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  #1  
Old 11 Jun 2007
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Question R80/7 tyre size for offroad.

I'm a wee bit confused about what tyre sizes I can fit to my '79 R80/7. For normal road use I use Michelin Macadam 50's. The Macadams were fitted to the bike when I bought it and I have no reason to change them for everyday use.

Now I am thinking of going a wee bit further afield and exploring some (not too demanding) tracks and trails. Having done some really mad offroad stuff in the sixties on old army Triumphs and BSA's ( basic road bikes with a solo saddle), I know that any solidly built road bike can hack a few potholes and gravel. I have therefore resisted the urge to buy a 'proper' RTW type bike (whatever that is?) and stick with the trusty airhead which I know is easily tough enough to put up with a few bumps and knocks.. The choice of bike is easy but now I'm stuck with the problem of getting suitable dual purpose tyres to fit the rims. I've read all the stuff about ' which tyre' and I'm quite up to speed on what's on the market.
The problem is, when I select my rim or tyre size (or my bike type) in the suppliers search engine, all I get is the standard ( recommended) range of road tyres for my bike. If I search for tyre type , I can see loads of great dual purpose and dirt tyres but not a set to match my bike or rim sizes. Sometimes I can find a front, sometimes a rear but never a matching pair. My knowledge of tyre sizing is obviously limited to vintage cross ply so I will throw the problem at this forum and see what turns up. Here is the low down.

Present tyres are Michelin Macadam 50's
3.25 x 19 Front. 4.00 x 18 Rear.

Wheels are alloy, rim sizes:-
185B x 19 Front. 215B x 18 Rear.

I NEED: A (preferably matched) set of tyres which will be suitable for mostly paved roads with occasional dirt, pothole, gravel and dodgy east European ( or even Russian) roads, farm tracks and camping trails. I intend to avoid sand and mud, ditches, rocks, corn fields, forests, watery stuff and anything which will cause my teeth ( and the bike) to rattle badly and which will make me fall on my ass too often..I probably won't exceed about 90 (ish) mph and I prefer to use inner tubes regardless of tyre type.!! I usually travel solo and I travel light but with standard Krauser touring panniers. I'm a canny rider and a canny Scot so I expect to see some miles for my pennies so soft sticky stuff doesn't tickle my sporran (so to speak!). Good mileage IS desireable but not at the expense of my life..!

I've read with interest the reports of such tyres as the TK80, Tourance, Distanzia and similar but can't really make any serious choice until I find out which of these are available to me. So...

First question. What alternate tyre sizes will fit my rims ( and the bike)?

Second question. What Tyres do other R80 owners use in rough terrain?
(R100 and other airheads too but not GS or G/S)

Third question. Think of a question I should have asked and answer it for me please. (That's not really a question..but you get the drift)

Could somebody explain the tyre size and rim size thing to me in simple terms? The way I understand it, some modern tyres seem to be only available in certain sizes not compatible with mine. I need a 185x19 front but some tyres are only available in 90/100x19. I need a 4.00x18 rear but many otherwise suitable tyres are not even listed in that size. What's a 120/80x18?. Will it fit a 215x18 rim? Duh!. I need help...

Hope you can help. I don't want to be stuck on Tarmac all my life.

Thanks in advance.
Ian.
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Old 12 Jun 2007
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Ian, you could hardly have picked a more technical subject...........

The last figures in your tyre sizes, ie, 19" and 18" refer to the wheel diameter in inches and will always be the same, whatever tyre you fit.
Starting with the front tyre, a 3.25x19. The 3.25 refers to the nominal width of the tyre, again in inches. The tyre wall depth will also be approx. the same, ie. 100% of the width. Alternatives that will fit may be marked with a metric size, eg 90/90x19. Here the tyre is approx. 90 mm wide, but the tyre wall depth is 90% of the width so is referred to as a low-profile tyre. On sports bikes this can be as low as 55%.
The rear tyre, a 400 x 18 is roughly 4 inches wide with a 4 inch side wall and 18 inches in diameter. The nearest metric equivalent would be 110/90 x 18. This is 110 mm wide with a side wall depth 90% of this, fitting on an 18 inch rim.
Just to throw a spanner in the works, there are also a few imperial, low profile fitments, eg 3.60 x 19, 4.10 x 18 or 4.60 x 18 etc. You won't find the kind of tyre you're looking for in these sizes. so forget I just mentioned it!
Your bike and wheel sizes do not lend themselves readily to off-road tyres. These generally being 21" and 17", front and rear respectively.

