8.8 is metric, grade 8 is SAE. Pretty much everything on the Lotus is metric, so you will need to use metric sized bolts. There is no such thing as a grade 8 metric bolt. On my car, all the suspension hardware that I can easily see (OEM) is 8.8, so that's what you should use.

In terms of strength, 8.8 is equivalent to Grade 5, 10.9 is equivalent to grade 8. There are also 12.9 metric bolts, which are a little stronger than 10.9, and are a higher alloy steel. One issue with the higher grade bolts is that although they are stronger, they are more brittle, meaning if they do fail, they will sometimes shear off instead of bending. For most of the bolts on the suspension, there shouldn't be any type of loading that makes this an issue, so you could use either one, but why change something that works fine, unless you have bent one or something?

 

There's a lot of science that goes into bolts, unless you have a specific goal in mind, I'd advocate replacing any suspension bolt with an equivalent in size, strength, etc.

Also, what you're describing is a situation where you can find metric bolts much more easily than standard ones. I've never been to CA but I've never ever heard of that, typically its more challenging to find metric fasteners.

fasteners are usually marked in such a way that indicates their specifications, if in doubt the bolts on the car should be able to "tell you" what they are.

Sector111 has a kit you can buy and they've done all the homework for you fyi. If you're literally just doing the bolts in the wishbones, why not just buy from your lotus dealer? Not only will the bolts be correct, I bet Lotus hasn't sourced them from China.

 

I supposed I should have worded it differently as I do understand that class and grade are different measurements. What I’m really trying to ask is if class 8.8(grade 5 equivalent) is good enough for suspension work or should I get class 10.9(grade 8 equivalent).

I have easy access to class 8.8 but class 10.9 isn’t as common unless I travel further out to Fastenal or something. I purchased mostly class 8.8 nuts and bolts but when I was putting them into the car, I paused to think if 8.8 is enough. But after much research it appears that only two bolts require class 10.9 which I believe are the bolts from the wishbone into the hub. The rest appear to be 8.8 so I think I’m good.

I rather not buy them from the dealer because I will have to drive an hour out to SF and then there is no guarantee that it’s in stock or if the parts guy will even have the right part in stock. But to be honest, I won’t be surprised if nuts and bolts from the dealership aren’t outsourced to an Asian country anyways. It appears the fasteners from Lowes and Fastenal are all made in Taiwan which IMO, is leaps and bounds above what comes out of the mainland.

 

For fasteners of just about any type & grade in the South Bay go to Olander!
The Olander Company Inc

IMHO 8.8 metric is ample for suspension use. As others have pointed they can handle the load and they bend vs breaking. Also consider that bending absorbs shock that would be transferred to the chassis (and potentially damaging).

Cheers,
Kiyoshi

 

Just be sure that wherever you buy nylocks that they are quality! Substandard nylocks were abundant a couple years ago. They either galled and froze before reaching appropriate torque values and then had to be cut off or the nylock inserts spun in the metal and same issues. Failure on a front or rear suspension piece is extremely dangerous or even deadly!

 

I'm in the process of doing an OE refresh on my Elise suspension.

The control arm hex head cap screws (HHCS) are class 8.8.

The HHCSs fastening the hubs to the uprights are class 10.9.

The SHCSs fastening the upper ball joint mount to the uprights are class 10.9.

 

As a rule of thumb, you can always use a higher class nut than spec'd but switching a bolt or stud to a higher class means more torque is required to maintain the pre-engineered amount of stretch. The one exception to this is to avoid using a nut made to a higher tensile strength by hardening to a level where it is brittle... and this only when a brittle failure is not only possible but would lead to catastrophic failure.

 

re: Suspension hardware

Is it too late at night..., but how does a compressive pre-load help a bolt in shear? We are talking about suspension bolts, not piston rod bolts that are loaded in tension....

We can talk about brittleness versus bolt grade. I realize that the Lotus suspension bolts are pretty large for the job in such a light car. I just like to have all grade 8 (SAE) or 10.x metric to secure my life... Am I misguided in my intuitive and irrational fear of all bolts with lower than SAE grade 8, for anything, except my washing machine and stove?

