New wheels - need help with tyre sizes
Hi,
I'm a little confused with all the different tyre sizes people are running on their G's. They all seem to have a different rolling cirumference which must affect the speedo. My W463 SWB 300GE has 16" alloys and 205/80 R16 tyres currently. I have just bought some 20" x 9 AMG style alloys (ET48) and I'm not sure what tyre size to put on them. As the wheel is 9", I assume I can only go to 265 width tyres, but as these are not a "standard" width, I will probably go with 255. Its the profile I'm not too sure about. In order to match the rolling circumference, I reckon I need 255/45 R20 tyres, assuming the ones on the car currently (205/80 R16) are indeed the correct ones for the car! Help please! Also, will my wheels/tyres fit in the standard arches? Thanks!
AMG wheels on the G have very limited tyre brands that produce the correct size. For the 18" versions with 285 width, only Yokohama and Pirelli of the major brands. For 20" I am not sure what the correct width should be, but you may indeed be limited in choice.
Try this site:
http://www.wheel-size.com/size/mercedes/g-class/2007/#trim-g-55-amg-eudm
AMG wheels on the G have very limited tyre brands that produce the correct size. For the 18" versions with 285 width, only Yokohama and Pirelli of the major brands. For 20" I am not sure what the correct width should be, but you may indeed be limited in choice.
Try this site:
http://www.wheel-size.com/size/mercedes/g-class/2007/#trim-g-55-amg-eudm
Actually, the wheels have just arrived and they are 20 x 9.5j so I'm guessing I can go upto 275 width tyres:
http://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart
Any help would be appreciated!
I believe that the wheels are effectively the same as the genuine AMG G Wagon 20" wheels part number:
A4634013002
What I need to know is will the clearance and speedo be the same for all G's? Are the AMG wheel designed for AMG G Wagons only? Will they fit with standard arches? What is the correct tyre size? I believe these wheels come with 275/50 R20 tyres but that would not match the rolling circumference of my existing tyres so are the speedos calibrated differently?
The wide tyre option for the 463 on 16" wheels is 265x65x16 which gives almost the same rolling circumference to the 205x80x16 standard tyre.
If you opt for the 275x50x20 wheel/ tyre option you will increase the rolling circumference by nearly 7% over the standard circumference with a corresponding error in the reading of your speedo ( it will read 7% slower than your actual speed).
You will need to get your speedo re-calibrated if you want it to be accurate. Only the later G350 and AMG G63 models run the 20" wheels and would have their speedos calibrated to suit.
The new size will fit under your arches provided that you have the standard 463 extensions although you should check that there is sufficient clearance between the tyre and the steering arm on full lock.
Thanks bigblock. With 265/65 R16, the speedo would be 2.2% faster than my current setup, ie. 61.3mph at 60mph speedo reading. Is that an acceptable variance or would Merc adjust for that at the factory if wider wheels were fitted?
7% difference is obviously not acceptable. Is there an easy/cheap way to recalibrate the speedo or is it better to try and match the rolling circumference with a smaller profile tyre like the 275/45 R20? I presume on a 1991 car I have an old fashioned speedo drive cable - is there an adapter that can be added to the cable to allow adjustment?
I have standard wheel arches. How would I check clearances before I buy tyres?
Before you worry too much, I'd check your current set up against a satnav which can give you accurate speed (at least if you're traveling in a straight line on the flat.
You might well find that your current speedo isn't all that accurate anyway. It could easily be out by as much as 7%.
I think the standard w463 sizes are actually 265 70 r16 and 265 60 r18
speedos usually over read by about 7%
Late vehicles with ESP have the tyre and wheel sizes programmed.
Before you worry too much, I'd check your current set up against a satnav which can give you accurate speed (at least if you're traveling in a straight line on the flat.
You might well find that your current speedo isn't all that accurate anyway. It could easily be out by as much as 7%.
Just took it out with a speedo app on my phone. Seems to be very slightly over reporting the speed. When the speedo said 50mph, we were doing 48mph according to the app. I guess that might be the allowance from the factory for the wider wheel option.
I think it's just that it's very rare to find a speedo especially of your vintage that is 100% accurate.
My advice would be to get the wheels and tyres that you want and will best suit the car and the sort of roads you want to drive on. Then get an accurate comparison between "real" speed and what your speedo says - then decide if you need to worry about whatever its inaccuracy is then.
I know nothing about technical matters but if your G is an automatic then I think the speedo drive comes from the transmission not the wheel (but others on here will no doubt correct me) and if so Adrian is the man who can source the necessary part to correct over/under reading.
Thanks bigblock. With 265/65 R16, the speedo would be 2.2% faster than my current setup, ie. 61.3mph at 60mph speedo reading. Is that an acceptable variance or would Merc adjust for that at the factory if wider wheels were fitted?
7% difference is obviously not acceptable. Is there an easy/cheap way to recalibrate the speedo or is it better to try and match the rolling circumference with a smaller profile tyre like the 275/45 R20? I presume on a 1991 car I have an old fashioned speedo drive cable - is there an adapter that can be added to the cable to allow adjustment?
I have standard wheel arches. How would I check clearances before I buy tyres?
A 2.2% variance in rolling circumference is not very significant and I doubt that MB would make any adjustment to the speedo calibration at the factory for this.
Even 7% is not really significant if the vehicle is not ESP equipped and the rolling circumference measurement is only used for the speedo reading. As others have said the speedo probably already reads 5-10% overspeed anyway.
The G Wagon relies quite a bit on a larger sidewall profile to soften the ride and I would not recommend a 275/45 R20 combination unless you like having you fillings rattled loose.
If you turn your existing wheel to full lock you can see the distance between the inside edge of the tyre and the steering arm. If you measure this gap you can then work out if the extra dimensions of the 275/50 R20 will fit without fouling the arm.
I'm with bigblock - I wouldn't recommend a very low profile tyre for your G. Maybe unless you're planning on doing all your driving on super smooth French motorways.
Thats one reason I did not go for anything bigger than 20" as I thought the ride would be unbearable, apart from it looking "wrong". I note that the new ones come with 21" now. I have bought a set of Pirelli MO fitment 265/45 R20 which is a standard ML tyre. I have not had them fitted yet. I'll see how they work out - they only result in 1.7% speedo difference. If they don't look or feel right, I may go for a larger profile and seek Adrian's help with the speedo!
JOIN THE GWOA
This website and forum are provided for the benefit of enthusiasts and owners of all Mercedes Benz off road vehicles, in particular the G Wagen. The costs of development, upkeep and provision of the site are met entirely by the annual subscriptions of club members. If you are using the site and are not a member of the G Wagen Owners Association please consider joining. You will have access to areas on the site that are not open to non members, to club trips and meetings and to technical assistance. In addition your contribution (only £25 annually) will help us maintain and develop our website for future users.
Who's new
- Jaffa_JIM_23
- Wrabstar
- GG
- KTMSCANIA22
- 280ge
Also forgot to mention I will be going for road tyres as I don't plan on going off road, keeping my 16" for winter/off road use as they have M+S Continental tyres on them.