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+--- Thread: T Rex backrest (/showthread.php?tid=8135)
T Rex backrest - jeffmazz_imp - 08-25-2021
Has anybody seen this T-Rex backrest yet? Or does anybody have one? I was wondering if it might be worth a try as the wife isn't comfortable with out one.
https://www.t-rex-racing.com/2010-2015-Honda-CB1100-Deluxe-Back-Rest-Grab-p/n42-13br.htm
RE: T Rex backrest - furious_blue_imp - 08-26-2021
(08-25-2021, 10:42 AM)jeffmazz_imp Wrote: Has anybody seen this T-Rex backrest yet? Or does anybody have one? I was wondering if it might be worth a try as the wife isn't comfortable with out one.
https://www.t-rex-racing.com/2010-2015-Honda-CB1100-Deluxe-Back-Rest-Grab-p/n42-13br.htm
I'm not a structural engineer, but that backrest looks like a lot of leveraged force where it's welded on with very little structural reinforcement. If they added some kind of bracing joining the underside of the luggage carrier plate to the underside of the grab bar it would look a little more sturdy over the long haul.
RE: T Rex backrest - The A-man - 08-26-2021
Well, I am a structural engineer, and I have to say kudos to furious blue for noting the obvious deficiency in this backrest. From what I can see, the attachment bolts for both the backrest and the luggage rack are placed in pure bending from inertial loads of the passenger body and from the mass of luggage. In both cases, putting the bolts in a bending load are both inefficient and prone to failure. As a minimum, the stiffness of the joint will be highly suspect, even if the bolts don't break. If they don't break immediately, I'd expect them to fatigue over time. That's just my humble opinion.
RE: T Rex backrest - furious_blue_imp - 08-26-2021
(08-26-2021, 05:42 AM)The A-man_imp Wrote: Well, I am a structural engineer, and I have to say kudos to furious blue for noting the obvious deficiency in this backrest. From what I can see, the attachment bolts for both the backrest and the luggage rack are placed in pure bending from inertial loads of the passenger body and from the mass of luggage. In both cases, putting the bolts in a bending load are both inefficient and prone to failure. As a minimum, the stiffness of the joint will be highly suspect, even if the bolts don't break. If they don't break immediately, I'd expect them to fatigue over time. That's just my humble opinion.
Good to hear from someone that knows what they're doing :-).
All I have is a few decades over which I've had 2 welded steel luggage carriers fail, one of the failures happened on a long trip when I was about 2000 miles away from home.
From those experiences, seeing geometry like that of the rack in question immediately make me wince.. Pavlov's Dog kind of wince...
RE: T Rex backrest - jeffmazz_imp - 08-26-2021
Thanks for the input gentlemen!! This rack will be a NO-GO for me.
RE: T Rex backrest - Dd808_imp - 09-09-2021
Ordered this the other day… I’ll let you know how it turns out if anyone is interested
RE: T Rex backrest - LikeAfox_imp - 09-15-2021
(09-09-2021, 05:08 AM)Dd808_imp Wrote: Ordered this the other day… I’ll let you know how it turns out if anyone is interestedI think we all know how it's going to turn out once you apply actual load
jeffmazz, I haven't seen a single backrest made for CB that had passenger comfort in mind. They are more of a compliance item, to help out in a pinch. They will keep your passenger from sliding backwards, but not resting.
I recommend you get a factory carrier bracket, it's nice and flat. Then get a quality aftermarket top box with a pad. Those are much more practical and the comfort pad is positioned higher, where it's actually useful. Most boxes like Givi or H&B are quick and easy to remove when not needed.
![[Image: ed80f10b2f24f655ac40cb1f12048ac2.jpeg]](https://cb1100forum.net/forum/uploads/imp/202109/ed80f10b2f24f655ac40cb1f12048ac2.jpeg)
RE: T Rex backrest - skenzie1340_imp - 09-16-2021
(08-26-2021, 05:42 AM)The A-man_imp Wrote: Well, I am a structural engineer, and I have to say kudos to furious blue for noting the obvious deficiency in this backrest. From what I can see, the attachment bolts for both the backrest and the luggage rack are placed in pure bending from inertial loads of the passenger body and from the mass of luggage. In both cases, putting the bolts in a bending load are both inefficient and prone to failure. As a minimum, the stiffness of the joint will be highly suspect, even if the bolts don't break. If they don't break immediately, I'd expect them to fatigue over time. That's just my humble opinion.
I don't know what the heck you just said, but I believe you! LOL