Anyone here with experience on chunky mud tyres? (esp Bridgestone M/T 674)

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When you say extremely steep terrain, I assumed you were talking about low range off-road conditions. To me extremely steep is in the 40 degree plus range, which the Jimny handles in low range even with the big tyres. For on road use, it is exactly as you have said.

I have no idea what the thread starter defines as extremely steep, in fact, as I suggested in my first response, if he can make it up the slope on the stock tires, he doesn't need a larger mud terrain tire, and since he has a stated concern on the impact of the larger tire on the vehicle's on road performance & noise, that a smaller, less aggressive tire would probably be the better option.

I certainly wouldn't be happy with the impact you describe the 235/75 as having - I don't know what re-gear options are available (I haven't done a whole lot of research yet), but I believe the transfer case used with the automatic offers reduction on high range which the manual one doesn't, so that might be one option.

For now I'll stick with the 215/75, they meet my requirements.

215/75R15 is a wise choice. 

From a gearing perspective, the auto has a 30% lower transfer ratio than the manual, so that difference is too much. I have ordered gears from Protrack,gr.  They do a 7%/77% and 17%/87% high/low reduction gears.


SAXI,, - Did you receive your gears from Protrack in Greece? What gearing did you go with in the end 7%/77% or 17%/87% for use with your 235/75 tyres? How did you find the reduction gears? Did they improve the on-road drivability? Were the gears good quality? Did you find that once fitted they caused a whine noise? Was 5th gear now a usable on-road gear? 
I have a siimilar dilema, I have 235/75 R15 tyres fitted and want the best reduction gearing for road use and am not sure whether the 7% or 17% gearing reduction would be best for road use? Any thoughts, suggestions and recommendations would be greatly appreciated.
Many thanks, David
 

Hi Fordem,
Re your comment:
"Using the stock 195/80R15 as a reference, a 215/75R15 is 1.52% taller and a 235/75R15, 5.8% taller - 1.52% is not a significant increase in size, so the impact you're feeling on road is more likely to be caused by the heavier, wider tire. 5.8% however is a substantial increase over stock, and given the impact I noted with the 215s, I would not consider that without some form of re-gearing.

I looked a little more closely at the numbers, the auto Jimnys use 4.3:1 axle gears, manuals use a 4.09:1, just around 5%"

Given the above, for road use only, using 235/75 R15 tyres, would you recommend the Protrack 7% High ratio reduction, rather than the TrailGear 17% High ratio reduction?
I am in a dilema as to which gears to get for road use?
Thanks, David