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Old 09-02-2015, 12:12 PM   #21
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A custom shock can be set up to operate correctly without a bumpstop, but using the tub of the car as your bumpstop is not the right way to do it. Just like the OP, pull your springs Then measure how much you need to limit bump travel to keep the tire from crashing into the tub, then put some bumpstops in that match that length when they are compressed.
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Old 09-02-2015, 02:08 PM   #22
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Originally Posted by hector View Post
Agreed, tire rubbing is not ideal. So in your opinion at least a +12 offset for a NA with 10" wheels?
The 10" 6UL is a +25, so based on what I've been told from others running 10s and 275s competitively, you want an offset in the ballpark of +17. The exact offset is going to change with camber settings, so I can't give you a definitive number.
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Old 09-03-2015, 12:11 AM   #23
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So lowering the perches in lieu of removing the springs worked fine. Rattle springs are the same as no springs. Turns out I cut the arches high enough but the tire hits the fender at the front upon turning in compressed. And of course the rear edge of the bumper too. I'll fix all that. But I'm currently at 25mm o/s. If I do the 6 or 10mm spacer thing I guess I'll need to remove even more of that front edge metal. But it looks like I could also hit the firewall at the rear?
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Old 09-03-2015, 10:47 AM   #24
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But it looks like I could also hit the firewall at the rear?

A good way to test this is to make some spacers out of PVC or washers and place them behind the wheel, on the studs. Then you can cycle the steering/travel and see what is binding where.
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Old 09-03-2015, 12:07 PM   #25
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A good way to test this is to make some spacers out of PVC or washers and place them behind the wheel, on the studs. Then you can cycle the steering/travel and see what is binding where.
Agreed, although I could be limited by current stud length. But since I should only need a couple threads, temporary washers should work.

How have people handled the shortening of the bumper rear edge? Obviously I could just cut it and put something over the raw edge. Any tricks for refolding it instead?
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Old 09-03-2015, 06:31 PM   #26
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I just cut it with the cutoff wheel in the angle grinder, try not to inhale the smoke it makes your throat scratchy. Its foamy plasticy stuff, no sharp edge from cutting. You'll probably end up having to drill a new hole for the fender to bumper bolt there to move it because I've had to cut through that. I forget if thats an issue with NBs or not.
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Old 09-03-2015, 06:47 PM   #27
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Can confirm that i hit there on an NB with +36 15x9s wrapped in 225/45 RS3s.
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Old 09-03-2015, 07:15 PM   #28
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Quote:
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I just cut it with the cutoff wheel in the angle grinder, try not to inhale the smoke it makes your throat scratchy. Its foamy plasticy stuff, no sharp edge from cutting. You'll probably end up having to drill a new hole for the fender to bumper bolt there to move it because I've had to cut through that. I forget if thats an issue with NBs or not.
Yeah, after looking at all the crap behind it...doublers etc, I just hacked it off with a high speed air saw. I saved the existing bolt, but it may have to go if I wind up offsetting the wheel more.

I've used home made bump packers in the past because I didn't know where to buy them. Anyone have a source? (It's like a split urethane washer that sits above the bump stop.)
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Old 09-03-2015, 10:10 PM   #29
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So I got home yesterday and spent a couple hours taking out the spring and trying spacers and whatnot. I took a bunch of pictures but nothing all that great except this picture.



I was tearing the car apart when he got home and he went inside and got his tools so he could help...... turn a one hour job into two hours.

Anyhow, back to my inconclusive results from a bunch of sorry pictures. This shot shows the shock compressed to travel ring and there's 3.5" from spring seat to seat.
Coil bind according to Hypercoils calculation happens at 2.875". So I have about 5/8" left but no way to get that since the tire is already contacting the fenderwell.



This picture is with full bump and the tire straight. Of course this maxed out the travel ring to its tell-tale position. This would only happen of course with the car driving straight
and hitting a steep bump. Obviously I cut only enough out of the fender so the tire would tuck under it. There isn't any rubber build-up behind the fender but there are some rub marks.



This is the tire under full bump and with as much turn as I could get out of it. At this much steering angle it is pushing the shock down so this is not full suspension travel.



Same scenario as above. Obviously you can see that the tire is compressing against the shock mount. A spacer would have to help this situation out. Thing is though, how often is this occuring?
Maybe those that are destroying tires in a short amount of time are encountering this situation for much of the run. I can't believe this is the case for me. However, what you can also see in that picture
is that some of the rubbing can't be caused with this steering angle. Look aft of the shock mount. See the rub marks that don't align with the angle of the tire?



