Wheel sizes

[BVM]

Hello,

i own a new everette morrison cobra 427 replica.
and i´m in the finishing stages of the car, so i need to buy the wheels.
i would like to put 17" wheels on it, but have no idea as to what sizes, backspacing, etc. the car would do best and tolerate.
i want to put the biggest size tolerable by the car.
i was thinking something along the lines of 245 for the front ones and like 305 for the back ones.
but i would like some imput on somebody here.

please let me know,
regards,
BVM

[scottj]

What suspension do you have?

[BVM]

chevy corvette dana 36 1984

thanks,
bruno

[Hotfingrs]

you can run 17 x 9 all the way around with a 6 1/2 inch back spacing. If you try to run wider on the rear, the offset has to go to the inside or else you'll end up sticking outside the body. The Vette suspension is about 6 inches wider that's why you need so much back spacing....

[scottj]

I've got '92 which is wider than yours by an inch front and rear, I think. You could calculate the difference to get your backspacing but I only have 1/8" tolerance.

Fronts are 275/40-17 on 10-1/2" w/8" backspacing (this retains zero scrub on an '88 and later front)
Rears are 335/35-17 on 12" w/8" backspacing.

You should be able to use 7-1/2" backspacing.

The sidewalls bulge out past the fenders which was acceptable to me, the alternative with the vette susp is a wheel with little or no dish.

Scott

[Tom Wells]

Hi Bruno,

I have an E-M also. Vintage 2001.

It has the Ford/Jag suspension but I don't know whether that will make any difference to the maximum wheel or tire widths you can use.

It _will_ make a difference in the back spacing as the Corvette suspension makes the wheel flanges sit further outboard, so the back spacings most probably will be more than what I used.

I have 17" x 9-1/2" rims in front, and in the rear 17" x 11".

Tires are 275/40-17 in the front and 315/35-17 in the rear. These are wider than what you plan to use, so you could use narrower wheels at both ends and most likely avoid problems.

So far, I've had no trouble in the front.

In the rear, one of the limiting factors is the seat buckets! The inside of the tire will touch the molded fiberglass at full compression of the back shocks, and it also touches the inside of the fender lip. We ground off a bit of the fender lip which reducees the ZZZZZZZZZZZZTT!! noise that accompanies the tire touching but doesn't eliminate it. Modifying the seat bucket looks to be way too much trouble...

What I plan to do is stiffen the back springs about 10% which should help a little.

BOTTOM LINE:

If you use a 17 x 10-1/2" rear wheel it may fit OK if the back spacing is right for your car. The 17 x 9-1/2" wheel does fine on mine in the front.

PROBLEM:

Just did a quick check at Tire Rack and couldn't find any 305/xx-17s at all! No 35s and no 40s.

WARNING:

Be sure you try any wheels on the car to see if they are going to fit. If they don't fit (wrong back space or whatever) be sure you can swap them for some that do fit! Your car/body combo may be different from mine - these are all hand-built bodies and frames...

Hope this helps,

Tom

[GeorgiaSnake]

BVM
I'm going through the same with my Unique FIA. I would suggest talking to the kit supplier and wheel suppliers. Compomotive is very helpful.
Good luck!

[Fred Douglass]

My builder, is going to be able to put a fairly-unique set of Trigos on my car. Though they'll be knowck-offs and 15" diameter, he's going out to 10.5"+ rim width in front and 12.75"+ on the rears. This fits fine with the Jag rear and modified ZMG up front. Unfortuinately, in 45-section tires, the supply of super-wide ones is limited indeed. The 305 is being discontinued by both Goodyear and BFG----apparently. Mickey Thompson does seem to have some in the wide-wide range (equivalent to 305s or even 315s)--but nobody seems to have anything DOT-rated near this. I have talked to several dealers, including Roger Kraus and haven't had the best of luck.

Any suggestions or other forms of help will be greatly appreciated!

[Tom Wells]

Hello Freddie,

You've just hit the one of the reasons I went to 17" wheels

Recognize that these comments don't apply to a trailer queen ; I use mine a lot on the street and as often as practical on the sports car track.

Here is why no 15" wheels ): in no particular order:

1) No 15" high speed rated tires, no V-rated, no Z-rated, no Y-rated. There actually are a few, but they are way too small for the Cobra. The P-rated or S-rated 15" tires that are available yield low traction (good for burnouts and power slides ). These low-speed rated tires aren't worth the risk of high speed cruising. But they are cheap . Most folks "get away" with using them because the cars are so light.

2) Room for really big brakes. When I used my "can't have too much horsepower" line in front of a sports car racer, he shot back "can't have too much brakes, either". I went with 13" rotors and big calipers.

3) Same problem with 16" wheels. The big brakes may fit inside some brands of 16" wheels and preserve some of the "look", but same problem here - no really good tire choices.

Grinning and ducking,

Tom

[Fred Douglass]

Good points all. I was told by a guy at House of Cobras that about 80% of the braking in severe conditions takes place up front anyway. Since you appear to have a motor wh/ would fit right in at the Reno Air Races, I would be interested in what you're running on your car. Rims, tires by brand, size, etc. I am going to be in DC from Feb 2-8, '03---where and when do you Capital Snakes get together?

