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Hi Guys,
My trackday NB, is experiencing a small amount of front internal wheel arch rubbing...just on the Strut Tower mount.
I have a reasonable clearance to guards, not rolled.

Wheels are 15x7 ET38 with 225 width R specs.
Camber is 3.2 deg...but could go more in the future.

Rubbing only happens under heavy weight transfer.

HSD Monopro 9kg/6kg Coilovers...upgraded (front only) to Eibach 10.5kg/mm springs.
Coilover Adjustment...Fr=Hard Rr=Middle
Bigger Sways Fr/Rr (both middle)

Ride Height was 4-1/4" and 4-1/2"...jacked it up 3/8" temporarily, to minimise rubbing.

My next step, is to fit Hub Centric Wheel Spacers just on the front...maybe 15mm thick....(effectively changing the offset to 23mm).

There are 2x Hub Centric Wheel Spacer options:-
1...4x holes...ie. fit new extended studs in the Rotor, then slide the spacer and wheel onto the studs and clamp with lug nuts.
2...8x holes...ie. secure Wheel Spacer to the Rotor with existing stud/nuts, then secure wheel to Spacer with the other 4x new studs/nuts

To me, I can see that the 8x stud method is probably more secure...but is possibly overcomplicated and heavy.
whereas
the 4x stud through-bolt method is less complex, but possibly a weaker connection.

My query is:- has anyone had experience with the through-bolt method??

Thanks,
Jim

Neither option is ideal. Personally I’d get better wheels, with a better offset and wider to carry the 225s better.

15mm is a lot for a slip on spacer on a track car, which sees way higher loads than your typical stance boi hard parker..
The bolt on spacers are a pain as you have to take the wheel off to torque them up, meaning a) it’s a two man job with someone on the brakes to stop the wheel turning, and b) you’ll most likely need to torque the spacer again after first session getting it hot, meaning wheels off, second person etc, which is a lot more inconvenient than just walking around with a torque wrench when the car is sitting between sessions.


Also if you are thinking 15mm which would make effective 23mm offset, then with 225 R specs I think you will be getting guard rubbing instead..
I have 215 R specs on +25 and I needed guards rolled a little and still get rubbing. I have about 3-3.5 camber on front

IMO, the rubbing on the wheel arch is more to do with not enough spring rate than offset issues.. 10.5kg springs up front isn’t a lot when you start talking sticky 225 R specs.

Hub centric - impressive sounding nonsense.

Bolt-on spacer - adding weight, complexity, and risk. Think of the failure modes, and you start thinking there has to be a better way. There is.

Slip-on spacer - cheaper, lighter, lower risk. Only failure mode is failure of wheel studs, which will probably have to be replaced by stronger lengthened studs anyway to get sufficient thread engagement with the spacer in place.

I had this problem, fixed by dialling up the ride height a few mm. This was of course rubbing on the top of the wheel arch, which I assume is the rubbing you complain of. In which case the spacers will do little to fix. If you go for stiffer front springs, you might have to think about the rears too.

15mmx2 is a significant increase in front track that will affect the handling, I'd expect the car to become more 'oversteery' unless the back was done too.

225s seem pretty big on those wheels, if you want/need that size I'd be looking at new wheels anyway. New wheels, longer wheel studs (with or without spacers), a bit more ride height and/or stiffer front springs, and you are looking good.

You have both spring perch and damper length adjustment on those coilovers. Extend the length of the shock ~5mm, or whatever is necessary so the wheel doesn't meet the arch at the top of it's travel. Then drop the spring perch to move back to your desired ride height. Job done, no money spent!

205 is a better size for track work on 15x7s. Leave the wheels and change the tyres

Thanks guys,
Just the detail I was hoping for....particularly the bit about retightening the Bolt-on style spacer.

After removing the Plastic wheel arch liners and raising Ride Height 1/4"...the Rubbing appears to be limited to the Inside top edge of the Tyre, on Strut Tower 'bulbous' area.....(it's polishing the tyre and the Strut Tower).

So, maybe I could get away with a much thinner spacer...say 5mm....which would hopefully eliminate the rubbing altogether and limit the design issues discussed....ie...oversteer etc. and it may also allow me to re-use the existing Wheel Studs...instead of going to the extended bolts.

At the time I replaced the HSD 9kg/mm fronts....I got talked into the 10.5kg by the Eibach dealer.

I was originally thinking 12.5kg, which according to your comments may help.
If so, I will need to replace the rears as well.....I'm thinking 8.93kg (currently 6kg).