After this I put on a 1/4" (just over 6mm, +19 offset) spacer. The tire would tuck under the fender but not without some serious force. And turning the wheel would likely result in it being cut.
This test is inconclusive as the fender needs to be cut for better results. Since I am going to NB front steering and suspension components, except lower arms, I will need to cut the
fender more as the NB spindle or the bearing have an extra 5mm of track per side as opposed to NA so I will be close to the 1/4" spacer test I did. It looks like it will just clear the
cutting I did on the front bumper and it didn't rub on the back part of the fender/fenderwell area.

For the hell of it I put another 1/4" spacer (about +12) and the tire wouldn't tuck under the fender with the minimal cutting I did. Again, inconclusive.
Maybe after I cut for the NB components I will try again.

Here are a couple of shots of the tires. They have always corded on the inside first, even the 245's so I don't know if that's a factor of too much negative camber.
These tires were flipped at least twice. They now have 65 runs. The first ten or so were with the Koni's that had bumpstops. Looking at these I find it hard to believe that the rubbing
is seriously affecting the tires. Or that it's seriously affecting performance since it seems to be more bump induced than steering/roll induced rubbing.




This is a shot of the shock tower just after the Penske's were installed. Definitely does not appear to be anywhere near as much rubbing. So either the bumpstops on the Koni's were
working or I was running out of travel. And since they were re-valved Sport bodies with factory NA mounts, that's likely. I remember getting some terminal mid-corner push from
time to time with the Koni's. Not so with the Penske's. Although I get corner exit push with the Penske's but after a couple of guys have driven the car and not complained about it,
it must be driver induced. Hopefully car and driver will be getting better soon.

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Old 09-25-2015, 06:55 AM   #30
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OK, so looking at the 949 website they are taking pre-orders for a 15x11 wheel as well as the 15x10 they usually offer. Since it has been stated that the 15x10 was meant for a 245 tire, it confuses me that a 15x11 would be made with an additional 8mm (5/16") towards the body side of the car.

If fitting a 275 on the 10" is supposed to require about 8mm worth of spacers to avoid hitting the shock tower, why make a wheel with an additional 8mm pushing into that direction? Was this wheel meant for a Miata suspended car but not one with a Miata frame? Or one that has mods beyond that allowed in the typical autox car? Or is Emilio trying to boost sales for spacer manufacturers? =)
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Old 09-25-2015, 02:45 PM   #31
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Our 15x10 was indeed optimized for 245/40's. One can not raise offset but one can easily fine tune lowering offset with spacers. This is how you make a race wheel when the cars vary so much. For 245's, bolt on and go. For 275's, get the 15x11's. Bob Bundy is right here, offset need to be +20 or a bit lower for 275's regardless of wheel width. So our 15x11 is +20. That gives racers the option of fine tuning those last few mm with spacers. Bob's car has slightly relocated upper shock mounts (inward) so he can run a few mm higher offset than most.

The SuperMiata billet mounts we have in production are significantly narrower than OEM to provide a bit more tire clearance. The billet coaxial perch mounts will have optional spacers and 2.5 perches to work with just about any Miata specific damper.
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Old 09-25-2015, 08:47 PM   #32
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Whats that +20 work out to in backspacing at the edge of the wheel (not the bead).
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Old 09-25-2015, 09:02 PM   #33
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Quote:
Originally Posted by Leafy View Post
Whats that +20 work out to in backspacing at the edge of the wheel (not the bead).
https://www.rimsntires.com/specspro.jsp
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Old 09-27-2015, 01:52 AM   #34
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Emilio

Awesome linked on-line wheel/tire visualization tool.

Can I ask- at 4.25" perch height front...stock centered bushings...how much camber will NA get approximately?

I am concerned that if I use upper offset ISC bushing I'll contact springs..and lower slips...so keeping it centered until you (Emilio) come out with camber solution..and getting what I can for camber.

If enough camber can be had it will help with clearance - I am rolling my fenders now, and want to clearance for up to 275/35x15.

Thanks
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Old 09-27-2015, 02:44 AM   #35
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Yes 15X11 ET20 is right on the money maybe a thin ~3mm spacer to fine tune depending on a few factors their is really not much room to deviate much. I am currently running 19.05mm offset and it required leaning the shock tops in ~8mm by slotting the stud holes in the shock tops to offset them. With 11's the sidewall of the tire will hit the spring as you add wheel cut. 2.25" ID springs over 2.5" helps a little the rest of needed clearance was leaning the shock in. it rubs the inner fender by the shock but not enough to damage the tire or wear it any faster than normal. leaning the shock changes the motion ratio on the shock but its a really small amount. You won't get away with offset upper bushings for adding camber need to add camber with the bottom arm somhow.
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