Tyres - what did you get?

**jimbomort** · 01-05-2010, 09:13 PM

Originally Posted by T&M

We got the Hancrooks and have to say that they are starting to look very ordinary at 20,000kms. We will definately be looking at an A/T (all terrain) tyre when these are ready to throw out, which will probably not be very long.

be interested to here how you go when you do as may do same, or may even go for low roll resistance, thinking at this stage of goign for larger diameter tyres, for increased ride hide and a better look, but fair bit to suss out first and then engineers cert needed and warranty issue decisions to consider

with all that said hope we get a fair bit more than 20k out of ours, if so that will be the least I've got out of any tyre I've ever had. Got 80k out of some michelin MXV3's on a series 2 liberty

**T&M** · 02-05-2010, 06:39 PM

Originally Posted by jimbomort

be interested to here how you go when you do as may do same, or may even go for low roll resistance, thinking at this stage of goign for larger diameter tyres, for increased ride hide and a better look, but fair bit to suss out first and then engineers cert needed and warranty issue decisions to consider

with all that said hope we get a fair bit more than 20k out of ours, if so that will be the least I've got out of any tyre I've ever had. Got 80k out of some michelin MXV3's on a series 2 liberty

It's not that hard to just go out and get the next diameter up in size. I have driven 4WD's for years and have always had larger diameter tyres on without any hassles. Of course check with your insurance first. Some insurance companies allow larger diameter tyres as long as they are on the policy. We will be getting larger ones when these are worn - which I'm afraid probably wont be long.

**jcubed** · 03-05-2010, 03:47 PM

Hi All,

I see some posters are considering larger tyres to improve ground clearance. Having done a relatively detailed study on this, I thought the attached results - written for publication in a local motoring magazine - may be useful.

The bottom line is, watch the LOAD RATING.

How to turn your sedan into an SUV – Part 1

After a lot of research you finally bought that new softroader and now discover that unbeknownst to you, the manufacturer has been somewhat creative in terms of specifying the ground clearance, providing an arbitrary value instead of the minimum.

Once your initial disappointment had been overcome – and this took a while - analyzing the situation presents the bottom line: This softroader was bought to do trails and sand – like the one you owned before - and once the ground clearance has been improved, this should be possible.

All that is required is the next tyre profile size. How difficult can this be, after all?

PLAN A: Increasing the tyre size

Upsizing the standard 215/65R16 tyres to either 215/70R16 or 225/70R16, should provide (theoretically) 11mm or 18mm of lift respectively. The latter option should do the trick nicely.

The resultant studying of various manufacturers’ tyre data sheets, together with numerous calculations, provided puzzling results, to say the least:

• Rolling circumference calculations did not add up to those provided on the data sheets
• The above values were useless anyway, due to the tyre flattening at the contact area when loaded
• The pressure at which the above Static Loaded Radius was valid, is not stated, etc.

But you knew you were beat when the table showed that the upgrade (or so you thought) to the 215/70R16 size resulted in a radius which was actually 1mm less than that of the smaller tyre.

After the initial bewilderment had died down and you could think straight again, you figured out that this was due to the load rating difference between the two tyre sizes – of the same type! The lower load rating of the theoretically larger tyre, resulted in a more pliant sidewall, resulting in a reduced radius.

The practical alternative was for the local tyre dealer to fit a different tyre type to three of the four wheels, attach them to the car and then compare the distance between the centre of each wheel and the ground to that of the original to confirm the lift, if any. A somewhat tedious process, the success of which depended to a large extent on the goodwill of the tyre supplier.

Summarizing the above practical difficulties, and adding some others below, showed this solution to really be a non-starter:

• Unless you’re a tyre expert – and this probably excludes the majority of us – the tables provided by the tyre manufacturers can at best be regarded as “for indication only”, and using so-called “tyre calculators” based on this information, will not necessarily lead to the right answer.

• Lift comparison calculations between different tyre sizes would only be valid if the load rating remained the same.

• In order to determine whether there is enough space inside the fender/wheel arch, each of these larger wheel/tyre combinations should be fitted to a rear and front hub and the suspension then fully compressed (up to the bump stop/damper limit) and in the case of the front wheels, the steering turned from lock to lock to see whether it does not rub anywhere. It is rather difficult for the non-specialist at home to compress an installed McPherson strut fully.

• The average brand-name 16” A/T tyre costs upwards of R1700. This multiplied by 5 (yes, don’t forget the spare) makes it an expensive option. And what to do with the almost new tyres that the vehicle came with? Due to tyres having a shelf life of around 6 years - as the rubber degrades regardless of use - they can’t necessarily be mothballed until selling the car with “virtually new tyres”.

• A number of softroaders come with a space-saver spare wheel. These tyres are not available in the same variety of sizes as normal tyres. But then again, for off-roading you would discard the Marie biscuit anyway and carry a full size spare.