That would then be 700lb/in (12.5kg) front and 500lb/in 98.93kg) rear.

Your comments are appreciated.

Cheers,
Jim

P.S. At sometime in the future I want to fit the Bauer ELBJs, I had on an earlier car, to grab some more Camber.
Therefore the spacer would need to be wider, in that case.
...or maybe the geometric arc produced, by fitting the ELBJ...would make the top of the tyre rotate down below the Strut Tower bulbous area and clear the rub zone.

Thanks ManiacLachy,
I missed your comment.

The HSD Monopros have ride height adjustment, Spring Preload adjustment (via Spring Perch) and 16 clicks soft to hard Damper adjustment.

When you say "extend the length of the shock ~5mm"...
Can you elaborate please.

Cheers,
Jim

pdsman53 wrote:Thanks ManiacLachy,
I missed your comment.

The HSD Monopros have ride height adjustment, Spring Preload adjustment (via Spring Perch) and 16 clicks soft to hard Damper adjustment.

When you say "extend the length of the shock ~5mm"...
Can you elaborate please.

Cheers,
Jim

There's a lot of misinformation out there about adjusting ride height, and it can be confusing. I'll try to explain as best I can.

You have 2 points of adjustment on your shocks, the spring perch (in the middle), and the shock length (at the bottom). The bottom adjuster is not "height adjustment", it's "shock length adjustment". It will affect ride height (as will adjusting the spring perch), but it's purpose is to make the entire body shock longer or shorter.

Shocks like Supermiata Xidas and Flyin' Miata Fox only have spring perch adjustment, the shocks are one piece as they were designed to fit the MX-5/Miata specifically, they are made at the correct length. BCs, Ohlins, HSDs, MCAs, etc are designed to work on a variety of platforms, so the shock length is adjustable to suit a range of cars and the length needs to be manually adjusted to suit each one.

The right way to set your ride height is to first set your shock length without a spring or bumpstop, so at full compression your wheel does not bottom out on the car. At full compression the shock should run out of compression travel before the wheel contacts the car. Then forget all about that bottom adjuster, imagine it's fixed, and adjust height by altering the spring perch (unless the spring is completely unbound at full droop - then more work is needed).

People incorrectly think adjusting the spring perch aka adjusting pre-load will affect the way the spring rate, with a steady rate rate spring it won't. It'll be a 9kg/mm spring regardless of how compressed it is, 9kg will result in 1mm of travel, 21kg will result in 3mm of travel. With a variable rate spring that would change, but that's not what we're playing with.

To set your ride height, raise the car by extending the shock length via the bottom adjuster by say 3-5mm (just enough so you don't contact the body), now the wheel has further to travel before it will hit the car, but shock still has the same amount of compression travel. This has the affect of making your shock reach full travel at the bumpstop sooner, hopefully before hitting the car.

Then lower the spring perch adjuster to lower the car to the height you want. This will alter where your car rests along the shocks complete travel. You basically swap a little droop travel for compression travel.

Hopefully that made some sense?

Thanks Maniac,
That makes sense.

Note:- The HSD install instruction is :-

"•For coilover setups, please ensure you have 0mm spring preload. The spring seat locking collar needs only to hold the spring captive.
•Height adjustment should be made by winding the damper in/out of the bottom bracket."

Are you suggesting that HSDs method is incorrect?...maybe their setup is a conservative one, for the road use ??

When I initially installed them, the wheels were off and the car supported on jackstands and endlinks released...the springs could be rotated in the perch.
This set was migrated from an earlier NA I had...so I left the bottom height adjustment...and they ended up @ 4-1/4" and 4-1/2" Ride Height.

From your initial comment:-
You suggested that the "easiest fix" would be to :-
a...lengthen the damper (~5mm), via bottom adjuster.
b...regain ride height by lowering the spring perch adjustment (presumably 5mm).

Correct me if I'm wrong...
I assume....to regain my ride height, the car would need to be on the ground (ie. preloaded springs), to make the adjustment.
If so...with the ~1000kg car on ground...then approx. 250kgs on each corner....therefore for a 10kg/mm spring, it should be compressed 25mm.
Therefore, for my ~5mm adjustment....the springs should still be compressed about 20mm.

That sounds fine...except that the Springs were initially "only just captured".
.....is there a situation where the Spring could flop about (not captured)......say on a bumpy road??

If not...then everything is hunky dory....."easy fix"....great, finished !!!

