Bash plate - how thick?
 

I am eyeing up a Moto Guzzi V85TT that will come with a bash plate but how thick would people expect the plate to be? This is not particular to the V85TT but a general enquiry about bash plates.

Thanks

The original one fitted to the R80G/S is around 2mm thick and too thin, I have seen a rock crack a sump through one but the optional model is 5mm thick and mine has taken hell of a beating without letting anything get through.
I have to add that I don't go trail riding on my G/S and the beating the bash plate has had is on bad roads in far off places.

I have ~ 2-4 mm thick plastic, flexible bash plate on my xt660z tenere and ktm 500 exc-f.
Works very well, cause can absorb some hits and it's not loud as metal one.

Kinda depends on how you plan to use it and how much extra weight you want to carry. On the KTM 790 some people are offering 5mm plates that weigh a ton, another company has a lighter 5mm HD plastic one (that I saw a video of one that had split), while the standard one is 2mm ally. I've stuck with the standard one because I don't plan to be motocrossing or bouncing over logs, YMMV.

The factory one on my CCM is 2mm but stainless steel and it’s way too heavy. I’ve made a few for various bikes over the years and generally used 3.0mm ally as a compromise between weight and toughness. So far all my crankcases have survived.

3mm isn’t indestructible but it would take a serious hit to get through - particularly on a small bike which most of my bash plates have been for.

4mm minimum. If you actually want it to be 'bashable' and not just look pretty.

I've made a few out of aluminium. Steel is just too heavy.

I would say 3mm minimum (sorry Ted) in Alu, in 4mm could be better but more complicate to bend if needed, in 5 or 6mm will look awesome but maybe too much.

I’ve made a few in 3 and 4, also combining both with the 4mm just for the bottom.

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4mm will require a bigger rock to smash it straight. That's for sure :D

Many a year since I did manual calcs on this stuff but there are too many variables to just shout out a number.

2mm sloped at 45 degrees at equivalent of 5mm flat to the impact. Google T34 tank.
A 10mm plate bolted to the engine mounts is just a way to transfer impact forces. Its like riding with a bowling ball stuffed down your shorts.
Hard armour like KC faced or tool steel will crack without a backing and create shrapnel while soft kevlar and plastics deform and absorb energy until they don't.
A box citadel structure is about five times stronger than the same thickness of plate supported on a "soft" structure.
Corroded materials have different properties so if you use steel or aluminum it'll degrade, so best to add a bit.
We don't know what's going to hit it. There is no Jane's book of gravel.

If we are guessing I'm going for the 3/64ths 1100 ally. At least if the welds penetrate it won't fold like a soggy kebab wrapper.

Andy

I'd be looking at something like 6061 T6 alloy, MUCH stronger that 1100 series, so you can use less of it for similar strength. You could even go 7000 series but it's pricey.
A little ribbing would greatly increase it's strength too - but you need a serious machine to do it.
Finally to make a good decision you need to factor in usage, likelihood of rock hits, and of course the weight of the bike matters a lot. Oh yeah, and your personal balancing point of risk versus weight :) and difficulty of construction.
On my R80G/S I used 1/4" 6061 plate - despite numerous bangs and rocks it's undented. But it took a 10 Ton hydraulic press to make the curve.

The responses have been interesting and I hadn’t really considered a plastic plate - part of me likes that idea but another part thinks that the metal route is a way to go. Perhaps a solution is to have a 2mm plate with a dipped powder coat - the dipping process gives a much thicker coating than spray powder coating (and, depending on the powder used, somewhat softer than spray powder) - so a strong core with a coating that has some give to it so spreading the load more. As has been said - the whole thing is just a means of transferring the load to whatever the mounting points are.

Perhaps I need to have a play at work with some aluminium sheet......

LOL are you traveling or racing? enduro riders have smaller bush plates then some here :)

All of the plates I've made are probably better described as skid plates rather than bash plates. All have been intended to deal with stones, small rocks, tree branches etc - the sort of stuff that's thrown up by the front wheel on loose surfaced roads. Nothing at the lump hammer level of impact. If your crankcases are in danger from those sorts of blows you're taking different roads to me.

I've used 3mm ally because for that sort of usage it's fine + any thicker and I can't work it with the facilities I have. My rule of thumb has been can I jack the bike up on it without it bending. Plastic of the kitchen cutting board variety (HDPE?) was something I looked at last time (and I even bought a couple on eBay) but I couldn't bend it and by the time I made up 'cut n shut' style brackets it was easier to swap to aluminium.

4mm alloy all day long. The best compromise between strength and fabrication ease.

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My 2013 KTM 690 R has a plastic plate as standard. I bought an aluminium one second hand but never fitted it because the plastic one was just fine, so sold the aluminium plate on. Plastic has a certain amount of flex which seems to me that it should reduce the forces that are transmitted onwards to wherever the plate is attached.

What you do otherwise probably depends what you have to protect which depends on how the bike was designed. I had a bash plate plus engine bars on a Tenere XT660Z but I still managed to skewer the bike on a sharp rock outcrop that found the gap between the plate and bars, and made a hole in the side of the engine. I had to walk 18km in boots and Moroccan heat to get a mobile signal to arrange recovery.