4th Gens on bigger than stock tyres

Question to anyone with a 4th Gen JB74 that is running an AT/MT in 215/75R15 or 235/75R15

Truthfully, what impact have they had on performance?

I'm quite shocked at fitting some 215/75R15 AT's to mine. It feels like I've lost 10% plus power or I'm driving with the handbrake on.

The tyres are barely any bigger than standard in terms of diameter. The maths say there should be about 11mm in it. But according to GPS it has made no impact on the accuracy of the speedo at all.

However it has had more impact on performance than fitting a set of 34" extreme mud tyres to a Discovery Tdi.

On a test stretch, the Jimny now clocks 4-5mph lower speed than it did previously. Which is a fairly significant drop. And you can feel you have far less overtaking capability now.

I'm a bit shocked at the impact on performance. The reason I'm questioning it is. The week before fitting the tyres, I had a new transfer box fitted by Suzuki (to solve it jumping out of low range). I'm sure this is unrelated, but it is the only other recent change to the vehicle. With the new transfer box and standard tyres, it went as well as it ever did. It was pretty instant on swapping the tyres over that caused the performance loss (or an amazing coincidence). But I want to rule out all scenarios, as going back to the standard tyres would require getting some extra wheels.

The Jimny seems to freewheel absolutely fine. Doesn't pull to one side or the other at all. Can't smell or feel anything getting unduly hot.


When people say the Jimny is slow, I've always contested it. As I thought it went rather well. And importantly felt very peppy, zingy and willing. Now though, I would indeed say it feels sluggish, underpowered and slow

I didn't have the original tyres on for long, but don't recall much of a difference fitting them. The larger ATs are likely to be significantly heavier than the stock tyres (about 4kg difference per wheel between stock alloys with 215/75 Yokohama ATs and stock steels with 195/80 Duelers) which will damp performance a bit. I didn't measure performance when I tested steels, just economy (about 2-3mpg worse with the larger tyres).

This is to be expected. You are now running with wider tyres so your footprint is bigger and that will create more drag. Add to that you have changed the gearing and cumulatively you have dented performance and increased fuel consumption. On my Landcruiser in standard trim 50-70 mph in 5th gear was 10 seconds. Change to A/T tyres and it went to 13 seconds. change again to M/T in 33" dia as apposed to 31" and it went to 16 seconds. Also adding lots of extras will make things worse. The Jimny is a lightweight motor and cannot cope with all the gear that my landcruiser could lug around.

Roger

300bhpton wrote: Question to anyone with a 4th Gen JB74 that is running an AT/MT in 215/75R15 or 235/75R15

Truthfully, what impact have they had on performance?

I'm quite shocked at fitting some 215/75R15 AT's to mine. It feels like I've lost 10% plus power or I'm driving with the handbrake on.

The tyres are barely any bigger than standard in terms of diameter. The maths say there should be about 11mm in it. But according to GPS it has made no impact on the accuracy of the speedo at all.

However it has had more impact on performance than fitting a set of 34" extreme mud tyres to a Discovery Tdi.

On a test stretch, the Jimny now clocks 4-5mph lower speed than it did previously. Which is a fairly significant drop. And you can feel you have far less overtaking capability now.

I'm a bit shocked at the impact on performance. The reason I'm questioning it is. The week before fitting the tyres, I had a new transfer box fitted by Suzuki (to solve it jumping out of low range). I'm sure this is unrelated, but it is the only other recent change to the vehicle. With the new transfer box and standard tyres, it went as well as it ever did. It was pretty instant on swapping the tyres over that caused the performance loss (or an amazing coincidence). But I want to rule out all scenarios, as going back to the standard tyres would require getting some extra wheels.

The Jimny seems to freewheel absolutely fine. Doesn't pull to one side or the other at all. Can't smell or feel anything getting unduly hot.


When people say the Jimny is slow, I've always contested it. As I thought it went rather well. And importantly felt very peppy, zingy and willing. Now though, I would indeed say it feels sluggish, underpowered and slow

I may be wrong, but havnt you also fitted some under plate protection recently too??

Ive lost a bit of zip too with 215/70/16's, but im still happy with performance.

Ive never understood folks who thinknthe jimny is slow, nor with cornering lean. I musr be a bit of a grandpa behind the wheel or something.

There's a very fine window for alterations to a Jimny before you affect the performance. Too much weight combined with taller tyres is going to hurt. Each on its own is less noticeable but cumulatively its game over.

Why not try to borrow some standard jim wheels for the weekend (Gen3 will do). You can always lend them yours, you would then get a better idea if it's the tyres or all of the mods you've done. I suspect Lambert is right, there's a limit to how far you can go without penalty. Chris