wm3 on the front with 7" centre forks? are you sure. I have wm2 on mine and it's a bit crowded.Beside if you go too big on the tyre the steering will be too slow for a racer.
H: Hubs, Wheels and Tyres Tyres
- Thread starter Bill Thomas
- Start date
John Renwick, Carletom Palmer and I all ran 18" WM-3 rims front and rear on Girdraulic Vincents, which are a 6" wide fork. The big wheels certainly work fine, but provide a lot slower steering.
The width of the rim is important for the actual profile it imparts to the tire. With the Dunlop K-124 I should have used a WM-2 because I flattened out the profile enough to run at the edge of the tire too quickly. However, the Avon tires are quite round and I would have had no problems with a WM-3 front.
With race tires I would advise you to find the tire you want and and build the wheel to the tire. I like the 18's because of the responsive steering and quick line changes you can make without any drama. On the Comet, I would be happy to run the same tire size front and rear. I have no experience on a twin, but I would probably do it. If I wanted a larger tire on the rear, then you have to check to see what is available in race rubber.
Both the AM22 and the Road Rider have same size front and rear tires available in good compounds, the A49 and the 308 on the AM22 and the A49 and the 633 (633 being sifter than the 308) on the RR.
If available, and you want a bigger rear tire, try the AM22 front with the AM23 rear. Avon makes one tire that is designed to run on an narrow rim, which they call "Cantilever". It is designed for a WM-3 and is available in two compounds, the 914 being harder than the 633 and softer than the 308.
The 18" wheels, being a little more popular in racing tend to have more compounds available also.
Here is the compound scale:
I would see what is available along these lines. The compounds are quite good and personally, I would not be concerned with the grip of a same size rear, but it depends upon Tom's skill level and confidence.
David
My Egli has WM3 rear and WM2 front. I used to run Avon AM22/23? (which many classic racers use) in 130/80/18 and 110/8018. I changed to 120/80/18 and 100/80/18 and found the change of direction hugely improved.
Bill
Bill
Correction. 130/65/VB18!
Now have Pirelli sport demon rear and Metzeler Me33 Competition compound front (no longer available).
Just about to change front to 90/90/18 Continental. I can't remember the type but it is one of the softest compounds I have felt.
Bill
On this Norvin racebike I'd prefer to go to 19's as I did on my racer for the extra ground clearance, but the selection of tires is not as good as 18's.........perhaps 18 on the rear and 19 on the front.
19 front 18 rear works just fine on mine.
Car crossply tyres had imperial designations like 5.20x13 but went metric 155x13 for radials. I had assumed that the change for bikes was similarly related to carcase construction.
Ground clearance is always a concern. There is nothing wrong with 19" and 18" or 19" and 19." Most racers are looking for more than good handling, they are looking for an advantage. It involves juggling the compromises. Steepening the rake, with tire selection for quicker handling or quickening the steering by going with smaller wheels. Often, you don't realize how fast or slow your bike steers until you go to a track like Laguna or Cresson, Texas and find yourself dealing with cork screws. If you are not passing bikes in corners it doesn't matter as much how quickly you can change lines in a corner.
It is perfectly reasonable to make a compromise until the time the rider thinks he needs something different. As an example, a new rider may want a soft rear tire until the time he has become comfortable with sliding the rear, then he may want a slightly harder tire.
Another compromise is tire width. A wider tire will generally provide more traction, but it difficult to know how much more traction you need or can put to use. The downside is the wider tire moves the contact patch further away from the center line of the bike. Then you have to lean the bike over more to get around the same corner and you have clearance issues.
Add to this that the resistance to turning the front wheel increases by the 4th power with wheel diameter increase and you are juggling a lot of compromises. The amateur racer has to make the best guesses on many items an pick the things that may have to be changed in the future.
David
It is perfectly reasonable to make a compromise until the time the rider thinks he needs something different. As an example, a new rider may want a soft rear tire until the time he has become comfortable with sliding the rear, then he may want a slightly harder tire.
Another compromise is tire width. A wider tire will generally provide more traction, but it difficult to know how much more traction you need or can put to use. The downside is the wider tire moves the contact patch further away from the center line of the bike. Then you have to lean the bike over more to get around the same corner and you have clearance issues.
Add to this that the resistance to turning the front wheel increases by the 4th power with wheel diameter increase and you are juggling a lot of compromises. The amateur racer has to make the best guesses on many items an pick the things that may have to be changed in the future.
David
All the quick blokes in C R M C and IH R O run on 18" rims, with the "fake" manxes and g50s. They jack up the footrests and have high level pipes.