92 replies to this topic

[Brandon]

38mm is the stock offset.  30mm is readily available and 25mm is a SM specific offset and the widest allowable by our rules.  the wider the offset the softer the spring rate the higher you need to run the car.....

So it's not beyond the pale to say offset is a suspension tuning capability?

 

And pardon my inexperience but what was the reasoning to support the use of +25s when it sounds as though folks who are "fast" seem to run the +38s (or at least not +25s)?

Was it a 'parity' issue (sorry - too early in the silly season for that word?  ) to keep the track widths the 'same' between NA/NBs?

[Kyle Disque]

Some quick math shows that a 7mm offset change results in about a 14lb wheel rate change.  Any change you're feeling is not from wheel rate.

 

Bushing condition, for example,  will cause far more variance in wheel rate than offset.

 

-Kyle

[Jim Drago]

Some quick math shows that a 7mm offset change results in about a 14lb wheel rate change.  Any change you're feeling is not from wheel rate.
 
Bushing condition, for example,  will cause far more variance in wheel rate than offset.
 
-Kyle

I agree 100%, I never "felt" the difference on track in just the offset change. However, the offset will change the cross weight, the change is also non linear, it depends on how close you are to true 50/50 weight distribution. Also to be noted, changing only the tires will change cross on the scales, but swapping from 25-30 or 30-25, we have seen about .3-.6 difference in cross. How much is tires, how much is cross, hard to say but we usually see a few tenths difference just changing tires

[Brandon]

So what's the amount of change when going from +25 to +38?  That's more than the 5-7 that's been noted so far...would it be a doubling or is it something else (exponential) with a lever involved?

[Ron Alan]

So it's not beyond the pale to say offset is a suspension tuning capability?

 

And pardon my inexperience but what was the reasoning to support the use of +25s when it sounds as though folks who are "fast" seem to run the +38s (or at least not +25s)?

Was it a 'parity' issue (sorry - too early in the silly season for that word?  ) to keep the track widths the 'same' between NA/NBs?

Well, if it was a parity issue, the NA car would be allowed the NB rear upright(5mm offset wider correct?)? Or maybe it is and someone has determined that this benefits one of the 2 cars? I would think track width would be a no brainer to allow to be identical?? But maybe the picture is bigger than I understand...any help?

[Kyle Disque]

Jim,

 

If you really want to chase your butt with moving tires around, try the bias cantilevered tires!  Radials are much more consistent.  We measure them in the Hoosier truck and pick the set that matches best, so they're pretty close to start with.  But they move around as they wear.

 

I struggle with why I get crosses dialed into to a tenth when I know that the tires will just throw it off anyway.

 

Changing crosses is likely just the slight change in ride height from the camber when you add/subtract offset.

 

I've thought about building a set of hub stands to do setups on rather than using wheels/tires.  That would at least eliminate one variable.  And with a tub car like an SM, it would make adjustments easier.   I was thinking you could just get some 1/2" or 3/4" aluminum plates that are about 6" x 18" and drill the bolt pattern into them at the right height.  If you wanted to be slick you could add some bearings to the base to allow them to be slip plates too.  To get them consistent you could drill all four at the same time in a stack.  KISS.

 

But I don't think that using offset to vary wheel rate is real.  The impact they have on track width and scrub radius seems like the biggest delta.  I doubt that aero is a factor either.  But that's much harder to predict.   You'd need a moving floor tunnel to measure it.  $$$$$$$$$$$$$$$$$$

 

Before the "symetric" rule we used to put all the spacers on one side on rovals.  Or all on just the loaded front.

 

-Kyle

[wheel]

Wait, you mean you don't use a moving floor tunnel?  No wonder Drago is in front…...

[Kyle Disque]

Wheel, if your floor is moving, it's time to switch to decaf.  

 

-Kyle

[FTodaro]

 

I've thought about building a set of hub stands to do setups on rather than using wheels/tires.  That would at least eliminate one variable.  And with a tub car like an SM, it would make adjustments easier.   I was thinking you could just get some 1/2" or 3/4" aluminum plates that are about 6" x 18" and drill the bolt pattern into them at the right height.  If you wanted to be slick you could add some bearings to the base to allow them to be slip plates too.  To get them consistent you could drill all four at the same time in a stack.  KISS.

 

 

-Kyle

We are getting a little off topic but i wanted to comment on the hub stands. A buddy of mine "John Guthrie" and i have spent some time analyzing Hub Stands because if we could have made them work it would have saved us tons of time in alignments because they can be had with toe measure and camber base plates on the unit.

 

We could never get the hub stands to duplicate what the car was doing with the tires on the car. we aligned two different cars on two different lifts doing the car with tires on it then checking the results with the hub stands and then did it the other way around. the hub stands gave you a different readings because the  spring rate was effected by them differently than the tire,  so we could not reproduce the set up going from hub stand to the wheels, and we could not accurately compensate for the difference consistently.

 

So our conclusion was they were not as accurate as doing an alignment with the tires on the car that your going race with.

[Kyle Disque]

Any spring rate difference with the hub stands should be minimal not affect crosses.  It might affect ride heights, but even then it would be tiny and easy  to predict.    It should also be pretty straight forward to get the same center of pressure under the hub by modifying the hub stands.  But I suspect that this isn't necessary.

 

Any effect the hub stands had on one corner, they would have the same effect on the opposite side.  Thus they would not change crosses.

