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right size for A65 rear tyre #443691
07/08/12 9:46 am
07/08/12 9:46 am
Joined: Jul 2010
Posts: 17
Galicia, Spain
Morguis Offline OP
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Galicia, Spain
Hi there. Now it's time to replace the rear tyre of my A65 IŽd like to know some question from your experience: BSA's Workshop manual says rear tyre size is 3.50x18, but mine has 4.00x18 (Metzeler Perfect 77). Is this a normal (from that time) improvement everybody did or maybe the bike "feels" better with factory size? Just in case I'd go with a 3.50, may I change rim size or same will work? Mine's is the early big enclosed chainguard model so there's not room enough for a wide tyre. Maybe some kind of question is somewhere in this forum. I've been searching under "right rear wheel size, correct rear tyre size, etcetera, etcetera, etcetera" with no succes. Sorry if I bother you all with such a silly question like this. Cheers.


1963 BSA A65 Star
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Re: right size for A65 rear tyre [Re: Morguis] #443693
07/08/12 9:52 am
07/08/12 9:52 am
Joined: Mar 2011
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derby england
wak Offline
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3.50 is correct but i would go 4.00 like the later ones.


BSA lightning
BSA B50MX
TRIUMPH TR6C
BSA BUSHMAN
BSA Gold Star Daytona
BSA Gold Star Scrambler
BSA Rocket Gold Star
BSA C15S
BSA Cyclone
Triumph T120
Triumph T100 Daytona
Triumph 5TA Trials
Triumph T100 Scrambles
Cheney 560 TT
Re: right size for A65 rear tyre [Re: Morguis] #443694
07/08/12 10:30 am
07/08/12 10:30 am
Joined: Aug 2001
Posts: 7,455
scotland
triton thrasher Offline
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Try a 3.50. It's cheaper, the steering might be better and it will fit more easily. The rim size will be fine.

On the other hand, a fatter rear tyre has the obvious advantage of making you imagine you have a bigger willy.


Amateur Loctite enthusiast.
Re: right size for A65 rear tyre [Re: Morguis] #443697
07/08/12 11:34 am
07/08/12 11:34 am
Joined: Mar 2011
Posts: 836
derby england
wak Offline
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Exactly and therefore a better ride !


BSA lightning
BSA B50MX
TRIUMPH TR6C
BSA BUSHMAN
BSA Gold Star Daytona
BSA Gold Star Scrambler
BSA Rocket Gold Star
BSA C15S
BSA Cyclone
Triumph T120
Triumph T100 Daytona
Triumph 5TA Trials
Triumph T100 Scrambles
Cheney 560 TT
Re: right size for A65 rear tyre [Re: Morguis] #443744
07/08/12 5:54 pm
07/08/12 5:54 pm
Joined: Jun 2002
Posts: 9,957
Scotland
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Stuart Online content
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Hi,

Up until the start of the 1971 season, BSA (and Triumph) fitted US-market models with a 4.00x18 rear tyre (with a 3.25x19 front) and models for all other markets (including GB and Spain) with a 3.50x18 rear (with either a 3.00x19 or 3.25x18 front).

From the start of the 1971 season, BSA (and Triumph) fitted all models (except triples) with 4.00x18 rear and 3.25x19 front tyres. Also, from 1968, 3.50-width tyres were superseded by 4.10 (very similar overall diameter but greater overall width) so tyre makers gradually stopped making 3.50x18, 3.50x19, 3.25x18 and 3.00x19, but carried on making 3.25x19 and 4.00x18.

So, depends what tyre size your bike has on the front - 3.25x19 front would be better with 4.00x18 rear; 90/90x19 front would be better with 100/90x18 rear (modern equivalent of 4.10x18).

Originally Posted By: Morguis
Sorry if I bother you all with such a silly question like this.

This sort of question is what the Forum is for. bigt

Hth.

Regards,

Re: right size for A65 rear tyre [Re: Morguis] #443745
07/08/12 6:09 pm
07/08/12 6:09 pm
Joined: Oct 2008
Posts: 5,014
Gnashville
DavidP Offline

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Gnashville
Again, Stuart has spoken truth.

I have never experienced a 4.00x18 on my 71. However, I just replaced a 4.25/85x18 with a 100/90x18. The narrower tire did improve the handling.
Full disclosure: New tire is Roadrider, old tire was a K81 copy, front tire is a 3.60x19 K81 which needs replacing.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
Re: right size for A65 rear tyre [Re: Morguis] #443789
07/08/12 11:49 pm
07/08/12 11:49 pm
Joined: Sep 2001
Posts: 2,796
Comox BC Canada
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Gordo in Comox Offline
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Comox BC Canada
I use Avon AM21 110/90/18 rear and Avon AM20 90/90/18 front on my 1965 T/R A65 and quite like the ride and handling.

