Topic: CB750 Race bike rims and tires

[turboguzzi]

you hit the nail in the head simon, found this weekend in the milan autojumble a new set of CBR900 cartridges still in the honda box that i plan to fit in a 38mm fork.... quite easy to do actually.
on top of that, and i hope old scrambelr doesnt mind a second opinion, the main problem emulators solve IMHO is the compression problem in " fixed orifice" old damper rods, i.e. harshness over fast , sudden bumps. more like you find in street riding. on a race track where it's more long undulation type of asphalt changes, shutting down the little rebound orifices and playing with oil weight can go great lengths, bump are rare....  both my race bikes are setup like that. it's not like emulators will do any harm, but dont think they are really needed in a road racer. 
cartridges sure take into another level, when you are starting to push the front you can actually feel the one way valve at the bottom of the tubes getting confused. the discs stack in the cartridge can handle this much better. next race bike has a duc 916 fork so that should  take care of.

[simon#42]

hi brent i dont have a problem with the 22 front on a 2.5 rim its just that i would much rather use the am23 , 130 non cantiliever rear on a 3.5 rim to go with it . as do most of the icgp racers where avon are the control tyre .

hi yossef , i use the cartridges out of honda rs125 forks these work very well . dont like the idea of emulators why not just do it properly .

[bwaller]

Understood. Mostly the narrow rim size issue stems from AHRMA if I recall so we're limited because of that.

EDIT:  Don't mean to overdo this Chris. Looks like a CB750 can use a WM4 rear in Historic, but WM5 (3") in Sportsman. In my case in Formula 500 it's 2:15 front, 2.5 rear.

[Old Scrambler]

Turbo..........2nds are good especially for desert

I was just offering Chris some beginner's advice thinking he may be running with OEM fork internals. Personally, I drilled my damper-rods and have used 15w ATF for more than 30-years on my street bike.   

[Kickstart]

Understood. Mostly the narrow rim size issue stems from AHRMA if I recall so we're limited because of that.

EDIT:  Don't mean to overdo this Chris. Looks like a CB750 can use a WM4 rear in Historic, but WM5 (3") in Sportsman. In my case in Formula 500 it's 2:15 front, 2.5 rear.

Oh, you're correct.  I was originally looking at the Sportsman rule 10.5.4 in the AHRMA handbook which just states:  "f) Wheel rim diameter must be at least 18 inches and cannot exceed WM3 (2.15 inches) width."... but I looked at the handbook again and see in another section of the rules they do allow a 3" rim on the 750's in the Sportsman class - 9.7.6: "Sportsman: Rim diameter must be at least 18 inches and not exceed WM3 (2.15 inches). WM5 (3.0 inches) rear rims are permitted on 750s only." 

Ok, so the recommendation for a CB750 race bike is to go to the WM5 (3") rear rim and run the standard AM23 130/70-18 tire?

Thanks,
Chris

[simon#42]

i think that combination would work well for you . not ideal but with the rim sizes you are allowed and the tyres that are available this is probably the best solution

[Kickstart]

I know this is an old thread... but I was hoping to get some help with replacement tires.

George hooked me up with his AM22 and AM23 (front and rear tires) last year - and they've been working out great for me.

However, after 5 track weekends (one track-day weekend, and 4 AHRMA race weekends), they're starting to look pretty rough... especially the back tire which has two tears on it (which I'm sure is due to my not-so-smooth downshifting more than any issues with the tire).

I was about the order another set, but I'm having a little trouble figuring out the correct compound to order.
George, I  believe the set I got from you (which you got from Brent) are:

• Front: AM22 110/80v-18 soft (compound 11382?)
• Rear: AM23 130/65VB18 (Cantilever) medium (12029?)

I can find the front tire easily online, but I can't seem to match up the rear information with what's available online:

Revzilla: https://www.revzilla.com/product/avon-am23-rear-race-tire has the Cantilever in soft, and they list a medium but it doesn't say Cantilever (and it's out of stock).

Bikebandit has the AM 23 130/65-18 in "Regular".  Not sure if regular is soft, and if it's a cantilever tire or not: http://www.bikebandit.com/tires-tubes/motorcycle-tires/avon-am23-race-motorcycle-tire

2wheel.com has the AM23 130/65VB-18 in "soft", but they show the compound as 12029c... which I thought was the medium  (do I actually have a soft rear on my bike?)

Competition Accessories has the AM23 130/65VB-18 in "medium", and they do state in the description that it's a cantilever, but they don't list the compound information.

Thoughts on which is which, or recommendations on what to order?
Also, I know earlier in this thread I was talking about rim sizes, I ended up with a 2.15x18 front, and 2.5x18 rear rim. 

