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-   -   Why do wheel sizes vary? (http://www.horizonsunlimited.com/hubb/bmw-tech/why-do-wheel-sizes-vary-7905)

hunternielson 19 Aug 2003 18:37

Why do wheel sizes vary?
Another Newbie question for you: Why do some big trail bikes have 18" rear wheels and others have 17" rear wheels? What are the advantages of each? I understand why a larger front would be better for off-road, but what about the rear?

I'm considering swapping to an 18" rear for my DAKAR, but wonder if it's worth the trouble.


John Ferris 20 Aug 2003 03:36

The old GS had an 18 inch rear wheel but it had 3 wheel lugs holding it on. The newer GS had a 17 inch rear wheel with 4 wheel lugs.
I think that you would have to change the rear drive.

Grant Johnson 20 Aug 2003 03:58

I think Hunter has an F650 Dakar, which comes with a 17. Swapping to an 18" rim is not worth doing. You can, but you'll almost certainly run into clearance problems with the fender.

All new "off-road" bikes and for that matter street bikes are using a 17" rear wheel.

An 18" rear used to be the standard.

Now manufacturers are using 17's primarily because they are using fatter rubber, which gives better traction (because we now have much more power) and a better ride. But fat rubber with an 18" rim makes the rear wheel just plain too tall and very heavy.

Grant Johnson

Seek, and ye shall find.


One world, Two wheels.

hunternielson 20 Aug 2003 14:42

Thanks guys,

Grant, if the 18" gets in the way of the fender and adds extra weight while screwing up the hight/geometry of an already tall bike, why do I find guys out there swearing by the change to their DAKAR to make it "off road worthy"? Does the larger wheel give improved (or perceived) improvements off road?

I'm pretty sure I'll stick with my 17" wheel. I'll throw on a rimlock and a knobby tire and go for it...my real worry now lies two threads earlier with my FI question.


Grant Johnson 24 Aug 2003 06:25

If people are DOING it and it works I sure won't argue - but my concerns stand if I was thinking about it for the first time.

True motocrossers are using 19" wheels these days, up from 18".

But for big dual purpose bikes, 17" rules as the standard.

Feel free to go 18", but I wouldn't bother - I suspect that those who swear by it are fairly typical - they put in a lot of work and expense so it HAS to be better. It may well be, and someone who really knows may have been the first and said it was better - so everyone follows. Doesn't mean Joe Average can tell the difference.

Practice with what you have, set it up right and ride and ride and ride.

A great rider on a crap bike will do things that seem impossible and magical to the average rider on a great bike.

Grant Johnson

Seek, and ye shall find.


One world, Two wheels.

AliBaba 25 Aug 2003 19:38

If you would like to use mx-tyres you will find that most of the manufactures only make them in 18" or 19" so a conversion will give you more tyres to choose from.
I use MT21 (17" - high profile) and find them good but if I have had 18" I could get used tyres (of many types) cheap from a mx-shop.
In some countries (Malawi, Kenya,...) they drive mx/enduro but not big bikes and then 18" it's easier to find then 17".

Yes, it's true that mx-drivers start to use 19" (often with a lower profile) but the enduro drivers still stick to 18" and a higher profile.

Most bikes today come with 17", but eg KTM uses 18".

Is it worth it? I don't think so but you might.... :-)

AliBaba R80GS

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