Of course those machines came with 18" both front and rear.

Gordo


Without frequent roadside repairs there is no fun in riding!
Re: right size for A65 rear tyre [Re: Morguis] #443881
07/09/12 6:56 pm
07/09/12 6:56 pm
Joined: Jul 2010
Posts: 17
Galicia, Spain
Morguis Offline OP
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Morguis  Offline OP
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Galicia, Spain
Thank you Wak, Triton T., STUART, David p. and Gordo, thank you very much. Your answers are very helpful. Maybe I shall go 3.50. Cheers!


1963 BSA A65 Star
Re: right size for A65 rear tyre [Re: Morguis] #444014
07/10/12 2:15 pm
07/10/12 2:15 pm
Joined: Aug 2001
Posts: 3,884
Cape Carteret, NC
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Mr Mike Offline
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Cape Carteret, NC
I went to 4.0 when my supplier of Chen Shins discontinued the 3.50x18. No problems in fit or ride on WM-2 rims, except the K-70 was twice as expensive.

Mr Mike

Re: right size for A65 rear tyre [Re: Stuart] #444038
07/10/12 6:05 pm
07/10/12 6:05 pm
Joined: Nov 2009
Posts: 273
UK
V
VicCyclone Offline
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UK
I think that the change was for the 67 season not 71. The 66 A65 parts book list both 2 x 19 and 3 x 18 rear rims. In 1967 only 3 x 18 rims are listed. My 68 Lightning certainly has a 3 x 18 original part numbered rim, rear with a 4,00 X 18 tyre which was standard. I cannot remember seing a twin after 67 with a 3.50 rear tire. Some of the singles kept 3.50s.


VicCyclone

1965 A50 Cyclone Clubman
1966 Victor GP
1967 Victor Special
1968 Victor Special
1968 A65L

2009 HD FXDC
Re: right size for A65 rear tyre [Re: VicCyclone] #658623
06/29/16 6:38 am
06/29/16 6:38 am
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Posts: 14
UK
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SteveT Offline
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Just a thought.... as anyone tried these?
http://www.conti-bike.co.uk/conticlassicattack/

Re: right size for A65 rear tyre [Re: SteveT] #658733
06/29/16 10:15 pm
06/29/16 10:15 pm
Joined: Feb 2007
Posts: 2,234
Atlanta, GA USA
S
Semper Gumby Offline
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Semper Gumby  Offline
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Originally Posted By SteveT
Just a thought.... as anyone tried these?
http://www.conti-bike.co.uk/conticlassicattack/


Yes. Don't.

I put the correct width rim for the tire on the back of my Thunderbolt and tried a 120/90-18. I was shocked to see after it was mounted that the profile of the tire from the rear was not round. It was an elipse shape that cause the handling to be quite twitchy. I have put about 3000 miles on the tire and worn it down to a more rounder profile and it does handle better but I will not be buying another of these tires for the BSA. The Michelin Pilot Active will be going back on the rear of the Thunderbolt. (forgive me for I have sinned and bought into marketing hype...)

Last edited by Semper Gumby; 06/29/16 10:16 pm.

Gaggle of BSAs
a Honda
an old BMW
and a Montesa
Parking lot Elf in training
Re: right size for A65 rear tyre [Re: Morguis] #658734
06/29/16 10:20 pm
06/29/16 10:20 pm
Joined: Feb 2007
Posts: 2,234
Atlanta, GA USA
S
Semper Gumby Offline
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Atlanta, GA USA
Originally Posted By Morguis
Hi there. Now it's time to replace the rear tyre of my A65 IŽd like to know some question from your experience: BSA's Workshop Manual says rear tyre size is 3.50x18, but mine has 4.00x18 (Metzeler Perfect 77). Is this a normal (from that time) improvement everybody did or maybe the bike "feels" better with factory size? Just in case I'd go with a 3.50, may I change rim size or same will work? Mine's is the early big enclosed chainguard model so there's not room enough for a wide tyre. Maybe some kind of question is somewhere in this forum. I've been searching under "right rear wheel size, correct rear tyre size, etcetera, etcetera, etcetera" with no succes. Sorry if I bother you all with such a silly question like this. Cheers.


Hi Morguis,

I have an original 1963 BSA Star 650 with the same 18" narrow rims you have. I put the Heidenau K34 on in the stock sizes -- 3.25-18 on the front and the 3.50-18 on the rear. The handling is light, quick and sure. The bike is an absolute pleasure to ride and there is plenty of room for the original stock fully enclosed chain guard.

Regards,

Gumby

Last edited by Semper Gumby; 06/29/16 10:23 pm.