• Also, in many softroaders the spare wheel is stored underneath the boot floor. The cavity may not be large enough to accommodate a bigger tyre. You could perhaps deflate the tyre and squeeze it in, but even if you have (of course you have!) a compressor to re-inflate prior to use, this is tedious. Well, for those of us with healthy spines, there is always the roof rack ….

• The torque decrease is proportional to the diameter increase. Even though it may not be much (3% and 5% respectively for the options above), the vehicle already does not have low range, and any further loss of low-speed crawling ability will detrimentally affect its off-road capability. The upshot is that at least the speedometer would now be less optimistic.

This clearly calls for an alternative solution.

Hope this helps, and not just adds to the confusion.

**T&M** · 03-05-2010, 08:58 PM

Hmmm... there's an interesting read! Most of this stuff is not rocket science you realise!

We're still getting the larger diameter tyres because that's what suits us. It may not suit everyone, but I am aware of the necessary details and the trade-offs required. I also have had past experience with this on other various vehicles too.... and know a couple of expert tyre people that can lend further advice and tech assistance.

The difference that eg. 11-18mm makes on a bumpy track could be the difference of driving through or getting hung up somewhere or maybe doing damage. Together with perhaps some slightly taller coils, should be a pretty good combo if keen to drive some dusty tracks.

Everyone has slightly different ideas of what they want to achieve - some lower and get larger wheels with lower profile tyres, others may leave their cars standard. It's all good!

**jimbomort** · 07-05-2010, 02:04 PM

Originally Posted by T&M

We're still getting the larger diameter tyres because that's what suits us. It may not suit everyone, but I am aware of the necessary details and the trade-offs required. I also have had past experience with this on other various vehicles too.... and know a couple of expert tyre people that can lend further advice and tech assistance.

The difference that eg. 11-18mm makes on a bumpy track could be the difference of driving through or getting hung up somewhere or maybe doing damage. Together with perhaps some slightly taller coils, should be a pretty good combo if keen to drive some dusty tracks.

Everyone has slightly different ideas of what they want to achieve - some lower and get larger wheels with lower profile tyres, others may leave their cars standard. It's all good!

yeh I too are still keen to increase clearance. Was thinking some tyres in 65 18's would be great, get the diameter increase while keeping the 65 series profile as a compromise tyre and would look great on the Tig. However they are clearly out, very little if anything available in those sizes. No matter look is not everything to me.

I've noticed that most 4wds have higher profile tyres, few go over 17's and most have 16inch rims. Am guessing higher profile tyres needed to have enough give for off road work. Sticking with around 65 profile probably a good compromise. Tyre bloke I spoke with seemed to think going up a bit wouldn't be much of a problem, though acknowledging they will roll a bit more in cornering. I'd prefer to keep to at least close to the same profile for that reason. I am not going to be a hard conernign junki, but current dynamics seem a good compromise.

Tyre diameter doesn't vary just with rim and profile. Looks like tyres with same rim and profile, increase in diameter as they get wider, just to confuse things. And looks like load rating important too if tyre on the road, will actually be truly larger in diameter. Complicated as jcubes article points out.

Tyres for R17's seem more expensive than R16's, so need to look into cost carefully

According to guy I spoke to, best thing re legalities, is to check insurance company is OK with, then tyre place will just check can turn etc Ok without any dramas. Didn't seem like an engineering cert was practically necessary? But I'll be checking that from a number of sources, and interested in others experiences.

According to guy I spoke with my current tyres (215 65 16's) are 685 mm in diameter. The best options looked to be:
235 65 17's, around 740mm (increase of 55mm in diamter)
or
225 75 16's around 745mm (increase of 60mm)
I am not certain these would fit, I expect they are probably at the upper limit if not over it.

To me doesn't seem a lot of point changing if cant get at least 20mm extra clearance out of it, or at least close.

Anyway be interested to hear others experiences or how you go T&M

**T&M** · 08-05-2010, 12:53 PM

These would be close to our choices:

Coopers -
ATR 215/70R16 708mm diameter Passenger construction or
ATR 225/75R16 747mm diameter Light Truck construction.

BF Goodrich -
All Terrain A/T LT215/70S16 2145mm circumference Light Truck construction

Mickey Thomson -
ATZ 5RIB LT225/75R16 747mm diameter Light Truck, 10 ply construction!

I have had excellent mileage out of all of these brands before.

... and you also know that the speedo actually "reads" incorrectly, that is; shows a speed higher than you are actually travelling. I have checked and rechecked this with 2 GPS units. So by fitting slightly larger tyres, it will go close to "correcting" the readout (without having to do any adjustments via vagcom etc...). Of course apart from the usual benefits of being to travel on some rougher roads without fear of damaging the stock factory tyres.