Engineering of Wheel Spacers
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Lonnie Pavtis
OldSStroker. The thick bolt-on spacers I routinely see are aluminum. This was my criteria for concern. Yes, the cast iron spacers on 1-ton duallies are strong & rightfully so being made from 1" thick cast iron with (8) 5/8" studs tolding them together. They are also approx 4" thick spacers .... not really comparable to our cars.
Those bolt-on spacers effectively change the offset of the alloy wheel and have at least the same amount of area as the mounting area of the wheels. Aluminum hubs (for cars) are not unusual. IMO, there's plenty of material in the aluminum spacer; at least 10 times the area of five 1/2 in studs.
I do not think the bending moment is much of an issue here (on a large truck with side loads from turns etc it can be)as we are not talking heavy loads (3500# car / 20 studs) as much as the effect of a loose wheel not providing enough clamping force to resist the shear force on the bolts (600ft.lb. engine x 2.5:1 converter mult., 2.48 low gear, 4.1 rear gear = 15,252 ft.lb. at the wheels)
Has anyone compared the area of 5 wheel studs to the area of the axle shaft at the wheel bearing? How many people here have broken an axle?
Five 1/2 studs have the equivalent area of one 1.12 dia shaft if you consider the full diameter. The smaller section of the root of the threads make them equivalent to about one .98 dia. shaft. With 12 mm studs, it's about 1.05 for the body dia. and .90 for the thread root area. Many studs fail in the thread root area, so that's the equivalent area I'd consider, especially in bending.
Also hub piloted mounting would be a definite strength advantage, but next to none of the aftermarket race wheels fall in this category either.
All in all, I would venture to say that 90% of these failures are directly related to loose wheels subjecting the studs to shear(retorque often to maintain proper preload), repeated tire changing (how many of you think of your studs wearing out) or overtightening (tightening past yield strength) via impact use.
For example, I often drive a Chevy 4x4 Tk (500hp 427, 4.56 gears) with 35x12.5 tires . You would be amazed on how often the studs need retorqued with aluminum wheels (I have also cracked 2 Weld wheels where the bolt in center meets the outer ring... 5400lb empty & a lot of bending stress due to tire height) First 50 miles (approx 1/4 turn), after 150 (approx 1/8 turn), recheck at 500 & occasionally a few will have noticible movement. After this, they rarely move. How many of you guys recheck your wheel 3 times & also use a torque wrench? It makes a big difference. Impact wrenches are for removing wheels, not installing them in my opinion. If you bolt on slicks every weekend, replace your studs frequently.
Food for thought..........
OldSStroker. The thick bolt-on spacers I routinely see are aluminum. This was my criteria for concern. Yes, the cast iron spacers on 1-ton duallies are strong & rightfully so being made from 1" thick cast iron with (8) 5/8" studs tolding them together. They are also approx 4" thick spacers .... not really comparable to our cars.
Those bolt-on spacers effectively change the offset of the alloy wheel and have at least the same amount of area as the mounting area of the wheels. Aluminum hubs (for cars) are not unusual. IMO, there's plenty of material in the aluminum spacer; at least 10 times the area of five 1/2 in studs.
I do not think the bending moment is much of an issue here (on a large truck with side loads from turns etc it can be)as we are not talking heavy loads (3500# car / 20 studs) as much as the effect of a loose wheel not providing enough clamping force to resist the shear force on the bolts (600ft.lb. engine x 2.5:1 converter mult., 2.48 low gear, 4.1 rear gear = 15,252 ft.lb. at the wheels)
Has anyone compared the area of 5 wheel studs to the area of the axle shaft at the wheel bearing? How many people here have broken an axle?
Five 1/2 studs have the equivalent area of one 1.12 dia shaft if you consider the full diameter. The smaller section of the root of the threads make them equivalent to about one .98 dia. shaft. With 12 mm studs, it's about 1.05 for the body dia. and .90 for the thread root area. Many studs fail in the thread root area, so that's the equivalent area I'd consider, especially in bending.
Also hub piloted mounting would be a definite strength advantage, but next to none of the aftermarket race wheels fall in this category either.
All in all, I would venture to say that 90% of these failures are directly related to loose wheels subjecting the studs to shear(retorque often to maintain proper preload), repeated tire changing (how many of you think of your studs wearing out) or overtightening (tightening past yield strength) via impact use.
