Best Size For A 5" Rear Rim

[rosok]

This might be a question for a vintage club. But here goes anyhow, a little background.

I've got an 86VFR750F that I'm recently now just using as a track bike. Yeah, yeah, I know, it's old. But so am I, so we just work well together.

Obviously I realized that the stock pre-radial tire rim sizes just wouldn't cut it, so I pulled them off and threw on a set of 17" wheels. A 3.5" front off an early 90's F2, and a 5" rear off a mid 90's F3. Some machining was required, but nothing beyond my capabilities. I'll find a couple photos to post.

 

I took the bike to the track last year for the first time. The Ridge Motorsport Park in Washington state. Two thumbs up!!!

I'm running a 120/70 up front and a 170/60 out back. Dunlop Q2's. Love the tires! After a bit I'm now running in the mid-to-quicker intermediate pack and having a blast. It's kind of fun running the old girl past all the newer iron on the track. I know, I know, it's not racing, just track days.

 

Anyways, to finally get to my point, I've noticed now that the Q2 is being replaced by the Q3 that the 170 rear size has been dropped. Only a 160 or 180 and bigger are offered. The 170 fits my 5" rim really well, and still clears my swing arm and chain. I cannot go to a 180 since I think it will be too wide, and anyway it would be too wide for a 5" wheel I believe. And I'd rather not go down to a 160, as I'd like to keep as much rubber on the road as possible, if for no other reason than to maintain confidence. But I really want to stick with the Dunlops, they are very confidence inspiring, and I imagine I'll like the Q3's even more.

 

Any thoughts on what I should do? Besides going out and buying something more modern . I really want to stick with a 170 out back if possible.

 

Thanks guys

 

[Hotfoot]

First thing to do, if you haven't already, is try to find out the ACTUAL width instead of the nominal width of the tires. I wish I had seen this earlier when I was at the track today, I could have asked some tire vendors! I went through something like this with my SuperSingle - the widest rear tire I can run is a 163mm tire, and I was very surprised to discover that the actual width of some tires labeled as 160 were much wider, up to 168mm wide for example!

 

Maybe our resident Dunlop answer man can find out the actual width of the Q3.

[Hotfoot]

I searched a bit for Q3 width info on the 160 size tire and here is what I found:

 

Inflated Width/Measuring Rim Width: 6.67 in. / 4.5 in.

Inflated Diameter: 24.97 in.

Acceptable Rim Width: 5.50 in./6.00 in.

Deepest Tread Depth: 7/32 in.

 

I presume this means it would fit a 5" rim, since I think that tire is made for a 4.5" rim and he info above seems to indicate it can fit on a larger one (5.5/6) - although I find the acceptable rim width info a little confusing, the way it is written.

[rosok]

I searched a bit for Q3 width info on the 160 size tire and here is what I found:

Inflated Width/Measuring Rim Width: 6.67 in. / 4.5 in.

Inflated Diameter: 24.97 in.

Acceptable Rim Width: 5.50 in./6.00 in.

Deepest Tread Depth: 7/32 in.

I presume this means it would fit a 5" rim, since I think that tire is made for a 4.5" rim and he info above seems to indicate it can fit on a larger one (5.5/6) - although I find the acceptable rim width info a little confusing, the way it is written.

Thanks Hotfoot. I guess I should also measure the Q2 170 series tire I currently have mounted on my 5" wheel. And do some comparisons to different tires mounted, though I think I'll have a hard time finding the actual measurements as mounted on a 5" wheel. That doesn't seem to be a popular size among sportbikes anymore I'm guessing. And of course I imagine the actual width will vary with rim size. Anyhow, I have some time to figure it out, since the Q2's I have mounted should hopefully last me 3-4 more sessions at least.

These photos show the amount of tire I'm using front and rear. You can see there is a little edge distance to go still, so maybe a 160 would still work for me? Though to get that extra edge usage I may have to pull off my footpeg feelers that are dragging slightly at this point (stock pegs). I'm running 30 psi F/R cold per local track guys recommendations.

[rosok]

I searched a bit for Q3 width info on the 160 size tire and here is what I found:

Inflated Width/Measuring Rim Width: 6.67 in. / 4.5 in.

Inflated Diameter: 24.97 in.

Acceptable Rim Width: 5.50 in./6.00 in.

Deepest Tread Depth: 7/32 in.

I presume this means it would fit a 5" rim, since I think that tire is made for a 4.5" rim and he info above seems to indicate it can fit on a larger one (5.5/6) - although I find the acceptable rim width info a little confusing, the way it is written.

