Custom widebody wheel fitment... (1g coilover/offset)

[Volume Eight]

a little history...
I just recently landed a sponsorship from a new company starting up locally. Its a 17,000sf custom shop, this place is insane. Has everything you could imagine as far as state of the art equipment, with some of the best body/paint/etc. guys ive seen. I dont think it will be long until theyre in the spotlight, hopefully with my car!

the good stuff...
Now they want to build out the car in the direction of show, but its my job to select the right parts to keep the car able to perform while maintaining a show quality look. So far we are planning to build a custom widebody kit with a sick paint scheme, fixed projector headlights and more. (i dont want to spoil it). Keep in mind that they are going to sponsor the car for Audio - Interior - Paint - Rims - Body Kit. Everything else is pretty much my responsibility as well as selecting the parts.

the problem...
Naturally, the most important and difficult part is in selecting the right tires and rims, and this is where i need your help. To suit the purpose of show without sacrificing TOO MUCH performance, i selected an 18x9.5 rim. I know, i know, "how could you put that size on a 1g", "theyre too heavy", "that would take alot of modifications" blah blah blah. The problems are already noted, this is why im looking for a solution...

the solution?...
As far as weight is concerned, Axis Reverbs come in an 18x9.5 with a 20mm offset and weigh in at 22.5lbs. I can live with that. For rubber, i was looking at BF goodrich g-force Drag radials size 265-40-18. Fitment is obviously the issue. I calculate a total backspacing of 6.5. I know this is excessive. There are still options. Spacers, adaptors etc can bring this to a reasonable backset.
First-Rubbing on the suspension in front is a major concern, so coilover choice is critical, as i still want to be able to accomodate an aggresive dive/squat. Here i was thinking of either Koni/DSS or just JIC both at stock ride height. I want to go for a spring rate of 325lbs in front and about 500-600lbs in back. Im just not sure if i will clear my huge diameter in a strong dive/squat. help?
Secondly-The offset. After spacers/adaptors the offset would be damn near 0. So i imagine i would need a new set of wheel bearings & axles every, say, 10 miles? Is there any way around this?

I know this is a ridiculously long post, but i really want to make this happen. I couldnt bear to see a widebody 1st gen where the tires are sunk about an inch inside the giant fender flares. I really want this car to be amazing, maybe even grace the cover of a magazine(not SCC) and give DSMers another reason to be proud to say they own one.

So thats all i have to say... now lets make this happen.

 

[wret]

I usually try to stay out of 1g discussions but...

What makes you thing 265/40/18's on +20 offset wheels won't fit?

Sounds like you have you're spring rates mixed up.

 

[jtmcinder]

I, too, am weak on 1Gs, but I suspect that 265/40/18 will fit on a 18x9.5 +20mm without a spacer. Another option, if the widebody is up to it, is 285/30/18 on 18x10.5s +12mm, which has the advantage of having a smaller-than-stock diameter, instead of larger-than-stock. Thus, it gives you better gearing. And 285/30/18 just looks plain nasty on a DSM or Evo.

If you replace the wheel bearings at the start of each season, then you should be OK. Just do it every year no matter what and then forget about it.

As to the springs, I have heard of 1G drag-racers running those sorts of numbers. From what I understand, 1Gs have less anti-squat geometry than 2Gs, so they have to use more rear spring. (1G motion ratios are also more similar front-to-rear than on a 2G, which is why 2G people always freak out when 1G people post their spring-rates.) Just make sure that the shocks are up to it. You will need a ton of rear rebound damping (and a decent amount of front compression) or the car will pitch on every shift. Don't want to break loose in every gear, right?

- Jtoby

 

[Greg Collier]

As to the springs, I have heard of 1G drag-racers running those sorts of numbers. From what I understand, 1Gs have less anti-squat geometry than 2Gs, so they have to use more rear spring. (1G motion ratios are also more similar front-to-rear than on a 2G, which is why 2G people always freak out when 1G people post their spring-rates.) Just make sure that the shocks are up to it. You will need a ton of rear rebound damping (and a decent amount of front compression) or the car will pitch on every shift. Don't want to break loose in every gear, right?

- Jtoby

I totally agree with Jtoby. Just make sure and compress your shocks (less) the springs to the bumpstop to calculate your clearance to the body, ie. flares, etc.. It would be a shame to damage any of the new work...

