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GT40 Tech - Chassis,Brakes,Tires,&Wheels Chassis and Handling.

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Old 21st November 2005, 06:36 AM   #1 (permalink)
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Wheel Spacers - Good, Bad or Dangerous ?

I am looking at the options available to move my wheels a little further out so as to "fill the guards" better. Around 3/4" at the rear & 1/2" at the front would do the job.

At the rear, I seem to have 4 choices :

- Get Simmons to rebuild the wheels with a 3/4" change in the off-set (huge $).

- A new chassis bracket for the lower a-arm that sets it all out 3/4" & a longer upper arm. (This would change the geometry, so I am not keen on this one).

- Just wind out the spherical joint adjustment as far as is sensible - but I'll probably only get about 1/2" with that.

- Use 3/4" wheel spacers - by far the simplest & cheapest.

At the front, I don't have much choice as the DRB uses an '87 Vette setup & the lower a-arms pivot in mountings well & truely welded into the chassis. So I figure that there are only 2 choices :

- Simmons wheel rebuild with 1/2" change in off-sets.

- 1/2" wheel spacers - again, simpler & much cheaper.

I have heard some conflicting stories about the safety of spacers, but suspect that they would be ok if they were machined accurately so that the circular locating lip on the hub mated exactly into the spacer, & the spacer had a matching lip which mated exactly into the wheel. Fixing the spacer to the wheel with c/s bolts would also probably be a good idea.

There is also the issue of whether longer studs are required, or if just longer lug-nuts are sufficient.

I would really appreciate any comments from the GT40 brotherhood.

Kind Regards,

Peter D.
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Old 21st November 2005, 08:56 AM   #2 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

For what it is worth, Porsche have been using wheel spacers on their cars for years without incident. Just need longer studs. Best of luck. Gregg
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Old 22nd November 2005, 06:13 AM   #3 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Spacers here in Victoria are illegal and would probably also void your insurance so just make sure that itís OK there in NSW first.

But if you are determined to get spacers, then the preferred option would be to get those that bolt to your hub via the standard studs, and then have their own studs for bolting to your wheels. The shear forces on the studs are much kinder in this arrangement because it doesnít rely so much on friction (wheel/spacer and spacer/hub) to prevent rotational slippage. Also, if the spacer is bolted to the hub, then you might be able to argue that they are not in fact spacers, but a fixed part of the hubÖ maybe.

Finally, if it is your intention to move the wheels out, then make sure that the resulting wheel offset is not too aggressive. If it is offset too far in either direction, then it will put undue strain on the wheel bearings.
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Old 23rd November 2005, 08:26 AM   #4 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Chris, I disagree.

Anything up to 15mm is not a problem as long as you still use the correct studs/bolts. It is no different to having the extra thickness cast on the wheel offset in the first place.

As Gregg says, porsches often come from the factory with spacers (it depended on what they had in stock at the build time apparently, so would use the narrow body wheels on a wide bodied car with spacers).

Obviously if your rules in your country state they cannot be used then that is a different issue, but personally I cannot see a problem with it, and have never heard of any of the owners of porsches over on rennlist experiencing problems either.

The key to secure wheels is having flat mating surfaces, and the correct studs/bolts.

Cheers,
John.
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Old 23rd November 2005, 09:10 AM   #5 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

[ QUOTE ]
no different to having the extra thickness cast on the wheel offset in the first place

[/ QUOTE ]

John, You may be ultimately correct about it being safe if the studs are of a strong enough material, but there is a difference to just having a different offset where the holes for the wheel nuts are drilled deeper so allowing the base of the nut to tighten closer to the hub. Purely from the perspective of lateral forces on the stud, the further away the bolt sits from the base of the stud, the greater the forces are on that stud.

Although it may not apply to this situation, my personal experience of use of spacers on Triumph TR6s (~10mm used to create space for ventilated disk brakes... a common mod for the track) is that they caused the studs to fatigue at the base and even break. It was a regular must-do check before running it on the track.
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Old 23rd November 2005, 10:36 AM   #6 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Hi
I've stated in other threads that I am against spacers. Lost a wheel on a Formula V with 3mm spacers - ripped the wheel bolts out the drum.

The way I see it is the law of levers
where the formula is force times distance from fulcrum / pivot.

The original wheel with no spacer is say 1mm from the fulcrum times force (one quarter of car weight or 250kg)
the moment force is thus 250kgmm (in reality the distance is a lot smaller than 1mm but this will give us a benchmark to compare against)

Move this out a further half inch and you get 13*250 = 3250kgmm of moment force (if this is the correct term - my physics was a long time ago but I remember the formulae)

This is the static load on the studs reduced by the number of studs and then seriously increased further by the 400hp/2 (2 whhl drive) from the engine, cornering force and braking force.

Sorry but something will give a lot quicker than the original non spacer design.

