Frame stiffness

[My98RT10]

Just a question regarding frame construction of our gen 2 cars. Reading the OEM shop manual it seems like there is no difference in frame construction between the roadster and the Coupe. On the other hand many people say that the Coupe is more rigid/stiff due to having a non detachable roof. However, the GTS roof panel does not seem to be real solid and I am assuming it will flex in various driving situations. So my question would be, if there is a tangible difference in chassis stiffness between the two models?

[dave6666]

No.

[stuntman]

Yes, but the GTS is still a wet noodle by today's standards.

[dave6666]

Yes, but the GTS is still a wet noodle by today's standards.

Please substantiate that with something besides, well, nothing at this point. Because previous discussions on the subject have pointed out how stiff the Gen 2 frame is. COMPLETELY CONTRARY to what you say yet again.

[daveg]

The mere fact that the GTS has a roof is going to make the car more ridged AND eliminate any cowl shake the convertible may have. When I put the Hardtop on my Vette Convertible, its a different car.

[Tom, F&L GoR]

I'm curious as well. Long ago on another forum someone claimed the RT was stiffer because the sport bar had more surrounding body material than the same frame piece does in the GTS. A common internet list has the Dodge Viper Coupe at 7,600 Nm/deg. And then there are magazine articles...

.11633

[stuntman]

Please substantiate that with something besides, well, nothing at this point. Because previous discussions on the subject have pointed out how stiff the Gen 2 frame is. COMPLETELY CONTRARY to what you say yet again.
Yet again? If you think the Viper has a stiff chassis, you don't drive many cars....

Post #28:
http://forums.viperclub.org/threads/664704-No-torsional-spec-for-rigidity-found-on-the-2013-srT-Viper

[gage]

Stats are like bikinis. What they show is interesting but what they hide is vital :)

I've always been leery of TR numbers because they can be calculated a few different ways (ex http://www.cadanda.com/CAD_PACE_1__67-75.pdf ) and because there isn't a standardized method that automakers measure them. Case in point, the 2003 Mustang according to your link should have more than double the observed stiffness, yet no one I know would confuse a 03 mustang as feeling stiffer than a Viper.

Now, to look at the numbers as they are, I think a very important point will be comparing Unibody vs Body on Frame. Most cars today are unibody, but the Viper still bucks this trend. The downside to body on frame is they will exhibit torsional rigidity loss because it's built to be stiff in 2 dimensions, not 3 like a unibody. And since torsional rigidity is basically grabbing the hood and trunk of a car and twisting, it's easy to see where a ladder frame will twist more easily than a unibody car. But it must be asked, how important is this twisting motion compared to lateral forces? A ladder frame can be very stiff against lateral forces, and the Viper fits that bill. My 2006 Pontiac GTO was much stiffer in the TR dept but because of the subframe design, you had alot of slop in the suspension that negatively impacted handling. The Viper with it's much less stiff frame handles worlds better than my old GTO with multiple subframes and rubber bushings everywhere along the frame. I also sometimes get cowl shake on these Ohio roads when there are alot of bumps and ridges, whereas the GTO did not. But on a smooth drag strip or race track? It does very very well. I think it's important to realize that TR is not the be all end all, *and* a car with more TR can handle much worse than a car with higher TR. Suspension setup, rollover stiffness, etc all contribute to how a car handles.

Bottom line for me is this: by that list the Mustang 2003 has a better frame due to higher TR. As someone who has driven both a Cobra and a Viper I would never confuse the Cobra as being the better handling platform.

[My98RT10]

I like the discussion and I learn from it. My initial point however was not so much as how the GEN2 compares to other makes (but for sure this interesting as well) but how GEN2 roadster compares to GEN2 Coupe. Both have the same frame construction and elements (body on frame). Have there been comparable measurements done between these 2?

[stuntman]

I agree that it's bad to draw handling conclusions based solely off of torsional rigidity numbers, since there are a ton of factors that go into making a car corner and handle well. It's also important to keep in mind that torsional rigidity is inherently higher in smaller cars than larger cars and heavier cars need greater torsional rigidity than lighter.

Torsional rigidity is important to allow the suspension to work efficiently and precisely. A flimsy car will not react to a small change (say a 50lb spring rate change) while a stiffer car would. There's no question the Viper is a brute car with huge tires, a balanced chassis, and high cornering capacity; but it does so with an inherently weaker ladder-frame chassis (vs. unibody).

