Tyre sizes for race bike

[ian400]

Is there any major issue with fitting a 120 70 17 front tyre to a nc23? This is for a streetstock bike so I'm limited to the standard 18 inch bt090 at the rear, if anyone knows a cheap supplier of bt090 please let me know, I can get a set loose for £180 so any better prices I'd be interested, cheers, also interested in wets, had a test session at pembrey and used my old tyres and had no confidence in them so didnt push too hard

[Adrian89]

I have a 120 70 17 front on my road bike, its not been on long and Ive not really done much riding on it so I cant really comment on how its effected the handling.

[CMSMJ1]

you'll not be able to really tell the difference..

I used 70 and 60 profile in race bikes adn road bikes..doesn't matter!

[kiwi racer]

120/60 or 120/70 either either is fine , just dont try to use a 160 rear , stick to a 150 and then find if you prefer the extra turn in or the fast turn stability with the fronts.
Try the GPR a 12s as well , very nice and passable in the wet if you cant use full wets in the rules.

Kiwi.

[amorti]

Just be careful if your forks are dropped thru the yokes, as of course the bigger tyre is at higher risk of clipping the mudguard on full compression.

[Pleiades]

Just be careful if your forks are dropped thru the yokes, as of course the bigger tyre is at higher risk of clipping the mudguard on full compression.

Do you mean the fender? If memory serves, it's attached to the fork lower, same as the wheel, so I would have thought that dropping/raising the forks would have zero chance of altering the relationship between the two.

...just dont try to use a 160 rear...

Kiwi, interested to know why you're not keen on the 160 rear? We all use them here in Aus, and they seem to do the trick. Mind you, I've not seen a 150 slick, so not had a chance to compare the two.

[kiwi racer]

...just dont try to use a 160 rear...

Kiwi, interested to know why you're not keen on the 160 rear? We all use them here in Aus, and they seem to do the trick. Mind you, I've not seen a 150 slick, so not had a chance to compare the two.[/quote]


Only too happy to clarify .....
The std 18 inch wheel is a 4.1/2 inch wide unit and as such is the optimum size for a 150 section tyre.
The std conversion (as i have done a few times) is to fit a 4.1/2 inch 17 inch wheel off an NSR or CBR600 or similar. This wheel is also suited to a 150 tyre.
The basis of my saying dont use a 160 is from the results my race team did when trying to develope the bike and found the ease of turn was much better and heaps more stable using the 150 in either a 60 or 70 aspect ratio. The biggest advatage was when we started to use the Dunlop slicks, the size is a bit weird in the form of a 165 / 65 x 17. this transired to as measured on the 4.1/2 inch rim as the same as a 150/60 when inflated so thats quite clearly where we had already found the best turn in / mid corner speed stability on the bike in a race enviroment.
We cant have been too far off because we still use the same format now with the 600 engine in the NC 23 frame and so far 6 championship wins in 7 years cant be too far off the mark aye.
One point is that if you fit a 17 inch rim tou must either adjust the height with a new shock or ride height adjuster bar but we always run the forks at std height with Ohlins emulators and racetech springs fitted.
The rear of the 600 / 400 hybrid is also an Ohlins and performs brilliantly.
The production tyre we use is a GPRa12 and find them to be a lovely bit of rubber.
I know im sponsored by Dunlop but i changed to them only after i found the Bridgestone and Pirellis spat me arse over tit more than once. The Dunlops have only resuled in 1 crash in 4 years now so make of that what you want.
Thanks for reading my dribble .
Kiwi.

[Pleiades]

Mmnnn, interesting, and not at all dribbly. The GPRa12 is a treaded tyre, right? We have the option for slicks over here, so we have Bridgestone and Dunlop 250GP tyres. The Bridgestone guys comes to almost every club meeting in Victoria, so a lot of us use the Bridgestones, but I hear the Dunlops are good as well.

A moot point for me at the mome, motor is still in bits, waiting for time and energy to become available...

[kiwi racer]

Mmnnn, interesting, and not at all dribbly. The GPRa12 is a treaded tyre, right? We have the option for slicks over here, so we have Bridgestone and Dunlop 250GP tyres. The Bridgestone guys comes to almost every club meeting in Victoria, so a lot of us use the Bridgestones, but I hear the Dunlops are good as well.

A moot point for me at the mome, motor is still in bits, waiting for time and energy to become available...

The Dunlop rear slick i use is the KR 108 - 165/55 x 17 and the front is a KR 106 - 120/70 x 17.
I dont know if you know Scotty T but he came and saw my bikes on his last visit to New Zealand . I wish you well in the racing and it pleases me to see you guys and girls get better and learn more about bikes and racing.
My main passtime now that i retired from racing is to mentor and assist racers of any level that wishes to learn , retain and take the odd risk of listening to an old buggers experiances and near misses to learn and stay safer in this sport. If what i have told you here is a benifit i have again reached a goal.
Again .... all the best and anytime i can help all you have to do is ask me the question. I have been racing these little Hondas and other not so wee machines since the early eighties so have a bit of knowledge lol.

Cheers, Kiwi.

[Pleiades]

Cheers, Kiwi. I still have a lot to learn, only been racing since 2009, although I am already an old man in his 40's.

Know Scotty, he is giving me an airbox that he has lying around. He is a good bloke, tends to let his lap times do the talking. Funny accent, though...

Will give the Dunlops a go when I get back on track and have the bike set up. I have saved to a file the advice you PM'd me about 29 setup and what have you, will give you a hoy when I have given it a go on track.