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 Post subject: Larger tyres versus CVs
PostPosted: Sat Jun 08, 2019 3:43 pm 
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Joined: Fri Apr 14, 2017 4:51 am
Posts: 7
On the DMax will fitting larger tyres (265/70/17) 804mm, stress the CV's more than a 50mm lift?

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PostPosted: Sat Jun 08, 2019 5:22 pm 
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Joined: Wed Feb 05, 2014 1:22 am
Posts: 615
Location: adelaide hills
In the drive train, the outer part of your tyres is after the CV's. Engine, gbox, trx case, axles, CV's, hubs, tyres.

CV's can't recieve more torque than what the engine / drive train is capable of providing.

Standard tyre 245 / 70 R 16 is nominally
16 x 25.4mm + 2 x (0.7 x 245)mm
= 406 + 343 mm
= 749mm diam

Yours will be
17 x 25.4 + 2(265 x 0.7)
= 802mm diam

I say nominally, because the inner diam of the tyre is smaller than the outer diam of the wheel, so total diam is smaller than the formula would suggest.

Anyway, using 802 vs 749 you'll need 7% more torque at the centre of the hub to get up the same hill. Your motor won't suddenly produce 7% more torque, so your CV's won't suffer from that. But if you used to get up the hill with your foot nearly flat to the floor, now you might need to have your foot flat to the floor, or through it.

So, no more torque through the CV's than what they were originally designed for, but perhaps for a little longer or more often. Depending how many big hills you go up, your right foot might be pushing harder, and more often, so CV's might they wear out quicker.

Much more likely to break CV's because you loose grip, spin the wheel, suddenly gain grip, wheel stops, engine doesn't....

Whereas a 50mm lift changes angles, something I can't comment on.

I've thought in the past that a 50mm suspension lift gets the cabin higher, so you don't get wet carpets, but it leaves the wishbones & rear axle & diff the same height, eg vulnerable to rocks. I've thought it's be nice to increase tyre diam 4", ie get the diff 2" higher. But then I spose the sidewalls would start bending or twisting or something. Hmm.., thinking out aloud, maybe put 17 or 18" wheels on, get the diff up, leave the CV's the same angle. Above my pay grade.

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PostPosted: Sun Jun 09, 2019 8:45 am 
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Joined: Fri Apr 14, 2017 4:51 am
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Thats good, we cant afford to pay any more. :D You've more or less confirmed what I thought Garrytre.

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PostPosted: Sun Jun 09, 2019 3:20 pm 
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Joined: Fri Mar 17, 2017 3:12 pm
Posts: 58
Location: Sunshine Coast
Hi wuigi
Got lost in the translation. I take it you have 17 inch rims Standard tires 255/65r17 .I fitted 265/70r17 (The only legal option ) and tow 2.5 ton of van and have not noticed any dramatic lack of power or fuel consumption. If you are worried about drive angle fit free wheeling hubs as a back up. And drive sensibly.


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PostPosted: Sun Jun 09, 2019 3:49 pm 
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Joined: Sat Oct 12, 2013 5:36 pm
Posts: 1546
wuigi
Any increase in ride height causes more CV drive angle. The problem is when on lock and when transferring power AND the CV is near it's maximum operating angle the CV may pop open. So as advised drive wisely.
The fitting of Free Wheel hubs allows trailer maneouvering without winding up and breaking CV's on hard surfaces. Not much fuel saving but it does mean the CV and the boots are stationary while driving and only turn when locked in for offroad stuff.


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PostPosted: Sun Jun 09, 2019 4:56 pm 
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Joined: Fri Apr 14, 2017 4:51 am
Posts: 7
Yes, still on standard wheels. Planning to do the change when the lease expires, how do the 265/70's look on these wheels?

The hubs are now on my list if I can get hold of a set.

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Last edited by wuigi on Tue Jun 11, 2019 4:08 am, edited 2 times in total.

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PostPosted: Mon Jun 10, 2019 11:29 am 
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Joined: Fri Mar 17, 2017 3:12 pm
Posts: 58
Location: Sunshine Coast
Hi Wuigi
265/70R17 tyres on the standard 17x7 rim. And Free wheeling hubs.


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PostPosted: Mon Jun 10, 2019 1:53 pm 
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Joined: Fri Apr 14, 2017 4:51 am
Posts: 7
Thanks for the view towtug, looks OK to me. Think I could try that with the tyres first without having to get different wheels.

What brand are the hubs?

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PostPosted: Mon Jun 10, 2019 2:21 pm 
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Joined: Fri Mar 17, 2017 3:12 pm
Posts: 58
Location: Sunshine Coast
One thing i forgot to mention! The speedo is spot on now.
The hubs are a different story and will cop a lot of feedback.
They are $100 ebay jobs but do have a 5 year guarantee. You can pay 3 times that amount for only 12 month guarantee. I do carry the original caps if the s#^$ hits the fan.


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