That time just after you decide but before you know what you want

[Frank Clark]

If I'm buying boxes of these, what lengths are the most commonly used?

For me 1/4 in 5/8", 3/4", 1", #10 in 5/8"

I would buy 25 of those, 10 of 1/4 1.25, 1.5, 2, 100 each of lock nuts, washers, fender washers and then replenish as needed.

I use more button head and than hex head, but that is preference.

I also used a good number of 1/4" and 3/8" counter sunk in 1" and 1.5". Everything that bolts through the floor (except seats/harnesses), I countersunk so they don't get clobbered when the car drags.

 

[Cam]

Decision made

Lots of good discussion going on, thanks everyone!

I want to take a second to thank the folks who reached out to me (you know who you are!). I've had a lot of really great conversations with various folks in the community and it's really helped me figure out what I want to do.

So I've taken the next step and crossed the line into soon-to-be-builder!

Factory deets:
Orange gel coat
Forgestar CF10 wheels, gunmetal
Dropped floor
Adjustable pedals
Lift kit
Race tail
FG Street splitter + tunnels
FG dash
FG A pillar covers
FG inner fender panels
CF rear wing
CF rear window vents
CF front fender vents
CF interior tub
Door mount mirrors
Single-piece windows
Standard shocks
Standard brakes

Looking forward to creating a build thread from the perspective of someone new to the world of hand built cars.

 

[Cam]

Started to do some more digging into tires -

Can anyone confirm whether a 335/25/20 will fit the SLC rear? I believe this is the z07 rear tire spec.

 

[A.J. Schreder]

CF tub. I can't imagine having my tub being so delicate. I've been hard on mine, have cut into it, made repairs...being a first timer I'm not too organized or precise.

I'm anxious to see the CF10 wheels. I came very close to choosing them, but went with the CF14

A.J.

 

[Cam]

CF tub. I can't imagine having my tub being so delicate. I've been hard on mine, have cut into it, made repairs...being a first timer I'm not too organized or precise.

I'm anxious to see the CF10 wheels. I came very close to choosing them, but went with the CF14

A.J.

Yes - it's going to pain me to cut into that piece. Measure 30x, cut once! What areas did you have to play with and repair? I've never seen photos of the cf tub on its own or the fg one really well. Is the tub just a single piece all the way around, or is the seam between the lower and upper rear bulkhead a split? I believe the upper portion the covers the overhead air tunnel is attached to the upper rear bulkhead portion.

To be honest CF10s weren't even on my radar until I saw that 1500ho thread. I think the concavity is going to give the car a very mean look! My second choice as the CF5Vs but just seemed like the majority of SLCs were running these. Either way all the wheel options look awesome.

 

[A.J. Schreder]

The tub is one piece. It is cut out where the seats go. So there are 2 large areas where the aluminum floor is exposed. The tub comes with a clear plastic protective cover (wrap) and I left mine on for protection. I sit on the sides of the tub all the time. When the body is off, on the passenger side I discovered the tub isn't strong enough to support my weight. It cracked about 4" at the front part of the door opening. I also cut a hole in the tub to make room for a storage bin next to the drivers seat. Getting the tub in and out by myself is difficult without bumping and knocking things around. As a rookie, not having an expensive surface to protect has been a relief, that's all.

The tub meets the ceiling panel at shoulder height. Both pieces compliment each other nicely and fit well. My roof needs to trimmed better at the front roll bar, so for not it stands out because it's drooping. You can see the part that's normally tucked up under the body in the rear. As you can see, my interior is a mess with all the dust from sanding. If the tub were carbon, I'd have to be far more anal and that would cost time.

Here's a few pics

The repair:

A.J.

 

[Cam]

Thanks AJ, those pics are helpful. It looks like there's a seam just below where the harness straps pass through to the rear? Did you cut that apart yourself? I plan to build some bracing so the tub and body are well supported, enough so people can sit on the pod to get in/out if necessary.

 

[A.J. Schreder]

I cut the holes for the harnesses. The ceiling panel is a separate piece from the tub. It has locating bumps that mate with the tub to ensure a great fit. It's a good looking joint.

If the body is in place, you can sit on the door opening all day, whether the tub is there or not. It's when the body is off that the tub can get cracked. And mind you, I was really putting a lot of weight on it, repeatedly. The drivers side held up, so I didn't think anything of it on the passenger side until "snap!" No big deal. Just glad it isn't carbon.