To go back to the original question, according to Popular Mechanics, October 1996; the GTS is 12% stiffer than the RT-10:

https://books.google.com/books?id=RWYEAAAAMBAJ&pg=PA77&lpg=PA77&dq=viper+rt10+vs+gts+torsional+rigidity&source=bl&ots=Ki2gY87qa6&sig=rC8sUKimRGvoB6JxoOzYjQxGyK4&hl=en&sa=X&ei=KPuYVfWCDJDBgwSxtqHgBw&ved=0CEAQ6AEwCQ#v=onepage&q=viper%20rt10%20vs%20gts%20torsional%20rigidity&f=falis

This is the first time I've seen 12%, typically 25% is quoted for both Gen 2 RT-10&GTS, but I would bet MotorTrend & other magazines took the 1996 GTS' press kit and mistakenly used it for the 1996 RT-10 as well (which had a mostly Gen 1 chassis and engine). The GTS is said to be 25% stiffer than the Gen 1, so I would imagine the 1996+ RT-10 is still at or slightly more than the Gen 1's 5,000lb-ft-degree.

[RTTTTed]

Either way, if you want better handling I suggest anti-toe bracket stiffeners, poly swaybar bushings as well as replacing the rubber rack and pinion bushings with aluminium.

The anti-toe stiffener brackets make a huge difference when braking or transitioning altitude, expecially through corners. It may only stiffen the frame slightly, but the handling difference is huge.

[nrs1]

Can the anti-toe stiffener brackets be used on a car that has had the frame/differential recall done? I've seen comments that this device could not be used if the recall was needed.

[stuntman]

According to EMI Racing, the toe deflection actually happens at the outer aluminum knuckle; not the inboard chassis-side mounting point. So the proper brackets will fit on 998-recalled cars while the ineffective inboard "toe stiffeners" will not fit on the drivers side of a 998-recalled car.

[kkiller46]

Stuntman - I can't find an EMI Racing web site. Can you enlighten me as to what the proper brackets are? And where to purchase?

[mblgjr]

Ipsco makes the inboard brackets.

Eric @ EMI is very experienced and I think used to be the go to for Penske shocks.

[RTTTTed]

My 99 GTS is one of the recall cars. Way I read it was that the recall was to check welds for cracks in rear susp and diff attachment points and steering crossmember. Here's the link to check if your car has had the RR diff mount bracket stiffened and replaced.

http://www.viperclub.org/howto/service-bulletins/pdf/RC_99802.pdf

When I installed my Anti-toe stiffener brackets I did have to do some grinding for them to fit the car. More grinding was required on my 1999 GTS than my 2001 GTS.

[stuntman]

Stuntman - I can't find an EMI Racing web site. Can you enlighten me as to what the proper brackets are? And where to purchase?
Directly from Erik Messley

emiracing@mindspring.com

He's a great guy, talented racer (pro GT wins in a Viper) and a suspension guru/Viper expert. His toe bracket mounts in a few minutes, is made out of hardened steel that's tig welded and nickel plated with aircraft grade hardware. It's top notch stuff.

[kkiller46]

Thanks much stuntman,

[RTTTTed]

I drag race my TT GTS sometimes. Last event I wheel hopped more than the 1/8th mile so I switched to 1/3 mile roll racing (40mph). I finished 2nd with 9.3@163mph Car developed a serious shake that was scary at 150mph so I quit running, came home and after speaking to Todd (American Racing Technologies) I welded gussetts into the A arm mounts to stiffen the frame as the frame is made to have the suspension brackets tear off in case of a crash. Todd said that over 1000whp they should be gussetted to stiffen the frame. I welded plates under the botom of the frame at the upper forward A arm mounts and welded plates inside the mounts to the diff mount framework. I then welded the openings in the lower A arm mounting upright solid to the lower frame rails.

I checked my MW axles and pulled my diff and checked the Quaife. Everything seemed good so I used a gussetted rear differential cover/diff mount on my diff (Thanks Joel Fortin) and re-installed the diff.

My wheel hop problem and the shake turned out to be the R888 tires got torn apart internally. Glad I quit running when it shook so badly. I'm sure a tire would have blown causing a crash if I'd kept running.

Ran Bremerton with Hoosier Quick Time Pros and NO shake!!!

Although changing tires is what fixed the car, I'm still glad that I stiffened the frame/susp points as the upper front A arm mounts did look to be deforming the frame. The lower A arm support frame Xmember was also slightly deformed at the opening. I'll be checking my rear suspension after hard usage now that I know.

[stuntman]

If you noticed a difference from stiffening the frame, you'll be blown away with the results of EMI's toe stiffeners which will reduce almost all your toe deflection which has been measured 1/2" of deflection by the outer aluminum knuckles!!!

