The SERIOUS Wheel & Tire Thread

[The Dark Side of Will]

Updating from The Mule thread, because I thought I had, but had not.

High tech stud installation:



Adapter with studs:



Adapter with studs storing washers and nuts:

[The Dark Side of Will]

I used the wheel adapter this morning and pulled some numbers. The outer lip of the C5 wheel will stick out 1/2" further than the outer lip of the Grand Prix wheel.

Here's my measurement rig:



The sockets are 1.500 +/-.005 tall and the measurement at static ride height is 1 5/32, so the outer lip of the Grand Prix wheel is actually just under 3/8" inside the outer lip of the stock fender.
I repeated the measurement with the Grand Prix wheel with the suspension at full droop. That measurement is 1 3/4".
The corresponding measurement with the C5 rear wheel is just under 2 1/4"... so the Corvette wheel will stick out 1/2".

Adapter installed:



Would need slight modifications actually to work:



C5 wheel in place:



Clearance to the strut:



Not quite a banana for scale:



That is the narrowest gap between the wheel and the strut. I could gain 1/8" of clearance by snagging a new pair of Koni struts and modifying them to have the sleeve seat on the original spring perch weld rather than on the clamp.
I currently have 325# x 12" springs. If tire clearance to the spring perch is a thing, I could step down to 10" springs to resolve that.

Beefy rear view for a Fiero, but no wider than stock on a C5:



Next step: grab a cheap @$$ Sumitomo 285/30 from Tire Rack and look at tire clearances.

Current tires are 245/50-16's and calc to 25.64" tall.
The 285/30-18's calc to 24.72" tall... going to lose a bit more gear than just the 3.61 to 3.94 swap. The gear swap will be 9% and I'll gain about another 4% RPM from the tire swap. But I'll also gain 4% in acceleration
The new tires will be 0.92" shorter than the old.

[The Dark Side of Will]

At a ride height of 15 7/16.

Height difference (245 on right is also at ~halfway through its tread depth)


Width difference (both are Sumitomos)

I have a feeling the tire will rub on the spring.

Your feelings are invalid.

However, it's really close, and probably would rub on a max effort corner. My finger won't fit. I'll see if I can get a better measurement, but I'd guess a 1/4-5/16" gap before initial contact. Initial contact would be harmless.
Also, as mentioned above, I can raise the spring perch over 1.5" by swapping to 10" springs. I'd probably up the rate to 400 in an effort to further copy-cat Steven, however.




Not too hideous, but needs moar low




No more stick-outy than the current 245's. If anything, it looks a smidge pokey-stretchy by comparison. I need to upgrade to a more expensive 285/30.



A smidge pokey-stretchy:



Needs moar low; ride height is 15 7/16 (center of axle to bottom edge of fender lip):

[The Dark Side of Will]

Took The Mule's suspension apart today. I surprised myself slightly by getting the spring out without unbolting anything but the top of the strut. I was *amazed* that after being installed close to 15 years, the spring perch still turned freely on the sleeve.

The 6 5/8" metal to metal travel limit checks out.
Full droop ride height: 19 5/8"
Metal to metal contact ride height: 12 1/4"
Bump stop *contact* ride height: 13 11/16"

ETA: "Metal-to-metal" means that the top of the strut body just touches the bottom "bell washer" that installs under the strut top bushing. The bell washer is there the retain the end of the strut approximately where it needs to be if the bushing comes apart. A really hard hit would both deflect and maybe tear the bushing as well as possibly flattening the bell washer, so this isn't he "structural contact" ride height that would do serious damage to the tub or the strut... that's maybe 1/4 - 3/8" more jounce travel that what I measured.

It's weird that the difference between the bump stop and metal-to-metal ride heights is 1 7/16", as the bump stop measures a smidge over 1 3/4". I may have compressed it *slightly* when positioning the suspension and could be off on the ride height a little bit, but I don't think those effects can turn 1 3/4 into 1 7/16.