A.J.

 

[Cam]

Started to do some more digging into tires -

Can anyone confirm whether a 335/25/20 will fit the SLC rear? I believe this is the z07 rear tire spec.

In addition to the clearance question, at what point in the process are you supposed to send the tires out to RCR?

 

[Mike]

I do not know if the frame/susp/body has changed since this post : http://www.gt40s.com/forum/rcr-forum-rcr40-slc-917-superlite-aero/37040-sl-c-tire-question.html - but this info may be beneficial.

The factory (Fran) should be able to tell you when they need the tires.

In addition to the clearance question, at what point in the process are you supposed to send the tires out to RCR?

 

[Cam]

Thanks Mike - based on what I could decipher it appears Alex had a problem because he tried to run an overall taller diameter tire. The 335/25/20 would bring it down about 0.5" compared to 325/30/20 so overall diameter would be ok. I'm just worried about the wider side wall interfering with chassis/suspension/body. I'll ping Fran and update the thread in a few days.

 

[Will Campbell]

Thanks Mike - based on what I could decipher it appears Alex had a problem because he tried to run an overall taller diameter tire. The 335/25/20 would bring it down about 0.5" compared to 325/30/20 so overall diameter would be ok. I'm just worried about the wider side wall interfering with chassis/suspension/body. I'll ping Fran and update the thread in a few days.

The problem with larger tires on the SL-C is diameter, not width, in most cases. There is plenty of room, in general, on the inside of the car, and the fender lip can be trimmed if needed for more width (or it can be controlled with offset).

It's really hard to get the rear tire out of the opening with the street suspension at full droop, even with the stock sizes. I struggled with this for a while, and recently learned that a very small jack can be used to lift the suspension arm enough to better center the wheel/tire assembly in the opening. With this, it is much easier and safer (i.e., less risk of damage to the body and skirts) to change tires.

The point of this is that unless you lift the lower suspension arm, even the stock diameter tires are difficult to change with the street suspension (because the race suspension has less travel, droop is reduced and it is easier to change a race car wheel and tire, ironcically). But lifting the arm, which allows the tire to be centered in the opening, allows the stock tire, and probably somewhat larger diameter tires to fit. But that means you'll always have to have a spare small jack to change the rears if you go any bigger in diameter.

A 325/30/19 Nitto Invo has an installed height of 26.77 inches, according to Nitto. That's about the max acceptable diameter, in my experience.

Using a tire size calculator, a 335/25/20 tire has a diameter of 26.6, a bit less, so it will likely fit.

Note that tire sizes vary in practice from their nominal specs, especially installed section width, so don't take calculations as gospel.

 

[Cam]

Good info Will - that's a good point, these cars have wheel wells which have arcs that come down below the widest point of the tire. So as the suspension droops it's going to bring that tire closer to interfering with the lowermost edges of the wheel wells. I'm running the inner fender liner option as well if that makes any difference.

I believe for the 20" rear option the 325/30/20 is the recommended size which surprised me a bit because it's a full 1" taller than the 19" size of 325/30/19. Trying to locate a 325/30/20 tire looks pretty difficult; super expensive or back ordered nationally for a few weeks! Going with a 335/25/20 opens up the options significantly! (4 vs 2, lol)

I hadn't thought that the body may be trimmed if necessary - not typical thinking for me as I'd never consider rolling or trimming the fenders on my street car. With these FG bodies it's easier to modify. I'm going to have to change up the way I approach problem solving with this project!

Also a good point about differences with respect to tire manufacturers and sizing not being the same despite the numbers matching. I've got an even better one - I ordered a (what I thought) was an exact match with my factory Pirelli P Zero and despite all the numbers and letters matching the sidewalls were different. Seems Pirelli has multiple P Zeros and the sidewall profile is different based on OEM they sell to and tire retailers such as Discount tire/Tire rack/etc. So I have 1 odd ball tire with a more vertical sidewall than my other 3 tires which have a more rounded profile. Drives my OCD crazy knowing it's like that.

 

[Cam]

In addition to the clearance question, at what point in the process are you supposed to send the tires out to RCR?

Got an answer from Fran - for the 20" rear recommended tire size is 305/30/20. Good news is this opens up the tire options pretty dramatically. Bad news is that reduces the tire width 20mm from the 19" option.

