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tire info
#718771 12/14/17 5:59 pm
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I'm putting tires on my 69 daytona bitsa. It has a 3.25 on the front. Is there room for a 3.50? I'm looking to use Dunlop K70 tires. Is the 3.50 the biggest that fits the rear? I know mine is close to the chain guard. Anyone running these tires?


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Re: tire info
dale sonny #718773 12/14/17 6:21 pm
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400-18 will fit the rear unless there is something unusual with your setup. On the front it depends almost entirely on your fender mounting. 350-19 will fit in with most configurations..........but no guarantees!

Re: tire info
dale sonny #718791 12/14/17 8:22 pm
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The 3:50 didn't fit the 69's fender when I tried using a K70. Had to get a 3:25

Re: tire info
dale sonny #718792 12/14/17 8:22 pm
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That was for the front I might add

Re: tire info
dale sonny #718820 12/15/17 7:39 am
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Hi,

Originally Posted by dale sonny
69 daytona bitsa.
I'm looking to use Dunlop K70 tires.
It has a 3.25 on the front. Is there room for a 3.50?

'69 T100C's (TR6C's) were fitted originally with 3.50 front tyres; however, being off-road-oriented, they weren't K70's. Why d'you want a 3.50 on a relatively-light road bike? confused

Also, being a bitsa, what's the distance between the fork leg centres in the yokes? If it's the earlier 6-1/2", it'll be more of a pita to fit a 3.50. frown

Originally Posted by dale sonny
rear?

As said, 4.00x18 was standard on US-market bikes, with 3.25x19 front.

Originally Posted by dale sonny
Anyone running these tires?

Unless you need some sort of off-tarmac capability, there are better ime. E.g. Avon Roadriders 90/90x19 front and 100/90x18 rear.

Hth.

Regards,

Re: tire info
Stuart #718869 12/15/17 4:53 pm
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Well Stuart, I'm an off road rider at heart. I race vintage and modern enduro's and harescrambles. There are some seasonal maintenance roads that I ride through here and there. So yes, this triumph will go off road. I didn't want the trials tread that the C's came with. I will do much more on road than off. I just thought a little bigger front tire may be better off road. I'll have to look closer at my bike. It has a 3.50 rear tire and it's close to the chain guard.


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Re: tire info
dale sonny #718882 12/15/17 6:18 pm
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Hi,

Originally Posted by dale sonny
I'm an off road rider at heart. I race vintage and modern enduro's and harescrambles. There are some seasonal maintenance roads that I ride through here and there. So yes, this triumph will go off road. I didn't want the trials tread that the C's came with. I will do much more on road than off. I just thought a little bigger front tire may be better off road.

Modern dual-sport tyres are probably better than K70's? And you'll find the overall width of a modern 90/90 similar to, or even slightly wider than, the 3.50 K70.

Originally Posted by dale sonny
my bike. It has a 3.50 rear tire and it's close to the chain guard.

Mmmm ... Edward Turner enlarged Tiger Cub bits for the C-range (unit 350/500) rather than downsizing 650 bits, which puts the C-range gearbox sprocket and chainline a little closer to the bike's centreline. frown If considering modern dual-sport tyres, maybe consider a 100-width rear or 'universal' (can be fitted to front or rear)? That'll be wider overall than a 3.50 but not as wide as a 4.00 or modern 110-width.

Hth.

Regards,

Re: tire info
dale sonny #718906 12/15/17 8:43 pm
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I have a 400-18 Continental TKC80 Twinduro on my T100A off roader, Sorry, no pic of the other side, but I do have an Alloy chainguard fitted. Not much room to spare, but it works for me!
[Linked Image]



Re: tire info
dale sonny #718959 12/16/17 2:42 am
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I was looking for tires for my 67 Tr6. They look great.
My bike still has the original tires but they are cracking. So if I went the continentals what would I need for keeping with the stock tire sizes ?
[Linked Image]

Last edited by Mori55; 12/16/17 2:54 am.
Re: tire info
dale sonny #718961 12/16/17 2:58 am
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Re: tire info
dale sonny #718966 12/16/17 3:27 am
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I found the back tire. I know the front is 3.50 19. What would that be ? They don’t mention that size. For the front they 100/90 or 110/80 so what would be closest to my front tire ?

Last edited by Mori55; 12/16/17 3:36 am.
Re: tire info
Mori55 #718998 12/16/17 3:29 pm
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3.50 is 100/90 in metric size. My front tyre is not a Continental, its a Mitas, and its a 21" rim. I was going for Mitas rear, but when it came the profile was too low, would have looked silly, and altered the gearing, so I went for the TKC80.




Re: tire info
tbird649 #719008 12/16/17 4:50 pm
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Hi,

Originally Posted by tbird649
3.50 is 100/90 in metric size.

Uh-uh, 100/90 is 4.10 in real money.