For example, I often drive a Chevy 4x4 Tk (500hp 427, 4.56 gears) with 35x12.5 tires . You would be amazed on how often the studs need retorqued with aluminum wheels (I have also cracked 2 Weld wheels where the bolt in center meets the outer ring... 5400lb empty & a lot of bending stress due to tire height) First 50 miles (approx 1/4 turn), after 150 (approx 1/8 turn), recheck at 500 & occasionally a few will have noticible movement. After this, they rarely move. How many of you guys recheck your wheel 3 times & also use a torque wrench? It makes a big difference. Impact wrenches are for removing wheels, not installing them in my opinion. If you bolt on slicks every weekend, replace your studs frequently.
Food for thought..........
If, however, the tightened bolt is loaded in use so that it is stretched beyond it's "yield point", and permanently stretches, it loses some of it's clamping force and the nut is now not at it's original torque. Properly designed and installed bolts don't do this. This is overload.
Even if the nuts are torqued properly, the clamping load and bolt stretch may not be up to the design, because of thread conditions. With low clamping load, the nut can work loose. Subsequent retorquing might get the load where it belongs.
The problem, IMO, is which conditon caused the loosening. If it was low clamping load, and you catch it on the retorque, you still have the design strength you need. If the studs yielded due to overload, they also started to neck down, or have a reduction in cross-sectional area, which is the beginning of the end. Lower area equals more stress which equals more yield which equals less area, etc.
Note that many engine builders use connecting rod bolt stretch instead of (or in addition to) torque to assure correct clamping loads. This isn't practical on wheels, of course.
FWIW, torquing wheel nuts in 20 or so lb-ft steps from 60 on up and in the "star" pattern goes a long way to getting even clamping and minimal distortion of brake disks.
Lunch time..more food for thought.
Registered User
Joined: Aug 1998
Posts: 520
From: Perryopolis, Pa
The overall point is that "aluminum" wheels are being bolted down not steel wheels. They are softer than steel & will take a set from the lug nut/washer seating into the wheel surface. Just look at a used aluminum racing wheel, you will see the washer indentation. Taper seat nuts are not usually as bad. Wheel loosening is not generally from the studs stretching, but from the wheel deforming under the nuts. This in turn reduces the bolt preload.
Same thing can happen with aluminum bolt on spacers. Unless you intend to remove the wheels to retorque the spacers, you may have a loosening problem. Some of you that put late model Vette/Camaro wheels on your IROC, may have first hand exparience with this. Personally I have never had a problem with thin aluminum spacers.
Steel wheels rarely need retorqued, at least the ones I have seen.
Same thing can happen with aluminum bolt on spacers. Unless you intend to remove the wheels to retorque the spacers, you may have a loosening problem. Some of you that put late model Vette/Camaro wheels on your IROC, may have first hand exparience with this. Personally I have never had a problem with thin aluminum spacers.
Steel wheels rarely need retorqued, at least the ones I have seen.
Registered User
Joined: Dec 2000
Posts: 766
From: GARDNERS,PA
I've bent (rotated) my rear studs about 5 times or so with stock salad shooters and ET Streets. I gradually increased the clamping load (more lugnut torque) until I had enough friction to hold for my launches. I ended up at 110 ft-lbs lug nut torque on stock rims. I believe that this is far above OEM recomendations and would probably scare me if I did the calculations on the proof strength of a stud, but I didn't have much choice. I think spacers on the rear would be a big no-no if your launching hard.
Steve
Steve
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Originally posted by SABLT194
I've bent (rotated) my rear studs about 5 times or so with stock salad shooters and ET Streets. I gradually increased the clamping load (more lugnut torque) until I had enough friction to hold for my launches. I ended up at 110 ft-lbs lug nut torque on stock rims. I believe that this is far above OEM recomendations and would probably scare me if I did the calculations on the proof strength of a stud, but I didn't have much choice. I think spacers on the rear would be a big no-no if your launching hard.
Steve
I've bent (rotated) my rear studs about 5 times or so with stock salad shooters and ET Streets. I gradually increased the clamping load (more lugnut torque) until I had enough friction to hold for my launches. I ended up at 110 ft-lbs lug nut torque on stock rims. I believe that this is far above OEM recomendations and would probably scare me if I did the calculations on the proof strength of a stud, but I didn't have much choice. I think spacers on the rear would be a big no-no if your launching hard.
