[Turbo329]

Guys,

I was wondering if this has ever been done before. If any club or pro racers have ever and a 16in rim in the front and a 17in rim in the back. I saw a photo recently from Eric Bostroms 2001 bike and the front wheel looked really small and questioned if it was a 16 inch and in the back was a 17in.

Does running mismatch rim sizes jack up the handling?

 

[mikstr]

The CBR900RR (92-99) ran a 16-inch front wheel (and one of the most popular mods for those bieks was fitting 17-inch front wheels from CBR600F3s and 94-97 VFR750s). The geometry could likely be made to work with a smaller front wheel, but you`d be facing a major hurdle when it comes to tire selection.....

 

[Turbo329]

The CBR900RR (92-99) ran a 16-inch front wheel (and one of the most popular mods for those bieks was fitting 17-inch front wheels from CBR600F3s and 94-97 VFR750s). The geometry could likely be made to work with a smaller front wheel, but you`d be facing a major hurdle when it comes to tire selection.....

Insightful. Thanks.

Would it sharpen handling?

 

[Multitard]

I'm pretty sure the Ducati moto gp bike GP9 used a 16" rear wheel and larger tire profile to decrease chatter.

 

[polePosition]

I'm pretty sure the Ducati moto gp bike GP9 used a 16" rear wheel and larger tire profile to decrease chatter.

Most of the GP grid todfay uses a 16.5" rims (not 16") not long ago (~10 years) it was a mix of 17" and 16.5".

However due to different tire section the circumference of the tire itself is almost identical to tires installed on the 17" rims.
In other words it’s the same size doughnut just the hole in the center is a bit smaller.

16.5" rims are widely used in both SBK and MotoGP as it provide better ripple absorption on extreme lean angles.

There is a wide selection of slicks on 16.5" tires.
However running slicks for a track day bike and especially might be too much, and quite likely better and chipper improvements exits.

 

[TrickLidz]

Don't know...but, I know that my old VF700 Honda had 16" rims and the handling SUCKED!!

 

[mikstr]

16" fronts were all the craze in the early to mid-80s (Interceptors, FZ750, GS750,.....), the last holdout being the aforementioned CBR900RR....

 

[Jami6989]

Most of the GP grid todfay uses a 16.5" rims (not 16") not long ago (~10 years) it was a mix of 17" and 16.5".

16.5" are REQUIRED in GPs.

2.8.1 Permitted wheel rim sizes are as follows:
Front
Rear
125cc
2.5" maximum width
3.5" maximum width
Moto2
3.75” x 17” only
6.00” x 17” only
MotoGP
4.0" maximum width
16.5” diameter only
6.25" maximum width
16.5” diameter only
In the MotoGP class for the seasons 2010, 2011, 2012, each manufacturer is restricted to two different widths of front wheel rim, and one width of rear wheel rim, within the maximum widths noted above. All MotoGP wheel rims must be 16.5” diameter.
Each MotoGP manufacturer must notify the Technical Director of their selected wheel sizes no later than the close of technical control at the first race of the 2010 season.

 

[Turbo329]

Thanks guys for the feedback. I basically want to know how the bike's handling would be affected if a 17.5 is out back and a 16.5 is in the front.

 

[polePosition]

16.5" are REQUIRED in GPs.

2.8.1 Permitted wheel rim sizes are as follows:
Each MotoGP manufacturer must notify the Technical Director of their selected wheel sizes no later than the close of technical control at the first race of the 2010 season.

It is like that since the control tire rules and it wasn't like that in the past.

Since most of the grid went to 16.5" somewhere in the late 90s' early 00s' there was no reason to continue 17" development and support.

 

[Busy Little Shop]

Mr.RC45 came stock with a 16 and when I raced it the 130/70/16 was
quick on the steering and meaty on the contact patch... when I
switched to a 17 magnesium Marchesini for lightness and ran the latest
rubber the new 120/70/17 slowed down the quickness of the steering
dramatically... to gain back the same quickness required a complete
different set up... so it doesn't matter the rim size when you take
the time and do a rake and trail study of your bike and then change
the set up to gain the desire of quickness...

To find the diameter of any tire size use my handy formula...

tire width x aspect ratio / metric conversion + rim size = diameter

130 x .7 x 2 / 25.4 + 16 = 23.16 inches or 588mm...

120 x .7 x 2 /25.4 +17 = 23.61 inches or 600mm...

So this drawing I made on my wall shows the diameter difference
between a 130/16 and a 120/17 is 12mm or .472 of an inch... what Honda
engineering did was split the size of the 120/70 and the 120/60 17
with a 130/70/16... if the tire companies would cooperate I believe
the 16 has chance for a strong come back... what gave the 16 a bad
name was the flexy frame of the Honda CBR900RR... when slapped on some
sticky rubber the frame just through in the towel...

 

[Plwtwo]

On 996/998 Duc's we used to run a 120/60 tire on the front..it helped turn in effort quite a bit..On the CBR900rr's the 16" front made it turn faster, but it sure was hard on the wrists/arms.

 

[Busy Little Shop]

On 996/998 Duc's we used to run a 120/60 tire on the front..it helped turn in effort quite a bit..On the CBR900rr's the 16" front made it turn faster, but it sure was hard on the wrists/arms.

True... a 20/60 tire will do that because the smaller diameter wheel
will effectively tuck the rake and subtract trail as a matter of
geometry...