The history is:-

. Before Dunlop introduced the K81/TT100, motorcycle tyres were 100%-aspect-ratio - section width (the numbers moulded on the sidewall) same as section height.

. Particularly the upcoming Triumph and BSA triples but also the contemporary Commando, RE Interceptor, etc. were needing wider rear tyres to cope with the increased engine power.

. If the width of the rear tyre was increased and 100%-aspect-ratio retained, not only would the wheel be a larger overall diameter, late-1960's sidewall material technology was struggling to control the power when cornering. frown

. So Dunlop designed the original 4.10 K81's to have the same section height as a 3.50 (so the wheel's overall diameter was the same, and having an eye on the Avons then dominating production racing and therefore the street go-faster market) but a greater section and overall width.

3.50 is, by definition, a 100%-aspect-ratio size; otoh, also by definition, 100/90 isn't - the "90" indicating the section height percentage (of the 100 mm. section width).

From personal first-hand experience, to get a 4.10x19 K81 in and out from between a pair of '69/'70-style Triumph or BSA fork legs with leg centres 6-3/4" apart requires either the tyre to be deflated or the mudguard and slider mountings to be removed.

Any more-modern-design 100/90 (e.g. Avon Roadrider) has a greater overall width than a 4.10 K81. It's almost certain you'll struggle to get a 100/90 even to work between '69/'70-style Triumph or BSA fork legs. frown

Hth.

Regards,

Re: tire info
dale sonny #719087 12/17/17 12:20 pm
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I'm glad somebody knows about tyre sizes Stuart! They drive me mad, every time I think I've got it sussed, I am proved wrong. The 110/90 /3.50 comparison came from a tyre company website, in fact from two different ones, I double checked because I thought the old tyre sizes were all 100% aspect. On the Mitas I bought for the rear wheel of my Triumph, the Mitas site had all dimensions of the various tyres in mm, I knew that space was tight, I chose something that was very close, slightly smaller in fact compared to the 4.00-18 Pirelli trials tyre that I had on the bike. When it came, it was miles smaller in diameter, nothing like the Mitas website said! I sent it back, actually very good service from a company called MyTyres, they sent a courier to collect it, FOC, even though they had supplied the tyre I had ordered.



Re: tire info
dale sonny #719127 12/17/17 6:32 pm
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sweet looking bike tbird. I was looking at the swing arm on my bike and noticed the tire is a 4.00. Not sure why I thought it was a 3.50. Thanks for the info.


69 Daytona/ scrambler
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assorted vintage dirt bike's
Re: tire info
tbird649 #719139 12/17/17 7:24 pm
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Hi,

Originally Posted by tbird649
The 110/90 /3.50 comparison came from a tyre company website, in fact from two different ones, I double checked

Mmmm ... the tyre companies use a different definition of "equivalent" to the rest of the English-speaking world ...

Originally Posted by tbird649
I thought the old tyre sizes were all 100% aspect.

The rule-of-thumb I use is:-

. if the (moulded) section width is divisible exactly by 0.25 (e.g. 3.25, 3.50, 4.00, etc.), it's 100%-aspect-ratio;

. if the (moulded) section width isn't divisible exactly by 0.25 (e.g. 3.60, 4.10, etc.), it isn't 100%-aspect-ratio (it's 82%);

. except 4.25; if that's low-profile, it has "/85" moulded, same format as a metric tyre;

. when comparing dimensions of tyres with different aspect ratios, the only meaningful comparisons are between overall diameters and widths.

Originally Posted by tbird649
the Mitas I bought for the rear wheel of my Triumph, the Mitas site had all dimensions of the various tyres in mm, I knew that space was tight, I chose something that was very close, slightly smaller in fact compared to the 4.00-18 Pirelli trials tyre that I had on the bike. When it came, it was miles smaller in diameter, nothing like the Mitas website said!

Mmmm ... intriguing ... just as matter of interest, did you try fitting and inflating the Mitas on a rim? I'm not so familiar with off-road tyres but I've found road tyres that I thought were way smaller compared to something they were supposed to be close to; fitted and inflated, they're much closer in overall size. confused Why? Dunno ...

Also as a matter of interest, which Mitas did you pick? Comparing Mitas and Conti overall dimensions, while the diameters seem very similar for any given section, the Mitas overall widths seem much greater (relatively)? Fwiw, this is similar to my experience with on-road tyres - the Avon Roadrider 4.00x18 is the same overall width as the 110/90x18; other makers' 4.00x18 have overall widths more like their 120/90x18. frown 'Mare.

Hth.

Regards,

Re: tire info
dale sonny #719147 12/17/17 8:13 pm
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I'm sure it was a Mitas E09, but looking on their website now, the smallest they list is a 120/90, and I know I wouldnt have gone for a 120. I think it was a 100/90, the tyre I was replacing was a 400-18 trials tyre. I didnt fit it, because looking at it, it was much smaller, and if I fitted it to try, I probably couldnt have returned it. I'm sure that their figures must have been wrong on their spec sheet. The Conti is a 400-18, there is not a lot of clearance, but it just fits, as did the Pirelli trials tyre.



