Rear Shimmy

Bear Chow · 01-20-2012, 08:48 AM

So logic tells me this isn't a problem but maybe, just maybe it is. Daughter's 1995 lumina has a terrible sway in the bag at low speeds. All four wheel are balanced. But I noticed in the back one is a 205 and one's a 215. So there is a slight height difference.

Being front wheel drive and the rear being IRS and no ABS. would that slight difference in size make this thing sway?

Logic tells me that it's a trailing system, so no power is being delivered to it. It's IRS so it should independently keep tire in the proper place. Compensating for that 1/2 inch should be par for the coarse.

blazerbrad · 01-20-2012, 08:58 AM

Different size rear tires can cause this sort of problem. Regardless of it being IRS it still have the same spring rates and wants to maintain the same suspesnion height side to side. The taller tire will cause that side to load more and mess up the weight distribution. To really know the height difference in tires you need the entire number (i.e. 215/60R15). 215 and 205 only verify there is 10 mm. difference in width and you need the aspect ratio to see the height.

I'm also not saying this is definitely the problem or the only problem. Might be one of those things where the difference size tires is exaggerating something else. Being a '95 when was the last time the rear shocks/struts were changed? How are the bushings in the suspension?

93 Krawler · 01-20-2012, 09:45 AM

I would think it would matter being different sizes. I've had the same size tires but different brands affect the vehicle.

01-20-2012, 08:48 AM	#1
Bear Chow Jeepless Join Date: Feb 2007 Location: Oxford, Oh Posts: 302	Rear Shimmy So logic tells me this isn't a problem but maybe, just maybe it is. Daughter's 1995 lumina has a terrible sway in the bag at low speeds. All four wheel are balanced. But I noticed in the back one is a 205 and one's a 215. So there is a slight height difference. Being front wheel drive and the rear being IRS and no ABS. would that slight difference in size make this thing sway? Logic tells me that it's a trailing system, so no power is being delivered to it. It's IRS so it should independently keep tire in the proper place. Compensating for that 1/2 inch should be par for the coarse.

01-20-2012, 08:58 AM	#2
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831 Images: 6	Different size rear tires can cause this sort of problem. Regardless of it being IRS it still have the same spring rates and wants to maintain the same suspesnion height side to side. The taller tire will cause that side to load more and mess up the weight distribution. To really know the height difference in tires you need the entire number (i.e. 215/60R15). 215 and 205 only verify there is 10 mm. difference in width and you need the aspect ratio to see the height. I'm also not saying this is definitely the problem or the only problem. Might be one of those things where the difference size tires is exaggerating something else. Being a '95 when was the last time the rear shocks/struts were changed? How are the bushings in the suspension?

01-20-2012, 09:45 AM	#3
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	I would think it would matter being different sizes. I've had the same size tires but different brands affect the vehicle.