Thanks!
Chris

[slikwilli420]

Hey Chris, you should reach out to Cindy with ARHMA, they can get you any tire you want and their prices can't be beat. I got a set of soft compound for $400 shipped. You really need to monitor heat cycles with these tires as well from what I have read. Plenty of guys are getting a lot more cycles than suggested, but many are running lighter bikes. My bike and me with gear is 650 or a hair over so I will be wearing out tires a lot faster than a guy on a 300lb XS650 that weights 200lbs.

If you are beating up the tires that badly, you could start with medium compound, which will take a little more time to get up to temp, but should last a little longer. The disadvantage is that you lose a few heat cycles vs the soft, but if you are actually wearing the tire out physically and not with excess heat cycles, this may work better for you.

Alternative to that, you could try the Conti's, which are about $100 per set cheaper. They are radial tires so they don't heat up the same way but do grip very well by reports I have heard.

Even after the relative few laps on track I have had, I have noticed some wear on the tires that I wasn't necessarily expecting.

May be an opportunity to switch to medium compound and get a rule on tire warmers passed with AHRMA.

[bwaller]

The tires I sent George are full soft and I only ever used soft. They wear no doubt. If you got 5 race weekends plus, I'm going to call you Houdini because that's pure magic!  I rarely got more than two weekends on a set.

My approach with Avon is to buy two fresh sets in November or December after the season ends. They do run out of stock here in NA. I was told they make two production runs, the 2nd in May so there should be a new flush of available tires for us now, but I've never had luck. I'm still waiting on one more AM23 (new vendor) that is still supposed to arrive. 

Radials are not allowed in our Period 2 classes here. TG didn't like the Conti's in the wet, liked them better when dry, but preferred the Avon's in the wet. The AHRMA deal sounds good. Heidenau's are another possibility, which seem to be available. They seem to work well, wet or dry, and I see more & more of them. Can't say they're equal to Avon, as I've never tried them. Tim Voyer here does though & likes them.

[slikwilli420]

A lot has to do with how you ride. I know race winners who get full seasons on a set. A heavy guy on a heavy bike like me will probably get pretty good at smoking soft compound tires in short order.

[simon#42]

a full season , really . i was lucky to get 20 laps out of a rear avon and that was on a 250 that weighed 200lb
you dont go racing to make tyres last .

[slikwilli420]

a full season , really . i was lucky to get 20 laps out of a rear avon and that was on a 250 that weighed 200lb
you dont go racing to make tyres last .

Yes really. I know they are made to wear out I just have not heard of guys having quite as bad of luck as your describing.

[bwaller]

I never considered wearing tires as bad luck Matt, but perhaps I do go through more than some. i don't consider that it's me or my bike that's at fault though. It's also a track surface issue, some wear tires aggressively and others, more simply, polish them. One track we're at twice this summer has tremendous grip but punishes tires. 

[simon#42]

avon are now the control tyre for icgp . all the front runners fit new tyres for every race .  a race is normally around 15 laps .
you could probably get two races out of a front but the faster you go the harder it is on the tyres .
while im sure you could get a tyre to last all season you could probably kick your crash helmet round faster .

[Kickstart]

Thanks for all the help! - changing the title of this thread to better reflect the content as it might help other new(er) racers.

Looks like George is going to hook me up again with a great deal on some tires he won't be able to use this year.  Hopefully we'll see George on the track next year.

So, only a few race weekends on these tires... wow.  I guess I pushed it with five weekends... call me Dani Pedrosa! 
I'm sure the extended life I got out of the tires has more to do with me not tearing up the track, but I'm trying to go a little faster each event... so we'll see if my tire life drops.  I'm pretty good with being smooth on the front brake, but I'm still a mess downshifting and I can sometimes hear (and feel) the rear skidding on downshifts at the end of fast straights.  I need to work on that.

Regarding the Conti's, I've had two other racers recommend those.  However, I'm not sure what I could put on a my rim combination (2.15x18 front and 2.5x18 rear)... what's odd is I could have sworn I got larger rims... I'll need to double check this.
 
There's the ContiRoadAttack 2 CR 110/80 (front) and 130/80 (rear), but it doesn't look like they fit my rims.. and,
there's the ContiAttack classic 90/90 (front - really too small) and the 120/90 (rear), where the rear will fit, but will be a little skinnier that the Avon 130.
Maybe I could put the ContiRoadAttack 100/90 on the front (even though it should have a 2.5 rim), and the ContiAttack classic 120/90 on the rear... but boy that seems a little klugey.

It would be nice to try a different tire, just to see what it feels like.

[simon#42]

i dont think a 90/90 on a 2.15 rim is too small , i use a conti classic attack of that size on my road bmw [ 2.15 rim ] and it works fine ,
i also use the 120 on the back [2.5 rim ] it is what conti recommended