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Thread: effects of wheel offset/back spacing and tire width on handling

  1. #11
    VCVC Member jrinaman's Avatar
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    Quote Originally Posted by Vanner68 View Post
    If you think about it, the further the centerline of the wheel is from the centerline of the kingpin, the more leverage the wheel has. I had a 74 Chevelle with deep dish 8" Cragars on the front (2" backspacing) If you let go of the steering wheel in a turn, the car would continue turning, would not straighten out until you turned the wheel back to manual. It could not be flat towed, once you went around a corner you had to stop and manually set the wheels straight again.
    I had several vehicles like that (not 2" though). my tow bar was useless on them. really cant recall an issue with handling but didn't cruise the interstates at 75 either. my van isn't really a concern at 55 but at 75, I don't feel I am in control but just guiding it down the path. before all of my other issues, before the replacing of anything that 'might' be the problem, before fixing the rotted spring hanger that actually was the problem and before adding these wheels and new tires, I would run 100 without issue and felt in control. while the wheels wasn't the cause of my other issues, they got put on right after the problems started. I would of never noticed the negative effect from too much offset with my rear end sending me all over the road already.
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

  2. #12
    VCVC Member jrinaman's Avatar
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    didnt rush out and buy wheels yet as just not finding enough info on this. i will share what little i did find for those interested. many have run offset rims with no noticable problems and very few had issue, however, the rare issue is exactly what i am experiencing. "loose at speed", "not connected", "not in control" and "forget about passing a semi at 60". most of those quotes are from people with more extreme changes. a more acurate measurement puts me just under 15 mm from stock offset, keep in mind this is 30mm if comparing hub to outer lip vs. hub to inner. when asking others with aftermarket rims, the few that actually knew their offset/backspacing had the same as me, all of them but my rotors ad 1/4"+ so their difference of 3/4" only gave them 9.5 mm offset. none of them noticed any issues but admitted they never see freeway speeds. of the limited info I heard or read (fact or barstool advice? I ignored the obvious internet babel), 5 or 6 mm deviation is acceptable but any increase creates a dead or loose feel at increased speeds. whichever wheel has the most weight/force at that particular moment is where it will go, not just from toe in but any resistance on tires, their both being pulled back and the increased offset results in both trying to toe out. my heavy toe setting 'may' of helped when conditions are ideal but actually created more tramlining when one wheel had more input than the other (so almost always!) I assume my increased caster effects it too. as Leroy mentioned, too much makes it feel lazy. 'lazy' may be more accurate than 'wanders'. a more accurate alignment revealed my heavy 1/8" was really 1/4"+. it is now 1/16"+. my true caster is 9 3/4 degrees. my easily available options are 5 3/4 or 7 3/4. I have heard the 'magic number' for our vans, or most older vehicles now running radials is 7 while factory spec is less. other than more of an attempt to recenter, difference in the +75 mph 'loose' feel was minor and have had all 3 angles but always with offset rims and heavy toe. having absolutely no luck finding a set of stock rims/tires to compare to and new rims is still the easiest "IF" there truly is an issue with offset.
    Last edited by jrinaman; 07-08-2019 at 02:44 PM.
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

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    VCVC Member jrinaman's Avatar
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    I couldn't find stock rims and decided to put this on the back burner. moved on to my 4.10 posi install and no sooner started and a set of rims fell in my lap. ended up finding monti carlo rims but didn't want to change more than one thing at a time. while the gearing is an improvement, handling was worse! (didn't expect any change). after triple checking everything and ready to give up, I calmed down enough to think. pulls into traffic under load and pulls off road if I quickly let off. kinda floats with normal accel/decal but worse than before the rear end swap. on a long shot, thought 'maybe' I was amplifying my existing problem and honestly ran out of other things to check. second step backwards, the test rims are also offset!! 215's instead of 225's and only a 3mm difference on offset. put them on anyways and made a difference! more stable, less pull and steering recenters better. FINALLY, a step forward! ordered 215-65-15's and 6" rims to put me within 2 mm of stock. was tempted to get the 8's but that left me 7 mm from stock (because of disc conversion). while that 7 mm probably would of been fine, the 2 mm puts me closer and takes it completely out of the equation.
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

