Which size? 17 inch or 18 inch tyres

[gavinnz]

Which size? 17 inch or 18 inch tyres.
The machine is in the planning stages only and is a classic racer based around a 1950's Moto Guzzi 500 ohv flat single engine.

Assuming these things.....

The frame and chassis geometry would be built to suit the tyre size.
In either 17 or 18, the tyres would have the same narrow width (90 or 100 front, 110 rear), construction and profile.
The same wire spoke wheel construction.
That the tyres are easy to get and they meet all regulations for the class.

Ideas I have had... wrong or right??


17 inch tyres.....

Less overall bike weight in spokes, rim, tube and tyre. All unsprung.
Lower overall centre of gravity.
Less and lower frontal area.
Shorter wheelbase.
Lower seat height.
Engine can move forward in the chassis.
Less total mass that is rotating at a smaller diameter....
Wheels would be easier to accelerate and decelerate... meaning more braking power can go into stopping forward momentum and more engine power will get to accelerate the bike forward.
Easier and faster turn into corners.
Being a flat single I have room above the engine to bring the engine up to achieve needed cornering clearance and bring the tank down for low overall build height.


18 inch tyres.

More cornering clearance.
Longer tyre footprint.
More high speed stability.


Seems a no brainer.... so what have I missed???
Regards
Gavin

[Kickaha]

What age bracket class is it being built for?, what wheels do the rules for that class allow?

[blackdog]

Longer tyre footprint.

you would be measuring the difference with feeler gauges......


More cornering clearance.

1/2" upright is only 1/4" at 45 degrees..........

[gavinnz]

What age bracket class is it being built for?, what wheels do the rules for that class allow?

"Assuming these things.....
....and they meet all regulations for the class."

Regards
Gavin

[gavinnz]

you would be measuring the difference with feeler gauges......



1/2" upright is only 1/4" at 45 degrees..........

I agree.
Gavin

[quickbuck]

Go with the 17's.
I think you missed one: Tyre Availability.....

[blackdog]

Go with the 17's.
I think you missed one: Tyre Availability.....

was thinkn' that, and price too. like car tyres more common=cheaper ie/ 17"s less than 16"s these days

[george formby]

Go with the 17's.
I think you missed one: Tyre Availability.....:yes:
My TDM has an 18" front which I am perfectly happy with but my tyre choices are very limited. Sports Touring or Adventure tyres, thats it, nothing soft. Damnit.:angry:
I must admit the 110/18/80 gives a quick turn in without flopping.

[quickbuck]

I must admit the 110/18/80 gives a quick turn in without flopping.

HECK, that is one very big tyre ;) (Yes, yes, I knew what you ment).

I would actually say the "Flopping" issue you have had in the past would actually be the shape of your rear tyre.... Could be wrong (often am) and it could well be a different sensation to the Flopping I experience....
Reminds me. Time to book the bike in for my Metzler M3 Front (now the rear is scrubbed).

[scracha]

:yes:
My TDM has an 18" front which I am perfectly happy with but my tyre choices are very limited. Sports Touring or Adventure tyres, thats it, nothing soft. Damnit.:angry:
I must admit the 110/18/80 gives a quick turn in without flopping.
Super soft sticky tyre = BT-012SS. The best I've used in the wet but wears out real fast. Metzler Z6 is best of both worlds on them but currently trying out a BT020 as much cheaper. Is your 98 a mark 2? I'm sure mine had a 120/70? The tediums tend to flop when the rear tyre is fooked or some dick has dropped the front forks too much.

[quickbuck]

The tediums tend to flop when the rear tyre is fooked ......
Heck,
You mean I am right more than once today????

[scracha]

Heck,
You mean I am right more than once today????
You'll make up for it tomorrow. Hell, you'd be as well just staying in bed.




classic racer based around a 1950's Moto Guzzi 500 ohv flat single engine.

We have all missed the main point of this thread. The guy is obviously a masochistic pervert.

[quickbuck]

You'll make up for it tomorrow. Hell, you'd be as well just staying in bed.




Bugger it, I'm taking the rest of the week off then.

I was actually right on half a dozen occasions today..... Made some very good educated guesses that turned out to be true.

Yup,
Tomorrow will be real sh1t...... Not good when I fix helicopter engines....

[Metastable]

Go 17, you have much more tire choices. All you need to do for the rear is put on a common front tire such as a 110/80-17 or .... a 120 that is pretty much what any sportbike takes.

Just make sure you install it in reverse tread pattern. The tread pattern should look like
>>>>>BIKE<<<< You could even just install the same thing on the front with regular rotation. i.e. I'd either go 110 on both or 110 front and 120 rear.

They handle pretty well apparently. It is what the guys do here in the CBR125R racing up, because they are mandated to use spec Pirelli tires.... and Pirelli doesn't make tires for that bike. :D
Read about it here... you can also see what it looks like:
http://www.passionperformance.ca/motorcycle/articles/3832/

The 120 rear might take a bit more abuse.