Gaggle of BSAs
a Honda
an old BMW
and a Montesa
Parking lot Elf in training
Re: right size for A65 rear tyre [Re: Semper Gumby] #658747
06/30/16 2:56 am
06/30/16 2:56 am
Joined: Jun 2002
Posts: 9,957
Scotland
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Stuart Online content
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Stuart  Online Content
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Scotland
Hi Bill,

Originally Posted By Semper Gumby
Originally Posted By SteveT
Just a thought.... as anyone tried these?
http://www.conti-bike.co.uk/conticlassicattack/

Yes. Don't.

I put the correct width rim for the tire on the back of my Thunderbolt

Just as a matter of interest, which rim width did you fit?

Originally Posted By Semper Gumby
Hi Morguis,

As he started the thread four years ago, I suspect he was happy with whatever he fitted. grin

Regards,

Re: right size for A65 rear tyre [Re: Stuart] #658838
06/30/16 5:42 pm
06/30/16 5:42 pm
Joined: Feb 2007
Posts: 2,234
Atlanta, GA USA
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Semper Gumby Offline
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Hi Stuart. 2.75 width recommended by Continental for this tire. It was great in the corners but twitchy when straight up. The profile reminded me of the 1970's racing Goodyears I have seen - an elipse. I should have said "Hi Steve T". Now that the center is worn down the handling is actually quite nice but getting to this point was not enjoyable.

Didn't realize the original post was that old. Heidenaus have been a new thing here in the States.

Last edited by Semper Gumby; 06/30/16 5:45 pm.

Gaggle of BSAs
a Honda
an old BMW
and a Montesa
Parking lot Elf in training
Re: right size for A65 rear tyre [Re: Semper Gumby] #658854
06/30/16 9:08 pm
06/30/16 9:08 pm
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Scotland
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Stuart Online content
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Hi Bill,

Originally Posted By Semper Gumby
2.75 width recommended by Continental for this tire.

Originally Posted By Semper Gumby
I was shocked to see after it was mounted that the profile of the tire from the rear was not round. It was an elipse shape that cause the handling to be quite twitchy.

Hmmm ... I wonder if Conti want a similar tread shape to the old TT100's, so there's a larger contact patch when the bike's leaned over than when it's upright?

Regards,

Re: right size for A65 rear tyre [Re: Morguis] #659363
07/05/16 3:55 am
07/05/16 3:55 am
Joined: Dec 2013
Posts: 16
Hants, UK
S
Starfire Offline
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Hants, UK
As an aside, why were the wheels different diameters? Is it a handling issue? I ask because on my A65, both rims are 19". One obvious disadvantage of this is both wheels touching the ground when on the centre stand.

Re: right size for A65 rear tyre [Re: Starfire] #659366
07/05/16 5:06 am
07/05/16 5:06 am
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Posts: 9,957
Scotland
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Stuart Online content
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Stuart  Online Content
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Hi,

Originally Posted By Starfire
why were the wheels different diameters?

The height of a tyre's section (visible as the tyre's walls) contributes to the overall diameter of the wheel. The height of a tyre's section is a function of its width so, if you want the overall diameter of both wheels to be roughly the same, because the front tyre is usually narrower than the rear, the front tyre section height will be smaller than the rear's, so the front tyre often starts off with a bigger 'ole in the middle, aka rim diameter.

This is easier to see if you look at a tyre company's website that gives overall diameters, e.g. http://www.avon-tyres.co.uk/motorcycle/roadrider. There you'll see that the common-on-Britbikes 3.25x19 front and 4.00x18 rear have similar overall diameters and, in turn, they're very similar to 100/90x19 (4.10x19), 110/90x18, 120/90x18 and even 130/90x17.

Overall diameters are mandated by authorities like the US DOT and European ETRTO so you can reckon on other makers' tyres being similar overall diameters for the same sections (the figures moulded on the tyre walls). The things you have to watch are: for the same sections, modern tyres are generally wider overall and overall widths vary more between makers than overall diameters; British motorcycle makers weren't at all generous with space between tyres and other bits of their bikes (so, say, a modern 3.25x19 won't always fit where a 1960's 3.25x19 did) and tyre makers recommend wider rims today than British motorcycle makers fitted 'back in the day'. frown

Originally Posted By Starfire
on my A65, both rims are 19". One obvious disadvantage of this is both wheels touching the ground when on the centre stand.

Depends what tyres you have fitted. An educated guess says originals were 3.25x19 front and 3.50x19 rear? What does the bike have now?

Also, does the bike have the correct centre stand fitted and are you sure its legs aren't bent/splayed and/or it doesn't go too far forward, dropping the bike lower again? Reason I ask is I know, for instance, that Triumph unit 350's/500's have two different centre stands; the range started in the 1950's on 17" wheels, went to 18" in the 1960's but, when 3.25x19 or 3.50x19 front and 4.00x18 rear tyres were fitted to US-market variants, the centre stand had to be extended to get those sizes off the ground.

Hth.

Regards,


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