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Driver72

By Driver72
in Racing, Strip, & Track

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Driver72 Enthusiast

Driver72

Posted
Posted

Why does a new Yukon XL 4x4 with the 6.2 V8 that weighs 300+ lbs more than a Sierra CC 4x4 with the 6.2 V8 have a top speed of 112 mph, while the Sierra has a top speed of 99?

 

I know, I know, "why does a truck need to go that fast?" Blah blah

If you're only going to ask that ridiculous question, move on, as we could all ask, "why does any vehicle in the US need to go above that speed too? Not the point, and not helpful.

 

What's also weird is the "speed limiter" trips at 97 mph but then allows it to creep up to 99 mph. Ruins any 1/4 mile drag run even in stock form, and ruins any attempt to see what it will do with any mods you care to add, unless you add a tune of course.

 

Just wondering if any GM folks here can answer why GM feels a larger, bigger brick SUV get's to go to 112 mph while the lighter truck the brick SUV is based on cuts in at 97 and tops off at 99.

Also makes for passing a 70 mph 18 wheeler in Texas on a speed limited road of 85 a bit hairy when half way through the pass the limiter kicks. Trucks from 30 years ago would safely go above 99 mph, what gives now?

MikeNH Senior Enthusiast

MikeNH

Posted
Posted

Could be a million different things. Maybe the SUV comes with higher speed rated tires, maybe the driveshaft is different (this is what has blown up on a few GM pickups doing dyno pulls), maybe the coil rear suspension adds some "points" in some incomprehensible GM decision making system.

 

Trucks 30 years ago didn't stop because computers were either in their infancy or non existent. And people understood they were responsible for their own actions and people didn't sue when they messed up.

 

 

So, I don't know specifically but thats a few thoughts.

Driver72 Enthusiast

Driver72

Posted
  • Author
Posted

I think the tires are basically the same ratings if i remember correctly from looking at them.

I would think the driveshaft would be the same too since a Yukon XL is essentially a Sierra with a cover and rear seats and a different interior, but the bones and everything else is the same.

 

The coil rear suspension may have something to do with it. Didn't know the Yukon uses it. But it may stay a bit more planted because of it, as well as having a bit more weight over the rear wheels too.

 

What's also strange is prior to 2015 I believe the Sierra's were allowed to go 110 mph. I think I read it in a magazine test where they showed top speed of 110 mph. So if they were allowed to go 110 a few years ago, wonder why not now?

 

These trucks actually get up to 97 pretty quickly when starting at 60 mph. A fast pass of 2 to 3 slow moving cars on an open two lane highway gets you to hit the 97 mph initial cut halfway through the pass, then 2 seconds later it hits 99 and that's all she wrote.

Colossus Senior Enthusiast

Colossus

Posted
Posted

Police Package Tahoe is good for 135 MPH. But it is only 2WD. 4WD models more or less have the same limitations as ours do.

kstruckcountry Senior Enthusiast

kstruckcountry

Posted
Posted

The SUV having a rear sway bar (and track bar?) could have something to do with it. I'd also guess the with the weight distribution of the SUV, the rear end is less likely to go ballistic at high speed.

 

Sent from my SM-G920V using Tapatalk

MikeNH Senior Enthusiast

MikeNH

Posted
Posted

I think the tires are basically the same ratings if i remember correctly from looking at them.

I would think the driveshaft would be the same too since a Yukon XL is essentially a Sierra with a cover and rear seats and a different interior, but the bones and everything else is the same.

 

The coil rear suspension may have something to do with it. Didn't know the Yukon uses it. But it may stay a bit more planted because of it, as well as having a bit more weight over the rear wheels too.

 

What's also strange is prior to 2015 I believe the Sierra's were allowed to go 110 mph. I think I read it in a magazine test where they showed top speed of 110 mph. So if they were allowed to go 110 a few years ago, wonder why not now?

 

These trucks actually get up to 97 pretty quickly when starting at 60 mph. A fast pass of 2 to 3 slow moving cars on an open two lane highway gets you to hit the 97 mph initial cut halfway through the pass, then 2 seconds later it hits 99 and that's all she wrote.

All the big SUVs use coils and have for a while (2500s excluded I think). The reasoning is going to be some obscure difference that only someone in engineering at GM would know.

barry G Senior Enthusiast

barry G

Posted
Posted

the back end is pretension in trucks for a load.

Speed does not add weight.

they need to limit...until modified.

 

tire rating is super easy today, they are all good... if you look for that sort of thing.

 

my 1996 hits 121 before causally sliding into fifth. Top speed unknown. Still climbing rapidly. I let off due to letter "S" tires (112mph)

 

..and I do have a custom 70000 psi back end, custom cross sills.. MANY times stronger than gm. Spring helpers set to trial and error tension.

