Rear Wheel 17 or 18"
 

Hi,

Apart from increasing top speed and reducing acceleration,
Please could someone explain the benefits of having an 18" rear wheel over a 17" with regards to off road capability and RTW availability?

Cheers.

RTW
The common belief is that there are many more bikes with 18 inch rear wheel around the world in less populated places .. think 250 trail bikes, 250 farm bikes etc. Therefore you are more likely to be able to conveniently buy a 18 tyre quickly and cheaply. It may not be the 'best' tyre but it will get you to a place where you should be able to get the tyre you want. I've had to inflate the available 18" tyre to 45 psi to get it to stop squirming! But it did get me going, avoiding waiting days for a 'good' tyre to arrive.

The difference in off road capability is much much less than the riders contribution ... the expression 90% rider 10% bike springs to mind. :scooter:

In terms of travel, as Warin has said it is down to availability when on the road, I have travelled using bikes with both and found 18" easier to find, 17" are around but can be more expensive.

Larger diameter wheels deal with obstacles more easily. Ergo enduro bikes, Dakar bikes etc run 18 inch rear wheels. Motorcross bikes use 19 inch rear wheels.

All run 21 inch front wheels.

Its all related to running the largest possible wheels on a bike designed to be ridden over rough surfaces

That depends on overall gearing. Wheel size is just a one component of the gearing equation. The easiest components to change are the sprockets. If you change wheel size by an inch, you could keep the same acceleration and top speed by changing front sprocket 1 tooth, or rear sprocket about 3 teeth. At the end of the day, no wheel size is any more or less restrictive to acceleration or top speed than any other ... because final drive ratios on chain drive bikes are so easy to change.

Modern MX bikes use a low profile 19" rear tyre for sidewall stiffness. The overall diameter is nearly the same as a normal 18".

Thanks for the replies,

I have just ordered an 18" rear wheel and have been looking on Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator to see how it affects the Speed, RPM and acceleration. It seems like a good site.
I am not too concerned with increasing top speed or acceleration :rofl:
I intend to put a more off road tyre on for those occasions were I can use it!

It looks like my stock 120/90/17 has near as damit the same circumference as a 120/80/18.
Add a 46T rear sprocket and RPM at 70Mph only slightly increases.
Hopefully this will make 2nd gear a little more useable.
Right now I am finding 1st revs high too soon, and I'm struggling to go slowly in 2nd because the RPM is too low,
I know 1 tooth will not make much difference but adding 2 means a new longer chain. Also I think a smaller front sprocket will affect it too much and REvs will be too high for any sort of motorway miles.

Waffling on now sorry :oops2:

18" rear tires are much cheaper than 17" and you have a much bigger range to choose from. (e.g. 140/80-18 are around AU$160-190, whereas 140/80-17 are AU$260+)

On smaller bikes that use 120 or 130 width, the cost-difference is negligible, but for bigger DP bikes upwards of 750cc, the narrower tires overheat and the 140 or 150 width can be very expensive. I think the wider 17" tires are generally made to be tubeless, thus adding to price, but I can be wrong.

I got myself a 18" rear wheel!
It came with a part worn 120/80/18 Tyre fitted.
The rim is the same width (2.5) as my 17".
I have read it is possible to fit a 130 or 140 wide tyre!
Is the any benefit of choosing wide/narrow tires?

Narrower tires generally provide more grip and less rolling resistance- in the 80's, manufacturers tend to go for wider back tires than they do now on trailbikes (e.g. XR500 came standard with 150 rear compared to 120 currently fitted on CRF450's).

Wider tires (generally) have a higher load carrying capability, and will run cooler and provide longer tire life.

What bike are you riding? No ones even asked. doh
What sort of riding are you doing? Going RTW? Out of EU? S. America? Adventure bike? Dual sport? :confused1:

Tire availability varies round the world. If you're building a Race Bike then the 18" is the better choice. Enduro racers use them for reasons layed out earlier, motocrossers use 19"'s for handling. For travel on a dual sport the common 17" tire is fine ... and IMO, preferred.