[RTTTTed]

Sorry stuntman,but I have Arrow toe brackets for years now. Huge difference. I did a HPDE with JonB at PIR and mentioned that the back of the car was floating during a corner and altitude transition. JonB told me that there could be as much as 3/4" deflection. Arrow Racing owed me a favor and although his Steel brackets aren't as pretty as JonB's PartsRack Billet mounts.

[RTTTTed]

Here`s the link to my How To. I took many pics while doing this.

http://thevipergarage.com/index.php/topic,354.msg3358.html#msg3358

- - - Updated - - -

Here`s the link to my How To. I took many pics while doing this.

http://thevipergarage.com/index.php/topic,354.msg3358.html#msg3358

[stuntman]

EMI measured the toe deflection in both road racing and drag racing and found over 1/2" (1/4"+ per side) of deflection from the outer aluminum knuckle, which was cured almost completely with the outboard EMI toe stiffeners, while he found virtually no improvement by stiffening the inboard toe link mounting point. The 24 Hours of Daytona and LeMans winning cars apparently did not need to reinforce the inboard points either.

[JonB ~ PartsRack]

Just a question regarding frame construction of our gen 2 cars. Reading the OEM shop manual it seems like there is no difference in frame construction between the roadster and the Coupe. On the other hand many people say that the Coupe is more rigid/stiff due to having a non detachable roof. However, the GTS roof panel does not seem to be real solid and I am assuming it will flex in various driving situations. So my question would be, if there is a tangible difference in chassis stiffness between the two models?

There is but ONE correct answer to the OPs specific question about GEN 2 RT vs GTS FRAME. And D6666 answered it correctly. I will add some adverbs: Absolutely, Positively, NO! But that NO relates to the FRAME question you appear to be asking twice, and then a third time you said "CHASSIS". You muddied the question a bit.

But if you change YEARS (The Year Matters) the answer changes.

[My98RT10]

Just a question regarding frame construction of our gen 2 cars. Reading the OEM shop manual it seems like there is no difference in frame construction between the roadster and the Coupe. On the other hand many people say that the Coupe is more rigid/stiff due to having a non detachable roof. However, the GTS roof panel does not seem to be real solid and I am assuming it will flex in various driving situations. So my question would be, if there is a tangible difference in chassis stiffness between the two models?

There is but ONE correct answer to the OPs specific question about GEN 2 RT vs GTS FRAME. And D6666 answered it correctly. I will add some adverbs: Absolutely, Positively, NO! But that NO relates to the FRAME question you appear to be asking twice, and then a third time you said "CHASSIS". You muddied the question a bit.

But if you change YEARS (The Year Matters) the answer changes.

Well, sorry for muddling the question, in German language Frame and Chassis actually mean the same... So, what would be your answer if question relates to Chassis (and what's the difference between the 2 Terms in your view)?

Maybe I rephrase my initial question this way: Does the Coupe handle better than the Roadster (both Gen 2, same year i.e. 1998, Roadster no roof attached) due to the fact, that the Coupe comes with a non-detachable Roof? I don't know if there are other key differences between the two models that could cause a difference in handling but I am in particular interested in the impact on handling created by the Coupe's roof. As for unibody constructions I can understand that Coupes should handle better as the whole construction is more stiff compared to a unibody Roadster because the Roof of the coupe is part of the unibody itself. But for Gen 2 Vipers my understanding is that the Roof of the Coupe is more or less just another (flexing) Body Panel attached/glued to a Gen 2 frame construction which is the same for Roadster and Coupe. I also think that all these body panels being bolted or glued on do not really contribute to stiffness of the whole construction, it is the frame construction that matters.... The answer I read from the responses so far is rather "No" than "Yes"!? But maybe my reading is incorrect.... Thanks again!

[stuntman]

Frame, chassis, its semantics and they are used interchangeably. The Gen 2 RT-10 & GTS share the same frame and obviously if you twisted the bare frame they would have the same torsional stiffness. I've never seen a number stated for the GTS' stiffness increase over the RT-10 other than Popular Mechanics who said 12% which I think is a bit vague and left to interpretation.

Although screwed and glues on, the addition of the GTS' roof does increase rigidity. You would be surprised how much most T-top and convertible cars are affected by the installation or removal of their hard tops. Most people probably cant feel a difference or can drive their car proficiently enough on track to feel a difference, but if you took a complete car to a K&C rig, the GTS would be stiffer than the RT-10. I doubt it would be huge and don't think it would even be 25% stiffer, but it would have more torsional rigidity. There are some good quotes in that link in post #7:

"2003 roadster was 31 percent stiffer than the old roadster, and even more rigid than the old GTS coupe"

This reads like the GTS is stiffer than the RT-10. Also while its quite a bit different and apples : oranges, the Gen 3 coupe is said to be 30% stiffer than the SRT10.