Theoretical top speed

[Bambi]

If you forget about the tire rating and aero. Has anyone more mathematically inclined than me figured out the rpm limited top speed in 8th gear?

was just driving my RR sport supercharged and hit 130 on a backroad (in mexico) without even trying. 118 limit kinda sucks. This truck should be able to go at least 150

 

[TReX-RAM]

If you forget about the tire rating and aero. Has anyone more mathematically inclined than me figured out the rpm limited top speed in 8th gear?

was just driving my RR sport supercharged and hit 130 on a backroad (in mexico) without even trying. 118 limit kinda sucks. This truck should be able to go at least 150

I wish the RR would still squat past 30mph. Or even ride high past 30. I don’t like it right sizing itself without an option to “opt-out”. Kinda like wearing your seatbelt, or not. Sometimes you feel more daring. Let me drive my car the way I want.

 

[Bambi]

I wish the RR would still squat past 30mph. Or even ride high past 30. I don’t like it right sizing itself without an option to “opt-out”. Kinda like wearing your seatbelt, or not. Sometimes you feel more daring. Let me drive my car the way I want.

I totally feel where you are coming from but this is basically “I want to be in extra dangerous territory sometimes!”

 

[shooter44]

Don’t know how fast it could go, but I know it gets to the governed top speed real quick, feels like a lot more in there. I’m guessing 155

 

[tripleB]

I haven't had to do Friday night drunken math since college so don't hold me to any of this.

Theoretical RPM 8th gear top speed, ignoring all losses, etc I get 242 MPH. Had to go digging for a few stats.
Had to go digging for gear stats and tire info.

The factory 35" tires according to Goodyear have an actual height of 34.6" giving 108.7" tire circumference.
5600RPM max (actually don't see this in writing, I'm just looking at images of the dash and it looks to be 5600RPM)
8th gear is 0.67:1
Final drive of 3.55:1

Transfer case is 2.46:1

Gives an overall top speed of 242 MPH or 98MPH in 4LO ????

 

[Podiesel]

It's the tires that require the limit. Those massive gumbies have some serious rotational mass and might come apart. FCA doesn't want any extra liability.
Hey hold my beer and watch how fast I can go!!

 

[tripleB]

It's the tires that require the limit. Those massive gumbies have some serious rotational mass and might come apart. FCA doesn't want any extra liability.
Hey hold my beer and watch how fast I can go!!

Agreed, they stated the 118MPH limit was due to the tire rating from the very beginning in the reveal.

@Bambi asked for theoretical RPM max speed ignoring tire ratings, so clearly someone should hold his
beer!!

 

[HeliPilot]

Within a few months, someone will release a tuner that will override the governor. Not saying you should, but you could run wut you brung for a short sprint!!

 

[TReX-RAM]

I totally feel where you are coming from but this is basically “I want to be in extra dangerous territory sometimes!”

Exactly, Baja in a TRX at 130 type of sh!t...I am with you

 

[Bambi]

That can’t be right. No way 8th gear is that tall

I haven't had to do Friday night drunken math since college so don't hold me to any of this.

View attachment 6161

Theoretical RPM 8th gear top speed, ignoring all losses, etc I get 242 MPH. Had to go digging for a few stats.
Had to go digging for gear stats and tire info.

The factory 35" tires according to Goodyear have an actual height of 34.6" giving 108.7" tire circumference.
5600RPM max (actually don't see this in writing, I'm just looking at images of the dash and it looks to be 5600RPM)
8th gear is 0.67:1
Final drive of 3.55:1

Transfer case is 2.46:1

Gives an overall top speed of 242 MPH or 98MPH in 4LO ????

 

[Solaris]

I don’t think you considered the weight.

 

[tripleB]

I don’t think you considered the weight.

Again, he asked for theoretical RPM limited top speed ignoring all else!

 

[tripleB]

That can’t be right. No way 8th gear is that tall

This was what I found for the ZF 8 speed in the 5th gen RAM. I assumed it was the same gearing in the TRX. It is listed in multiple forums as that, so yes, those are unconfirmed as I couldn't find it in any official capacity.

1) 4.71:1
2) 3.14:1
3) 2.10:1
4) 1.67:1
5) 1.29:1
6) 1.00:1
7) 0.84:1
8) 0.67:1
Reverse) 3.30:1

 

[Bambi]

I just can’t wrap my head around two things. One why would ram (or most of the other cars this is in) need that much room between drag limited top speed and that number? Second based on what I know other cars rev limit at it doesn’t feel correct

maybe use your formula on the lower gears so somone can confirm?

 

[TReX-RAM]

I just can’t wrap my head around two things. One why would ram (or most of the other cars this is in) need that much room between drag limited top speed and that number? Second based on what I know other cars rev limit at it doesn’t feel correct

maybe use your formula on the lower gears so somone can confirm?

Anything with 702hp should be ZR rated...done

 

[tripleB]

I just can’t wrap my head around two things. One why would ram (or most of the other cars this is in) need that much room between drag limited top speed and that number? Second based on what I know other cars rev limit at it doesn’t feel correct

maybe use your formula on the lower gears so somone can confirm?

Again, like I stated at first, don't hold me to any of this. It was a quick search for gear ratios, final drive, tire size (and actual diameter) and looking at a pic of the tach to get max RPM. it appears to show either 5600 or 5700 ?? Cant tell for sure.

With all else equal, its the tire size that is driving that speed through the roof. Cars are going to have much smaller tires so even with all the same gearing they will have a much lower top speed. The smaller tires will allow them to accelerate quicker, but at the cost of top speed. So technically, given enough power to overcome all other resistances a 37" tire would give you an even higher theoretical top speed.

The Hellcats have 275/40R20 which so an actual height of 28.1 so if the TRX had the same 28.1 tire size, top speed is only 197MPH.

Gear	Ratio	MPH
1	4.71​	34​
2	3.14​	52​
3	2.1​	77​
4	1.67​	97​
5	1.29​	126​
6	1​	162​
7	0.84​	193​
8	0.67​	242​

 

[Solaris]

Again, he asked for theoretical RPM limited top speed ignoring all else!

I’m a Sith I only deal in absolutes... lol

anyway strap a couple hoverboards to the tranny and maybe you can get er up to 2 something.!

 

[Jackson]

Solaris,
Please remember that Bambi asked very politely not to bring up that night. He’s just now able to walk properly. Any mention of trannys, strapping anything on or hoverboards and he goes for one of his BIG guns.

J

P.S. I think BBB is correct on the theoretical top speed. It gets a bit trickier to calculate the friction, wind resistance, etc. When we calculate slip on a propeller it’s really similar using a similar type of formula.

 

[Bambi]

I’m a Sith I only deal in absolutes... lol

anyway strap a couple hoverboards to the tranny and maybe you can get er up to 2 something.!

Hm. Anyone with a truck able to tell me what the revs are at highway speed?

 

[nutgambler]

80 mph rpms are like 2200,
at 110 mph rpms are like 3600 if I remember correctly ..