ETA: I just realized that this discrepancy is there because the top of the bump stop fits into the bell of the bell washer, so the bell washer cuts down on the difference between metal-to-metal and touching the bump stop.

Full droop travel:



Metal-to-metal contact:



Gap to the outer fender lip:



Gap to the rear trim strip:



Gap to the front trim strip:



From the four photos above, rubbing on the front trim strip is probably the first contact point, but it can be mitigated by moving the wheel back in the wheel house a bit. An adjustable trailing arm could do this on an '88 and a custom fully adjustable control arm could do it on an early car.

2 7/8" from the tread surface to the rear fascia:



Can't really get a comparable measurement, but ~2" for the corresponding measurement to the quarter panel:



Inner lip clearance to everything in front of the axle--nothing is even close to the top of the tire:



Inner lip clearance to everything behind the axle--I can still get my finger between the top of the tire and the wheel well liner:



The toe link is danger close to the frame rail:



I bumped my spring rate up 200 ppi, shortened the springs by 2", lowered the car slightly to a 15 3/8" ride height... and the spring perch barely moved



The spring is seated directly against the strut top plate, so it won't be going up any more. If I build a fancier top mount with an axial load spherical bearing and a needle bearing set to let the spring squirm, the perch could come down another 1/2" easily. Shoot, I may have to go to 8" springs.

Also, flipping the strut top plates, or making new ones that put a spherical bearing strut top mount ABOVE the top of the strut tower could lower the metal-to-metal contact ride height by *maybe* as much as 2", but that really just means that the current metal-to-metal height becomes the new bump stop height. Still not bad, though. I haven't run the numbers yet to see if I can get 8" springs that will have enough travel from ~15" static ride height to hit the bump stops a meaningful distance before they coil bind.

If I could get the current metal-to-metal height to be the new bump stop height (unlikely that everything can package in the space available), then a 14 3/4" ride height, which is about what Steven's running, would still have 2.5" of compression travel before even touching the bump stop. With 550# springs, that's 1375 extra pounds on the outside tire in a corner... that's a LOT of cornering g's!

Currently, at 15 3/8", I'm only 1 11/16" off the bump stops.

[The Dark Side of Will]

New wheel adapters arrived while I was in London, ordered from here: http://www.motorsport-tech.com/wheel_adapters.html
Made in the USA and CHEAP, too! $70ish each. The other places I looked at were $90-$100+



Now both 285's are mounted:

[The Dark Side of Will]

I bought some fender washers from McMaster-Carr and bolted up the C5 ZO6 wheel.
I used stacks of three totaling 0.180" to space the wheel out enough to clear the strut.

The base C5 outer lip position was just a hair under 2 1/8".
The C5 ZO6 outer lip position was just a hair under 2 7/16".

This means the ZO6 wheel sticks out 5/16" further with 3/16" of extra spacer. This means that with the same spacer thickness, the ZO6 wheel would only stick out 1/8" more than the base C5 wheel. However, the base c5 wheel has that weird lip profile I discussed above. In light of that, in terms of tire fitment, the difference is probably 3/16" or 1/4".

EDIT: I can't do simple math. The C5 ZO6 outer lip with 3/4" spacers would be in the same position as the base C5 lip with 1" spacers. Fortunately, 3/4" is still a workable adapter thickness. I'm tempted to order one 3/4" thick so it will be ready for test fitting when I get my struts modified.

[pmbrunelle]

So I'm adding stuff to my Rockauto cart, and I'm optimising to avoid parts coming from warehouse A, B, C, etc...

Dorman 610-323 would have added an additional shipment to my order.

Through Rockauto, which led me to Raybestos, I found that Raybestos offers (what they claim to be) an equivalent part:
Raybestos 28879B

Raybestos.png (149.44 KiB) Viewed 3580 times

Following the link to the product page, the few specs that Raybestos does share appear to be equivalent to those of the Dorman 610-323.

I believe I have genuine Dorman studs laying around, so when I receive the Raybestos studs, I should be able to compare them.

****************************************

Oops, RA only has 5 Raybestos studs available, but I need 10. I guess I won't be ordering these right away; I'll try to bundle them with a future order.

