Bad handling with wide front tires
11-29-2015, 07:31 PM
#1
Bad handling with wide front tires
I have 295/50/15 tires on 10" American mags all around. On rough roads it's terrible, darts around. Suspension is stock and in decent shape. Wondering what changes I might make to improve things (and keep the wide tires). I have power steering and am using later radial tire Corvette alignment specs. Would that bump steer modification help?
Thanks.
Thanks.
11-29-2015, 08:04 PM
#2
Team Owner
First make one change at a time
Naturally tire pressures, I let a little air out on the streets (few pounds) so the tire is more piable to uneven road conditions.
First for the most benefit, I would immediately put more positive castor up front first than where you are at (put another degree more to start and check that it still turns. Without even asking you where you are at!
Second I would check your true toe, especially the rear again, because I don't see many that truly get the backs done right!
Check those shims in the back and see if you have any excess movement of the rear arms, spindles in and out to see if you have any rear steer! Even though you said it is in good shape!
PS nice looking car! Your tastes in how your's looks is very similar to mine. Also can we see a side view, to see what rims, etc.? Cool!
Bump steer won't do anything for straight line darting all over! It is a turn geometry improvement to maintain the tie rod arc , so it stays more consistent without a bump! Is about the simpliest way of putting it, without getting all technical!
First for the most benefit, I would immediately put more positive castor up front first than where you are at (put another degree more to start and check that it still turns. Without even asking you where you are at!
Second I would check your true toe, especially the rear again, because I don't see many that truly get the backs done right!
Check those shims in the back and see if you have any excess movement of the rear arms, spindles in and out to see if you have any rear steer! Even though you said it is in good shape!
PS nice looking car! Your tastes in how your's looks is very similar to mine. Also can we see a side view, to see what rims, etc.? Cool!
Bump steer won't do anything for straight line darting all over! It is a turn geometry improvement to maintain the tie rod arc , so it stays more consistent without a bump! Is about the simpliest way of putting it, without getting all technical!
Last edited by TCracingCA; 11-29-2015 at 08:21 PM.
11-29-2015, 08:05 PM
#3
Le Mans Master
A) What is your alignment?
B) What is your intended usage?
Yes, big front tires will "tramline" on ANY car.
However, IF your usage is (billiard table) smooth race track surface, AND you intend to actually use the potential engineered into your Corvette (with RACE tires) THEN, you would be well advised to use "square" wheel/tire mounting, so that your balance will be "neutral".
B) What is your intended usage?
Yes, big front tires will "tramline" on ANY car.
However, IF your usage is (billiard table) smooth race track surface, AND you intend to actually use the potential engineered into your Corvette (with RACE tires) THEN, you would be well advised to use "square" wheel/tire mounting, so that your balance will be "neutral".
11-29-2015, 08:06 PM
#4
Safety Car
Member Since: Feb 2007
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Have you had it to an alignment shop? If not, you may want to start there. I know if the toe isn't set correctly, it will tend to jump all over.
Also, that's a great looking ride! Need more pics from the side and rear of the car.
From what I can see of this pic, the flares look great! And you still have the hide-away headlights. Again, looks great!
Try the alignment (reputable) shop. At the very least they can give you some suggestions.
Pat
Also, that's a great looking ride! Need more pics from the side and rear of the car.
From what I can see of this pic, the flares look great! And you still have the hide-away headlights. Again, looks great!
Try the alignment (reputable) shop. At the very least they can give you some suggestions.
Pat
11-29-2015, 08:18 PM
#5
Team Owner
Ps with modified cars
A long long long time ago, I take my own alignment specs into a shop and never allow some computer program to pick a record of what is best on my cars, unless you have a true guy who does Corvettes and does it based on knowledge and parameters as to what you have bought him. Actually i don't even take it to anyone anymore! Those guys who knew, are all mostly dead now!
Last edited by TCracingCA; 11-29-2015 at 08:19 PM.
11-29-2015, 08:27 PM
#6
Paid Senior Member
My ZR1 with the widest production tires GM ever installed does the same thing at low speeds. it follows every contour in the road. If you want the grip at speed then that's the trade off. My C7 with slightly less wide and softer all season tires is not near as bad. The upside is that it keeps your attention on the road.
Last edited by fullcontrol; 11-29-2015 at 08:29 PM.
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s n v f f (11-25-2021)
11-29-2015, 08:36 PM
#7
Team Owner
Cant help on the tire road walking car...
But lets hear more on your car...pictures/engine/usage...
But lets hear more on your car...pictures/engine/usage...
