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Lotus in the Peak
28th - 30th June 2024

Suspension Failure!


DeanB

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I managed about 15 laps at the Lotus on Track track day at Blyton on Saturday before a bolt in my rear suspension snapped.

Luckily, there was very little collateral damage but it could have been horrible. The bolt was the one that holds the toe link to the hub carrier. It was supplied with a supposedly uprated toe link kit, which has a rose joint instead of a ball joint.

I only bought the kit and had it fitted last January, and it has probably only done 1500 miles, give or take, with two and a bit track days (it has toyo 888s and Nitrons so grips a fair bit more than standard).

 

So I rang the suppliers who said they have had this problem before on perhaps two kits a year, and their analysis of the snapped bolts suggested they had been over - torqued.

I thought two failures a year sounds like a worryingly high number.

 

I don't think the bolt was over torqued.

 

So I rang Mike Flounders my old mate from Tollbar Racing for his opinion. His first question was what strength are the bolts? I told him 8.8 as the suppliers of the kit say they are the optimum, and that higher tensile bolts are too brittle. Mike was adamant this was nonsense and said he would not consider it safe to use anything other than 12.9 strength. He did say the higher tensile bolts are more brittle but they are nevertheless still a lot stronger in this application.

 

Incidentally Jody told me he has seen a lot of failures with bzp (bright zinc plated) bolts (which these were) and he wonders if the plating process can damage them.

 

I have decided to get some black 12.9s and replace the inner and outer bolts on both sides given that Mike has built countless racing cars and knows his stuff.

 

I was wondering though what mloc thought of the whole thing?

What bolts are other people using?

 

Thanks in advance guys

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A lot of the consensus in vx220 land is that 10.9 is the sweetspot as they are more resistant to fatigue than a 12.9 in HCBs and ToeLinks. As a regularly replaced item in a race car 12.9 is probably best but if your planning on fitting and forgetting for a few years 10.9 is probably the best compromise.

 

 

Sent from my iPhone using Tapatalk

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BZP bolts are often not rated for strength at all.  Also, the strength relates to the load the bolt can sustain under axial tension, rather than bending load (see below).

 

I'm not going to suggest that Mike doesn't know his stuff, but one problem with fitting stronger bolts to the original design is that you can transfer the stresses from somewhere designed to flex to somewhere else that isn't.

 

Perhaps Lotus designed around an 8.8, or perhaps it was the bolt that they had 1000s of in the parts bin.

 

One other problem with rose joints is lack of lubrication / dirt ingress causing it to seize (as I'm sure you already know).  If a joint were starting to seize, rather than acting as a ball-joint it would transfer a bending load to a bolts at either end.  once this starts, it is massively amplified in the bottom of the threads and causes fatigue cracking at the bottom of a thread.  It is nearly impossible to identify during any inspection (even if you took the bolts out and did a dye-penetrant inspection, then refitted the good ones).  Once fatigue has started, a stronger but more brittle bolt is more likely to snap under impact load compared to high cornering loads.  With racing situations, frequent examination / replacement would reduce this risk.

 

I had the Spitfire toe-links fitted some years ago and have done loads more than 2 track days (albeit slower than you...) on sticky tyres.  I don't know what bolts are fitted though.  I could check if you want ?

 

Some kits also come with a small shroud to fit over the inboard links, this spreads the load to the chassis through extra fixings, but obviously isn't your issue if your failure was at the hub end.

 

Worth contacting DerbyJim, who had a similar failure.  I'm pretty sure his was also at the outboard end (of the OS toelink).

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Bloody hell Dean, i hope there was not any damage when it happend? 

 

On my S2 Exige i fitted alternative suppliers toe link kit. It was a lot cheaper than everything else, but the rod ends looked a very good spec. It was all fitted just before going to Spa. 

When i got back i did my usual checks and found some play in one of the newly fitted rod ends. That was less than 1000 miles including the trackday at Spa. I felt lucky that the whole trip was mainly wet meaning i could not really push the car any where as much has i could have in the dry. I dare not think what could have happened. 