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But, If the springs could flop about...sh*t!!!

Then I should use your "correct method".

So, to do it correctly...what I should do is :-
1...wheels off, car on Jackstands
2...full droop (release swaybar endlinks etc.)
3...Fit Dampers (without springs/bumpstops)
4...adjust Damper length on bottom adjuster...to clear bodywork
5...fit springs/bumpstop etc. and preload to desired ride height.

..(I guess this is when corner weight adjustment would be done, if I had the gear?)

then...wheels on, remove jacks and adjust swaybar endlinks (no preload).

Your comments would be much appreciated.
Cheers,
Jim

P.S. how do I determine the correct Bumpstop length?.
..is it a matter of:-
If it gets destroyed...it's too long?
and
If there's no damage...it's too short??

It's complicated, right?

pdsman53 wrote:Are you suggesting that HSDs method is incorrect?...maybe their setup is a conservative one, for the road use ??

A lot of manufacturers say to do it that way because it's simple, one point of adjustment, and easy to communicate. I do think HSD's prescription of zero load on the spring is a bad design and could be an issue for my method on your car. MCA are the ones who detailed it the way I laid it out for you.

You're right, you don't want the spring floating loosely at full droop. Maybe very slightly, but once you've let it out all the way so the spring is extended dropping the perch further so that it could tip over will be a disaster. Some companies use helper springs in that case, as a spacer and to keep the spring in place with very low rate.

Try it the way I've suggested to as far as you can go. But keep the spring captive (or very slightly loose). I wouldn't worry about pulling the shock apart at this stage.

Actually, do it in reverse, lower the spring perch as much as possible while keeping the spring captive, see if you get any drop in height (you'll need to let the suspension settle a little, maybe a trip around the block). Then hopefully you can extend the shock to raise the car.

If that doesn't work you could look into shock spacers that go between the top of the shock and the body. https://www.topmiata.com/product/top-mount-spacers/

FWIW, I had HSDs and hated them I wasn't very impressed with them, but mine were also knocking after a couple of months, I sold them pretty quickly (with full disclosure about the issues)

See:
https://mcasuspension.com/technical/11/Ride-Height-Adjustment

pdsman - I also have MCA pdf's with diagrams showing all about the adjustments discussed here. PM me with your email address if you want them.
Cheers, Gregg

RS2000 wrote:See:
https://mcasuspension.com/technical/11/Ride-Height-Adjustment

pdsman - I also have MCA pdf's with diagrams showing all about the adjustments discussed here. PM me with your email address if you want them.
Cheers, Gregg

Good link, thanks RS2000.

I understand more now, than I did prior to this discussion....that's a good thing!

Moving forward, I'm going to fit some bolt-through Wheel Spacers....but limit them to 6mm, which will hopefully eliminate the sidewall/shoulder rub.
(...and hopefully, later on, it should allow me to gain some additional Camber, via the ELBJs I have).

Then I'll have a crack at your Damper/Spring adjustment suggestions....which should hopefully gain back the ride height.
(...without having to buy new springs...that's a win).

Thanks again for your help...it's invaluable to be able to bounce ideas in layman terms, off guys with more experience.

Cheers...Well done.
Jim

Hey Maniac.
...the Green Machine gave me a good tip a while back, on Coil Spring Spacers.

"Chop them out of Kitchen Plastic Bread Cutting Boards".
I thought that was a great idea.

pdsman53 wrote:Hey Maniac.
...the Green Machine gave me a good tip a while back, on Coil Spring Spacers.

"Chop them out of Kitchen Plastic Bread Cutting Boards".
I thought that was a great idea.

To spell that out a bit, the use I am familiar with is to cut them to the shape of the top mount, and use them between the top of the top mount and the underside of the shock mounting surface on the car. This drops the whole shock assembly including spring, and depending on the thickness of the spacer, may require longer studs/bolts to ensure adequate thread engagement. Useful if you are running something like ... umm ... drop spindles. That will raise your ride height without changing droop/bump movement, but that is not the problem here it seems.

The wheel spacer will move the tyre out away from the springs/shock, and should reduce/eliminate rubbing. But adding in more neg camber will reverse that, and may re-introduce the rubbing.

In all this messing around, you should check if you are running NB8B front upper arms with the reinforcement plate that can contact the shock body and damage it in certain circumstances. I have ground mine out so the problem will not arise (I think there is a photo on my build thread). The problem seems most severe on very low cars running lots of neg, and perhaps certain brands of shock which are of slightly wider diameter.