R17 up front (and on the rear for the street).

Since a tuner is not yet available (and might never be), I intend to have some 1/4-mile fun with the stock engine but...the truck must hook. I want 60' times under 1.8 seconds. Otherwise, there is scant motivation for me to proceed. I haven't spent much money on these plans...yet. So I have to ask you experienced guys, will these mods achieve my goals? Your input will be greatly appreciated before I make an expensive mistake! :Hey:

Thanks!

Tom/TN
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Oh no i got you im just surprised was really suprised when i took one off and was like WTF MY BACK lol
:LOL: yeah I know what you mean..getting the wheel back on after removing it is quite a task!
 

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I was not aware of the governor/tuner issue. Thanks for the heads-up on that and all other informative replies. A temporary solution for me (until tuner availability) might be to run our local 1/8 mile track instead of our 1/4 mile track...heh heh!
I've solved the "smaller-tires-but-no-tuner-available-so-the-govenor-kicks-in-at-1000ft-problem". Hypertech makes a speedo calibrator that IS compatible with the 2011 up computers - I am running one in mine right now. Works just like the handheld tuners but only has options to check and clear DTCs and correct for tire size. I haven't had the opportunity to run at the track with the new set up, but my speedo is accurate with 30 inch tires. (had to tell the computer 29 inches!?)
:smileup:
 

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Discussion Starter · #24 ·
I've solved the "smaller-tires-but-no-tuner-available-so-the-govenor-kicks-in-at-1000ft-problem". Hypertech makes a speedo calibrator that IS compatible with the 2011 up computers - I am running one in mine right now. Works just like the handheld tuners but only has options to check and clear DTCs and correct for tire size. I haven't had the opportunity to run at the track with the new set up, but my speedo is accurate with 30 inch tires. (had to tell the computer 29 inches!?)
:smileup:
Hmmm....I don't understand the 29" part--why?
 

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Hmmm....I don't understand the 29" part--why?
Likely because of tolerances. For example, remember the old days when police packages had "certified" speedometers? That is because standard speedometers are allowed an accuracy tolerance - I've have heard up to +/- 3%. Also, 30 inches is what my P275/70R17 tire is "speced" at, per tirerack, but just like when setting up stagger at a dirt track, you really need to measure the circumferance to get a truly accurate number as two different tires could easily measure 2 inches in circumferance different despite the same sidewall specs. When I put the 285/70R17s on my 2500 CTD, which are "speced" at 32.8 inches and I set my programmer to 32.75 inches since it uses .25 inch increments, you would think that would be the most accurate setting...nope. When I passed a radar sign, my speed was still off. I had to use either 33 or 32.5 (I don't remember which, just that it is .25 off). Now when I pass a radar sign, my speedo is dead on.

When I put the P275/60R17s on my 2011, I set the programmer to 30 inches. I passed a radar sign and my speedo still read higher than the sign indicated. I haven't passed a radar sign with the new setting, therefore my previous statement was not 100% correct, but the point is they need some tweaking to be precise. I'm willing to have my speedo err on the slow side to give me a little extra cushion so I don't hit the govenor at the track, so I set it to 29 inches for now. I was running 14.3 @ 98mph. Since then, I now have the shorter tires for more gear, removed the clutch fan, put in a 180 t-stat and removed the spare tire. I'm shooting for 13.9s. Will all that get me up to 105 mph?? If the air is good it might (my Camaro used to run 13.8 at 105 mph stock with drag radials) and if the speedo is off the wrong direction by even 1%, it could hit the govenor. If I really wanted to make sure, I could set it to 24 inches at the track and it would probably read about 70mph when I'm at 105!
 

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Likely because of tolerances. For example, remember the old days when police packages had "certified" speedometers? That is because standard speedometers are allowed an accuracy tolerance - I've have heard up to +/- 3%. Also, 30 inches is what my P275/70R17 tire is "speced" at, per tirerack, but just like when setting up stagger at a dirt track, you really need to measure the circumferance to get a truly accurate number as two different tires could easily measure 2 inches in circumferance different despite the same sidewall specs. When I put the 285/70R17s on my 2500 CTD, which are "speced" at 32.8 inches and I set my programmer to 32.75 inches since it uses .25 inch increments, you would think that would be the most accurate setting...nope. When I passed a radar sign, my speed was still off. I had to use either 33 or 32.5 (I don't remember which, just that it is .25 off). Now when I pass a radar sign, my speedo is dead on.

When I put the P275/60R17s on my 2011, I set the programmer to 30 inches. I passed a radar sign and my speedo still read higher than the sign indicated. I haven't passed a radar sign with the new setting, therefore my previous statement was not 100% correct, but the point is they need some tweaking to be precise. I'm willing to have my speedo err on the slow side to give me a little extra cushion so I don't hit the govenor at the track, so I set it to 29 inches for now. I was running 14.3 @ 98mph. Since then, I now have the shorter tires for more gear, removed the clutch fan, put in a 180 t-stat and removed the spare tire. I'm shooting for 13.9s. Will all that get me up to 105 mph?? If the air is good it might (my Camaro used to run 13.8 at 105 mph stock with drag radials) and if the speedo is off the wrong direction by even 1%, it could hit the govenor. If I really wanted to make sure, I could set it to 24 inches at the track and it would probably read about 70mph when I'm at 105!
When you run shorter tires you will trap at a lower speed. When I was stock I would run my street tires and trap at 97ish and on my slicks I would trap at 95ish
 

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When you run shorter tires you will trap at a lower speed. When I was stock I would run my street tires and trap at 97ish and on my slicks I would trap at 95ish
It depends on your setup. Since a shorter tire gives you a deeper effective gear ratio, you will accelerate faster - this is a given. If you still have rpms left at the end of the track with the tall tires, then you will be able to take advantange of those available rpms with the shorter tire and potentially trap higher. Specifically, if it takes you 1320 feet to accelerate to 97mph with the tall tires and you are now accelerating faster with the shorter tires, you should hit the same 97mph around 1200 feet and then surpass it by the 1320 mark - this is all providing you haven't run out of rpm. The only way you should trap slower is if you ran out of motor because you now have too deep of a gear.
 