[Tom Wells]

Hi Freddie,

Glad to contribute to the confusion, er, clear up a few points

The Capital Area Cobra Club meets at the Vienna Inn on Rte 123 near Tyson's Corner every Saturday at 8 AM - it is called the "grease-up" for reasons which are obvious after you've experienced their cuisine. You are most welcome to join in if you happen to be around.

The web site for the DC area club is

Capital Area Cobra Club

and it has members from all over the DC/VA/MD area, including a temp from Louisiana and an NC deserter.

My wheels are:

Front: 17 x 9.5, 5.5" back spacing
Rear: 17 x 11, 4.75" backspacing
Bolt Circle: 5 on 4.75 (Jag or uh, Chevy)

The backspace can be a little bit misleading as it is entirely dependent on the dimensions of both the suspension and the body.

Case in point: my front hubs are made by Baer specifically for their bigger brakes and are 0.3" narrower per side than the stock Mustang II pieces that are widely used. This translates directly into .3" less back space needed per side than the "norm".

The rear uses 3.8S/420G Jag wishbones and axles. These are wider than the XKE and narrower than the XJ. So if you have an XKE rear, you'd need different back spacing than I use.

Also, the seat buckets in the E-M body determine how far inward the tires can be placed, restricting tire width.

Having said all that ("all them caveats!"), I actually have two sets of wheels.

The ones in the photos in my gallery are Compomotives and are shod with Michelin Pilots, 275/40-17 front and 315/35-17 rear.

The other set which cost a lot less and looks just as good are identical in specification and will be used for the track. They are made by Team III Wheels, their model ACIII, and are shod with exactly the same size tires in Kumho brand Victoracer V700s ("stickies", not for extended street use, although they are DOT legal).

As to braking on the track or under emergency conditions, I'd surmise greater than 90% is done by the fronts. As a laugh (well a stressful laugh) when I really got on the brakes at the track, the rear shocks being too short tried to lift the rear end off the ground and very nearly succeeded

See if you can warn us, er, let us know if you can make the "grease-up". We'd enjoy your company I'm sure.

Regards,

Tom

[Fred Douglass]

Tom
I'm going to be in DC itself---at some huge hotel on Capitol Hill---working to get a video-journalism "station" set up for the Junior Statesmen Foundation---the convention is for that February 7-9 week-end. The "Grease-up" sounds good! H-m-m-m "Sliders"* for breakfast---sounds okay. With the latest medical revelations, re beef, red meat, lard, oil, etc. I may have TWO! Do you recall the scene in Woody Allen's "Sleeper" when the doctor who thawed him out of cryogenic "sleep" is asking him all these questions about things we (in the 20th century) thought were severely unhealthy to ingest/smoke? It's worth renting the movie just for that scene alone---although there's also that VW in the cave scene........

Thanks, Tom...I'll try to contact you once down in DC--should I bring all my "Country Gentlemen" CDs? Ooops wait, the pipes, the pipes...

*check with a USN type, if y'all ain't one!

[Tom Wells]

Hello Freddie,

Remind me when you are ready to go in Feb. I live on Capitol Hill, so if I have an empty seat (bride declines/car is operable etc etc) I could swing by and pick you up that Saturday.

Tom

[Fred Douglass]

you are now in my will!

E-mail me your phone number, etc. in a timely fashion (some time before the Sattidee in question) and I will be there. If you pull up to pick me up, it'll wow the kids BIG TIME! Some of the kids (ahem!) will WOW you too---don't let your wife see this!

[ENTDOC]

You should consider narrowing the rear corvette susp,that way you could use deep dish, small backspace wheels.My hunter has narrowed corvette susp and it looks good. chuck

[BVM]

i don´t think that can be done with my tipe of suspension...

so far i have gotten really different opinions as far as sizes go.

this is all EM fault they cannot just close shop like they did!! now i´m left wondering what to do!! haha

[ENTDOC]

Give me a call sometime and I can explain how to measure for backspace on your car,however, any corvette susp can be narrowed easily. chuck 864- 292-6889

[aumoore]

Yes the Corvette rear suspension can be narrowed but it may require modifying the attachment points for the rear suspension (i.e. the forward trailing link points will be too far outboard if you narrow the rear suspension. Also the front suspension cannot be narrowed unless you modify the front crossmember and the steering rack. If this was my car I would not attempt to modify the frame. The EM frame is very well engineered.

I would just get some Team III wheels or PS engineering wheels made to fit my suspension. If you call Enzo at Finish Line he should be able to help as he used to have a EM cobra with the corvette suspension. He is also a Team III dealer.

[scottj]

BVM,
EM would have given you a conservative recommendation. If running the largest tire and wheel combo that the car will "tolerate" is your desire, I would suggest borrowing a Vette wheel, mock it up, and take measurements. Thats what I did. The first point of interference in the rear with regard to backspacing was the hub carrier. Even factory Corvette Grand Sport wheels rubbed the hub carrier where toe adjustment rod bolts to it. Remember the GS wheel maximized backspacing to run an 11" wheel with the stock width Vette body. I clearanced that area on the carrier with a hand grinder. In front the frame is the first point of interference.

I would be very concerned about narrowing the suspension any significant amount. I haven't run the vette suspension in my suspension analysis software but it would be interesting to see what narrowing it would do to instant centers, static and dynamic roll centers, camber gain, etc. Dick Gulstrand who has done alot of work with the vette susp recommends narrowing it only a very small amount to keep effects to those areas to a minimum.
Scott