How did you check? Measure the inner lip of the wheels...I have wheels here without tires and they are 2.5" and 3.5". If you go back in the archives of this thread that is the spec on F1 wheels.

 

Ok sins i am starting to get confused can some one tell me what tire is best for trackdays. I highlight that, not racing. Casual trakdays and fast canyon carving. Any recommendations?

 

Stock hurricane wheels are 2.5" and 3.5" as stamped on the wheels on my bike.

 

There is more than one correct answer to the best tire size, but I chose to go with Factory Pro's recommendations on tire size. They have a nice little article with all their previous 'top secret' information back when they used to race these bikes competitively that has some good information.. scroll towards the bottom of the link: CBR600, hurricane, jet, carb, tune, tuning, Data by EC997a Eddy Current Dynamometer The tire brand suggestions are outdated, but the sizing info is not.

They were probably using bias ply tires back in the day, but I use the same sizes in Avon radials as mentioned previously and they are both designed to be mounted on 2.5" and 3.5" rims respectively. I also know that the Dunlop GT501 bias ply tire in a 150/70 size is recommended for a 3.5" rim so it specifically is fine to use. Other brands or radial tires may not be designed for the narrower 3.5" rear wheel.

edit: This whole topic is unfortunately good media for creating an argument since there isn't any one right answer that fits everyone's opinion..

 

Your right, I was looking at outer width, which is around 3.5/4.5" nominal.

 

Ok then i think that the best choice for me is Michelin Pilot Street 110/70 and 140/70, tho not sure if to go with radial or bias. sins i am looking for grip i am leaning to radial tho i might have it wrog

 

I agree this topic is one that can turn into argument pretty easily, but that is not my intent. Mostly trying to verify information that I have found in studying the tire question in depth. To be honest it is one area that is very confusing. The same issue exists with my Norton having been fitted with bicycle tires back in the day.


The only real consideration is for safety as wider tires will be pinched and change the profile. Straight line tire patch probably isn't as much of an issue as side profile when cornering.


I've read so much on this that in the end I just went with Bias Ply in the stock sizes. There were a lot of comments on 120 width causing handling problems on the front.


On the rear, most are more concerned with the "look" rather than the actual handling of the bike. I'm pretty sure that 140 width is okay on the 3.5 wheel but anything more than that may cause issues with tire profile and handling. The only real solution to this is to change the swing arm and wheel to a newer style that will accept a wider tire.


Changing the swing arm and wheel to get a larger tire profile does not take into account frame geometry and design. Most of these machines went through considerable design analysis and increasing tire contact area can create frame flex issues although the CBR frame is pretty stout so not likely.


If you look at the history of the CBR and the evolution, one of the prime concerns was to reduce the weight of the bike because increasing HP was much more difficult. The development of the sport bike really was tied to the "package" and the CBR continued to beat the competition via weight and balance more than sheer horsepower. As tires improved the frame and suspension technology had to follow in order to provide the proper package and compete with other manufacturers.


There are so many factors that can be detrimental to handling that are discussed on these forums with most being concerned with the look of the bike more than the performance. Tires can also change the rake and trail of the bike resulting in dangerous handling issues if not understood by the owner, yet that is rarely discussed.


Many of these bikes have been modified so much over the years that few have ever experienced the handling and performance of the original bike so have no point of reference to determine if the tires they have are the best for the bike. In my investigation I paid close attention to the comments from those who understood the original and had tried other combinations and in the end the best choice was to stay close to the OEM tire sizes and bias ply. The assumption that tires have improved since the late 80's is correct to some degree, but along with this the motorcycles have evolved as well. What is good today was not understood back then and as such there can be issues with putting modern rubber on an old bike.

 

This is from a detailed article on the improvements between the F2 and the F3...specifically tires:

"To enhance cornering performance and, by extension, the CBR's competitiveness in racing applications, the rear wheel's rim size is increased from 4.5 inches to 5 inches to permit mounting of fatter 6-inch street tires and wider racing slicks that offer improved grip.

