My Chiffon Ivory JB74 SZ5 - blog/mods/build thread

Tyres....

So 4 and half years ago I fitted some Maxxis Wormdrive AT-980 tyres in 215/75R15. They have done almost 30,000 miles and I've been extremely happy with them on all surfaces and have surpassed my expectations of All Terrains, so much so that I even fitted a set to the Land Rover Ninety.

The fronts have worn quite a bit in this time. It's partly my fault, I should have rotated the tyres, but never got around to it. There was still some life in them, but the fronts were low enough that I decided to change them. Also my recent trip to Salisbury Plain where I got beached a few times on the diffs really sealed the decision to upgrade to a different size.

Now, as many of us do, I've been thinking of tyres for some time. I've had many thoughts on this.

I'm a big believer in tall narrow tyres. So in an ideal world the size I wanted to go for is a 6.50 x 16, which seems to be the size you find on Japanese modified Jimny's.

 
 

Sadly this size is non-existent in the UK. I did find them in France, but at near to £180/tyre it just didn't make sense. Such a shame 

My next thought was 205 x 16 (205/80R16), which are slightly fatter and slightly shorter than a 6.50 x 16, but fairly similar and available in the UK. In theory these should be approx 28.9" tall, a reasonable jump up from the 215/75 at 27.7". The next hurdle is finding some suitable 16" rims. Once again this proved a bit of an issue. I could find wide 7" steel rims at sensible money, but these are too wide for such narrow tyres. I wanted a 5.5 or 6.0" tops. I did find some nice alloy rims of the right dimensions, but they worked out at close to £1300 just for the rims!!! So this ultimately was binned as an idea on the grounds of cost.

Following this, I've heard and seen people running 30.9.50R15's, now technically they need a wider rim than the factory rim, but they will fit and go on. My only reservations here were, they might rub some of the plastic. And as this is my daily driver I didn't want to run the risk of disabling the vehicle fitting new tyres that didn't fit. Its not the time of year to really be messing about outside trimming wheel arches and the like and my knee injury really prevents me doing this without help from others anyway presently. I'd hoped to find some steel wheels going cheap that I could buy and get a single tyre this size mounted to fit for size, but this didn't pan out.

I was also concerned about gearing. A 30.9.50R15 is approx 29.5" tall. I've love to buy the SUMO Gears reduction gearset from Jimnybits, its a bit of an expense at almost £1000   but I've not been able to find anyone willing to install the gears. So this was also out as an option.

In the end I've gone for the option I didn't think I'd even consider which is 235/75R15. These are also 28.9" tall, so match the 205 x 16's in height, but are of course fatter. Although in the grand scheme of things, still fairly narrow. For instance a Land Rover 90 would have come on 235/85R16's, taller but same width and normally considered a narrow tyre. The Jimny is smaller and lighter, but the wheelbase is not so different.

I've also had quite the internal debate on whether I should go for MT's or AT's. Ultimately I'd love MT's and think they always look better. But the reality is, this is my daily driver and while it does go off road, it doesn't do anything extreme off road. I've also been hugely impressed with the Maxxis Wormdrives, reinforced in Salisbury Plain, where the tyres performed brilliantly in terms of traction.

So my final decision was a set of five 235/75R15 Maxxis Wormdrives. This is the first time I've ever replaced tyres with the same pattern. I've always gone for something different in the past. Which is a real testament to how good the Wormdrives have been.

I've only done some road miles so far. I'm pleased to say I've not really noticed a huge difference in performance from the 215's. Which has surprised me, as I noticed more of a drop going from the stock 195's to the 215 AT's originally. I would say it also feels like it rides a little better too, a tad smoother and more supple. I wasn't really expecting this, I'm not sure if its just that they are new tyres or the increased sidewall height or a combo of both. MPG I'll have to report back on. And I've not taken them off road yet, so don't know how they have impacted low first and the crawl speed. 

One thing of note however, despite having now gone up two tyre sizes. The speedo still reads fast. Not as bad as before, but it is still 2-3mph fast at 30mph.

Digging the new look, this size seems to fill the arches better with the 2" lift.

 

 

Nice. And I agree that a 650-16 would be perfect and also an excuse to get a set of the grand vitara 5 spoke alloys that I love. The only thing is the 235 is fairly narrow but a jimny is very light so I'd be interested to see what you find off road with regards to ground pressure and it's effect on traction. I know your worms are more aggressive than my at5's which have massively improved my traction over the duelers so I'm interested in your findings given just a size change?

Done a few miles on the new tyres now, including a longish run down to Reading and back yesterday.

Overall very pleased, it does ride better and somehow feels higher up. I know it isn't much in real terms. But it does make the vehicle feel more Tonka toy to drive.

Performance wise, in 30mph zones and on country roads with some inclines you can notice the different gearing. Say anything below 3000rpm but mostly sub 2000rpm stuff. It still goes well, but you can tell the gearing is a little taller. I've also found that you can end up running in 4th more, where previously you'd be in 5th. I think this is more just getting used to the different speed ranges than anything else.

If you put your foot down, say 3000rpm+ and especially  wide open throttle to the red line it seems to go every bit as well as it did before. I can still see the same speeds on the speedo on the same bits of roads.

MPG I will still need to report back on. But I can say the numbers reported by the OBC have dropped. Although you need to bear in mind that you are covering a different distance now, due to the increase in tyre circumference. I think mpg will be impacted, but I'd guess not by as much as OBC will claim.

I've also been through some of the radar speed signs and the speedo at 30mph is much more accurate. Probably only 1mph out now. Harder to tell at higher speeds. But it must be better overall.

 Still need to take it off road properly, but no complaints thus far.

 

 

235/75r15 are 4.3% bigger than 215/75r15 so all things been equal you should have seen a 4.3% drop in the indicated speed and a 4.3% drop in fuel economy as the ECU thinks you have gone 4.3% less distance.

4.3% at 30mph is only 1.3mph so if you noticed about 1mph less on the speedo then that is about right.

If you got an indicated 40mpg before, your ECU will indicate 38.3mpg and given the extra weight of the tyres around 1 - 2 mpg that might be about right.

Still no one fitted bigger tyres to get better fuel economy.

It does look really good on the bigger tyres, especially with the 2" lift.

Robin