[RDjase]

For pre 72 the regs are 18inch minimum and 2.5 max rim width.

MNZ Rule 25-3-2

I got that out of the rule book, cant seem to get the website to work tho. just comes up blank pages

Try these links

http://www.mnz.co.nz/competitionrules.aspx

http://www.motorcyclingnz.co.nz/download/2010_MoMS_Chapter_25_Road_Racing_Post_Classic.pdf

http://www.motorcyclingnz.co.nz/download/2010_MoMS_Chapter_23_Road_Racing_Classic.pdf

I run Pirelli Sport demons on my LC and they work well, good in the wet too. 100/90/18 front and 110/80/18rear. on 1.85 rims

http://www.nwa.co.nz/product_detail.php?P_ID=3150

I got some used Avon AM 22 and 23 to try. At $900 a pair I will probably stick with the demons at $320 a pair tho

Bridgestone BT45 are another option

[gavinnz]

http://www.motorcyclingnz.co.nz/download/2010_MoMS_Chapter_23_Road_Racing_Classic.pdf

Thanks for those links I only had the NZCRR site to go from.
From your above link I get for pre 1963...
"All wheels must be of the wire spoked type with rim widths the same as specified for
the original manufactured machine. Maximum rim width is WM 3 (2.15 inches inside
width)."

So no mention of diameter for Classic racing. I bunch of smaller cc bikes of the era including quite a few Moto Guzzi and Aermacchi etc had 17 inch wheels as standard on their road machines.

I still have some LC random small odds and ends in the shed from 15 years ago.... suppose I should hurl them at trademe one day.

Regards
Gavin

[george formby]

Super soft sticky tyre = BT-012SS. The best I've used in the wet but wears out real fast. Metzler Z6 is best of both worlds on them but currently trying out a BT020 as much cheaper. Is your 98 a mark 2? I'm sure mine had a 120/70? The tediums tend to flop when the rear tyre is fooked or some dick has dropped the front forks too much.

I run BT021's & am very happy with grip, particularly the front & they have quite a steep profile giving very good turn in. Great in the wet too.
Yup, I have a MKII, definitely an 18' front. Bridgestone recommended the 012's but i hvae never seen the correct size front listed.
Sorry to go off thread, such a rarity to talk tediums..
Worn Conti's make the bike flop & when you reach the edge of the tyre you can feel it, the bike stops leaning. Weird!

[Dodgyiti]

Go with the 17's.
I think you missed one: Tyre Availability.....

Hi Gavin:wavey:
Yep, the selection of 18's is crap and becoming less and less as time goes on. All my friggin bikes take 18's and it sucks reading all about new and improved tyre designs only to go to the manufacturer's web site and find they only come in 17':brick:

Lacing 17' rims to the Guzzi hubs shouldn't hurt, but being a single and chain drive you will not be limited by the rear hub/diff anyway like the twins.

Regards,

Mike.

[Racey Rider]

In Partnership with my sponsor Northwest Motorcycles (http://www.northwest.co.nz/) I will be requesting Steve import a range of the German Heidenau brand Race tires in 18" and some 16".

If you let me know what size you are after, I will get some brought into NZ. (No obligation to buy)
'Eta' end of May. Here's (http://www.reifenwerk-heidenau.de/modules/reifenliste/view.php?point=3&rtyp=19&PHPSESSID=4e4aac5cf264b239671b049cfd4f252d&sv=1) a small selection of Race stuff (RSW means Racing Soft Warm) some 18"

A couple of options we have in the country already.
90/90-18 (http://www.trademe.co.nz/Browse/Listing.aspx?id=279822854)
3.00-18 (http://www.trademe.co.nz/Browse/Listing.aspx?id=279821806)
110/80-18 (http://www.trademe.co.nz/Browse/Listing.aspx?id=279820879)

[scracha]

Yup, I have a MKII, definitely an 18' front. Bridgestone recommended the 012's but i hvae never seen the correct size front listed.

Yeah 18" front (much nicer on gravel thankyou very much) but I'm sure mine ran the wider 120/70 but you said you run a 110?

[gavinnz]

I called Ken McIntosh today who confirmed that tyre diameter is not covered under register rules for pre '63 Modified class
So I can use 17inch tyres.

No one has come up with a reason not to which is good! Means I might beon the right track.... no pun intended!
Regards
Gavin

[RDjase]

I called Ken McIntosh today who confirmed that tyre diameter is not covered under register rules for pre '63 Modified class
So I can use 17inch tyres.

No one has come up with a reason not to which is good! Means I might beon the right track.... no pun intended!
Regards
Gavin

How are you getting on with the bike build?

My LC is getting a winter tidy up