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Here's the difference on my slips, both days were higher DA than normal,
my best ever trap was a 13.8 at 98.5mph on my DR's

MPH doesn't really change with lower gears or smaller tires, ET's just get quicker (in my experience)

32" Tall 305/50R20 Grappler's on stock 20's (3.55's)
(lost traction, one wheel peel at launch on the first pass)


27.5" Tall 295/45R17 DR's on 17"x 9" Moto Metal wheels (4.30:1 effective)




 

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Discussion Starter · #31 ·
Yes, I know, I've weighed mine on a shop scale while rotating my tires. But that's with the tires. Wheel for wheel without tires, the R/T wheel is about the same weight as a sport wheel or any other 20 wheel. Although it looked like the 17 inchers were a good bit lighter.
I carefully weighed my 2011 ST 17" X 7" steel spare w/new Goodyear Wrangler SR-A 265/70R17 tire = 68.5 lbs.

Also, FYI:

Spare tire cable and ratchet assembly = 5.7 lbs.
Jack and handle = 9 lbs.
Tailgate = 57.5 lbs.

So, the mere removal of these parts saves 140 lbs. :smileup:
 

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Discussion Starter · #33 · (Edited)
Ha...it's interesting that you mentioned battery relocation. I am in the process of doing exactly that with a generic Summit kit. I figured that the weight loss from the rear would complicate launch traction and decided to redistribute a few pounds from the front to the rear. I just bolted the new plastic battery box to the passenger side behind the wheel well. I haven't run the cables yet but the kit came with 20' of 2 gauge cable. I've done this before and it definitely helps.

By the way, you have an awesome truck. :smileup:
 

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Ha...it's interesting that you mentioned battery relocation. I am in the process of doing exactly that with a generic Summit kit. I figured that the weight loss from the rear would complicate launch traction and decided to redistribute a few pounds from the front to the rear. I just bolted the new plastic battery box to the passenger side behind the wheel well. I haven't run the cables yet but the kit came with 20' of 2 gauge cable. I've done this before and it definitely helps.

By the way, you have an awesome truck. :smileup:
do you have the part number on summit..I think I'm gonna go that route to although does anyone know about the nhra rules about battery location? or is that just battery shutoff switch..
 

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Nice, mind posting pictures of the rest of the wiring?

chefred, I think when relocating a battery to the trunk you also need a vent(but if the bed is open then it's all good I'd assume). I also don't think gel type batteries need to be vented. I don't think you can run the cable through the cabin either, but you probably wouldn't likely do this with a truck anyway...
 

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My installation of the box...
I will apologize in advance for hijacking the tread, but I am starting to see the potential to fail tech inspection at the track:

First, a bungee strap will NOT pass track tech to mount a battery. If not using the OEM mount, you must use at least 3/8" bolts/threaded rods (j-bolts are not acceptable either).

Second, I'm pretty sure you will require the battery disconnect switch with the relocated battery. I will be at Virginia Motorsports Park in Richmond this weekend for the Mopar Spring Fling - I will ask the tech inspectors to confirm, but I know this is the case for a car. Disconnect switches can be tricky as not all switches are NHRA approved. Also they must be tied in to the POSITIVE cable, not the negative cable, yet still shut a running vehicle down when switched off. If you wire straight between the positive battery terminal and the rest of the wiring circuit and turn the switch off while the vehicle is running, it will continue to run on the alternator and fail tech inspection.
 

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Discussion Starter · #40 ·
I will apologize in advance for hijacking the tread, but I am starting to see the potential to fail tech inspection at the track:

First, a bungee strap will NOT pass track tech to mount a battery. If not using the OEM mount, you must use at least 3/8" bolts/threaded rods (j-bolts are not acceptable either).

Second, I'm pretty sure you will require the battery disconnect switch with the relocated battery. I will be at Virginia Motorsports Park in Richmond this weekend for the Mopar Spring Fling - I will ask the tech inspectors to confirm, but I know this is the case for a car. Disconnect switches can be tricky as not all switches are NHRA approved. Also they must be tied in to the POSITIVE cable, not the negative cable, yet still shut a running vehicle down when switched off. If you wire straight between the positive battery terminal and the rest of the wiring circuit and turn the switch off while the vehicle is running, it will continue to run on the alternator and fail tech inspection.
Thanks for your constructive comments. The battery relocation job is incomplete. Most of my projects tend to be works in progress. I do things that are supposed to be fun when I feel like it. Otherwise, it is not much fun.

The bungee cord does not "hold" the battery. It only secures the plastic lid of the battery box. The box itself is bolted through the truck bed floor with three 3/8" bolts. I am working on a hardware retainer for the battery that should meet inspection standards--again, at my leisurely pace. Your comments about a cut off switch are well taken however and I'm pondering that.

Pics are here: My Hemi
 
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