[pmbrunelle]

I ended up getting Dorman 610-323, so no evaluation of Raybestos.

********************************************************************************

I was able to order the Enkei PF05 wheels through a local distributor.

Leadtime is 3-4 (unknown really) months, subject to the standard coronavirus delays.

I don't mind that the leadtime is unknown, as the payment terms are cash on delivery, so if for whatever reason there's a delay or problem (Enkei factory burning up, or the boat sinking), I won't be chasing after my money.

[pmbrunelle]

What's the chance my 255/40R17 tire with 40 mm offset will clear the stock (or KYB) spring perch?

Car is away in winter storage, and my wheel/tire combo won't be ready for a number of months.

I was thinking I could start working on a pair of struts with coilover sleeves, but maybe it's not necessary from a perch clearance perspective?

[The Dark Side of Will]

That's really close to the same height as my 285/30, but I couldn't tell you how it will work relative to the stock spring perch.
It'll also depend on the wheel offset.
Do you have 17x9 or 9.5?

A 17x9-30 should push the tire out to the "just barely clears the fender" point, which would give you maximum clearance to the spring perch.

[pmbrunelle]

17x9 with 40 mm offset.

I was hesitant to buy a pair of stock (well, KYB) struts to test if my tires would clear the stock perches, because if the stock strut didn't work, I would need to have the weld turned into a shoulder by fieroguru. In that case, it would be a headache to send him my struts to have him modify them, and then ship back...

However, I just did a feasibility study to see if I would be able to turn the weld into a shoulder myself.

IMG_5705.JPG (325.91 KiB) Viewed 3498 times

YES!

It's a workable setup as long as I use a socket as a counterweight for the taco clamp.

Since it seems like I can make any of these three configurations from a new stock strut:
Stock perch
Weld turned into shoulder
Weld completely flattened with sleeve on taco clamp

I may as well move forward and buy these KYB struts.

[The Dark Side of Will]

Congrats! New industrial capabilities!
I wouldn't have thought you'd need to spin the thing fast enough for the balance from the taco clamp to affect lathe operation.

And with a 40 offset, you can add up to a 10mm spacer if you need a little more room

[Shaun41178(2)]

Been thinking of getting some rota slipstream.

Two options.

15x8 with a 40 offset
16 8 with a 48 offset.

88 formula with guru coilover style strut.

Right now I have a 16x7 with 35mm offset line I rpf01.

Online wheel calcs say the 48 offset has the rim sitting 26mm more inboard than the konei.

I am assuming they should fit with a 9 inch wide tire?

[The Dark Side of Will]

16x8 with 25 offset from a '90's Grand Prix misses the knuckle by maybe 1/4" on an '84-'87 car. I don't think the '88 knuckles allow quite 23mm more wheel clearance there, so I think you'd need a spacer to run 16x8 w/ 48 offset.

The larger wheels can be run with high offsets like that because they go "over the top" of the knuckle. The 16's do not.

[Shaun41178(2)]

I used a telescoping gauge to measure the distamce between my konei wheel 16x7 35 offset to the strut and knuckle assembly.

I had about 1-1/16 inch clearance. The offset calc said the 16×8 48 offset would sit in about 1 inch closer. That seems very close to my measurement which means with the tire it might not clear.

I'll prob have to settle with the 15x8 with the 40mm offset

.https://www.1010tires.com/Tools/Wheel-Offset-Calculator#

[The Dark Side of Will]

With those numbers, you'll end up with ~1mm between the wheel and your knuckle. Will be interesting to see if it scrapes during hard cornering.

[Shaun41178(2)]

This is for the rear not sure if that matters

[The Dark Side of Will]

I was referring to the rear.
You just looking for drag wheels?

[Shaun41178(2)]

Yes

[Honest Don]

I'd do 15s and a set of these:

https://www.jegs.com/i/Mickey-Thompson/ ... 0/10002/-1


https://www.youtube.com/watch?v=ZUjyiiThHkw