Cause of instability in rutted roads?

[427v8]

What causes a car to follow the ruts in a road. You know thse well worn asphault roads that have rits where the cars go.

I have removed almost all of the bump steer, but I do have big wide square walled tires...

Still Why would the car be so weird in ruts?

Is there anything I can do about it?

Thanks O Gurus of Pro Touring!

[David Pozzi]

It's probably more related to the tires. The old bias ply or pre-bias ply tires used to really jerk when crossing ruts or pavement changes. Radials are a TON better for that, but most radials are almost bias ply in their chord angles. Tread pattern is important too.

What tires do you have?

[79T/Aman]

I think you know the answer as you emphasized " big wide square walled tires "

[CAMAROBOY69]

Just like they said. Wide tires. What size are your tires exactly?

[brianj5600]

Square walled tires sound like bias plies. They tend to chase lines in the road. I am barely old enough to have bias ply experience, but I can defiately appreciate radials. Could it also be a toe problem or even caster?

[427v8]

The are 255 60 R17 Kuhmo Ecsta MX's on 17" x9" Torque Thrust II's

Stock '69 Corvette tires I believe were F70 15's

I am sure it's the wide tires, I guess I'm wondering why wide tires make the car wander in ruts.

Is it just due to torque loads of the edges of the tires?
Or some scrub radius thing??

[nancejd]

I think it's because the ruts typically aren't as wide as your tires. Most cars have about a 195 tire, so a wide tire doesn't ride in the bottom of the rut, it wanders from side to side.

[CAMAROBOY69]

Those are on the front of your car??
255/60-17 is close to 29" tall and 10"wide. That would definetly explain why your car is all over the road. :eek:

[427v8]

It's the right height for the car. They are 27" tall same as stock. Smaller tires look funny.

they are a lot wider tho.

[Marcus SC&C]

Bumpsteer is one of the main things and it sounds like you`ve taken care of most of that (Guldstrand kit?). Scrub radius contributes also. Alignment can make a big difference too. 0* camber will generally have the least tendency to wander or tramline although it won`t yield the best results in the corners. A fair amount of + caster will help reduce the wandering to an extent. What are you running for alignment specs? Marcus

[Chevies4me]

This may sound off to you,but I had that problem with my truck.I have pretty wide tires on it also.Changed them back to the originals,new ball joints and alignment,no help.Changed the power steering belt and didn't pull in the rut again.HTH

[Ralph LoGrasso]

This may sound off to you,but I had that problem with my truck.I have pretty wide tires on it also.Changed them back to the originals,new ball joints and alignment,no help.Changed the power steering belt and didn't pull in the rut again.HTH


My Tahoe follows ruts in the road as well. It can be a pain on older Highways. I run 305/70/16 Toyo Open Country (33x12.50).

[JLM]

The problem is the width of the tire. As stated previously most cars driving on roads have smaller section width tires so the ruts tend to be smaller. My 2003 Cobra had this problem very badly. It also had 275/40/17 rubber on 9" factory wheels up front and in the rear. Even my previous GT mustang with 245/45/17 rubber exhibited this problem. I got used to it, but if it's really concerning to you you might try dropping down the section width a bit.

[427v8]

The bumpsteer is pretty close to zero, like >.010" I have a home made rack and pinion conversion. No power all manual. :-) BTW, the car is much better with the rack. The on-center feel of the stock Vette suspension is HORRIBLE

It's interesting to hear that a 2003 cobra has that problem.

I'm guessing that runing on the edges of the tires causes the tires to want to torque to one side or the other...?

[JLM]

The Cobra had less issues than my previous GT. Likely do to better suspention components (better shocks/struts, higher rate springs, better CG vs RC) but it is still there. I can honestly say I have never driven a car with wide front tires that didn't exhibit this problem at least slightly.

Even my mother's Volvo S60 will do this on bad roads. I beleive the section width for the tires on that car is a 225 or 235.

At one point while I still had my 2002 GT it had 18X8.5 wheels up front with a 235/35/18 up front. the section width was actually reduced from the stock 245/45/17 rubber by about half and inch to an inch observed. I noticed a pretty big difference in driving dynamics concerning road wondering. The smaller section width really helps on highly used streets. Unfortunately I also noticed a reduction in road holding power, the car was much more prone to push through a corner at the limit.

It's a trade-off. You had stated earlier that you liked the look with the larger tires rather than smaller. There's probably a bit of performance benefit there as well. You'll likely have to decide which is most important to you.

[paul67]

When I repaired a BMW and fitted 17" rims with wide tyres from the factory 16" rims it used to follow ruts in the road terrible when I took it to be retracked they found the rear camber was out about 1/2 deg to 3/4 from 1 side to the other, when they corrected it and i watched him do it the car moved across about 1" and down this showed the car was crabbing down the road after the car drove like it was on rails and did not wander when I took it over the same road. See if you can get it checked on a 4 wheel laser, also check to see if the front wheel centre is the same distance to the rear wheel on both sides . If the car is a camaro is the front sub in straight could move if curbed theres loads of things but always look at the cheap opps first. Is sub in straight , are casters the same this can cause 1 wheel to sit back more than the other, camber, tracking, rear axle in straight, if you can sit car on 4 stands remove wheels, find centre of car front to back find centre of car left to right measure out all around car about 1to 2 ft wide and draw lines,
so that you have a box around car now drop plum lines off the centre of hubs and measure distances to the centre lines as this are your datums, but make sure the height of the hubs is the same all round, once you have done this it will show if the car suspension is square to the car, if not alter to suit then get the tracking set.
paul67

[427v8]

You know that is a very interenting idea.
The Vette has different track width front and rear. I wonder if making them the same you improve this problem...

Also I will make sure the camber etc are the same side to side and that the car is square. But I know all vettes have this problem so I'd put my money on the track width front to rear...