Tyre Sizes

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Vitesse
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Location: Crowcombe

Tyre Sizes

Post by Vitesse »

So, first ride out on my new (to me) 350 Sport (1977, alloy wheels) and apart from burning a hole in my jeans for the left pipe (rearsets, no heatshield) all went well.

Only after did I look at the tyre sizes. Now I know that originally it will have been 3.25 & 4.10 x 18 and that these don't translate easily to modern sizes but what I have surely can't be right? 90/90 front and 120/90. Was this ever a known combination of sizes? Looks wrong to me - wider than my Guzzi rear! Might explain why the centre stand hardly lifts the rear wheel off the deck. On an MT2.15 rim I'd expect 100/90, 110/90 or 110/80. Is there a general concensus?

That said it handled well enough although I'm running it in (only 40 miles since a complete rebuild 10 years ago!) so wasn't trying too hard. As the tyres are probably 20 years old they may well get changed soon but I'm just curious whether anyone else has seen a 120 on one of these.

EDIT: Just to save anyone asking - yes, I've done the maths!
A 4.10" equates to 104mm thus with 100% profile 104mm tyre height.
100/90 gives 90mm tyre height.
110/90 gives 99mm tyre height.
110/80 gives 88mm tyre height.
120/90 gives 108mm tyre height.

So all except the 120 will lower the gearing . . .

EDIT: Just in case anyone is coming to this from a search for the same question . . . Further down it is explained that the 4.10 tyre size is actually an early lower profile tyre and replaced a 3.50 width (4.10/90). The tyre height for this works out as 94mm which makes a lot more sense!
Last edited by Vitesse on 13 May 2021 17:37, edited 4 times in total.
Steve Brown
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Re: Tyre Sizes

Post by Steve Brown »

The burnt leggings is a right of passage into Morini world-welcome!
The front tyre is about right but the rear is way over. A 110/90 or 110/80 as you suggest is close enough and I'm sure that's what's on mine. A lot of folk put a wider tyre on the front but in my opinion it slows down the steering too much and spoils the Morini ride. Others (plenty) will disagree, it's like the oil question! :lol:
Oh and some of the modern tyres can be got in 3.25 as well.
All donations to the rest home for old Camels, Leicestershire.
George 350
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Re: Tyre Sizes

Post by George 350 »

As always, tyres are subjective. Most people who like to ride briskly run 90/90 front, 110/80 or 110/90 rears in either Avon Roadrider or Bridgestone BT45's (now Roadrider mk2 and BT46's respectively).
Me? I'm in the Bridgestone camp. Up the tyre pressures from book to the low 30's is best.
That said, I am hearing really good things about the Conti 'Klassic Attack' radials, although not yet on a Morini. Anyone done so?

If you fit them yourself, be ready to use a LOT of tyre soap and around 80-90psi to get the bu%#ers to seat properly!

Regards, George.
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
MickeyMoto
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Re: Tyre Sizes

Post by MickeyMoto »

I run 100 90 and 110 90 Avons at 32 and 36psi.

I find with a tired centre stand the rear tyre is touching the deck.

I had 90 90 and 100 90s and found the handling too flighty for my liking. Each to their own. Shame we can't fit 120 70 and 190 55!!!
mbmm350s
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Location: Berkshire UK

Re: Tyre Sizes

Post by mbmm350s »

Pretty much the same Avon Roadrider 90/90 and 110/90 31/34 a bit lower on the pressures
Not saying anything Mike but I am a light weight. :D

Seriously anything but 20 year old tyres - though I have a usable Pirelli Gordon 4.10 H 18 with a 1980 date code you could have for originality.
Mark
Vitesse
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Location: Crowcombe

Re: Tyre Sizes

Post by Vitesse »

Thanks. That all tallies with my initial thoughts. I'll probably stick with these whilst running in then go to more sensible sizes (110/90 rear seems the obvious choice) after. As I've a Guzzi Le Mans I'm familiar with with near impossible tyre fitting and have had good experiences of BT45s.

I see that some 4.10 x 18s do exist (other than off road ones) - Bridgestone BW202, Avon Distanzia, Heidenau. Anyone ever bothered with these or does everyone go to the lower profile (like with Guzzis)?
Mepstein
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Location: Newark, Delaware, USA

Re: Tyre Sizes

Post by Mepstein »

20 years - scary
“The general rule of the thumb when it comes to motorcycle tire age is to change your tires once they're five years old from the date of manufacture. However, with good maintenance and regular checks at a professional motorcycle shop, they can last a bit longer.”
MickeyMoto
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Re: Tyre Sizes

Post by MickeyMoto »

mbmm350s wrote:
Not saying anything Mike but I am a light weight. :D

Mark
So I've heard.. :)

I see Avon recommend 90 90 front and 100 90 rear. Pressures recommended are 29/36 psi

https://www.avontyres.com/en-gb/tyres/r ... e_spec=350
Silverspur
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Re: Tyre Sizes

Post by Silverspur »

MickeyMoto wrote:
mbmm350s wrote:
Not saying anything Mike but I am a light weight. :D

Mark
So I've heard.. :)

I see Avon recommend 90 90 front and 100 90 rear. Pressures recommended are 29/36 psi

https://www.avontyres.com/en-gb/tyres/r ... e_spec=350

This is what I use. Handles beautifully.
George 350
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Re: Tyre Sizes

Post by George 350 »

See next for edited post.
Last edited by George 350 on 18 Jul 2020 22:03, edited 1 time in total.
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
George 350
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Location: Northampton

Re: Tyre Sizes

Post by George 350 »

Going back to Steve's original post, when Dunlop introduced the K81(later renamed TT100) back in the late 60's, it was the first low aspect ratio motorcycle tyre with a 90% aspect ratio, and as such a 4.10 was a direct replacement for a 3.50", and a 3.60 was a 3.25" replacement. Thus from Steve's numbers a 4.10 would have a rolling radius of around 93-94mm.

Pirelli must have done the same for the Gordon, as 6000rpm always equalled 80mph whether on Pirelli, Dunlop and Avon 4.10's or on Michelin M45's in 3.50x18.
The 110/80x18 Bridgestone brings the 6000rpm speed down slightly - probably75-76mph, but not enough to really notice.
George
350 sport 1978, 350 Strada 1978
650 Norton 1967, 650 Kawasaki 1977 and 650 Enfield 2019
Vitesse
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Re: Tyre Sizes

Post by Vitesse »

Thanks for that George. That clears up my confusion on the 4.10 nomenclature. I was trying to understand how all the accepted tyres were so much smaller.
EVguru
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Re: Tyre Sizes

Post by EVguru »

George 350 wrote:As always, tyres are subjective. Most people who like to ride briskly run 90/90 front, 110/80 or 110/90 rears in either Avon Roadrider or Bridgestone BT45's (now Roadrider mk2 and BT46's respectively).
Me? I'm in the Bridgestone camp. Up the tyre pressures from book to the low 30's is best.
That said, I am hearing really good things about the Conti 'Klassic Attack' radials, although not yet on a Morini. Anyone done so?

If you fit them yourself, be ready to use a LOT of tyre soap and around 80-90psi to get the bu%#ers to seat properly!

Regards, George.
I wrote about Classic Attack's in ATG.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
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