18x11 (R) trailing arm clearance
 

Many folks have been asking me how much clearance there is between my 18x11 +48 offset rear wheels, 295-30 tires and the tubular trailing arms. Attaching a good pic. You can see that it's pretty tight. You can squeeze a 305-30 Hoosier on there as they're just a tad wider than the Pirelli P Zeros (a very wide tire in this size), but a 315 will not work.

Regards,

Gene
PS- Thanks for the pic, Daniels.

Excellent contribution (as usual) Gene. Thanks!

heres a shit from the outside. Not that relevent to the topic but shows how much needs to be removed from the 1/4 pannnel.

Is that 18x11 wide wheels and 295 tires on all fours ? Did you pull the fenders on the front ?

I know that he is running 18"x10" on front with 285. THe 18"x11" is only for the rear.

I wish they made aftermarket trailing arms for the FC. Right now my 18x10 are CLOSE (couple of mm) from the trailing arms.

It looks like there is some rubbing between the tire and the trailing arm? Or was that something else?


On an FC- if you have power (300hp/tq+) you will get rubbing between the tire and the trailing arm, even with 1/4" of static clearance.

Gene,
If'n I may chime in. I run Brads old 17x11 CCWs in the rear 50mm offset with 275 HooHoos.
I have coilovers and the M2 trailing arms. Suspension travel will affect interference issues.
At near full droop on my car the tire rubs on the trailing arms. And I have the trailing arms shimmed all the way inboard at the chassis end. When on the track tire and hub flex can eat up several mm of clearance. I found this out the hard way. I'd estimate I had 2 mm of clearence between tire/wheel and trailing arm with the suspension statically loaded. Then I went to VIR and with the rear suspension dynamically loaded up (acceleration and cornering) I did groove the trailing arm on the drivers side to a depth of about 1-2mm. So I shimmed the chassis end of the trailing arm over some more and the problem went away.

So just a word of caution when we start speaking of clearences in the 1-2mm or the thickness of a sheet of paper one may not be accounting for all tolerances.

Food for thought,
Crispy

You're too kind :)

Gene

No, that's fingerprints.

Gene

Good point. I'll keep an eye on it. May be exacerbated by using a taller sidewall ( a la 305) as well.

Gene

I would be very leery of those tires rubbing when on the track. Tires move around a lot due to sidewall flex. Granted the most movement is at the bottom of the tire where the contact patch is, but the entire carcass moves around during high cornering loads. I'd shoot for more space there.

Here are some pics showing my 245/45/16 tires during cornering. At rest the sidewalls stick out almost a 1/4" past the wheel lip.
https://www.rx7club.com/attachment.p...hmentid=110930

https://www.rx7club.com/attachment.p...hmentid=110931

True true, but the 16's also have a much taller sidewall allowing more flex.

True the 17" or 18" should not flex as much but fact is a few fractions of an inch is not enough clearance during cornering. If 17" or 18" tires didn't have sidewall flex during cornering none of us would ever have the need to run negative camber...

Noted. Will have to test them out. The good news is that the picture is somewhat misleading. That is, there's about a finger's width of clearance between the tire and the trailing arm near the rim (i.e. where the tire mounts to the rim). That's approximately 1/2" (depending on how large your fingers are, of course). I don't expect the tire to flex more than 1/2" in that area (likely at max section width, though), but Crispy's comment about hub flex may certainly play a role too.

In summary, don't buy 18x11's with +48mm offset (and wide tires) for track use until I can get some data.


Thanks guys,

Gene

You might be surprised. I've got rubber marks on my stock trailing arms from one of my 10"/275 combos... either the 17x10 +44 Fikses w/ 275/40's or the 18x10 +42 BBS w/ 275/35. Nothing that looks like rim contact, so i'm not too stressed about it.

back from the dead ;o)

This question is for Gene and Crispy,

So to generalize, the main issue here is the trailing arm clearance correct (assuming that we are talking about ~2.5" springs)? Ignoring the trailing arms, how much of a gap would you say there was between the coils and the tires on your car in the rear? What diameter coils are you running and what tires are you currently using, this thread is pretty old so you may be using different rubber now?



thanks,
Rob

The coil diameter should be a non issue in the rear. The coils sit above wheel/tire in back.

damn, how did I not notice that. I just went out to the car and verified it.

-Rob

Wanklin,
So what would your question then be? I've run 275/40 R17 Hoohoos on 17x11 CCWs with 50mm offset and had rim to trailing arm contact (aftermarket M2 arms). I reshimmed the arms all the way inboard and I now have enough clearance. Minimal 1-2 mm but it's enough. And FWIW the rubbing was only under severe dynamic loading. Just enough flex in the suspension bushings/joints and wheel rim and bearings for thre rim contact the trailing arm. I can load the suspension up pretty good on Hoohoos :D On the street I run the Kinesis K58 18x10 rims. I'm not sure what the offset is but IIRC it's 50mm also. With a 285/35 R18 Bridgestone Potensa S02A's. No interference issues with trailing arms.
HTH,
Crispy

It looks like the collar could be an issue though, it's tough to tell with the car on jackstands.

What would you estimate the gap is between the tire and strut assembly? I appreciate your clarification on the trailing arm clearance and offset. I am working on something that will eliminate the trailing arm issue, which is why I ask about the strut clearance.

Also do you by chance know the true width of the rim?

last question, what did you do to your fenders to make your current setup fit?



thanks,
Rob

I'll take a look this weekend and let you know exactly

sorry I don't. Both wheels (CCW and Kinesis) were bought used with tires mounted. A call to either vender will most likely get you an answer

In the rear, a little bit oif fender roll at the upper most part of the lip. Approx. a 6 inch section. Rolled them myslef :)

Crispy