 

[JrCRXHF]

i am along the same lines i want the widest possible tire and wheel combo to fix on my 92 laser AWD with D2 coilovers for next summer autoX. and i was thinking of spring rates on the car around 550lb up front and 650lb out back. i know there springs come in Kg but i will convert the spring rates just before i buy.

let me know what you guys think. i wan my DSM to be just as good as my CRX in the turns.

I don't really mean to jack the post but it is along the same lines of wide tires.

please post some pics to if possable.

 

[Volume Eight]

What makes you thing 265/40/18's on +20 offset wheels won't fit?

Because after calculating a 6.5" backset(with tires on the rims), i figure there will be clearance/rubbing problems inside the wheel well especially at lock in front. I believe Greg runs a 5.5" with a tight fit if om not mistaken... So i figured a 1" adapter would correct the backset, however then the offset would be equivalent to -5.4mm offset. That worries me on a car that was intended for a +46mm offset. So i was hoping to find someone to clarify from real world applications?

Another option, if the widebody is up to it, is 285/30/18 on 18x10.5s +12mm, which has the advantage of having a smaller-than-stock diameter, instead of larger-than-stock. Thus, it gives you better gearing. And 285/30/18 just looks plain nasty on a DSM or Evo.

If you replace the wheel bearings at the start of each season, then you should be OK. Just do it every year no matter what and then forget about it.

Jtoby, I had thought about 8x10.5 believe it or not, but they only come in a +35mm offset, and have a 2 1/2" lip, so inside clearance would be even worse. Is there still a way to make it possible?

As far as replacing the wheel bearings every year, that is doable, what about other drivetrain parts? Should i worry about axles, or even brakes being ruined due to the strain placed on them?

I totally agree with Jtoby. Just make sure and compress your shocks (less) the springs to the bumpstop to calculate your clearance to the body, ie. flares, etc.. It would be a shame to damage any of the new work...

Do you feel that konis and DSS coilovers would be adequate. I was thinking of custom ordering a longer spring from DSS, would this help, or is it unnecessary?

I don't really mean to jack the post but it is along the same lines of wide tires.

THIEF!


Thanks again for all the help guys, i really appreciate it. This is something im really just starting to learn about.

 

[wret]

Because after calculating a 6.5" backset(with tires on the rims), i figure there will be clearance/rubbing problems inside the wheel well especially at lock in front. I believe Greg runs a 5.5" with a tight fit if om not mistaken... So i figured a 1" adapter would correct the backset, however then the offset would be equivalent to -5.4mm offset. That worries me on a car that was intended for a +46mm offset. So i was hoping to find someone to clarify from real world applications?

I don't think you need to worry about the backspacing but those tires will be way tall. You will need to go down at least to 35 series for that wide a tire. And, as jtoby indicated, if you go any wider than 265, you will need to drop another step in sidewall height.

 

[Volume Eight]

I don't think you need to worry about the backspacing but those tires will be way tall. You will need to go down at least to 35 series for that wide a tire. And, as jtoby indicated, if you go any wider than 265, you will need to drop another step in sidewall height.

Below is a link to the available tire sizes. I really want to go with these tires, and by going to a 275/35/18, i can shave off some diameter (1/2") and its only .2 more section width. is 25.6" diameter too much for a stock height 1g?

http://www.bfgoodrichtires.com/assets/pdf/gforce_ta_drag_radial.pdf

 

[Greg Collier]

I'm sure the Konis & DSS coilovers should be adequate but I can't endorse a setup I have no personal experience with. It's a bang for the buck kind of thing and as you well know I put my JIC's through a real workout every race. Tally all the costs including the special order springs and the answers will stare you in the face. Just make sure you have your suspension, rims and tires, dialed in before they start fabrication on the body. It really sucks to have the body parts flying off the first time you make a turn or launch the car,(this I have personal experience with), but that's why we're having this discussion...

BTW I do have a 5.5 B/S with plenty of room for the 275/40-17's and they are custom built 2-pc Bogart Racing wheels that weigh 13.5 lbs each.

Greg

 

[jtmcinder]

If those are the only tires you will consider, then go with the 275/40/17s. 275s are plenty, the gearing is OK, and more sidewall is always better. And there are lots of nice 17x9s, 17x9.5s, and 17x10s out there in lots of different offsets.

