[wishiwerefaster]

I've got a question that's been burning a hole in my pocket ever since I first read about the car. Lotus is using a unique method of bonding the tub & other parts together. How does this hold up under long term use?

Before everybody jumps on me for being a ninny, it might be worthwhile pointing out that S2000s had problems with tearing a welded part (front strut mount, IIRC?) after ~2 years of autocross use with R compound tires. That experience makes me wonder about this method of bonding the chassis.

Presumably Lotus planned for that level of usage (and more), but....

So, does anybody have any ideas on how well the thing holds together long term? Do they hang together like tanks, or tear themselves apart like the S2000? Data from the European side of the pond, perhaps?

Thanks!

Frank

 

[shinoo]

About 7 yrs ago I spoke with a rep from the chassis manufacturer(Hydro Raufoss) at the SAE show. He suggested the tub should last less than 100k miles. Seems they're lasting MUCH longer. The Brits have been driving/tracking the heck out of their cars for many years without any major complaints of chassis failure. There are plenty of cars with 100k+ miles on them that seem to be in good shape. You might post this question on seloc.org. Seems the only chassis durability issue I've seen is the corrosion issue.

 

[MattG]

There have been no adhesive-related chassis failures of the Elise as far as I've heard, and this goes back to the first generation model. However, the adhesive used in the chassis WAS changed at some point in time to the new red color. This could have some effect on longevity.

 

[raggedy1]

i had stated earlier that I will keep this car as LONG AS IT STAYS GLUED together.

Hmmm, I hope she doesn't fall apart at the seams.

I've had my MR2T for over 13 years and plan on keeping the Elise at least as long...

 

[Genjuro]

Isn't every bond point also secured with screws?

 

[Stan]

Here's a shot showing where s2000s have some frame trouble. You can see that the bracket for the a-arms is welded onto the unibody. Via some spot welds. After hard use with race rubber they fatigue from the loads and bending and then let go. You can see that it's an inherently inexpensive design, and prone to such issues.

Earlier Elises had some footwell corrosion issues. And on tracked cars there were some rear toe link issues on samples with the earlier uprights. Our cars have the latest beefed up stuff. The bonds seem to hold up just fine, and since 1996.

We even have the bolts that Lotus suggests Exige owners upgrade to for their suspension uprights.

Our a-arm mounts are quite strong and use steel bushings with wide heads glued to the aluminum. They bend but don't break in accidents. Here is a shot...looks pretty strong. You can see the bonded in black bushings. You can see the mount for the lower arms at the front of the footwells too.

Footwell view - see the a-arm bolt? (bolt & black bonded in bushing)

I'm sure we'll find out more about the car as the calendar flips...

 

[meat]

I've never heard of an adhesive failure in the car (S1 or S2).

The footwell corrosion issue relates to moisture that is trapped under a footwell "mat" that was glued down in some cars. Once the moisture is trapped a chemical reaction took place and began to corrode the AL floor. Note - the floor is not structural to the car.

 

[MattG]

Isn't every bond point also secured with screws?

No. Some type of rivet is used, but I'm 99% certain they do nothing more than hold the pieces together while the adhesive cures. They do not provide any significant mechanical strength.

 

[Derek]

No. Some type of rivet is used, but I'm 99% certain they do nothing more than hold the pieces together while the adhesive cures. They do not provide any significant mechanical strength.

This is Lotus, everything is there for a reason. If it didn't need to be there it would be removed. The rivets are there to prevent peeling that could occur in an accident. I think the term they used was "shearing force".

 

[Stan]

It sounds like some aren't comfortable with the structural adhesive concept. Well it's used as an adjunct to normal steel on countless unibody cars.

Look at it another way. It allowed Lotus to produce the Elise.

And another way. It allowed Lotus to use very high strength aluminum. If Lotus welded the alloy extrusions together in lieu of glue, the final result would be considerably weaker! Because when you weld you melt the different piece together and then the assembly cools off. This renders the alloy near the weld weaker because the heat treatment is lost.

And another way: Look at that S2000 image. Those little round spot welds are what is holding the suspension arm mount to the unibody. They are prone to corrosion and live in a water trapping area. Lotus is using many times the square inches of bonded area so the stresses are very spread out. Honda's a-arm mount would be stronger if some structural adhesive was also used in the area.

 

[zvezdah1]

They spot weld the sheet metal on the a-arm brackets on the S2K?
No wonder they're having failure issues, ouch.
Chris

 

[wishiwerefaster]

They spot weld the sheet metal on the a-arm brackets on the S2K?
No wonder they're having failure issues, ouch.
Chris

I don't think that they do anymore. It was an issue on 2000-03 (?) S2000s -- I believe that Honda beefed up the mounting point with the 2004 upgrades.

I appreciate all of the feedback here. Thanks!

Frank

 

[thegit]

The adhesive is sucessful in all types of impact except one (peeling apart force, iirc).
The Ejots (expanding, self tapping rivets) are insurance, and are a hint of the type of riveting that would have been used if CIBA's adhesive failed the crash and durability testing.
Welding was out of the question for extrusions this thin. the damage to the aluminum by welding would have to be counteracted by much thicker alu, like the competing Renault spyder that had a welded chassis from the same source at the same time as the Elise S1.
m