OK so just had new tires, balanced, brakes, and alignment done
The car feels great until I get over 100mph then I get a shake or a wobble

I can feel it in the steering wheel and the gas pedal, as soon as I get back under 100 it's sturdy again
My guess is that a wheel was not balance correctly

The Indy I used is extremely reputable and they guaranty there work
I will contact them tomorrow but I want to make sure I'm not blaming them for something unrelated if that makes sense

Thoughts, advice would be appreciated

Thanks

 

Start with having a high speed road force balance done. I just went through this same issue. Had tires installed at a local chain because of a great price (dropped the wheels off, didn't trust them with the car). The car had a front end and possible left rear shake at speeds between 90 and 100 mph. I didn't even bother going back to them for the free lifetime balancing. Instead I paid my local speed shop to do a proper road force balance. The shaking is completely gone. In the end it cost about the same as having the speed shop do the install from the start.

edit: from my the service bill of $110
all wheels have been road force balanced only one wheel was required to be dismounted and spun inside the tire to achieve proper road force

 

Cool thanks I know the feeling of not wanting to return but as I said it was a reputable shop so I will give them a chance to correct
Happy to here it was an easy fix

 

what is a high speed road force balance, how is it different than conventional balance? after swapped to 20" wheels few weeks ago, at about 90 mph there is steering wheel shake. However highway 35 toward downtown Dallas isn't the greatest. Want to test it on smoother road before re-balance. Local AD Porsche want $189.00

 

Normal spin balances do just that, spin the tire to find the light spot then you put weights there to even it out. Road force balancing puts a roller against the tire while spinning to simulate the force of a car on the road. Hunter machines are the best. See this link:

http://www.motorweek.org/features/go...orce_balancing

 

definitely need that...thanks!!

 

So had the wheels rebalance and while doing this they found that the front wheel is not straight, just a little off but enough to cause a shake at high speed.

I guest if I drive normal there is no trouble but of course now I want new wheels

I would like to try a set of 18" wheels so I could have more tire just not sure what would work

I also just got these new tires so it would be better to get a set of 19" that I could move them to however when looking at wheel choices I do not seem to find the same sizes

If I'm not mistaken my wheels are 19x8.5 and 19x11.5

Most wheels are either 11 or 12

Would a 18x12 work on a 2006 c4s

 

You probably already know but your post is a little confusing. 19" tires will not work on 18" wheels. The tire size needs to match wheel diameter. This has nothing to do with the tire width. So if you want to use this as an opportunity to switch to 18" wheels you will need new 18" tires to match.

You could source a single 19" wheel to replace your bent one. Try the dismantlers or ebay for a used single wheel (ladismantlers.com is just one place). New from the dealer the wheel will be quite expensive. Unfortunately single wheels don't come up too often here in the marketplace though. Maybe post a WTB ad and try your luck.

There are also places that can straighten out bent wheels too, depending upon how severe the damage is. Your best bet here is to ask for a local recommendation.

Or you could switch to a full set of four new 19" wheels and have your tires moved over to the new setup. Use this as an opportunity to change the look of your car without having to buy new tires too.

 

Choice #1
My goal would be to end up with a new set of 18" rims 18x8.5 and 18x11.5 or 12 with new matching 18"tires but I am not sure if this set up would fit - to wide for the rear, brake caliper clearance?

Choice #2
If I stayed with 19" and got a new set does my 305/30 tire fit on a 11" rim as it is now on a 11.5" and would I want to get an 11" rim when stock is 11.5?

 

Here's one, when it rains, my 997 starts shaking like crazy when driving around 80mph. First, I thought my tires or suspension was failing. When I got on the same stretch of highway on dry days, I can get up to 100+ mph without any shaking.

 

If you have aftermarket wheels they could be a poor design and hold water inside the wheel messing up the balance
I had a set of dpe wheels that did this - was not very happy

 

I've had my car for 7 years. I'm running 20" HRE597r w/ MPSS. I don't recall having this issue until recent. I had a GT3 front cover installed a couple years ago, which may be influencing the aerodynamics. Not sure.
Its also possible that I've never driven my car at that speed during rain.

 

Next time this happens try pulling over and checking the inner wheel see if you are collecting water

 

You're going to have to do a little more research...clearance issues have as much to do with et as they do with width. Go here to find out more:

http://www.1010tires.com/Tools/Wheel-Offset-Calculator#

 

jhbrennan is correct, the online calculators are the best place to go. In general you can fit the same width wheels in 18" as you can for 19" but there is so much more information needed to be certain. To properly compare wheel/tire setups you need to know wheel diameters (18" vs 19"), widths, offsets and full tire sizes (305/30R19 for example) for both the originals and the new setup.

Your goal is to make sure the outer rolling diameters are close, within 3% to 5% or less. Also check outer edge differences due to offset/width differences. If the new wheels are inset relative to the current wheels use spacers to push them out. If they poke out relative to the current set then they won't fit - you can't remove offset unless you took the wheels to a machine shop and had the hubs cut down. Next check the inner edge. If inner and outer offsets look good then the calipers should clear. When going to smaller diameter and wider at the same time it's best to do the online comparisons and then test fit a wheel before mounting a tire to verify caliper clearance. Same widths or going narrower with the correct offsets will clear calipers except in rare cases of aftermarket wheels.

305's will fit a 11" wide tire, I had them on my rears for a while. They are a bit more square profile. Use the online calculators with the different wheel specs but same tire sizes to see the differences.

And finally if you go aftermarket most vendors already know the sizes you would need. Lean on them for their experience and confirm their exchange policy if the widths/offsets are wrong for your car.