Dalara Wheelbase

It does sound like your panels were much more inconsistent in terms of quality than the Greenwood. I would expect a panel with that significant a deviation in thickness would be far more prone to expansion/contraction issues, no?

I've seen cars with the add on panels kept clearly separated, I guess you have to like that style to go with it.

I'm not entirely clear on where you used the 3M tape - you sourced a body-color film that is close to your paint or used clear 3M tape to help manage seam cracking? The link just shows cars with decals plastered - unless that is what they use to disguise potential cracking panel seams?

The panels were terrible but physics are physics

CLTE issues still apply. The 3M product is clear and is also used as stone gaurd. I used tailor cut patches over the steel to glass panel joints, I will take photo when I return home. The material and adhesive is perfect for this application. Just apply with a heat gun and it covers perfectly.

Thank you for all your advice. Look forward to the pics.

If you have the name of the specific 3M product that would also be helpful, I know they have a wide range of films. I have used Xpel clear film for stoneguard & spoiler overlap protection, but not any 3M product. The Xpel film is visible due to the thickness.

Hi I totally agree that they are different but I would not really say radically different you are looking at about a difference in expansion of about 0.5mm per m fibre glass has more expansion, with a 80oC temperature change

I would agree it could crack paint but unless you had a longish panel I feel it would be difficult to just look at and spot.

Dave

Once the materials move independently they will start to crack, even a small amount

I will reference this (because it is convienient and possibly correct ):
http://www.moldedfiberglass.com/sit...FG_Technical_Design_Guide_FRP_Composite_0.pdf

Fiberglass Reinforced Thermoset Polyester (not just glass fiber, it is resin too) = 14x10^-6 in/(in F)
Steel = 6.7x10^-6 in/(in F)

Delta is 7.3x10^-6 in/(inF)

I live in Michigan and we have temp swings from -5 F to 100F so total swing is 105F

To total difference in expansion is 0.0000073 in/(in F) *105F = 0.00077in/in so over 1 meter = 0.03177in = 0.81mm polyester fiberglass vs steel

**Check the math on this because I did it pretty quickly.

Ok so this is very simplified and assumes the CTE is consistent for polyester glass across all temps but it really is not and for sprayed or hand layup it is really unkown what the CTE is but no matter what and how you configure it the difference in CTE for steel is about half of that of the Polyester Glass. Elongation is low for the fiber glass at about 1.6% and so it does not take to much stretch before it gives out. It is not like it has a compliant joint that will allow infinite movement (like a rubber joint). The other point is overtime the resin continues to get brittle and makes the situation even worse. So the value may seem small but even small will crack.

As far as length not sure how to really speculate on that because it does not have a fixed end and chase all the expansion to go in one direction but if it did the joint line is longer than 1m so the total expansion may be more like 1mm-1.2mm

At the end of it all the math is cool but it does crack and you don't have to look far on the internet to see similar stories of Class "A" panel cracks. I have them on my car as an example but fortunately I knew where going to show up and planned for it.