Steve
Registered User
Joined: Jul 2000
Posts: 520
From: MD
That really depends on the wheels... My '97 WS6 had a separate card in the golve box about the wheels and among other things specified 75lb/ft for the lugs (I don't remember what the acutal owner's manual stated but the card specifide to ignore torque specs and cleaning recomendations from it). My '83 and 87 3rd gens both with aluminum wheels specified 75 and 85 (forgot which is which), and all of them specify 100 for the steel mini spare.
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Originally posted by WS6 TA
That really depends on the wheels... My '97 WS6 had a separate card in the golve box about the wheels and among other things specified 75lb/ft for the lugs (I don't remember what the acutal owner's manual stated but the card specifide to ignore torque specs and cleaning recomendations from it). My '83 and 87 3rd gens both with aluminum wheels specified 75 and 85 (forgot which is which), and all of them specify 100 for the steel mini spare.
That really depends on the wheels... My '97 WS6 had a separate card in the golve box about the wheels and among other things specified 75lb/ft for the lugs (I don't remember what the acutal owner's manual stated but the card specifide to ignore torque specs and cleaning recomendations from it). My '83 and 87 3rd gens both with aluminum wheels specified 75 and 85 (forgot which is which), and all of them specify 100 for the steel mini spare.
Registered User
Joined: Jul 2000
Posts: 520
From: MD
Hum… probably would have helped if I had sigs turned on before now… I really don’t pay attention to names since I signed on as WS6 TA something like 3 years ago when my ’97 WS6 was them main car that I tinkered with… Probably haven’t touched that one for about that long…
Registered User
Joined: Aug 2001
Posts: 2,400
From: Michigan's left coast
Originally posted by Injuneer
Stock wheels on stock studs should be torqued to 100ft-lb.... right out of the Owner's Manual.
Stock wheels on stock studs should be torqued to 100ft-lb.... right out of the Owner's Manual.
Registered User
Joined: Jan 2000
Posts: 100
From: W Hartford, CT
I guess I'm jumping in a little late here... Comparing shear area of the axle related to the area of the 5 studs to figure out strength isn't the whole picture, since the studs are very much a shear load (figure from the end of the lugnut to the root of the stud at the hub is about .400), while the axle is strictly in torsion. The bolt circle is 4.75", so each stud is 2.375" away from the axle centerline.
Minor Dia of M12x1.5=10.376mm min = .131in^2
Grade 10.9 = 10*100=1000 MPA tensile strength = 145000 psi
Shear Stress = Force * Area, 145000 psi * .131 * 5 = 95021 lbf
Torque = Force * Distance, 95021 * 2.375"/12 = 18800 ft-lbs
Your axle will break well before you can get the 18,800 ft-lbs to the studs.
So... your five Grade 10.9 M12x1.5 bolts on a 4.75" bolt circle should take 18,800 ft-lbs w/o breaking if you analyze it as strictly shear (with no stress concentration factors, ect, and I'm sure I'm forgetting some things too). Slip-on spacers add whatever thickness to the original gap between the end of the lugnut and the base of the thread, increasing the bending load, while bolt-on adapters will generally keep the bending load on the studs the same as a rim would, not increasing the stress any, and not weakening the design. I crunched out bending calcs a while back just to see, but don't have the spare minutes right now.
Andris
Minor Dia of M12x1.5=10.376mm min = .131in^2
Grade 10.9 = 10*100=1000 MPA tensile strength = 145000 psi
Shear Stress = Force * Area, 145000 psi * .131 * 5 = 95021 lbf
Torque = Force * Distance, 95021 * 2.375"/12 = 18800 ft-lbs
Your axle will break well before you can get the 18,800 ft-lbs to the studs.
So... your five Grade 10.9 M12x1.5 bolts on a 4.75" bolt circle should take 18,800 ft-lbs w/o breaking if you analyze it as strictly shear (with no stress concentration factors, ect, and I'm sure I'm forgetting some things too). Slip-on spacers add whatever thickness to the original gap between the end of the lugnut and the base of the thread, increasing the bending load, while bolt-on adapters will generally keep the bending load on the studs the same as a rim would, not increasing the stress any, and not weakening the design. I crunched out bending calcs a while back just to see, but don't have the spare minutes right now.
Andris
Thread Starter
Moderator
Joined: Dec 1969
Posts: 10,745
From: Buffalo, New York
Originally posted by Z28tt
I guess I'm jumping in a little late here... Comparing shear area of the axle related to the area of the 5 studs to figure out strength isn't the whole picture, since the studs are very much a shear load (figure from the end of the lugnut to the root of the stud at the hub is about .400), while the axle is strictly in torsion. The bolt circle is 4.75", so each stud is 2.375" away from the axle centerline.