11-29-2015, 09:30 PM
#9
Pro
My ZR1 with the widest production tires GM ever installed does the same thing at low speeds. it follows every contour in the road. If you want the grip at speed then that's the trade off. My C7 with slightly less wide and softer all season tires is not near as bad. The upside is that it keeps your attention on the road.
11-29-2015, 10:22 PM
#10
Thanks for the replies. I haven't been driving it much the last few years and forget what the front alignment specs are. I do recall I set it to the first year Corvette that had radials, which were different from the '66 specs. I'll have another look. The rear I haven't touched in 30 years, time for a look there for sure.
Tires, yes, that's what's got me going now. My old Radial T/As are ancient and I need to replace them but with the same size only if I can improve the rough road handling. I took the fronts down to 20lbs. yesterday and it did help, was afraid to go lower.
What are the offset A arms about, more caster ability?
Tires, yes, that's what's got me going now. My old Radial T/As are ancient and I need to replace them but with the same size only if I can improve the rough road handling. I took the fronts down to 20lbs. yesterday and it did help, was afraid to go lower.
What are the offset A arms about, more caster ability?
11-30-2015, 12:43 AM
#11
Team Owner
Good profile
20 lbs is too low for normal usage and you with those radials should shoot for about 32 lbs is good for street op, no less!
Offset arms- you have rear trailing arms that give you more tire clearance, but you have 295 already. Off-set cross shafts for the front a-arms exist, but mainly to restore the ability to get geometry back from an accident. Some of us racers have found some gains in negative camber and positive camber with those.
Yes you need to shake, wiggle, beat on it, pull, tug, basically even eye ball, etc. to get an idea as to how your parts are doing, their condition. Your primary problem could be ball joints or everything!
I have operated big tired cars on roads and yes you have to pay attention, but I feel safe and never uncomfortable driving them, if aligned to the best for the conditions and with everything in good condition. Yes 295 is pushing it out close to what is street friendly, but I have never considered 295 to not be streetable!
Your rims are more than likely backspaced at about 3-3/4 to 3-7/8 at both the front and rear based on the look of your flares! You more than likely get rubbing near full steering on the fronts.
Looking at the side profile was requested to see your cool car, but looking at that front you appear to be pushed out to the fender already in a positive camber already or you could have it turned to the left, but it still looks close. At first I thought if you did not have flares, it might be hard to get that extra castor with a big 295 up there, but you have flares-- but I am not seeing that you have much room! Now I want to see close ups of both front wheel wells on your cool car? Many also run a smaller tire in the front for the sake of clearance and castor!
Offset arms- you have rear trailing arms that give you more tire clearance, but you have 295 already. Off-set cross shafts for the front a-arms exist, but mainly to restore the ability to get geometry back from an accident. Some of us racers have found some gains in negative camber and positive camber with those.
Yes you need to shake, wiggle, beat on it, pull, tug, basically even eye ball, etc. to get an idea as to how your parts are doing, their condition. Your primary problem could be ball joints or everything!
I have operated big tired cars on roads and yes you have to pay attention, but I feel safe and never uncomfortable driving them, if aligned to the best for the conditions and with everything in good condition. Yes 295 is pushing it out close to what is street friendly, but I have never considered 295 to not be streetable!
Your rims are more than likely backspaced at about 3-3/4 to 3-7/8 at both the front and rear based on the look of your flares! You more than likely get rubbing near full steering on the fronts.
Looking at the side profile was requested to see your cool car, but looking at that front you appear to be pushed out to the fender already in a positive camber already or you could have it turned to the left, but it still looks close. At first I thought if you did not have flares, it might be hard to get that extra castor with a big 295 up there, but you have flares-- but I am not seeing that you have much room! Now I want to see close ups of both front wheel wells on your cool car? Many also run a smaller tire in the front for the sake of clearance and castor!
Last edited by TCracingCA; 11-30-2015 at 01:04 AM.
11-30-2015, 07:44 AM
#13
Race Director
I have a low mileage Ford Lightning PU with 295-45/18 tires (newly replaced) and nearly perfect alignment and it follows every pebble, groove, ripple and hump in the pavement - a chore to drive on less than perfect streets. My Mustang GT with barely smaller tires tracks just fine - don't really understand the difference.
You should also take a close look at all your suspension components for wear in addition to the comments above. Make sure your wheel bearings are adjusted properly and no excess play. Check the idler arm and tie rod ends for play or wear. Check your steering box for correct centering and adjustment and check the steering rag joint for signs of movement between the pieces when the steering wheel is rocked. When your front wheels are pointed straight ahead you should not have any play in your steering wheel when gently rocking it from side to side. If you do - have someone gently rock it and study the suspension components to try and identify where the play is taking place.