Just squaring it up made the back wheels look like they were too far in the wells.

Added some concentric spacers..

it feels even more like a race version of something they never built.

80 inches track width.

 

I bet the limiter stuff changes again someday. I had concluded after driving my dad's 2016, they are all limited to the automatics ability.

Everything else is willing.

 

..except for the wipers. they start floating at 85, and good chance to be gone by 130. :)

Colossus Senior Enthusiast

Colossus

Posted
Posted

That's alright. The trucks are made to work, not to go to the track with.

Driver72 Enthusiast

Driver72

Posted
  • Author
Posted

That's alright. The trucks are made to work, not to go to the track with.

 

 

Trucks are also made for play. Going to a track occasionally is play no matter what type of vehicle it is. ;)

8secpumpgasdaddy Enthusiast

8secpumpgasdaddy

Posted
Posted

 

 

Trucks are also made for play. Going to a track occasionally is play no matter what type of vehicle it is. ;)

 

ditto

KARNUT Senior Enthusiast

KARNUT

Posted
Posted

Yea work, warlock, Gmc gentlemen Jim, 454 SS, Little Red express 5.3 SS, Ram Hemi RT, 70 Chey CST-C10 402 tack dash. Me and my family owned most of these and used them for work and play. Almost forgot V-10 viper pickup.The quickest I've been in the 1/4 mile has been in a truck. My 92 Chevy 12s, my brothers little red 11s, his sons 2010 ram deisel 10s. The Ram was his daily work truck.

Driver72 Enthusiast

Driver72

Posted
  • Author
Posted

Yea work, warlock, Gmc gentlemen Jim, 454 SS, Little Red express 5.3 SS, Ram Hemi RT, 70 Chey CST-C10 402 tack dash. Me and my family owned most of these and used them for work and play. Almost forgot V-10 viper pickup.The quickest I've been in the 1/4 mile has been in a truck. My 92 Chevy 12s, my brothers little red 11s, his sons 2010 ram deisel 10s. The Ram was his daily work truck.

 

 

Sadly the slowest vehicle I've ever owned in probably 45-50 vehicles has been this new 2017 Sierra with 6.2 V8

99 mph top speed. LOL And at 99 mph it feels like it's just barely working, it does 99 mph with EASE.

In college I had an early 90's Festiva from Ford with a tiny little 1.5L engine or something like that. 5 speed manual. 13" wheels that were as wide as a pedal bicycle these days.

I think that little thing went into the triple digits, screaming like a pig, but it did it. LOL

I mean I don't expect a truck to do 130 mph or anything but come on, the tires are rated to 115 mph. So 110 mph top speed like the 2014's should be doable EASY. Other than adding the 8 speed auto, don't think there has been any drivetrain parts different from 2014.

If they had issues with the driveshaft, DESIGN A NEW DRIVESHAFT GM, or outsource it from another company that makes them better and stronger that can handle 110 mph like the 2014 GM trucks were limited at.

KARNUT Senior Enthusiast

KARNUT

Posted
Posted

 

 

Sadly the slowest vehicle I've ever owned in probably 45-50 vehicles has been this new 2017 Sierra with 6.2 V8

99 mph top speed. LOL And at 99 mph it feels like it's just barely working, it does 99 mph with EASE.

In college I had an early 90's Festiva from Ford with a tiny little 1.5L engine or something like that. 5 speed manual. 13" wheels that were as wide as a pedal bicycle these days.

I think that little thing went into the triple digits, screaming like a pig, but it did it. LOL

I mean I don't expect a truck to do 130 mph or anything but come on, the tires are rated to 115 mph. So 110 mph top speed like the 2014's should be doable EASY. Other than adding the 8 speed auto, don't think there has been any drivetrain parts different from 2014.

If they had issues with the driveshaft, DESIGN A NEW DRIVESHAFT GM, or outsource it from another company that makes them better and stronger that can handle 110 mph like the 2014 GM trucks were limited at.

I still don't believe the whole drive shaft thing. My 92 is as long as my 14 was. That truck has always been a weekend warrior from the original owner to now with me. It can be tuned to over 600HP with a pulley and race gas. It has the original driveshaft. The first owner did test and tune often. The second owner a friend of the first hauled motorcycles to shows. Five years ago when I bought it I took it to Baytown with a mild tune and ran 12s on street tires. If we have to be concerned about driveshafts now that alone will keep me away from the brand. I'd be curious to see if the police Tahoe has a different driveshaft. Tire ratings fine, driveshafts no.

 

 

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