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    Certifiable Vanatic Leroy Jackson's Avatar
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    Quote Originally Posted by jrinaman View Post
    I couldn't find stock rims and decided to put this on the back burner. moved on to my 4.10 posi install and no sooner started and a set of rims fell in my lap. ended up finding monti carlo rims but didn't want to change more than one thing at a time. while the gearing is an improvement, handling was worse! (didn't expect any change). after triple checking everything and ready to give up, I calmed down enough to think. pulls into traffic under load and pulls off road if I quickly let off. kinda floats with normal accel/decal but worse than before the rear end swap. on a long shot, thought 'maybe' I was amplifying my existing problem and honestly ran out of other things to check. second step backwards, the test rims are also offset!! 215's instead of 225's and only a 3mm difference on offset. put them on anyways and made a difference! more stable, less pull and steering recenters better. FINALLY, a step forward! ordered 215-65-15's and 6" rims to put me within 2 mm of stock. was tempted to get the 8's but that left me 7 mm from stock (because of disc conversion). while that 7 mm probably would of been fine, the 2 mm puts me closer and takes it completely out of the equation.

    I think I know your problem...you are taking your measurements in metric. These vans were built in American units.
    The Raped Ape
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  5. #15
    VCVC Member jrinaman's Avatar
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    Quote Originally Posted by Leroy Jackson View Post
    I think I know your problem...you are taking your measurements in metric. These vans were built in American units.
    in 55 years, don't think I ever measured anything in metric. I have spent a lot of time converting inches to mm just to buy the metric part or materials. as for the rims, offset is in mm while backspacing is inches. my issue was offset (centerline of rim/tire) so easier to convert my numbers to mm once and search rims by offset. my centerline was almost 3/4" off, I believe this was the issue. my junkyard rims were still 1/2" off but made a HUGE difference. my new rims are 1/8" off and had tires mounted yesterday, should get them on today. I have passed on many longer trips, including the nats because of the loose feel at speed. probably a hundred people and dozens of early owners have commented that any 50 year old van rides like that, yet not one single person drove it or even went for a ride. 5 years ago, I towed my camper at 85 and thought nothing of it. today, even 20 miles on the interstate just isn't worth the ride.
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

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    Certifiable Vanatic Leroy Jackson's Avatar
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    Was it already mentioned to pull the springs off a d physically check all of the bushings?

    My van, the previous owner stuffed the spring eyes full of braided line instead of finding new bushings.

    Needless to say, fixing that issue netted some very positive gains in the handling department.

    Also:
    Rebuild the steering gear
    Using a return to center steering damper
    swaybars front and rear
    Shimming front end for positive caster
    Centering the axles
    Toe in 1/4 in
    Balancing the drive shaft
    setting the pinion angles correctly
    Balancing the wheels

    All these steps got my van to do California highway speeds (90+ in some areas) and not feel like a death trap. Still was no canyon carver though.
    The Raped Ape
    1970 G-20 Krylon black
    Swing up cargo doors
    Supercharged 383
    4L80E transmission
    Detroit trutrac rear limited slip

  7. #17
    VCVC Member jrinaman's Avatar
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    Quote Originally Posted by Leroy Jackson View Post
    Was it already mentioned to pull the springs off a d physically check all of the bushings?

    My van, the previous owner stuffed the spring eyes full of braided line instead of finding new bushings.

    Needless to say, fixing that issue netted some very positive gains in the handling department.

    Also:
    Rebuild the steering gear
    Using a return to center steering damper
    swaybars front and rear
    Shimming front end for positive caster
    Centering the axles
    Toe in 1/4 in
    Balancing the drive shaft
    setting the pinion angles correctly
    Balancing the wheels

    All these steps got my van to do California highway speeds (90+ in some areas) and not feel like a death trap. Still was no canyon carver though.
    the wheels made a huge improvement. I only considered offset as an issue as one last thing before I sold it or converted to rack and pinion $$$. steering box professionally rebuilt, including machining of gears. front and rear sway bars, tried castor everywhere between 0 and 11, toe in from 0 to 3/8", pinion within 1 degree, all wheels balanced with new tires, new tie rod ends, drag link, spring bushings, stiffened all 4 springs, new wheel bearings, replaced all lugs and studs, installed hubcentric rings, replaced a hub that race had 1/8" slop, new king pins, new top bearing and adjusted steering column, checked axles for square (center to center and diagonal) probably dozens more but cant remember. some of those was clearly an issue but none of it helped. rims made enough difference to notice at parking lot speeds. 60+ was a white knuckle ride, sundays test drive was a comfortable 80 and went to 85 and let go of the wheel just to see what would happen. while my initial problem was fixed several years ago, it was never like it was before all that. the new rims seem to of corrected it. what is ironic is I bought the old rims to rule out rims being an issue!
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

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