Anton

 

+Glen - Hmm A pretty impressive hotel indeed. Yes what I was referring to was that a higher tensile strength bolt needs a higher torque to cause the required stretch. Undertorquing will not stretch the bolt enough and it can loosen from things as simple as thermal expansion and contraction.

 

Yes what I was referring to was that a higher tensile strength bolt needs a higher torque to cause the required stretch. Undertorquing will not stretch the bolt enough and it can loosen from things as simple as thermal expansion and contraction.

How much a fastener elastically stretches is not a function of the material strength. It's a function of torque applied, fastener dimensions, nut factor and material modulus of elasticity. These parameters do not change due to differences in material strength. Given a specific applied torque, a class 12.9 M8 will stretch just as much as a class 8.8 M8. A class 12.9 M8 can be stretched farther than a class 8.8 M8, but the torque must increase to do so.

 

The modulus of elasticity of steel is relatively constant, regardless of heat treatment or alloy characteristics, which are what determine strength.

This means that yes, the modulus of elasticity for Gr2 bolts is the same as Gr8, 8.8, 12.9, etc. For a given torque, as long as they don't yield, they will provide the same clamping force, and the stretch the same amount.

'Normal' bolts do not yield when you tighten them, the only case where a bolt would yield is a plastic region bolt such as a cylinder head bolt. The reason this is done is that the torque-clamping force curve levels out for a little bit once the bolt enters the plastic region (yields), meaning that even when someone overtightens the bolt, the clamping force stays the same.

Anyway, in the case of suspension bolts, they should not ever yield.

Now, bolted joints in shear are a whole different discussion:
A properly design shear connection does not involve the bolt resisting any shear forces. The bolt only provides sufficient clamping force that the friction between the clamped parts resists shear. In the case of suspension, this is typically the inner steel sleeve through a bushing. The bolt clamps the attachment points on the frame around the sleeve with enough clamping force that the sleeve does not move relative to the frame. The bushings then ride on this sleeve. Think about it this way: if the bolt was in shear, then that sleeve would have to be press fit around the bolt, otherwise the sleeve would rattle around on the bolt.

This is less obvious on structural shear connections, but just as true: the surface area of the connection is what defines how many bolts are needed, not the shear strength of the bolt.

Now, as far as the difference between soft, weak bolts (Gr5) and hard, strong bolts (Gr8): The main consideration in many cases is actually hardness more than strength. If the bolt experiences any wear, it needs to be hard.

The yield/ultimate strength of the bolt should be only relevant if the joint fails to work as designed. Either the bolt comes loose, or it is overloaded such that clamping force/friction is not sufficient. The difference is what happens in that situation.

A softer steel will have a lot more strain between yield and ultimate failure. A harder material will be more brittle. What this means is that Gr5 bolts will typically bend, Gr8 will break. So in choosing fasteners, we are concerned with what the failure mode will be if the joint becomes loose or overloaded. Since it is basically impossible to predict what the load will be in such a failure scenario, it is often better to assume that the load will be so high that even the stronger bolt will fail, in which case we may want to use the softer bolt in the hope that it will bend rather than break, which, in the case of a control arm for example, leaves us with some damaged parts as opposed to a wheel leaving the vehicle.

This is why it is not always a good idea to substitute Gr8 bolts for Gr5.

As far as who is or isn't an engineer, what does it matter? I am one, and am wrong at least 90% of the time (according to my wife). Many engineers I know are totally full of it, and many mechanics or machinists I know, know twice as much actual engineering.

 

Yep - well put, pwildfire.

As far as who is or isn't an engineer, what does it matter? I am one, and am wrong at least 90% of the time (according to my wife). Many engineers I know are totally full of it, and many mechanics or machinists I know, know twice as much actual engineering.

Agreed. I get schooled by machinists more often than I care to admit.

 

One other thing to remember, paint a line on the nut or bolt to the surface with some fingernail polish preferably dark color, dark red, dark green or black preferably where you can see it without removing the wheels as an inspection tool, if the paint is cracked, line misaligned you know bolt/ nut has moved and you have a problem. I like fingernail polish because it comes with a little brush in the bottle, it's easy to keep the toolbox. This is a quick and easy inspection tool.
Cheers

 

I use the little aerosol paint markers, but otherwise agree with the above.