Bandog Posted February 10, 2017 Share Posted February 10, 2017 Recently unmounted my tow plate from the rear crossmember. I had mounted it with some M12 x 130 stainless, but had a sinking feeling about towing the car trailer and us parting company on the M1 because they are not strong enough. Am I right, and should I get some grade 10 bolts to make double sure. Or are the stainless ones adequate? I am leaning towards getting some grade 10 high tensile, and appropriate nuts. Any input greatly appreciated thanks Quote Link to comment Share on other sites More sharing options...
jason110 Posted February 10, 2017 Share Posted February 10, 2017 I would use 10.8 or 10.4 (can't remember the exact number) tensile strength bolts. Those were the bolts supplied when I fitted the towbar to my van. From Quote Link to comment Share on other sites More sharing options...
Maverik Posted February 10, 2017 Share Posted February 10, 2017 Your standard 8.8 grade should be sufficient usually M16 I think. 8.8 is often considered "high tensile" in automotive circles, as coming from offshore engineering side that's often the lowest of the "high tensile" group. In replace of "structural" bolts on a truck I'd use a grade 80 Stainless steel bolt which pretty much equates to an 8.8 bzp steel bolt. You have to remember the higher the tensile strength the less tough the material is, I'd argue you need a bit of both for tow linkages duew to the dynamic loading so would opt for 8.8's or equivalent. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted February 10, 2017 Share Posted February 10, 2017 Don't use stainless, it's more brittle. Buy 8.8 BZP steel ones. It's not like they're likely to rust through any time soon... Quote Link to comment Share on other sites More sharing options...
Bandog Posted February 10, 2017 Author Share Posted February 10, 2017 Thanks men Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 11, 2017 Share Posted February 11, 2017 Yup, 8.8s are ideal here. Quote Link to comment Share on other sites More sharing options...
neil110 Posted February 11, 2017 Share Posted February 11, 2017 So the 12.9 I used for my NATO hitch are a bit of overkill then? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 11, 2017 Share Posted February 11, 2017 Yeah, 8.8 are standard bolts for tow hitches, no need for anything more at all. In fact, under stress, 12.9 is more brittle and less stretch, so could break where an 8.8 would just deform a little. Having said that, I doubt it will cause you any problems unless you do silly things with it In short, for bolting anything to the outside or a LR 8.8 is more than enough, and actually preferable at times. Quote Link to comment Share on other sites More sharing options...
Bandog Posted February 11, 2017 Author Share Posted February 11, 2017 OK thanks. So in the same breath, am I going to be OK with the stainless ones or no? Thanks bowie 69 Quote Link to comment Share on other sites More sharing options...
Snagger Posted February 11, 2017 Share Posted February 11, 2017 It depends on the stainless grade - it's not all the same. They are far more brittle than mild steel, though, so I'd recommend the standard 8.8 or 10.8. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted February 11, 2017 Share Posted February 11, 2017 Mild steel bolts. Mo Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 11, 2017 Share Posted February 11, 2017 Don't bother with stainless except in non-critical aesthetic areas. Quote Link to comment Share on other sites More sharing options...
neil110 Posted February 12, 2017 Share Posted February 12, 2017 23 hours ago, Bowie69 said: Yeah, 8.8 are standard bolts for tow hitches, no need for anything more at all. In fact, under stress, 12.9 is more brittle and less stretch, so could break where an 8.8 would just deform a little. Having said that, I doubt it will cause you any problems unless you do silly things with it In short, for bolting anything to the outside or a LR 8.8 is more than enough, and actually preferable at times. Just use the old girl for towing a GKN rapier trailer, usually overloaded with logs, occasional bit of muddy stuff getting in, around and out of the wood yard but nothing serious. I thought the number referred to the tensile strength of the bolt as in the amount of load it could take, in tension, before catastrophic failure? Quote Link to comment Share on other sites More sharing options...
Davo Posted February 12, 2017 Share Posted February 12, 2017 On 2/11/2017 at 5:54 PM, Bowie69 said: Yeah, 8.8 are standard bolts for tow hitches, no need for anything more at all. In fact, under stress, 12.9 is more brittle and less stretch, so could break where an 8.8 would just deform a little. Having said that, I doubt it will cause you any problems unless you do silly things with it In short, for bolting anything to the outside or a LR 8.8 is more than enough, and actually preferable at times. I think the idea is while the higher grades are not as "stretchy", this occurs when a lower grade would have failed already. I realise that this could turn into another highly technical and out-of-control thread but that's the principle I've worked on, so, with my mostly-Imperial-bolted car, Grade 5 is used for most things and Grade 8 for the bullbar and so on. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted February 12, 2017 Share Posted February 12, 2017 Yep, also, the 8.8 will go back into shape, as springy, the 12.9 may deform and not go back at all, leading to the nuts coming undone or worse. Fastenings are complicated Quote Link to comment Share on other sites More sharing options...
Bandog Posted February 14, 2017 Author Share Posted February 14, 2017 Thanks bowie. 8.8 it is then. Just in case (x4) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.