Oscillating vibration at high speeds...
03-18-2016, 08:40 PM
#1
5th Gear
Thread Starter
Join Date: Feb 2016
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
Oscillating vibration at high speeds...
I have a 2000 Boxster 5-speed which I track (~5-6x a year). Its got new rear rotors and pads, new front pads (fairly new rotors), and brand new Hankook Ventus V12 EVOs. Rims are 18s.
I've been struggling with vibrations at higher speeds (+70 MPH). I believe the vibration is coming from the rear because I feel it in the seat, not the steering wheel. I do not know if this can be misleading, sort of like referred pain can lead you the wrong way. Steering wheel is steady, though. Curiously, the vibration comes and goes, on about a 2-second interval. This is true at any gear, and with or without the clutch engaged. I do not have warped rotors, as there is no issue with braking. I found another thread that describes this perfectly, and amazingly, the OP on that 2012 thread also was using Hankook Ventus V12 Evo's. There was some discussion about the quality of Hankook tires on that thread. So, I am reconsidering going back to the Michelins after this set wears out. Would an out of round tire cause this?
I get that this is a process of elimination. The new tires just came back from being mounted and RF balanced, but I did not witness the RF balancing myself. I may have to get that redone just to be sure. And I don't believe the oscillating nature of the vibration is something I would expect from a tire balancing issue, but I could easily be out of bounds on that.
With the previous set of Hankooks, I was there for the RFB. My rims had the following runouts:
Driver front 0.026, no weights added
Passenger front 0.024, 0.5 oz added to inside rim
Driver rear 0.034, but corrected to 0.014 after indexing the tire, weight added
Passenger rear 0.023, added 2.5 oz to outside rim
I have zero experience with this, but the tech said that the driver rear runout was barely in spec before indexing the tire. It was the only one he indexed. The rims have been worked on in the past to repair damage.
Subject to a rebalancing, I want to get opinions on what else might cause the vibration other than tire related (incl. pressures, balancing, etc)...I'm imagining what else back there could cause this. Things like suspension and sway bars and bushings are unlikely, as all this was upgraded in last two years. Motor mount is 3 years new, and I just had semi-solid transmission mounts put in earlier this year. Exhaust is tight and intact.
Would bearing be an issue? It's got a new bearing on one rear side (installed earlier this year), but I didn't also replace the other at the same time. I've had bearings wear out before, and until now, have always noticed a worn bearing by the sound, vs. a vibration of any kind. But now that I am tracking the car, I am curious if that accelerates bearing wear (I live in South/Central TX).
Hoping some of you experienced folk out there can chime in...
I've been struggling with vibrations at higher speeds (+70 MPH). I believe the vibration is coming from the rear because I feel it in the seat, not the steering wheel. I do not know if this can be misleading, sort of like referred pain can lead you the wrong way. Steering wheel is steady, though. Curiously, the vibration comes and goes, on about a 2-second interval. This is true at any gear, and with or without the clutch engaged. I do not have warped rotors, as there is no issue with braking. I found another thread that describes this perfectly, and amazingly, the OP on that 2012 thread also was using Hankook Ventus V12 Evo's. There was some discussion about the quality of Hankook tires on that thread. So, I am reconsidering going back to the Michelins after this set wears out. Would an out of round tire cause this?
I get that this is a process of elimination. The new tires just came back from being mounted and RF balanced, but I did not witness the RF balancing myself. I may have to get that redone just to be sure. And I don't believe the oscillating nature of the vibration is something I would expect from a tire balancing issue, but I could easily be out of bounds on that.
With the previous set of Hankooks, I was there for the RFB. My rims had the following runouts:
Driver front 0.026, no weights added
Passenger front 0.024, 0.5 oz added to inside rim
Driver rear 0.034, but corrected to 0.014 after indexing the tire, weight added
Passenger rear 0.023, added 2.5 oz to outside rim
I have zero experience with this, but the tech said that the driver rear runout was barely in spec before indexing the tire. It was the only one he indexed. The rims have been worked on in the past to repair damage.
Subject to a rebalancing, I want to get opinions on what else might cause the vibration other than tire related (incl. pressures, balancing, etc)...I'm imagining what else back there could cause this. Things like suspension and sway bars and bushings are unlikely, as all this was upgraded in last two years. Motor mount is 3 years new, and I just had semi-solid transmission mounts put in earlier this year. Exhaust is tight and intact.
Would bearing be an issue? It's got a new bearing on one rear side (installed earlier this year), but I didn't also replace the other at the same time. I've had bearings wear out before, and until now, have always noticed a worn bearing by the sound, vs. a vibration of any kind. But now that I am tracking the car, I am curious if that accelerates bearing wear (I live in South/Central TX).