Since a wider rear tire introduces greater stresses to a motorcycle's suspension and frame, the CBR features a 2mm larger diameter - and now hollow - swingarm pivot shaft (up from 15mm to 17mm) for lighter weight as well as increased strength. This combines with increased front fork triple-clamp rigidity for an overall improvement in chassis integrity."

 

Great information Dennis. I also don't want to start an argument here with anyone as it's a waste of time & forum space

I agree the 120 front is too wide for a 2.5" wheel, and I have not been able to find any 120 wide front tires with a recommended rim width of 2.5" either. They will definitely be pinched on the rim and have a less than optimal contact patch & profile. Even the 110/70 is designed for a wider wheel than the 110/80, and is pushing the limits of the wheel in that size.

As most reading this probably already know, different manufacturers of tires have varying specs with the same size tire such as overall width, tread width, and recommended rim size. Any time I'm considering a tire size other than OEM on anything (car, truck, bike) I will get the technical specs on each tire & compare. The most important measurement, as I mentioned before, is recommended rim width. As long as your wheels fall within the range for the tire, ideally right in the middle, the contact patch and profile should not be compromised. This does not take into effect the added stress to suspension & frame as you mentioned in the last post, and I didn't really consider before, but it is also a factor to think about. I don't have the engineering & physics education to explain it though

The only oddball tire that I've run across so far is the Dunlop GT501 bias rear that is a 150/70-17 but is recommended for a 3.5" wide wheel. I don't know how a 130/80 and a 150/70 can be recommended for the same width wheel, but that one is. I considered using it due to the fact it has the same sidewall height as the OE tire and wouldn't change ride height, but didn't see any performance advantage vs. the 140. I'm pretty sure the Hurricane will drag pegs & hard parts before you exceed the limits of the tire.

 

It basically is about the amount of force applied to the frame and suspension due to adding more tire contact surface or due to softer rubber compounds which grip more. While it seems like more tire would be better, that assumes that the bike is designed to take the increased forces. I know with my Norton this is a big issue because the frame has a tendency to flex even with the standard tire sizes.


This is much more complicated than most of us understand. The original F1 design was based on the available tires and was tested extensively during the design phase to insure that the component designs were sound. If you read about the development history Honda was very conservative and took 2 years to develop the Hurricane even with strong competition from other manufacturers. They were pushing the limits of the technology.


The biggest issue we owners face now is the very limited selection of tires because of the evolution of the bikes. Rubber compounds have improved considerably and that alone results in extra stress on the frame and suspension even when using OEM sizing. Adding additional width and subsequent tire contact area just increases the stress to the bike.


It would be interesting to do a study on F1's with frame cracks (a common failure) and see what tires were on the bikes during their lifetime. It could be related.


The main point that I am trying to make is that increasing tire width in order to get a more modern look is not a good idea without looking at frame, swing arm, wheel and suspension modifications in order to insure the integrity of the bike, not to mention the profile issues with putting wider tires on the wrong wheel width.


In my opinion the 110 front tire is the best choice with the existing front forks and suspension. A wider tire up front will change the handling and slow down response. Fork tube flex may also come in to play due to the increased contact area imparting higher forces particularly during braking. There really isn't much structure holding the fork tubes from rotating or twisting not to mention bending in severe cases. The yokes also will have increased stress and given that original the design and development was controlled by minimizing weight it would be interesting to know what safety factor was used in the design of these components.


I think that anything wider than 140 on the rear using the stock wheel will change the profile enough to create handling problems and stress the tires in a way they were not designed for. The additional contact surface even with a 140 tire along with the softer rubber compounds in most newer tires could impart additional stress to the frame and suspension so that should be considered and I would keep an eye on the frame in the areas known to crack.


I realize there are a lot of owners who have wider tires on their bikes and believe they handle fine. I'm not saying you can't do it, just be aware that you may be pushing the limits and there could be issues.