High Diff gears Question

[jktom]

Hi all, bit of a strange one, but thought I would put it out there.
If I were running higher / taller diff rations, where is the effect more noticeable, 1st gear or 5th/6th.
Reason - i run 32" E Load rated tyres, and since I have installed them, have noticed a real choppy ride. My gut tells me it is the tryes. I am thinking of changing to D or C load tyres, but to do this, have to got to 33's or 285's as almost all tyres in 265 are E rated. I already have 3.73 gears. So if I change the tyre size, where will I notice the difference the most, 1st gear or 5th / 6th gear. I know there is about a 3% difference in all gears.
Thanks

[task82]

G'day mate, I've recently put on 285/70R17's to my 2011 JKwith standard gearing. I do a whole lot of highway km's and the biggest thing I have found is I need to drop down to 5th when going up hills, other than that it's all the same. Around the city i find i need to put a bit of extra weight on the accelerator when taking off at lights, no big deal though.

My fuel consumption has also gone up which was to be expected. Also, my speedo was out until I used the AEV Procal that I got from Jeep Konection in Melbourne.

Hope this helps

[Paul-JK]

I'd say that sounds about right......you'd have a bit more difficulty in pulling away (a bit like trying to pull away in second gear though not as pronounced) and then it should be doing lower rev's overall at an equivalent speed. That means in general you'll want to be in a lower gear at an equivalent speed to keep it in the main torque/power band and 6th will be less useful when it comes to hills as the rev's may be too low.

I know mine's an auto and therefore the 'box will help a bit but I didn't notice a great deal of difference in the drivability when I went to 285's. I can tell a difference, but if someone who didn't know the car got in and drove it they wouldn't think anything was wrong. It's not that noticeable. It might be with the 3.21 ratios but not with the 3.73's.

[Banshee]

I have 3.21s & there is bugger all difference between 255/75R17s OEM & 285/70R17 Bighorns to me. (Although the M/T is ~15mm larger in diameter.)

Mind you, with the 3.21:1 diff ratio, 6th is virtually useless on anything except flat road or downhill, anyway. And 5th isn't much better. Local driving rarely sees my above 4th, and that is only if I don't have to accelerate uphill. (I live in the Blue Mountains, so guess how often that is!)

[jktom]

I know there is an effect. i can do all the calculations etc, and it is about 3%. My question is would you notice that 3% more off the mark or in 5th / 6th. My gut tells me you would notice it more in 5th and 6th, as 150 - 200 revs being dropped in these gears is noticeable. However in 1st gear, where it is lower geared, more effective torque because of the gears, you would not really notice it. You could take it further to suggest that you not notice it in low range.
So if you would not notice it in low range, and you would in 6th, my guess is that 1st is somewhere in between?
PS. I know its a dumb question, but i am really confused. I have spoken to two so called experts who race cars, one told me 1st gear is most noticable, the other said top gear.

[Banshee]

I would agree with 5th, 6th.

For a racer, acceleration in 1st is what they need off the mark, but for normal driving it is the top gear/s where the rev difference is largest that you will notice it.

[Paul-JK]

Doesn't surprise me that a racer thinks 1st's the problem. He has to pull away quick and higher gearing will make that harder. I assume at higher speed he'll be rev'ing the nuts of whatever he's driving and he just drives in whichever gear feels right. He's not looking at how drivable the car drives at a certain speed in a certain gear.

My guess would be that under normal conditions it'll be 5th and 6th that you'll notice it most in normal road driving. I'd say that while you'll notice it in 1st, you'll adapt to it and work with it whereas you can't do that with the high gears. In higher gears if it won't pull it won't pull and there's nothing you can do other than change gear. Obviously you'll notice it more in 1st when fully loaded or towing, but as you say, it's only a 3% change so it shouldn't make that much difference.