97C5ENVY

******** DISCLAIMER ********
THE FOLLOWING INFORMATION IS AN ACCOUNT OF MY OWN EXPERIENCES, AND ANYONE WHO USES THIS INFORMATION DOES SO AT THEIR OWN RISK.

The following is detailed information on everything that you will need know to run 345/30/19 tires on 19x12 rims, on a '97-'04 C5. If you have any questions feel free to ask.

There are three phases to this project:
- Tubbing your C5
- Limiting the Shock Travel
- Determining the Rims Offset

Depending on how fast you want to complete this project will all depend on what order you complete the phases. To minimize down-time or wait-time, I personally would order the rims first as they can take up to 4 weeks for a manufacturer to make and ship. Second I'd send off the shocks to get modified because this takes about two weeks to get back. And third I'd tub the C5, this phase can be done over the span of one weekend (Sat & Sun). So with this information you be the judge as to when and what order to do each phase.

Tubbing your C5:
The following information is a compilation of my own experience and tips received from fellow forum members, and was born out of the desire to run wider wheels WITHOUT spending $2000+ for someone to tub my car. Here's a "How To" write up I did on Tubbing a C5 for less then $50. All the info you need is in this PDF (follow link): http://www2.stonemedia.com/~e_lynch/...te/tubbing.pdf

Limiting the Shock Travel:
The following specifications were created by myself, and was born out of the desire to run wider wheels WITHOUT spending $600+ for the LPE Shock Kit (Shock-Travel-Limiter & Shock-Mount-Relocation-Bracket), and still keep the wheels tucked under the rear fenders. Quick background info on this shock-limiting issue: First of all, in order to run any rim wider then 19x11.5" and still keep the wheels under the fender you will need to limit the downward travel of the rear wheels (in other words limit the total expanded length of the shock). From my understanding LPE achieves this with a new upper Shock-Mount-Relocation-Bracket that basically just has a deeper "hat", thus allowing the shock to sit deeper into the shock tower (effectively reducing the total downward travel of the rear wheel). However this gives rise to another problem, when the shock bottoms out (total shock compression) the wheels will now hit the top of the inside fender well. This is fixed with a Shock-Travel-Limiter (which is a thick disk type spacer that slips over the shocks center rod), thus effectively limiting the shocks upward travel. Both pieces work together to achieve the result needed to push the wheels further under the car. I however came up with an alternative to the LPE Shock Kit. My idea was to modify the shock directly. Since there are many different brands of shocks being used on the C5 you will have to approach this phase with caution. The main thing here is to measure the total EXPANDED length of the shock (with the shock standing on the floor measure from the floor to top of shock rod). Take the shocks total length and subtract 18", this difference DIFF1 will be the amount that the shock needs to be shortened. This can be done by adding a spacer in the size of DIFF1 to the shock internally(DANGER: THIS CAN ONLY BE DONE BY THE SHOCK MANUFACTURER!). So be sure to check with the shock manufacturer to see if they will modify the shock for you. The rest of this phase is Bilstein specific. Since I already had Bilstein Sport Shocks, and I knew that Bilstein will modify your shocks for $65 each, so I had Bilstein do the modifications. If you have Bilstein Sport Shocks, then all you have to do is send Bilstein your rear shocks and have them add a 1.125" spacer inside the shock body to shorten the total expanded length of the shock. This modification achieves the same desired result as the LPE Shock kit, but for only $130 (the cost of modifying two shocks). Another advantage to this is that Bilstein will also re-valve your shocks (make them stiffer or softer) if you want them too, and it's all covered under the original $65 (per shock) charge. Just give them a call at Ph# 800-537-1085 to discuss any question you may have.

