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Stock 190mm front axles tough enough to turn 35s?

AMCheese

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Looks like Ford is offering a factory lift and 35" wheels on the base model. This is important because I want the 7 speed manual.

My question is are the stock 190mm front axles tough enough to turn the 35s? On the SASQ pack I think the front axle is 220mm.

Should there be any concern here?
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TyRy07

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I’m not an engineer by any means but I would think under normal daily use it would be perfectly fine. Hard wheeling/crawling may be a different story.
 

HoosierDaddy

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Squatch

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For mall-crawling? Almost guaranteed.

For anything else? Keep your right foot out of it. It's almost always someone who thinks they just need to give it more gas that breaks an axle, etc.
 

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MaverickMan

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Just for the Non-Metric people....

190mm = 7.480"
220mm = 8.660"

30mm Difference = 1.180"
Im actually disappointed there when I see it in inches. Thats barely living up to 90s ranger and explorer specs. I hope the casting quality and design is significantly better. That or Ford is begging people who wheel to SFA swap it.
 
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AMCheese

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May be better to stick to 33"s, much less leverage on the front 190mm axle. Or get forced into the auto.
 

Imissmy1996bronco

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It looks like the 210 is roughly 30-50% stronger than the 190 concerning torque rating.

Concerning overall strength though, keep in mind that this isn't a solid axle. In a SFA forces from the large tires are translated directly into the tube and the differential. In an IFS setup, those same forces are translated into the a-arms. This means the only significant forces that should be acting on the differential will be the torque from the tires

If you keep the front dif open, it should theoretically be fine on 35s, but if you put a locker on there, I wouldn't bet on it lasting very long, especially if you have a tuned motor.

If I get the chance I'll throw another post with some quick math compared to some conservative torque ratings from Dana.
 

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Did not think about the IFS. I guess the shorter the axle to the diff makes it stronger, or would that make it more rigid, breaking instead of flexing?
 

Imissmy1996bronco

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edit/update list at bottom of post.

Fair warning, math ahead, and I’m using this post to explain all my reasoning in case any of you want to poke holes in it.

Tl;dr. If you blow the differential or axle shafts, it will be by mashing the throttle in low range, in first gear, and on some surface that nearly or completely locks up the tires. If you are going to keep your shenanigans to 4H and keep the diff open, you should be fine even running 35s, if you want to use 33s, the m190 should definitely be sufficient, but I wouldn’t trust it with a locker. Someone with more automotive focused engineering experience may have better insight here though.


Disclaimer: I wrote this post bourbon in hand, so take it all with a grain of salt, and if you put 35s on your bronco and your diff blows up, well, it’s not my fault, I’m just some guy on the internet doing math.

Okay, so both the 2.3 with the 94.7 crawl ratio, and the 2.7 with the 64.7 crawl ratio come in slightly under 30,000 ft-lbs at the wheels, so I’m going to round up to that number to keep it on the conservative side.

both lockers and larger tires will affect the strength of an independent differential in the same way, which is they make it more difficult for slippage to happen (and slippage reduces stress on the differential), larger tires increase the moment arm that the frictional force can use to react against the torque coming from the differential, while lockers make it more likely that you will get into a situation where neither tire will spin to release energy.

so, using this document from Dana

http://global.dana.com/~/media/dana...ochures/lv-drivelinecapabilities-brochure.pdf

we can reasonably assume the weakest torque rating for a m190 is 2000 nm, which translates to about 1472 ft-lbs. (edit1: this number is for a driveshaft for the same vehicle category as the m190, so we can use it as an assumption, but it is not a rating for the differential)

so that is the torque you can reliably put on the input to the differential with the output held stationary.

well, that’s a pretty big gap between 30,000 and 1472, first, remember that the torque rating is on the input, not the output, so we can divide that 30,000 by 4.7 (since this was used to get the final crawl ratio, this also makes it independent of the gear ratio on the differential). That leaves use with ~6400 foot lbs, a lot closer to our rating, but that is still a lot more than the diff is rated for. (Edit2, the rear axle, is rated for ~6000 ft lbs, and I will update with proper front diff ratings if I find them, the m210 is likely similar) (edit3, axle input limits for solid axles have been found, m190 should be similar to a Dana 30, so that means my original estimate of 1472 is pretty close to the rating.)