A 325/25/20 would keep the overall diameter lower but based on the other thread corvette owners running that size may have had tire/wheel issues when running into potholes. Bummer.

As far as tire need date seems like there isn't a hard need time and there isn't a "too early" date either. So if anyone's looking at tires and they're backordered it's probably not an issue. I imagine forgestar is taking several weeks for delivery anyway so anything in the 8-12 week time would probably be about right.

 

[Cam]

Some more clarification on tires in case anyone reads this later.

It seems so long as you stay near the recommended overall height of the 325/30/19 which is about 26.7" you're fine. Pushing past about 27" overall height may be a bit risky. So with this in mind there's a good chance that the 335/25/20 I was thinking about could work. The only bummer here is that tire selection sucks. If I back the width down to a 325/25/20 the tire options open dramatically. This results in an overall height of 26.4" and shouldn't cause the tire to be stretched. That's what I'm leaning toward for the rear.

On the front the recommended size of 285/30/19 also yields a fair number of tire choices. Unfortunately not any I want to run. If we push it down to a 275/30/19 the Michelin PSS is available (non run flat) which is what I'm aiming to run in the rear. Again, not much stretch and overall tire diameter changes by about -0.2" overall. Likely not an appreciable loss of front grip by going with a narrower tire. Front wheels are either 9.5" or 10" so I need to confirm whether the 275 is an appropriate fit for a 10" wheel if that's what is part of the kit. Doesn't strike me as being a real stretch. If that doesn't work then going to a 295/25/19 could be in the running but here the risk is rubbing the tire at full lock. Anyone already have experience with clearances at the front and whether it's wiser to go with the 275 instead of the 295?

I'm sure I'm overthinking this but my goal is to go with the best reasonable street tire I can given that this car will see limited but hard miles. At 3-4K miles per year and maybe 1-2 track days (if that) replacing tires every 2 years would be an acceptable trade for running sticky rubber every time I strap in.

 

[Will Campbell]

Another issue is front/rear balance. Tire size (mostly width, which most easily translates to contact patch area) is one way to balance the car. IOW, if you want to solve an understeer problem, more tire in the front might help, assuming you had adequate aero force to keep heat in the front.

One thing to avoid, IMO, is too much of a delta (compared to the stock one) between the front and rears. It's easier to go wider in the rear, which looks good, but may actually increase understeer.

 

[Cam]

Another issue is front/rear balance. Tire size (mostly width, which most easily translates to contact patch area) is one way to balance the car. IOW, if you want to solve an understeer problem, more tire in the front might help, assuming you had adequate aero force to keep heat in the front.

One thing to avoid, IMO, is too much of a delta (compared to the stock one) between the front and rears. It's easier to go wider in the rear, which looks good, but may actually increase understeer.

Using factory alignment specs how is the car setup - is it biased toward understeer as it is?

 

[Will Campbell]

Using factory alignment specs how is the car setup - is it biased toward understeer as it is?

Alignment specs are just one of a myriad set of things that affect handling. Spring rates, shock settings, ride height, tire pressures, tire sizes, tire compounds, contact patch area (surprisingly, tires of the same nominal size don't always have the same contact patch area, which is what actually transmits torque), aerodynamics, the way the car was built in terms of overall weight, and weight distribution, etc all have a measurable effect on handling.

An owner-built car will have too many variables that aren't under the designers control, so it's hard to make statements like "it understeers" or "It's loose in high-speed bends". You just have to drive your car, and make changes until it handles perfectly- accounting for your tastes, how the car was built, and driving conditions.

Luckily the SL-C is very responsive to changes, and a long record of success on the track proves the geometry is very good. So making the car handle the way you want to is just a matter of working on it until it's right.

 

[Scott Rowland]

I bought a harbor freight elcetric shear today. It goes through 14ga (0.080") aluminum like its nothing for $50. Not sure if the cars come with all the close out panels now or not, if not, then you will be making and cutting them out if you wanted them. Great tool for cutting lots of sheet alum on the cheap and quick.

 

[Will Campbell]

Speaking of Harbor Freight, their small 1.5 ton jack that is perfect for lifting the lower control arm on the rear to make removing and installing the wheel/tire easier just went on sale.

Here's a link to the item. Just $59 with the coupon you can get anywhere, on redeem online.