Same with the rear suspension as someone mentioned above. It's not uncommon to have in-out play at the side yoke into the differential and movement of the tire when grabbed at the 6 and 12 o'clock positions and rocked and doesn't usually mean anything. but if you have play at the spindle or if trying to move the tire while holding it at the 3 and 9 o'clock positions shows play at the trailing arm forward bolt (especially if shims are missing or loose), that will cause problems.
And I will chime in on trying to get as much caster in the front alignment as possible. Off set upper a-arm shafts can provide more caster but you may still have some adjustment left. A couple of photos of your upper a-arms and the shim packs can provide some indication is this might be possible.
You should also take a close look at all your suspension components for wear in addition to the comments above. Make sure your wheel bearings are adjusted properly and no excess play. Check the idler arm and tie rod ends for play or wear. Check your steering box for correct centering and adjustment and check the steering rag joint for signs of movement between the pieces when the steering wheel is rocked. When your front wheels are pointed straight ahead you should not have any play in your steering wheel when gently rocking it from side to side. If you do - have someone gently rock it and study the suspension components to try and identify where the play is taking place.
Same with the rear suspension as someone mentioned above. It's not uncommon to have in-out play at the side yoke into the differential and movement of the tire when grabbed at the 6 and 12 o'clock positions and rocked and doesn't usually mean anything. but if you have play at the spindle or if trying to move the tire while holding it at the 3 and 9 o'clock positions shows play at the trailing arm forward bolt (especially if shims are missing or loose), that will cause problems.
And I will chime in on trying to get as much caster in the front alignment as possible. Off set upper a-arm shafts can provide more caster but you may still have some adjustment left. A couple of photos of your upper a-arms and the shim packs can provide some indication is this might be possible.
Last edited by DansYellow66; 11-30-2015 at 03:59 PM. Reason: Gadzooks - thinkin a-arm shafts and wrote trailing arms??? Must drink more coffee.
11-30-2015, 08:26 AM
#14
Drifting
If you are running really old tires that have had the car sitting on them for 2 years with no movement......you need tires! All of the above advice is good after a better set of tires since if you're going to drive the car you have to have anyway. Then, confirm your problems again before an alignment. With new tires a prediction for corrective alignment will be easier.
In road racing we cycle through a tires life in 1 to 2 weekends. Old tires from the last race after sitting for 1 month to 3 months do a lot of strange things.
Steve
In road racing we cycle through a tires life in 1 to 2 weekends. Old tires from the last race after sitting for 1 month to 3 months do a lot of strange things.
Steve
Last edited by C2Racer; 11-30-2015 at 08:27 AM.
11-30-2015, 12:50 PM
#15
Le Mans Master
If you are running really old tires that have had the car sitting on them for 2 years with no movement......you need tires! All of the above advice is good after a better set of tires since if you're going to drive the car you have to have anyway. Then, confirm your problems again before an alignment. With new tires a prediction for corrective alignment will be easier.
In road racing we cycle through a tires life in 1 to 2 weekends. Old tires from the last race after sitting for 1 month to 3 months do a lot of strange things.
Steve
In road racing we cycle through a tires life in 1 to 2 weekends. Old tires from the last race after sitting for 1 month to 3 months do a lot of strange things.
Steve
Last edited by 63Corvette; 11-30-2015 at 12:51 PM.
11-30-2015, 12:54 PM
#16
Race Director
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Ten-inch wheels likely have a lot of negative offset to provide sufficient inside clearance, and this dramatically increases the scrub radius over what was already a relatively large positive value with the OE wheels.
Increasing positive scrub radius increases the lever arm between the center of the contact patch and the steering axis, so uneven road surfaces and uneven braking cause lots of "steering wheel wiggle" and "wheel fight" on the part of the driver. That's why modern, wide-tired cars have zero to slightly negative scrub radius, which is obtained with wheels that have large positive offset.
The bottom line is that there is no solution to the problem unless you redesign the suspension for less scrub radius or go to a narrower, less negative offset wheel to reduce scrub radius.
Duke
Increasing positive scrub radius increases the lever arm between the center of the contact patch and the steering axis, so uneven road surfaces and uneven braking cause lots of "steering wheel wiggle" and "wheel fight" on the part of the driver. That's why modern, wide-tired cars have zero to slightly negative scrub radius, which is obtained with wheels that have large positive offset.
The bottom line is that there is no solution to the problem unless you redesign the suspension for less scrub radius or go to a narrower, less negative offset wheel to reduce scrub radius.
Duke
Last edited by SWCDuke; 11-30-2015 at 12:55 PM.