 

Just a guess, but I think you're making Jims and my point about tire inconsistencies.   Did you try rotating the tires on the same car or swapping them from the other car?  I've done that and it always changes the crosses.  Even brand new radial tires will be off enough to see it in the crosses if you swap them around.

 

What did you use to provide slip at the scale/hub stand?  Not having the flexible rubber tire will magnify any binding issues, so you need something to release binding at all four corners.  Old tricks like trash bags won't work.  You will need something like a ball bearing turn plate at all four corners.

 

I'm sure your saw what you saw.  The question is just why. 

 

Just a data point, most, if not all, F1, Indy, DP, Grand Am GT teams use hub stands.

 

Here is a picture of the Brumos guys using their hub stands.  It looks like that might be inset to get the COP closer and they do have bearings at the bottom to release bind.  http://www.racemsm.c...achment_id=1844   Click on the picture for a larger version.

 

-Kyle

[wheel]

Back to the original question.  There are a group of Spec Mustangs, on the west coast, who run a spec wheel Jongbloed Wheel, Part# 70010545 - 18” X 10.5” front and rear    

 

They do not have any issues with wheel reliability, as far as I know.

wheel

[Alberto]

We are getting a little off topic but i wanted to comment on the hub stands. A buddy of mine "John Guthrie" and i have spent some time analyzing Hub Stands because if we could have made them work it would have saved us tons of time in alignments because they can be had with toe measure and camber base plates on the unit.

 

 

 

FYI

 

Iron Canyon recently introduced hub stands to go along with their alignment kit:

http://www.ironcanyo...-hubplates.html

 

I think Flyin Miata also has something.

[FTodaro]

Any spring rate difference with the hub stands should be minimal not affect crosses.  It might affect ride heights, but even then it would be tiny and easy  to predict.    It should also be pretty straight forward to get the same center of pressure under the hub by modifying the hub stands.  But I suspect that this isn't necessary.

 

Any effect the hub stands had on one corner, they would have the same effect on the opposite side.  Thus they would not change crosses.

 

Just a guess, but I think you're making Jims and my point about tire inconsistencies.   Did you try rotating the tires on the same car or swapping them from the other car?  I've done that and it always changes the crosses.  Even brand new radial tires will be off enough to see it in the crosses if you swap them around.

 

What did you use to provide slip at the scale/hub stand?  Not having the flexible rubber tire will magnify any binding issues, so you need something to release binding at all four corners.  Old tricks like trash bags won't work.  You will need something like a ball bearing turn plate at all four corners.

 

I'm sure your saw what you saw.  The question is just why. 

 

Just a data point, most, if not all, F1, Indy, DP, Grand Am GT teams use hub stands.

 

Here is a picture of the Brumos guys using their hub stands.  It looks like that might be inset to get the COP closer and they do have bearings at the bottom to release bind.  http://www.racemsm.c...achment_id=1844   Click on the picture for a larger version.

 

-Kyle

i use gallon zip lock bags with oil in them.

It affected camber and cross, my point is when you went from hub stand to tires the camber and cross would change.

so if you put a set up on the car with the stands then when to the track with tires you did not end up with what you though you would.

the height of the jack stand changes the outcome. most are taller than the tires from hub to ground. 

 

Alberto, i am aware of the iron canyon set up, with the built in toe gauge and camber plate. vary interesting to me if i could get them to work for me.

 

sorry for the hijack.

[Bench Racer]

What mfg./model hub stands did you use?

 

Did you call the hub stand mfg. and discuss the differences?

 

Yes Saul, I'm asking questions. Do you have a root cause of Frank's hub stand issue? 

 

Matbe we can lure Jay Lutz into this communication, he represented Middler Brothers/Tanner motorsports hub stands.

[GROOTS]

OK .  Back to topic.  Has anyone tried  D-Force wheels. Reliable ?  Weight ?  Advertised at true 13 lbs. How true is it ?

[Tom Sager]

OK .  Back to topic.  Has anyone tried  D-Force wheels. Reliable ?  Weight ?  Advertised at true 13 lbs. How true is it ?

What they're selling now weigh 13.5 - 13.7 pounds from what I've seen.  The earlier wheels were very close to 13.0 but they would bend very easily.  The current heavier wheels are much stronger.  

[philstireservice]

What they're selling now weigh 13.5 - 13.7 pounds from what I've seen.  The earlier wheels were very close to 13.0 but they would bend very easily.  The current heavier wheels are much stronger.  

 Fits in with every other SM wheel....Although some spoke designs lend themselves to more strength.

[Jeff Wasilko]

OK .  Back to topic.  Has anyone tried  D-Force wheels. Reliable ?  Weight ?  Advertised at true 13 lbs. How true is it ?

I've been using them for 3+ years--they're local to me. Both generations of wheels have been ok for me, but the new ones are a little more solid-looking.

[Brandon]

So which model of the D-Force wheels are potentially stronger?  The 5 or multi-spoke?

 

Yes I am in the market for another set of wheels and am disappointed the TD2's are no longer available.

My options for white wheels is severely limited...

[philstireservice]

So which model of the D-Force wheels are potentially stronger?  The 5 or multi-spoke?

 

Yes I am in the market for another set of wheels and am disappointed the TD2's are no longer available.

My options for white wheels is severely limited...

 

D-Force only makes a 5 spoke. The Jongbloeds are the multispoke.The Jongbloed has 14 attachment points = stronger design (think BBS)