When you mail out your shocks be sure to include a note that states what work you want them to perform, and how you want to handle billing (they do take credit cards). Note that if you send in more then just the rear shocks be clear that you only want the 1.125" spacers added to the REAR SHOCKS. Their mailing address is:

Bilstein of America
Repair Dept
Attn: Jack French
14102 Stowe Dr.
Poway, CA 92064

Determining the Rims Offset:
The following specifications were created by myself, and was born out of the desire to run wider wheels and still keep the wheels tucked under the rear fenders. First a little background info on the offset issue: Originally I was running 19x12 rims with a 70mm offset. This is perfect for those who don't have any type of a Shock Travel Limiter, however your wheels will stick out ~7/8" past the fender lip. The max offset that you can have without causing interference is 74mm, however you will be right on the edge of interference, so be cautious when using this offset....and yes your wheels will still stick out about ~3/4". OK, now on to the good stuff. I took numerous measurements to figure out exactly what the maximum offset I could use without causing any kind of interference. I came up with an 84mm offset as the prime choice. I could have gone with an 86mm offset, but I would have been right on the edge of interference. Anyway, when I went to have my wheels worked on by FIKSE they told me that the closest they could get to 84mm without going over was 82.5mm, so I agreed. And that's what I got. Now, when compared to a LPE Mini-Tubbed Z06 with the LPE Shock Kit, my wheels stick out only 1/16" further, not much considering the tire's section width is 13.6". Plus, I believe this small difference can be corrected by running the little more aggressive Z06 alignment (more negative camber).

Brief Overview:
All that is really needed to run 19x12 rims and still keep the wheels under the fender is a 1-1/4" mini-tub (if you don't plan on tubbing the liners) or a 1-1/2" mini-tub(with tubbed liners), modified shocks with a maximum of an 18" total expanded length, and an 82.5mm wheel offset.

Parting Note:
An offset larger then 86mm can be used to push the wheel deeper under the car, just be sure to take numerous measurements from all angles to ensure proper clearance for the offset you wish to use. Of course a bigger mini-tub will be needed (up to 2" can be done), followed by a shorter shock travel which can be done by using bigger internal spacers. However, keep in mind that by shortening the shocks travel (regardless if you're using the LPE Shock Kit or not) you are reducing the shocks intended operating range. Shortening the shock too much can translate into poor shock performance or even shock breakage. So keep the size of the internal spacers to the bare minimum needed to achieve your goals.

[EDIT] FYI: The desired wheel offset was determined first, that in-turn lead to determining how much the shock needed to be modified to achieve this offset.

:cheers:


[Modified by 97C5ENVY, 4:18 PM 3/12/2004]

leaftye

You definitely went all out! This looks great, and is now part of my Corvette reference collection.

Wadoka

Did you submit this to Tech Tips yet? The archive is a little more permanent.

QuickSilver2002

Good Job. This is what makes a forum cool.

kumar75150

u wanna do my car? :D

Hirohawa

I just ordered the wide fenders made by ACP that are 3/4" wider. I am also thinking of doing this and having new barrels put in at HRE to run wider 335s in the rear.

Is 19" rear wheels better for tubbing or worse?

ALLKAR

Awesome Post!! Thanks!! :cheers: :cheers:
How about Coilovers for the rear?


[Modified by ALLKAR, 9:53 PM 3/10/2004]

dads01dream

Great writeup, thanks! :cheers:

vettethret

Both myself and allkar have coil overs with a 2" shorter shock body and spring for the slammed application. I was thinking of getting 20x12 and running the 345 back tire. I would want to keep my car slammed like in the picture. Would I have less chance of running into problems with a 20" wheel? Excellent write up, unfortunatley I have absolutley 0 skill at this type of stuff and would have to have someone tub it for me. :thumbs: :cheers:

97C5ENVY

vettethret - Who makes a 345 for a 20" rim? If there is such a beast then I would guess that you have about another 3/16"- 1/4" clearence before hitting the upper Control Arm (the main issue that the Shock Travel Limiters are used for to work around). If you get these wheels you can slam the car but you'll have to go with a bigger mini-tub, shorter shock travel and bigger wheel offset. The reason being is that currently the 345/30/19 sticks out ~1/4", this is even the case for the LPE tubbed cars, and you'll want to keep the whole tire under the fender. :cheers:

Hirohawa - I'd go with 19" rears, because this will give you a little more Control Arm clearence to work with.:cheers:

allkar - If you have shorter shocks by using coilover then you already have half the battle won.:cheers:


[Modified by 97C5ENVY, 6:51 AM 3/11/2004]

EatRice

Nice write up...one question. The vette is made of fiberglass and not SMC? I have heard someone say glass and someone say SMC.