[img]/ubbthreads/images/graemlins/nono.gif[/img] [img]/ubbthreads/images/graemlins/nono.gif[/img]
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Old 23rd November 2005, 12:41 PM   #7 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

I have to believe spacers on the rear are a lot safer than
front spacers since they don't see turning loads.

MikeD
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Old 23rd November 2005, 01:19 PM   #8 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Spacers on the front will change scrub radius. In nearly every case this will make the car harder to drive. AND is dangerious. Now if you need to move the wheel out 60 thousands to final fit that last little bit of wheel weight clearance then don't worry about it, but three quarters of an inch is far beyond where I would want to go on a ontrack ride along.

As far as front to back goes, other than the scrub radius issue I think the rear is more dangerious. On a GT40 the rear tires already are wider thus more cornering force is applied to the wheel studs. On top of that we have at least a couple hundred foot pounds of torque added to the loading.

Lastly believe it or not a front tire/wheel comming off is easier to save that a rear. The consequences of either, at anything like the speeds these cars can achieve is ..... well....think about it.

Lastly lastly It will break when you need it to stay on the most. Hard on the brakes into or hard on the power out of a fast corner. Think freeway ramp big hard concrete wall.

I would get the wheels done right if it was me. If this is not possible then the threaded spacers (both wheel and hub studs) are much better than simple flat spacers with 5 holes in them.

Sorry.... I know we are all on a buget but I would hate to hear you destroyed your whole investment over this.
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Old 23rd November 2005, 04:11 PM   #9 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Ian, if you pulled the studs out of the hubs I would suggest you did not use long enough studs, so did not have enough threads engaged. Either that or your hubs were sh@gged anyway and would have failed regardless of spacers.

All your discussion on fulcrum is - err - irelevant when talking the thickness of spacer we are here, imo.
Lets go buy a wheel with a greater offset, but still the same bolt hole depth (& so stud length). You still get the increased moments your talking about. Does that mean it will fall off ?

Now lets look at production cars, say a VW Golf. The same hub is likely to be used for the entire range, yet the base models will have significantly different offset, diameter and width of wheels/tyres. If you are suggesting the designers designed the cars to be this marginal for the top of the range version, I would be very surprised. Lets not forget these cars get raced & rallied all over the world.

I accept that buying the correct offset wheels and having the correct track width to start with is favourite, but I don't buy the safety issue card you guys are playing. I do agree though that going too wide is a bad thing. If a race parts supplier stocks the spacers you would expect them to be selling them. Why would they stock a part that never sells...
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Old 23rd November 2005, 05:01 PM   #10 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

John
Studs were long enough - removed all the tgreads from the drum on all 5 studs. Yes they could have been overtightened / shagged at some stage but having a wheel overtake me once I would never use spacers again.

You can also bet that if a manufacturer eg VW changes the offsets they have been tested to distruction and will be thus within acceptabe engineering tolerences for VW anf their insurance underwriters.

That said to each his own and if someone wants to use spacers it's up to them.PeterD asked a question and I have said as I see it

I may be wrong and the could have many trouble free miles

Ian
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Old 23rd November 2005, 06:41 PM   #11 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Interestingly [img]/ubbthreads/images/graemlins/tongue.gif[/img] The corvette wheel hub has 5 12mm studs holding the wheel on and only 4 ~8mm bolts holding the hub to the upright --- and lotsa leverage at that point [img]/ubbthreads/images/graemlins/confused.gif[/img]
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Old 23rd November 2005, 06:52 PM   #12 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Just to add our experience for what it's worth, we run spacers (about 0.25") on the rears when running slicks.

The 2nd set of rims Roy has are of a slightly different offset and would foul where the lower arm attaches to the upright without the spacer.

We have run these wheels on Soft 11" Avon slicks for the past 10 years without any problem at all. The uprights have Ford hubs with Roy Smarts Knock-on adapters so one big centre 3-eared lug secures all.(handed obviously)

Onboard logging has shown peak cornering loads in excess of 1.75G and the only problem we have experienced was some local failure of the rear hub (was cracking and flexing) probably due to excessive lightening/loading.

The spacer was always loose till recently when Roy fitted them to the wheels (just so we don't forget to pack em!)

He machined them himself to be a good fit - one thing though, I guess the loading is somewhat different to a 5-stud setup due to the knock on fitment.

Anyway - just thought some might be interested... [img]/ubbthreads/images/graemlins/smile.gif[/img]
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Old 24th November 2005, 02:42 AM   #13 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Wow Guys - thanks for all the responses !