I did source my own bolts and used 12.9 as advised at the time and torqued accordingly. I did buy a pack of these with the intention of replacing them every year or so. 

 

I have used a popular suppliers bolt kit previously on a suspension refresh and found some of the bolts couldn't even make the required torque settings and just stretched. 

 

I did replace the toe link kit with the Spitfire version. Boy what a difference in quality. Almost too good to be underneath the car and not be seen. Everything needed come in the kit. 

Yes its not the cheapest, but as i found out you get what you pay for.  

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Thanks guys.

 

I'm thinking careful inspection of the rod ends on a regular basis to check they are free is very important. I also think changing the bolts annually is a good idea as it isn't a big job. I can have it done as part of a service.

 

 

Dobbo it would be good to know what bolts Spitfire recommend and use if you can find out?

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Gaz is a decent bloke - he'll give you advice I'm sure.

 

My car has his kit too - I will have a look and see if I can see what grade the bolts are.

 

Discussion of bolt grades and torque here. http://forums.seloc.org/viewthread.php?tid=419913&page=1#pid7201290

 

And http://forums.seloc.org/viewthread.php?tid=405715&page=1#pid6962758

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Martin I daren't email Spitfire. They will say, with some justification, that I should have bought one of their kits!

And I will feel like a cock.

 

 

You should know I would never say such a thing Dean!  

 

As we humans perceive and react to everything within our own minds, clearly other people cannot make us feel like a cock, we can only do that to ourselves.   :)

 

 

Sorry Dean couldn't resist.

 

 

 

 

 

 

 

OK, quite a bit of mis info so let's clear that up first.

BZP is quite acceptable and has no negative influence at all if it is done correctly, but it does have to be done correctly and the items checked for embrittlement afterwards especially with high tensile bolts of 10.9 spec and above. This is not a cheap process which is why we do not buy cheap bolts, nor do we buy bolts from any source that cannot supply the conformation certificates if requested.

If you have any doubts simply ask your supplier for certs, if they say it's not possible then you already have your answer.

 

The problem with 12.9 bolts is that although you do get a higher clamping force they also operate very close to their fail point and when clumped from the side can snap in a single event. They are also far more critical to being fitted as they are nominally loaded to 90% of their proof load, should your torque wrench be out by 3-5nm, maybe the nut or bolt was slightly greasy and you may be up to 95%+ proof load before you move off the spot.

A softer bolt is more forgiving, although the actual capacity is lower it has a higher percentage of capacity remaining after torquing and may be bent significantly before ultimate failure, this gives you the opportunity to research the funny noise and slight steering twitch before it fails.

 

We use a mixture of 8.8 and 10.9 depending upon position, we also offer M12 8.8  upgrades for several models which gives you the best of both worlds as the strength is higher than a 10.9 M10 but with all the 8.8 advantages mentioned above.

 

To be clear the M10 8.8 as spec'd by Lotus should be sufficient.

 

No need for me to comment on a kit which snaps bolts regularly, you can probably work that out for yourself. I'm guessing you have the recessed M10 uprights? and the other member also the same upright?

Strange why this is not a problem with all aftermarket kits though?

 

No need for me to comment on a kit which needs a bearing after 1000 miles either, only to suggest that after buying a new bearing, paying to have it fitted, then a geo and then VAT the kit turned out not to be quite as cheap as you first thought, probably more expensive than a quality kit.

And you still have have 3 more bearings   :)

We offer a 3 year warranty on our custom made bearings, with a 100% service record to date on about 500+ kits (2000 bearings) over six years.

The rest of the kit should last the life of the car as it is made from superior materials, 7068 and 7075 aerospace grade aluminium alloys, 316 stainless brackets, and better protected then the car itself.

 

 

Did someone post you only get what you pay for???

 

If you drop me a message please Dean I will sort something out for you, no sales talk I promise, already done that   :)

 

 

:)

Gaz

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