Thanks Hotfoot. I guess I should also measure the Q2 170 series tire I currently have mounted on my 5" wheel. And do some comparisons to different tires mounted, though I think I'll have a hard time finding the actual measurements as mounted on a 5" wheel. That doesn't seem to be a popular size among sportbikes anymore I'm guessing. And of course I imagine the actual width will vary with rim size. Anyhow, I have some time to figure it out, since the Q2's I have mounted should hopefully last me 3-4 more sessions at least.

These photos show the amount of tire I'm using front and rear. You can see there is a little edge distance to go still, so maybe a 160 would still work for me? Though to get that extra edge usage I may have to pull off my footpeg feelers that are dragging slightly at this point (stock pegs). I'm running 30 psi F/R cold per local track guys recommendations.

[rchase]

VERY pretty bike. Until recently my main track bike as a 1989 Yamaha FZR400. Despite the age a vintage bike is still a lot of fun on the track.

 

I don't have much to add to the topic but huge thumbs up for someone else who's obtuse enough (like me) to take an older bike out to the track!!!

[rchase]

Actually. After thinking about this for a minute I do have some stuff to add.

 

Since 18 inch tires are getting rather rare for the FZR's a number of the owners have done complete conversions to 17inch wheels. Often the conversion process involves a full swing arm and fork transplant. A good friend of mine transplanted forks off of a GSXR1000 onto his FZR400. A bit of research and you might be able to find some compatibility between your frame and another front end and swing arm that could be adapted onto the bike to give you as much flexibility as you wanted with tire sizes. Another advantage of doing a full front end and rear end swap is the ability to take advantage of more modern suspension components. The FZR forks are so outdated that they only have preload adjustment and require the shock to be opened up and shimmed manually to adjust them.

[rosok]

Actually. After thinking about this for a minute I do have some stuff to add.

 

Since 18 inch tires are getting rather rare for the FZR's a number of the owners have done complete conversions to 17inch wheels. Often the conversion process involves a full swing arm and fork transplant. A good friend of mine transplanted forks off of a GSXR1000 onto his FZR400. A bit of research and you might be able to find some compatibility between your frame and another front end and swing arm that could be adapted onto the bike to give you as much flexibility as you wanted with tire sizes. Another advantage of doing a full front end and rear end swap is the ability to take advantage of more modern suspension components. The FZR forks are so outdated that they only have preload adjustment and require the shock to be opened up and shimmed manually to adjust them.

I've thought about doing what you've suggested, but I stayed with just doing the rims.......for now. Money, or lack of, being one reason. But another being I just didnt want to change the bike that much. And as it stands now i can go completely back to original very easily.

 

I'm not racing, but i still wanted to upgrade to wider radial tires so i could run at a decent pace on the track. And I've found I can do that with what Ive got right now. My suspension is non-adjustable as well except for preload. Skinny fork legs, 37mm if you can believe, with no fork brace! Small unfloating front discs, rear shock with virtually no damping left. Its great!! My only saving grace is that "The Ridge" is so nice and smooth, I don't think I'd be able to run the bike on any of the rougher tracks, definately none in western Canada.

By the way, I really wanted one of those FZR's you got back when they came out, they received rave reviews on thier handling. But I couldnt give up my RZ350.

 

I'm secretly hoping Dunlop man Steve Brubaker will pipe in on this..........

[faffi]

I searched a bit for Q3 width info on the 160 size tire and here is what I found:

 

Inflated Width/Measuring Rim Width: 6.67 in. / 4.5 in.

Inflated Diameter: 24.97 in.

Acceptable Rim Width: 5.50 in./6.00 in.

Deepest Tread Depth: 7/32 in.

 

I presume this means it would fit a 5" rim, since I think that tire is made for a 4.5" rim and he info above seems to indicate it can fit on a larger one (5.5/6) - although I find the acceptable rim width info a little confusing, the way it is written.

 

I'm pretty sure that's a cut&paste error (by Dunlop), there is no way a 160 is meant for a 5.5 and especially not a 6.0 rim. So most likely it will work with 4.5 and 5.0.

[rchase]

 

I've thought about doing what you've suggested, but I stayed with just doing the rims.......for now. Money, or lack of, being one reason. But another being I just didnt want to change the bike that much. And as it stands now i can go completely back to original very easily.