Allthrottleandsomebottle

And a few of my install pics showing taping, top fitting in the back..........the more the merrier.
I sure used his pictures/info to get mine done :cheers:

Ruby6spd

Nice write-up. I have been thinking about doing this work myself also - the prices that the shops are charging for this work is out of control. I never could understand what was so complicated if you took your time with your measurements and materials.

:cheers: :cheers:

ALLKAR

:cool: Looks like it's time to get the HREs reworked! :smash:

runamuk

Thanks for the info, I tubbed my car and found the hardest part was refitting the carpet :cheers:

chrislee2

I have a question about running the wider tires. I too have mini-tubbed (almost 2" ) and am running 335's.

Here's the thing that's driving me crazy - the decreased handling.
When I was running autocross this past summer, I noticed that my car would "plow" far more often than it used to. At the end of the fall when I put my snow tires on I couldn't believe how much more nimble my car actually felt. Sure I lost traction off the line but I was able to corner much better. And this is on the freaking snow tires! The other thing that I really noticed was that my car was not being "thrown" around by the ruts in the road anymore.

What the heck happened? Has anyone else had this expirence? If you're running 345's in the rear you've got to be feeling the same things I was.
Is there any solution for this problem?

Thanks!

R6_C5_CLS55

Thanks a lot for the write-up and research.

Am I correct in my statement that, based on the increase in allowabe offset (from 74mm max to 86mm max, a difference of 12mm in offset) that your shock mod or the LPE relocation mod gets you an additional 24mm of total straignt-line clearance between the inner lip of the wheel and the upper control arm, for a total straight-line clearance of 46mm (22 + 24) when compared with a stock 18 x 9.5 rear wheel mounted?

Using the example of the stock 18 x 9.5 inch rear wheels that have 63mm of offset, there is already a straignt line gap of ~22 mm, hence the max allowable offset of 74 mm without a shock relocation or shock modification (22/2 + 63 = 74 mm). By using the shock modification or relocation, you have a maximum allowable offset of 86mm (per your description), which translates into an additional 12mm of allowable offset (86 - 74 = 12mm) or 24mm of straight-line clearance (12*2 = 24mm). The original 22 mm straight-line clearance plus the 24mm of straight-line clearance nets you a total clearance of 46mm (if measured with the stock 18 x 9.5 rear wheel).

-or-

86 mm max - 63mm original offset = 23mm additional allowable offset = 46 mm straight-line clearance between the inner wheel lip and the upper control arm.

Dope

Of course the car is going to handle worse. You put some big giant tires in the back without some big giant tires in the front, and the car is going to understeer terribly. If you want to run 335/345 in the back, and still handle very well, you should probably have 305/315s in the front or so. Having large tires in the back only is just a cosmetic and/or straight line traction thing.

For example, most f-body guys run 315/35/17 all around for track use. The guys running 275s up front and 315s out back have terrible understeer. The vette is a bit different creature, I suspect it is due mainly to the better weight distribution. You usually want a bigger tire out back than in the front, but not TOO much bigger.

Dope

chrislee2

I am running 295's in the front when I'm running the 335's in the rear. Mebbe I should go a little wider then? hmmm

Dope

Yeah, I would say a 315 would be ideal. But that's just me. I run 295 rear and 275 front on my 99, and it's a pretty good combo. Still understeers a bit though. 295 and 335 is twice the difference that I have.

Dope