Hi krew,

wondering if anyone can point me to a resource, or chime in with their expertise, regarding the effect of wheel diameter on performance and handling dynamics.

I understand the effect of front wheel diameter on steering speed and ability to take bumps...but Im curious about the effects of rear wheel diameter.

It seems curious to me that the K1 and 16v RS had a 17" front and an 18" rear rather than 17" at both ends. what was the reason for this?

Smaller front wheel lowers centre of gravity and transfers weight forward. The bike will dip into corners more easily and make it easier to get around corners, like altering understeer and oversteer in a car but it will also reduce ground clearance on corners. The same result to some effect can also be achieved by increasing rear wheel diameter but without affecting ground clearance.

The manufacturing accountants' input is probably that a larger rear wheel raises gearing and is probably a cheaper manufacturing route than tooling up for and making a very limited run of higher geared final drive or gearbox units [though changing a ratio or two isn't a huge problem] which would also be needed for a more powerful bike with a higher top speed.

For most of us in normal road riding we would manage with either I should think.

92KK 84WW Olaf wrote:Smaller front wheel lowers centre of gravity and transfers weight forward. The bike will dip into corners more easily and make it easier to get around corners, like altering understeer and oversteer in a car but it will also reduce ground clearance on corners. The same result to some effect can also be achieved by increasing rear wheel diameter but without affecting ground clearance.

Changing a front wheel on a given machine might lower the front end by half an inch, but I challenge anyone who thinks that they can feel that very slight difference in steering geometry. If that was the case then try dropping the forks through the top yoke by 13mm and see if you can feel that.
The heros and posers will say that it makes a huge difference and that they can fell it, but try it for yourself.

BobT wrote:

92KK 84WW Olaf wrote:Smaller front wheel lowers centre of gravity and transfers weight forward. The bike will dip into corners more easily and make it easier to get around corners, like altering understeer and oversteer in a car but it will also reduce ground clearance on corners. The same result to some effect can also be achieved by increasing rear wheel diameter but without affecting ground clearance.

Changing a front wheel on a given machine might lower the front end by half an inch, but I challenge anyone who thinks that they can feel that very slight difference in steering geometry. If that was the case then try dropping the forks through the top yoke by 13mm and see if you can feel that.
The heros and posers will say that it makes a huge difference and that they can fell it, but try it for yourself.

Bob - you never tried riding a LeMans IV MkI and Mk2 back-to-back. That 16" front wheel on the MkI really, really, really screwed up the steering characteristics of the Guzzi. It just flopped in everywhere - it was truly horrible. It was the only Guzzi I never wrote about because I couldn't find anything nice to say about it; the factory obviously agreed because they reverted to an 18" wheel for the second run.

On road riding with a touring configuration its not going to make a big difference but I did find it does become noticeable when you are travelling with gear on a trip.

All the stickers say not to exceed 120kmh with panniers and kit on, but little changes become noticeable at that speed, although a slightly off tyre pressure will be much more noticeable.

I have used 100/90, 110/80 and 110/90 front tyres, prefer the 110/90 but it raises the front end by 9mm. It may well be subjective but I don't notice a big change in handling but feels nicer on the road. On the other hand instead of 130/90 rear I use 140/80 which drops the rear all of 5mm along with a further drop on the suspension. All taken together means I can get my feet on the ground better making the K more manouverable in a car park etc.. It's not a sports bike and not ridden like one and in those conditions as BobT says not so noticeable.

Handling is no just a matter of wheel diameter.
The angle of the steering axle, the value of the trail, the lenght of the wheelbase are also important factors.
About the wheels, if you consider 2 wheels of the same weight, the smaller one will be more reactive to turn because of gyroscopic efforts that are less than a bigger diameter.
But a big diameter wheel is more stable, and gives more confort because it bumps less on road holes than small wheels. That's why off road bikes have an 21 inch wheel, to climb easier on obstacles.
The width of tyre and rim are also important: the larger they are, the heavier is the handling.
On modern road bikes, the large tyres are pretty stupid: they just are designed to imitate race bikes, but to keep an acceptable handling they oblige to have a reduced direction angle, with a high risk of death wobbles, and you have to put knees on the tar if you want to make it turn.
Yet...