Minor Dia of M12x1.5=10.376mm min = .131in^2
Grade 10.9 = 10*100=1000 MPA tensile strength = 145000 psi
Shear Stress = Force * Area, 145000 psi * .131 * 5 = 95021 lbf
Torque = Force * Distance, 95021 * 2.375"/12 = 18800 ft-lbs
Your axle will break well before you can get the 18,800 ft-lbs to the studs.
So... your five Grade 10.9 M12x1.5 bolts on a 4.75" bolt circle should take 18,800 ft-lbs w/o breaking if you analyze it as strictly shear (with no stress concentration factors, ect, and I'm sure I'm forgetting some things too). Slip-on spacers add whatever thickness to the original gap between the end of the lugnut and the base of the thread, increasing the bending load, while bolt-on adapters will generally keep the bending load on the studs the same as a rim would, not increasing the stress any, and not weakening the design. I crunched out bending calcs a while back just to see, but don't have the spare minutes right now.
Andris
I guess I'm jumping in a little late here... Comparing shear area of the axle related to the area of the 5 studs to figure out strength isn't the whole picture, since the studs are very much a shear load (figure from the end of the lugnut to the root of the stud at the hub is about .400), while the axle is strictly in torsion. The bolt circle is 4.75", so each stud is 2.375" away from the axle centerline.
Minor Dia of M12x1.5=10.376mm min = .131in^2
Grade 10.9 = 10*100=1000 MPA tensile strength = 145000 psi
Shear Stress = Force * Area, 145000 psi * .131 * 5 = 95021 lbf
Torque = Force * Distance, 95021 * 2.375"/12 = 18800 ft-lbs
Your axle will break well before you can get the 18,800 ft-lbs to the studs.
So... your five Grade 10.9 M12x1.5 bolts on a 4.75" bolt circle should take 18,800 ft-lbs w/o breaking if you analyze it as strictly shear (with no stress concentration factors, ect, and I'm sure I'm forgetting some things too). Slip-on spacers add whatever thickness to the original gap between the end of the lugnut and the base of the thread, increasing the bending load, while bolt-on adapters will generally keep the bending load on the studs the same as a rim would, not increasing the stress any, and not weakening the design. I crunched out bending calcs a while back just to see, but don't have the spare minutes right now.
Andris
Rich Krause
Registered User
Joined: Jan 2000
Posts: 100
From: W Hartford, CT
The above was just shear stress - i.e. two plates sliding past each other, such as the wheel rear face and the hub front face. There was no bending above. If no one else crunches out bending for the studs, I'll get to it tonight or tomorrow.
Andris
Andris
Registered User
Joined: Jan 1999
Posts: 884
From: I reached back like a pimp and smacked that LS1....
I used a .250 hub centric aluminum spacer on the rear of my 634rwhp car last year. Stock sized studs, torqued to 100ft lbs. I never had a problem with the lugs loosening/etc, but after reading all of this I am considering removing them.
What are the chances of the wheel/spacer/rotor combination rotating on the axle with properly torqued lug nuts?
I just can't imagine that happening with 5 lugs torqed to 100ft lbs.
Maybe the real problem is the distance of the nut from the shoulder of the stud.
If the hub of the wheel is .250 thick, the rotor is .100 and the axle is .500, than the bottom of the lug is approx .850 from the shoulder of the stud. Now if you add a .250 spacer, or have a wheel that has a .500 thick hub, the distance from the bottom of the lug and the stud shoulder is now 1.100, having more chance of stud 'bending'.
I would tend to think that at a given stud diameter, a joint that places the nut closer to the shoulder of the stud would be stronger.
What are the chances of the wheel/spacer/rotor combination rotating on the axle with properly torqued lug nuts?
I just can't imagine that happening with 5 lugs torqed to 100ft lbs.
Maybe the real problem is the distance of the nut from the shoulder of the stud.
If the hub of the wheel is .250 thick, the rotor is .100 and the axle is .500, than the bottom of the lug is approx .850 from the shoulder of the stud. Now if you add a .250 spacer, or have a wheel that has a .500 thick hub, the distance from the bottom of the lug and the stud shoulder is now 1.100, having more chance of stud 'bending'.
I would tend to think that at a given stud diameter, a joint that places the nut closer to the shoulder of the stud would be stronger.
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