Observation and question about high speed (85-180mph) really tight vibration.

[triblk6spd]

Sooo here in Texas the toll road speed limit is 85mph so on a daily basis I'm over that speed and closer to 100 and more. My observation and question is: from basically 85mph and up I can feel a very tight vibration coming from what seems to be the rear of the vehicle. I wouldn't pay much attention to it if my rear view mirror wasn't shaking to the point that I can't see what type of car is behind me. Side view mirrors are perfect....no shake at all. The vibration is 100% speed related not rpm...5th and 6th 85mph and higher. Maybe it's just me and I worry about nothing but does anyone else notice this at high speeds? I know it's a hand built car and I'v retorqued my wheels even though I'm sure they went the problem and retorqued underhood X brace .
No steering wheel shake at all.
No brake shudder at all.
Perfectly smooth under 85mph.
Thanks all!
....and don't everyone at once run out and blown down the hi way at 150 mph to see what I'm talking about.

[Divexxtreme]

No such vibrations at any speeds here. I'd take it to your dealer as soon as possible if I were you. Just to be safe.

Scott

[Jack B]

Speed related and no steering wheel vibration limits what the causes could be:
driveshaft
rear wheel/tire
half shafts

There are other possibilities, but, the above three are a good place to start.

[Jack B]

Speed related and no steering wheel vibration limits what the causes could be:
driveshaft
rear wheel/tire
half shafts

There are other possibilities, but, the above three are a good place to start.

[FSTENUF]

I had the same issue in my gen II. only in 6th gear and only over 85 MPH. It was coming from behind the drivers seat. found out it was the rear drivers side a arm.

[triblk6spd]

Thanks guys. Just let my Viper tech know I'd wanted to come in on Wednesday. I'll post up my findings. In the meantime if yall think of anything else feel free to post up.

[Viktimize]

Wheel balancing is always the first thing to check when it comes to odd vibrations or shakes. After that I would be looking at all of the links and bushings in the rear. I had something weird going on with my Gen3, turned out I had a torn rear toe link boot. I replaced it and all was well.

[TrackAire]

Regarding tire/wheel balance issue, the key is not only balance but a round tire and wheel. You can glue a piece of 2x4 board to your tire and I can get it to "balance" on a machine, but how would it ride??

There are machines that measure both the roundness of the tire (you'll never get an egg shaped tire to ride smooth regardless of how it is balanced) and if the wheel is true and not bent. Make sure the dealer is aware of this. Sometimes tires have a defect where the belts overlap weird and you just end up with an out of round tire....only fix is replacement.

Having said all that, I've found most tire and wheel issues tend to vibrate under the speeds you're experiencing the vibration. Maybe more of a half shaft/CV issue?

Maybe the rear hub bearing is way loose and not torqued to spec?

Good luck with getting it figured out.

[financialman]

My car does not vibrate at any speed, very smooth.

I had a car that did that in the past, it was just a out of balance wheel, easy fix.

[Jack B]

Excellent comment, that is the Hunter "road force" balancer. The larger the wheel/tire, the more issues you will have. The problem is, you need to find a shop that uses it in the "road force" mode. A lot of shops have the Hunter machine, but, merely use it to do base balancing.

Regarding tire/wheel balance issue, the key is not only balance but a round tire and wheel. You can glue a piece of 2x4 board to your tire and I can get it to "balance" on a machine, but how would it ride??

There are machines that measure both the roundness of the tire (you'll never get an egg shaped tire to ride smooth regardless of how it is balanced) and if the wheel is true and not bent. Make sure the dealer is aware of this. Sometimes tires have a defect where the belts overlap weird and you just end up with an out of round tire....only fix is replacement.

Having said all that, I've found most tire and wheel issues tend to vibrate under the speeds you're experiencing the vibration. Maybe more of a half shaft/CV issue?

Maybe the rear hub bearing is way loose and not torqued to spec?

Good luck with getting it figured out.

[slitherv10]

I know exactly what it is.......its the mirror...it needs tightening.

[triblk6spd]

I'm gonna head over to Elite Racing Development tomorrow and have them take a look. I'll ask about road force balance mode.
I wish it was the mirror. Might need tightening too lol you never know.

[triblk6spd]

Ok both tires aren't perfect one is worse than the other. Both "balanced" out ok but in roadforce mode neither could be adjusted to get the number in the acceptable range (20 and below) One got to 34...not much change from initial number and the other to 26 from 48....huge improvement but still not below 20. I'll mount these up today and take a blast down the toll road. Wish me luck!