Check on the video that big tyres and sport geometry are not always an avantage, specially in curves under 100 mph...

And to underscore that.....look at bicycle tyres, the fastest track tyres are the thinnest going. Admittedly with a lot of power you need more tyre to get it on the road, but bicycle handling is brilliant.

Oh, BMW do make bicycles so not entirely off topic.

floyd wrote:Hi krew,

wondering if anyone can point me to a resource, or chime in with their expertise, regarding the effect of wheel diameter on performance and handling dynamics.

I understand the effect of front wheel diameter on steering speed and ability to take bumps...but Im curious about the effects of rear wheel diameter.

It seems curious to me that the K1 and 16v RS had a 17" front and an 18" rear rather than 17" at both ends. what was the reason for this?

I really don't understand this at all Floyd

the k1 and 16 valve jobies with big rear rims have an 18 inch front and an 18 inch rear ,... where did you get the idea that they put an 17 on the front ?

all the above comments are true ...but did anyone think about it on the subject of k bikes ?

perhaps the lower profile rear 18 inch rubber gave a much more tractable feel  (and it does just that, in spades  )...all well and good for road bikes , and the convention keeps going on ..

you might have to consider that radial type tyres of the lower profile variety were not "at that time " extremely common at all, nor were really good shockie designs with rebound damping for a start .

I guess for us older folks .we do remember the changes in technologies ... the radial tuned suspension theologies in cars ..and anything on the road for that matter .

but now with technologies of advanced compounds of rubber and stuff ...there are some amazing results ...but consider that there was no way of releasing a 200 hp bike to the open market at that time .  but for racing, we would all be riding around on bloody "bantam bsa" type thingys (hmm  royal enfield 500 single carries a bit of sway here) ...thank heavens for "Ariel " Vincent " and many more "outside the box" thinkers

interesting thread ..I wonder where it will take us ?

The K100 2V has a 18 front and 17 rear
the K1 K100RS 16V and K1100RS have a 17 front and 18 rear
The K1100LT has a 18 front and 17 rear
I think that the factory went with those sizes because they were popular sizes at the time and slowly evolved to using wider rims and then 17 front and rear with the production of the K1200 models
Many bikes of the era of the K100 had the 18 front and 17 rear which is what my Z1300 Kawasaki has along with most of the big bikes of the day.

RicK G wrote:the K1 K100RS 16V and K1100RS have a 17 front and 18 rear

I'll second that because mine is exactly that.

I know that dropping my front end by 13mm makes a difference that you can feel.  I prefer a nimble, agile bike over a bike that is stable at all costs.  Same reason I'd never put a shorter shock on the rear to lower the seat height, it slows the turnability of the bike way too much.

A smaller front wheel doesn't just lower the front (which it might not do anyway if the fork length has been altered at the same time to adjust for the height difference).  A smaller front wheel turns into a corner more easily as it has less gyroscopic effect which makes the wheel want to stay where it is.

All that said, My K100RT with its narrow 18" front and 17" rear is much easier to ride around town than the RS4V with its wider radials and 17"F wheel which seems to steer like a truck at low speeds.

Al

Hi Charlie,
36 31 2 310 708 CAST RIM, YELLOW FRONT - 3,50X17
36 31 2 311 272 CAST RIM SILVER FRONT - 3,50X17

As stated above, fitted to K1, k100rs 16v 👍

as arrived off a k1 rear ...now silver
there may have been more options and I'm sure trapper etc could contribute
not sure about the front though ..

Yeah, 4.5x18 rear and 3.5x17 front...

I'm considering the 4.5x18 rear mod to go with my k11 18" front... Or k1200 17's...

Going to put my beast back into RS mode now that I do all my off roading on Yammy XT

yeah the xt is better for the dirt ....um easier to pick up at least ....depending on how you load it up
water and fuel held high can be a backbreaker

good luck

My 85 K100 had 18" wheels front and rear. I suspect that the rear wheel was widened (weld bead all around the wheel on both sides), but don't know if any other mods were done. Did "Y" spoke rear wheels come in 18"?