Yeah, the cosmetically-inclined would prefer 18s, but why not aim to teach as well as impress?

- Jtoby

 

[Greg Collier]

Yeah, the cosmetically-inclined would prefer 18s, but why not aim to teach as well as impress?

- Jtoby

Oh I agree, definitely do the 18s... My note was addressing the inside clearance of my 275s not the height. As I had already answered your pm, be sure when your cutting the rear fender well to give yourself a decent margin from the monobody seam.

Greg

 

[Volume Eight]

Oh I agree, definitely do the 18s... My note was addressing the inside clearance of my 275s not the height. As I had already answered your pm, be sure when your cutting the rear fender well to give yourself a decent margin from the monobody seam.

Greg

i think Jtoby was saying to go with 17s Greg, do you agree with the 17s, or do you really say to do the 18s?

Below are my strongest choices right now. Ive been looking non-stop for the last few days, and this is what i have come up with.

Gram Lights T57RC 18x9.5 (either 22mm or 12mm offset - im leaning towards 12mm)
http://www.rayswheels.co.jp/cgi-bin/cgi2/english/getWheelItem.cgi?maker=GRAM&model=060_T57RC#
Michelin Pilot Sport Cup 265/35/18
http://michelinman.com/assets/pdfs/doc_pilotsportcup.pdf

With this setup i calculate b/s to be between 5.72-6.18, and overall dimension to be 25.2. This is with the 12mm offset. opinions?

****edit****

i just got a call back from a distributor for gram lights... the T57RC arent available for another 3 months...

 

[jtmcinder]

If you spend the money to go super light, then 18s are fine and will provide good lateral grip. But if this is a drag car, then I'd drop back to the 17s to get more sidewall for the same total diameter. I prefer the gearing provided by tires in the 245/40/17 range, but if you have the power, then 275/40/17 has been done.

Given that cosmetics is an issue, another thing to keep in mind is how wide this body kit will be. If it's super wide, 315/35/17 is the same diameter as 275/40/17. And the idea of seeing the tires from a 'Vette on a DSM has its appeal.

If someone would make a 265/40/16 or 275/40/16 in a DOT R-compound, I would be tempted to name any future children for them. (This is easy for me to say, ever since that judge mandated the cutting of my tubes, but we needn't get into that here.)

- Jtoby

 

[Greg Collier]

With any custom fabrication you're trying to push the envelope making all the components work together creating "the look" and still be functionable. It's a trial and error process that even the most talented fabricators have to deal with. Doing this with "off the shelf" products is a difficult, timely, and often expensive task. There were many times I wish I had certain components to do a mock up of an assembly to insure that my concept would work. In some situations I've been able to get manufacturer sponsors to loan me parts for those applications on the concept that they'll get credit for their parts being used on my car. I also have boxes of brand new and unused parts that I've purchased that still sit in my garage because I was going on the wrong path.

Bottom line: You know the 17s will work but the 18s were your first choice in the concept of your design. You have to ask yourself if you want to take the risk, and hopefully an educated risk to follow through on your original concept. If you're trying to do something unique, a one off, you're only going to get, "I think it'll work", or "my best guess would be", from the people you're asking the questions of. We can't take responsibility for your vision, this is your child. We will however, continue to give you our best educated guesses, but it's up to you to take the risk's to make your dream become a reality...

Greg

 

[Volume Eight]

Greg,

you pretty much said it. that was a great post. Im just about ready to run the risk and just go for it, ive done way too much crunching numbers and technical thinking, its time to apply the knowledge now. I thank everyone who has helped out in this thread.

With that said, i have one last question for you Greg.

Youre running a 5.5" b/s on a 9.6" wheel... That means that your offset would have to be approx. 5.08mm. What are your experiences with that kind of an offset, and how it affects the wheel bearings etc. What have you done to accomodate for this setup?

Thanks again to everyone!

Peace

 

[Greg Collier]

I'm glad that we've been of some small help in your endeavor (personally Jtoby, aka.. DSM "guru" of suspensions should get the kudos). As far as my wheel bearings, I've changed them at the beginning of each race session without any problems throughout the year.
As you continue your build keep us informed of the progress (pictures would be nice), and I'm sure you'll have plenty of new questions that we'd be happy to give you our best guesses... of course taking absolutely no responsibility for those answers

Greg