Re: tire info
tbird649 #719171 12/17/17 10:57 pm
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Originally Posted by tbird649
I have a 400-18 Continental TKC80 Twinduro on my T100A off roader, Sorry, no pic of the other side, but I do have an Alloy chainguard fitted. Not much room to spare, but it works for me!
[Linked Image]


Oh God... I could want one of those...
facepalm


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Re: tire info
Stuart #719189 12/18/17 3:03 am
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Hi,

Originally Posted by tbird649
I think it was a 100/90, the tyre I was replacing was a 400-18 trials tyre.
I'm sure that their figures must have been wrong on their spec sheet.

Ah, then what you posted earlier:-

Originally Posted by tbird649
the Mitas I bought for the rear wheel of my Triumph, the Mitas site had all dimensions of the various tyres in mm, I knew that space was tight, I chose something that was very close, slightly smaller in fact compared to the 4.00-18 Pirelli trials tyre that I had on the bike. When it came, it was miles smaller in diameter, nothing like the Mitas website said!

... makes more sense ... as above, a 100/90 is 4.10 in old money, which has a similar section height to a 3.50 so, yes, it would've been "smaller in diameter" than any 4.00 (section width and height) tyre.

However, the 100/90-"equivalent"-4.10 section width isn't directly comparable to a 4.00 section width, because they're all different aspect ratios (respectively: 90%, 82% and 100%) - 4.00 is always wider overall than 4.10 (and 100/90) ...

As I posted earlier, the only way to do a meaningful comparison of tyres with different aspect ratios is by comparing overall diameters and widths. As you were looking for something narrower than the Pirelli, really you first needed to know what Pirelli reckoned the overall width was, then go hunting through the tyre makers' websites for either a 4.00x18 that the maker reckoned was narrower overall or a 110/90. Fwiw, ime 120/90's tend to be a similar overall diameter to a 4.00 but a greater overall width; anything a little narrower overall than a 4.00 is more likely to be a 110/90, but then you have to put up with a smaller overall diameter too. frown

Couple of other wrinkles to be aware of:-

. Note I've written, "what Pirelli reckoned the overall width was"; that's because overall widths of modern 4.00's are likely based on them being on a 2.50 (WM4 equivalent) rim, whereas you've got a 2.15 or WM3 in the back of your T100A? If so, if you'd actually measured the overall width of the 4.00 Pirelli on a 2.15 rim, you'd have likely found it slightly narrower than "what Pirelli reckoned"; similarly, other makers' 4.00 are likely to end up slightly narrower overall mounted on a 2.15/WM3 compared to what their websites/manuals reckon on a 2.50 rim.

. Also confusing is off-road tyre makers' appear to quote two "overall diameters": the smaller one appears to be similar to an on-road tyre of the same section - Mitas calls this "Design Overall diameter" while Conti calls it "New Overall diameter"; the larger one (about an inch larger), both Mitas and Conti call "In service Overall diameter"? confused

Hth?

Regards,

Re: tire info
dale sonny #719234 12/18/17 2:01 pm
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This is all great information. I worked in a auto repair shop for 20+ years. We also had a tire store. If you took 2 tires of the same size from different manufacturers and put them next to each other they sometimes would be different diameters. Sometimes the overall height would be as much as an inch different. I'm not sure about motorcycle tires, but they probably have the same results.


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Re: tire info
dale sonny #719359 12/19/17 10:27 am
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Hi,

Originally Posted by dale sonny
If you took 2 tires of the same size from different manufacturers and put them next to each other they sometimes would be different diameters. Sometimes the overall height would be as much as an inch different. I'm not sure about motorcycle tires, but they probably have the same results.

Strictly-speaking, that shouldn't be the case; if you look at the tyre makers that publish overall dimensions (certainly Avon, Dunlop, Continental, Mitas), the overall diameters for each section are within a few millimetres of each other despite the different makers; overall diameter for each section could be mandated by the likes of ETRTO, US DOT, etc.? Also, on cars, vans, etc. you can't have wildly-different overall diameters with correct inflation or you bugger the diff.

As I suggested to "tbird649" earlier in the thread, actually mounting and inflating two apparently different-size tyres on the same-width rims might've shown they were actually much closer in overall diameter than first appearance (although that was before he posted the smaller tyre was a smaller section smile). Dunno why that is but I have seen it.

Hth.

Regards,

Re: tire info
dale sonny #719427 12/19/17 10:01 pm
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Your right Stuart, but apparently the manufacturers don't follow mandates. We took 4 different manufacturers tires and put them side by side. We put a straight edge across the top. 3 were close, a few millimeters as you say. One was 1 inch shorter than the rest.


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