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What is stonger 8.8 or 10.8 bolts?
steve m - 3/1/12 at 02:08 PM

Hi

I am changing all the bolts etc on the front suspension, and have both 8.8 and 10.8 bolts to choose from (8mm thread)

What if either would be the stronger?

Steve

Ben_Copeland - 3/1/12 at 02:12 PM

I always thought higher the number stronger it was....

Although 8.8 is plenty

[Edited on 3/1/12 by Ben_Copeland]

Myke 2463 - 3/1/12 at 02:13 PM

10.8

rost - 3/1/12 at 02:22 PM

Are you sure you've got 10.8 grade bolts? The standard is for 10.9.
IIRC 10.9 grade bolts have a tensile strength that is around 200N/mm^2 higher than the 8.8 ones and they're a fair bit harder.

Grade 8.8 bolts should be fine with their 600N/mm^2

[Edited on 3/1/12 by rost]

steve m - 3/1/12 at 02:30 PM

Rost

you are right, they are 10.9 bolts, and i have enough to do all the jobs both sides with out mixing things up,

So if 10.9 is much stronger than 8.8, i will use the 10.9s

thanks guys

Steve

samjc - 3/1/12 at 02:43 PM

Ive been told 8.8 are ample as the higher the number the stringer they are but more strength means they are brital under vibration so could crack or so in told as ill be using 8.8 is their no sec in the iva regs.

pekwah1 - 3/1/12 at 03:02 PM

damn you and your garage steve!!!!
just went out to work on the car as it was sunny, 10 minutes later i'm getting peed down on!!!!

StrikerChris - 3/1/12 at 03:51 PM

I've seen more snapped 10.9 bolts in work(heavy industry) than 8.8 They tend to snap like carrots rather than stretch or bend like 8.8's. That said if you've hit something hard enough in your car to snap one,the bolt would be the least of your worries!

Irony - 3/1/12 at 05:22 PM

From what I have read/heard I have ASSUMED that 8.8 will be okay for my suspension bolts. There is a post on here where a guy says you could swing a entire car from a single m12 8.8 bolt.

mad4x4 - 3/1/12 at 05:40 PM

Yeah 8.8 are good enough for suspension just make sure they are stamped bolts so MR IVA can verify there strength.

MikeRJ - 3/1/12 at 06:28 PM

quote:
Originally posted by Irony
From what I have read/heard I have ASSUMED that 8.8 will be okay for my suspension bolts. There is a post on here where a guy says you could swing a entire car from a single m12 8.8 bolt.


A single M6 8.8 bolt could support the weight of a smallish car (~1.3 tonnes). An M12 bolt could support several cars; it would take about 5 1/2 tonnes to reach it's yield strength in tension.

mcerd1 - 3/1/12 at 07:01 PM

quote:
Originally posted by StrikerChris
I've seen more snapped 10.9 bolts in work(heavy industry) than 8.8 They tend to snap like carrots rather than stretch or bend like 8.8's. That said if you've hit something hard enough in your car to snap one,the bolt would be the least of your worries!

^^ that's spot on

the first part of the number is its tensile strength , but the second part is how brittle they are (the higher the number the more brittle / less tough)

but I wouldn't worry about the 10.9's - I know most of the bolts on the sierra's are 10.9's

steve m - 3/1/12 at 07:10 PM

"Yeah 8.8 are good enough for suspension just make sure they are stamped bolts so MR IVA can verify there strength. "

that bit does not concern me, as been on the road 12 years

But all the other info is very usefull

Steve

rost - 3/1/12 at 09:29 PM

Small Example:
8.8 bolts have a maximum tensile strenght of about 800n/mm^2, lets say shear strenght would be around 90% of that:
For a single M12 bolt: (((pi*12mm^2)/4)*(800n/mm^2*.9))/9.81m/s^2=8297Kg that can be suspended from a single bolt.

Simon - 3/1/12 at 10:38 PM

quote:
Originally posted by rost
Small Example:
8.8 bolts have a maximum tensile strenght of about 800n/mm^2, lets say shear strenght would be around 90% of that:
For a single M12 bolt: (((pi*12mm^2)/4)*(800n/mm^2*.9))/9.81m/s^2=8297Kg that can be suspended from a single bolt.


In other words, a bus

ATB

Simon