Hoping some of you experienced folk out there can chime in...
03-19-2016, 01:51 PM
#2
Race Director
This:
I have zero experience with this, but the tech said that the driver rear runout was barely in spec before indexing the tire. It was the only one he indexed. The rims have been worked on in the past to repair damage.
is important.
Damaged/and re-worked rims even on a car driven on the street are always suspect. Porsche cautions against any welding/machining repairs of its wheels. I think this a good guideline to follow for any other wheels too.
You can carefully inspect the wheels for any signs of cracks or excessive run out -- one wheel is already at the edge in this regard which is I think significant -- but I'd seriously consider new wheels.
On a tracked car -- even a street car in some circumstances -- wheels can be a wear item.
If you want before you consider springing for new wheels, and I would advise it, be sure if the tires are uni-directional they are mounted the right way on the rims. Be sure all 4 tires are of the same hardness, and load capacity.
I assume alignment is good? That you do not feel, can't detect any signs of feathering/cupping of any tire's tread surface that might suggest one or more wheels is not in proper alignment?
It should go without saying and I know you have already done this but be sure the tires are inflated to their proper pressure.
For a wheel bearing I do not think it would be bad enough to manifest the behavior you report and not make noise. A new rear wheel bearing is not that much money and like tires for a tracked car is a wear item. So, if you are not against throwing money at the behavior a new wheel bearing might be the place to throw your money. Frankly, though, I don't hold much hope this will prove to be the solution.
I have zero experience with this, but the tech said that the driver rear runout was barely in spec before indexing the tire. It was the only one he indexed. The rims have been worked on in the past to repair damage.
is important.
Damaged/and re-worked rims even on a car driven on the street are always suspect. Porsche cautions against any welding/machining repairs of its wheels. I think this a good guideline to follow for any other wheels too.
You can carefully inspect the wheels for any signs of cracks or excessive run out -- one wheel is already at the edge in this regard which is I think significant -- but I'd seriously consider new wheels.
On a tracked car -- even a street car in some circumstances -- wheels can be a wear item.
If you want before you consider springing for new wheels, and I would advise it, be sure if the tires are uni-directional they are mounted the right way on the rims. Be sure all 4 tires are of the same hardness, and load capacity.
I assume alignment is good? That you do not feel, can't detect any signs of feathering/cupping of any tire's tread surface that might suggest one or more wheels is not in proper alignment?
It should go without saying and I know you have already done this but be sure the tires are inflated to their proper pressure.
For a wheel bearing I do not think it would be bad enough to manifest the behavior you report and not make noise. A new rear wheel bearing is not that much money and like tires for a tracked car is a wear item. So, if you are not against throwing money at the behavior a new wheel bearing might be the place to throw your money. Frankly, though, I don't hold much hope this will prove to be the solution.
03-19-2016, 05:38 PM
#3
Rennlist Member
Sounds like you are experiencing the result of the cumulative effects of degrading your vehicle. #1 changing from Michelin to Hankook, a properly balanced wheel & tire assembly needs weights on the 2 extreme edges of the wheel, inner rim & outer rim. With a true rim & quality tire you can cheat for cosmetic purposes & place the weights on the inner backside edges or sometimes weight is only needed in one position. Worn wheel bearings will contribute to the vibration severity. Incorrect orientation of the tread pattern will not affect ride smoothness until they have thousands of miles on them. Non-stock trans or engine mounts will degrade ride quality. Any good tire balancer can & should observe a tire spinning on the balancer & determine if it is likely to cause a ride disturbance. Why they fail to inform the vehicle owner to expect a issue is beyond me. For all of the above reasons & more, when I buy tires they always have the word Michelin on the sidewalls.
If the steering wheel is steady the problem comes from the rear. If you tires are stock size Porsche calls for 36 psi in rear, if you are not loaded down & no passengers you can run 33psi to see if that makes a difference in the vibration.
If the steering wheel is steady the problem comes from the rear. If you tires are stock size Porsche calls for 36 psi in rear, if you are not loaded down & no passengers you can run 33psi to see if that makes a difference in the vibration.
Last edited by Byprodriver; 03-19-2016 at 05:43 PM. Reason: more info
03-23-2016, 10:59 AM
#4
5th Gear
Thread Starter
Join Date: Feb 2016
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
This problem has been solved. Took wheel assemblies to a wheel restorer. They worked on 3 of the 4 rims, and remounted tires on their GPS9700 RFB. Vibration is gone. And I am relieved.
03-23-2016, 07:56 PM
#5
Race Director
The wheels probably should be replaced.