I guess that the crux of the matter is reduced to a few basic issues :

a) Simple Vertical Loading : Basic flat spacers are suspect. However, if spacers are correctly machined to reproduce the circular locating recess & lip, then all vertical shear stresses would be borne by these lips/recesses, not by the studs at all. The attached pic is an attempt to illustrate the lip/recess scenario.

b) Lateral Loading : I can see two elements here -

- Static lateral load on the studs nearest the ground - this is where Ian's "law of levers" comes in. Somewhere between the tops of the hub/spacer/wheel mating surfaces & the top studs becomes the fulcrum point, & the wider the spacer, the more tension is placed on the bottom studs (just imagine a huge spacer that put the wheels 6' outside the car & you can see why the tensional stress in the lower studs goes up with spacers).

- Dynamic lateral load due to cornering - in terms of the purely horizontal forces, I think that is a non-issue for spacers as they would be the same as for no spacers - the same additional tensional stress applied along the studs.

However, there is an added vertical force component (extra down force on the outer wheel), & it might appear that that "Ian's Law" would come into play again in terms of the extra "leverage" applied courtesy of the spacers - but I don't think so. At the end of the day, the outer wheel on a corner cops all the stress & the bottom of the wheel is forced inwards, thus countering "Ian's Law" in terms of tension on the lower studs.

c) Rotational Loading : If the spacers have stud holes which are a close interference fit over the studs, the shear forces across the bolts at the hub/spacer interface would be no worse than those at a normal hub/wheel interface. In fact, I would argue that they may actually be less as there is now 2 frictional interfaces - hub/spacer & spacer/wheel, rather than just the one interface of hub/wheel.

Well, if you are not now confused, I certainly am !!

All in all, I am not too worried about the off-set & stud strength issues - the Vette hubs were designed for a car twice the weight of a '40, so if you take into account the factor of safety built in for Vettes & then include the half-weight of a '40, I reckon we are ok as long as the spacers are machined to utilise the circular location lip.

Kind Regards,

Peter D.
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Old 24th November 2005, 03:26 AM   #14 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Here's another idea-----bolt the spacer to the hub then bolt the wheel to the spacer--this is a 2" job [img]/ubbthreads/images/graemlins/crazy.gif[/img]
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Old 26th November 2005, 08:19 AM   #15 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Chris - that is exactly how I pictured a "correct" spacer, recess on the bottom (inside) & lip on the top (outside).

With 2" to play with, there is no problem with the double stud/bolt setup, but with a spacer of only 1/2 to 3/4", I can see trouble with bolting the spacer to the hub - not enough depth to accommodate the normal lug nuts, so you would have to use c/s bolts thru from the front with nuts behind the hub flange. Given that, it would seem logical to then fit longer studs right thru the whole assembly (assuming a good interfernce fit all the way thru) so that you can take advantage of the stud heads behind the hub flange ?

What do you reckon ?

Kind Regards,

Peter D.
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Old 27th November 2005, 02:05 AM   #16 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

OK I were gonna use them then how about taping the holes and treading studs thur both the spacer and the hub. You could also take some of the load off the wheel studs with 5 more holes thru the spacer and into an aditional five threaded holes in the hub. 3 would more than likely be enough. Kind of like a reverce of the above picture. Solves the problem of thread depth and leaverage on the studs because the spacer can't transfer loads to the studs because it is bolted down to the hub.
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Old 27th November 2005, 07:48 AM   #17 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Howard - the jury is still out ! FWIW, I feel a little uncomfortable with any shear planes (hub/spacer or spacer/wheel) encountering studs/bolts at the threads - hence my suggestion of an interference fit for the studs thru the spacer - clear shank all the way at both shear planes & the threads at the ends just take tension as per normal. This would make the hub+spacer appear just the same as a rather thick hub flange.

I reckon that you are right about securing the spacer to the hub - that way, it just becomes a part of the hub, end of story. Perhaps the simplest way to achieve this is to just do 5 tapped holes in between the standard studs & run c/s bolts from the spacer into tapped hub flange holes (& if there is clearance on the inner face of the hub flange, add washers & nuts).

Does that make sense ?

Kind Regards,

Peter D.
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Old 27th November 2005, 02:11 PM   #18 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Peter, I think you are right about the thread shear issue. Maybe the best way would be to press the spacer onto the unthreaded shanks portions then begin the threads just above the mateing surface of the spacer. I think this is what you said. I still would like the spacer at least indexed to the hub but would prefer to have it bolted to the hub face at least in 3 places.

Anyway no matter how you do it use very high (best availible) quality hardware(studs).

Again read up on kingpin offset. 3/4" spacers at the front might be a lot of kingpin offset (scrub radius) increase.
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Old 27th November 2005, 06:28 PM   #19 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

This is a different animal...but a friend of mine runs a 3000hp top fuel dragster with simple aluminum slip-on spacers for a 5 stud application. I don't know how much more dynamic lateral G's are but 3000hp to HUGE drag slicks doesn't seem to be a problem.
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Old 27th November 2005, 07:13 PM   #20 (permalink)
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Re: Wheel Spacers - Good, Bad or Dangerous ?

Peter D,

I use these on the back of my 40 1" thick, check it out.
http://www.skulte.com/
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