TOPIC:

Thanks for your help Tg
Probably i´ll try to advance timing 2 degree's (like said KZB29). It´s woth th effort? i suppose is possible by slotting Dyna S plate.

you can try, actually very little effort to do
make sure you go on the track after the change for at least 10-15 mins to check that you dont get detonation when the engine is REALLY hot. It could feel very good initially, less so after a while when everything is scorching hot.

On the street advanced spark always feels like the engine is more responsive, but very few people keep full throttle for 15 mins, so they never discover if the motor is at the edge of detonation.

The funny thing is that if your combustion chamber and pistons are reworked for good squish action, the turbulence speeds up combustion so you need LESS spark advance than stock. In my race motors that have well designed squish area, i get best power as checked on the dyno with only 28 degs max advance, makes engine run cooler too and it doesnt detonate even with the 12:1 CR i use.

You dont have to believe me of course, just read Kevin cameron's article about Rob muzzy, tuner for Lawson and Rainey Kawas who was doing exactly that already 30 years ago...

In early May there will be a a vintage festival at Jarama track where i´ll check some changes.
Cams and specially rake, weight distribution and suspensions set up with a tyre for 18¨ 2.15 tubeless front wheel. (rear stock 18¨ 2.15¨ tube wheel)

I think the best for these rims would be Avon 110/80 18 front and 130/65 18¨ rear (this cantilever type tyre allows the narrow 2.15 wheel), but i´ll go with Bt´s 45 like TG said.

So i need to know the best choice for front tyre keeping my 4¨ rear tyre (around 116/90 18).
110/80 18¨? is it a rare combination?

leitz, not sure i remember what's your 4" rear... for a 2.15" front wold not go wider than 100

BT45 are reasonable choice, choose the sizes according to the recommendation table, don't go wider than recommended for the rim size.

Racing Avons very good choice but expensive, the rear cantilever is a great tire that works with narrow rims.

Another possibility is to change your complete wheels to GPZ750, quite cheap to find used, "bolt on",the rear is 3" that gives you more options.

last, check out also Heidenau, K65/K64, a bit cheaper....

Bridgestone recomendations table for 100/80 is "2.15 to 2.75" and for 110/80 is "2.15 to 3" so in both cases will fit.
I suppose the wider one gives more grip and slower steering

Bicomponent poliurethane coat:

your are bit cutting corners/cheating here 2.15" is the narrower rim option recommended....
guess i should have been more explicit and add "makes sure you are using the wider rim recomended" i.e in your case 2.50-2.75-3.00.

see here the first pic. this is my street bike, and this is an Avon RoadRider fitted on the stock 2.15. see how the profile is squashed and a good 20mm of thread are unused? i lean pretty hard also on the street and usually I use all the thread on most tires/bikes, but not here.... rim is simply too narrow to use all the tire, the edge of the thread is almost parrallel to the rim. even rossi will not use all the thread acceptable on the street maybe, but not on track. and makes the bike "almost" too easy to flick.

dont know how much of the thread you are using, maybe post a pic, but at the end of the track day you should check if you use all the thread. like in the second pic, that's a 110 conti on a 3", all thread used, that's a good sign. the conti is a bit special as it really needs a 3" to work well.
i doubt if even the 100/80 on a 2.15 will work well. dont get offended, but if you are using the stock 2.15 maybe you should go with a BT45 90 front... only experience and the amount of thread used will tell you.

Rear tyre seems distorted but is an optical effect

these are 1.85¨ rim 3.25" tyre and rear 2.15 rim 4" tyre. Both are the stock tyres and wheels and i get my knee down on track.

At front i use almost all thread but a bit less on rear. Bike put lot of weight at front on lean angle and although i feel safe with this 3.25 (90/90 19) tyre I´m not sure if it is right for this heavy bike.

Anyway with 18" front wheel would gain more agility and easy knee down i hope.

I found this info in an australian forum about a P&M Z650 with Z1r front wheel raced by Keith Ferrel who explains some interesting things about his bike:

"Richard and Peter at P&M built me a special chassis to take a Z650 donk tuned by Leon Moss of LEDAR. It was a little shorter-1.5 inches-but was just like a normal twin shock P&M 1000 chassis. It was No.23 and was supplied just-only just-in time for the 1978 MGP. I got it together and ran it up at midnight the night before we left for the Island.I used Kawasaki forks with the same internal mods as Grant's KR750, a Z1R 18 inch front wheel and the P&M Cambray rear wheel.It was the best road race bike I ever owned and was a real blast to ride. It would pull 11,400 RPM down to Brandish-about 150MPH. The engine had 96 BHP on the Ledar dyno and was strong all the way. I never knew where I was going on the Mountain Circuit and I did'nt get round very fast despite having a good bike for the job. I had many good rides on it and I eventually sold it to a Scots guy who told me he beat Haslam's lap record at Knockhill on it. LEDAR fixed it for me to be the Pirahana ignition sponsored rider.It was so crap I bought a Boyer system, flogged the Pirahana's and got a reliable bike.I kept the stickers on though! Dave Rawlings of Dunlop gave me some of the special tyres used in the Kork Ballington KR 500 GP project when it came to the end. He said they would last Kork a practice session at a GP. They lasted me a couple of meetings and my results got better. When I went back to normal tyres from Ken Inwood I was back where I started."

Anyway he does not specify the measure of the tires

Have you considered racing coatings?

swaintech.com/race-coatings/motorcycle-c...oatings-price-sheet/

Good luck out there!

yep, nice story but not much help indeed. plus the racing tires they had back at the time don't even exist anymore. like 18" slicks....

not managing to follow exactly what front rim you want to have, but in any case, if it's a 1.85-2.15 dont go wider that 90. for 100-110 front you need a 2.50-2.75. the 110 radials will work even better with a 3.00, quite simple....

and dont get too hung up on knee dragging, even if it's quite typical attitude of newbies: dragging knees being more important than actually going fast not the same thing! as many race instructors will tell you, it should be a by-product of you cornering fast, not an end in itself...

as you can see from the pic, even when i am in hard battle i am not trying to actually touch with the knee, i am just lightly skimming the track, so when you pass with it over the apex curb it doesn't catch your leg.





engine coatings, if it's any help i can tell you that my motor did 5 full seasons, thats a good 30 racing weekends without ever needed to be open, and losing zero power. if you are thinking about power gains because of lower friction, dream on youll be lucky to get anything that can be even measured on the dyno consistently.

If there were no engine restrictions, I'd find a wrecked '83 GPz750 and build it with an 810 Kit !

Sounds like you're having a lot of fun.

Thanks to all and sorry for my poor english.
Tg: the tire i want to fit is z1r 2.15 18"
19" stock gets more tire on asphalt so more grip than 18" due to the bigger diameter. If i fit 90/90 18 will get less grip ( and better steering) than stock 90/90 19".
So maybe z1r wheel is not the best option if i can't fit 100/80 18 tire (better grip and steering)
Am i right?