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Sky65 (11-30-2015)
11-30-2015, 03:33 PM
#17
Drifting
You're hanging with the check book racers now Garrett 
Steve
11-30-2015, 04:01 PM
#19
Thanks again guys. In the side photo the wheels are turned left, they sit centered in the wells going straight and don't ever rub. I put those store bought flares on around 1980, the fenders were just cut round with the tires sticking out when I got it. It had GR50 (265) 50/15s on 8 inch rims in front back then and I don't recall the bad handling then. The bigger wheels and tires fit the front flares much nicer, plus I can rotate them all around. I don't recall it handling that badly even with the larger tires but that was long ago, could be tire age, worse roads, bad memory. I replaced all the suspension components less than 10K miles ago but again 20-30 years ago. I don't see any shift in the upper A arm bushings, and I also see that I have the caster kicked back as far as I can with the rear of the A frame up to the headers. Perhaps those special upper A-frames will help.
I agree the scrub radius may be the main issue, and I can easily test it with the 15x7 wheels and small tires off my S10 pickup. After taking it out on Saturday I came home and noticed a Thanksgiving rebate of $75 on a set of tires online that expires today (which prompted my asking you guys), but after your combined insight I am going to wait and do some inspection and testing first. Unfortunately won't likely happen until the Christmas holidays. In the mean time please provide any additional comments.
Thanks, Paul
I agree the scrub radius may be the main issue, and I can easily test it with the 15x7 wheels and small tires off my S10 pickup. After taking it out on Saturday I came home and noticed a Thanksgiving rebate of $75 on a set of tires online that expires today (which prompted my asking you guys), but after your combined insight I am going to wait and do some inspection and testing first. Unfortunately won't likely happen until the Christmas holidays. In the mean time please provide any additional comments.
Thanks, Paul
11-30-2015, 04:16 PM
#20
Team Owner
I thought the scrub radius was the other thread?
Ten-inch wheels likely have a lot of negative offset to provide sufficient inside clearance, and this dramatically increases the scrub radius over what was already a relatively large positive value with the OE wheels.
Increasing positive scrub radius increases the lever arm between the center of the contact patch and the steering axis, so uneven road surfaces and uneven braking cause lots of "steering wheel wiggle" and "wheel fight" on the part of the driver. That's why modern, wide-tired cars have zero to slightly negative scrub radius, which is obtained with wheels that have large positive offset.
The bottom line is that there is no solution to the problem unless you redesign the suspension for less scrub radius or go to a narrower, less negative offset wheel to reduce scrub radius.
Duke
Increasing positive scrub radius increases the lever arm between the center of the contact patch and the steering axis, so uneven road surfaces and uneven braking cause lots of "steering wheel wiggle" and "wheel fight" on the part of the driver. That's why modern, wide-tired cars have zero to slightly negative scrub radius, which is obtained with wheels that have large positive offset.
The bottom line is that there is no solution to the problem unless you redesign the suspension for less scrub radius or go to a narrower, less negative offset wheel to reduce scrub radius.
Duke
And even though it will lose half of those that read it, this is about the best simple explanation shared by Duke that I have ever seen written on the topic. Yes it is designed in based on the tire sizes stock and when you start changing to wider rims and tires, you get this characteristic (because I don't classify it in my miniscule brain as a problem, but just as a characteristic!). So the below is for anti-wiggle and the weight room is for the wheel fight. And for those that don't hit the weight room, you can install larger tires and just go practice your parallel parking!
I know a lot of guys take off the steering dampers! Even though I have big ground clearance limited aftermarket oil pans, I have a modified bracket off of the center link that directs the steering damper outward to clear the pan and I run a heavier than stock unit from I believe a ""truck"". I also run a 12:1 manual steering box (absolutely no steering slop-- but not sure if anyone sells such these days- very go kart like) plus I run a larger 69-82 center link and I brace that also. I run crossbrace on the upper a-arms, essentially tying the towers together-- basically anything that I can to make that front end more positive and less inclined to deflection or flexing. I also have aluminum front hubs and drilled and slotted front rotors to take weight off.
A lot of different sensations getting talked about in this thread, from wondering to wiggle to fight to deflection, to flex, to worn out, to you name it! We have just about all of the racer crowd in on this one now. Basically the guys pushing the larger tire sizes and the most knowledgeable crowd on the subject.
Lastly I am a very clean apex type of driver, even on the surface streets and I never stay in my own lane "anywhere anyways" going into a turn or coming out of a turn, unless a Cop sees me making a turn (then I pretend that I am being good!
)! I own the road 
(and people just fail to understand that! 
), so I mine as well use every inch of it!
Last edited by TCracingCA; 11-30-2015 at 04:41 PM.