In this part of the world (USA, Canada, Latin America) 17" tires are cheaper and more common than 18" tires. I ride a DR650, it uses a 120/17 in stock form. You can go BIGGER (many run a 130). It rides fine with a 130. Both easily available in the Americas.

Both sizes are common are available in street, dual sport and knobby style tires. If you go above a 130 on the DR650, handling goes to Hell. This pretty much true for the KLR, F650 a few other dual sport bikes. A wide tire can ruin handling.

More dirt biased dual sport bikes use 18" rear tires. (XR650, XR400, XR250) Not sure what the Yam's use ... we haven't had XT600 here since 1995, but I think it's a 120 or 130/17, same as KLR or DR650.

Throughout Mexico and Latin America it's easier to find a 17" dual sport rear tire than an 18". You WILL find 18" for small (80cc to 250cc) bikes with narrow rims. Those tire won't fit your wider 17 or 18" rim. Years ago, 18" tires were more common, but no longer the case around here. Maybe in Europe you don't find 17"'s as common dual sport bikes aren't sold there?

As long as you travel where 18"'s are sold you'll be OK. Over here there are not many street biased dual sport tires in 18" size ... and the 18" dirt tires can be quite expensive.

Good luck with the new wheel ... hope it fits on the bike OK. bier

:oops2:

He seemed happy with the responses: everyone kept it general. Sure he would have come back with a response on what he rides (and where) if he felt it's relevant.

Or maybe not everybody's looking for a tech-wiz and folders full of data :innocent:

Hi,

My bike is an Xt600e,
Coming from a road bike background I was a little concerned about these 50/50 dual sport tyres. They sound 50% crap lol. So I put some Conti Trail attack 2 tires on it for 90% road use and got some second hand wheels for off-road (Michelin T63). I figured I could just change the wheels over for when I can go green Lane or trail riding. As I could do with a new back tyre I was wondering weather it was worth getting a 130 instead of a 120. I would like to go Round The World but responsibilities dictate I generally just go Round The Wales :mchappy:

Thanks for all your help/advice.

The Conti's are great road tires, should be great on your XT. Good choice. Are you using your 18" rear wheel for the Conti's? Still running the 21" front wheel? 130 rear?

If you really want the BEST road set up on your XT, I would go with WIDE 17" wheels front and rear. Then you can run proper Sports bike tires and pretend your riding IOM. :thumbup1:

The T63's are not 50/50 tires ... should be quite good off road. In very deep mud you may want something even more aggressive. But generally very good, IMO, and even pretty good on dry roads, not so much on WET roads.

50/50 is something like a Kenda 270, Shinko 244, Heidenau K60 Scout, Bridgestone Trail Wing, Mefo and Mitas and many others. 50/50 tires can be quite good both ON and Off road. Good on easy dirt and gravel roads and mild trails too. NOT good in Mud. My Shinko 244 rear and T63 front works well for just about everything.

50/50's are great for travel due to how versatile they are and long lasting too.

For rain riding on pavement try Avon Distanzia, Michelin Anakee or Metzeler Tourance. You can get them in either 17" or 18" rear, 21" front. Great road tires on wet roads, IMO and a bit longer lasting than your Conti's.

bier

I have an 03 XT600E, is it just a straight swap between the 17" and 18" wheels or do you have to do more mods and is it easy enough to do??

Wayne

The wheel came off an older bike, 3AJ I think, It's alloy rim and came with a 40 tooth sprocket.. not good with the stock 15t front sprocket! I popped on a 46T from J&S :thumbup1:

The only other thing you might consider;; if you are struggling to put a foot down with a 17" wheel it will be even higher with an 18", but it will help a bit by getting an 80/18 instead of a 90/18 Tyre.

Other than that it just goes on OK.