For a worst case scenario on either diff, you would want to use this number, because this is assuming the other axle is spinning in the air, and not taking any of the torque off the front, but since that would require you to be high centered while rock crawling with the front axle locked up, let’s use a 66% multiplier in the pursuit of a more reasonable situation, so even though the front axle is locked up, the rear axle only has enough load on it to require about 1/3rd of the system torque.

This gets us down to about ~4300 lb-ft. (Edit4, the m190 has a rating of 3687 ft lbs, or 5000nm, so it is actually really close to this scenario.)

Now yes, this is still a good bit higher than the rating, but remember, there are quite a few factors mitigating ever reaching this situation. For one (though I don’t know if this applies to the bronco) a lot of vehicles limit max torque in first gear just to avoid these kind of situations. The 2000 nm rating is the lowest I could justify for the m190, it is likely higher than that. (edit4, it is 5000nm)

And to reach this situation, you need to be in low range, first gear, mashing the throttle to max torque, with the rear axle able to spin (though locked to the same speed as the front), and both front tires held stationary (unless the axle is locked, in which case only one needs to be). That is a pretty rare, and honestly stupid situation to be in.

Now let’s compare 33s to the 32s, those only apply an extra half inch of moment arm to the cv shaft. (I’m assuming true tire diameters because I’m lazy). That extra half inch means an extra 3% of moment. So with 33s on, you should be at 97% strength of what you would have with the oem tires, and I guarantee that the engineers are using a higher margin than .03 on this thing.

(35s would be a little over 9% more stress)

It also looks like the weak point is more likely to be a cv joint than the diff in this system, but that’s based on a pretty quick glance through the Dana document.

Basically, if you don’t put a locker in it, and as long as the a-arms and other components are the same as the Sasquatch (and from what we’ve seen the only difference is the coil overs and the diff), then you should be fine even going up to 35s on the m190.

edit1: looks like that 2,000 nm number is for a drive shaft, not the differential, this is why you don’t drink and math kids.

edit2: the m190 and the m210 use the same spline shaft for axle shafts, so I suspect ford uses the same axles/cv joints regardless of the diff. Also, the m220 ring and pinion gear in the rear has a torque rating of 8200 nm or 6000 ft lbs, which, if you recall was roughly the worst case torque case. This is probably pretty similar to the m210, still looking for documentation to confirm numbers on the front diffs though.

edit3: the following document shows input torque rating for solid axles, the m190 is roughly equivalent to a Dana 30 in this respect, so my original number is still a close estimate.

https://danamedia.concentrekdev.com/cfs/files/media/8noM33P7W9GALAPhL/x5302-dag.pdf?store=original

edit4: found a table with ring and pinion ratings by diameter. Looks like the m210 is slightly weaker than previously projected (6500nm rating), but is still a pretty stout unit. The m190 has a 5000nm rating.

https://www.therangerstation.com/ranger-tech/dana-advantek-axles-ford-ranger/

2E248B2B-F439-4181-9020-136C35DE8BBA.png
 
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Imissmy1996bronco

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Did not think about the IFS. I guess the shorter the axle to the diff makes it stronger, or would that make it more rigid, breaking instead of flexing?
The weak point is much more likely to be the cv joints than the axle itself. It is likely to be stronger than a solid axle compared to the ifs just due to the flex and bending loads from the tire being flung around being transmitted to the a-arms, and not the axle tube.

edit: I meant the diff and axle shafts will be more isolated from stress, not that it’s necessarily going to be able to handle large tires
 
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AMCheese

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Doesn't sound like putting a lift and some bigger tires will be an issue.
 

MaverickMan

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I personally dont do much of anything crazy in rocks. Mud water and tall hills is my jam. I want the factory front locker because of the iron housing. The locker will really only assist me when im trying like hell to get up somewhere slick. But yeah a dana 30 was not what i was hoping for on a almost 5000lb rig. Hopefully like the early broncos they will figure that out in a year or so.
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