 

I'm not racing, but i still wanted to upgrade to wider radial tires so i could run at a decent pace on the track. And I've found I can do that with what Ive got right now. My suspension is non-adjustable as well except for preload. Skinny fork legs, 37mm if you can believe, with no fork brace! Small unfloating front discs, rear shock with virtually no damping left. Its great!! My only saving grace is that "The Ridge" is so nice and smooth, I don't think I'd be able to run the bike on any of the rougher tracks, definately none in western Canada.

By the way, I really wanted one of those FZR's you got back when they came out, they received rave reviews on thier handling. But I couldnt give up my RZ350.

 

I'm secretly hoping Dunlop man Steve Brubaker will pipe in on this..........

 

 

Totally understand that. I stuck with the 18 inch tires on my FZR because it's a big part of what gives the bike part of it's handling personality.

 

Just wanted to throw that out there as an option just in case you had not considered it. It's pretty amazing what you can create rummaging through parts bins. There's an amazing amount of compatibility between bikes since many manufacturers parts binned themselves from vendors such as Nissin, Showa, Brembo and others. My buddies FZR is put together from Ducati, Suzuki and Yamaha parts.

 

Speaking of Parts Binning and the FZR's. Bimota parts binned a whole bike with the Bimota YB7. It's really a Yamaha FZR400.

 

Good luck to you in finding some good tires to go on that VFR. Not to age myself buy I remember drooling over those when they were relatively new. That's one really nice bike in great condition. It's super nice to see stuff like that going to track days.

[Hotfoot]

I found quite a few places on the web indicating that a 160/60 tire should fit on a 5" wheel. Here is an interesting thread showing actual width measurements for tires mounted on various rim sizes:

 

http://www.supermotojunkie.com/showthread.php?145216-Actual-Tire-Width!-DOT-and-Race-Slick

[rosok]

I found quite a few places on the web indicating that a 160/60 tire should fit on a 5" wheel. Here is an interesting thread showing actual width measurements for tires mounted on various rim sizes:

http://www.supermotojunkie.com/showthread.php?145216-Actual-Tire-Width!-DOT-and-Race-Slick

Hey thanks Hotfoot. That's a good link.

I did some measuring of my own, and my 170/60 Q2 on the 5" wheel measures out at 7" wide (+- 1/16"). The 160/60 Michelin 2CT on my wife's Ninja 650 4.5" rear rim measures 6.5" (+- 1/16"). When you consider how small a contact patch is on a motorcycle tire, that extra 1/2" of width probably makes a difference. But I guess it's probably a moot point if the 170 width is no longer available. I'm probably making too big a deal over it, a 160 would probably work fine for my few track days. It's just a confidence thing, you know. And being confident in your tires is huge in riding a bike at elevated speeds around corners.

[faffi]

You will also have to lean over farther with a wider tyre for any given corner speed, and with the limited power of your bike I doubt you will notice any reduction in grip. Well, you may notice it, but then it may just be in your head

 

But seriously, there should not be any noticeable change in grip unless you are down to the final second or two possible to withdraw from your bike regarding lap times. Not your limits, but the sort of limits Spies and Lorenzo etc. can muster. There will, however, be benefits with a narrower tyre, at least in theory. Change of direction should take less effort, unsprung weight should be less for better acceleration and better suspension action, you do not have to lean as far, the rear wheel's trajectory will be closer to that of the front tyre improving neutrality, deflection from bumps will be less improving stability and overall the bike should be nimbler and more neutral. There really is just one benefit on a race track with wider tyres, and that is grip. But since a 250 hp race bike can survive with a 190 mm wide tyre, I'm sure a 160 will be sufficient for your 100 ponies. After all, the 50+ hp Moto3 bikes have 115/70 rears and they corner faster than any other current road race machine, and IIRC the old GP250 class with 100+ hp used 160 mm wide rears.

[rosok]

Ah yes, all good points Eirik. I think it all would be in my head .

 

and i just realized that a little of my thinking too is that a 170 looks cooler than a 160. Not as cool as a 180 or 190, but the best I could do. Does using the word cool age me?

 

But I also realized there was one other important reason for me using a 170/60, and that was overall diameter, which is greater than a 160/60. Because the bike originally came with a tall tire on an 18inch wheel, switching to the 17inch affected my geometry and rear ride height. Playing around with the mounts on a slightly newer stock shock i was able to regain that ride height, but only if i use a 170 tire in conjunction.

 

Ah the trials and tribulations of customizing a bike.........

[faffi]

If cornering clearance isn't an issue, you can lower the front a bit to sharpen the steering. When you require more cornering clearance, you will probably also demand a better shock, and you can buy a longer one to raise the rear. Or, for cost saving, you can fit shorter link arms and raise the rear that way, even with the stock shock.