Your wheels are not air-proof so you will need inner tubes, even though the tyre may be marked as tubeless.

Try Cambrian Tyres in Aberystwyth who have an enormous amount of advice, expertise and tyres in stock.

Hope all this helps in some way.
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Old 18 Jun 2007
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R80 Tyres

Hi,
Thanks for the explanation. I think I have it fairly well sorted now. I've found various suitable tyres which will fit my rims. All I have to do now is read through the general tyre forum and see what others have said about them.
Thanks for your invaluable help.
Ian
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Old 27 Jun 2007
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Ian, I have the same bike as you, mine's an ex-Met Police bike. I too am looking for some dual purpose rubber for it and would be interested to know what you ultimately fit to the bike.

The problem as I see it is width: on my bike there is precious little clearance between the sidewall of the tire and the driveshaft. Knobs on the tire would seem to rub.
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Old 28 Jun 2007
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R80/7 Tyres

Hi Mac,

I don't know what tyres you have looked at yet. There is a only small selection out there due to the wheel sizes. I'm trying to avoid out and out knobblies. I don't think the bike will like them and neither will I although I read in another forum that one BMW ( not an R80 either!) owner had that problem and cured it by shaving off a little rubber from the knobbles ( or knobbs or knobblies whatever!).
I suppose it can be done but it raises a few issues that I don't want to get into right now if there is an alternative.

What I have been doing lately , is reading up on certain tyres generally. Then , if I think they look promising, I go to the manufacturers site and check out the sizes. More often than not, the good ones are only available for 21" fronts and 17" rears. ( Or some other non compatible size) Dratt!
I've established what the alternative sizes are for the bike so its just a question of trawling through all the suppliers lists and see what I can get that fits.

Since I intend going across Russia, I had thought about buying tyres somewhere along the route. ( I will be mailing a spare set of road tyres to Korea for the highway touring bit of the trip)
A company called MITAS ( an amalgamation of Michelin and Veritas) manufacture a huge selection of off road tyres in Praque or thereabouts. There appeared to be dozens of compatible sizes and offroad styles from mild to totally mad.
I read about some RTW guys who have used them and are quite complementary about the performance and mileage when compared to some of the Top Shelf tyres we are always hearing about from the RTW riders. These guys were doing much more offroading and in more difficult terrain than me and my R80 will attempt. I am in the process of checking them out but I am still hopefull that I will find something more widely available.

On the up side ( for me) is that I just won a pair of original alloy R80 wheels, fitted with Metzelers, on ebay. The wheels have still got the original paint on them and look fantastic compared to mine which have had years of quick sprays or hand painted silver to keep them from looking really cruddy. Best bit is I got 'em for less than £50 delivered. ( Happy Chappie!)

The significance of that is, I now have a spare set of wheels which will make it a lot easier to mess about a bit with tyres whilst keeping the bike on the road.

I'm currently working on a web page where I will post all the fine detail, piccies and techie stuff that I am researching ( Including mapping, gps, kit etc.) hopefully, with some answers and solutions. I will also be posting articles and piccies of and about R80/7's. ( maybe R90/R100 and other Airheads.)
If you would like to contribute a pennies worth , piccies, articles whatever, please let me know! (Tech tips wanted!)
I'll send you the link when it's up ( very soon!) Also, if you would like some links to all the tyre manufacturers sites that I have found, let me know, I can post them here until the web page is up.
If you have any queries or further questions, please feel free to ask.
Thanks for taking the time to reply!
Ian
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