Only with the drum brake on the K75c and some R models around mid 80s

Another thing when considering wheel & tyre sizes is the load pound ratings & componds (hard or Soft).
Mates used to install smaller diameter wheels with fatter widths ( often GSXR wheel conversions).
This always made me laugh during my Harley days. Blokes would spend thousands to convert there bikes wheels & tyre sizes, Often stuffing there handling & locking them selves in to sport bike type tyres at larger dollars & less millage.
 At the time a rear 140/18 metzler was costing me $240 and last up to 18000km
 mate would spend $650 on his 260/17 & only last him 4000km
Know which I'd prefer give me the best millage for my bucks.

arbalest wrote:My 85 K100 had 18" wheels front and rear. I suspect that the rear wheel was widened . . ..

What was the size of the rear tire when you got the moto?

I use 110/80/18 Front and 140/70/17 on all my Ks....83 K100RS, 84 K100RT, K1100LT. But I do have also  have K1100RS set for my K1100LT and dont use it because I prefer the LT set up and handling.

arbalest wrote:My 85 K100 had 18" wheels front and rear. I suspect that the rear wheel was widened (weld bead all around the wheel on both sides), but don't know if any other mods were done. Did "Y" spoke rear wheels come in 18"?

Not unusual 'back in the day'. Sold by Luftmeister and welded up by a California-based company that still does wheel widening. The idea then was to be able to use on K75/K100 the not-so-common-any-longer 160/60ZR18 radials that were used on R1100 & K1100RS.

I simply went for an 18" rear three spoke from a K1100RS with a K75S 18" front three spoke on my K100RS Down Undah.

K11RS & K75 wheels used, not R11. The only viable tyre option out back on the K11RS wheel is 160/60ZR18, same as for the enlarged five spoke 18" rear.

Thanks for the info.

Avoid R11 front wheel because most use a speedo drive on the left which requires a different bearing & spacers. As well on R11 rears there is enough difference between models (RS, RT, R) to avoid them and just use K11RS wheel unless you've got the variety to compare against each other.

Thanks for that.

Does anyone know of a darkside tire to fit the 3 spoke K1100 rear rim?

K11RS 18" is a tight fit 'tween calliper & tyre/rim, but it can be done.

Or you could use the narrower K11LT rear three spoke and you'll be laughing, with 140/80R17 tyre.

Tire size?

Two Wheels Better wrote:K11RS 18" is a tight fit 'tween calliper & tyre/rim, but it can be done.

Or you could use the narrower K11LT rear three spoke and you'll be laughing, with 140/80R17 tyre.

Asking about darkside tire because I am building a sidecar rig.

arbalest wrote:Tire size?

As above, K11RS rear wheel use 160/60ZR18 tyre.

Any problems mounting that car tire to the motorcycle Wheel?

arbalest wrote:Any problems mounting that car tire to the motorcycle Wheel?

That's not in my experience or interest, but perhaps someone else...

Thanks.

Car tyres are not meant to go onto motorcycle rims, the tyre bead will not mount onto the rim correctly and under hard cornering can roll off the bead and instantly go flat. Make an adapter and use a car wheel which along with being safer will also give you a far greater range of tyres.

I have a car tyre on the rear of my sidecar, not fitted to a K wheel though. Its on a custom made 15" wheel. If you use a 17" K1200RS wheel you might find a car tyre to suit. Many modern sidecar rigs are fitting car tyres direct to the wider 17" rims used on current bikes.

Two Wheels Better wrote:

arbalest wrote:My 85 K100 had 18" wheels front and rear. I suspect that the rear wheel was widened (weld bead all around the wheel on both sides), but don't know if any other mods were done. Did "Y" spoke rear wheels come in 18"?

Not unusual 'back in the day'. Sold by Luftmeister and welded up by a California-based company that still does wheel widening. The idea then was to be able to use on K75/K100 the not-so-common-any-longer 160/60ZR18 radials that were used on R1100 & K1100RS.

Wow... I've been searching for such enlarged rims for years, to build a endurance racer K100. Regulations were limiting the width to 4.00, OEM 3 spokes rims are 4'50 wide, so not admitted. What is the width of these Luftmeister rims?
Thanks, it puts an end to my quest!