[bayviper]

I noticed the same thing over a certain speed. Let me know the findings.

[XSnake]

Wheel balance as others have said. See if you picked up any rubber pickup inside your wheel barrels.

[Brian E]

Ok both tires aren't perfect one is worse than the other. Both "balanced" out ok but in roadforce mode neither could be adjusted to get the number in the acceptable range (20 and below) One got to 34...not much change from initial number and the other to 26 from 48....huge improvement but still not below 20. I'll mount these up today and take a blast down the toll road. Wish me luck!

Did they break the bead loose and rotate the tire 180 degrees on the rim? Thats what I have seen Tire Rack do when they encounter a problem trying to perform a roadforce balance.

[TrackAire]

Did they break the bead loose and rotate the tire 180 degrees on the rim? Thats what I have seen Tire Rack do when they encounter a problem trying to perform a roadforce balance.

I do believe that the higher end road force balance machines will actually tell you what needs to be done (as you said, rotating the tire 180 degrees) once it balances and measures the roundess of both the wheel and tire.

Because of the speeds that the vibrations are happening, I keep thinking its not the tire but instead the wheel is tweaked or the hub bearings, half shafts, driveshaft or cv's have issues. I'm not sure if anything in the transmission/clutch can cause this where it's just shaking the review mirror but the outside mirrors are fine.

Hopefully it is just a defective tire that is covered under warranty.

[BlknBlu]

alignment may be off too if the balancing does not check out.

Bruce

[triblk6spd]

Ok yep both wheels and tires were broken loose and repositioned according to the machine. Just went for a drive. Slightly better but still no whwre near perfect. I think I'm gonna try to borrow a set of new wheels and tires and see what happens. I know every car guy in Austin and not a single Gen V Viper guy. Both tires may have slight flat spots as the car has been sitting at a dealership for almost 2 years...I wonder if this coukd be at least part of the issue. One might think this would be more of an issue though with all the cars sitting at dealerships. I'll report back. Thanks all for the input!

This sounds ridiculous but the ONLY thing that shakes is the mirror. The damn mirror does not seem loose to me at all....it can't be the effing mirror itself can it?

[mblgjr]

Thats kinda high on the roadforce fig.

Did they take a bunch if weight? More than 1oz?

[ViperSmith]

Could simply be the glass in the mirror.

But if the car sat for 2 years there could be flat spots you simply can't see

[Ripper]

If it is a tire issue one way that might help rule it out would be to play with tire psi.. Won't cost a dime to let some air out , go cruise , see if anything changes... Then try the opposite , add pressure and see what happens

[Martin]

Am I reading this right - you get the vibration continuously from 85 mph through 180 mph? If that's the case, it's not the wheel balance... You'd go through a couple of resonant frequencies across that range, and you'd feel the vibration get really bad, settle down, and then get really bad again as your speed increases.

Could be the obvious things as noted above, or it could be aerodynamic. If something is out of whack, you can get some buffeting - and depending on where it's happening and if the airflow is physically limited to a certain mass-flow, the buffeting could create a fairly constant frequency from the point where it starts on up. I'd be tempted to have a look at rear cooling ducts, etc.

[TrackAire]

Am I reading this right - you get the vibration continuously from 85 mph through 180 mph? If that's the case, it's not the wheel balance... You'd go through a couple of resonant frequencies across that range, and you'd feel the vibration get really bad, settle down, and then get really bad again as your speed increases.

Could be the obvious things as noted above, or it could be aerodynamic. If something is out of whack, you can get some buffeting - and depending on where it's happening and if the airflow is physically limited to a certain mass-flow, the buffeting could create a fairly constant frequency from the point where it starts on up. I'd be tempted to have a look at rear cooling ducts, etc.

Good call....maybe run the car up to speed on a dyno and see if the vibration is still there.

[triblk6spd]

Dang ya I was thinking the same thing. I did check and recheck the front and rear wheel wells and the brake cooling stuff behind them. I also checked and retightened the rear diffuser hardware.
Gonna borrow a set of rear wheels and tires and if that doesn't she'd some light then hit the dyno for a quick pull. I'd like to get a baseline before mods start anyway.
The wind buffeting thing could definitely be the issue. Thanks again all!